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Clean Air Program -- Assesment of the Safety, Health, Environmental and System Risks of Alternative Fuel



Clean Air Program

Summary Assesment of the Safety, Health, Environmental and System Risks of Alternative Fuel


PREFACE

National goals for both energy security and clean air have resulted in heightened interest in theuse of alternative motor fuels (AMFs) in the transportation market. The growth of interest inalternative fuels has expanded not only the numbers of alternative fuel vehicles, but also the listof viable alternative transportation fuels.

Thus, an increasing number of transit fleets and other fleet owners are operating vehicles onalternative fuels often with a minimum of technical guidance related to the possible safety oroperational impacts on traditional fleet operations, including fueling, inspecting, and cleaningvehicles, as well as performing the light and heavy maintenance activities necessary to keep thefleet in operation.

Moreover, the buildings or facilities used for storing, loading, and maintaining alternative fuelvehicles form an important portion of a fleet operation. Here, the experience with fire andbuilding codes is not yet complete. This situation requires additional care on the part of theowners of these facilities to recognize all hazards associated with the use of alternative fuelvehicles and to ensure that these hazards are properly addressed in the design and operation ofthe facility.

Experience has shown that not all local community and regulatory groups view the use ofalternative fuels as a purely positive option. Transit properties and others who propose the use ofalternative fuels need to deal not only with the perceptions of fire and building code officials whogrant approvals, but also with the perceptions and concerns of community and neighborhoodorganizations. The concerns of these groups are not limited to fleet operations, but may alsoinclude the production of the alternative fuel and the transportation of the fuel to the point of use.

In view of the diversity of these safety concerns, as well as the number of possible hazards, acomprehensive and systematic program is needed to recognize and organize the existingknowledge about the health, safety, and environmental hazards of alternative fuels and to identifywhere additional study is needed. The objective of this report is assist the Volpe Center, FTAand DOE in providing information on these issues to the transit and fleet operator communitywhile avoiding a commitment to or bias against any given fuel or point of view.

This report presents the results of a research effort undertaken for the Volpe NationalTransportation Systems Center. This work was funded jointly by the U.S. Department ofTransportation, Federal Transit Administration Office of Engineering and the U.S.Department of Energy, Alternative Fuels Utilization and Analysis Division. The interest,insight and advice of David Knapton of the Volpe National Transportation Systems Center,John Russell of the U.S. Department of Energy, and Tony Yen and Steven Sill of theFederal Transit Administration are gratefully acknowledged.


TABLE OF CONTENTS

    LIST OF FIGURES
    LIST OF TABLES
    EXECUTIVE SUMMARY
    LIST OF ACRONYMS

  1. INTRODUCTION

      1.1 Background
      1.2 Objectives and Scope

  2. PREPARATION AND ORGANIZATION OF REPORT

      2.1 Information Sources
      2.2 Organization of Report

  3. PRODUCTION, BULK TRANSPORT, AND BULK STORAGE OF ALTERNATIVE FUELS

      3.1 Introduction
      3.2 Methodology
      3.3 Issues Associated with Bulk Transport and Storage of Alternative Fuels

        3.3.1 Methanol/Methanol Blends
        3.3.2 Ethanol/Ethanol Blends
        3.3.3 Compressed Natural Gas
        3.3.4 Liquefied Natural Gas
        3.3.5 Propane
        3.3.6 Biodiesel
        3.3.7 Hydrogen
        3.3.8 Electricity

      3.4 Assessment of Alternative Fuel - Bulk Transport, Transfer, and Fleet Storage Safety Risks

        3.4.1 Introduction
        3.4.2 Assessment of Relative Potential for Spills and Leaks
        3.4.3 Assessment of Safety Hazards
        3.4.4 Assessment of Health Hazards
        3.4.5 Assessment of Environmental Hazards

  4. USE OF ALTERNATIVE FUELS BY VEHICLE FLEETS

      4.1 Introduction
      4.2 Objectives and Scope

        4.2.1 Fuels Included
        4.2.2 Hazardous Properties Included
        4.2.3 Accident Events Included

      4.3 Summary List of Alternative Fuel Hazards for Vehicle Fleet Operations

        4.3.1 Overview of Alternative Fuel Hazards
        4.3.2 Safety Hazards Considered

      4.4 Summary List of Alternative Fuel Hazards
      4.5 Alternative Fuel Safety Case Studies

        4.5.1 Methanol Vehicle Fire
        4.5.2 LNG Bus Explosion
        4.5.3 High Pressure CNG Fittings as Projectiles
        4.5.4 Propane Tank Damage
        4.5.5 Pressure Relief Device (PRD) Failure on CNG Bus
        4.5.6 CNG Cascade Relief Valve Failure
        4.5.7 Static Electricity Ignition of Venting CNG
        4.5.8 CNG Bus Drive-Away and Fire
        4.5.9 Propane Leak from Faulty Installation

  5. APPENDIX A. SOURCES FOR ALTERNATIVE FUEL SAFETY

      INFORMATION


LIST OF FIGURES

  1. Flash Point Temperatures for Liquid AMFs
  2. Fuel Volatility--Reid Vapor Pressure (@ 38C)
  3. Autoignition Temperature
  4. Flammability Limits Range
  5. Relative Heat Release Rate for Liquid Pool Fires

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LIST OF TABLES

  1. Relative Potential for Spills During Transport
  2. Relative Potential for Leaks During Transport
  3. Relative Potential for Spills During Unloading
  4. Relative Potential for Leaks During Unloading
  5. Relative Potential for Spills During Fleet Storage
  6. Relative Potential for Leaks During Fleet Storage
  7. (A-H). Compressed Natural Gas (CNG)
  8. (A-H). Liquefied Natural Gas (LNG)
  9. (A-H). Propane
  10. (A-H). Methanol
  11. (A-H). Ethanol
  12. (A-H). Biodiesel
  13. (A-H). Hydrogen
  14. (A-H). Electricity

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EXECUTIVE SUMMARY

A. BACKGROUND

National goals for energy security and clean air have resulted in a heightened interest in theuse of alternative transportation fuels. This growing interest in alternative fuels has led toboth an increase in the number of alternative fuel vehicles, and to an expansion in the list ofcandidate alternative fuels.

This summary assessment consists of two parts. The first part considers the hazardsassociated with the bulk transport and storage of alternative fuels. The second part considersthe hazards associated with the operation, fueling, and maintenance of alternative-fuel vehiclefleets. The report does not cover estimating the hazard probability or calculating the overallrisk.

Both sections of the hazard assessment discussion include information on the followingalternative fuels:

1. Compressed Natural Gas (CNG)

2. Liquefied (LNG)

3. Propane

4. Methanol and methanol blends

5. Ethanol and ethanol blends

6. Biodiesel blends In this analysis biodiesel fuel is considered to be a mixture of 10-30 percent of a vegetable oilester, such as methyl soyate, and conventional diesel fuel.

7. Hydrogen

8. Electricity

B. PRODUCTION, TRANSPORT AND BULK STORAGE HAZARDS

The types of hazards which may be encountered are categorized as follows:

Safety Issues, including fire hazards and other hazards

Health Issues, including fuel toxicity

Environmental Issues, including effects of fuel spills.

Highlights of this analysis follow.

Fire Hazards

Since all fuels burn, they constitute fire hazards to a greater or lesser degree. However,fuels vary widely in the degree of flammability. Of the many combustion-related propertiesof substance, fuel flammability limits and pool burn rate are especially relevant to a safetyhazard analysis.

Fuel Flammability Limits

Flammability limits are a basic measure of flammability. Flammability limits are the rangeof composition over which mixtures of fuel and air will burn. At an ambient temperature of

22C, natural gas in the form of CNG or LNG has the widest flammability limits. Due toincreased volatility at higher temperatures, the alcohols, methanol and ethanol have extendedflammability limits at elevated temperatures (60C). Biodiesel fuel is below its flashpoint at22C and shows a flammable range only at elevated temperatures.

Fuel Pool Burn Rate

If liquid fuels spill and ignite, the pool burn rate is a measure of the rate at which a givensize spill will burn and release heat. Since fuels burn only when they are in gaseous form,the pool burn rate tends to be limited by the rate of vaporization. Thus, the pool burn ratesfor the alcohols, which have relatively high heats of vaporization, are lower than those forhydrocarbon fuels like gasoline or propane. Note too, that the gaseous fuels hydrogen andcompressed natural gas can have very high heat release rates since the burn rate for thesefuels is not limited by the need to first vaporize a liquid.

Health Hazards

In addition to fire hazards, the use of alternative fuels can present health hazards. For mostfuel health effects, inhalation of fuel vapors is the most likely exposure route. The thresholdlimit value for the health effects of fuel vapors is a measure of fuel toxicity. The limits forall fuels except LNG vapor (considered to be nearly pure methane), and hydrogen are basedon toxic effects. The limit values for these fuels are based on the lower flammability limitand the premise that inhalation of a flammable mixture of fuel and air constitutes a healthhazard. In the case of hydrogen and natural gas, excessive exposure can also result inasphyxiation. However, approximately 140,000 ppm (14 percent) of an inert gas would berequired to lower the oxygen concentration of air to less than the 18 percent, the limit for abreathable atmosphere.

Methanol and methanol blends are the most toxic AMFs for inhalation-exposure with athreshold limit value - time weight average (TLV-TWA) concentration value of 200 ppm. By comparison, the next lowest TLV-TWA concentration value for an AMF includes ethanol1,000 ppm, followed by natural gas at a value of 10,500 ppm. In addition, there is anOSHA-set personnel exposure time limit (PEL) of 1,000 ppm for propane.

Environmental Hazards

The spill or leak of an AMF is not likely to result in any long term environmental damage. A review of the potential environmental hazards for each AMF, that is not gaseous at normaltemperatures and pressures, shows that all of the liquid AMFs are biodegradable over areasonably short period of time (i.e., a period of several months or less). The major concernis that the liquid AMF should be prevented from entering into any waterway or drainagesystem. Aside from any consideration of aquatic toxicity, there is actually a potentialfire/explosion safety hazard situation created when a flammable or combustible liquid entersa waterway where there are covered sections where vapors can accumulate. This problem isparticularly acute for the alcohols (methanol and ethanol) since they are soluble in water. Once such alcohol AMFs have mixed with water there is no simple and low cost method forseparating them out.

C. FLEET USE HAZARDS

This portion of the work was structured around a summary list of safety, fire, and healthhazards for each alternative fuel in fleet use. In each instance, the assessment of theconsequences of the hazards and of the state of knowledge concerning the hazards is basedon a comparison with diesel or gasoline fuel as currently used by fleet operators and transitagencies.

To construct the summary list of hazards associated with the fleet use of alternative fuels, thefollowing eight hazardous properties are included:

(a) Flammability

(b) Corrosivity

(c) Toxicity (including asphyxiation)

(d) High pressure

(e) High temperature

(f) Cryogenic temperature

(g) Mechanical energy (includes energy stored as potential or kinetic energy)

(h) Electrical energy

The existence of these hazardous properties and their associated hazards is not sufficient tocause an accident. Some event is necessary before the hazard and the hazard consequencesare realized.

The application of the eight hazardous properties to the eight alternative fuels produces anumber of hazards. The more significant hazards for each fuel are:

CNG - Important hazardous properties and hazards for CNG include:

Flammability hazard -- fire or explosion from ignition of gas leaks. Such gasleaks can occur from fuel dispenser or fuel system damage, use of impropercomponents, or poor overall design. High pressure natural gas leaks canignite from static electricity. Several such cases have already occurred, someresulting in the loss of the vehicle.

Toxicity hazard natural gas can accumulate in enclosed spaces. Theodorant may not provide sufficient warning of the actual gas concentration.

High pressure hazard fuel tank explosion, missile damage from failure orimproper assembly or disassembly of fuel system components. Flailing of fuelhoses and fuel lines.

Mechanical energy hazard natural gas compressors have rotating and/orreciprocating parts moving it high speeds. Failure of such equipment couldlead to missile damage from fragments.

LNG - Important hazardous properties and hazards for LNG include:

Flammability hazard fire or explosion from ignition of leaks of fuel. Non-odorized fuel gas increases the hazard. Note that the design base forcryogenic fuel system components is still relatively small.

Toxicity hazard asphyxiation from exposure to non-odorized fuel gas.

High pressure hazard while LNG storage pressures are not as high as thosefor CNG, they are still significant. Also, trapped liquid fuel can produceextremely high pressures upon warming and vaporization.

Cryogenic hazards LNG presents several hazards associated with thecryogenic property of the fuel:

Personal injury may occur from exposure to cold fuel or fuel vapors. This is especially true if proper personal protective gear is not worn.

Structural failure can occur due to stress from contraction of structuralmembers exposed to cold fuel or fuel vapors.

Structural failure can also occur due to embrittlement of materialsexposed to cold fuel or fuel vapors.

Propane - Important hazardous properties and hazards for propane include:

Flammability hazard propane gas can collect in low spaces; large propanevapor clouds can detonate.

Toxicity hazard propane gas can collect in low spaces and thereforedisplace the air necessary for breathing.

Methanol and Methanol Blends - Important hazardous properties and hazards for methanol and methanol blends include:

Flammability hazard vapors in fuel tanks are within the flammable rangefor typical ambient temperatures.

Flammability hazard the flames from methanol fires are not as luminous asthose from other hydrocarbons. While this serves to limit fire injury anddamage, it can also make initial detection of methanol fires more difficult.

Corrosivity hazard being a polar liquid, methanol is slightly acidic and cancorrode some active metals.

Ethanol and Ethanol Blends - Important hazardous properties and hazards forethanol and ethanol blends include:

Flammability hazard vapors in fuel tanks are within the flammable rangefor typical ambient temperatures.

Corrosivity hazard being a polar liquid, ethanol is slightly acidic and cancorrode some active metals.

Toxicity hazard ingestion of a fuel billed as food-based, but which must bedenatured, i.e., made poisonous.

Biodiesel - Important hazardous properties and hazards for the biodiesel component of biodiesel fuel blends include:

Corrosivity hazard elastomer or polymer component failure due to thecomposition difference between biodiesel fuel and gasoline or conventionaldiesel fuel is a type of corrosivity hazard.

Toxicity hazard ingestion of a fuel which has been billed as non-toxic, butwhich is generally an ester of a fatty acid and methanol. If ingested themethanol component is released. In primates (including humans) this cancause toxic effects.

Hydrogen - Important hazardous properties and hazards for hydrogen include:

Flammability hazard fire or explosion from ignition (especially staticignition) of gas releases or gas leaks. Note that hydrogen fuel is a non-odorized flammable gas.

Corrosivity hazard hydrogen embrittlement of certain materials represents atype of corrosivity hazard associated with hydrogen.

High pressure hazard fuel tank explosion, missile damage from failure orimproper assembly or disassembly of hydrogen fuel system parts.

Electricity - Important hazardous properties and hazards for electricity include:

Flammability hazard fire caused by electrical malfunctions, such as shortcircuits.

Corrosivity, toxicity, or high temperature hazard from contact with batteryelectrolyte.

Electrical energy hazard electric shock.

D. CONCLUDING REMARKS

No fuel is free from hazards. Although some fuel hazards are obvious, a systematicconsideration of hazardous properties and hazards can identify hazards which may have beenoverlooked. Hazards differ for various alternative fuels. This implies that:

Modifications of equipment and procedures will be required for eachalternative fuel.

No alternative fuel will be a "drop in" replacement for the status quo.

The full report from this study provides a framework for organizing information aboutadditional hazardous properties and hazards. However, a risk assessment, includinginformation about hazard probabilities and hazard consequences, can support conclusionsabout the safety ranking of various fuels, fuel systems, fueling equipment, and overallstrategies for using alternative fuels.

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LIST OF ACRONYMS

ACGIH American Conference of Governmental Industrial Hygienists
AMF Alternative motor fuel
API American Petroleum Institute
BLEVE Boiling Liquid Expanding Vapor Explosion
C Celsius
CAP Clean Air Program
CARB California Air Resources Board
CNG Compressed natural gas
CO Carbon monoxide
DOE Department of Energy
EMI Electromagnetic interference
EPA Environmental Protection Agency
F Fahrenheit
FTA Federal Transit Administration
kPa Kilo Pascals (1 psia = 6.9 kPa)
LNG Liquefied natural gas
LPG Liquefied petroleum gas
MPa Mega Pascals
M-100 Neat (100 percent) methanol
M-85 Mixture of 85 percent methanol and 15 percent gasoline
NFPA National Fire Protection Association
NIOSH National Institutes of Occupational Safety and Health
NOx Nitrogen oxides
OEM Original equipment manufacturer
OSHA Occupational Safety and Health Administration
PEL Personal exposure limit
PRD Pressure relief device
psi Pounds per square inch
psig Pounds per square inch gage
RFG Reformulated gasoline
RLM Refrigerated liquid methane
RMP Risk Management Plan
RPT Rapid-phase transition
RVP Reid vapor pressure
SCRTD Southern California Rapid Transit District
STEL Short term exposure limit
TLV Threshold limit value
TWA Time-weighted average
VNTSC Volpe National Transportation Systems Center

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1. INTRODUCTION

1.1 BACKGROUND

The national goals for both energy security and clean air have resulted in heightened interestin the use of alternative motor fuels (AMFs) in the transportation market. The EnergyPolicy Act of 1992 (EPACT) contains specific requirements for fleet use of alternative fuels. In a number of regions of the country, primarily where air quality is an issue, state and localclean air initiatives and fuel mandates have been enacted for certain vehicle classes. Thesemandates will have consequences for a number of transit and other fleets that must complywith local, state, and federal regulations while continuing to provide the highest qualitytransit programs and other services in their areas.

Other government programs have sought to encourage the use of alternative fuels throughgrants and awards for alternative fuel demonstration programs. For example, as part of itsClean Air Program (CAP), the Federal Transit Administration (FTA) has awarded grants foralternative fuel demonstration programs. The Department of Energy, through the NationalRenewable Energy Laboratory has also funded a number of alternative fuel demonstrationprograms, such as the comprehensive CleanFleet program involving Federal Expressmedium-duty delivery trucks.

Growth of interest in alternative fuels has expanded not only the number of alternative fuelvehicles, but also the list of viable alternative transportation fuels. In recognition of theincreasing need to more fully understand critical aspects of the candidate AMFs, the FTAand the Volpe National Transportation Systems Center (VNTSC) have established a programthat addresses the safety hazards and operational issues associated with the use of alternativefuels by vehicle fleet operators.

This effort to supply additional information concerning the safety hazard implications of allAMFs is timely. An increasing number of transit fleets and other fleet owners are operatingvehicles on alternative fuels often with a minimum of technical guidance related to thepossible safety or operational impacts on their facilities, as well as those related to theproduction, transport, and bulk storage of alternative fuels that support these demonstrations.

The environmental, safety hazard, and health aspects analysis of AMFs have become morecomplex in recent years. Several developments have contributed to this complexity. Thefirst development is the increasing number of candidate alternative fuels. For example, atfirst, methanol was the only alternative fuel being seriously considered for transit use. Theearly commitment by Detroit Diesel Corporation to provide a methanol fueled-engine fortransit use contributed to this emphasis. However, natural gas engine development soonfollowed, with the natural gas being stored in compressed form.

The roster of alternative fuels used in transit has now expanded to include methanol andmethanol blends (M-100 and M-85), ethanol and ethanol blends (E-95 and E-85), compressednatural gas (CNG), propane (LPG), liquefied natural gas (LNG), bio-diesel, and electric batteries, with additional interest in reformulated gasoline and advanced diesel, fuel cells,and even hydrogen as fuels for transit and other fleets.

The second development is the realization that some previous safety analyses haveconcentrated on only a portion of the total transit or fleet operation. Transit properties andfleet operators must consider the entire path from the fuel supplier all the way to the vehiclefuel tank. Also, fleet operations involve not only operating alternative fuel vehicles inrevenue service, but also fueling, inspecting, cleaning, washing, and performing the light andheavy maintenance activities necessary to keep the fleet in operation.

The buildings or facilities used for storing, loading, maintaining, and sometimes fueling,alternative fuel vehicles form an important portion of a fleet operation. Here, thedevelopment of fire and building codes is not yet complete. This requires additional care onthe part of the designers and owners of these facilities to consider all hazards associated withthe use of alternative fuel vehicles and to ensure that these hazards are properly addressed inthe plans for and the operation of the facility.

The third development, which adds to the complexity of alternative fuel use, is therecognition that more hazards must be considered than the traditional "Will it burn orexplode?" examination of fuel issues. The use of compressed gases raises issues concerninghigh fuel system pressures. LNG has the potential to cause blindness if splashed in the face. Methanol and denatured ethanol are toxic to humans. Ethanol fuel raises the issue ofdiversion for non-authorized use. Several fuels demand a further scrutiny of the need forpersonal protective gear.

Lastly, the experience of some transit properties and private fleet operators has shown thatnot all local community and regulatory groups view the use of alternative fuels as a purelypositive option. Opposition from neighborhood groups has already caused alternative fuelplans in several cities to be changed or curtailed. Transit properties and others who proposethe use of alternative fuels need to deal not only with the perceptions of fire and buildingcode officials who grant approvals, but also with the perceptions and concerns of communityand neighborhood organizations. The concerns of these groups are not limited to fleetoperations, but may also include the production of the alternative fuel and the transportationof the fuel to the point of use. It is important that the fleet operator recognize at thebeginning of a conversion to alternative fuels the types of safety issues that will need to beaddressed to satisfy these constituencies.

In view of the diversity of these safety concerns, as well as the number of possible hazards,a comprehensive and systematic program is needed to recognize and organize the existingknowledge about the health, safety, and environmental hazards of alternative fuels and toidentify where additional study is needed.

The existence of special safety concerns does not mean that alternative fuels are inherentlymore dangerous than conventional fuels, but does emphasize that forethought, goodengineering, and thorough training are requisites for the safe and successful use ofalternative fuels. Programs in which alternative fuels are used while all other aspects of thefleet operations remain unchanged are apt to have difficulties.

1.2 OBJECTIVES AND SCOPE

This study is intended to provide a systematic assessment of the safety hazards of AMFsfrom

a fleet operations perspective. It is narrowly focused on the hazards associated with moving

the fuel from the point of production to the point of use (bulk transport), the process of

transferring the fuel from the transport vehicle, and on-site storage at the fleet operator's

facility. The types of hazards that may be encountered during bulk transport, transfer, and

storage generation have been categorized as follows:

Safety Issues

- Fire Hazards

- Other Hazards

Health Issues

- Fuel Toxicity - inhalation/skin exposure

Environmental Issues

- Effects of spills

Six candidate fleet motor fuels received primary consideration during the assessment process.

These fuels and the automotive engines that are specifically designed to use the fuel have

been the subject of extensive research and development. The fuels are:

Compressed Natural Gas (CNG)

Liquefied Natural Gas (LNG)

Propane

Methanol and Methanol Blends (M-85, etc.)

Ethanol and Ethanol Blends (E-85, etc.)

Biodiesel

Hydrogen

Electricity

Hydrogen-fueled vehicles, including those using a fuel cell-electric drive, are just beingintroduced into actual operations on a prototype/demonstration basis. Battery-poweredvehicles have received increased attention in recent years, including a number of applicationsinvolving battery electric transit buses.

The overall objective of this report is to organize, analyze, and present existing information

about the potential hazards of the AMFs selected for this study. The specific focus is on the

hazards associated with potential leaks and spills of the AMFs in the bulk transport,

unloading, fleet storage processes, and fleet operations.

It should be noted that all of the potential hazards considered in this report are "acute"

hazards, i.e., immediate- or short-term hazards. Long-term ("chronic") hazards have notbeen

addressed.

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2. PREPARATION AND ORGANIZATION OF REPORT

2.1 INFORMATION SOURCES

The major sources of information used to conduct the assessment of safety, health, andenvironmental hazards associated with each AMF come from the following:

Recent key reports that cover one or more of the hazard assessment issues.

Information gathered through contacts and interviews with industry officials,trade groups, and government agencies.

The key references used to acquire information are provided at the end of this report inReferences - Section Three.

The following agencies and organizations were contacted for information on AMFs:

U.S. Department of Energy

U.S. Environmental Protection Agency

U.S. Department of Transportation

Gas Research Institute

National Hydrogen Association

National Soydiesel Development Board

Massachusetts Division of Energy Resources

New York State Energy Research and Development Authority

Boston Gas Company

Boston Edison -- Travelectric Services Corp.

Commonwealth Gas Company

2.2 ORGANIZATION OF REPORT

This report is composed of two main sections reflecting the two project tasks. The firstsection, "Production, Bulk Transport, and Bulk Storage of Alternative Fuels," focuses on thehazards associated with moving the fuel from the point of production to the point of use atthe fleet operators facility. The second section, "Use of Alternative Fuels by VehicleFleets," focuses on the operation, fueling, and maintenance of alternative fuel vehicles. Bothsections include discussion of the following fuels:

Compressed Natural Gas (CNG)

Liquified Natural Gas (LNG)

Propane

Methanol and methanol blends

Ethanol and ethanol blends

Biodiesel

Hydrogen

Electricity

Within the first section, the report is organized around a discussion of the properties, safetyissues, health issues, and environmental issues applicable to each alternative fuel, withsections on methodology, an analysis of issues, and a summary assessment of risks. Thesafety issues considered include:

General properties affecting fire hazards

Fire hazards during transport

Fire hazards during unloading to fleet storage

Fire hazards during fleet storage

Other hazards (e.g., high pressure, low temperature)

Within the second section, the report is organized around a summary list of hazards of eachalternative fuel. An introductory discussion considers the types of hazards considered andthe distinctions between hazardous fuel properties, hazards, and risks. The summary list ofhazards follows. It is accompanied by a selection of actual case histories which serve toillustrate various hazards in the summary list of hazards.

For the summary list of hazards of alternative fuels, the following hazardous properties areconsidered:

1. Flammability

2. Corrosivity

3. Toxicity (including asphyxiation)

4. High pressure

5. High temperature

6. Cryogenic temperature

7. Mechanical energy

8. Electrical energy

Although this document intends to be a comprehensive list of safety hazards, it is not a riskassessment in which the risk associated with the use of various alternative fuels are ranked orcompared. The definitions on the following page will help clarify these terms as used in thisreport.

Two separate sections of source material are included. Appendix A, titled "Sources forAlternative Fuel Safety Information" provides a bibliography, by categories, which givesbasic information for readers. Specific references in the text of the report are given in"References Section 3" and "References Section 4."

DEFINITIONS

An accident is a general term for an unplanned event with undesirable consequences.

A hazardous property (or hazardous condition) is a physical or chemical property of a substanceor situation that has the potential to cause harm. For example, a substance may be flammable orit may be contained under a high pressure.

A hazard is the combination of a hazardous property with an outcome that can cause damage orharm to people, property, or the environment. For example, a material which is flammable mayignite and result in a fire. Or a material at high pressure may release that pressure quickly,resulting in an explosion. Thus, it is common to speak of "fire hazards" or "explosion hazards"or to discuss the hazard of fire or the hazard of explosion.

A hazard event (or initiating event, or just event) is an occurrence involving equipment failure,human action or external cause that results in a hazard. For example, the ignition of a flammablematerial can cause a fire, while the rupture of a pressure vessel can result in an explosion.

The hazard probability is the chance that the hazard will occur. The hazard probability may bethought of as the combination of a hazardous property with the probability of one or moreinitiating events. For example, the probability of a fire may depend on the probability that a fuelspill could occur coupled with the probability that an ignition source is available. Hazardprobability may be expressed in purely numerical terms, such as the number of expected eventsper year or by using other qualitative or quantitative scales.

The severity of a hazard is a measure of the possible consequences of that hazard in terms ofproperty damage or the amount of injury. For example, the severity of a fire hazard may beranked by the dollar value of the property which may be destroyed. Other qualitative orquantitative scales of severity may also be used. A given hazard may have many possibleconsequences, so the severity of a hazard often depends on the hazard scenario. For example,for a given type of fuel, the fire hazard severity may be greater if the amount of fuel is greater,or if the equipment configuration allows it to burn more rapidly. Or, the severity of an electricalshock hazard is usually greater if the voltage is greater.

Risk is the combination of a hazard, a hazard probability, and a severity. For example, the riskof a vehicle fire is a combination of (a) the hazard the vehicle burning, the hazard probability (b) the chance of this event occurring, and (c) the severity of the damage the amount ofdamage to the vehicle and/or the extent of injury to the occupants.

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3. PRODUCTION, BULK TRANSPORT, AND BULK STORAGE OF ALTERNATIVE FUELS

3.1 INTRODUCTION

This section provides a detailed description of each AMF of interest, along with a discussionof its special characteristics that affect safety, health, and the environment. Each AMF ispresented separately using the following format:

General Description

(A brief summary of production sources and the general characteristics of the fuel.)

Safety Issues

(a) General Properties Affecting Fire Hazards

(b) Fire Hazards During Transport

(c) Fire Hazards During Unloading to Fleet Storage

(d) Fire Hazards During Fleet Storage

(e) Other Hazards (e.g., high pressure, low temperature)

Health Issues

Environmental Issues

The order of presentation of the AMFs is as follows:

Methanol/Methanol Blends

Ethanol/Ethanol Blends

Compressed Natural Gas

Liquefied Natural Gas

Propane

Biodiesel

Hydrogen

Electricity

3.2 METHODOLOGY

It was apparent after a number of the key reports and reference documents had been collectedthat the amount of information available is very extensive. In order to provide acomprehensive and understandable assessment, the methodology used to extract informationwas based on setting up a specific framework along the following lines:

General properties of the AMF that affect fire hazards

Potential fire hazards during bulk transport

Potential fire hazards during unloading to fleet storage

Potential fire hazards during fleet storage

Other safety hazards, particularly high pressure and low (cryogenic) temperatures thataffect personnel safety

Toxicity of the fuel based on inhalation, skin contact, and ingestion

Environmental effects of spills on land or water

This same framework is used for the presentation on each AMF in Section 3.3 Analysisof Issues. The information in this section represents a synthesis of the specific safety andhealth concerns derived from a relatively large number of documents.

Section 3.4 Summary Assessment of Risk provides a summary assessment of thesafety, health, and environmental issues on a comparative basis. This assessment is intendedto provide a broader understanding of the relative ranking of each AMF with regard to:

the relative potential for an AMF leak or spill during bulk transport and storageoperations; and

the relative consequences of an AMF leak or spill in the context of safety, health, andenvironmental impacts.

3.3 ISSUES ASSOCIATED WITH BULK TRANSPORT AND STORAGE OF

ALTERNATIVE FUELS

3.3.1 Methanol/Methanol Blends

General Description

Methanol or methyl alcohol is a clear colorless liquid that can be made from a variety ofsources including coal and natural gas. All methanol used commercially in the United Statesis manufactured from natural gas because this is by far the most economical feedstock.

Often, methanol fuel is designated M-100 to identify it as essentially 100% pure methanol. A popular methanol blend composed of 85% methanol and 15% unleaded gasoline isdesignated as M-85. The addition of 15 percent unleaded gasoline increases both the flameluminosity and the fuel volatility. The latter effect both increases the cold starting capabilityand also generally makes the vapors present in fuel tank ullage spaces too rich to beflammable.

Typically, M-85 is considered as an alternative fuel for light and medium duty gasoline(spark ignition) engine applications whereas M-100 is typically used in heavy duty diesel(compression ignition) engine applications. M-85 is also used in the flexible fuel vehicle(FFV) application where such vehicles can operate on any mixture in proportions of M-85and conventional unleaded gasoline.

3.3.1.1 Safety Issues

(a) General Properties Affecting Fire Hazards

The physical properties of methanol that affect fire hazards include its volatility, flash pointtemperature, range of flammability limits, autoignition temperature, and electricalconductivity. There are other properties of importance that affect the consequences orpotential damage associated with a methanol (or any alternative fuel) fire. These include theburn rate of liquid pools, the heating value of the fuel, flame temperature, and thermalradiation emitted from the fire.

Section 3.3 of this report provides a relative comparison of the physical characteristics ofeach alternative fuel that affects the safety, health, or environmental effects associated withits use. In this section, the major physical characteristics that differentiate the hazardsassociated with each fuel are summarized.

One general physical characteristic that differentiates methanol from other fuels is itscorrosive characteristics. Methanol is incompatible with several types of materials normallyused in petroleum storage and transfer systems, including aluminum, magnesium, rubberizedcomponents, and some other types of gasket and sealing materials.1 Therefore it is necessaryto take special precautions to ensure that methanol is transported or stored in containers andtransfer lines that have been specifically selected for that purpose.

The other significant difference between methanol and other AMFs is that it is considered tobe more toxic. However, exposure limits for inhalation of methanol vapor are only slightlylower than those for gasoline (200 ppm threshold limit value [TLV] for methanol vapor; 300ppm for gasoline vapor).2 Since gasoline is much more volatile than methanol, it is likelythat more gasoline vapors will be generated for an equivalent spill volume and therefore aremore likely to be hazardous to the persons exposed.

NFPA 325M -- Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids,1991 Edition provides a Health Hazard Rating that provides an assessment of exposure risksfor fire fighters. Methanol, along with natural gas, gasoline, and propane, has a hazarddegree of 1, which is a material that, on exposure, would cause irritation, but only minorresidual injury and is considered as only slightly hazardous to health. All of the other AMFshave a hazard degree of 0 which means that under fire conditions, they offer no hazardbeyond that of ordinary combustible material.

One other general property of methanol is the low flame luminosity of a pure (M-100)methanol fire. This makes it difficult to see the fire or even estimate its size, particularly ifit occurs in bright daylight. The methanol blends (M-85) have increased visibility becausethe burning of the gasoline fraction produces some luminance.3

One other property of interest is the relative vapor density of methanol compared to air; at1.11, methanol vapor is heavier than air. Therefore the vapor will tend to accumulate atground level or in low-lying areas such as maintenance pits.4 If the methanol vapor is not quickly dissipated through adequate ventilation, it will linger in the low-lying areas creatingan increasing opportunity for exposure to an ignition source and a subsequent fire.

The addition of unleaded gasoline to methanol to create M-85 can improve the cold startingcapabilities and increase the flame luminosity of the fuel. With regard to some of the keycharacteristics noted above, the presence of the gasoline can be expected to reduce thecorrosivity of the M-85 compared to M-100, but it will also increase the toxic healthhazards.3

(b) Fire Hazards During Transport

The bulk transport of methanol is usually done by a standard petroleum products tanker truckwhich carries approximately 10,000 gallons of fuel. From a fire hazard perspective, there islittle discernible difference in the bulk transport of methanol compared to gasoline or diesel. There is no reason to expect that methanol transportation, in general, will be any moresubject to leaks or spills than conventional gasoline or diesel transport. However, onespecific issue that must be considered is the possible use of materials that may not bemethanol compatible in the tanker truck. This could become a problem if there is a long-term exposure of methanol to seals and gaskets that may deteriorate and become subject toleaks.

One physical characteristic of methanol that is an important fire hazard consideration duringboth transport and storage is the combination of vapor pressure and flammability limits. ForM-100, vapor/air mixtures are potentially flammable at volume concentrations ranging from6.7 to 36 percent. In a fuel or storage tank, a methanol liquid temperature between 10C to43C (approximately 50F to 110F) at standard atmospheric pressure will create aflammable vapor/air mixture.4 Therefore any ullage space in a container or storage tank thatis vented to the atmosphere will contain flammable vapor-air mixtures at normal ambienttemperatures found in transport and storage operations.

This condition is different from the ullage space in a gasoline container or storage tank wherethe vapor concentration will be above the flammable limits range at normal temperature andpressure (i.e., too "rich"). In the case of diesel fuel, which is much less volatile thanmethanol, the vapor/air mixture in the headspace will generally be below the flammablelimits (i.e., too "lean") at normal ambient temperatures.

Therefore, with methanol, it is extremely important to ensure that there are strong safeguardsagainst any ignition sources inside the tank and that any vent lines or other openings haveflame arrestors. Any fill lines must extend below the liquid methanol surface to provide aseal between any external ignition sources and the methanol/air vapor.

The transport of M-85, assuming that it is not blended on-site at the fleet operators facility,mitigates some of the problems noted above for M-100. In general, M-85 is quite similar togasoline in its flammability characteristics because the fuel vapor is composed primarily ofgasoline.3 Under normal circumstances, the headspace in the container or storage volumewill contain a vapor/air mixture that is above the flammability limits concentration range,i.e., too rich to burn.

(c) Fire Hazards During Unloading to Fleet Storage

The transfer of methanol from the bulk transport tanker truck to fleet storage must take intoaccount the fact that any vapor/air mixture that leaks during the transfer operation will createa flammable volume. In addition, any methanol spill will quickly vaporize and formflammable vapor/air mixtures. For this reason, it is essential that all hose connectors havemechanical locking features, vapor recovery devices be in place between the tanker truck andthe fuel storage tank, and that grounding devices be provided to prevent static electricaldischarges from taking place. As noted earlier, any vent lines should have spark arrestorsand the fill line should extend to the bottom of the storage tank.

(d) Fire Hazards During Fleet Storage

Methanol fuel is typically stored in an underground tank that is sized to meet the needs offleet operations. The installation must be designed to use methanol compatible materials toavoid long term degradation and leaks. Fuel storage tanks designed for diesel or gasolineuse may not be methanol compatible.

The fire hazards associated with M-100 storage will be greater than for diesel fuel storagebecause it is a much more volatile fuel. A spill or leak of M-100 will create a much largervolume of flammable vapor/air mixture than an equivalent diesel spill. However, the firehazards associated with methanol storage should be approximately the same as, or lowerthan, with gasoline storage. Gasoline is more volatile than methanol; however, the potentialrange of flammability limits for M-100 is much greater (6.7% to 36%) than for gasoline(1.4% to 7.6%). This means that, considering an equivalent spill or leak (volume) of fuel,there will be an increased probability that the methanol/air vapor will come in contact withan external ignition source when compared to gasoline.

It should be noted that the range of flammability limits for most AMFs are highly dependentupon the maximum temperature of the fuel. For example, if M-100 is only exposed to amaximum temperature of 22C (70F) it is only possible to reach a maximum volumeconcentration of approximately 13% methanol based on its equilibrium vapor pressure at

22C and at atmospheric pressure. Therefore, the actual range of flammability limits formethanol may not be greater than the range for other AMFs.

The use of M-85 is primarily considered as an AMF for light and medium duty gasolineengines; therefore, it is appropriate to consider the fire hazards as being comparable to thatof gasoline. In fact the volatility and flammability limits of M-85 are very similar to thosefor gasoline because the fuel vapors from the blend are composed primarily of gasoline. Therefore, all of the precautions that are normally associated with gasoline storage must beobserved. These are primarily those that are designed to minimize the presence of anyexternal ignition sources. In addition, the presence of methanol requires that the storage tankinstallation must be methanol compatible.

3.3.1.2 Health Issues

Exposure to methanol can occur through inhalation of vapor, or through ingestion or skincontact with the liquid fuel. The toxic effects of methanol are the same regardless of themeans of exposure. Considering the fact that methanol is quite volatile, it is most likely thatthe typical route for exposure is through inhalation of methanol vapors.

Among the AMFs considered in this study, methanol vapor is considered the most toxic forinhalation exposure. The measure of fuel toxicity is the threshold limit value (TLV) forvapor exposure and it can be expressed in terms of either a time-weighted average (TWA)for an eight-hour workday or a 40-hour week, or as a short term exposure limit (STEL)expressing the maximum concentration allowable for a 15-minute exposure. For methanolvapor, the TLV-TWA value is 200 ppm, while the TLV-STEL value is 250 ppm.2 OtherAMF vapors have toxicity (TLV-TWA) concentration values that are at least five timeshigher. As noted earlier, none of the AMFs are considered to be serious health hazards bythe NFPA based on potential exposure during fire fighting activities.

Interestingly, conventional gasoline has a TLV-TWA close to that of methanol (300 ppmversus 200 ppm) and it is more volatile. Therefore, the toxic exposure risks with both ofthese fuels are likely to be similar. Diesel fuel vapors are apparently much more toxic thaneither methanol or gasoline since the TLV-TWA value for kerosene (as a proxy for dieselfuel) is only 14 ppm.2 Fortunately, diesel fuel is relatively non-volatile at normal ambienttemperature, therefore vapor exposure is not a significant issue.

The health issues with M-85 are similar to M-100. Considering the relative vapor toxicityand volatility of both methanol and gasoline, M-85 must be considered in the same healthhazards category as M-100.

Personnel involved in the bulk transport and storage of both M-85 and M-100 must beprotected from exposure through proper design of tanks and transfer lines, selection ofmethanol compatible materials, use of personnel protection equipment, and proper training toavoid accidental exposure. Something as simple as a drain line for a fuel filter or a transferhose for emptying fuel tanks can help to reduce exposure for the personnel working on theequipment.

3.3.1.3 Environmental Issues

The major environmental issues of concern with all liquid AMFs is a fuel spill, particularly aspill that reaches a sewer or drainage system. The release of flammable liquids into a sewersystem is prohibited by NFPA-30 -- Flammable and Combustible Liquids Code. One of thephysical properties of methanol that affects fuel spills is its water solubility. Normally, fuelhandling facilities that have an emergency drain connecting to a sewer will have a separatoror clarifier to ensure that the fuel (gasoline or diesel) will not reach the sewer. Thisapproach will not work with methanol since it is soluble in water and will pass directlythrough the separator. Methods for separating methanol from water exist but they are quitecomplex and costly. Therefore, the best approach is to ensure that any spills in a facility are absolutely prevented from entering any drain through the use of impoundment systems tocontain the entire volume of any potential above ground spill. In a bulk transport situationthere is obviously no way to provide such assurance for any type of liquid AMF.

Fortunately, methanol is quite volatile so that it will not persist for a long period of timewhen exposed to the environment. Methanol also biodegrades quickly.

3.3.2 Ethanol/Ethanol Blends

General Description

Ethanol is produced by the fermentation of plant sugars. Typically, it is produced in theUnited States from corn and other grain products, while some imported ethanol is producedfrom sugar cane. Like methanol, ethanol is a pure organic substance whose physical andchemical properties are invariant, unlike some other AMFs such as natural gas or propanewhich are mixtures of different hydrocarbon molecules with no standard or averagecomposition.

Pure or neat ethanol (E-100) is rarely used for transportation applications because of theconcern about intentional ingestion. In fact, ethanol for commercial or industrial use isalways denatured (small amount of toxic substance added) to avoid the federal alcoholicbeverage tax. Therefore, it is unlikely that ingestion would be a serious problem. For heavyduty diesel (compression ignition) engine applications, such as transit buses, two ethanolblends have been used:

Ethanol E-95, composed of 95 percent ethanol and 5 percent unleaded gasoline.

Ethanol E-93, composed of 93 percent ethanol, 5 percent methanol, and 2 percentkerosene.

Both blends have been used in Detroit Diesel heavy duty engines similar to the 23:1 highcompression ratio engines developed for methanol. For light and medium duty gasoline(spark ignition) engine applications, the typical ethanol blend is 85% ethanol and 15%unleaded gasoline. This fuel is similar to M-85; therefore, it can be used in flexible fuelvehicles which can ignite any mixture composition of E-85 and unleaded gasoline.

3.3.2.1 Safety Issues

(a) General Properties Affecting Fire Hazards

The general properties of ethanol (C2 H5 OH) are relatively similar to those of methanol(CH3 OH). With respect to fire hazards, ethanol is less volatile than methanol (the Reidvapor pressure of ethanol is less than half that of methanol) and the range of flammabilitylimits is smaller. On this basis alone, ethanol is safer than methanol. However, as pointedout above, there are relatively few situations where the ethanol will be in a pure form since itis usually used as either E-95 or E-85. With both ethanol and methanol blends, any fuel vapors will contain a substantial percentage of gasoline, therefore there would be very littledifference in the flammability characteristics of the two fuels.3

There are other general physical characteristics of pure ethanol that are important from asafety perspective. While ethanol is less corrosive to metals, gaskets, and seals thanmethanol, it is still necessary to make sure that any container, transfer lines, and fittings aremade from materials that are ethanol compatible. Ethanol vapor is much heavier than air(much more so than methanol) so that any vapor from a leak will move downwards andcollect in low lying areas where it may linger as a flammable vapor/air mixture unless thereis adequate ventilation. Fortunately ethanol, similar to gasoline, has a relatively low odorthreshold such that personnel in the vicinity of a leak of E-100 or any blend should be able torapidly detect it. As noted in Reference 2, there is considerable variation in the reportedodor threshold data for various AMFs, particularly ethanol and methanol. Therefore, thedetection of a leak of any AMF by odor is subject to a number of variables.

(b) Fire Hazards During Transport

The bulk transport of pure ethanol or ethanol blends by tanker truck will be subject to thesame types of hazards as other bulk transportation of petroleum products. As long as thetanker truck container, lines, and fittings are constructed from ethanol compatible materials,there would be no reason to expect an increased rate of leaks or spills when compared to theequivalent volume of gasoline or diesel fuel transported.

As with M-100, the bulk transport and storage of E-100 will involve an ullage spacevapor/air mixture that is in the flammable range at volume concentrations from 3.3 to 19%,corresponding to ethanol tank temperatures between 4C and 46C (approx. 40-115F).4Therefore, stringent precautions have to be taken to avoid the possibility of ignition sourcesinside any container or tank containing E-100.

Ethanol blends, typically E-85, that are transported will exhibit volatility and flammabilitycharacteristics that are very similar to gasoline because the fuel vapors will be composedprimarily of gasoline. As with methanol blends, the headspace vapor/air mixture for E-85will be above the flammability limits concentration range.

(c) Fire Hazards During Unloading to Storage

The transfer of E-100 from bulk transport truck to fleet storage must take into account thevolatility and flammability of any leaked or spilled fuel. The following precautions arenecessary:

hose connections with mechanical locking fasteners;

vapor recovery devices; and

grounding devices to prevent static electric discharge.

The unloading of E-100 and ethanol blends must be accomplished at the same level of safetystandards as used for gasoline. These standards are spelled out in NFPA30--Flammable andCombustible Liquids Code and NFPA30A--Automotive and Marine Service Station Code. These codes address fueling facility, storage, and handling requirements for all flammableand combustible liquids including both M-100 and E-100. It is of interest to note that theNFPA classification for gasoline, M-100, and E-100 is exactly the same (Class IB flammableliquids defined as those having closed-cup flash points below 23C and having a boiling pointat or above 38C). This is an example of the need to consider the spectrum of fire hazardproperties when considering AMFs because as discussed above, the ullage space hazardsalone make the transport and transfer of E-100 (and M-100) an increased fire hazard riskwhen compared to the blended fuels and gasoline.

(d) Fire Hazards During Fleet Storage

Ethanol fuel storage requires the selection of materials that will not degrade over the longterm. Fuel tanks designed for diesel or gasoline use may not be ethanol compatible.

The safety precautions that must be taken with ethanol storage are similar to those formethanol and include:

Positive prevention of ignition sources entering the storage space by providingsuch devices as spark arrestors in vent pipes, properly sized ground straps, and fillpipes extending to the bottom of the tank; and

Prohibiting the placement of any pumps or other equipment within the storagetank that can create an ignition source.

All of the above requirements for the prevention of ignition sources, leaks and spills, andadequate provision for handling any leakage of spills when storing or handling ethanol (andany other NFPA-designated flammable or combustible liquids) are spelled out in great detailin the applicable NFPA codes. For example, typical ignition sources identified in NFPA30include:

open flames

lightning

hot surfaces

radiant heat

smoking

cutting and welding

spontaneous ignition

frictional heat or sparks

static electricity

electrical sparks

stray currents

ovens, furnaces, heatingequipment

Therefore, there is a very substantial base of experience in handling and storage of suchflammable liquid AMFs, such as E-100, E-85, M-100, and M-85. The experience has beencodified into the NFPA codes which are used by local regulatory authorities (or alternatively,the Uniform Fire Code which is used more often in the Western part of the U.S.). On thepresumption that these codes are followed by the agencies involved in the bulk transport and storage of AMFs, in cooperation with local fire authorities, there is no reason to expect agreater incidence of fires in ethanol (or other AMF) storage situations then for a comparablenumber of gasoline storage facilities.

3.3.2.2 Health Issues

Ethanol is less toxic than methanol. The threshold limit value-time weighted average (TLV-TWA) concentration for ethanol vapor is 1,000 ppm compared to 200 ppm for methanol. Extensive skin exposure to ethanol can cause redness and irritation. Concern aboutintentional ingestion of ethanol by employees is mitigated by the fact that alcohols intendedfor industrial use must be denatured in order to avoid the federal alcoholic beverage tax. Denatured alcohol is ethanol that contains a small amount of a toxic substance such asmethanol or gasoline, which cannot be removed easily by chemical or physical means. However, ethanol fuels have been widely advertised as food-based, so there may beconfusion among some users concerning the denatured status of fuel ethanol.

3.3.2.3 Environmental Issues

The major environmental concern with ethanol is the same as for methanol; since it is watersoluble, it is necessary to take stringent precautions in order to ensure that any ethanol spilldoes not reach a sewer or drainage system. These same precautions cannot be assured forthe bulk fuel transport situation.

3.3.3 Compressed Natural Gas

3.3.3.1 General Description

Natural gas has been used as a vehicle fuel in the United States for several decades. Becauseof the residential and industrial use of natural gas, the industry has its own distributionsystem and supply network that is much more extensive than for any other liquid or gaseousAMF. The issues of bulk transport and storage are completely different from most of theother AMFs which are typically transported to fleet storage via tanker truck, unless thenatural gas has been liquefied. (Liquefied Natural Gas [LNG] is presented in the nextsection.)

The typical fuel system for natural gas vehicles is one with highly compressed (typically 20to 25 MPa or 3,000 to 3,600 psi) gas stored in high pressure cylinders on the vehicle. Thecontainment of natural gas at such high pressures requires very strong storage tanks whichare both heavy and relatively costly. This distinguishing feature of CNG is the one that hasthe most impact on safety issues.

CNG is generally produced on-site at a fleet fueling facility using compressors fed from anearby natural gas pipeline in conjunction with some limited high pressure on-site storage. For example, with very large fleets, the preferred approach will involve direct fast fill from the compressor where the compressor flow rate is sufficient to fill a vehicle tank in less than10 minutes. In order to accomplish this filling effectively, an intermediate high pressurestorage tank with a volume of 3 to 4 times the vehicle fuel tank capacity is required.5 Forslow fill (overnight), there is no need for a large storage tank, a small buffer tank issufficient.

3.3.3.2 Safety Issues

(a) General Properties Affecting Fire Hazards

Natural gas is a mixture of gases comprised primarily of methane with small amounts ofethane, propane, and butane. These heavier hydrocarbons (i.e., ethane, propane, and butane)tend to reduce the octane rating of natural gas. Therefore, the actual composition of thenatural gas plays an important role in the performance of fleet vehicles. For the purposes ofdiscussion in this report, the physical properties are based on the properties of the principalcomponent, methane, unless otherwise specifically noted. The typical range of methane forpipeline natural gas in various parts of the country is from approximately 80% to 95%. TheCalifornia Air Resources Board (CARB) has adopted specifications for natural gas as avehicular fuel which require that the methane content be greater than 88%. Even with thistype of specification, there is still considerable variation possible in the general physicalproperties of natural gas.

The physical properties of natural gas that affect safety include the autoignition temperatureand the flammability limits range. The autoignition temperature (also known as ignitiontemperature) is the lowest temperature at which a substance will ignite through heat alone,without an additional spark or flame. The ignition temperature of natural gas varies withfuel composition, but it is always lower than that of pure methane. The estimated ignitiontemperature of natural gas is in the range from 450-500C. The flammability limits rangefor natural gas is approximately 5% to 15% volume concentration.

More importantly, the leakage of compressed natural gas will immediately form a largegas/air mixture volume that is in the flammable range within a portion of the immediate areaaround the leak. A unit volume of CNG at 25 MPa psi will expand by approximately 200times when released to the atmosphere. The ignition energy required is very small forvirtually all of the AMF vapor/air mixtures being considered (in the range fromapproximately 0.15 to 0.30 millijoules).2 Therefore, the existence of a CNG leak creates anincreased probability of exposure to a stray ignition source such as a static electric sparkwhen compared to the leakage of an equivalent mass of an AMF that is expelled in a liquidform and vaporizes over a period of time.

Natural gas is colorless, tasteless, and relatively nontoxic. An odorant is added in suchamounts to make the odor noticeable at 1/5 of the lower flammability limit of 5%. Thus, theodor threshold for CNG is approximately 10,000 ppm. Therefore, personnel in the vicinityof a natural gas leak will be able to detect the presence well before the gas has reached theflammable limit in the area adjacent to the person.

The most unique physical characteristic of CNG does not derive from the physical propertiesof methane, but from the fact that the gas is stored at an extremely high pressure for use as avehicular fuel. The presence of material stored and transferred at pressures that far exceedthe normal experience of most fleet operations personnel raises the standard of precautionand training required. Inadvertent opening of valves or loosening of fittings containing highpressure natural gas will not only lead to creation of a fire hazard, but can also result in thehigh velocity ejection of metal parts or fragments that could be lethal to nearby personnel.

The existence of the high pressure methane gas also leads to thermodynamic expansion considerations which have not been addressed thoroughly in prior studies of CNG safety. The rapid expansion of methane gas from a high pressure cylinder or transfer line leak toatmospheric pressure will inevitably result in a significant cooling effect which will result ina vapor cloud of very cold and dense gas. Conventional practice has been to assume that anyleak of CNG will rise immediately due to the fact that methane at normal temperatures islighter than air. Consequently, safety design practices have been focused on ceilingventilation and detection of methane vapors. In fact, it is highly likely that any significantleakage from storage tanks and transfer lines will migrate down and fill in low lying areas asit is moved about by any wind or circulatory effects. Ultimately, the methane will warm upand rise (assuming a flammable mixture has not come into contact with an ignition source),but it is extremely difficult to estimate the time involved and the configuration of theflammable methane/air mixture during that time period.

(b) Fire Hazards During Transport

In most cases, the only "transport" issue involves the connection from the existing naturalgas pipeline to the fleet operators compressor station. The local gas utility will typicallywork with the fleet operator to provide an underground supply delivering pipeline qualitynatural gas at pressures ranging from 5 to 50 psig. While this is a much lower pressure,there is still a significant potential for a massive gas release if there is some unauthorizeddigging or trenching at the connection line resulting in a line break, or in the event of an on-site accident resulting in a line rupture at the connection to the compressor station. Onenecessary provision is a rapid and positive means of shutting off the supply flow from thepipeline in the event of any type of leak in the supply line.

In some cases, natural gas is delivered to the fleet user in compressed form by means of atruck trailer containing compressed gas. This type of gas delivery may be used on apermanent basis for small users who cannot justify the cost of a compressor station, or on atemporary basis to users whose compressor station is unavailable.

In this case, issues arise concerning the crashworthiness of the trailer: while the gas cylindersthemselves are robust, the valves and associated piping may be vulnerable. Also, it ispossible that the tanks might be exposed to a gasoline- or diesel-fueled fire should the tractortrailer truck be involved in a traffic accident.

The use of the CNG delivery trailer also requires that flexible connections be made andbroken in the course of each delivery. Experience shows that extra vigilance is necessary during truck loading and unloading because of the making and breaking of connections,possibility of leaking connections, possibility of truck movement when connected, etc.

(c) Fire Hazards During Transfer to Fleet Storage

In the case of CNG, the process involves the compression of the natural gas to the desiredpressure (approximately 25 MPa, 3600 psi) and transfer to the storage tank systems. Thereare various approaches that can be used for the CNG storage depending upon whether a fastfill (i.e., approximately 9,000 SCF of gas transferred to a vehicle in less than 10 minutes) ora slow fill (many hours or overnight) approach is used. In either case, however, there issome limited storage involved at pressures from 20 or 25 MPa (slow fill) up to 35 MPa forfast fill operations.

Pipeline natural gas contains small amounts of nitrogen, carbon dioxide, hydrogen sulfide,and helium. The quantity of these contaminant gases can vary from zero to a few percentdepending upon the source and seasonal effects. More importantly, the pipeline gas cancontain water vapor in amounts up to 112 mg/m3 (7 lbs. per million cubic feet) of gas.

The carbon dioxide and hydrogen sulfide components of natural gas, in the presence ofwater, can be corrosive to carbon steel. The corrosive effect is increased by pressure. Sincethe pressure considered in CNG vehicle applications is so high, there is a real concern aboutexcessive corrosion leading to the sudden explosive rupture of a container. NFPA 52 --Compressed Natural Gas (CNG) Vehicular Fuel Systems, 1992 Edition provides that the gasquality in any pressurized system components handling CNG comply with the followingspecification:

H2S and soluble sulfides partial pressure 0.35 kPa, max

Water vapor 112 mg/m3 (7.0 lb./MMSCF), max

CO2 partial pressure 48 kPa, max

O2 0.5 volume %, max

The NFPA committee involved in developing the standard relied on field experience andresearch which led them to believe that if the water content is limited as specified above, thepotential for corrosion problems is not a major concern. It should be noted that a watervapor content of 112 mg/m3 amounts to a very small concentration of water vapors;therefore, natural gas at or below this level is quite dry. The federal government has taken amore conservative position due to the corrosion failure of a cylinder comprising one ofseveral in a tube trailer in 1978. As a result, U.S. DOT has specified the composition ofCNG being transported in interstate commerce. The limits for the corrosive components arevery low, including an upper limit for water vapor set at 8 milligrams per cubic meter ofgas.

The existence of this potential problem with the corrosive properties of natural gas makes itnecessary to dry and treat the gas before high pressure storage whenever such corrosiveconstituents are in place. NFPA 52 also states that cast iron, plastic, galvanized aluminum, and copper alloys exceeding 70% copper are not approved for CNG service because thesematerials lack the necessary strength or resistance to corrosion required for CNG service.

In addition to the NFPA standard, the Society of Automotive Engineers has established SAEJ1616 Recommended Practice for Compressed Natural Gas Vehicle Fuel with provisionsintended to protect the interior of the fuel container, as well as other fuel systemcomponents, from corrosion.6

All of the above serves to point out that there is a substantial level of care which must betaken in the design and operation of high pressure CNG storage systems in order to avoidleaks or ruptures. In the event of a leak or rupture, the CNG fuel flow rate out of thestorage tank or piping can be very high, and any ensuing fire (or explosion) will be likely tohave a very high heat release rate. Compounding this problem is the difficulty of shuttingoff the CNG leak and extinguishing the fire.

(d) Fire Hazards During Storage

The amount of CNG that has to be stored at the fleet operator's facility is a function of thefill technique. For fast fill, the CNG storage volume should be at least 3 times (often up to4 times) the individual fleet vehicle fuel tank volume. For a typical 40-foot bus, the fueltanks would require approximately 250 kg. of CNG. This would mean a buffer storagecapacity of approximately 750 to 1,000 kg. Compared to other AMFs, this storage volumeis fairly small, thereby reducing the total potential fire and explosion impact of a massiverupture of the storage tank.

A slow fill system would have a much smaller buffer storage system because thecompression system would typically be sized to handle the maximum number of vehicles tobe fueled on an overnight basis.

In the unlikely event that a fleet operator decided to fast fill from a mobile CNG tube trailertruck, the amount of CNG stored on-site would increase substantially. If more than onetrailer were present on the site, the total amount of CNG would be in the order of 6,000 kg(13,000 lb). The Environmental Protection Agency has recently (Federal Register, January31, 1994, pp. 4478-4499) issued a Final Rule promulgating a list of regulated substances andthresholds required under Section 112(r) of the Clean Air Act, as amended. Methane is onthe list of regulated flammable substances with a threshold quantity of 4550 kg (10,000 lb). A facility storing more than this threshold amount is subject to the development andsubmission of a Risk Management Plan (RMP) which includes a hazard assessment, aprevention program, and an emergency response program. The RMP requirement is in therulemaking process currently; the proposed rule was published on October 20, 1993 (58 FR54190).

This requirement is much more applicable to the storage of LNG, hydrogen, and propanewhere there is more likely to be more than 4550 kg (10,000 lb.) stored at a facility. Thisthreshold quantity can easily be exceeded for AMFs used in medium to large fleetoperations.

3.3.3.3 Health Issues

The principal constituents of natural gas, methane, ethane, and propane, are not consideredto be toxic. The American Conference of Governmental Industrial Hygienists (ACGIH)considers those gases as simple asphyxiants, which are a health risk simply because they candisplace oxygen in a closed environment. The Occupational Safety and HealthAdministration (OSHA) has set a time-weighted average (TWA) personal exposure limit(PEL) of 1,000 ppm for propane. A number of minor constituents of natural gas haveACGIH-listed threshold limit values (TLVs), including butane - 800 ppm, pentane - 600ppm, hexane - 50 ppm, and heptane - 400 ppm. The effective TLV for an average naturalgas composition, considering all of these limits, is about 10,500 ppm.3

The odor threshold of odorized natural gas is about 10,000 ppm. Therefore, it is unlikelythat personnel will be unknowingly exposed to the TLV concentration since they can detect itby odor.

3.3.3.4 Environmental Issues

There are no significant environmental hazards associated with the accidental discharge ofCNG.

3.3.4 Liquefied Natural Gas

3.3.4.1 General Description

Liquefied natural gas (LNG) is produced by cooling natural gas and purifying it to a desiredmethane content. The typical methane content is approximately 95% for the conventionalLNG produced at a peak shaving plant. Peak shaving involves the liquefaction of natural gasby utility companies during periods of low gas demand (summer) with subsequentregasification during peak demand (winter). It is relatively easy to remove the non-methaneconstituents of natural gas during liquefaction. Therefore, it has been possible for LNGsuppliers to provide a highly purified form of LNG known as Refrigerated Liquid Methane(RLM) which is approximately 99% methane.

The primary advantage of LNG compared to CNG is that it can be stored at a relatively lowpressure (20 to 150 psi) at about one-third the volume and one-third the weight of anequivalent CNG storage tank system. The big disadvantage is the need to deal with thestorage and handling of a cryogenic (-160C, -260F) fluid through the entire process ofbulk transport and transfer to fleet storage.

3.3.4.2 Safety Issues

(a) General Properties Affecting Fire Hazards

Even though the end product of the use of CNG and LNG for vehicular applications isessentially the same, the general properties affecting safety are quite different. On one hand,LNG is a more refined and consistent product with none of the problems associated withcorrosive effects on tank storage associated with water vapor and other contaminants. On theother, the cryogenic temperature makes it extremely difficult or impossible to add anodorant. Therefore, with no natural odor of its own, there is no way for personnel to detectleaks unless the leak is sufficiently large to create a visible condensation cloud or localizedfrost formation. It is essential that methane gas detectors be placed in any area where LNGis being transferred or stored.

The cryogenic temperature associated with LNG systems creates a number of generalizedsafety considerations for bulk transfer and storage. Most importantly, LNG is a fuel thatrequires intensive monitoring and control because of the constant heating of the fuel whichtakes place due to the extreme temperature differential between ambient and LNG fueltemperatures. Even with highly insulated tanks, there will always be a continuous build upof internal pressure and a need to eventually use the fuel vapor or safely vent it to theatmosphere. When transferring LNG, considerable care has to be taken to cool down thetransfer lines in order to avoid excessive amounts of vapor from being formed.

The constant vaporization of the fuel also has an interesting effect on the properties of thefuel, unless it is a highly purified form of LNG, i.e., RLM. The methane in the fuel willboil off before some of the other hydrocarbon components such as propane and butane. Therefore, if LNG is stored over an extensive period of time without withdrawal andreplenishment the methane content will continuously decrease and the actual physicalcharacteristics of the fuel will change to some extent. This is known as "weathering" of thefuel.7

Another consideration is that under low temperatures, many materials undergo changes intheir strength characteristics making them potentially unsafe for their intended use. Forexample, materials such as carbon steel lose ductility at low temperature, and materials suchas rubber and some plastics have a drastically reduced ductility and impact strength such thatthey will shatter when dropped.

As before, many of these potential issues have been identified and addressed in the variouscodes that have been developed by the NFPA and under the Uniform Fire Code. Forexample, the NFPA has the following national standards and codes applicable to LNG:

NFPA 59A -- Standard for Production, Storage, and Handling of LiquefiedNatural Gas

NFPA 57 (draft) -- Standard for Liquefied Natural Gas Vehicular Fuel Systems (final code expected to be published in 1995)

(b) Fire Hazards During Transport

LNG may either be liquefied on-site or it can be delivered to fleet storage using a standard10,000 gallon LNG tanker truck. In general, only the largest fleet operators would find on-site liquefaction to be advantageous. Typical LNG storage vessels, including those used onthe tanker truck, have the following basic components:

Inner pressure vessel made from nickel steel or aluminum alloys exhibitinghigh strength characteristics under cryogenic temperatures

Several inches of insulation in a vacuum environment between the outer jacketand the inner pressure vessel. Stationary tanks often use finely ground perlitepowder, while portable tanks often use aluminized mylar super-insulation.

outer vessel made of carbon steel and not normally exposed to cryogenictemperatures

control equipment consisting of loading and unloading equipment (piping,valves, gages, pump, etc.) and safety equipment (pressure relief valve, burst disk,gas detectors, safety shut off valves, etc.)

The double walled construction of the LNG tanker truck is inherently more robust than theequivalent tanker truck design for transport of other liquid AMFs. Therefore, the transportof LNG is safer from the perspective of fuel spills resulting from a tank rupture during anaccident. A rupture of the outer vessel would cause the loss of insulation and result in anincreased venting of LNG vapor. While this is of concern, it is relatively minor comparedto the prospect of an LNG spill.

An explosion of an LNG container is a highly unlikely event that is possible only if thepressure relief equipment or system fails completely or if there is some combination of anunusually high vaporization rate (due to loss of insulation) and some obstruction of theventing and pressure relief system preventing adequate vapor flow from the inner pressurevessel with a resultant pressure build up. If the pressure builds up to the point where thevessel bursts, the resulting explosion is known as a BLEVE (boiling liquid expanding vaporexplosion) with the container pieces propelled outward at a very high velocity.7 This is ahighly unlikely event due to the extensive requirements for pressure relief including pressurerelief valves and burst discs that are built into the design codes. (There have been no reportsin the literature reviewed of any BLEVE occurring with LNG.)

In the event that the LNG vessel is ruptured in a transport accident and the LNG is spilled,there will be a high probability of a fire because a flammable natural gas vapor/air mixturewill be formed immediately in the vicinity of the LNG pool. In an accident situation, thereis a high likelihood of ignition sources due to either electrical sparking, hot surface, orpossibly a fuel fire created from the tanker truck engine fuel or other vehicles involved in theaccident. The vapor cloud from an LNG pool will be denser than the ambient air; therefore,it will tend to flow along the ground surface, dispersed by any prevailing winds.

When spilled along the ground or any other warm surface, LNG boils quickly and vaporizes. A high volume spill will cause a pool of LNG to accumulate and the boiling rate will decrease from an initial high value to a low value as the ground under the pool cools. Theheat release rate from an LNG pool fire will be approximately 60% greater than that of agasoline pool fire of equivalent size.

(c) Fire Hazards During Transfer to Fleet Storage

The transfer of LNG from a tanker truck to fleet storage is a complex process that involvesthe active participation of both the tanker truck driver and a representative of the fleetoperator. A partial listing of some of the steps involved provides some indication of thesafety precautions that are necessary.7

After the truck is chocked and the engine is shut off, a grounding cable is attachedto the truck to ground any electrostatic discharge.

A flexible liquid transfer hose is attached to the tanker and purged with LNG toremove all air.

A fleet operator representative will open the storage vessel liquid fill line and thedriver will open the trailer's main liquid valve.

The driver will control the pressure in the trailer tank via a pressure building linewhere LNG is vaporized and returned to the tank to maintain a pressuredifferential of at least 15 psi between the tanker and the storage vessel.

The driver will use a mechanical means to maintain a tight connection at the hosecoupler to compensate for differential expansion.

The safety features that are typical of truck storage transfer of LNG include equipmentdesign such as trailer liquid valves that are interlocked with the truck brake system to preventfuel transfer before the truck is properly secured; remote-controlled, redundant liquid valves;storage vessel alarms to prevent overfill; and long drain lines for safety-directing ventedLNG vapor.

The complexity of the fuel transfer arrangement creates the potential for leaks and spillsthrough human error and equipment failure. One of the particular concerns is that the fueltransfer equipment goes through a continuous cycle of cool down to cryogenic temperaturesand warm up to ambient temperature. This type of thermal cooling can create additionalstresses on equipment and sealing devices which could result in decreased reliability overtime.

(d) Fire Hazards During Fleet Storage

LNG storage facility requirements for a total on-site storage capacity of 70,000 gallons orless are defined in the draft NFPA 57 -- Standard for Liquefied Natural Gas (LNG) VehicularFuel Systems. NFPA 59A -- Standard for the Production, Storage, and Handling ofLiquefied Natural Gas (LNG) is applicable to storage volumes above 70,000 gallons. Both ofthese standards address similar issues including siting of the storage tank, provision for spilland leak control, and the basic design of the storage container and LNG transfer equipment.

One of the major provisions at any LNG storage facility is the requirement to provide animpounding area surrounding the container to minimize the possibility of accidental dischargeof LNG from endangering adjoining property on important process equipment and structure,or reaching waterways. This requirement ensures that any size spill at a fleet storage facilitywill be fully contained and the risk of any fire damage will be minimized.

(e) Other Hazards

LNG has a unique safety hazard among the AMFs because of the potential exposure ofpersonnel to cryogenic temperatures. Workers can receive cryogenic burns from direct bodycontact with cryogenic liquids, metals, and cold gas. Exposure to LNG or direct contactwith metal at cryogenic temperatures can damage skin tissue more rapidly than when exposedto vapor. It is also possible for personnel to move away from the cold gas before injury.

The risk of cryogenic burns through accidental exposure can be reduced by the use ofappropriate protective clothing. Depending upon the risk of exposure, this protection canrange from loose fitting fire resistant gloves and full face shields to special extra protectionmulti-layer clothing.

Another unusual hazard associated with aged LNG will arise in the unlikely event that thereis a large spill of LNG onto a body of water. This could occur in an accident situationinvolving an LNG transport vehicle container rupture and spill into an adjacent water body. The hazard is known as a rapid-phase transition (RPT) -- in this case a rapid transformationfrom the liquid phase to vapor. If significant vaporization occurs in a short time period, theprocess can, and usually does, resemble an explosion.8

The RPT "explosion" phenomenon for LNG on water has been observed in a number ofsituations and has been studied extensively in both laboratory and large scale tests. Thetemperature of the water and the actual composition of the LNG are important factors indetermining whether an RPT will take place. It should also be noted that RPTs have beenobtained for pure liquefied propane with water temperature in the range of 55C (130F).

3.3.4.3 Health Issues

The principal constituents of natural gas, methane, ethane, and propane, are not consideredto be toxic. The American Conference of Governmental Industrial Hygienists (ACGIH)considers those gases as simple asphyxiants, which are a health risk simply because they candisplace oxygen in a closed environment. The Occupational Safety and HealthAdministration (OSHA) has set a time-weighted average (TWA) personal exposure limit(PEL) of 1,000 ppm for propane. A number of the minor constituents of natural gas haveACGIH listed threshold limit values (TLVs), including butane - 800 ppm, pentane - 600ppm, hexane - 50 ppm, and heptane - 400 ppm. The effective TLV for an average naturalgas composition, considering all of these limits, is about 10,500 ppm.3

Unlike CNG, LNG cannot be odorized; therefore, there is some concern about the ability ofpersonnel to detect TLV concentrations. This is another reason to ensure that methanedetectors are in place wherever personnel may be exposed.

3.3.4.4 Environmental Issues

There are no significant environmental hazards associated with the accidental discharge ofLNG.

3.3.5 Propane

3.3.5.1 General Discussion

Propane, which is otherwise known as liquefied petroleum gas, consists of a mixture ofpropane, propylene, butane, and butene. These gases are referred to as natural gas liquidssince they are present in wellhead natural gas. Liquefaction of these gases will occur bycompressing them to pressures above 800 kPa (120 psi) at room temperature. The termpropane is used in this section to reflect the fact that this AMF is typically composed of morethan 95% propane. The term also reflects industry practice for the gas as a motor fuel.

Approximately 60% of the U.S. propane supply comes from the processing (stripping) ofwellhead natural gas and the remaining 40% is a by-product of petroleum refining. Propanefor use in vehicle fleet operations has to be formulated so that it contains at least 95%propane and contains no more than 2.5% butane and heavier hydrocarbons. ASTMspecifications for propane meeting this requirement include those for commercial propanewhich is suitable for light duty internal combustion engine applications and special dutypropane which is suitable for heavy duty applications.

There is a substantial base of experience with propane as an automotive fuel since it is thethird most heavily used fuel, after gasoline and diesel fuel. It is estimated that there areapproximately 350,000 propane vehicles in operation, with most of them being aftermarketconversions of gasoline vehicles. Historically, propane was used extensively in transit

applications from the 1940s up to 1970. The largest single user was the Chicago TransitAuthority which in 1970 operated 1,400 propane buses, reportedly with a good safetyrecord.5

3.3.5.2 Safety Issues

(a) General Properties Affecting Fire Hazards

Propane is an extremely volatile fuel compared to the other liquid AMFs being considered. The Reid vapor pressure (RVP) of propane is more than an order of magnitude greater thangasoline which is the next most volatile fuel (1400 kPa versus 100 kPa). Propane is storedunder moderate pressure (110 to 150 psi) at ambient temperatures to maintain it in a liquidstate. In the event of an accidental release of propane to the atmosphere, about one-third ofthe liquid flashes to vapor at a temperature of -70F or lower.5 Leaking propane will discharge at a high velocity due to the pressure differential, turning the liquid into anatomized spray with the droplets typically evaporating before they can fall to the ground. Larger spill quantities will form a boiling pool on the ground surface which will cool downand essentially stop active boiling of the pool when the ground surface becomes sufficientlycool. Vaporization will continue until all of the propane evaporates.

Due to the rapid vaporization of propane, the pool burn rate is the highest of all the liquidAMFs considered. As a result, the heat release rate from a propane fire is approximatelytwice that of a gasoline fire for the same liquid spill volume. The flammability limits rangefor propane is similar to that for gasoline. Consequently, when compared to accidental spillsof an equivalent volume of gasoline, propane vapor is more apt to come into contact with anignition source due simply to the much higher volatility of the fuel and the resulting largervolume of flammable propane/air mixture.

Another physical characteristic of interest is that propane vapor is heavier than air so it willdescend from the point of a leak and accumulate and linger in low-lying areas unless there isadequate ventilation.

(b) Fire Hazards During Transport

Propane fuel is typically delivered to fleet storage via tanker trucks with capacities up toapproximately 10,000 gallons. All propane tanker trucks must conform to applicable U.S.DOT regulations regarding Hazardous Materials Regulations and Federal Motor CarrierSafety Regulations. The regulations specify the materials design factors and pressure reliefconsiderations for cargo transport. A major concern is the setting of pressure relief valvesso that the container will not vent propane vapor in the event of an unusually warm day. Allof these containers are typically manufactured from steel and are qualified under the ASMEpressure vessel code. The minimum design pressure for the container is based on the vaporpressure of the propane at 45C (115F). Since the vapor pressure for commercial propaneat that temperature is 243 psig, the design pressure typically is 250 psig with a safety factorof 4:1, for the tank stress calculations and selection of tank construction materials.

These pressure requirements result in a very strong tank container design. The net effect isthat the container for propane on a tanker truck will be much more rugged and resistant torupture from mechanical forces associated with an accident when compared to the transportof other liquid AMFs that are not pressurized, with the exception of the double shell tank forLNG.

On the other hand, the transport of a liquid fuel at moderately high pressure means that thereis an increased probability of fuel leaks at joints and fittings. The piping system includinghoses, along with fittings and valves will all be designed to code requirements for theexpected pressures. But with any piece of equipment that is in frequent use on the road,there is an increased likelihood of eventual wear and vibration that could create theopportunity for small leaks.

(c) Fire Hazards During Unloading to Fleet Storage

Propane is typically transferred from the tanker truck to fleet storage by pumping it from atruck into the storage container. As with any transfer of fuel, this is likely to be the mostpotentially hazardous part of the bulk transport to storage process. The fact that personnelare dealing with pressurized valves and lines, where any human error may result in a seriousdischarge of propane, makes it a point of concern.

Fortunately, propane is odorized so that the presence of a small leak may be detected by thepresence of its odor in the vicinity of any personnel responsible for unloading it. However,as noted earlier, propane vapor will descend and in the absence of any circulating air, it maygo undetected in a low-lying area.

(d) Fire Hazards During Storage

All propane storage containers are constructed according to the appropriate ASME PressureVessel Code. Design pressures are usually on the order of 250 psig with the pressure releasedevices typically set in the vicinity of 375 psig. Normally, underground tank installation isspecified for liquid fuels such as gasoline and diesel, mainly because it eliminates the hazardof fuel spills caused by vehicles running into the tank, and also because it allows more spacefor parking of vehicles. Propane, however, is ordinarily stored in above-ground tanksconstructed of thick guage steel. The tanks are strong enough to be supported by concrete orsteel saddles without deforming. The tanks are then surrounded by heavy upright steel pipesstructurally mounted in concrete to act as a barrier against vehicle intrusion into the tankarea.5

The structural strength of the storage tank and the proper design of all piping, valves, andfittings should provide a high level of protection against any massive leaks. The weakestpoints in any pressurized system like a propane storage system will be at any joints,connections, or fittings where there are always possibilities for developing small leaks overtime. The odorization of propane along with the proper placement of combustible gasdetectors and the natural ventilation in an outdoor area should help to prevent any seriousfire hazard from developing.

One of the major safety considerations with the storage of propane is the possibility of apressure buildup in the tank due to external heating from a fire combined with a failure ofthe pressure relief or venting system. The resultant explosion of the tank due tooverpressure would lead to a BLEVE incident. The fact that all of the applicable codes andfederal regulations for container design provide for the placement of pressure relief devices,and the subsequent testing of those devices on a regular basis, leads to the conclusion that thelikelihood of an overpressure leading to a BLEVE is exceedingly small, particularly in afixed storage facility situation. Unlike an accident situation with a transport vehicle where itis possible to roll over and damage the pressure relief and other protective equipment, there is little reason to expect that multiple devices for pressure relief at a stationary facility wouldsimultaneously fail.

(e) Other Hazards

Since propane is stored under pressure during bulk transport and storage operations, there isa potential hazard associated with an inadvertent opening of a fitting or plug which couldbecome a projectile. In addition, when propane expands out of a leak or hole, the rapidvaporization or flashing of the liquid causes the stream to reach temperatures that can causefreeze burns.

When compared to other AMFs, the potential high pressure hazard with propane is much lessthan with CNG (3600 psi vs. 150 psi); and the freeze burn hazard is much less than withLNG, because the propane liquid starts at ambient temperature as it leaves the tank.

3.3.5.3 Health Issues

Since propane for fleet use is a mixture of hydrocarbons, the toxicity of the fuel is difficultto determine. The major constituent, pure propane, is considered to be a simple asphyxiantby the ACGIH and does not have an assigned TLV. The other significant, but muchsmaller, constituent is butane which has a TWA-TLV of 800 ppm. OSHA has set a PEL of1000 ppm for propane, with the requirement that exposure to more than half this levelrequires that a medical monitoring program be instituted. Other than this OSHArequirement, there is no other agency or body that has established an exposure limit forpropane.

It should also be noted that propane has been reported to contain a relatively high level ofradon gas, with radon concentrations in propane that are well above current EPA guidelinesfor radon exposure.9 Since the exposure of personnel to propane will be limited, thepotential exposure to radon gas should not be a serious problem.

3.3.5.4 Environmental Issues

There are no significant environmental issues associated with the spill of propane, since theliquid will quickly vaporize.

3.3.6 Biodiesel

3.3.6.1 General Discussion

Biodiesel is an AMF that is derived from biological sources such as soybean oil, rapeseedoil, other vegetable oils, animal fats, or used cooking oil and fats. The chemical process forcreating biodiesel involves mixing the oil with alcohol in the presence of a chemical catalystsuch as sodium hydroxide. This process produces a "methyl ester" if methanol is used (typically the most common for economic reasons), or an "ethyl ester" if ethanol is used. In either case, the reaction also produces glycerin which is a valuable co-product. Eithermethyl ester or ethyl ester can be used neat (100%) or blended with conventional diesel("petrodiesel") as a fuel for diesel (compression ignition) engines.

Current efforts to commercialize biodiesel in the United States were started by the NationalSoyDiesel Development Board (NSDB) in 1992. The emphasis of their activity is on the useof soybean oil methyl ester (SME) blended with petrodiesel at a 20% volume SME/80%petrodiesel (BD-20) and a 30%/70% blend (BD-30). These blends are believed to offer thebest balance of cost and engine emissions characteristics. NSDB reports that as of thebeginning of 1994, biodiesel had accumulated nearly eight million miles in demonstrationsinvolving more than 1,500 vehicles in fleets across the country, particularly in urban buses.10

Methyl ester made from rapeseed oil (RME) is in widespread use in Europe due to a total ornear-total exemption from fuel taxes in most EC countries. As a result, there is a muchlarger base of operating experience with biodiesel in Europe amounting to several hundredtimes more vehicles and miles than in the U.S.

3.3.6.2 Safety Issues

(a) General Properties Affecting Fire Hazards

Data for the properties of soybean oil methyl ester (SME) indicate that it is a safer fuel thandiesel, which in turn, makes it safer than the other AMFs considered. For example, theflash point for SME is 218C (425F) compared to approximately 73C (160 F) for theaverage No. 2 diesel fuel. It also has an extremely low vapor pressure, less than 1.3 x 10 - 5kPa at 72C. Therefore, when SME is blended with petrodiesel to create BD-20, theresultant flash point for the mixture is 118C, still well above that for the petrodiesel alone.

Past experience with neat (100%) biodiesel has indicated that it is incompatibile to immerse itwith certain rubbers and plastics, but not with metals. Reports indicate that nitrile rubberand polyurethane-based compounds showed unacceptable deterioration while other elastomerssuch as SBR, butadiene, isoprene, hypalon, silicon, and polysulphide were not resistant toneat biodiesel. Acceptable replacement materials include fluorine - rubber (Viton A®) andpolypropylene- and polyethylene-based plastics.10 Therefore, the selection of materials toavoid degradation of seals, fittings, and hoses is important for biodiesel applications.

An unusual physical characteristic of biodiesel that has a fire hazard implication is thepossibility of spontaneous combustion in highly unsaturated materials such as some vegetableoils and methyl ester which oxidize in the air. This is classically known as the "oily rag"problem where the rag is placed in a confined space, such as a pile in the corner, and thereis no way for the generated heat of oxidation to dissipate. The higher temperatureaccelerates the oxidation process giving off even more heat until the pile of rags begins tosmolder and then burn. Since oil-soaked rags or other materials such as filters in typicalpetrodiesel operations are not subject to spontaneous combustion, it will be necessary to alert personnel (e.g., at the fleet operator's fuel storage and maintenance facilities) of the potentialfor spontaneous combustion. This is not a serious problem and can be simply resolved byhaving closed metal cans for storing oil soaked rags and other oily combustible material.

(b) Fire Hazards During Transport

Due to the very low volatility and high flash point temperature of neat biodiesel and blends(BD-20, BD-30), there are no specific fire hazard problems during transport. Any leak orspill is less likely to ignite than diesel or gasoline under equivalent conditions. Biodiesel-compatible materials should be selected to avoid problems of degradation of seals andfittings.

(c) Fire Hazards During Unloading to Storage

There are no specific fire hazards. Unloading equipment should be designed to handlebiodiesel to avoid any possibility of leaks.

(d) Fire Hazards During Fleet Storage

There are no specific fire hazards, other than the potential spontaneous combustion issuenoted above.

3.3.6.3 Health Issues

Because there are essentially no vapors generated at normal transport and storagetemperatures, pure or neat biodiesel can only be considered as a potential health hazard dueto ingestion. Pure biodiesel looks and smells like a food product and could conceivably beingested. If biodiesel were ingested, enzymes in the body would break the ester back into itsoriginal components, e.g., soybean oil and methanol.11 This raises the potential issue ofmethanol toxicity as a potential health hazard associated with biodiesel. Consequently,biodiesel cannot be considered to be non-toxic, as often cited in the promotional literature.

3.3.6.4 Environmental Issues

Biodiesel is considered to be biodegradable based on the chemical nature of the materials. Test data indicates that biodiesel is in the same range as biodegradable soaps and detergents. Therefore there are no significant environmental hazards associated with biodiesel.

3.3.7 Hydrogen

3.3.7.1 General Description

Hydrogen is unique among AMFs because it cannot be produced directly, as in drilling awell for petroleum oil and natural gas. Hydrogen must be extracted chemically fromhydrogen-rich materials such as natural gas, water, coal, or plant matter. A substantialquantity of hydrogen is produced each year in the U.S. -- about 8.5 billion kilograms peryear.

About 95% of the hydrogen in the U.S. is produced by steam reforming, a chemical processthat makes hydrogen from a mixture of water and a hydrocarbon feedstock, such as naturalgas. When steam and methane contained in the natural gas are combined at high pressureand temperature, a chemical reaction converts them into hydrogen and carbon dioxide. Theoverall energy efficiency of the process, i.e., the energy content of the hydrogen produceddivided by the total energy (natural gas and energy used to run the reformer) consumed, isapproximately 65%. Other techniques for producing hydrogen, including off-gas cleanup andelectrolysis, are much more costly.

Over the long term, it may be possible to consider large scale electrolysis (passing anelectrical current through water to split individual water molecules into hydrogen andoxygen) using sunlight on photovoltaic cells as the electrical power source, or some otherrenewable energy source such as wind power. Hydrogen obtained using this approach istermed "solar hydrogen" or "renewable hydrogen."

The actual use of hydrogen in automotive vehicles is limited to experimental and prototypevehicles. A number of prototype vehicles burn hydrogen directly using modified automotiveengines. There are also a number of vehicles that use the hydrogen in a fuel cell to produceelectrical power for electrical motor drives, i.e., a hydrogen powered electric vehicle.

In addition to the direct use of hydrogen there has been a demonstration program involvingblends of up 15 percent in volume of hydrogen added to natural gas to create "hythane." Inthis case, the hydrogen provides up to 5 percent of the energy content of the blend.

3.3.7.2 Safety Issues

(a) General Properties Affecting Fire Hazards

Hydrogen is a difficult fuel to deal with because of its physical properties. One of these wellknown properties is that as a gas its density is very low -- only 1/15th that of air. Therefore,for any practical applications, it is necessary to either compress the hydrogen or liquefy it. The problem with compressed gaseous hydrogen in a fleet vehicle application is the weight ofthe high pressure tanks. It has been estimated that the weight of the compressed hydrogenwill only vary from 1 to 7% of the total weight of the tank. Fortunately, the energy densityof hydrogen is very high so that 1 kg of hydrogen contains approximately 2.5 times moreenergy than 1 kg of natural gas. Therefore, assuming an equivalent engine efficiency, theweight of a vehicle's compressed hydrogen fuel storage system will be similar to that for aCNG fuel storage system. The alternatives to compressed hydrogen tanks on the vehicle include liquefied hydrogen, an on-board converter fueled by methanol to create hydrogen,and storage of hydrogen in metal hydride systems. All of these techniques are the subject ofresearch.12

For bulk distribution of hydrogen, the most common method by far is to liquefy thehydrogen and transport it by truck trailers, barges, or railcars. At atmospheric pressure,liquid hydrogen (known as LH2) boils at -253C (423F), which is only about 20C aboveabsolute zero. The process of hydrogen liquefaction, storage, and distribution is challenging,to say the least. Hydrogen is usually liquefied in a complex multi-stage process that involvesthe use of liquid nitrogen (boiling point of approximately -200C). Special precautions arerequired during liquefaction to maintain the proportions of two types of hydrogen moleculesin order to avoid excessive internal heating and vaporization while the LH2 is beingtransported or in storage. LH2 requires special insulation to maintain liquid conditions aslong as possible.12

The physical property of hydrogen that creates the most significant fire hazard is theextremely wide range of flammability limits, i.e., from 4% to 75% by volume. This rangeis twice that of methanol which has the next widest range. In effect, any release of hydrogeninto the air results in a much larger volume of a flammable mixture than an equivalentamount of any other AMF.

More importantly, the potential for an explosion or detonation of a flammable hydrogen-airmixture is very high. The ignition energy for hydrogen-air mixtures is much lower than forhydrocarbon-air mixtures. Very low energy sparks, such as from a static electric discharge,can lead to ignition; and if the burning gas is even slightly confined, the resulting pressurerise can lead to a detonation.

Among the other physical properties of hydrogen that are of interest is the propensity of thegas to leak more easily than other AMF gases due to the relatively small size of thehydrogen molecule. Since hydrogen gas is colorless and odorless, leaking hydrogen cannotbe detected unless an odorant, or possibly a colorant, has been added to the gas. Addition ofodorant or colorant would be very difficult to implement in situations requiring liquefactionof the hydrogen. To compound matters, the flame of burning hydrogen is invisible indaylight, therefore adding an extra safety concern for personnel working near hydrogen tanksor transfer lines.13

Finally, hydrogen will diffuse into steel and other metal and cause a phenomenon known as"hydrogen embrittlement." This is a serious concern in any situation involving storage ortransfer of hydrogen gas under pressure. Proper material selection and technology isavailable to prevent embrittlement, but there may be situations where such precautions havenot been taken due to some oversight or error.

(b) Fire Hazards During Transport

It is assumed that the typical bulk transport mechanism for hydrogen-to-fleet storage will beliquefied hydrogen (LH2) delivered by a specialized tanker truck. Under such conditions, the situation is analogous to transport of LNG. The tanker truck for LH2 has to be constructedsimilar to the double walled configuration for LNG, but with a very high level of insulationdue to the fact that the LH2 is much colder than LNG. Thus, the LH2 tanker truck design isexpected to be even more robust than an LNG tanker truck in an accident situation.

In the event of a loss of insulation due to an accident, the rate of LH2 vaporization wouldincrease rapidly. Provisions are made in the design of storage vessels for venting andpressure relief in order to avoid any rupture of the inner tank containing the LH2. Thepotential for ignition of hydrogen gas that is vented out at a high rate (as the result of anaccident or other incident that causes loss of insulation) is an obvious fire hazard.

The rupture of the inner vessel would lead to a massive spill of LH2. This is a particularlytroublesome scenario because a flammable hydrogen air mixture would be immediatelyformed in the vicinity of the LH2 pool and would quickly form a much larger volume offlammable gas as hydrogen boils off from the pool. Since the hydrogen gas is cold, it willbe relatively dense and may stay in proximity to the ground for some period of time. Theignition energy required to initiate a hydrogen/air fire is very low so that the probability ofan ignition source within a large flammable gas cloud in the accident area is quite high.

Another major hazard with a spill of LH2 is that contact between the LH2 and air can resultin condensation of air and its oxygen and nitrogen components. A mixture of hydrogen andliquid oxygen is potentially explosive even though the quantities involved are likely to besmall.13

(c) Fire Hazards During Transfer to Fleet Storage

The transfer of LH2 from the tanker truck to fleet storage is a complex process similar to thatof LNG. There is the potential for leaks and spills due to the number of steps that areinvolved combined with the possibility of human error. Some of these specific concerns,which have been cited in the discussion of LNG, include the thermal cycling of fuel transferequipment leading to additional stress on connection equipment and sealing devices.

(d) Fire Hazards During Fleet Storage

The storage facility requirements for LH2 are spelled out in NFPA 50 B Liquid HydrogenSystems - Consumer Sites. This standard addresses siting of the storage tank, provisions forspill or leak control, and the basic design of the storage container and LH2 transferequipment.

As with LNG, it is necessary to insure that any accidental discharge does not endangeradjoining property or reach any waterways, particularly those connecting to covered drainagesystems. This is accomplished by providing an impoundment area surrounding the container.

(e) Other Hazards

LH2 is very dangerous to personnel because cryogenic burns will result from direct bodycontact with (1) the liquid; (2) metals at LH2 cryogenic temperatures; and, to a lesser extent,(3) with the cold vapors.

3.3.7.3 Health Issues

Hydrogen is not considered to be toxic. However, it is a simple asphyxiant which is a healthrisk because it can displace oxygen in a closed environment.

3.3.7.4 Environmental Issues

There are no significant environmental hazards associated with the accidental discharge ofLH2.

3.3.8 Electricity

3.3.8.1 General Description

Electricity can be considered as an AMF based on the use of electrically powered fleetvehicles using batteries as the energy storage medium. Most fleet applications currentlyconsidered involve vehicle tours that are relatively short and low speed, e.g., shuttle service,due to the limited range (less than 100 miles) and power of battery electric-powered vehicles. Typical battery recharging times are on the order of 6 to 8 hours requiring that fleet vehiclesbe recharged overnight. The current research focus for electric propulsion vehicles is in thearea of battery development where the goal is to develop batteries that have low initial cost,high specific energy (Wh/kg), and high power density.

The bulk transport of electricity via the electric power distribution system is a fundamentalpart of the nation's infrastructure. The hazards associated with high voltage power lines,substation transformers, and local power distribution systems are well known. The NationalElectrical Code developed under the auspices of the NFPA covers the safety and protectionmeasures associated with the provision of electrical service to the facilities.

3.3.8.2 Safety Issues

All of the safety issues associated with electricity are directly related to the transmission ofelectric power to the recharging station at the fleet facility. There is no storage issue sincethe electrical energy is stored in the on-board batteries.

The major safety concern is the exposure of personnel to electrical hazards as they work withthe recharging system and connecting the vehicles to that system. This is not expected to bea serious safety hazard because the normal design practices for setting up the connectionsinvolve safeguards to ensure that personnel are protected from direct exposure to electricalhazards.

One of the safety advantages of electricity compared to the other AMFs is that all facilitypersonnel are generally familiar with the hazards associated with electrical power. Therefore, personnel working with the recharging system can be expected to be aware of thedangers and follow the proper safety procedures.

3.3.8.3 Health Issues

There are no specific health hazards associated with the transmission and use of electricity ata fleet facility.

3.3.8.4 Environmental Issues

There are no specific environmental hazards associated with the transmission and use ofelectricity at a fleet facility.

3.4 ASSESSMENT OF ALTERNATIVE FUEL BULK TRANSPORT, TRANSFER,

AND FLEET STORAGE SAFETY RISKS

3.4.1 Introduction

The previous section provided a detailed discussion of the safety, health, and environmentalissues associated with the bulk transport, unloading and transfer, and fleet storage issuesassociated with each individual AMF. In this section, the individual issues are combinedwith the intent of conducting a summary assessment. This assessment is divided into twoparts:

An assessment of the relative potential for AMF leakage or spills during bulktransport and storage operations; and

An assessment of the consequences of a fuel spill or leak in the context of safety,health, and environmental risks.

In the absence of reliable statistical data on accidental releases of the various AMFs duringbulk transport and storage, the following assessments are largely subjective. However, thereare a number of physical and engineering principles that have been used as a guide in thisassessment. Briefly, they are as follows.

1. The standard for assessment is based on both diesel and gasoline. These fuels aretransported, handled, and stored at ambient temperatures and pressures and theyare stable during long term storage.

2. The risk of a leak or spill increases as the transport and storage pressure of theAMF increases. Even with systems designed for high pressures, human errors,manufacturing defects, and material weaknesses are bound to take their toll.

3. The risk of a leak or spill increases as the amplitude and frequency of thetemperature changes imposed on transport, transfer, and storage equipment isincreased.

4. AMF storage systems that require active intervention (either automated or manual)in order to maintain the safety and quality of the fuel product are inherently morecomplex. Increased complexity leads to increased risk of leaks or spills throughhuman error or mechanical/electrical failure.

3.4.2 Assessment of Relative Potential for Spills and Leaks

The first step in developing a summary assessment of bulk transport and storage risks is toexamine the potential for accidental release of each AMF during each step in the transportand storage process. The following discussion considers the relative potential for accidentalrelease based on the characteristics of each fuel and its transport and storage requirements.

Hydrogen is not considered in this part of the assessment because there are a number ofpotential issues regarding transport and storage modes that must be resolved through furtherresearch and development. For example, it may be determined that the best approach is touse methanol and reform it directly on the vehicle to create an on-board hydrogen source.

Electricity is not considered in any part of the assessment because it is completely differentfrom the perspective of bulk transport and storage characteristics.

3.4.2.1 Bulk Transport

The major concern regarding accidental release during bulk transport is based on an accidentscenario where the transport tank is damaged and a large amount of fuel is spilled. Thepossibility of leaks during transport is minimized by the selection of appropriate materialsand proper design in accordance with the applicable material standards. Nonetheless, thereare still fuel-related factors that would affect the relative potential for leaks. The ranking ispresented in matrix format in Tables 3-1 and 3-2 for purposes of simplicity and convenience.

TABLE 3-1. RELATIVE POTENTIAL FOR SPILLS DURING TRANSPORT

AMF Relative Spill Potential

(compared togasoline/diesel truckspill)

Reason
LNG Lower Double walled cryogenictransport tank
Propane Lower High pressure transport tank
Gasoline/Diesel Reference Fuels
Ethanol/Ethanol Blend Same Same tank structure asgasoline/diesel
Methanol/MethanolBlend Same Same tank structure asgasoline/diesel

TABLE 3-2. RELATIVE POTENTIAL FOR LEAKS DURING TRANSPORT

AMF Relative Leak Potential

(compared togasoline/diesel tankertruck)

Reason
Gasoline/Diesel
Reference Fuels
Ethanol/EthanolBlends Somewhat Higher Potential corrosion effects
Methanol/MethanolBlends Somewhat Higher Potential corrosion effects
Propane Higher Pressures up to 375 psi
LNG Higher 300 F temperature differentialsand pressures up to 150 psi

Tables 3-1 and 3-2 point out that the conditions which tend to create leaks (i.e., highpressure and temperature differentials) lead to bulk transport container designs that are morerobust and less likely to be ruptured and spill the fuel cargo in an accident situation.

3.4.2.2 Unloading to Fleet Storage

The potential for spills and leaks during unloading operations is directly related to thepressure of the AMF, temperature differentials, and any corrosive characteristics of the fuel. The rationale for this statement is based on the observation that the existence of highpressure is more likely to lead to a massive rupture of material (e.g., transfer hose, flexiblecoupling) if it has been weakened by fatigue or temperature cycling, or if there is a materialdefect. A large temperature differential requires a more complex system to maintain controlwith increased possibilities for human error or equipment malfunction. The effects ofcorrosion on unloading equipment strength and integrity are an obvious concern.

CNG is treated as a special case in this study because the unloading to fleet storage consistsof the process of taking pipeline quality gas, compressing it, purifying and drying it, andthen maintaining a relatively small amount in storage prior to dispensing to the vehicle. Theunloading process tends to be continuous during the time that fleet vehicles are being filled. The process is also highly automated and does not require direct personnel involvement suchas that for tanker truck unloading, therefore reducing the opportunity for human error.

Considering all of the above, Tables 3-3 and 3-4 provide an assessment of the relative risk ofspills and leaks during unloading operations.

3.4.2.3 Fleet Storage

The potential for spills and leaks during fleet storage is similar to that for the unloading ofAMFs as noted in Tables 3-5 and 3-6.

3.4.3 Assessment of Safety Hazards

The assessment of safety hazards includes fire hazards, other hazards, health effects, andenvironmental effects. The most difficult area to assess is that of fire hazards because itcomprises two parts:

the likelihood that the vapor/air mixture from a leak or spill will ignite from aspark or other ignition source, including coming in contact with a heat sourcesufficient to raise the vapor to its autoignition temperature; and

upon ignition, the relative safety hazard associated with the size and intensity ofthe ensuing fire or explosion.

The relative probability of ignition of an AMF leak or spill can be determined from thephysical properties of the fuel and the physical requirements for transport and storage. Theconsequences of a fire or explosion depend upon the amount of fuel released. For the caseof a massive spill, the volume of fuel stored becomes an important issue.

TABLE 3-3. RELATIVE POTENTIAL FOR SPILLS DURING UNLOADING

AMF Relative Spill Potential

(compared togasoline/diesel truckspill)

Reason
Gasoline/Diesel Reference Fuels
Ethanol/EthanolBlends Slightly Higher Potential corrosion effects
Methanol/MethanolBlends Somewhat Higher Potential corrosion effects
CNG Higher Pipeline gas corrosion effects andfailure of high pressure (3600 -5000 psi) transfer equipment
Propane Higher Combination of moderately highpressure (375 psi) and equipmentfailure
LNG Higher Combination of temperaturecycling/mechanical failure andcomplexity of transfer process

TABLE 3-4. RELATIVE POTENTIAL FOR LEAKS DURING UNLOADING

AMF Relative Leak Potential

(compared togasoline/diesel tankertruck)

Reason
Gasoline/Diesel
Reference Fuels
Ethanol/EthanolBlends Slightly Higher Potential corrosion effects
Methanol/MethanolBlends Somewhat Higher Potential corrosion effects
Propane Higher Moderately high pressure
CNG Higher High pressure
LNG Higher Temperature differential andmoderate pressure

TABLE 3-5. RELATIVE POTENTIAL FOR SPILLS DURING FLEET STORAGE

AMF Relative Spill Potential

(compared togasoline/diesel truckspill)

Reason
Gasoline/Diesel Reference Fuels
Ethanol/EthanolBlends Slightly Higher Potential corrosion effects
Methanol/MethanolBlends Somewhat Higher Potential corrosion effects
Propane Higher Moderately high pressure andequipment failure
CNG Higher High pressure and equipmentfailure
LNG Higher Complexity of container systemto maintain cryogenictemperatures

TABLE 3-6. RELATIVE POTENTIAL FOR LEAKS DURING FLEET STORAGE

AMF Relative Leak Potential

(compared togasoline/diesel truck)

Reason
Gasoline/Diesel Reference Fuels
Ethanol/EthanolBlends Slightly Higher Potential corrosion effects
Methanol/MethanolBlends Somewhat Higher Potential corrosion effects
LNG Higher Temperature differentials
Propane Higher Moderately high pressure
CNG Higher High pressure

For the case of bulk transport of liquid AMFs, the maximum typical volume of the standardfuel tanker truck is approximately the same -- 10,000 gallons. Therefore, the hazards of amassive spill depend mostly upon the physical characteristics of the burning vapor/airmixture, the heat release rate and flame radiation levels. In the case of fleet storage, theapproximation can be made that, for a fleet of equivalent size, the amount of fleet storagerequired is based on the energy density of the fuel. Assuming one unit mass (kg) of dieselfuel, the following equivalent amounts of fuel (as indicated in the left-hand box) are requiredto provide the same fleet miles, including engine fuel efficiency effects.

The size of a fire for a massive spill of the liquid AMFs will depend upon the volume of fuelspilled from a storage tank. Assuming a uniform unconfined depth for the liquid pool, thearea will be directly proportional to the volume. Again, using diesel fuel as the reference,the box on the right indicates the relative volume of liquid fuel that must be stored to achievethe equivalent fleet miles.

It should be noted that total fleet storage capacity may require the use of several storagetanks. In that case, the maximum size of the fire from a spill would most likely be based onthe capacity of a single tank.

The total potential exposure based on total storage capacity with most AMFs at the fleetoperator's facility is approximately two to three times greater than diesel fuel based on thepotential area of a liquid pool. The total fire hazard exposure would depend upon the highlyunlikely event that all of the individual storage tanks would become involved in the course ofan accident.

The only fuel not noted above is CNG. As discussed in Section 2, the fleet storagerequirements for CNG will be quite small, on the order of 3 to 4 times the vehicle fuelcapacity of an individual vehicle for fast fill operators. Therefore, for most CNG-fueledfleets, where the number of vehicles would be relatively large, the total heat release potentialfrom a storage tank fire will be quite small compared to the other AMFs.

3.4.3.1 Potential for Ignition

In the event of a leak or spill, the physical properties of the AMF that have a direct impacton the potential for ignition include:

Flash Point (applicable to fuels stored as a liquid) -- at temperatures below thispoint, a liquid will not produce sufficient vapors to form an ignitable mixture withair near the surface of the liquid.

Fuel Volatility (applicable to fuels stored as a liquid at the referencedtemperature) -- measured by Reid vapor pressure, i.e., the pressure exerted bythe vapor over the liquid in a closed container at 38C (100F).

Autoignition Temperature -- the minimum temperature required to cause self-sustained combustion in air due to heat alone, without any additional spark orflame. The autoignition temperature is also known as the self-ignitiontemperature, or simply the ignition temperature.

Flammability Limits -- The range of fuel concentration in air, expressed as avolume percentage, that will support combustion. A concentration below thelower flammability limit will not propagate flame due to insufficient fuel, i.e., too"lean." A concentration above the upper flammability limit will not propagateflame due to an excess of fuels, i.e., too "rich."

Electrical Conductivity -- the degree to which a fluid will conduct electricitymeasured in microsiemens per meter (s/m). Materials with lower conductivityare more likely to build up and experience static discharges due to sloshing (liquidfuels) or flowing.

In order to provide some perspective on these different properties for each of the AMFs, aseries of figures have been prepared which illustrate the differences, and the effect onignition potential.

Figure 3-1 shows the flash point temperature for all of the liquid AMFs. Propane andLNG are not shown because they are gases at ordinary temperatures and pressures. Thefigure illustrates the fact that diesel and soy-diesel are inherently much less prone to ignitionbecause at normal temperatures, the liquid fuel is far below the flash point. Therefore, thespilled or leaked fuel would have to come in contact with a heat source in order to elevatethe liquid temperature to the point where flammable vapor/air mixtures could be formed. Gasoline, on the other hand, will always be above the flash point; therefore, a spill or leakwill immediately have a vapor/air mixture generated. Methanol and ethanol are less prone toignition when the liquid temperature is quite cold, but once it gets above 10C (50F),flammable vapors will be generated.

Figure 3-2 illustrates the fuel volatility for all of the liquid AMFs as measured by the Reidvapor pressure in kPa (6.9 kPa = 1 psia). As would be expected, the liquid fuel with thelowest flash point (gasoline) has the highest volatility. Propane is shown in this figure (notto scale) simply to illustrate the fact that it is extremely volatile, and upon release of thispressurized liquid, approximately one-third immediately flashes to vapor. Thus, a spill ofpropane is inherently much more prone to ignition than any of the other liquid fuels shown.

Figure 3-3 illustrates the autoignition temperature for a wide range of AMFs. It is ofinterest to note that in this case, the reference fuels, diesel and gasoline actually have thelowest autoignition temperatures. Fortunately, even for diesel which has the lowestautoignition temperature of those shown in the figure (230C or approximately 450F) theactual temperatures are quite high and not likely to be encountered unless a fire had alreadybeen initiated, or unless the fuel vapors came into direct contact with some very hot engineparts, e.g., the exhaust manifold.

It is very important to remember that the values for propane and for methane shown inFigure 3-3 are for the pure gases. The AMFs, natural gas and vehicular propane, arevariable mixtures of gases with autoignition temperatures that will be lower than the pure gasvalues shown. For example, natural gas is estimated to have an autoignition temperaturerange of 450-500C, compared to the value of 540C for pure methane.

Figure 3-4 shows the flammability limits range for a number of AMFs. This range is animportant determinant of the likelihood of ignition. If the range is extremely wide, as it isfor hydrogen, then the likelihood of encountering a flammable mixture is higher for a givenvolume of fuel because the total volume of the flammable mixture is much larger. Methanol,and to a lesser extent ethanol, also have fairly wide flammability limits; therefore, those fuelsare much more prone to encountering an ignition source for a given volume of vapor than theother AMFs. In order to demonstrate the effect of temperature on the flammability limitsrange for ethanol and methanol, an intermediate line shows the maximum volumeconcentration that can be achieved for a normal temperature of 22C (70F). This linedemonstrates that at this temperature, the "effective" flammability limits range for ethanoland methanol are equivalent to, or less than, most other AMFs.

It is also necessary to note that ethanol and methanol are less volatile fuels such that it willtake a longer time for a leak or spill of liquid to create the same volume of vapor, comparedto the equivalent liquid volume of the more volatile fuels. If a leak of methanol or ethanoloccurs at a liquid temperature well above the flash point, flammable vapors will be

immediately formed and may linger in low lying areas. When compared to other heavier-than-air vapors such as propane, the wider flammability limits of ethanol and methanol createa higher probability of ignition under equivalent conditions.

The electrical conductivity of the fuel is important, as explained in the definitions ofphysical properties, in determining the effects of potential static electric discharges wheneverfuels are in rapid movement such as the discharge from a high pressure tank or line. In mostcases, adequate protection can be obtained by grounding the container or transfer line. However, there have been some situations reported where compressed natural gas, which isessentially non-conductive, escaping from a cylinder apparently ignited from a static electricdischarge. The same type of phenomena may also develop with a high pressure leak ofpropane since the liquid fuel is quickly atomized while fuel flashes into vapor.

For the other liquid fuels, both gasoline and diesel have very low conductivities, withgasoline having a value of 1 x 10 - 6 S/m and diesel having a value of 1 x 10 - 4 S/m. Bothmethanol (44 S/m) and ethanol (0.14 S/m) have much higher electrical conductivitieswhich will help to reduce static charge buildup. This is fortunate since both of these fuels instorage are likely to have ullage space vapor/air mixtures that are in the flammable range.

3.4.3.2 Consequences of Ignition

The major consequences of a fire include the damage within the fire area and the exposure ofpersonnel and objects to thermal radiation outside the immediate area of the fire. There isalso the possibility of the explosive or detonation type of burning of a vapor cloud which cancause an overpressure hazard.

The prediction of the actual consequences of the ignition of a leak or spill of an AMF is avery complex process because it is dependent upon so many different physical variables. Forexample, there are three basic scenarios for the burning of a liquid AMF.

A pool fire in which a fire or fire plume is established on an evaporating (andburning) pool of the liquid.

A vapor fire in which the ignition of an established plume (or cloud) of vaporresults in the formation of a propagating fire.

An explosive or detonation type of burning in a vapor cloud.

In order to consider the relative impact of AMF fires, it is obvious that the amount of fuelspilled is the most important factor. The size of potential spills during bulk transport andstorage have been discussed previously in this section. The next consideration is the thermalradiation from fire.

A substantial amount of theoretical and experimentalwork has been accomplished on the subject of poolfires. Some of the experimental work includedmeasurements of the thermal radiation from pool firesof LNG, propane, and kerosene (GRI, 1982).14 Asindicated in the box to the right, the relative thermalradiation (kW/m2) at the initial stages (first fiveminutes) of the fire normalized to kerosene (approximately 30 kW/m2) are as shown.

The reduced radiation intensity for propane andkerosene pool fires is attributed primarily to the sootthat is generated with these fires which tends to maskthe flames. Interestingly enough, these results do notextend to the case of a vapor cloud fire. Experimentalresults comparing the emissive power of LNG andpropane cloud fires showed that they were essentiallythe same.14 The comparative data for cloud and poolfires normalized to the emissive power of an LNGpool fire (in the range of 200 kW/m2) is illustrated inthe box to the right.

In most instances of an AMF spill, it is anticipated that with ignition, a pool fire will ensue. For this reason, an LNG fire is expected to be more hazardous than other AMF spill fires ofequivalent volume occurring under similar weather conditions. However, since there are somany variables associated with predicting the size, shape, and thermal radiation effects of anAMF spill fire, it is not possible to make a relative assessment that would be valid for allconditions. It can simply be stated that on an overall (equivalent volume) basis, the ignitionof either LNG or propane will have much greater consequences in terms of radiationintensity than that associated with other AMFs such as methanol/blends and ethanol/blends.

One other way to assess the potential consequences of an AMF spill fire is to consider thecombustion energy released from a pool fire. There is some evidence to suggest that thefraction of combustion energy radiated from many types of hydrocarbon fuel fires includingmethane, natural gas, and propane is in the range of 20 to 25%. Therefore, someapproximation of the overall radiative effects of a pool fire can be estimated from the heatrelease rate.

Figure 3-5 presents the relative heat release rate for liquid pool fires based on the mass rateat which liquid fuel is consumed per unit area and the heat content of the fuel. The heatrelease rate has been normalized to diesel, i.e., diesel pool fire heat release = 1.0. SinceFigure 3-5 provides a comparison for pools of equal size, it provides an indication of theconsequences of ignition of a complete spill of the contents of an AMF tank truck (assumingthey all carry approximately 10,000 gallons) for all of the fuels shown. The figure clearlyillustrates that the overall radiation effects resulting from a propane or LNG ignition and poolfire will be much more severe than that of an equivalent diesel spill. Conversely, the heatrelease and overall radiation effects from an ethanol or methanol spill fire will be a smallfraction (approximately 25%) of that of the diesel fire.

One factor that is not shown in Figure 3-5 is the flame spread rate, i.e., the speed at which aflame will spread across the surface of a liquid pool of fuel. This could be an importantfactor in personal safety in that it defines the potential time that an individual has to moveaway from the pool. Based on limited data available, the flame spread rate for gasoline isthe quickest at 4-6 meters/second (13-20 feet/second) while that for methanol isapproximately 2-4 m/s (7-13 ft./s). A diesel pool fire, on the other hand, will spread veryslowly at 0.02 - 0.08 m/s (0.8 - 3.2 inches/second).2 This is due to the fact that the dieselfuel will have to be heated up to its flash point before sufficient flammable vapor can begenerated.

It is not as simple to characterize the heat release rate for CNG. The lowest flame speed(laminar burning velocity) for methane is approximately 0.4 m/s (1.3 ft./s). Any turbulencesuch as that caused by wind in the flammable gas mixtures will tend to dramatically increasethe flame speed, therefore, it is likely that under most situations the flame will propagatevery quickly with very little chance for personnel to react. Maximum flame speeds ofapproximately 10 to 15 m/s (33-50 ft./s) have been measured. One big problem with a CNGfire is that it is absolutely essential to cut off the CNG supply before attempting to extinguishit. Otherwise, there is the risk of another accumulation of flammable gas and subsequent re-ignition.

The consequences of ignition of a major spill at the fleet operator's facility will depend uponthe volume of fuel stored. Using the volume equivalents to achieve the same energyequivalent mileage range for the fleet, as indicated earlier in the text, it will be necessary tostore a greater volume of all liquid AMFs compared to diesel, ranging from 1.9 times forpropane to 2.7 times for methanol. However, it is not possible to make a direct link betweenthese increased volumes and increased fire hazards because the larger volumes are likely tobe stored in separate tanks with appropriate separation and protection to avoid the spill firefrom affecting adjacent tanks.

3.4.3.3 Other Hazards

This category includes the safety hazards associated with high pressures and low (cryogenic)temperatures. In terms of a relative assessment of the hazards for all of the AMFsconsidered (both primary and secondary); they can be ranked as follows:

High Pressure Hazards Ranking Low Temperature Hazards Ranking
CNG

Propane

LNG

Methanol

Ethanol

Biodiesel

LNG

CNG

Propane

Methanol

Ethanol

Biodiesel

With regard to the high pressure hazard rankings, only CNG and propane are normally atsufficiently high pressure to cause problems with personnel safety for those working in closeproximity. LNG is transported and stored at relatively low pressure but if there is somemalfunction in the venting and pressure relief system, there is some possibility of a rapidpressure buildup due to thermal effects. The other AMFs are not subject to such pressurebuildup.

Low temperature hazards are typically associated with LNG due to its cryogenic storagetemperature. CNG and propane will become very cold when they expand from theirrespective storage pressures to atmospheric pressure; therefore, there is some lowtemperature hazard associated with these AMFs. The remaining fuels do not pose anyproblems with regard to low temperature hazards.

3.4.4 Assessment of Health Hazards

Most of the AMFs considered in this study are effectivelynon-toxic, particularly when they are compared toconventional fuels such as gasoline. The relative ranking ofthe AMFs on the basis of potential health hazards topersonnel are indicated in the box to the right.

Methanol and methanol blends are the most toxic AMFs forinhalation-exposure with a threshold limit value - time weightaverage (TLV-TWA) concentration value of 200 ppm. Bycomparison, the next lowest TLV-TWA concentration valuefor an AMF includes ethanol 1,000 ppm, followed by naturalgas at a value of 10,500 ppm. In addition, there is an OSHA-set personnel exposure time limit (PEL) of 1,000 ppm forpropane.

The toxicity of the vapors should be considered in the context of the volatility of the fuel. For example, while gasoline has a higher TLV-TWA (300 ppm) than methanol, gasoline isalso more volatile with a vapor pressure (RVP) approximately 2.3 times greater thanmethanol; therefore, personnel working in the presence of both of these fuels are more likelyto be exposed to gasoline vapors than methanol vapors.

There is a similar concern with regard to an extremely volatile fuel such as propane whichhas a PEL of 1,000 ppm. Propane is generally required to be odorized such that aconcentration of 1/5th of the lower flammable limit is detectable, i.e., approximately 4,200ppm. Therefore, leaks of propane may result in concentrations of propane vapors that arewell below the flammable limit and cannot be detected by odor, but still be in a concentrationrange that could reach the OSHA PEL value. By contrast, gasoline is detectable by odor at aconcentration of 0.2 ppm; therefore, the same type of personnel health hazard does not applyto gasoline.

The reported data on odor detectability of methanol is not consistent, with values from 100ppm to nearly 6,000 ppm cited in the literature. Assuming that an average value of 2,000ppm is correct, it would be possible for personnel to be exposed to concentration values wellabove the TLV-TWA.

In all of these situations it is possible to use gas detectors (either fixed or portable) in areaswhere personnel are likely to be exposed to AMF vapors over an extended period of time. This would be an effective means of mitigating the potential health hazards associated withany particular AMF.

The ranking of biodiesel is based on the possibility of ingestion due to its vegetable oilappearance and odor. The human body will break down the biodiesel into its originalcomponents, e.g., soybean oil and methanol. This raises the potential of methanol toxicitydepending upon the volume ingested.

3.4.5 Assessment of Environmental Hazards

The spill or leak of an AMF is not likely to result in any long term environmental damage. A review of the potential environmental hazards for each AMF, that is not gaseous at normaltemperatures and pressures, shows that all of the liquid AMFs are biodegradable over areasonably short period of time (i.e., a period of several months or less). The major concernis that the liquid AMF should be prevented from entering into any waterway or drainagesystem. Aside from any consideration of aquatic toxicity, there is actually a potentialfire/explosion safety hazard situation created when a flammable or combustible liquid entersa waterway where there are covered sections where vapors can accumulate.

This above problem is particularly acute for the alcohols (methanol and ethanol) since theyare soluble in water. Once such alcohol AMFs have mixed with water there is no simple andlow cost method for separating them out. In a fixed facility situation, it is necessary toensure that any AMF spill will not endanger any other portion of the facility or neighboringenvirons, and that they will not enter into any drainage system. This is achieved throughvarious forms of impoundment systems (e.g., dikes) that are sized to handle any conceivablespill. During bulk transport, a spill can occur anywhere, including an area adjacent to awaterway or drainage system.

REFERENCES SECTION THREE

1. "Challenges for Integration of Alternative Fuels in the Transit Industry," by M.E.Maggio, T.H. Maze, K.M. Waggoner, and J. Dobie, in Transportation ResearchRecord 1308, TRB, National Research Council, Washington, D.C. (1991) pp. 93-100.

2. "Properties of Alternative Fuels," by M.J. Murphy, FTA Report No. OH-06-0060-92-5, U.S. Department of Transportation, Office of Technical Assistance and Safety(August 1992).

3. "Effects of Alternative Fuels on the U.S. Trucking Industry," Report prepared for theATA Foundation, Inc., Trucking Research Institute by Battelle and Gannett Fleming,(November 1990).

4. "Safe Operating Procedures for Alternative Fuel Buses, A Synthesis of TransitPractice," by G.V. Hemsley, Transit Cooperative Research Program Synthesis 1, TRB,National Research Council, Washington, D.C. (1993).

5. "Public Transportation Alternative Fuels -- A Perspective for Small TransportationOperations," Final Report prepared for the California Department of Transportation,Division of Mass Transit Operations, by Booz-Allen & Hamilton (June, 1992).

6. "Recommended Practice for Compressed Natural Gas Fuel," SAE Surface VehicleRecommended Practice J1616, February 1994.

7. "An Introduction to LNG Vehicle Safety," Draft Report prepared for Gas ResearchInstitute by Science Application International Corporation (December, 1991).

8. "MIT - GRI LNG Safety and Research Workshop, Volume I Rapid-Phase Transitions,"prepared for the Gas Research Institute by the Massachusetts Institute of Technology,(August, 1982).

9. "Indoor Air Quality Environmental Information Handbook: Radon," Department ofEnergy report, DOE/PE/72013-2, pp. 2-29.

10. "Biodiesel -- A Technology, Performance and Regulatory Overview," prepared for theNational Soydiesel Development Board by American Bio Fuels Association andInformation Resources, Inc. (February, 1994).

11. Industrial Toxicology, Edited by Phillip L. Williams and James L. Burson. VanNostrand Reinhold, New York, 1985. p. 248.

12. "Hydrogen as a Fuel," Congressional Research Service Report for Congress, 93-350SPR, prepared by Daniel Morgan (March, 1993).

13. Fire Protection Handbook, Fifteenth Edition, National Fire Protection Association,Quincy, MA (1981), pp. 4-46.

14. "Liquefied Natural Gas Safety Workshop Proceedings - Volume III, LNG Fire andCombustion," prepared for the Gas Research Institute by Technology & ManagementSystems, (July, 1982).

Return to Table of Contents


4. USE OF ALTERNATIVE FUELS BY VEHICLE FLEETS

4.1 INTRODUCTION

This section of the report is structured around a summary list or catalog of safety, fire, andhealth hazards (dangers) for each alternative fuel. In each instance, the assessment of theconsequences of the hazards and of the state of knowledge concerning the hazards is basedon a comparison to diesel or gasoline fuel as currently used by fleet operators and transitproperties. This choice of a baseline was made to prevent the use of project resources tomerely document safety knowledge that is generally available to and already practiced bytransit and other fleet operators who use conventional gasoline- or diesel-fueled vehicles. Information for the summary list was derived from discussions with VNTSC, DOE and FTAstaff, literature searches, telephone interviews, and site visits.

In order to place this summary list of hazards in context, the summary list is preceded by adiscussion of the distinctions between hazardous fuel properties, hazards, and risks. Thesummary list of hazards is supplemented by case histories of actual incidents involvingalternative motor fuels. These case histories, though anecdotal in natural, can serve toillustrate and extend the discussion of individual hazards.

In addition to organizing the substance of this part of the report, this summary list of hazardswill provide a checklist for fleet operators who are considering alternative fuels and a guideto the state of knowledge and knowledge gaps concerning the various alternative fuels.

4.2 OBJECTIVES AND SCOPE

The objective of this section is to review and assess the hazards associated with the fleet useof alternative fuels for motor vehicle fleet operations, within the following scope limitations:

This report does not cover hazards to the environment and is not an environmentalassessment of alternative fuel use.

The report is not a risk assessment and does not evaluate hazard probabilities, sothere are no numerical ratings or rankings of fuels or hazards according to theiroverall risk.

Obviously, no list of hazards can be exhaustive. An attempt has been made to identify allmajor hazards and to choose and/or emphasize those fuel-hazard combinations which werejudged to be most serious thereby focusing the available project resources on the mostsignificant hazards, while still meeting the objective of providing an overall survey of each ofthe alternative fuels.

4.2.1 Fuels Included

In this report, safety, fire, and health hazards are reviewed for each of the following fuelslisted below. The number designation is the same as that used in the Summary List ofAlternative Fuel Hazards as found in Tables 4-1 to 4-8. These tables commence with 4-1(a)through 4-1(h) and continue on successively from 4-8(a) through 4-8(h) for each of the listedfuels and their hazardous properties.

1. Compressed natural gas (CNG)

2. Liquefied natural gas (LNG)

3. Propane

4. Methanol and methanol blends

5. Ethanol and ethanol blends

6. Biodiesel

7. Hydrogen

8. Electricity

The last two fuels, electricity and hydrogen have been given less emphasis because the use ofthese fuels is likely to be further in the future. Reformulated gasoline and reformulateddiesel have not been included in the hazard list because they are so similar to fuels that arealready in widespread use that no additional hazard issues were identified.

4.2.2 Hazardous Properties Included

For the review of hazards of alternative fuels, the following hazardous properties areconsidered:

(a) Flammability

(b) Corrosivity

(c) Toxicity (including asphyxiation)

(d) High pressure

(e) High temperature

(f) Cryogenic temperature

(g) Mechanical energy

(h) Electrical energy

Other hazards that are not included in this report:

Vacuum

Radiation (radioactivity)

Etiologic (bacterial, viral, etc.)

Shock sensitive materials

Noise and vibration

This list is not an exhaustive list of all possible hazardous properties but rather those deemedto be most relevant to the use of alternative fuels in motor vehicles. For example,radioactive materials, shock-sensitive materials, and vacuums all present hazardous propertiesthat can result in hazards, but these hazardous properties are not relevant in the context ofalternative-fueled vehicles.

Some hazardous properties in the list are relevant only in the context of certain alternativefuels or certain vehicle and/or fuel system designs. For example, some electric vehicles mayhave batteries whose electrolyte is at a high temperature. Thus, the high temperaturehazardous property is relevant to this fuel, but not to other fuels which are stored and used atnormal temperatures or even to other battery designs, such as lead-acid cells, which do notemploy high temperatures.

4.2.3 Accident Events Included

The existence of these hazardous properties and their associated hazards is not sufficient tocause an accident. Some type of accident event is necessary before the hazard and thehazard consequences are realized. While the events which lead to accidents are many andvaried, most such events can be classified into several broad categories:

Initial Events:

Improper design

Improper installation

Improper repair

Operating Events:

Structural failure from material failure (from corrosion, fatigue, or other causes)

Loss of containment from material failure

Operator error

Traffic accident

4.3 SUMMARY LIST OF ALTERNATIVE FUEL HAZARDS FOR VEHICLE FLEET

OPERATIONS

4.3.1 Overview of Alternative Fuel Hazards

A general discussion follows of hazards associated with each of the previously mentionedhazardous properties. All discussion is in the context of the use of alternative fuels by motorvehicles. The numbering of these hazards follows the numbering which is used in thesubsequent Summary List of Alternate Fuel Hazards Tables 4-1 through 4-8 (sections a-h).

4.3.2 Safety Hazards Considered

(a) Hazardous Property = Flammability

All conventional and alternative fuels are flammable. The flammability of these fuels mayresult in:

A pooled fuel fire

A fuel vapor fire

An explosion (if the hot products of combustion are confined and prevented fromfreely expanding into the atmosphere)

A BLEVE (boiling liquid expanding vapor explosion)

Exposure to fire from other causes, e.g., vehicle fuel tank exposed to a vehicleelectrical system fire

(b) Hazardous Property = Corrosivity

Most fuels are not particularly corrosive. However, some battery electrolytes are stronglyacidic or strongly basic. Also, materials compatibility problems may result in fuel leaks thatpresent a fire hazard. The corrosive nature of these substances may result in:

Failure of vehicle structural components from loss of strength due to corrosion

Fuel leaks due to failure of fuel system components

Injuries due to chemical burns

(c) Hazardous Property = Toxicity

The toxic nature of some fuels may result in:

Acute health effects from fuel vapor inhalation

Chronic health effects from fuel vapor inhalation

Health effects from absorption of fuel through the skin

Even for fuels that are non-toxic, the displacement of breathable air by a gaseous fuel mayresult in:

Asphyxiation

Some fuels, such as ethanol and bio-diesel, are advertised to be derived from food crops. This may tempt some people to risk ingestion, even though both of these fuels are processedso as to make them toxic:

Ingestion

(d) Hazardous Property = High Pressure

Pressure is defined as force per unit area. As many simple calculations and unfortunateexperiences have shown, even a seemingly modest pressure over a modestly large areapresents a large force. High pressure can result in:

Pressure vessel rupture

Components acting as projectiles during disassembly

Reaction force from high-pressure jets

(e) Hazardous Property = High Temperature

The hazards associated with high temperatures are generally well-recognized:

Loss of material strength

Burn injuries from human exposure to high temperatures

Possible fire initiation from the exposure of flammable materials to hightemperatures

(f) Hazardous Property = Cryogenic Temperature

Cryogenic temperatures are generally regarded as those less than -150 C. The hazards ofsuch low temperatures are both obvious and subtle:

Cryogenic burn injuries from human exposure to low temperatures

Structural failure due to stress from contraction of cooled components

Structural failure of materials due to embrittlement at low temperatures

(g) Hazardous Property = Mechanical Energy

The hazardous property of mechanical energy indicates the kinetic energy of rapidly movingparts or the potential energy of a large mass at an elevation. The danger from kinetic energyincreases with the mass of parts and with the velocity, either linear or rotational. The dangerfrom potential energy increases with the mass and the height. The mechanical energyhazardous property can cause:

Separation or fragmentation of moving parts

Crushing or impact from falling parts

(h) Hazardous Property = Electrical Energy

Electricity presents a number of familiar hazards, especially electric shock. The severity ofthese hazards depends on both the voltage and current available. While current flow is thefactor that causes the injury in electric shock, higher voltages lead to greater danger. Ingeneral, voltages in excess of 50 volts are considered potentially lethal.

Electric shock injuries

Fire from electrical shorts

Possible health effects from electromagnetic radiation

4.4 SUMMARY LIST OF ALTERNATIVE FUEL HAZARDS

The summary list of alternative fuel hazards follows.

TABLE 4-1(A). COMPRESSED NATURAL GAS (CNG) -- FLAMMABILITY

Hazard --Event

Background Consequences Knowledge
Fire -- fromgas supplypipeline leaks Because of the economics of CNGcompression, there is an incentive to usepipeline supply pressures to the compressorthat are much higher than those normally usedfor local natural gas distribution. Therefore,some transit operations with CNG fleets havenatural gas supplies of 200-400 psig or moreon the property, whereas normal natural gaslocal distribution pressures seldom exceed 10-80 psig.

The high line pressure meansthat large amounts of fuel canbe released quickly. There is a substantial body ofknowledge about corrosion andleak hazards of natural gaspipelines and such accidents aregenerally infrequent. However,heavy use of road salt maysubject pipelines under bustraffic areas to a corrosiveenvironment not normally seenin rural settings.
2-17

Fire -- fromdamaged gassupplypipelines

Because of the economics of CNGcompression, there is an incentive to usepipeline supply pressures to the compressorthat are much higher than those normally usedfor natural gas distribution. Some transitoperations with CNG fleets have natural gassupplies of 200-400 psig or more on theproperty. Any construction work on thepremises can endanger that piping. Construction crews working on the premisesmay not expect this level of danger.

The high line pressure meansthat large amounts of fuel canbe released quickly. Since such high gas pressuresare not often used in urbanareas and seldom used onprivate property, there is littleexperience with damagepotential. Contractors andothers may not be prepared forthe possibility of such releaseswithin an urban area.
Fire -- fromgas meteringequipmentafter vehiclecollisiondamage Because of the economics of CNGcompression, there is an incentive to usepipeline supply pressures to the compressorthat are much higher than those normally usedfor natural gas distribution. Some transitoperations with CNG fleets have natural gassupplies of 200-400 psig or more on theproperty. The high line pressure meansthat large amounts of fuel canbe released quickly. Engineering design for crashprotection is reasonably well-known and can be applied tomitigate this hazard.
Fire -- fromleakingundergroundCNG piping tofueling islanddue tocorrosion Piping from the compressor to the dispenserhas pressures of 3000-4000 psig. Such pipingis often made of stainless steel. Althoughstainless steel resists many types of corrosion,some types of stainless steel are verysusceptible to chloride corrosion. Of course, incold climates, sodium chloride is commonlyused as road salt. The high line pressure meansthat large amounts of fuel canbe released quickly. Although high pressure gaspiping is often made of stainlesssteel, there is little experiencewith this type of service overthe long term. Most CNGfacilities are just a few years oldor less.
Fire -- fromgas dispensingequipmentafter vehiclecollisiondamage Piping from the compressor to the dispenserhas pressures of 3000-4000 psig. Whilefueling island collisions may be rare, there isthe potential to release large amounts of fuel. The high line pressure meansthat large amounts of fuel canbe released quickly. Engineering design for crashprotection is reasonably well-known and can be applied tomitigate this hazard.
Vehicle fire --from fuelsystem leaksdue to poordesign The use of compressed natural gas fuelinvolves materials, components, andtechniques which have not been generallyused on motor vehicles. Often, productionCNG vehicles differ significantly in design from"breadboard" prototypes previously used bygas utilities and others as demonstration CNGfleets. Fires from liquid fuels are limitedby the relatively slowevaporation of the fuel. Forgaseous fuels, this limitationdoes not exist and large firescan develop quickly. The design experience base foruse of high pressure gaseousfuels on vehicles is stillrelatively small. Although CNGvehicles have been operating fora number of years, many weresmall volume conversions andthe engineering experiencegained was not necessarilytransferred or transferrable toother installers.
Vehicle fire --from fuelsystem leaksdue toimproperinstallation Many CNG vehicles are converted from otherfuels. The experience and skill of those doingsuch conversions is highly variable. Examination of converted vehicles has shownexamples of fuel lines in openings withoutgrommets, fuel lines routed too close to theexhaust system, and CNG tanks that were tooclose to other components. Past experiencehas shown that not all of those personneldoing these conversions are familiar with theprovisions of NFPA-52. Fires from liquid fuels are limitedby the relatively slowevaporation of the fuel. Forgaseous fuels, this limitationdoes not exist and large firescan develop quickly. The experience base forinstallations using high pressuregaseous fuels on any given typeor model of vehicle is stillrelatively small. Although CNGvehicles have been operating fora number of years, many weresmall volume conversions ofunique design and theengineering experience gainedwas not necessarily transferredor transferrable to larger fleets. Additional information onconversion kits for CNG is givenin . "Evaluation of Aftermarket Fuel Delivery Systems for Natural Gas Vehicles and LPG Vehicles," by B. Willson,NREL report NREL/TP-420-4892, (1992)..
Vehicle fire --from fuelsystem leaksdue tocomponentfailure. The use of compressed natural gas fuelinvolves materials and components which havenot been generally used on motor vehicles. And new component designs may not provereliable. An example, is the number (at least50) of Mirada PRD. A pressure relief device (PRD) is connected to a compressed gas cylinder to relieve excess pressure. PRDsmay act from excess pressure through the use of a burst disk, or from excessive temperature, through theuse of a fusible plug. Most PRDs used on CNG vehicles incorporate both types of protection. failures observed intransit bus fleets in 1993-1994. Each of thesefailures resulted in a major fuel release. Fires from liquid fuels are limitedby the relatively slowevaporation of the fuel. Forgaseous fuels, this limitationdoes not exist and large firescan develop quickly. An example of componentfailure is the PRD failuresobserved in CNG transit buses. An early review of natural gasvehicle safety concerns is givenin. . "Natural Gas Fuel Tanks for Automobiles: Safety Problems," F.A. Jennings and W.R. Studhalter, ASMEpaper 71-PVP-62, May 1971.
Vehicle fire --from otherthanalternativefuel source Fleet experience shows that many vehicle firesare of electrical origin. These fires theninvolve other vehicle components, such asplastic parts and eventually involve the vehiclefuel system. A major vehicle fire is almostcertain to cause the CNG tanksto vent through the thermalprotection devices. This willcause a rapid release of naturalgas fuel and will make the firemuch more intense. Moreover,the natural gas supply maymake extinguishment of the fireinadvisable. To date, no CNG vehicles areknow to have been involved in avehicle fire whose origin wasnot in the fuel system. However, vehicle fires do occurand experience with natural gasin stationary applicationsindicates that the presence of anatural gas supply canexacerbate fire damage.
Fire -- afterdrive-awayduring fueling Properly designed break away connectors canprevent most large fuel releases. Also, manyCNG vehicles have ignition interlocks thatprevent the vehicle from starting while the fueldoor is open. But these fittings and interlockscannot protect against all drive-awayscenarios. Static electricity may ignite suchfuel releases. This scenario was the cause ofa fire in Las Vegas which destroyed a transitbus. Any large fire has the potentialto destroy the vehicle and/orinjure employees. In addition, afueling island fire could put thefleet out of commission bypreventing fueling. One such fire has occurred inLas Vegas. The number of CNGtransit busdrive-aways to date is probably small,perhaps less than a dozen, so it isdifficult to extrapolate a rate of fireincidence. For typical diesel bus fleets of200-300 buses, drive-aways occur aboutonce a month.
Fire -- from staticignition of fueltanks duringventing At least a dozen such fires have already occurred as CNGtanks were vented to the atmosphere. Static charges aremore likely to build up where droplets or particles arecontained in a high velocity gas stream. When compressednatural gas escapes, droplets may be formed from coolingand subsequent condensation of water or heavyhydrocarbons in the gas, or from entrained compressor oil. Some of these fires have destroyedvehicles. The properties of static electricity aregenerally well-known, but are not alwaysapplied by operators of alternative fuelfleets. The generation of staticdischarges from jets is discussed in . "Sparks from Steam," A.F. Anderson, Electronics and Power, January 1978. p. 50-53..
Vehicleexplosion -- fromfuel system leaks Transit buses have fairly large volume enclosed spaces,especially the passenger compartment. If these spaces fillwith a flammable mixture, a significant explosion can occur. When ignited, a confined natural gas-airmixture can produce pressures of up to800 kPa -- far more than vehicle glass orbody structures can withstand. One such explosion has occurred, in anarticulated transit bus under repair atHouston Metro. An analysis of fuel gasleakage into the interior of a vehicle isgiven in . "Efflux of Gaseous Hydrogen or Methane Fuels from the Interior of an Automobile," J.M. Arvidson, et al., National Bureau ofStandards report COM-75-10288, 1 March 1975..
Buildingexplosion -- fromvehicle fuelsystem leaks Such leaks can form a flammable zone inside vehiclestorage and maintenance buildings and if ignited can causebuilding explosions and serious injuries. Experience to datesuggests that fuel system leaks will be relatively frequentuntil the technology of CNG use on vehicles becomes moremature. When ignited, a confined natural gas-airmixture can produce pressures of up to800 kPa -- far more than vehiclestructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. Though some fluid dynamic modeling offuel system leaks has been done forFTA, there is a lack of experimental dataon flammable plume behavior and also alack of codes and standards to guide thedesign of buildings for this fuel.
Buildingexplosion -- fromvehicle PRDfailure Such leaks can form a large flammable zone inside vehiclestorage and maintenance buildings and if ignited can causebuilding explosions and serious injuries. Experience to datesuggests that PRD failures will be relatively frequent untilthe technology of CNG use on vehicles becomes moremature. PRD failures are different from other fuel systemleaks in that the flow rate of escaping gas is quite large,often 1-2 kg/s. When ignited, a confined natural gas-airmixture can produce pressures of up to800 kPa -- far more than buildingstructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. Though some fluid dynamic modeling offuel system leaks has been done forFTA, there is a lack of experimental dataon flammable plume behavior and also alack of codes and standards to guide thedesign of buildings for this fuel.

TABLE 4-1(B). COMPRESSED NATURAL GAS (CNG) -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Explosion -- ofvehicle fuel tankdue to internalcorrosion While the hydrocarbon constituents of natural gas arerelatively benign, several impurities must be controlled toprevent excessive internal tank corrosion. These includewater and sulfur, arsenic, and mercury compounds. Thespecific requirements will depend on the materials ofconstruction of the tank. The amount of stored energy in a CNGfuel tank is substantial and the rate ofenergy release in case of tank rupture ishigh. Any pressure vessel explosion ispotentially serious. The knowledge of fuel quality needed forgood tank performance is generally good. However, often little is known about thelevels of impurities in the natural gassupply being used. The absence of aspecification for natural gas delivered tothe consumer exacerbates this situation. Some relevant information on natural gasimpurities is given in . "Gas Quality Specifications for Compressed Natural Gas (CNG) Vehicle Fuel," in Gas Quality, edited by G.J. van Rossum,(1986). p. 37..
Erosion -- due toimpurities in gas While not strictly speaking corrosion, the effects of erosionare similar: a removal of material and a weakening of thestrength of the component. Impurities which may beresponsible include particulates, gas hydrates, and icecrystals. CNG components are under highpressure and loss of strength could resultin a serious sudden release of pressure. To date, no pressure vessel or line isknown to have failed to contain thepressure due to erosion. However,numerous problems have occurred withCNG fuel nozzles due to erosion by solidimpurities in the fuel or by ice or gashydrate crystals.

TABLE 4-1(C). COMPRESSED NATURAL GAS (CNG) -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Adverse healtheffects -- fromexposure tonatural gas Although natural gas has a low order of toxicity, it is notnon-toxic. Some higher hydrocarbons found in natural gasare neurotoxins. Natural gas may also contain benzene,arsenic,. "Determination of Arsenic and Arsenic Compounds in Natural Gas Samples," Kurt J. Irgolic, Dale Spall, B.K. Puri, DrewIlger, and Ralph A. Zingaro, Applied Organometallic Chemistry, 5, 117-124 (1991).. "Organic Arsenic Compounds in Petroleum and Natural Gas," Kurt J. Irgolic and Bal K. Puri, NATO ASI Series, Vol G 23,Metal Speciation in the Environment, ed. by J.A.C. Broekaert, S. Grucer, and F. Adams, Springer-Verlag, 1990. and heavy metals, such as mercury,. "Gas Quality Specifications for Compressed Natural Gas (CNG) Vehicle Fuel," Frank V. Wilby, in Gas Quality, ed. By G.J.van Rossum, Elsevier, 1986. p. 37. thatare toxic. Some higher hydrocarbons found innatural gas are neurotoxins. Chronicexposure to these compounds hascaused health effects. However, theincidence of health effects in the naturalgas industry is generally low. Because the composition of natural gasis variable, accurate information on theminor constituents of natural gas is notalways available.
Asphyxiation --from displacementof air Natural gas is lighter than air and can collect in vessels andequipment that are not top-ventilated. This can includesome vehicle compartments as well as facilities. A personwho enters an atmosphere lacking in oxygen can loseconsciousness in as little as 20 seconds and may die in 3-4minutes. If a person does not receive fresh airquickly, serious injury can occur. The causes and effects of asphyxiationare discussed in standard safetytexts.. See for example, Fundamentals of Industrial Hygiene, Third Edition, National Safety Council, (1988). p. 367.
Adverse healtheffects -- fromindoor exposureto formaldehyde invehicle exhaust Incomplete combustion of methane produces formaldehyde,an irritant and a possible weak carcinogen. Due tocombustion quenching, natural gas engines produce someformaldehyde emissions, especially when cold. Thoughcatalytic converters can control formaldehyde, these are noteffective during pull-out when engine and exhaust systemare cold. Numerous transit facilities already have indoor airquality problems during pull-out and employees may besensitive, both physically and politically to this issue. Aldehydes are very irritating to the eyes,nose, and respiratory system. Excessivealdehyde levels have led to employeediscomfort and complaints. Measurements made by Battelle for FTAhave shown that formaldehydeconcentrations are higher in the vicinityof CNG buses during morning pull-outthan during diesel buses.

TABLE 4-1(D). COMPRESSED NATURAL GAS (CNG) -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledg he consequencesof various component failures.
Missile damage-- fromflying about of partsduring disassembly CNG fuel systems are under high pressure. Improperdisassembly procedures or faulty pressure indicationscan cause parts to act as projectiles. Studies ofprojectile impacts have shown that the energy that couldbe imparted to standard fuel system fittings by CNGwould be sufficient to cause the death of large laboratorytest animals. Although the projectiles may not belarge or heavy, the close proximity ofpeople increases the risk. Such incidents have been reported intransit CNG operations. In somecasesgaultyss ledworkers to erroneously believe thesystem was not under pressure.
Missile damage-- frompressure ure gages ledworkers to erroneouslybelieve the system wasnot onary applications,the vehicleenvironment can bemore severe andpressure gage failuresmay be expected tooccur more frequentlythan in stationaryapplications. Although the projectiles from a failed gage may not belarge or heavy, the close proximity of people increasesthe risk. Gage manufacturers generally includefeatures to insure that any failure doesnot occur on the front of the gage. However, proper installation of the gageis necessary for those features to beeffective. No such incident involving aCNG vehicle is known to date.
Flailing damage --from fueling hosefailure CNG fueling hoses carry gas at high pressure. A brokenhose will flail wildly if unrestrained. Excess flow devicesmay help, but due to the high fill rates required for fleetoperations, the allowable flow rate must be relativelylarge. Although the fueling hose may not beespecially heavy, the necessary closeproximity of people greatly increases therisk. Good information about the frequencyof hose failures in CNG service is notavailable. There has been one incidentwhere a plugged vent hose on a ventednozzle ruptured and struck a fueler.

TABLE 4-1(E). COMPRESSED NATURAL GAS (CNG) -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Natural gas is not stored or used at high temperaturesand does not present a significant high temperaturehazard.

-- --

TABLE 4-1(F). COMPRESSED NATURAL GAS (CNG) -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
Injury -- from contactwith cold components. High pressure gas releases produce vigorous cooling dueto expansion of the gas. Unlike cryogenic fuels whichfeature low temperatures, the low temperatures fromCNG releases can be unexpected. Personal injury due to frostbite canoccur. Release of CNG can producetemperatures of -100 C or less.

TABLE 4-1(G). COMPRESSED NATURAL GAS (CNG) -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
Missile damage --and/or injury fromcatastrophiccompressor failure. Natural gas compressors are large rotating machines. Mechanical failure could produce flying fragments. Damage or injury due to flyingfragments. The fragments may severgas or electric lines and generateadditional hazards. A number of compressor stations haveexperienced serious mechanical failuresof compressor units, e.g., sheared headbolts. In the chemical process industry,the incidence of compressor failure hasbeen estimated to be 2000/106 hrs.
Falling hazard -- fromhandling of heavy fueltanks. CNG fuel tanks, particularly when grouped in racks, areheavier than conventional diesel fuel tanks. Equipmentand procedures will have to be developed for handlingthese heavy components. Even in the absence of anyneed for repair, the tanks will need to be removed forinspection and recertification. Failure to handle heavy fuel tanksadequately can cause personal injuryand damage to the tanks. Although a number of fleets operateCNG vehicles, the author is not awareof any refined system for handling CNGfuel tanks during routine maintenance. A number of fleets have plans toconstruct specialized tank handlingequipment, but there is as yet noexperience on the success of thoseplans.

TABLE 4-1(H). COMPRESSED NATURAL GAS (CNG) -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
Electric shock -- fromelectrical supply tonatural gas compressorstations. Natural gas compressor stations require large primemovers. If these are electrically operated, the size of themotors needed requires high voltage and high current. Electric shock can cause serious or fatalinjuries. The design and precautions necessaryto handle electrical loads safely arewell-developed. The National ElectricalCode (NFPA-70) summarizes thisknowledge.

TABLE 4-2(A). LIQUEFIED NATURAL GAS (LNG) -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- from LNGdispensing equipmentafter vehicle collisiondamage While fueling island collisions may be rare, there is thepotential to release large amounts of fuel. The rapid evaporation of LNG on warmsurfaces means that large amounts offuel vapor can be released quickly. Design for crash protection isreasonably well-known and can beapplied to LNG fueling dispensers tomitigate this hazard.
Fire -- in LNG fuelstorage facility LNG fuel storage facilities must contain moderately largequantities of flammable liquefied gas if they are to fuel alarge fleet. To date, these facilities are located aboveground and are subject to various component failures. Elimination of all local sources of ignition is the key tosafety since small leaks and venting of LNG are relativelycommon occurances. A fire in the vicinity of an LNG storagetank can result in rapid venting of largeamounts of fuel. Numerous reviews of LNG facilities forgas utility peak-shaving plants havebeen made. One short general reviewis presented in a NIOSH report.. "Safety Information Profile Liquefied Natural Gas Usage in Industry," E.D. Pearlman and G.W. Pearson, NIOSH report124043, June 1981.
Vehicle fire -- fromfuel system leaks dueto poor design The use of liquefied natural gas involves materials,components, and techniques which have not beengenerally used on motor vehicles. Production LNGvehicles will differ significantly in design from prototypespreviously used by gas utilities and others asdemonstration LNG fleets. Fires from conventional fuels are limitedby the relatively slow evaporation of thefuel. For gaseous fuels, this limitationdoes not exist and large fires candevelop quickly. The design experience base for use ofnatural gas fuel (LNG or CNG) onvehicles is still relatively small,especially for a given type of vehicle. The total number of LNG-fueledvehicles that have ever been in servicein the world is probably fewer than 1000vehicles.
Vehicle fire -- fromfuel system leaks dueto improper installation. Many natural gas vehicles are converted from other fuels. The experience and skill of those doing such conversionsare highly variable. LNG vehicle fuel systems are underrelatively high pressure, 80 to 200 psig. Thus, any fuel leak can releaserelatively large amounts of fuel quickly. As noted above, the design experiencebase for use of natural gas fuel on anygiven type of vehicle is still relativelysmall.
Vehicle fire -- fromfuel system leaks dueto component failure. The use of cryogenic fuels involves materials andcomponents which have not been generally used onmotor vehicles. LNG vehicle fuel systems are underrelatively high pressure, 60 to 200 psig. Thus, any fuel leak can releaserelatively large amounts of fuel quickly. There is essentially no body ofknowledge on the design of cryogeniccomponents for motor vehicle service. The lessons learned on the limited LNGvehicle demonstrations to date have notbeen collected and codified in theliterature for use by automotiveengineers new to this fuel. Some dataon the failure rates of components instationary service is listed in. . "LNG Safety Research in the U.S.A.", S. Atallah and A.L. Schneider, Journal of Hazardous Materials, Vol. 8, pp. 25-42,1983.Vehicle service is more severe andlikely to result in higher failure rates.
Vehicle Fire -- fromother than alternativefuel source. Fleet experience shows that many vehicle fires are ofelectrical origin. These fires then involve other vehiclecomponents, such as plastic parts, and eventually involvethe vehicle fuel system. Because of the low boiling point of LNG,a BLEVE of the LNG fuel tank ispossible. More likely is rapid venting ofnatural gas. To date, no LNG vehicles are known tohave been involved in a vehicle firewhose origin was not in the fuel system. However, such vehicle fires do occurand experience with natural gas instationary applications indicates that thepresence of a pressurized natural gassupply can increase the severity of firedamage.
Fire -- after drive awayduring fueling. Properly designed break away connectors can preventmost large fuel releases. But these fittings cannotprotect against all drive-away scenarios. Some LNGvehicles have ignition interlocks to prevent the vehiclefrom being started with the fuel door open. Suchinterlocks can help reduce the frequency of drive-aways. Any large fire has the potential todestroy the vehicle and/or injureemployees. In addition, a fueling islandfire could put the fleet out of commissionby preventing fueling. For typical diesel bus fleets of 200-300buses, drive-aways occur about once amonth. Experience with CNG fleetsshows that drive-aways still occur. Thefrequency for LNG fleets is yet to bedetermined.
Vehicle explosion --from fuel system leaks. Transit buses have fairly large volume enclosed spaces,especially the passenger compartment. If these spacesfill with a flammable mixture, a significant explosion canoccur. One such explosion has occurred, a transit bus atHouston Metro. When ignited, a confined natural gas-airmixture can produce pressures of up to800 kPa -- far more than vehiclewindows or body structures canwithstand. One such explosion has occurred, in anarticulated transit bus under repair atHouston Metro. Information on theefficacy of various common ignitionsources is given in. . "Ignition Sources of LNG Vapor Clouds," D.J. Jeffres, N.A. Moussa, R.N. Caron, and D.S. Allen, Gas Research Institutereport GRI-80/0108, 1980.
Building explosion --from vehicle fuelsystem leaks Such leaks can form a flammable zone inside vehiclestorage and maintenance buildings and, if ignited, cancause building explosions and serious injuries. Experience to date suggests that fuel system leaks willbe relatively frequent until the technology of natural gasvehicles becomes more mature. Since natural gas fromLNG is not odorized, some leaks may go unnoticed. When ignited, a confined natural gas-airmixture can produce pressures of up to800 kPa -- far more than buildingstructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. Though some fluid dynamic modeling ofCNG fuel system leaks has been donefor FTA, and much modeling of outdoorLNG releases has been performed,there is a lack of data on LNGflammable plume behavior insidebuildings. There is also a lack of codesand standards to guide the design ofbuildings for this fuel.
Building explosion --from vehicle tankventing. If LNG vehicles are not operated frequently, pressure willbuild in the fuel tanks. Eventually such pressure will bevented through a pressure relief valve. Such gasreleases can form a large flammable zone inside vehiclestorage and maintenance buildings, and if, ignited cancause building explosions and serious injuries. Ventingepisodes may be relatively frequent until the experiencebase with LNG vehicles increases. When ignited, a confined natural gas-airmixture can produce pressures of up to800 kPa -- far more than buildingstructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. No study is available of the frequencyof unanticipated indoor LNG venting ina large fleet. Current LNG vehiclesmust be used every 3-10 days toprevent venting.

TABLE 4-2(B). LIQUEFIED NATURAL GAS (LNG) -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Seal failures -- fromlack of low temperaturecapability. While LNG is not corrosive per se, its cryogenicproperties can have deleterious effects on gaskets, o-rings, and other seals. Seal failures usually result in fuel leaks. Such leaks can lead to fire, injury, andexplosion hazards. Experience to date with LNG equipmentshows that fuel leaks are common. Seal failures have been observed onLNG fueling nozzles.

TABLE 4-2(C). LIQUEFIED NATURAL GAS (LNG) -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Asphyxiation -- fromdisplacement of air. LNG vapors are heavier than air and can collect in lowareas and in vessels and equipment that are not well-ventilated. This can include some vehicle portions aswell as facilities. Since LNG is not odorized, peopleentering the space may not be aware that gas is present. If a person does not receive fresh airquickly, serious injury can occur. The causes and effects of asphyxiationare discussed in standard safetytexts.. See for example, Fundamentals of Industrial Hygiene, Third Edition, National Safety Council, (1988). p. 367.
Adverse healtheffects -- from indoorexposure toformaldehyde in vehicleexhaust Incomplete combustion of methane can produceformaldehyde, an irritant and a possible weakcarcinogen. Though catalytic converters can controlformaldehyde, these are not effective during pull-outwhen engine and exhaust system are cold. Numeroustransit facilities already have indoor air quality problemsduring pull-out and employees may be sensitive, bothphysically and politically to this issue. Aldehydes are very irritating to the eyes,nose, and respiratory system. Excessive aldehyde levels have led toemployee discomfort and complaints. Measurements made by Battelle forFTA have shown that formaldehydeconcentrations are higher in the vicinityof CNG buses during morning pull-outthan during diesel buses. Since LNGfleets have the same natural gasengine, they are expected to show asimilar effect.

TABLE 4-2(D). LIQUEFIED NATURAL GAS (LNG) -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
Explosion -- fromcorrosion of vehiclefuel tank. While the pressure in LNG fuel tanks is not as high as inCNG tanks, they are still pressure vessels and containenergy in the form of gas maintained at pressure. Muchmore information is needed about the range of chemicalsthat may contact the fuel tanks and the possiblecorrosive effects. Such agents include road salt,pressure washing detergents, engine oil, brake fluid, etc. It is known that most stainless steel alloys are quitesusceptible to chloride attack.

The amount of stored energy issubstantial and the rate of energyrelease is high. Any pressure vesselexplosion is potentially serious. More information is needed on thechemical environment seen by LNG fueltanks and the possible corrosive effecton the tanks.
Explosion -- frommechanical damage tovehicle fuel tank. While the pressure in LNG fuel tanks is not as high as inCNG tanks, they are still pressure vessels and containenergy in the form of supercooled liquid and gasmaintained at pressure. Any tank in the undercarriage ofthe vehicle is potentially subject to damage from roaddebris.

The amount of stored energy is thesubstantial and the rate of energyrelease is high. Any pressure vesselexplosion is potentially serious. Since the internal pressures are quitesimilar, the frequency of propane tankfailures may serve as a guide here.
Explosion -- fromrapid heat transfer totank. An explosion of a 9000-gallon liquid hydrogen tankoccurred because cooling water applied to the tank aftera fire entered, combined with a loss of vacuum in theinsulating layer, resulted in rapid heat transfer to theliquid in the tank. The same phenomena is expected toapply to liquefied natural gas tanks. The force of the explosion tore a 1440-pound bulkhead from the tank whichwas propelled 250 feet from the originallocation. This incident is described in an articleentitled "How Safe is the Storage ofLiquid Hydrogen.". "How Safe is the Storage of Liquid Hydrogen," by M.A.K. Lodhi and R.W. Mires, International Journal of HydrogenEnergy, 14, 35, (1989).
Explosion -- fromtrapped LNG. Trapped LNG which warms produces extremely highpressures if it is confined. Good design includespressure relief at all points where LNG could be trapped. Good design also prevents moisture from accumulatingthat could form ice plugs and defeat pressure reliefdevices. The amount of stored energy is thesubstantial and the rate of energyrelease is high. Any pressure vesselexplosion is potentially serious. The physical principles behind thishazard are well-known. The frequencyin vehicle fleet operation is not known.

TABLE 4-2(E). LIQUEFIED NATURAL GAS (LNG) -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Liquified natural gas is not stored or used at hightemperatures and does not present a significant hightemperature hazard.

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TABLE 4-2(F). LIQUEFIED NATURAL GAS (LNG) -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
Injury -- from skincontact with coldcomponents. Skin can adhere to cold surfaces and be torn away. Skincontact with LNG can also cause frostbite or cryogenicburns within a few seconds. Frostbite and personal injury can result. The flesh-tearing hazard is mentionedin "Safe Handling of Cryogenic Liquids,"Compressed Gas Assoc. publicationCGA P-12-1993, but no indication isgiven as to the frequency ofoccurrence. Some minor cases of LNGfuel-related frostbite have occurred inLNG fleet vehicle operations.
Injury -- from skincontact with LNG spillsor leaks. Skin contact with LNG can cause frostbite or cryogenicburns within a few seconds. Frostbite and personal injury can result. The flesh-tearing hazard is mentionedin "Safe Handling of Cryogenic Liquids,"Compressed Gas Assoc. publicationCGA P-12-1993, but no indication isgiven as to the frequency ofoccurrence. Some minor cases offrostbite from LNG fuel spills haveoccurred.
Injury -- from eyecontact with LNG spillsor leaks. If LNG were to be splashed into the eyes, it would freezethe lens and make it opaque. Eye protection for fuelersand mechanics is important, but not always used. Eye contact with LNG can causeimmediate and permanent blindness. A search of the literature did not revealany such injuries to date.
Structural failure --due to contraction Structural materials will contract substantially whenexposed to cryogenic temperatures. If they are notdesigned for such contraction, permanent deformation ordamage may result. If the material is brittle, stresscracking may result. If the structural member is free to move,there may be no consequence at all. On the other hand, if the member isconstrained, large stresses will build up. If the member is also embrittled due tolow temperature, then cracking andstructural failure of the member mayoccur. Such failure may endanger thevehicle or vehicle safety components. The calculation of the degree ofcontraction with temperature is atextbook problem in engineering. However, if spills and leaks areunanticipated, then the designer maynot have made any provision for suchan occurrence.
Structural failure --due to embrittlement Many materials, including common steel, become brittleat cryogenic temperatures. Although components thatare normally at cryogenic temperatures can be designedfor this service, LNG spills can adversely affect thestructural integrity of the components that are contacted. During the time that the materials arecold and brittle, structural failure mayoccur that may endanger the vehicle orvehicle safety components. Since the appearance of the materialmay not change, observers may notrealize that the strength has been lost. This effect is the basis for any numberof laboratory demonstrations ofcryogenic effects and there is asubstantial body of knowledge on theeffect of temperature materialproperties. This knowledge should beapplied if the designer believes thematerial may be exposed to LNG.

TABLE 4-2(G). LIQUEFIED NATURAL GAS (LNG) -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Use of liquefied natural gas fuel does not result insignificant amounts of stored mechanical energy andhence there is no significant mechanical energy hazards.

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TABLE 4-2(H). LIQUEFIED NATURAL GAS (LNG) -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Liquefied natural gas fuel does not involve storedelectrical energy and does not present a significantelectrical hazard. -- --

TABLE 4-3(A). PROPANE -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- from propanedispensing equipmentafter vehicle collisiondamage. While fueling island collisions may be rare, a fire resultingfrom such a collision could put the fueling facility out ofservice. Damage and/or injury from fire, possibledisruption of service. Engineering design for vehicle crashprotection is reasonably well-known andcan be applied.
Fire -- after drive-awayduring fueling. Properly designed break-away connectors can preventmost large fuel releases. But these fittings cannotprotect against all drive-away scenarios. Any large fire has the potential todestroy the vehicle and/or injureemployees. In addition, a fueling islandfire could put the fleet out of commissionby preventing fueling. For typical diesel bus fleets of 200-300buses, drive-aways occur about once amonth.
Fire -- from overfillingtanks. Propane has a much higher volumetric expansion thandoes water. Therefore, it is necessary to limit theeffective capacity of propane fuel tanks to about 80percent of the water volume. If this is not done, movingthe vehicle into a warmer location can result in a releaseof liquid propane through the tank relief valve. Often, such tank-venting incidents occurat night after the vehicle has beenfueled and then parked indoors. Ifignition of the vented propane occurs,the resulting fire can cause considerableproperty damage. At least several hundred propane over-filling fires occur each year. Foradditional information, seeReference. "Propane Over-filling Fires," Noel de Nevers, Fire Journal, September, 1987. p. 80..
Fire -- from staticignition of ventedtanks. During some vehicle maintenance procedures, thevehicle tanks may have to be emptied of fuel. However,effective procedures may not always be used to emptyfuel tanks. Allowing a jet of gaseous fuel and fueldroplets to impinge on another object can cause anaccumulation of static electricity. Similar fires while venting natural gasfuel tanks have destroyed the vehicle. The principles of static electricity aregenerally well-known, but are notalways applied by operators ofalternative fuel fleets.
Vehicle fire -- fromfuel system leaks dueto poor design. While the number of propane-fueled vehicles exceedsthat for many other alternative fuels, most propane fuelsystems are still designed by aftermarket converters whomay not have the vehicle design resources of an OEMautomobile manufacturer. Vehicle fires can result in damage tovehicle, cargo, and occupants. The design experience base for the use of propane on vehicles is still muchsmaller than for gasoline or diesel.
Vehicle fire -- fromfuel system leaks dueto improper installation. Many propane vehicles are converted from other fuels. The experience and skill of those doing such conversionsare highly variable. Vehicle fires can result in damage tovehicle, cargo, and occupants. The design experience base for the use of propane on vehicles is still muchsmaller than for gasoline or diesel fuel. Additional information on propane conversion kits is given in Reference. "Evaluation of Aftermarket Fuel Delivery Systems for Natural Gas Vehicles and LPG Vehicles," by B. Willson, NRELreport NREL/TP-420-4892, (1992)..
Vehicle fire -- fromfuel system leaks dueto component failure. While the number of propane-fueled vehicles exceedsthat for many other alternative fuels, propane fuelsystems components still do not have the experiencebase of other fuels. Vehicle fires can result in damage tovehicle, cargo, and occupants. The design experience base for the use of propane on vehicles is still muchsmaller than for gasoline or diesel.
Vehicle Fire -- fromother than alternativefuel source. Fleet experience shows that many vehicle fires are ofelectrical origin. These fires then involve other vehiclecomponents, such as plastic parts, and eventually involvethe vehicle fuel system. Because of the low boiling point ofpropane, a BLEVE of the propane fueltank is possible. More likely is rapidventing of propane gas. Such vehicle fires do occur andexperience with propane in stationaryapplications indicates that the presenceof a propane supply can increase theseverity of fire damage by feedingadditional fuel to the fire.
Vehicle explosion --from fuel system leaks NFPA-58 contains venting provisions to be followed toaddress this hazard. When ignited, a confined propane gas-air mixture can produce pressures of upto 800 kPa -- far more than vehiclewindows or body structures canwithstand. A number of such explosions haveoccurred in recreational vehicles wherethe on-board supply of propane wasused for heating and/or cooking.
Building explosion --from vehicle fuelsystem leaks Such leaks can form a flammable zone inside vehiclestorage and maintenance buildings and, if ignited, cancause building explosions and serious injuries. When ignited, a confined propane gas-air mixture can produce pressures of upto 800 kPa -- far more than buildingstructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. The National Electric containsprovisions for use of explosion-proofelectrical devices in the lower levels ofbuildings where propane is used.

TABLE 4-3(B). PROPANE -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Propane fuel is not corrosive and does not present asignificant corrosivity hazard.

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TABLE 4-3(C). PROPANE -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Asphyxiation -- fromdisplacement of air. Propane gas is heavier than air and can collect in lowareas and in unventilated spaces, such as maintenancepits. If a person does not receive fresh airsoon, serious injury can occur. The causes and effects of asphyxiationare discussed in standard safetytexts.. See for example, Fundamentals of Industrial Hygiene, Third Edition, National Safety Council, (1988). p. 367.
Health effects -- fromfuel toxicity. OSHA has set a time-weighted average (TWA) of 1000ppm as the personal exposure limit for propane vapor. Other authorities, such as the American Conference ofGovernmental Industrial Hygienists (ACGIH) do notsupport the view that propane is toxic and list it as asimple asphyxiant. Conversations with NIOSH did notreveal the rational for a more stringent classification. Probably none, since the more stringenttoxicity concern seems to be withoutbasis. The basis for this OSHA personalexposure limit may be vague, but it'scurrently the law.

TABLE 4-3(D). PROPANE -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
Explosion -- fromcorrosion of fuel tank. While the pressure in propane fuel tanks is not as highas in CNG tanks, they are still pressure vessels andcontain energy in the form of liquefied gas maintained atpressure.

Any pressure vessel explosion ispotentially serious. An approximate failure rate for pressurevessels of all types is about one failureper year per 10,000 vessels inservice.. "Pressure Vessel Failure: Statistics and Probabilities," J.R. Engel, Nuclear Safety, Vol. 15, July 1974. Not all such failures arecatastrophic.
Explosion -- frommechanical damage tofuel tank. While the pressure in propane fuel tanks is not as highas in CNG tanks, they are still pressure vessels andcontain energy in the form of liquefied gas maintained atpressure. If the propane fuel tank is mounted in thevehicle undercarriage, then it is susceptible to failurefrom mechanical damage from road debris, etc.

Any pressure vessel explosion ispotentially serious. See above.

TABLE 4-3(E). PROPANE -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Propane is not stored or used at high temperatures anddoes not present a significant high temperature hazard. -- --

TABLE 4-3(F). PROPANE -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
Injury -- from contactwith cold components. Release of propane produces vigorous cooling due toevaporation of liquid propane and subsequent expansionof the gas. Unlike cryogenic fuels which feature lowtemperatures, the low temperatures from propanereleases can be unexpected. Personal injury due to frostbite canoccur. Release of propane can producetemperatures of -40C or less.

TABLE 4-3(G). PROPANE -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Use of propane fuel does not result in significantamounts of stored mechanical energy and hence there isno significant mechanical energy hazards.

-- --

TABLE 4-3(H). PROPANE -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of propane fuel does not involve stored electricalenergy and does not present a significant electricalhazard. -- --

TABLE 4-4(A). METHANOL -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- from fueldispensing equipmentafter vehicle collisiondamage. The danger of methanol fueling island collisions is similarto that from gasoline fueling islands. Such a collision could result in a fire. Design for crash protection isreasonably well-known and can beapplied.
Vehicle fire -- fromfuel system leaks dueto poor design. Although methanol fuel systems are nearly the same asthose generally used on motor vehicles, there can bechallenges in the selection of compatible materials. Any fuel system fire can damage orconsume the vehicle. The US EPA has compared the vehiclefire rate as a function of Reid vaporpressure (RVP) of the fuel and foundthat as the fuel vapor pressuredecreases, there are fewer vehiclefires.. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A. Machiele, SAE paper 901113 (1990). Methanol has a lower RVPthan gasoline.
Vehicle fire -- fromfuel system leaks dueto component failure. The use of methanol requires some changes in fuelsystem materials and components. Any fuel system fire can damage orconsume the vehicle. The US EPA has compared the vehiclefire rate as a function of Reid vaporpressure of the fuel and found that asthe fuel vapor pressure decreases,there are fewer vehicle fires.. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A. Machiele, SAE paper 901113 (1990). Methanol has a lower RVP thangasoline.
Vehicle Fire -- fromother than alternativefuel source. Fleet experience shows that many vehicle fires are ofelectrical origin. These fires then involve other vehiclecomponents, such as plastic parts, and eventually involvethe vehicle fuel system. The consequences of such a fire will bevery like that of a gasoline fire of similarorigin. The overall fire rate for medium andheavy duty trucks is about 6 fires per100 million miles of operation.. Fire rate data from "Heavy Truck Fuel System Safety Study," U.S. Department of Transportation report DOT HS 807 484,September 1989. p. 52. Most such fires originate in theelectrical system.
Fire -- after drive-awayduring fueling. Properly designed break-away connectors can preventmost such fuel releases. Although unlikely, a fueling island firecould put the fleet out of commission bypreventing fueling. At retail gasoline stations, one oilcompany study found one servicestation fire due to a drive-away per 75million fuelings. Since the vaporpressure of methanol is lower, the firerate would be expected to be somewhatlower.

TABLE 4-4(B). METHANOL -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Corrosion -- to metalcomponents. Being a polar liquid, methanol is slightly acidic. Thus, itcan corrode electropositive metals such as aluminum andzinc. Therefore, materials traditionally used withhydrocarbon fuels may not be satisfactory in contact withmethanol. The large M-85 vehicle program instigated bythe California Energy Commission has produced a wealthof information concerning proper materials selection formethanol fuel. Efforts by Ford and General Motors havealso led to materials specifications. Such corrosion can fuel leaks if fuelsystem components are not made ofmethanol-compatible materials. Information contained in Perry'sChemical Engineer's Handbook coversthe basic materials data formethanol.. Perry's Chemical Engineers' Handbook, Sixth Edition, Robert H. Perry and Don Green. p. 23-29. The CanadianOxygenated Fuels Association hasproduced a guide to methanol fuelingsystem design.. "Methanol Fueling Systems Guide," Canadian Oxygenated Fuels Association report, 27 October 1992. Additionalinformation on materials compatibilitymay require laboratory testing.
Seal failures --deterioration of gasketsand seals While methanol is not very corrosive per se, it can havedeleterious effects on gaskets, o-rings, and other sealswhich were optimized for other fuels, such as gasoline ordiesel. Seal failures usually result in fuel leaks. Such leaks can lead to fire, injury, andexplosion hazards. See above note for corrosion.

TABLE 4-4(C). METHANOL -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Adverse healtheffects -- fromexposure to fuelvapors. Methanol vapors are toxic and excessive exposure tomethanol vapors can cause adverse health effects,including blindness. In humans and other primates, methanolis a neurotoxin and excessive exposurecan cause blindness and death. In non-primates, methanol is metabolized. Therefore, methanol is consideredbiodegradable in the environment. General information on methanol healtheffects is given in Reference . "Automotive Methanol Vapors and Human Health: An Evaluation of Existing Scientific Information and Issues for FutureResearch," Health Effects Institute report, May 1987..NIOSH studied exposure of bus fuelersand mechanics to methanol at SCRTDand found the methanol vapor exposureto be negligible compared to acceptedhealth standards.
Adverse healtheffects -- from skincontact with fuel . Excessive skin contact with methanol can cause adversehealth effects, including blindness. The use of glovesand other personal protective gear is recommended aswell as procedures to minimize skin contact with fuel. In humans and other primates, methanolis a neurotoxin and excessive exposurecan cause blindness and death. NIOSH studied the exposure of busmechanics to methanol at SCRTD andfound the exposure to be generallyacceptable if good work practices wereused for breaking into the fuel system. Complete information on selection ofproper protective gear is given inReference . "A Guide for Evaluating the Performance of Chemical Protective Clothing," Michael M. Roder, NIOSH report, June 1990..

TABLE 4-4(D). METHANOL -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Methanol is not stored or used at high pressures anddoes not present a significant high pressure hazard.

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TABLE 4-4(E). METHANOL -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Methanol is not stored or used at high temperatures anddoes not present a significant high temperature hazard.

-- --

TABLE 4(F). METHANOL -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Methanol is not stored or used at cryogenic temperaturesand does not present a significant cryogenic temperaturehazard.

-- --

TABLE 4-4(G). METHANOL -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of methanol fuel does not involve equipmentwith significant amounts of stored mechanical energy andhence does not present a significant mechanical energyhazard.

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TABLE 4(H). METHANOL -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of methanol fuel does not involve storedelectrical energy and does not present a significantelectrical hazard. -- --

TABLE 4-5(A). ETHANOL -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- from fueldispensing equipmentafter vehicle collisiondamage. The danger of ethanol fueling island collisions is similarto that from gasoline fueling islands. Such a collision could result in a fire. Design for crash protection isreasonably well-known and can beapplied.
Vehicle fire -- fromfuel system leaks dueto poor design. Although ethanol fuel systems are nearly the same asthose generally used on motor vehicles, there can bechallenges in the selection of compatible materials. Any fuel system fire can damage orconsume the vehicle. The US EPA has compared the vehiclefire rate as a function of Reid vaporpressure of the fuel and found that asthe fuel vapor pressure decreases,there are fewer vehicle fires.. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A. Machiele, SAE paper 901113 (1990). Ethanol has a lower RVP than gasoline.
Vehicle fire -- fromfuel system leaks dueto component failure. The use of ethanol requires some changes in fuel systemmaterials and components. Any fuel system fire can damage orconsume the vehicle. The US EPA has compared the vehiclefire rate as a function of Reid vaporpressure of the fuel and found that asthe fuel vapor pressure decreases,there are fewer vehicle fires.. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A. Machiele, SAE paper 901113 (1990). Ethanol has a lower RVP than gasoline.
Vehicle Fire -- fromother than alternativefuel source Fleet experience shows that many vehicle fires are ofelectrical origin. These fires then involve other vehiclecomponents, such as plastic parts, and eventually involvethe vehicle fuel system. The consequences of such a fire will bevery like that of a gasoline fire of similarorigin. The overall fire rate for medium andheavy duty trucks is about 6 fires per100 million miles of operation.. Fire rate data from "Heavy Truck Fuel System Safety Study," U.S. Department of Transportation report DOT HS 807 484,September 1989. p. 52. Most such fires originate in theelectrical system.
Fire -- after drive awayduring fueling Properly designed break away connectors can preventmost such fuel releases. Although unlikely, a fueling island firecould put the fleet out of commission bypreventing fueling. At retail gasoline stations, one oilcompany study found one servicestation fire due to a drive-away per 75million fuelings. Since the vaporpressure of ethanol is lower thangasoline, the fire rate would beexpected to be somewhat lower.

TABLE 4-5(B). ETHANOL -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Corrosion -- to metalcomponents. Being a polar liquid, ethanol is slightly acidic. Thus, itcan corrode electropositive metals such as aluminum andzinc. Such corrosion can fuel leaks if fuelsystem components are not made ofethanol-compatible materials. Information contained in Perry'sChemical Engineer's Handbook coversthe basic materials data forethanol.. Perry's Chemical Engineers' Handbook, Sixth Edition, Robert H. Perry and Don Green. p. 23-26. The large M-85 vehicleprogram instigated by the CaliforniaEnergy Commission has produced awealth of information concerning propermaterials selection for methanol fuel. Efforts by Ford and General Motorshave also led to materials specificationsfor methanol. It is likely that most ofthis experience will transfer over toethanol fuel, given the chemicalsimilarity of methanol and ethanol. Additional information on materialscompatibility may require laboratorytesting.
Seal failures --deterioration of gasketsand seals. While ethanol is not very corrosive per se, it can havedeleterious effects on gaskets, o-rings, and other sealswhich were optimized for other fuels, such as gasoline ordiesel. Seal failures usually result in fuel leaks. Such leaks can lead to fire, injury, andexplosion hazards. See above note for corrosion.

TABLE 4-5(C). ETHANOL -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Adverse healtheffects -- fromexposure to fuelvapors. Ethanol vapors are toxic and excessive exposure tomethanol vapors can cause adverse health effects. TheTLV for ethanol is 1000 ppm. (The odor threshold isabout 5 ppm.) Ethanol toxicity can cause long-termhealth effects as well as intoxication dueto acute vapor exposures. NIOSH studied exposure of bus fuelersto methanol at SCRTD and found theexposure to be negligible compared toaccepted health standards. Byextension, the exposure to ethanol,which has a higher TLV and lowervolatility than methanol is also likely tobe negligible.
Adverse healtheffects -- fromingestion of fuel. Normally, there would be little temptation to ingest fuel. However, ethanol fuel is widely advertised as beinggrain-based. And not all people may understand that thedenaturing process involves the addition of toxicsubstances to the ethanol, and a point not often made inthe marketing of this fuel. The health consequences depend onthe denaturant used. Data from the American Association ofPoison Control Centers indicates thatabout 30,000 people are treated foralcohol poisoning or overdose eachyear.
Adverse healtheffects -- from skincontact with fuel. While ethanol is not especially toxic via dermal exposure,excessive skin contact with any fuel should be avoided. The use of gloves and other personal protective gear isrecommended to minimize skin contact with fuel. Contact with ethanol can cause skindrying and irritation. Due to the long history of the use ofethanol as a solvent, the health effectsof pure ethanol are well-documented. See for example Patty's IndustrialHygiene.. Patty's Industrial Hygiene and Toxicology, 3rd revised edition, George D Clayton and Florence E. Clayton, (1982). p.4541ff.

TABLE 4-5(D). ETHANOL -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Ethanol fuel is not stored or used at high pressures anddoes not present a significant high pressure hazard. -- --

TABLE 4-5(E). ETHANOL -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Ethanol fuel is not stored or used at high temperaturesand does not present a significant high temperaturehazard.

-- --

TABLE 4-5(F). ETHANOL -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Ethanol fuel is not stored or used at cryogenictemperatures and does not present a cryogenictemperature hazard.

-- --

TABLE 5(G). ETHANOL -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of ethanol fuel does not involve storedmechanical energy and hence does not present significant mechanical energy hazards.

-- --

TABLE 5(H). ETHANOL -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of ethanol fuel does not involve stored electricalenergy and does not present a significant electricalhazard. -- --

TABLE 4-6(A). BIODIESEL -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- from fueldispensing equipmentafter vehicle collisiondamage. The danger of biodiesel fueling island collisions is similarto that from conventional diesel fueling islands. Such a collision could result in a fire. Design for crash protection isreasonably well-known and can beapplied.
Vehicle fire -- fromfuel system leaks dueto poor design. Although biodiesel fuel systems are nearly the same asthose generally used on motor vehicles, there can bechallenges in the selection of compatible materials. Fires from low-volatility liquid fuels tendto be limited by the relatively slowevaporation of the fuel. Still, any fuelsystem fire can damage or consume thevehicle. Because the flammability of biodieselfuel is similar to that of diesel fuel, thewide experience with conventionaldiesel fuels is applicable here.
Vehicle fire -- fromfuel system leaks dueto component failure. The use of biodiesel requires some changes in fuelsystem materials and components. Fires from low-volatility liquid fuels tendto be limited by the relatively slowevaporation of the fuel. Still, any fuelsystem fire can damage or consume thevehicle. Because the flammability of biodieselfuel is similar to that of diesel fuel, thewide experience with conventionaldiesel fuels is applicable here.
Vehicle Fire -- fromother than alternativefuel source. Fleet experience shows that many vehicle fires are ofelectrical origin. These fires then involve other vehiclecomponents, such as plastic parts, and eventually involvethe vehicle fuel system. The severity of such fires is expected tobe similar to that of fires that involve adiesel fuel system. Because the flammability of biodieselfuel is similar to that of diesel fuel, thewide experience with conventionaldiesel fuels is applicable here.
Fire -- after drive-awayduring fueling. Properly designed break-away connectors can preventmost such fuel releases. Moreover, like diesel fuel,biodiesel fuel is below its flash point at ambienttemperatures. Therefore, an immediate fire from spilledfuel is most unlikely. Although unlikely, a fueling island firecould put the fleet out of commission bypreventing fueling. Because the flammability of biodieselfuel is similar to that of diesel fuel, thewide experience with conventionaldiesel fuels is applicable here.

TABLE 4-6(B). BIODIESEL -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Seal Failures --deterioration of gasketsand seals. Biodiesel fuel can attack gaskets and seals that wouldwork well with conventional diesel fuels. While such failures may merely result inimpaired operation of the vehicle, sealfailures that result in fuel leaks canresult in vehicle fires. Early results with biodiesel fueldemonstration fleets have shown thatseal problems do occur. It is not knownhow easily materials may be foundwhich are acceptable.

TABLE 4-6(C). BIODIESEL -- TOXICITY

Note: Since most biodiesel fuel is used as part of a mixture with diesel fuel, the toxicity properties of biodiesel fuel mixtures are usually determined by the diesel fuelcomponent.

Hazard -- Event Background Consequences Knowledge
Adverse HealthEffects -- from skincontact with fuel. While biodiesel fuel is not expected to be especially toxicvia dermal exposure, excessive skin contact with any fuelshould be avoided. The use of gloves and otherpersonal protective gear is recommended to minimizeskin contact with fuel. The human health effects of biodieselare not as yet well-defined. Healtheffects of the methanol componentinclude possible visual impairment andserious injury for severe exposures. There is little information on the toxicityof biodiesel fuel, particularly consideringthat methanol toxicity primarily affectshumans and primates.
Adverse HealthEffects -- fromingestion of fuel. While ingestion of fuel would not normally be considereda hazard, there is marketing information that stresses thefood crop origins of biodiesel fuel. However, biodieselfuel is not just vegetable oil, it has been reacted withmethanol. If ingested it will be broken down by the bodyinto vegetable oil and methanol, which has toxic effects. The human health effects of biodieselare not as yet well-defined. Healtheffects of the methanol componentinclude possible visual impairment andserious injury for severe exposures. There is little information on the toxicityof biodiesel fuel, particularly consideringthat methanol toxicity primarily affectshumans and primates.

TABLE 4-6(D). BIODIESEL -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Biodiesel fuel is not used at high pressure and does notpresent a significant high-pressure hazard. -- --

TABLE 4-6(E). BIODIESEL -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Biodiesel fuel is not stored at high temperatures anddoes not present a significant high temperature hazard. -- --

TABLE 4-6(F). BIODIESEL -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Biodiesel fuel is not stored at cryogenic temperatures anddoes not present a significant cryogenic hazard.

-- --

TABLE 4-6(G). BIODIESEL -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of biodiesel fuel does not involve a significantamount of stored mechanical energy.

-- --

TABLE 4-6(H). BIODIESEL -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of biodiesel fuel does not involve storedelectrical energy and does not present a significantelectrical hazard. -- --

TABLE 4-7(A). HYDROGEN -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- from leakingunderground piping tofueling island aftercorrosion. Piping from the compressor to the dispenser haspressures of 3000-4000 psig. Although such piping isoften made of stainless steel, which resists many typesof corrosion, some types of stainless steel are verysusceptible to chloride corrosion. The high line pressure means that largeamounts of fuel can be released quickly. The oil refining industry hasconsiderable experience with hydrogenat high pressures. Work and reports ofthe American Petroleum Institute (API)should be consulted for information.
Fire -- from gasdispensing equipmentafter vehicle collisiondamage. Piping from the hydrogen supply to the dispenser mayhave pressures of 3000-4000 psig. While fueling islandcollisions may be rare, there is the potential to releaselarge amounts of fuel. The high line pressure means that largeamounts of fuel can be released quickly. Design for crash protection isreasonably well-known and can beapplied.
Vehicle fire -- fromfuel system leaks dueto poor design. The use of compressed gases involves materials,components, and techniques which have not beengenerally used on motor vehicles. Fires from liquid fuels are limited by therelatively slow evaporation of the fuel. For gaseous fuels this limitation doesnot exist and large fires can developquickly. The design experience base for use ofhigh pressure gaseous fuels on vehiclesis still relatively small. This is especiallytrue for hydrogen-fueled vehicles.
Vehicle fire -- fromfuel system leaks dueto improper installation. Many hydrogen-fueled vehicles are apt to be convertedfrom other fuels. The experience and skill of those doingsuch conversions is highly variable. Fires from liquid fuels are limited by therelatively slow evaporation of the fuel. For gaseous fuels this limitation doesnot exist and large fires can developquickly. The experience base for installationsusing high pressure gaseous fuels onvehicles is still relatively small. This isespecially true for hydrogen-fueledvehicles.
Vehicle fire -- fromfuel system leaks dueto component failure. The use of hydrogen gas involves materials andcomponents which have not been generally used onmotor vehicles. Fires from liquid fuels are limited by therelatively slow evaporation of the fuel. For gaseous fuels this limitation doesnot exist and large fires can developquickly. The experience base for componentsfor high pressure gaseous fuels onvehicles is still relatively small. This isespecially true for hydrogen-fueledvehicles.
Vehicle Fire -- fromother than alternativefuel source. Fleet experience shows that many vehicle fires are ofelectrical origin. These fires then involve other vehiclecomponents, such as plastic parts, and eventually involvethe vehicle fuel system. A gaseous fuel under high pressure hasthe potential to significantly increase thesize and intensity of a vehicle fire. Vehicle fires do occur. However, weare not aware of any experience withvehicle fires that involved hydrogen.
Fire -- after drive-awayduring fueling. Properly designed break-away connectors can preventmost large fuel releases. But these fittings cannotprotect against all drive-away scenarios. Static electricitymay ignite such fuel releases. The ignition energy forhydrogen is lower than for other fuels. Any large fire has the potential todestroy the vehicle and/or injureemployees. In addition, a fueling islandfire could put the fleet out of commissionby preventing fueling. The type and configuration of hydrogenfueling dispensers remains to bedetermined. The hazard depends onthe configuration of the fuelingdispenser.
Fire -- from staticignition of ventedtanks. Several such fires have already occurred as CNG tankswere vented to the atmosphere. If hydrogen tanks arevented, a similar possibility exists. Hydrogen has anespecially low threshold for static ignition, compared tohydrocarbon fuels. Some of these natural gas fires havedestroyed vehicles, a hydrogen firewould be expected to be similarlydamaging. The properties of static electricity aregenerally well-known, but are notalways applied by operators ofalternative fuel fleets.
Vehicle explosion --from fuel system leaks. A vehicle explosion from leaking methane has occurredin a transit bus at Houston Metro. Like LNG vapor,hydrogen does not have an odor to warn of leaks andsuch an explosion with hydrogen is also possible. When ignited, a confined hydrogen gas-air mixture can produce pressures of upto 800 kPa -- far more than vehicleglass or body structures can withstand. One flammable gas explosion ofmethane has occurred in an articulatedtransit bus under repair at HoustonMetro. An analysis of fuel gas leakageinto the interior of a vehicle is given inReference. "Efflux of Gaseous Hydrogen or Methane Fuels from the Interior of an Automobile," J.M. Arvidson, et al., NationalBureau of Standards report COM-75-10288, 1 March 1975..
Building explosion --from vehicle fuelsystem leaks. Such leaks can form a flammable zone inside vehiclestorage and maintenance buildings and if ignited cancause building explosions and serious injuries. Experience to date with compressed natural gassuggests that fuel system leaks will be relatively frequentuntil the technology for high pressure gaseous fuel useon vehicles becomes more mature. When ignited, a confined hydrogen gas-air mixture can produce pressures of upto 800 kPa -- far more than vehiclestructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. Though some fluid dynamic modeling ofleaks from high pressure gaseous fuelsystems has been done for the FTA,there is a lack of experimental data onflammable plume behavior and also alack of codes and standards to guidethe design of buildings for this fuel.
Building explosion --from vehicle PRDfailure. Such leaks can form a large flammable zone insidevehicle storage and maintenance buildings and if ignitedcan cause building explosions and serious injuries. Experience to date suggests that PRD failures will berelatively frequent until the technology for use on vehiclesbecomes more mature. When ignited, a confined hydrogen gas-air mixture can produce pressures of upto 800 kPa -- far more than buildingstructures can withstand. For example,overpressures greater than 7 - 15 kPawill cause a brick wall to fail. Though some fluid dynamic modeling ofleaks from high pressure gaseous fuelsystems has been done for the FTA,there is a lack of experimental data onflammable plume behavior and also alack of codes and standards to guidethe design of buildings for this fuel.

TABLE 4-7(B). HYDROGEN -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Embrittlement ofMetals -- fromexposure to hydrogen. Hydrogen can cause embrittlement of metal alloys. Thiscan cause catastrophic failure of pressure vesselscontaining hydrogen fuel. The failure of a component containinghydrogen gas at high pressure canresult in a loss of fuel and a fire and/ora pressure vessel failure withconsequent damage or injury. Hydrogen embrittlement has beenextensively studied in other industries.However, technology transfer to transitmay be poor.

TABLE 4-7(C). HYDROGEN -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Asphyxiation -- fromdisplacement of air. Although hydrogen it non-toxic, it is lighter than air andcan collect in enclosed spaces which are not vented atthe top. If enough air is displaced, asphyxiation mayoccur. If a person does not receive fresh airquickly, serious injury can occur. The medical effects of asphyxiation aredescribed in standard occupationalhealth references.

TABLE 4-7(D). HYDROGEN -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
Explosion -- of vehiclefuel tank. Even though CNG fuel tanks must meet rigorousstandards, several fuel tanks have failed due tounforeseen environmental conditions. Thus, it is likelythat the same hazard will apply to tanks with pressurizedhydrogen. The amount of stored energy issubstantial and the rate of energyrelease is high. Any pressure vesselexplosion is potentially serious. If hydrogen is stored on-board in fueltanks that are similar to those used forcompressed natural gas, thenengineering information for CNG willapply.
Missile damage --from flying about ofparts duringdisassembly. Compressed hydrogen fuel systems are under highpressure. Improper disassembly procedures or faultypressure indications can cause parts to act as projectiles. Although the projectiles may not belarge or heavy, the close proximity ofpeople increases the risk. Several such incidents have occurredin CNG fleets and fleets using highpressure hydrogen may also expectthem too.
Missile damage --from pressure gagefailure. Pressure gages are known to fail under pressure. Whilethe hazard is largely controlled in stationary applications,the vehicle environment can be more severe. Although the projectiles may not belarge or heavy, the close proximity ofpeople increases the risk. Gage manufacturers generally includefeatures to insure that any failure doesnot occur on the front of the gage. However, proper installation of the gageis necessary for those features to beeffective. No such incident involving ahydrogen vehicle is known to date.
Flailing damage --from fueling hosefailure. Compressed hydrogen fueling hoses will carry gas athigh pressure. A broken hose will flail wildly ifunrestrained. Excess flow devices may help, but due tothe high fill rates required for fleet operations, theallowable flow rate must be relatively large. Although the fueling hose may not beespecially heavy, the necessary closeproximity of people greatly increases therisk. The configuration of hydrogen fuelingdispensers remains uncertain. However, for high pressure hydrogengas, the hazard is likely to be similar tothat for CNG.
Explosion -- fromcorrosion of fuel tank. Compressed hydrogen fuel tanks will contain a lot ofenergy in the form of a large volume of gas maintained athigh pressure. If less than chemically pure hydrogen isused as a fuel, corrosion from impurities may occur. The amount of stored energy issubstantial and the rate of energyrelease is high. Any pressure vesselexplosion is potentially serious. No incidents with hydrogen vehicletanks are known.
Explosion -- frommechanical damage tofuel tank. Compressed hydrogen fuel tanks contain a lot of energyin the form of a large volume of gas maintained at highpressure.

The amount of stored energy issubstantial and the rate of energyrelease is high. Any pressure vesselexplosion is potentially serious. Experience with CNG tanks shows thatmechanical damage of vehicle fueltanks is possible if the tanks areexposed to road hazards.

TABLE 4-7(E). HYDROGEN -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Hydrogen is not stored at high temperatures and doesnot present a significant high temperature hazard. -- --

TABLE 4-7(F). HYDROGEN -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. This analysis assumes that the hydrogen is stored as acompressed gas. If it is stored in cryogenic form, thenthe hazard events listed for liquefied natural gas willapply. -- --

TABLE 4-7(G). HYDROGEN -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of hydrogen does not involve a significantamount of stored mechanical energy.

-- --

TABLE 4-7(H). HYDROGEN -- ELECTRICAL ENERGY

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. Hydrogen fuel does not involve stored electrical energyand does not present a significant electrical hazard. -- --

TABLE 4-8(A). ELECTRICITY -- FLAMMABILITY

Hazard -- Event Background Consequences Knowledge
Fire -- due to electricalshort or overload. Currently, most fires on heavy duty fleet vehiclesoriginate as electrical fires. Electric vehicles will have amuch greater power capability and hence a greaterpotential hazard. A fire can result in damage to or loss ofthe vehicle as well as injury to theoccupants. Recently (June 1994) two Ford Ecostarelectric vehicles experienced electricalfires during battery charging.
Fire -- due to electricalcomponent failure. Currently, most fires on heavy duty fleet vehiclesoriginate as electrical fires. Electric vehicles will have amuch greater power capability and hence a greaterpotential hazard. A fire can result in damage to or loss ofthe vehicle as well as injury to theoccupants. Several experimental electric vehicleshave suffered electrical fires, includingmost recently the Ford Ecostar.
Fire -- due to contactwith hot electrolyte. Some battery systems use very hot electrolytes. Sincethe autoignition temperature of hydrocarbons can be aslow as 220C, contact with heat from the battery couldlead to a vehicle fire. A fire can result in damage to or loss ofthe vehicle as well as injury to theoccupants. Both the electrolyte temperature andthe ignition temperatures of othermaterials are reasonably well-known. The major uncertainty is the ability toisolate the high temperature in all typesof normal operation and during trafficaccidents.

TABLE 4-8(B). ELECTRICITY -- CORROSIVITY

Hazard -- Event Background Consequences Knowledge
Corrosion -- frombattery electrolyte. Most battery systems proposed for electric vehicles haveelectrolytes which are corrosive. Leakage of thiselectrolyte can cause damage to and/or failure of othervehicle components. A recent example from a non-electric vehicle is the failure of CNG fuel tanks fromspilled electrolyte from batteries carried to start othervehicles. The consequences can be either minoror major depending on the vehiclecomponent affected and the importanceof that component to maintaining safeoperation of the vehicle. Little data are available on the degreeto which this will be a problem in actualelectric vehicles.
Corrosion -- fromelectrolysis. Leakage current may cause electrolysis of metal vehiclecomponents. While such electrolysis could take placewith current battery-powered accessory circuits, thelarger currents and higher voltages used for electricpropulsion could increase the danger of electrolyticcorrosion. The consequences can be either minoror major depending on the vehiclecomponent affected and the importanceof that component to maintaining safeoperation of the vehicle. Little data are available on the degreeto which this will be a problem in actualelectric vehicles.

TABLE 4-8(C). ELECTRICITY -- TOXICITY

Hazard -- Event Background Consequences Knowledge
Health hazard -- fromcontact with batteryelectrolyte. Many candidate battery electrolytes are corrosive andtoxic. They are potential hazardous via skin contact orinhalation of fumes or vapors. The toxic consequences depends on thecomposition of the electrolyte. The degree of knowledge depends onthe material composition(s) involved.

TABLE 4-8(D). ELECTRICITY -- HIGH PRESSURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of electricity does not involve high pressuresand hence there is not a significant high pressure hazardassociated with the use of electricity. -- --

TABLE 4-8(E). ELECTRICITY -- HIGH TEMPERATURE

Hazard -- Event Background Consequences Knowledge
Burns -- from contactwith battery. Some proposed battery systems operate at hightemperatures. Contact with such temperatures couldoccur during vehicle repair and cause unexpected burns. Any burn is a potentially serious injury. The degree of hazard depends on thetype of battery system used and on thedesign configuration of the vehicle.
Burns -- from contactwith leaking batteryelectrolyte aftercomponent failure. Some proposed battery systems operate at hightemperatures. Contact with such temperatures couldcause burns. Any burn is a potentially serious injury. The degree of hazard depends on thetype of battery system used and on thedesign configuration of the vehicle.
Burns -- from contactwith leaking batteryelectrolyte after trafficaccident. Some proposed battery systems operate at hightemperatures. A damaged battery pack could leakelectrolyte at high temperature. Contact with suchtemperatures could cause burns. Any burn is a potentially serious injury. The degree of hazard depends on thetype of battery system used and on thedesign configuration of the vehicle.

TABLE 4-8(F). ELECTRICITY -- CRYOGENIC TEMPERATURE

Hazard -- Event Background Consequences Knowledge
None -- no significanthazards identified. The use of electricity does not involve cryogenictemperatures and hence there is not a significantcryogenic temperature hazard. -- --

TABLE 4-8(G). ELECTRICITY -- MECHANICAL ENERGY

Hazard -- Event Background Consequences Knowledge
Lifting-falling hazard

-- from changingbattery packs.

Electric vehicle battery packs are not expected to last thelife of the vehicle and will need to be replaced. Suchbattery packs are heavy components and will requirespecial handling. Given the weight of battery packs, afalling battery pack could cause serioustrauma. Although engines and transmissions areheavy components which are routinelyreplaced, experience with suchtechniques may not provide muchinformation on battery packs which areseveral times as heavy and whichrequire different handling techniques.

TABLE 4-8(H). ELECTRICITY -- ELECTRICAL ENERGY

Hazard-- Event Background Consequences Knowledge
Shock hazard -- frombattery chargerconnection. Electric vehicles are likely to employ much highervoltages than used for vehicle accessory circuits, asmany as several hundred volts. Battery chargerconnections are subject to severe handling and abuse. Connections may need to be made to vehicles which arewet with road salt or during heavy rains. Major electric shocks can cause deathor injury. Even minor electric shockscan cause injury by causing involuntarymovement. The hazards associated with electricshock are well-known, but there isrelatively little experience with thehazard from electric vehicles ineveryday use.
Shock hazard -- fromon-board electricsupply during vehiclerepair. Electric vehicles are likely to employ much highervoltages than used for vehicle accessory circuits, asmany as several hundred volts. Mechanics and otherswho repair vehicles will need to follow strict proceduresto avoid electric shocks. Major electric shocks can cause deathor injury. Even minor electric shockscan cause injury by causing involuntarymovement. The hazards associated with electricshock are well-known: voltages lessthan 24 volts are not considered topresent a shock hazard, while voltagesgreater than 50 volts are consideredpotentially lethal.. Accident Prevention Manual for Industrial Operations, Ninth Edition, National Safety Council, (1988). p. 377. There isrelatively little experience with thehazard from electric vehicles ineveryday use.
Shock hazard -- fromon-board electricsupply due tocomponent failure. Electric vehicles are likely to employ much highervoltages than used for vehicle accessory circuits, asmany as several hundred volts. A component failurecould expose the occupants to these voltages. Major electric shocks can cause deathor injury. Even minor electric shockscan cause injury by causing involuntarymovement. The hazards associated with electricshock are well-known, but there isrelatively little experience with thehazard from electric vehicles ineveryday use.
Shock hazard -- fromon-board electricsupply after trafficaccident. Electric vehicles are likely to employ much highervoltages than used for vehicle accessory circuits, asmany as several hundred volts. A damaged electricalsystem component could expose the occupants to thesevoltages. Major electric shocks can cause deathor injury. Even minor electric shockscan cause injury by causing involuntarymovement. The hazards associated with electricshock are well-known, but there isrelatively little experience with thehazard from electric vehicles ineveryday use.
Electromagnetic fielddamage -- fromelectric tractionequipment. Cargo carried on-board vehicles commonly includesmagnetic data processing media as well as a variety ofelectronic devices which may be subject to interferencefrom electromagnetic fields arising from electric tractionequipment. Because of the relatively large powerinvolved in electric traction as well as the complexwaveforms generated by traction control modules, suchinterference may be much more severe than fromtraditional vehicle electrical systems. Damage to electronic media orinterference with the operation ofelectronic devices. While the principles of EMI control arewell-known, it is difficult to predictwhether a given device in a real-worldsituation will be affected by EMI.
Electric and magneticfield health effects --from electric tractionequipment. Several types of health effects have been imputed tohuman exposure to electric and/or magnetic fields. Themain concern is possible elevated rates of cancer,though various other physiological changes are alsosuspected to be caused by electric and/or magneticfields. The suggested health effects ofexposure to electromagnetic radiationare serious, especially cancers, such asleukemia. However, the cause andeffect and dose response relationshipsare far from proven. Much additional information is neededconfirm or deny the various hypotheseson health effects of electromagneticfields. The physical principles involvedare well-described in Reference. "Health Effects of Extremely Low-Frequency (50- and 60-Hz) Electric and Magnetic Fields," Donald W. Zipse, IEEETransactions on Industry Applications, 29, 447 (1993).. Asummary of the issues is given inReference. "Health Effects of Low-Frequency Electric and Magnetic Fields," Environmental Science and Technology, 27, 42 (1993).. Current epidemiologicresults are reviewed in Reference. "Overview of Epidemiologic Research on Electric and Magnetic Fields and Cancer," David A. Savitz, American IndustrialHygiene Association Journal, 54, 197 (1993).. A report on the most recent results isgiven in Reference. "Findings Point to Complexity of Health Effects of Electric, Magnetic Fields," Bette Hileman, Chemical and EngineeringNews, 18 July 1994, p. 27..

4.5 ALTERNATIVE FUEL SAFETY CASE STUDIES

While the summary list of hazards provides a systematic approach to alternative fuel hazards,that summary list does not allow highlighting of any case histories of safety incidents thathave actually occurred. Therefore, the case histories below are presented.

4.5.1 Methanol Vehicle Fire

A medium-duty local delivery truck running on M-85 fuel experienced a fuel system leak andfire. The situation was first noticed while the truck was on the freeway and the drivernoticed the check engine light on. Upon pulling over, the driver saw flames coming from theengine compartment. He tried to extinguish the fire with a hand extinguisher, but was notsuccessful. The local fire department was called and extinguished the fire.

A methanol fuel leak had occurred in the vicinity of the cold start injector. The leaking fuelignited, probably on the exhaust manifold, and caused a fire in the front end of the truck. Although no cargo was damaged or destroyed, the engine compartment was extensivelydamaged and the vehicle was a total loss. Ironically, the incident occurred in SouthernCalifornia where cold-start injectors are not needed for vehicle operation.

4.5.2 LNG Bus Explosion

A methane explosion occurred inside an LNG-powered transit vehicle on December 6, 1992. The vehicle, a 60-ft. articulated bus had just been delivered and was being readied foroperation on LNG. The manufacturer's representative was repairing a natural gas fuel systemleak when a combustible gas detector located on-board the vehicle sounded an alarm. Although such repairs were supposed to be performed outdoors, the weather was inclementand the work was being done in a normal bus repair bay. After becoming aware of the leak,the mechanic used a switch to override this alarm to start the bus to move it outside.However, when the bus was started, a relay in the air conditioning system ignited aflammable methane-air mixture that had accumlated in the interior of the bus. The resultingexplosion blew out all of the windows on the bus as well as the roof hatches and the bellows.

4.5.3 High Pressure CNG Fittings As Projectiles

A large transit property with CNG buses reported that on several occasions, experiencedmechanics had loosened CNG fuel line fittings with as much as 600 psig pressure on thesystem. The pressure gages on the vehicles were faulty and often indicated zero even withthis much pressure. Thus, mechanics thought the system was at zero pressure even though itwas not. The result was fittings flying across the shop "like from a shotgun."

4.5.4 Propane Tank Damage

A recreational vehicle was fitted with a propane tank underneath the vehicle's floor. Sometime later, the owner noticed that water had accumulated on the floor inside the vehicle. To clean out the drain hole in the floor, the vehicle owner got a drill and drilled out the drainholes. In doing so, he drilled into the propane tank. A large propane leak ensued, but therewas no fire.

4.5.5 Pressure Relief Device (PRD) Failure on CNG Bus

Several transit properties using CNG have experienced PRD failures. One fleet of about 100CNG buses has experienced seven such failures in a one-year period. These failures haveresulted in the release of one or more full tanks of CNG into the bus fueling area. One suchfailure occurred when a recently fueled CNG bus with roof-mounted tanks was taken into thegarage for light maintenance. A PRD failure occurred and the gas-fired infrared heaters inuse in the shop ignited the escaping gas. Damage from fire and water used to fight the firewas fairly extensive.

4.5.6 CNG Cascade Relief Valve Failure

At midnight, a night shift mechanic for a fleet of medium-duty CNG vehicles noticed a strongodor of natural gas in the parking lot. He traced it to the cascade and found a relief valvestuck open on the top tank. He closed the valve on that cylinder in the cascade to isolate theleak from the balance of the tanks. The relief valve was later replaced.

4.5.7 Static Electricity Ignition of Venting CNG

A fire occurred during the calibration of a CNG dispenser. The calibration procedureinvolved filling a portable cylinder from the dispenser and weighing the portable cylinder toascertain the mass of gas dispensed. The portable cylinder is then vented and the process isrepeated. On this occasion, when the natural gas was being vented from 2,300 psig toatmospheric pressure, a fire occurred when the pressure was around 1500 psig. Since the jetof gas was directed towards the dispenser, the dispenser was extensively damaged. The firewas judged to have been ignited from a static electricity discharge.

This incident is described in the December 1992 issue of Natural Gas Fuels magazine, p. 22.

4.5.8 CNG Bus Drive-Away and Fire

A driver fueled a paratransit bus at a CNG dispenser island in the morning before starting amorning run, but forgot to disconnect the fueling hose. After driving about 12 feet there wasa loud pop at the rear of the vehicle. The driver walked to the rear of the bus and heard aloud hissing sound of CNG escaping from the bus fuel system, which had just beenpressurized to 3000 psig. The driver returned to the bus, shut off the engine and ran to amaintenance bay to tell a mechanic. Just when the driver reached the maintenance shop, theescaping CNG ignited. The vehicle was totally destroyed and three others were damaged. The source of ignition was considered to be static electricity.

4.5.9 Propane Leak from Faulty Installation

A mechanic for a medium duty propane vehicle fleet found a small leak around the threadson the body of the valve on the propane vehicle fuel tank. The valve had a threadedconnection which had not been tightened sufficiently. The leak was repaired by the upfitterwho turned the fitting one more turn into the threaded tank connection.

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APPENDIX A

SOURCES FOR ALTERNATIVE FUEL SAFETY INFORMATION

In addition to the specific references listed in "References - Section Three," the followingsources contain more general information on alternative fuel safety:

General Information Hazard and Risk Analysis:

"Issues in Comparative Risk Assessment of Different Energy Sources," Sam Haddad andAdrian Gheorghe, International Journal of Global Energy Issues, Volume 4, 1992. p. 174.

General Information on Alternative Fuels:

"Properties of Alternative Fuels," Michael J. Murphy, FTA report FTA-OH-06-0060-94-1,March 1994.

"Replacing Gasoline: Alternative Fuels for Light-Duty Vehicles, Office of TechnologyAssessment report, September 1990.

"Safe Operating Procedures for Alternative Fuel Buses," Geoffrey V. Hemsley, TransportationResearch Board report, TCRP Synthesis 1, 1988.

Alternative Fuels Training:

"Compressed Natural Gas Fuel Use Training Manual," FTA report FTA-OH-0060-92-3,September 1992.

"Liquefied Natural Gas Fuel Use: Basis Training Manual, FTA report, May 1994.

"Methanol Use Training Manual," FTA report UMTA-OH-06-0056-90-1, January 1990.

CNG:

"Compressed Natural Gas (CNG) Vehicular Fuel Systems, National Fire ProtectionAssociation standard NFPA 52 (1992).

"Gaseous Fuel Safety Assessment for Light-Duty Automotive Vehicles," M.C. Krupka, A.T.Peaslee, and H.L. Laquer, Los Alamos report LA-9829-MS, November 1983.

"Regulations for Compressed Natural Gas," Railroad Commission of Texas, November 1990.

LNG:

"Fire and Explosion Hazards Associated with Liquefied Natural Gas," David Burgess andMichael G. Zabetakis, U.S. Bureau of Mines Report of Investigations 6099, 1962.

"Introduction to LNG Vehicle Safety," Delma Bratvold and David Friedman, Gas ResearchInstitute report GRI-92/0465, 1992.

"Introduction to LNG for Personnel Safety," Accident Prevention Committee of the OperatingSection, American Gas Association, 1973.

"Production, Storage, and Handling of Liquefied Natural Gas (LNG)," National FireProtection Association standard NFPA 59A, 1990.

Propane:

"An Assessment of Propane as an Alternative Transportation Fuel," R.F. Webb Corporationreport for the National Propane Gas Association, June 1989.

"Working with Propane, Dispensing Product," Propane Gas Association of Canada publication100-1-88.

Methanol:

"Automotive Methanol Vapors and Human Health," Health Effects Institute special report,May 1987.

"Methanol Fueling Systems Guide," Canadian Oxygenated Fuels Association report, 27 Oct1992.

"Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A.Machiele, SAE paper 901113, (1990).

Ethanol:

"Analysis of the Economic and Environmental Effects of Ethanol as an Automotive Fuel,"U.S. EPA Office of Mobile Sources report, April 1990.

Biodiesel:

"Biodiesel: A Technology, Performance and Regulatory Overview," National SoyDieselDevelopment Board report, February 1994.

Hydrogen:

"Hydrogen Vehicles: An Evaluation of Fuel Storage, Performance, Safety, EnvironmentalImpacts, and Cost," M.A. DeLuchi, International Journal of Hydrogen Energy, Vol. 14, 1989. pp. 81-130.

"Research on the Hazards Associated with the Production and Handling of Liquid Hydrogen,"M.G. Zabetakis and D.S. Burgess," U.S. Bureau of Mines Report of Investigations 5707,1961.

Electricity:

"An Illustrated Guide to Electrical Safety," William S. Watkins, Editor, American Society ofSafety Engineers publication, 1983. [While not specifically directed towards electric vehicles,this publication contains a good summary of the principles of electrical safety as well as ofrelevant OSHA regulations.]

"National Electric Code," National Fire Protection Association, NFPA-70, 1993.

"Overview of Epidemiologic Research on Electric and Magnetic Fields and Cancer," David A.Savitz, American Industrial Hygiene Association Journal, Vol. 54, 1993, pp. 197-204.

Selected References:

Use of Alternative Fuels by Vehicle Fleets

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