U.S. Department of Transportation

Federal Transit Agency

FTA-MA-90-7007-95-1

DOT-VNTSC-FTA-95-5

CLEAN AIR PROGRAM

SUMMARY OF ASSESSMENT OF THE

SAFETY, HEALTH, ENVIRONMENTAL

AND SYSTEM RISKS OF ALTERNATIVE

FUELS

U.S. Department of Transportation

Research and Special Programs Administration

John A. Volpe National Transportation Systems Center

Cambridge, MA 02142

Federal Transit Administration

August 1995 Final Report

PDF Edition April 1999
NOTICE

This document is disseminated under the sponsorship

of the Department of Transportation in the interest of

information exchange. The United States Government

assumes no liability for its contents or use thereof.

NOTICE

The United States Government does not endorse

products or manufacturers. Trade or manufacturers'

names appear herein solely because they are

considered essential to the objective of this report.
REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188 

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1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE

August 1995 

3. REPORT TYPE AND DATES COVERED 

 Final Report – March 1995 

4. TITLE AND SUBTITLE 

Summary of Assessment of the Safety, Health, Environmental and System Risks of 

Alternative Fuels

6. AUTHOR(S) 

Michael J. Murphy, H. Norman Ketola, Phani K. Raj 

5. FUNDING NUMBERS

U5022/TT422 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 

Battelle* Technology & Management Systems, Inc. 

Columbus, OH Burlington, MA 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

DOT-VNTSC-FTA-95-5 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 

U.S. Department of Transportation U.S. Department of Energy 

Federal Transit Administration Alternative Fuels 

Office of Safety and Security Utilization Division 

Washington, DC20590 Washington, DC 20585 

10. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

FTA-MA-90-7007-95-1 

11. SUPPLEMENTARY NOTES

* Under contract to: U.S. Department of Transportation 

 Volpe National Transportation Systems Center 

 Cambridge, MA 02142 

12a. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the National Technical Information 

Service, Springfield, VA 22161 

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words) 

This is a handbook of safety, health, and the environmental issues of the production, bulk transport, and bulk storage of alternative fuels with emphasis on 

transport and storage. Fuels included are: 1) compressed natural gas, 2) liquefied natural gas, 3) propane, 4) methanol and methanol blends, 5) ethanol and 

ethanol blends, 6) biodiesel, 7) hydrogen, and 8) electricity. Material in the handbook is organized by fuel and by the following topics: 1) general properties of 

the fuel that effects fire hazards, 2) potential fire hazards during bulk transport, 3) potential fire hazards during unloading to bulk storage, 4) potential fire 

hazards during fleet storage, 5) other safety hazards, particularly, high pressure and low (cryogenic) temperatures, 6) toxicity of the fuel, and 7) environmental 

effects of spills onto land or water. Specific properties of the alternative fuels examined include: 1) flash point temperature, 2) range of flammability limits, 3) 

autoignition temperature, 4) flame temperature, luminosity, and thermal radiation, 5) electrical conductivity, 6) storage temperature and pressure, 7) toxicity of 

the fuel based on inhalation, skin contact, and ingestion, 8) compatibility (i.e. corrosivity) with other materials, and 9) time or ageing effects. The consequence 

or potential damage from fire or explosion are given. The hazards of the fuels discussed in the handbook are, in some cases, compared to the reference fuels of 

gasoline or diesel fuel. In many instances, the state of knowledge of specific hazards and/or ongoing research are noted. 

15. NUMBER OF PAGES

144 

14. SUBJECT TERMS

Alternative Fuels, compressed natural gas, liquefied natural gas, propane, methanol and methanol 

blends, ethanol and ethanol blends, biodiesel, hydrogen, and electricity, safety, health, environmental, 

system risks 

16. PRICE CODE 

17.SECURITY 

CLASSIFICATION OF 

REPORT

Unclassified 

18.SECURITY 

CLASSIFICATION OF THIS 

PAGE

Unclassified 

19. SECURITY 

CLASSIFICATION OF THIS 

ABSTRACT

Unclassified 

20. LIMITATION OF ABSTRACT

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89) 

Prescribed by ANSI Std. 239-18 

298-102

iii

PREFACE

National goals for both energy security and clean air have resulted in heightened interest

in the use of alternative motor fuels (AMFs) in the transportation market. The growth of

interest in alternative fuels has expanded not only the numbers of alternative fuel

vehicles, but also the list of viable alternative transportation fuels.

Thus, an increasing number of transit fleets and other fleet owners are operating vehicles

on alternative fuels - often with a minimum of technical guidance related to the possible

safety or operational impacts on traditional fleet operations, including fueling, inspecting,

and cleaning vehicles, as well as performing the light and heavy maintenance activities

necessary to keep the fleet in operation.

Moreover, the buildings or facilities used for storing, loading, and maintaining alternative

fuel vehicles form an important portion of a fleet operation. Here, the experience with

fire and building codes is not yet complete. This situation requires additional care on the

part of the owners of these facilities to recognize all hazards associated with the use of

alternative fuel vehicles and to ensure that these hazards are properly addressed in the

design and operation of the facility.

Experience has shown that not all local community and regulatory groups view the use of

alternative fuels as a purely positive option. Transit properties and others who propose

the use of alternative fuels need to deal not only with the perceptions of fire and building

code officials who grant approvals, but also with the perceptions and concerns of

community and neighborhood organizations. The concerns of these groups are not

limited to fleet operations, but may also include 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, a comprehensive and systematic program is needed to recognize and organize

the existing knowledge about the health, safety, and environmental hazards of alternative

fuels and to identify where additional study is needed. The objective of this report is

assist the Volpe Center, FTA and DOE in providing information on these issues to the

transit and fleet operator community while 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 National

Transportation Systems Center. This work was funded jointly by the U.S. Department of

Transportation, 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

the Federal Transit Administration are gratefully acknowledged.
iv
v

TABLE OF CONTENTS

Section Page

1. INTRODUCTION 1-1

 1.1 Background . . . . . . 1-1

 1.2 Objectives and Scope . . . . . 1-3

2. PREPARATION AND ORGANIZATION OF REPORT 2-1

 2.1 Information Sources . . . . . 2-1

 2.2 Organization of Report . . . . . 2-2

3. PRODUCTION, BULK TRANSPORT, AND BULK STORAGE OF

 ALTERNATIVE FUELS 3-1

 3.1 Introduction . . . . . . 3-1

 3.2 Methodology . . . . . . 3-1

 3.3 Issues Associated with Bulk Transport and Storage of

 Alternative Fuels . . . . . 3-2

 3.3.1 Methanol/Methanol Blends . . . . 3-2

 3.3.1.1 Safety Issues . . . . . 3-3

 3.3.1.2 Health Issues. . . . . 3-6

 3.3.1.3 Environmental Issues . . . . 3-6

 3.3.2 Ethanol/Ethanol Blends . . . . 3-7

 3.3.2.1 Safety Issues . . . . 3-7

 3.3.2.2 Health Issues . . . . 3-10

 3.3.2.3 Environmental Issues . . . . 3-10

 3.3.3 Compressed Natural Gas . . . . 3-10

 3.3.3.1 General Description . . . . 3-10

 3.3.3.2 Safety Issues . . . . 3-11

 3.3.3.3 Health Issues . . . . 3-15

 3.3.3.4 Environmental Issues . . . 3-15

 3.3.4 Liquefied Natural Gas . . . . 3-15
vi

TABLE OF CONTENTS (cont.)

Section Page

 3.3.4.1 General Description . . . . 3-15

 3.3.4.2 Safety Issues . . . . 3-16

 3.3.4.3 Health Issues. . . . . 3-19

 3.3.4.4 Environmental Issues . . . . 3-20

 3.3.5 Propane . . . . . 3-20

 3.3.5.1 General Discussion . . . . 3-20

 3.3.5.2 Safety Issues . . . . 3-20

 3.3.5.3 Health Issues . . . . 3-23

 3.3.5.4 Environmental Issues . . . . 3-23

 3.3.6 Biodiesel . . . . . 3-23

 3.3.6.1 General Description . . . . 3-23

 3.3.6.2 Safety Issues . . . . . 3-24

 3.3.6.3 Health Issues. . . . . 3-25

 3.3.6.4 Environmental Issues . . . . 3-25

 3.3.7 Hydrogen . . . . . 3-25

 3.3.7.1 General Description . . . . 3-25

 3.3.7.2 Safety Issues . . . . . 3-26

 3.3.7.3 Health Issues. . . . . 3-29

 3.3.7.4 Environmental Issues . . . . 3-29

 3.3.8 Electricity . . . . . 3-29

 3.3.8.1 General Description . . . . 3-29

 3.3.8.2 Safety Issues . . . . . 3-29

 3.3.8.3 Health Issues. . . . . 3-30

 3.3.8.4 Environmental Issues . . . . 3-30

 3.4 Assessment of Alternative Fuel - Bulk Transport, Transfer, and

 Fleet Storage Safety Risks . . . . 3-30

 3.4.1 Introduction . . . . . 3-30

 3.4.2 Assessment of Relative Potential for Spills and Leaks . 3-31
vii

TABLE OF CONTENTS (cont.)

Section Page

 3.4.2.1 Bulk Transport . . . . 3-31

 3.4.2.2 Unloading to Fleet Storage . . . 3-33

 3.4.2.3 Fleet Storage . . . . . 3-33

 3.4.3 Assessment of Safety Hazards . . . 3-33

 3.4.3.1 Potential for Ignition . . . . 3-37

 3.4.3.2 Consequences of Ignition . . . 3-41

 3.4.3.3 Other Hazards . . . . 3-44

 3.4.4 Assessment of Health Hazards . . . 3-45

 3.4.5 Assessment of Environmental Hazards . . 3-46

4. USE OF ALTERNATIVE FUELS BY VEHICLE FLEETS . 4-1

 4.1 Introduction . . . . . 4-1

 4.2 Objectives and Scope . . . . 4-1

 4.2.1 Fuels Included . . . . . 4-2

 4.2.2 Hazardous Properties Included . . . 4-2

 4.2.3 Accident Events Included . . . 4-3

 4.3 Summary List of Alternative Fuel Hazards for Vehicle Fleet

 Operations . . . . . 4-3

 4.3.1 Overview of Alternative Fuel Hazards . . 4-3

 4.3.2 Safety Hazards Considered . . . 4-4

 4.4 Summary List of Alternative Fuel Hazards . . 4-7

 4.5 Alternative Fuel Safety Case Studies . . . 4-60

 4.5.1 Methanol Vehicle Fire . . . . 4-60

 4.5.2 LNG Bus Explosion . . . . 4-60
viii

TABLE OF CONTENTS (cont.)

Section Page

 4.5.3 High Pressure CNG Fittings as Projectiles . . 4-60

 4.5.4 Propane Tank Damage . . . . 4-61

 4.5.5 Pressure Relief Device (PRD) Failure on CNG Bus . 4-61

 4.5.6 CNG Cascade Relief Valve Failure . . 4-61

 4.5.7 Static Electricity Ignition of Venting CNG . . 4-61

 4.5.8 CNG Bus Drive-Away and Fire . . . 4-61

 4.5.9 Propane Leak from Faulty Installation . . 4-62

APPENDIX A. SOURCES FOR ALTERNATIVE FUEL SAFETY

 INFORMATION . . . . A-1

REFERENCES - SECTION THREE . . . . R-1

REFERENCES - SECTION FOUR . . . . R-3
ix/x

LIST OF FIGURES

Figure Page

3-1. Flash Point Temperatures for Liquid AMFs . . 3-38

3-2. Fuel Volatility-Reid Vapor Pressure (@38 C) . . 3-39

3-3. Autoignition Temperature . . . . 3-40

3-4. Flammability Limits Range . . . . 3-41

3-5. Relative Heat Release Rate for Liquid Pool Fires . . 3-44

LIST OF TABLES

Table Page

3-1. Relative Potential for Spills During Transport . . 3-32

3-2. Relative Potential for Leaks During Transport . . 3-32

3-3. Relative Potential for Spills During Unloading . . 3-34

3-4. Relative Potential for Leaks During Unloading . . 3-34

3-5. Relative Potential for Spills During Fleet Storage . . 3-35

3-6. Relative Potential for Leaks During Fleet Storage . . 3-35

4-1 (A-H). Compressed Natural Gas (CNG) . . . 4-8

4-2 (A-H). Liquefied Natural Gas (LNG) . . . 4-19

4-3 (A-H). Propane . . . . . 4-28

4-4 (A-H). Methanol . . . . . 4-33

4-5 (A-H). Ethanol. . . . . . 4-38

4-6 (A-H). Biodiesel . . . . . 4-43

4-7 (A-H). Hydrogen . . . . . 4-48

4-8 (A-H). Electricity . . . . . 4-53

xi

EXECUTIVE SUMMARY

A. BACKGROUND

National goals for energy security and clean air have resulted in a heightened interest in

the use of alternative transportation fuels. This growing interest in alternative fuels has

led to both an increase in the number of alternative fuel vehicles, and to an expansion in

the list of candidate alternative fuels.

This summary assessment consists of two parts. The first part considers the hazards

associated with the bulk transport and storage of alternative fuels. The second part

considers the hazards associated with the operation, fueling, and maintenance of

alternative-fuel vehicle fleets. The report does not cover estimating the hazard

probability or calculating the overall risk.

Both sections of the hazard assessment discussion include information on the following

alternative fuels:

 1. Compressed Natural Gas (CNG)

 2. Liquefied (LNG)

 3. Propane

 4. Methanol and methanol blends

 5. Ethanol and ethanol blends

 6. Biodiesel blends1

 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.

---------------

 1 In this analysis biodiesel fuel is considered to be a mixture of 10-30 percent of a vegetable oil ester, such as methyl

soyate, and conventional diesel fuel.
xii

Fire Hazards

Since all fuels bum, they constitute fire hazards to a greater or lesser degree. However,

fuels vary widely in the degree of flammability. Of the many combustion-related

properties of substance, fuel flammability limits and pool bum rate are especially relevant

to a safety hazard analysis.

Fuel Flammability Limits

Flammability limits are a basic measure of flammability. Flammability limits are the

range of composition over which mixtures of fuel and air will bum. At an ambient

temperature of 22 C, natural gas in the form of CNG or LNG has the widest flammability

limits. Due to increased volatility at higher temperatures, the alcohols, methanol and

ethanol have extended flammability limits at elevated temperatures (60 C). Biodiesel

fuel is below its flashpoint at 22 C 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 given

size spill will burn and release heat. Since fuels bum only when they are in gaseous

form, the pool bum rate tends to be limited by the rate of vaporization. Thus, the pool

burn rates for the alcohols, which have relatively high heats of vaporization, are lower

than those for hydrocarbon fuels like gasoline or propane. Note too, that the gaseous

fuels hydrogen and compressed natural gas can have very high heat release rates since the

bum rate for these fuels 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

most fuel health effects, inhalation of fuel vapors is the most likely exposure route. The

threshold limit value for the health effects of fuel vapors is a measure of fuel toxicity.

The limits for all fuels except LNG vapor (considered to be nearly pure methane), and

hydrogen are based on toxic effects. The limit values for these fuels are based on the

lower flammability limit and the premise that inhalation of a flammable mixture of fuel

and air constitutes a health hazard. In the case of hydrogen and natural gas, excessive

exposure can also result in asphyxiation. However, approximately 140,000 ppm (14

percent) of an inert gas would be required to lower the oxygen concentration of air to less

than the 18 percent, the limit for a breathable atmosphere.

Methanol and methanol blends are the most toxic AMFs for inhalation-exposure with a

threshold 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

ethanol 1,000 ppm, followed by natural gas at a value of 10,500 ppm. In addition, there

is an OSHA-set personnel exposure time limit (PEL) of 1,000 ppm for propane.
xiii

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 normal temperatures and pressures, shows that all of the liquid AMFs are

biodegradable over a reasonably short period of time (i.e., a period of several months or

less). The major concern is that the liquid AMF should be prevented from entering into

any waterway or drainage system. Aside from any consideration of aquatic toxicity,

there is actually a potential fire/explosion safety hazard situation created when a

flammable or combustible liquid enters a waterway where there are covered sections

where vapors can accumulate. This problem is particularly 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 for separating them out.

C. FLEET USE HAZARDS

This portion of the work was structured around a summary list of safety, fire, and health

hazards for each alternative fuel in fleet use. In each instance, the assessment of the

consequences of the hazards and of the state of knowledge concerning the hazards is

based on a comparison with diesel or gasoline fuel as currently used by fleet operators

and transit agencies.

To construct the summary list of hazards associated with the fleet use of alternative fuels,

the following 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

to cause an accident. Some event is necessary before the hazard and the hazard

consequences are realized.

The application of the eight hazardous properties to the eight alternative fuels produces a

number of hazards. The more significant hazards for each fuel are:
xiv

CNG - Important hazardous properties and hazards for CNG include:

• Flammability hazard -- fire or explosion from ignition of gas leaks. Such gas leaks

can occur from fuel dispenser or fuel system damage, use of improper components, or

poor overall design. High pressure natural gas leaks can ignite from static electricity.

Several such cases have already occurred, some resulting in the loss of the vehicle.

• Toxicity hazard - natural gas can accumulate in enclosed spaces. The odorant may

not provide sufficient warning of the actual gas concentration.

• High pressure hazard - fuel tank explosion, missile damage from failure or improper

assembly or disassembly of fuel system components. Flailing of fuel hoses and fuel

lines.

• Mechanical energy hazard - natural gas compressors have rotating and/or

reciprocating parts moving it high speeds. Failure of such equipment could lead 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 for cryogenic 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 those for CNG, they

are still significant. Also, trapped liquid fuel can produce extremely high pressures

upon warming and vaporization.

• Cryogenic hazards - LNG presents several hazards associated with the cryogenic

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 structural

members exposed to cold fuel or fuel vapors.

Structural failure can also occur due to embrittlement of materials exposed 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 propane vapor

clouds can detonate.

• Toxicity hazard - propane gas can collect in low spaces and therefore displace the air

necessary for breathing.
xv

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 range for typical

ambient temperatures.

• Flammability hazard - the flames from methanol fires are not as luminous as those

from other hydrocarbons. While this serves to limit fire injury and damage, it can

also make initial detection of methanol fires more difficult.

• Corrosivity hazard - being a polar liquid, methanol is slightly acidic and can corrode

some active metals.

Ethanol and Ethanol Blends - Important hazardous properties and hazards for ethanol

and ethanol blends include:

• Flammability hazard - vapors in fuel tanks are within the flammable range for typical

ambient temperatures.

• Corrosivity hazard - being a polar liquid, ethanol is slightly acidic and can corrode

some active metals.

• Toxicity hazard - ingestion of a fuel billed as food-based, but which must be

denatured, 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 the composition

difference between biodiesel fuel and gasoline or conventional diesel fuel is a type of

corrosivity hazard.

• Toxicity hazard - ingestion of a fuel which has been billed as non-toxic, but which is

generally an ester of a fatty acid and methanol. If ingested the methanol component

is released. In primates (including humans) this can cause toxic effects.

Hydrogen - Important hazardous properties and hazards for hydrogen include:

• Flammability hazard - fire or explosion from ignition (especially static ignition) of

gas releases or gas leaks. Note that hydrogen fuel is a non-odorized flammable gas.

• Corrosivity hazard - hydrogen embrittlement of certain materials represents a type of

corrosivity hazard associated with hydrogen.

• High pressure hazard - fuel tank explosion, missile damage from failure or improper

assembly or disassembly of hydrogen fuel system parts.
xvi/xvii

Electricity - important hazardous properties and hazards for electricity include:

• Flammability hazard - fire caused by electrical malfunctions, such as short circuits.

• Corrosivity, toxicity, or high temperature hazard – from contact with battery

electrolyte.

• Electrical energy hazard - electric shock.

D. CONCLUDING REMARKS

No fuel is free from hazards. Although some fuel hazards are obvious, a systematic

consideration of hazardous properties and hazards can identify hazards which may have

been overlooked. Hazards differ for various alternative fuels. This implies that:

• Modifications of equipment and procedures will be required for each alternative 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 about

additional hazardous properties and hazards. However, a risk assessment, including

information about hazard probabilities and hazard consequences, can support conclusions

about the safety ranking of various fuels, fuel systems, fueling equipment, and overall

strategies for using alternative fuels.

xviii

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 interface

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 Agency

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 valve

TWA Time-weighted average

VNTSC Volpe National Transportation Systems Center
1-1

1. INTRODUCTION

1.1 BACKGROUND

The national goals for both energy security and clean air have resulted in heightened interest

in the use of alternative motor fuels (AMFs) in the transportation market. The Energy Policy

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 local clean

air initiatives and fuel mandates have been enacted for certain vehicle classes. These

mandates will have consequences for a number of transit and other fleets that must comply

with local, state, and federal regulations while continuing to provide the highest quality

transit programs and other services in their areas.

Other government programs have sought to encourage the use of alternative fuels through

grants and awards for alternative fuel demonstration programs. For example, as part of its

Clean Air Program (CAP), the Federal Transit Administration (FTA) has awarded grants for

alternative fuel demonstration programs. The Department of Energy, through the National

Renewable Energy Laboratory has also funded a number of alternative fuel demonstration

programs, such as the comprehensive CleanFleet program involving Federal Express

medium-duty delivery trucks.

Growth of interest in alternative fuels has expanded not only the number of alternative fuel

vehicles, but also the list of viable alternative transportation fuels. In recognition of the

increasing need to more fully understand critical aspects of the candidate AMFs, the FTA

and the Volpe National Transportation Systems Center (VNTSC) have established a program

that addresses the safety hazards and operational issues associated with the use of alternative

fuels by vehicle fleet operators.

This effort to supply additional information concerning the safety hazard implications of all

AMFs is timely. An increasing number of transit fleets and other fleet owners are operating

vehicles on alternative fuels - often with a minimum of technical guidance related to the

possible safety or operational impacts on their facilities, as well as those related to the

production, transport, and bulk storage of alternative fuels that support these demonstrations.

The environmental, safety hazard, and health aspects analysis of AMFs have become more

complex in recent years. Several developments have contributed to this complexity. The

first development is the increasing number of candidate alternative fuels. For example, at

first, methanol was the only alternative fuel being seriously considered for transit use. The

early commitment by Detroit Diesel Corporation to provide a methanol fueled-engine for

transit use contributed to this emphasis. However, natural gas engine development soon

followed, with the natural gas being stored in compressed form.

The roster of alternative fuels used in transit has now expanded to include methanol and

methanol blends (M-100 and M-85), ethanol and ethanol blends (E-95 and E-85),

compressed natural gas (CNG), propane (LPG), liquefied natural gas (LNG), bio-diesel, and
1-2

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 have

concentrated on only a portion of the total transit or fleet operation. Transit properties and

fleet operators must consider the entire path from the fuel supplier all the way to the vehicle

fuel tank. Also, fleet operations involve not only operating alternative fuel vehicles in

revenue service, but also fueling, inspecting, cleaning, washing, and performing the light and

heavy 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, the

development of fire and building codes is not yet complete. This requires additional care on

the part of the designers and owners of these facilities to consider all hazards associated with

the use of alternative fuel vehicles and to ensure that these hazards are properly addressed in

the plans for and the operation of the facility.

The third development, which adds to the complexity of alternative fuel use, is the

recognition that more hazards must be considered than the traditional "Will it bum or

explode?" examination of fuel issues. The use of compressed gases raises issues concerning

high 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 of

diversion for non-authorized use. Several fuels demand a further scrutiny of the need for

personal protective gear.

Lastly, the experience of some transit properties and private fleet operators has shown that

not all local community and regulatory groups view the use of alternative fuels as a purely

positive option. Opposition from neighborhood groups has already caused alternative fuel

plans in several cities to be changed or curtailed. Transit properties and others who propose

the use of alternative fuels need to deal not only with the perceptions of fire and building

code officials who grant approvals, but also with the perceptions and concerns of community

and neighborhood organizations. The concerns of these groups are not limited to fleet

operations, but may also include the production of the alternative fuel and the transportation

of the fuel to the point of use. It is important that the fleet operator recognize at the

beginning of a conversion to alternative fuels the types of safety issues that will need to be

addressed 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 existing

knowledge about the health, safety, and environmental hazards of alternative fuels and to

identify where additional study is needed.

The existence of special safety concerns does not mean that alternative fuels are inherently

more dangerous than conventional fuels, but does emphasize that forethought, good

engineering, and thorough training are requisites for the safe and successful use of alternative

fuels. Programs in which alternative fuels are used while all other aspects of the fleet

operations remain unchanged are apt to have difficulties.
1-3/1-4

1.2 OBJECTIVES AND SCOPE

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

from 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 being

introduced into actual operations on a prototype/demonstration basis. Battery-powered

vehicles have received increased attention in recent years, including a number of applications

involving 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 not been

addressed.

2-1

2. PREPARATION AND ORGANIZATION OF REPORT

2.1 INFORMATION SOURCES

The major sources of information used to conduct the assessment of safety, health, and

environmental 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 in

References - 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 first

section, "Production, Bulk Transport, and Bulk Storage of Alternative Fuels," focuses on the

hazards associated with moving the fuel from the point of production to the point of use at

the fleet operators facility. The second section, "Use of Alternative Fuels by Vehicle Fleets,"
2-2

focuses on the operation, fueling, and maintenance of alternative fuel vehicles. Both sections

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, safety

issues, health issues, and environmental issues applicable to each alternative fuel, with

sections on methodology, an analysis of issues, and a summary assessment of risks. The

safety 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 each

alternative fuel. An introductory discussion considers the types of hazards considered and

the distinctions between hazardous fuel properties, hazards, and risks. The summary list of

hazards follows. It is accompanied by a selection of actual case histories which serve to

illustrate various hazards in the summary list of hazards.

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

considered:

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 risk

assessment in which the risk associated with the use of various alternative fuels are ranked or

compared. The definitions on the following page will help clarify these terms as used in this

report.

Two separate sections of source material are included. Appendix A, titled "Sources for

Alternative Fuel Safety Information" provides a bibliography, by categories, which gives
2-3

basic information for readers. Specific references in the text of the report are given in

"References - Section 3" and "References - Section 4."
2-4

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

substance of situation that has the potential to cause harm. For example, a substance may be

flammable or it may be contained under a high pressure.

A hazard is the combination of a hazardous property with an outcome that can cause damage

or harm to people, property, or the environment. For example, a material which is

flammable may ignite 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 occurence involving equipment

failure, human action or external cause that results in a hazard. For example, the ignition of

a flammable material 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 may be thought

of as a combination of a hazardous property with the probability of one or more initiating

events. For example, the probability of a fire may depend on the probability that a fuel spill

could occur coupled with the probability that an ignition source is available. Hazard

probability may be expressed in purely numerical terms, such as the number of expected

events per 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 of

property damage or the amount of injury. For example, the severity of a fire hazard may be

ranked by the dollar value of the property which may be destroyed. Other qualitative or

quantitative scales of severity may also be used. A given hazard may have many possible

consequences, 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 electrical shock 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

risk of 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 of damage to the vehicle and/or the extent of injury to the occupants.
3-1

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 discussion

of its special characteristics that affect safety, health, and the environment. Each AMF is

presented 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 collected

that the amount of information available is very extensive. In order to provide a

comprehensive and understandable assessment, the methodology used to extract information

was 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
3-2

• Other safety hazards, particularly high pressure and low (cryogenic) temperatures that

affect 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 - Analysis of

Issues. The information in this section represents a synthesis of the specific safety and health

concerns derived from a relatively large number of documents.

Section 3.4 - Summary Assessment of Risk - provides a summary assessment of the safety,

health, and environmental issues on a comparative basis. This assessment is intended to

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 storage

operations; and

• the relative consequences of an AMF leak or spill in the context of safety, health, and

environmental 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 of

sources including coal and natural gas. All methanol used commercially in the United States

is 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 is

designated as M-85. The addition of 15 percent unleaded gasoline increases both the name

luminosity and the fuel volatility. The latter effect both increases the cold starting capability

and also generally makes the vapors present in fuel tank ullage spaces too rich to be

flammable.

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-85

and conventional unleaded gasoline.
3-3

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 point

temperature, range of flammability limits, autoignition temperature, and electrical

conductivity. There are other properties of importance that affect the consequences or

potential damage associated with a methanol (or any alternative fuel) fire. These include the

bum rate of liquid pools, the heating value of the fuel, flame temperature, and thermal

radiation emitted from the fire.

Section 3.3 of this report provides a relative comparison of the physical characteristics of

each alternative fuel that affects the safety, health, or environmental effects associated with

its use. In this section, the major physical characteristics that differentiate the hazards

associated with each fuel are summarized.

One general physical characteristic that differentiates methanol from other fuels is its

corrosive characteristics. Methanol is incompatible with several types of materials normally

used in petroleum storage and transfer systems, including aluminum, magnesium, rubberized

components, and some other types of gasket and sealing materials1

 Therefore it is necessary

to take special precautions to ensure that methanol is transported or stored in containers and

transfer lines that have been specifically selected for that purpose.

The other significant difference between methanol and other AMFs is that it is considered to

be more toxic. However, exposure limits for inhalation of methanol vapor are only slightly

lower than those for gasoline (200 ppm threshold limit value [TLV] for methanol vapor; 300

ppm for gasoline vapor)2

 Since gasoline is much more volatile than methanol, it is likely that

more gasoline vapors will be generated for an equivalent spill volume and therefore are more

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 risks

for fire fighters. Methanol, along with natural gas, gasoline, and propane, has a hazard

degree of 1, which is a material that, on exposure, would cause irritation, but only minor

residual injury and is considered as only slightly hazardous to health. All of the other AMFs

have a hazard degree of 0 which means that under fire conditions, they offer no hazard

beyond 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 if it

occurs in bright daylight. The methanol blends (M-85) have increased visibility because the

burning of the gasoline fraction produces some luminance3

One other property of interest is the relative vapor density of methanol compared to air; at 1.

II, methanol vapor is heavier than air. Therefore the vapor will tend to accumulate at ground

level or in low-lying areas such as maintenance pits4

 If the methanol vapor is not quickly

dissipated through adequate ventilation, it will linger in the low-lying areas creating an

increasing opportunity for exposure to an ignition source and a subsequent fire.
3-4

The addition of unleaded gasoline to methanol to create M-85 can improve the cold starting

capabilities and increase the flame luminosity of the fuel. With regard to some of the key

characteristics noted above, the presence of the gasoline can be expected to reduce the

corrosivity of the M-85 compared to M-100, but it will also increase the toxic health hazards.'

 (b) Fire Hazards During Transport

The bulk transport of methanol is usually done by a standard petroleum products tanker truck

which carries approximately 10,000 gallons of fuel. From a fire hazard perspective, there is

little 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 more

subject to leaks or spills than conventional gasoline or diesel transport. However, one

specific issue that must be considered is the possible use of materials that may not be

methanol compatible in the tanker truck. This could become a problem if there is a longterm exposure of methanol to seals and gaskets that may deteriorate and become subject to

leaks.

One physical characteristic of methanol that is an important fire hazard consideration during

both transport and storage is the combination of vapor pressure and flammability limits. For

M-100, vapor/air mixtures are potentially flammable at volume concentrations ranging from

6.7 to 36 percent. In a fuel or storage tank, a methanol liquid temperature between 10°C to

43°C (approximately 50°F to 110°F) at standard atmospheric pressure will create a

flammable vapor/air mixture.4 Therefore any ullage space in a container or storage tank that

is vented to the atmosphere will contain flammable vapor-air mixtures at normal ambient

temperatures found in transport and storage operations.

This condition is different from the ullage space in a gasoline container or storage tank where

the vapor concentration will be above the flammable limits range at normal temperature and

pressure (i.e., too "rich"). In the case of diesel fuel, which is much less volatile than

methanol, the vapor/air mixture in the headspace will generally be below the flammable

limits (i.e., too "lean") at normal ambient temperatures.

Therefore, with methanol, it is extremely important to ensure that there are strong safeguards

against any ignition sources inside the tank and that any vent lines or other openings have

flame arrestors. Any fill lines must extend below the liquid methanol surface to provide a

seal 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 to

gasoline in its flammability characteristics because the fuel vapor is composed primarily of

gasoline.3

 Under normal circumstances, the headspace in the container or Storage volume

will contain a vapor/air mixture that is above the flammability limits concentration range,

i.e., too rich to burn.
3-5

 (c) Fire Hazards During Unloading to Fleet Storage

The transfer of methanol from the bulk transport tanker truck to fleet storage must take into

account the fact that any vapor/air mixture that leaks during the transfer operation will create

a flammable volume. In addition, any methanol spill will quickly vaporize and form

flammable vapor/air mixtures. For this reason, it is essential that all hose connectors have

mechanical locking features, vapor recovery devices be in place between the tanker truck and

the fuel storage tank, and that grounding devices be provided to prevent static electrical

discharges from taking place. As noted earlier, any vent lines should have spark arrestors

and 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 of

fleet operations. The installation must be designed to use methanol compatible materials to

avoid long term degradation and leaks. Fuel storage tanks designed for diesel or gasoline use

may not be methanol compatible.

The fire hazards associated with M-100 storage will be greater than for diesel fuel storage

because it is a much more volatile fuel. A spill or leak of M-100 will create a much larger

volume of flammable vapor/air mixture than an equivalent diesel spill. However, the fire

hazards associated with methanol storage should be approximately the same as, or lower

than, with gasoline storage. Gasoline is more volatile than methanol; however, the potential

range 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 with

an external ignition source when compared to gasoline.

It should be noted that the range of flammability limits for most AMFs are highly dependent

upon the maximum temperature of the fuel. For example, if M-100 is only exposed to a

maximum temperature of 22 C (70 F) it is only possible to reach a maximum volume

concentration of approximately 13% methanol based on its equilibrium vapor pressure at 22

C and at atmospheric pressure. Therefore, the actual range of flammability limits for

methanol 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 gasoline

engines; therefore, it is appropriate to consider the fire hazards as being comparable to that of

gasoline. In fact the volatility and flammability limits of M-85 are very similar to those for

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 be

observed. These are primarily those that are designed to minimize the presence of any

external ignition sources. In addition, the presence of methanol requires that the storage tank

installation must be methanol compatible.

 
3-6

3.3.1.2 Health Issues

Exposure to methanol can occur through inhalation of vapor, or through ingestion or skin

contact with the liquid fuel. The toxic effects of methanol are the same regardless of the

means of exposure. Considering the fact that methanol is quite volatile, it is most likely that

the typical route for exposure is through inhalation of methanol vapors.

Among the AMFs considered in this study, methanol vapor is considered the most toxic for

inhalation exposure. The measure of fuel toxicity is the threshold limit value (TLV) for

vapor 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 methanol

vapor, the TLV-TWA value is 200 ppm, while the TLV-STEL value is 250 ppm.2

 Other

AMF vapors have toxicity (TLV-TWA) concentration values that are at least five times

higher. As noted earlier, none of the AMFs are considered to be serious health hazards by

the NFPA based on potential exposure during fire fighting activities.

Interestingly, conventional gasoline has a TLV-TWA close to that of methanol (300 ppm

versus 200 ppm) and it is more volatile. Therefore, the toxic exposure risks with both of

these fuels are likely to be similar. Diesel fuel vapors are apparently much more toxic than

either methanol or gasoline since the TLV-TWA value for kerosene (as a proxy for diesel

fuel) is only 14 ppm.2

 Fortunately, diesel fuel is relatively non-volatile at normal ambient

temperature, therefore vapor exposure is not a significant issue.

The health issues with M-85 are similar to M-100. Considering the relative vapor toxicity

and volatility of both methanol and gasoline, M-85 must be considered in the same health

hazards category as M-100.

Personnel involved in the bulk transport and storage of both M-85 and M-100 must be

protected from exposure through proper design of tanks and transfer lines, selection of

methanol compatible materials, use of personnel protection equipment, and proper training to

avoid accidental exposure. Something as simple as a drain line for a fuel filter or a transfer

hose for emptying fuel tanks can help to reduce exposure for the personnel working on the

equipment.

 3.3.1.3 Environmental Issues

The major environmental issues of concern with all liquid AMFs is a fuel spill, particularly a

spill that reaches a sewer or drainage system. The release of flammable liquids into a sewer

system is prohibited by NFPA-30 - Flammable and Combustible Liquids Code. One of the

physical properties of methanol that affects fuel spills is its water solubility. Normally, fuel

handling facilities that have an emergency drain connecting to a sewer will have a separator

or clarifier to ensure that the fuel (gasoline or diesel) will not reach the sewer. This approach

will not work with methanol since it is soluble in water and will pass directly through the

separator. Methods for separating methanol from water exist but they are quite complex and

costly. Therefore, the best approach is to ensure that any spills in a facility are absolutely
3-7

prevented from entering any drain through the use of impoundment systems to contain the

entire volume of any potential above ground spill. In a bulk transport situation there 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 time

when 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 the

United States from corn and other grain products, while some imported ethanol is produced

from sugar cane. Like methanol, ethanol is a pure organic substance whose physical and

chemical properties are invariant, unlike some other AMFs such as natural gas or propane

which are mixtures of different hydrocarbon molecules with no standard or average

composition.

Pure or neat ethanol (E-100) is rarely used for transportation applications because of the

concern about intentional ingestion. In fact, ethanol for commercial or industrial use is

always denatured (small amount of toxic substance added) to avoid the federal alcoholic

beverage tax. Therefore, it is unlikely that ingestion would be a serious problem. For heavy

duty diesel (compression ignition) engine applications, such as transit buses, two ethanol

blends 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 percent

kerosene.

Both blends have been used in Detroit Diesel heavy duty engines similar to the 23:1 high

compression 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 fuel

vehicles 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 Reid

vapor pressure of ethanol is less than half that of methanol) and the range of flammability

limits is smaller. On this basis alone, ethanol is safer than methanol. However, as pointed

out above, there are relatively few situations where the ethanol will be in a pure form since it

is usually used as either E-95 or E-85. With both ethanol and methanol blends, any fuel
3-8

vapors will contain a substantial percentage of gasoline, therefore there would be very little

difference in the flammability characteristics of the two fuels.3

There are other general physical characteristics of pure ethanol that are important from a

safety perspective. While ethanol is less corrosive to metals, gaskets, and seals than

methanol, it is still necessary to make sure that any container, transfer lines, and fittings are

made 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 and

collect in low lying areas where it may linger as a flammable vapor/air mixture unless there

is adequate ventilation. Fortunately ethanol, similar to gasoline, has a relatively low odor

threshold such that personnel in the vicinity of a leak of E-100 or any blend should be able to

rapidly detect it. As noted in Reference 2, there is considerable variation in the reported odor

threshold data for various AMFs, particularly ethanol and methanol. Therefore, the detection

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 the

same types of hazards as other bulk transportation of petroleum products. As long as the

tanker 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 the

equivalent volume of gasoline or diesel fuel transported.

As with M-100, the bulk transport and storage of E-100 will involve an ullage space

vapor/air mixture that is in the flammable range at volume concentrations from 3.3 to 19%,

corresponding to ethanol tank temperatures between 4°C and 46°C (approx. 40-115°F).4

Therefore, stringent precautions have to be taken to avoid the possibility of ignition sources

inside any container or tank containing E-100.

Ethanol blends, typically E-85, that are transported will exhibit volatility and flammability

characteristics that are very similar to gasoline because the fuel vapors will be composed

primarily of gasoline. As with methanol blends, the headspace vapor/air mixture for E-85

will 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 the

volatility and flammability of any leaked or spilled fuel. The following precautions are

necessary:

• hose connections with mechanical locking fasteners;

• vapor recovery devices; and

• grounding devices to prevent static electric discharge.
3-9

 The unloading of E-100 and ethanol blends must be accomplished at the same level of safety

standards as used for gasoline. These standards are spelled out in NFPA30-Flammable and

Combustible Liquids Code and NFPA30A-,Automotive and Marine Service Station Code.

These codes address fueling facility, storage, and handling requirements for all flammable

and combustible liquids including both M-100 and E-100. It is of interest to note that the

NFPA classification for gasoline, M-100, and E-100 is exactly the same (Class IB flammable

liquids defined as those having closed-cup flash points below 23°C and having a boiling

point at or above 38°C). This is an example of the need to consider the spectrum of fire

hazard properties when considering AMFs because as discussed above, the ullage space

hazards alone make the transport and transfer of E- 100 (and M-100) an increased fire hazard

risk when 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 long

term. 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 for

methanol and include:

• Positive prevention of ignition sources entering the storage space by providing such

devices as spark arrestors in vent pipes, properly sized ground straps, and fill pipes

extending to the bottom of the tank; and

• Prohibiting the placement of any pumps or other equipment within the storage tank that

can create an ignition source.

All of the above requirements for the prevention of ignition sources, leaks and spills, and

adequate provision for handling any leakage of spills when storing or handling ethanol (and

any other NFPA-designated flammable or combustible liquids) are spelled out in great detail

in the applicable NFPA codes. For example, typical ignition sources identified in NFPA30

include:

• 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, heating equipment

 Therefore, there is a very substantial base of experience in handling and storage of such

flammable liquid AMFs, such as E-100, E-85, M-100, and M-85. The experience has been

codified 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 the

presumption 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 a
3-10

greater incidence of fires in ethanol (or other AMF) storage situations then for a comparable

number of gasoline storage facilities.

 3.3.2.2 Health Issues

Ethanol is less toxic than methanol. The threshold limit value-time weighted average (TLVTWA) 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 about

intentional ingestion of ethanol by employees is mitigated by the fact that alcohols intended

for 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 as

methanol 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 be

confusion 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 water

soluble, it is necessary to take stringent precautions in order to ensure that any ethanol spill

does not reach a sewer or drainage system. These same precautions cannot be assured for the

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. Because

of the residential and industrial use of natural gas, the industry has its own distribution

system and supply network that is much more extensive than for any other liquid or gaseous

AMF. The issues of bulk transport and storage are completely different from most of the

other AMFs which are typically transported to fleet storage via tanker truck, unless the

natural gas has been liquefied. (Liquefied Natural Gas [LNG] is presented in the next

section.)

The typical fuel system for natural gas vehicles is one with highly compressed (typically 20

to 25 MPa or 3,000 to 3,600 psi) gas stored in high pressure cylinders on the vehicle. The

containment of natural gas at such high pressures requires very strong storage tanks which

are both heavy and relatively costly. This distinguishing feature of CNG is the one that has

the most impact on safety issues.

CNG is generally produced on-site at a fleet fueling facility using compressors fed from a

nearby 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 than
3-11

10 minutes. In order to accomplish this filling effectively, an intermediate high pressure

storage tank with a volume of 3 to 4 times the vehicle fuel tank capacity is required.5

 For

slow fill (overnight), there is no need for a large storage tank, a small buffer tank is

sufficient.

 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 of

ethane, 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 the

natural gas plays an important role in the performance of fleet vehicles. For the purposes of

discussion in this report, the physical properties are based on the properties of the principal

component, methane, unless otherwise specifically noted. The typical range of methane for

pipeline natural gas in various parts of the country is from approximately 80% to 95%. The

California Air Resources Board (CARB) has adopted specifications for natural gas as a

vehicular fuel which require that the methane content be greater than 88%. Even with this

type of specification, there is still considerable variation possible in the general physical

properties of natural gas.

The physical properties of natural gas that affect safety include the autoignition temperature

and the flammability limits range. The autoignition temperature (also known as ignition

temperature) 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 with fuel

composition, but it is always lower than that of pure methane. The estimated ignition

temperature of natural gas is in the range from 450-500°C. The flammability limits range for

natural gas is approximately 5% to 15% volume concentration.

More importantly, the leakage of compressed natural gas will immediately form a large

gas/air mixture volume that is in the flammable range within a portion of the immediate area

around the leak. A unit volume of CNG at 25 MPa psi will expand by approximately 200

times when released to the atmosphere. The ignition energy required is very small for

virtually all of the AMF vapor/air mixtures being considered (in the range from

approximately 0.15 to 0.30 millijoules)2. Therefore, the existence of a CNG leak creates an

increased probability of exposure to a stray ignition source such as a static electric spark

when compared to the leakage of an equivalent mass of an AMF that is expelled in a liquid

form and vaporizes over a period of time.

Natural gas is colorless, tasteless, and relatively nontoxic. An odorant is added in such

amounts to make the odor noticeable at 115 of the lower flammability limit of 5%. Thus, the

odor threshold for CNG is approximately 10,000 ppm. Therefore, personnel in the vicinity

of a natural gas leak will be able to detect the presence well before the gas has reached the

flammable limit in the area adjacent to the person.
3-12

The most unique physical characteristic of CNG does not derive from the physical properties

of methane, but from the fact that the gas is stored at an extremely high pressure for use as a

vehicular fuel. The presence of material stored and transferred at pressures that far exceed

the normal experience of most fleet operations personnel raises the standard of precaution

and training required. Inadvertent opening of valves or loosening of fittings containing high

pressure natural gas will not only lead to creation of a fire hazard, but can also result in the

high 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 to

atmospheric pressure will inevitably result in a significant cooling effect which will result in

a vapor cloud of very cold and dense gas. Conventional practice has been to assume that any

leak of CNG will rise immediately due to the fact that methane at normal temperatures is

lighter than air. Consequently, safety design practices have been focused on ceiling

ventilation and detection of methane vapors. In fact, it is highly likely that any significant

leakage from storage tanks and transfer lines will migrate down and fill in low lying areas as

it is moved about by any wind or circulatory effects. Ultimately, the methane will warm up

and 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 the

flammable 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 natural gas

pipeline to the fleet operators compressor station. The local gas utility will typically work

with the fleet operator to provide an underground supply delivering pipeline quality natural

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 unauthorized digging 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. One necessary

provision is a rapid and positive means of shutting off the supply flow from the pipeline 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 a

truck trailer containing compressed gas. This type of gas delivery may be used on a

permanent basis for small users who cannot justify the cost of a compressor station, or on a

temporary basis to users whose compressor station is unavailable.

In this case, issues arise concerning the crashworthiness of the trailer: while the gas cylinders

themselves are robust, the valves and associated piping may be vulnerable. Also, it is

possible that the tanks might be exposed to a gasoline- or diesel-fueled fire should the tractor

trailer truck be involved in a traffic accident.

The use of the CNG delivery trailer also requires that flexible connections be made and

broken in the course of each delivery. Experience shows that extra vigilance is necessary
3-13

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 desired

pressure (approximately 25 MPa, 3600 psi) and transfer to the storage tank systems. There

are various approaches that can be used for the CNG storage depending upon whether a fast

fill (i.e., approximately 9,000 SCF of gas transferred to a vehicle in less than 10 minutes) or a

slow fill (many hours or overnight) approach is used. In either case, however, there is some

limited storage involved at pressures from 20 or 25 MPa (slow fill) up to 35 MPa for fast 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 percent

depending upon the source and seasonal effects. More importantly, the pipeline gas can

contain 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 of

water, can be corrosive to carbon steel. The corrosive effect is increased by pressure. Since

the pressure considered in CNG vehicle applications is so high, there is a real concern about

excessive corrosion leading to the sudden explosive rupture of a container. NFPA 52

Compressed Natural Gas (CNG) Vehicular Fuel Systems, 1992 Edition provides that the gas

quality in any pressurized system components handling CNG comply with the following

specification:

• H2

S and soluble sulfides partial pressure ..... ............................................ 0.35 kPa, max

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

• C02 partial pressure ........................................... ............................ ................ 48 kPa, max

• 02

 .......................... .................................................................................0.5 volume %, max

The NFPA committee involved in developing the standard relied on field experience and

research which led them to believe that if the water content is limited as specified above, the

potential for corrosion problems is not a major concern. It should be noted that a water vapor

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 a more

conservative position due to the corrosion failure of a cylinder comprising one of several in a

tube trailer in 1978. As a result, U.S. DOT has specified the composition of CNG being

transported in interstate commerce. The limits for the corrosive components are very low,

including an upper limit for water vapor set at 8 milligrams per cubic meter of gas.

The existence of this potential problem with the corrosive properties of natural gas makes it

necessary to dry and treat the gas before high pressure storage whenever such corrosive

constituents 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 these

materials lack the necessary strength or resistance to corrosion required for CNG service.
3-14

In addition to the NFPA standard, the Society of Automotive Engineers has established SAE

J1616 Recommended Practice for Compressed Natural Gas Vehicle Fuel with provisions

intended to protect the interior of the fuel container, as well as other fuel system components,

from corrosion.6

All of the above serves to point out that there is a substantial level of care which must be

taken in the design and operation of high pressure CNG storage systems in order to avoid

leaks or ruptures. In the event of a leak or rupture, the CNG fuel flow rate out of the storage

tank or piping can be very high, and any ensuing fire (or explosion) will be likely to have a

very high heat release rate. Compounding this problem is the difficulty of shutting off 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 the fill

technique. For fast fill, the CNG storage volume should be at least 3 times (often up to 4

times) the individual fleet vehicle fuel tank volume. For a typical 40-foot bus, the fuel tanks

would require approximately 250 kg. of CNG. This would mean a buffer storage capacity of

approximately 750 to 1,000 kg. Compared to other AMFs, this storage volume is fairly

small, thereby reducing the total potential fire and explosion impact of a massive rupture of

the storage tank.

A slow fill system would have a much smaller buffer storage system because the

compression system would typically be sized to handle the maximum number of vehicles to

be fueled on an overnight basis.

In the unlikely event that a fleet operator decided to fast fill from a mobile CNG tube trailer

truck, the amount of CNG stored on- site would increase substantially. If more than one

trailer 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, January

31, 1994, pp. 4478-4499) issued a Final Rule promulgating a list of regulated substances and

thresholds required under Section 112(r) of the Clean Air Act, as amended. Methane is on

the 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 and

submission of a Risk Management Plan (RMP) which includes a hazard assessment, a

prevention program, and an emergency response program. The RMP requirement is in the

rulemaking process currently; the proposed rule was published on October 20, 1993 (58 FR

54190).

This requirement is much more applicable to the storage of LNG, hydrogen, and propane

where there is more likely to be more than 4550 kg (10,000 lb.) stored at a facility. This

threshold quantity can easily be exceeded for AMFs used in medium to large fleet operations.
3-15

3.3.3.3 Health Issues

The principal constituents of natural gas, methane, ethane, and propane, are not considered to

be toxic. The American Conference of Governmental Industrial Hygienists (ACGIH)

considers those gases as simple asphyxiants, which are a health risk simply because they can

displace oxygen in a closed environment. The Occupational Safety and Health

Administration (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 have

ACGIH-listed threshold limit values (TLVs), including butane - 800 ppm, pentane - 600

ppm, hexane - 50 ppm, and heptane - 400 ppm. The effective TLV for an average natural gas

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 unlikely that

personnel will be unknowingly exposed to the TLV concentration since they can detect it by

odor.

 3.3.3.4 Environmental Issues

There are no significant environmental hazards associated with the accidental discharge of

CNG.

 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 desired

methane content. The typical methane content is approximately 95% for the conventional

LNG produced at a peak shaving plant. Peak shaving involves the liquefaction of natural gas

by utility companies during periods of low gas demand (summer) with subsequent

regasification during peak demand (winter). It is relatively easy to remove the non-methane

constituents of natural gas during liquefaction. Therefore, it has been possible for LNG

suppliers 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 low

pressure (20 to 150 psi) at about one- third the volume and one-third the weight of an

equivalent CNG storage tank system. The big disadvantage is the need to deal with the

storage and handling of a cryogenic (-160°C, -260°F) fluid through the entire process of bulk

transport and transfer to fleet storage.
3-16

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 is

essentially 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 with

corrosive effects on tank storage associated with water vapor and other contaminants. On the

other, the cryogenic temperature makes it extremely difficult or impossible to add an odorant.

Therefore, with no natural odor of its own, there is no way for personnel to detect leaks

unless the leak is sufficiently large to create a visible condensation cloud or localized frost

formation. It is essential that methane gas detectors be placed in any area where LNG is

being transferred or stored.

The cryogenic temperature associated with LNG systems creates a number of generalized

safety considerations for bulk transfer and storage. Most importantly, LNG is a fuel that

requires intensive monitoring and control because of the constant heating of the fuel which

takes place due to the extreme temperature differential between ambient and LNG fuel

temperatures. Even with highly insulated tanks, there will always be a continuous build up

of internal pressure and a need to eventually use the fuel vapor or safely vent it to the

atmosphere. When transferring LNG, considerable care has to be taken to cool down the

transfer 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 the

fuel, unless it is a highly purified form of LNG, i.e., RLM. The methane in the fuel will boil

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 and

replenishment the methane content will continuously decrease and the actual physical

characteristics of the fuel will change to some extent. This is known as "weathering" of the

fuel. 7

Another consideration is that under low temperatures, many materials undergo changes in

their strength characteristics making them potentially unsafe for their intended use. For

example, materials such as carbon steel lose ductility at low temperature, and materials such

as rubber and some plastics have a drastically reduced ductility and impact strength such that

they will shatter when dropped.

As before, many of these potential issues have been identified and addressed in the various

codes that have been developed by the NFPA and under the Uniform Fire Code. For

example, the NFPA has the following national standards and codes applicable to LNG:

• NFPA 59A - Standard for Production, Storage, and Handling of Liquefied Natural Gas

• NFPA 57 (draft) - Standard for Liquefied Natural Gas Vehicular Fuel Systems (final code

expected to be published in 1995)
3-17

 (b) Fire Hazards During Transport

LNG may either be liquefied on-site or it can be delivered to fleet storage using a standard

10,000 gallon LNG tanker truck. In general, only the largest fleet operators would find onsite liquefaction to be advantageous. Typical LNG storage vessels, including those used on

the tanker truck, have the following basic components:

• INNER PRESSURE VESSEL made from nickel steel or aluminum alloys exhibiting high

strength characteristics under cryogenic temperatures

• Several inches of INSULATION in a vacuum environment between the outer jacket and

the inner pressure vessel. Stationary tanks often use finely ground perlite powder, while

portable tanks often use aluminized mylar super-insulation.

• OUTER VESSEL made of carbon steel and not normally exposed to cryogenic

temperatures

• 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 the

equivalent tanker truck design for transport of other liquid AMFs. Therefore, the transport of

LNG is safer from the perspective of fuel spills resulting from a tank rupture during an

accident. A rupture of the outer vessel would cause the loss of insulation and result in an

increased venting of LNG vapor. While this is of concern, it is relatively minor compared to

the prospect of an LNG spill.

An explosion of an LNG container is a highly unlikely event that is possible only if the

pressure relief equipment or system fails completely or if there is some combination of an

unusually high vaporization rate (due to loss of insulation) and some obstruction of the

venting and pressure relief system preventing adequate vapor flow from the inner pressure

vessel with a resultant pressure build up. If the pressure builds up to the point where the

vessel bursts, the resulting explosion is known as a BLEVE (boiling liquid expanding vapor

explosion) with the container pieces propelled outward at a very high velocity.7 This is a

highly unlikely event due to the extensive requirements for pressure relief including pressure

relief valves and burst discs that are built into the design codes. (There have been no reports

in 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 mixture

will be formed immediately in the vicinity of the LNG pool. In an accident situation, there is

a high likelihood of ignition sources due to either electrical sparking, hot surface, or possibly

a fuel fire created from the tanker truck engine fuel or other vehicles involved in the accident.

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. The
3-18

heat release rate from an LNG pool fire will be approximately 60% greater than that of a

gasoline 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 involves

the active participation of both the tanker truck driver and a representative of the fleet

operator. A partial listing of some of the steps involved provides some indication of the

safety precautions that are necessary.7

• After the truck is chocked and the engine is shut off, a grounding cable is attached to the

truck to ground any electrostatic discharge.

• A flexible liquid transfer hose is attached to the tanker and purged with LNG to remove

all air.

• A fleet operator representative will open the storage vessel liquid fill line and the driver

will open the trailer's main liquid valve.

• The driver will control the pressure in the trailer tank via a pressure building line where

LNG is vaporized and returned to the tank to maintain a pressure differential 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 hose coupler

to compensate for differential expansion.

The safety features that are typical of truck storage transfer of LNG include equipment

design such as trailer liquid valves that are interlocked with the truck brake system to prevent

fuel 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 vented

LNG vapor.

The complexity of the fuel transfer arrangement creates the potential for leaks and spills

through human error and equipment failure. One of the particular concerns is that the fuel

transfer equipment goes through a continuous cycle of cool down to cryogenic temperatures

and warm up to ambient temperature. This type of thermal cooling can create additional

stresses on equipment and sealing devices which could result in decreased reliability over

time.

 (d) Fire Hazards During Fleet Storage

LNG storage facility requirements for a total on-site storage capacity of 70,000 gallons or

less are defined in the draft NFPA 57 - Standard for Liquefied Natural Gas (LNG) Vehicular

Fuel Systems. NFPA 59A - Standard for the Production, Storage, and Handling of Liquefied

Natural Gas (LNG) is applicable to storage volumes above 70,000 gallons. Both of these

standards address similar issues including siting of the storage tank, provision for spill and

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 an

impounding area surrounding the container to minimize the possibility of accidental
3-19

discharge of 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 facility will 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 of

personnel to cryogenic temperatures. Workers can receive cryogenic burns from direct body

contact with cryogenic liquids, metals, and cold gas. Exposure to LNG or direct contact

with metal at cryogenic temperatures can damage skin tissue more rapidly than when

exposed to vapor. It is also possible for personnel to move away from the cold gas before

injury.

The risk of cryogenic bums through accidental exposure can be reduced by the use of

appropriate protective clothing. Depending upon the risk of exposure, this protection can

range from loose fitting fire resistant gloves and full face shields to special extra protection

multi-layer clothing.

Another unusual hazard associated with aged LNG will arise in the unlikely event that there

is a large spill of LNG onto a body of water. This could occur in an accident situation

involving 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 transformation

from the liquid phase to vapor. If significant vaporization occurs in a short time period, the

process can, and usually does, resemble an explosion.8

The RPT "explosion" phenomenon for LNG on water has been observed in a number of

situations and has been studied extensively in both laboratory and large scale tests. The

temperature of the water and the actual composition of the LNG are important factors in

determining whether an RPT will take place. It should also be noted that RPTs have been

obtained for pure liquefied propane with water temperature in the range of 55°C (I 30°F).

 3.3.4.3 Health Issues

The principal constituents of natural gas, methane, ethane, and propane, are not considered to

be toxic. The American Conference of Governmental Industrial Hygienists (ACGIH)

considers those gases as simple asphyxiants, which are a health risk simply because they can

displace oxygen in a closed environment. The Occupational Safety and Health

Administration (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 have

ACGIH listed threshold limit values (TLVs), including butane - 800 ppm, pentane - 600

ppm, hexane - 50 ppm, and heptane - 400 ppm. The effective TLV for an average natural gas

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 of

personnel to detect TLV concentrations. This is another reason to ensure that methane

detectors are in place wherever personnel may be exposed.
3-20

3.3.4.4 Environmental Issues

There are no significant environmental hazards associated with the accidental discharge of

LNG.

 3.3.5 Propane

3.3.5.1 General Discussion

Propane, which is otherwise known as liquefied petroleum gas, consists of a mixture of

propane, propylene, butane, and butene. These gases are referred to as natural gas liquids

since they are present in wellhead natural gas. Liquefaction of these gases will occur by

compressing them to pressures above 800 kPa (120 psi) at room temperature. The term

propane is used in this section to reflect the fact that this AMF is typically composed of

more than 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) of

wellhead natural gas and the remaining 40% is a by-product of petroleum refining. Propane

for 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. ASTM

specifications for propane meeting this requirement include those for commercial propane

which is suitable for light duty internal combustion engine applications and special duty

propane which is suitable for heavy duty applications.

There is a substantial base of experience with propane as an automotive fuel since it is the

third most heavily used fuel, after gasoline and diesel fuel. It is estimated that there are

approximately 350,000 propane vehicles in operation, with most of them being aftermarket

conversions of gasoline vehicles. Historically, propane was used extensively in transit

applications from the 1940s up to 1970. The largest single user was the Chicago Transit

Authority which in 1970 operated 1,400 propane buses, reportedly with a good safety

record.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 than

gasoline which is the next most volatile fuel (1400 kPa versus 100 kPa). Propane is stored

under moderate pressure (I 10 to 150 psi) at ambient temperatures to maintain it in a liquid

state. In the event of an accidental release of propane to the atmosphere, about one-third of

the liquid flashes to vapor at a temperature of -70~o~F or lower.5~ Leaking propane will

discharge at a high velocity due to the pressure differential, turning the liquid into an

atomized 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 down
3-21

and essentially stop active boiling of the pool when the ground surface becomes sufficiently

cool. Vaporization will continue until all of the propane evaporates.

Due to the rapid vaporization of propane, the pool bum rate is the highest of all the liquid

AMFs considered. As a result, the heat release rate from a propane fire is approximately

twice that of a gasoline fire for the same liquid spill volume. The flammability limits range

for propane is similar to that for gasoline. Consequently, when compared to accidental spills

of an equivalent volume of gasoline, propane vapor is more apt to come into contact with an

ignition source due simply to the much higher volatility of the fuel and the resulting larger

volume of flammable propane/air mixture.

Another physical characteristic of interest is that propane vapor is heavier than air so it will

descend from the point of a leak and accumulate and linger in low-lying areas unless there is

adequate ventilation.

 (b) Fire Hazards During Transport

Propane fuel is typically delivered to fleet storage via tanker trucks with capacities up to

approximately 10,000 gallons. All propane tanker trucks must conform to applicable U.S.

DOT regulations regarding Hazardous Materials Regulations and Federal Motor Carrier

Safety Regulations. The regulations specify the materials design factors and pressure relief

considerations for cargo transport. A major concern is the setting of pressure relief valves so

that the container will not vent propane vapor in the event of an unusually warm day. All of

these containers are typically manufactured from steel and are qualified under the ASME

pressure vessel code. The minimum design pressure for the container is based on the vapor

pressure of the propane at 45°C (115°F). Since the vapor pressure for commercial propane at

that temperature is 243 psig, the design pressure typically is 250 psig with a safety factor of

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 is

that the container for propane on a tanker truck will be much more rugged and resistant to

rupture from mechanical forces associated with an accident when compared to the transport

of other liquid AMFs that are not pressurized, with the exception of the double shell tank for

LNG.

On the other hand, the transport of a liquid fuel at moderately high pressure means that there

is an increased probability of fuel leaks at joints and fittings. The piping system including

hoses, along with fittings and valves will all be designed to code requirements for the

expected 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 the opportunity for

small leaks.
3-22

 (c) Fire Hazards During Unloading to Fleet Storage

Propane is typically transferred from the tanker truck to fleet storage by pumping it from a

truck into the storage container. As with any transfer of fuel, this is likely to be the most

potentially hazardous part of the bulk transport to storage process. The fact that personnel

are dealing with pressurized valves and lines, where any human error may result in a serious

discharge of propane, makes it a point of concern.

Fortunately, propane is odorized so that the presence of a small leak may be detected by the

presence 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 may

go undetected in a low-lying area.

 (d) Fire Hazards During Storage

All propane storage containers are constructed according to the appropriate ASME Pressure

Vessel Code. Design pressures are usually on the order of 250 psig with the pressure release

devices typically set in the vicinity of 375 psig. Normally, underground tank installation is

specified for liquid fuels such as gasoline and diesel, mainly because it eliminates the hazard

of fuel spills caused by vehicles running into the tank, and also because it allows more space

for parking of vehicles. Propane, however, is ordinarily stored in above-ground tanks

constructed of thick guage steel. The tanks are strong enough to be supported by concrete or

steel saddles without deforming. The tanks are then surrounded by heavy upright steel pipes

structurally mounted in concrete to act as a barrier against vehicle intrusion into the tank

area.5

The structural strength of the storage tank and the proper design of all piping, valves, and

fittings should provide a high level of protection against any massive leaks. The weakest

points 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 over

time. The odorization of propane along with the proper placement of combustible gas

detectors and the natural ventilation in an outdoor area should help to prevent any serious fire

hazard from developing.

One of the major safety considerations with the storage of propane is the possibility of a

pressure buildup in the tank due to external heating from a fire combined with a failure of the

pressure relief or venting system. The resultant explosion of the tank due to overpressure

would lead to a BLEVE incident. The fact that all of the applicable codes and federal

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 the

likelihood of an overpressure leading to a BLEVE is exceedingly small, particularly in a

fixed storage facility situation. Unlike an accident situation with a transport vehicle where it

is 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 would

simultaneously fail.
3-23

 (e) Other Hazards

Since propane is stored under pressure during bulk transport and storage operations, there is a

potential hazard associated with an inadvertent opening of a fitting or plug which could

become a projectile. In addition, when propane expands out of a leak or hole, the rapid

vaporization or flashing of the liquid causes the stream to reach temperatures that can cause

freeze bums.

When compared to other AMFs, the potential high pressure hazard with propane is much less

than with CNG (3600 psi vs. 150 psi); and the freeze burn hazard is much less than with

LNG, 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 difficult to

determine. The major constituent, pure propane, is considered to be a simple asphyxiant by

the ACGIH and does not have an assigned TLV. The other significant, but much smaller,

constituent is butane which has a TWA-TLV of 800 ppm. OSHA has set a PEL of 1000 ppm

for propane, with the requirement that exposure to more than half this level requires that a

medical monitoring program be instituted. Other than this OSHA requirement, there is no

other agency or body that has established an exposure limit for propane.

It should also be noted that propane has been reported to contain a relatively high level of

radon gas, with radon concentrations in propane that are well above current EPA guidelines

for radon exposure.9 Since the exposure of personnel to propane will be limited, the potential

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 the

liquid 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, rapeseed oil,

other vegetable oils, animal fats, or used cooking oil and fats. The chemical process for

creating biodiesel involves mixing the oil with alcohol in the presence of a chemical catalyst

such 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. Either methyl

ester or ethyl ester can be used neat (100%) or blended with conventional diesel

("petrodiesel") as a fuel for diesel (compression ignition) engines.
3-24

Current efforts to commercialize biodiesel in the United States were started by the National

SoyDiesel Development Board (NSDB) in 1992. The emphasis of their activity is on the use

of 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 the

best balance of cost and engine emissions characteristics. NSDB reports that as of the

beginning of 1994, biodiesel had accumulated nearly eight million miles in demonstrations

involving 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 or

near-total exemption from fuel taxes in most EC countries. As a result, there is a much larger

base of operating experience with biodiesel in Europe amounting to several hundred times

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 than

diesel, which in turn, makes it safer than the other AMFs considered. For example, the flash

point for SME is 218°C (425°F) compared to approximately 73°C (160°F) for the average

No. 2 diesel fuel. It also has an extremely low vapor pressure, less than 1.3 x 10-5 kPa at

72°C. Therefore, when SME is blended with petrodiesel to create BD-20, the resultant flash

point for the mixture is 118°C, still well above that for the petrodiesel alone.

Past experience with neat (100%) biodiesel has indicated that it is incompatible to immerse it

with certain rubbers and plastics, but not with metals. Reports indicate that nitrile rubber and

polyurethane-based compounds showed unacceptable deterioration while other elastomers

such as SBR, butadiene, isoprene, hypalon, silicon, and polysulphide were not resistant to

neat biodiesel. Acceptable replacement materials include fluorine - rubber (Viton A) and

polypropylene- and polyethylene-based plastics10 Therefore, the selection of materials to

avoid degradation of seals, fittings, and hoses is important for biodiesel applications.

An unusual physical characteristic of blodiesel that has a fire hazard implication is the

possibility of spontaneous combustion in highly unsaturated materials such as some

vegetable oils 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 there is no way for the generated heat of oxidation to dissipate. The higher temperature

accelerates the oxidation process giving off even more heat until the pile of rags begins to

smolder and then burn. Since oil-soaked rags or other materials such as filters in typical

petrodiesel 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 potential

for spontaneous combustion. This is not a serious problem and can be simply resolved by

having closed metal cans for storing oil soaked rags and other oily combustible material.
3-25

 (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 or

spill is less likely to ignite than diesel or gasoline under equivalent conditions. Biodieselcompatible materials should be selected to avoid problems of degradation of seals and

fittings.

 (c) Fire Hazards During Unloading to Storage

There are no specific fire hazards. Unloading equipment should be designed to handle

biodiesel to avoid any possibility of leaks.

 (d) Fire Hazards During Fleet Storage

There are no specific fire hazards, other than the potential spontaneous combustion issue

noted above.

 3.3.6.3 Health Issues

Because there are essentially no vapors generated at normal transport and storage

temperatures, pure or neat biodiesel can only be considered as a potential health hazard due

to ingestion. Pure biodiesel looks and smells like a food product and could conceivably be

ingested. If biodiesel were ingested, enzymes in the body would break the ester back into its

original components, e.g., soybean oil and methanol.11 This raises the potential issue of

methanol 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 a well

for petroleum oil and natural gas. Hydrogen must be extracted chemically from hydrogenrich materials such as natural gas, water, coal, or plant matter. A substantial quantity of

hydrogen is produced each year in the U.S. - about 8.5 billion kilograms per year.
3-26

About 95% of the hydrogen in the U.S. is produced by steam reforming, a chemical process

that makes hydrogen from a mixture of water and a hydrocarbon feedstock, such as natural

gas. When steam and methane contained in the natural gas are combined at high pressure

and temperature, a chemical reaction converts them into hydrogen and carbon dioxide. The

overall energy efficiency of the process, i.e., the energy content of the hydrogen produced

divided by the total energy (natural gas and energy used to run the reformer) consumed, is

approximately 65%. Other techniques for producing hydrogen, including off-gas cleanup

and electrolysis, are much more costly.

Over the long term, it may be possible to consider large scale electrolysis (passing an

electrical current through water to split individual water molecules into hydrogen and

oxygen) using sunlight on photovoltaic cells as the electrical power source, or some other

renewable energy source such as wind power. Hydrogen obtained using this approach is

termed "solar hydrogen" or "renewable hydrogen."

The actual use of hydrogen in automotive vehicles is limited to experimental and prototype

vehicles. A number of prototype vehicles bum hydrogen directly using modified automotive

engines. There are also a number of vehicles that use the hydrogen in a fuel cell to produce

electrical 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 involving

blends of up 15 percent in volume of hydrogen added to natural gas to create "hythane." In

this 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 well

known 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

of the high pressure tanks. It has been estimated that the weight of the compressed hydrogen

will only vary from 1 to 7% of the total weight of the tank. Fortunately, the energy density

of hydrogen is very high so that I kg of hydrogen contains approximately 2.5 times more

energy than 1 kg of natural gas. Therefore, assuming an equivalent engine efficiency, the

weight of a vehicle's compressed hydrogen fuel storage system will be similar to that for a

CNG 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 of

research.12

For bulk distribution of hydrogen, the most common method by far is to liquefy the hydrogen

and transport it by truck trailers, barges, or railcars. At atmospheric pressure, liquid

hydrogen (known as LH2) boils at -253°C (423°F), which is only about 20°C above absolute

zero. The process of hydrogen liquefaction, storage, and distribution is challenging, to say

the least.
3-27

Hydrogen is usually liquefied in a complex multi-stage process that involves the use of liquid

nitrogen (boiling point of approximately -200°C). Special precautions are required during

liquefaction to maintain the proportions of two types of hydrogen molecules in order to avoid

excessive internal heating and vaporization while the LH2 is being transported or in storage.

LH2 requires special insulation to maintain liquid conditions as long as possible. 12

The physical property of hydrogen that creates the most significant fire hazard is the

extremely wide range of flammability limits, i.e., from 4% to 75% by volume. This range is

twice that of methanol which has the next widest range. In effect, any release of hydrogen

into the air results in a much larger volume of a flammable mixture than an equivalent

amount of any other AMF.

More importantly, the potential for an explosion or detonation of a flammable hydrogen-air

mixture is very high. The ignition energy for hydrogen-air mixtures is much lower than for

hydrocarbon-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 pressure

rise can lead to a detonation.

Among the other physical properties of hydrogen that are of interest is the propensity of the

gas to leak more easily than other AMF gases due to the relatively small size of the hydrogen

molecule. Since hydrogen gas is colorless and odorless, leaking hydrogen cannot be detected

unless an odorant, or possibly a colorant, has been added to the gas. Addition of odorant or

colorant would be very difficult to implement in situations requiring liquefaction of the

hydrogen. To compound matters, the flame of burning hydrogen is invisible in daylight,

therefore adding an extra safety concern for personnel working near hydrogen tanks or

transfer lines. "

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 or

transfer of hydrogen gas under pressure. Proper material selection and technology is

available to prevent embrittlement, but there may be situations where such precautions have

not 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 be

liquefied 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 constructed

similar to the double walled configuration for LNG, but with a very high level of insulation

due to the fact that the LH2 is much colder than LNG. Thus, the LH2 tanker truck design is

expected 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 would

increase rapidly. Provisions are made in the design of storage vessels for venting and

pressure relief in order to avoid any rupture of the inner tank containing the LH2. The
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potential for ignition of hydrogen gas that is vented out at a high rate (as the result of an

accident 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 particularly

troublesome scenario because a flammable hydrogen air mixture would be immediately

formed in the vicinity of the LH2 pool and would quickly form a much larger volume of

flammable gas as hydrogen boils off from the pool. Since the hydrogen gas is cold, it will be

relatively dense and may stay in proximity to the ground for some period of time. The

ignition energy required to initiate a hydrogen/air fire is very low so that the probability of an

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 result in

condensation of air and its oxygen and nitrogen components. A mixture of hydrogen and

liquid oxygen is potentially explosive even though the quantities involved are likely to be

small."

 (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 that

of LNG. There is the potential for leaks and spills due to the number of steps that are

involved 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 transfer

equipment 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 Hydrogen

Systems - Consumer Sites. This standard addresses siting of the storage tank, provisions for

spill or leak control, and the basic design of the storage container and LH2 transfer

equipment.

As with LNG, it is necessary to insure that any accidental discharge does not endanger

adjoining property or reach any waterways, particularly those connecting to covered drainage

systems. 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 body

contact with (1) the liquid; (2) metals at LH2 cryogenic temperatures; and, to a lesser extent,

(3) with the cold vapors.
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3.3.7.3 Health Issues

Hydrogen is not considered to be toxic. However, it is a simple asphyxiant which is a health

risk 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 of

LH2.

3.3.8 Electricity

3.3.8.1 General Description

Electricity can be considered as an AMF based on the use of electrically powered fleet

vehicles using batteries as the energy storage medium. Most fleet applications currently

considered 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 vehicles

be recharged overnight. The current research focus for electric propulsion vehicles is in the

area 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 fundamental

part of the nation's infrastructure. The hazards associated with high voltage power lines,

substation transformers, and local power distribution systems are well known. The National

Electrical Code developed under the auspices of the NFPA covers the safety and protection

measures 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 of

electric power to the recharging station at the fleet facility. There is no storage issue since

the electrical energy is stored in the on-board batteries.

The major safety concern is the exposure of personnel to electrical hazards as they work with

the recharging system and connecting the vehicles to that system. This is not expected to be

a serious safety hazard because the normal design practices for setting up the connections

involve safeguards to ensure that personnel are protected from direct exposure to electrical

hazards.

One of the safety advantages of electricity compared to the other AMFs is that all facility

personnel are generally familiar with the hazards associated with electrical power.

Therefore,
3-30

personnel working with the recharging system can be expected to be aware of the dangers

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 at

a fleet facility.

3.3.8.4 Environmental Issues

There are no specific environmental hazards associated with the transmission and use of

electricity 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 environmental

issues associated with the bulk transport, unloading and transfer, and fleet storage issues

associated with each individual AMF. In this section, the individual issues are combined

with the intent of conducting a summary assessment. This assessment is divided into two

parts:

• An assessment of the relative potential for AMF leakage or spills during bulk transport

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 during

bulk transport and storage, the following assessments are largely subjective. However, there

are a number of physical and engineering principles that have been used as a guide in this

assessment. Briefly, they are as follows.

1. The standard for assessment is based on both diesel and gasoline. These fuels are

transported, handled, and stored at ambient temperatures and pressures and they are

stable during long term storage.

2. The risk of a leak or spill increases as the transport and storage pressure of the AMF

increases. Even with systems designed for high pressures, human errors, manufacturing

defects, and material weaknesses are bound to take their toll.
3-31

3. The risk of a leak or spill increases as the amplitude and frequency of the temperature

changes imposed on transport, transfer, and storage equipment is increased.

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 more complex.

Increased complexity leads to increased risk of leaks or spills through human 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 to

examine the potential for accidental release of each AMF during each step in the transport

and storage process. The following discussion considers the relative potential for accidental

release 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 of

potential issues regarding transport and storage modes that must be resolved through further

research and development. For example, it may be determined that the best approach is to

use 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 different

from 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 accident

scenario where the transport tank is damaged and a large amount of fuel is spilled. The

possibility of leaks during transport is minimized by the selection of appropriate materials

and proper design in accordance with the applicable material standards. Nonetheless, there

are still fuel-related factors that would affect the relative potential for leaks. The ranking is

presented in matrix format in Tables 3-1 and 3-2 for purposes of simplicity and convenience.
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TABLE 3-1. RELATIVE POTENTIAL FOR SPILLS DURING TRANSPORT

AMF

RELATIVE SPILL

POTENTIAL

(COMPARED TO

GASOLINE/ DIESEL

TRUCK SPILL) REASON

LNG Lower Double walled cryogenic

transport tank

Propane Lower High pressure transport tank

Gasoline/Diesel Reference Fuels

Ethanol/Ethanol Blend Same Same tank structure as

gasoline/diesel

Methanol/Methanol Blend Same Same tank structure as

gasoline/diesel

 TABLE 3-2 RELATIVE POTENTIAL FOR LEAKS DURING TRANSPORT

AMF

RELATIVE LEAK

POTENTIAL

(COMPARED TO

GASOLINE/ DIESEL

TANKER TRUCK) REASON

Gasoline/Diesel Reference Fuels

Ethanol/Ethanol Blends Somewhat Higher Potential corrosion effects

Methanol/Methanol Blends Somewhat Higher Potential corrosion effects

Propane Higher Pressures up to 375 psi

LNG Higher 300°F temperature

differentials and pressures up

to 150 psi

 Tables 3-1 and 3-2 point out that the conditions which tend to create leaks (i.e., high

pressure and temperature differentials) lead to bulk transport container designs that are more

robust and less likely to be ruptured and spill the fuel cargo in an accident situation.
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3.4.2.2 Unloading to Fleet Storage

The potential for spills and leaks during unloading operations is directly related to the

pressure 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 high pressure

is more likely to lead to a massive rupture of material (e.g., transfer hose, flexible coupling)

if it has been weakened by fatigue or temperature cycling, or if there is a material defect. A

large temperature differential requires a more complex system to maintain control with

increased possibilities for human error or equipment malfunction. The effects of corrosion

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 consists

of the process of taking pipeline quality gas, compressing it, purifying and drying it, and then

maintaining a relatively small amount in storage prior to dispensing to the vehicle. The

unloading 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 such

as 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 of

spills 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 of

AMFs 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, and

environmental effects. The most difficult area to assess is that of fire hazards because it

comprises two parts:

• the likelihood that the vapor/air mixture from a leak or spill will ignite from a spark or

other ignition source, including coming in contact with a heat source sufficient to raise

the vapor to its autoignition temperature; and

• upon ignition, the relative safety hazard associated with the size and intensity of the

ensuing fire or explosion.

The relative probability of ignition of an AMF leak or spill can be determined from the

physical properties of the fuel and the physical requirements for transport and storage. The

consequences of a fire or explosion depend upon the amount of fuel released. For the case of

a massive spill, the volume of fuel stored becomes an important issue.
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TABLE 3-3. RELATIVE POTENTIAL FOR SPILLS DURING UNLOADING

AMF

RELATIVE SPILL

POTENTIAL

(COMPARED TO

GASOLINE/ DIESEL

TRUCK SPILL) REASON

Gasoline/Diesel Reference Fuels

Ethanol/Ethanol Blends Slightly Higher Potential corrosion effects

Methanol/Methanol Blends Somewhat Higher Potential corrosion effects

CNG Higher Pipeline gas corrosion effects

and failure of high pressure

(3600-5000 psi) transfer

equipment

Propane Higher Combination of moderately

high pressure (375 psi) and

equipment failure

LNG Higher Combination of temperature

cycling/mechanical failure

and complexity of transfer

process

TABLE 3-4. RELATIVE POTENTIAL FOR LEAKS DURING UNLOADING

AMF

RELATIVE LEAK

POTENTIAL

(COMPARED TO

GASOLINE/ DIESEL

TANKER TRUCK) REASON

Gasoline/Diesel Reference Fuels

Ethanol/Ethanol Blends Slightly Higher Potential corrosion effects

Methanol/Methanol Blends Somewhat Higher Potential corrosion effects

Propane Higher Moderately high pressure

CNG Higher High pressure

LNG Higher Temperature differential and

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

AMF

RELATIVE SPILL

POTENTIAL

(COMPARED TO

GASOLINE/ DIESEL

TRUCK) REASON

Gasoline/Diesel Reference Fuels

Ethanol/Ethanol Blends Slightly Higher Potential corrosion effects

Methanol/Methanol Blends Somewhat Higher Potential corrosion effects

LNG Higher Moderately high pressure

and equipment failure

Propane Higher High pressure and equipment

failure

CNG Higher Complexity of container

system to maintain cryogenic

temperatures

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

AMF

RELATIVE LEAK

POTENTIAL

(COMPARED TO

GASOLINE/ DIESEL

TRUCK) REASON

Gasoline/Diesel Reference Fuels

Ethanol/Ethanol Blends Somewhat Higher Potential corrosion effects

Methanol/Methanol Blends Somewhat Higher Potential corrosion effects

LNG Higher Temperature differentials

Propane Higher Moderately high pressure

CNG Higher High pressure
3-36

For the case of bulk transport of liquid AMFs, the maximum typical volume of the standard

fuel tanker truck is approximately the same - 10,000 gallons. Therefore, the hazards of a

massive spill depend mostly upon the physical characteristics of the burning vapor/air

mixture, the heat release rate and flame radiation levels. In the case of fleet storage, the

approximation can be made that, for a fleet of equivalent size, the amount of fleet storage

required is based on the energy density of the fuel. Assuming one unit mass (kg) of diesel

fuel, the following equivalent amounts of fuel (as indicated in the left-hand box) are required

to 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 fuel

spilled from a storage tank. Assuming a uniform unconfined depth for the liquid pool, the

area 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 achieve the

equivalent fleet miles.

Equivalent Fleet Miles – Mass Equivalent Fleet Miles - Volume

 Diesel 1.00 Diesel 1.0

 CNG/LNG 1.15 Propane 1.9

 Propane 1.15 Ethanol 2.1

 Ethanol 1.90 LNG 2.3

 Methanol 2.50 Methanol 2.7

(Data from Reference 5) (Data from Reference 5)

 It should be noted that total fleet storage capacity may require the use of several storage

tanks. In that case, the maximum size of the fire from a spill would most likely be based on

the capacity of a single tank.

The total potential exposure based on total storage capacity with most AMFs at the fleet

operator's facility is approximately two to three times greater than diesel fuel based on the

potential area of a liquid pool. The total fire hazard exposure would depend upon the highly

unlikely event that all of the individual storage tanks would become involved in the course of

an accident.

The only fuel not noted above is CNG. As discussed in Section 2, the fleet storage

requirements for CNG will be quite small, on the order of 3 to 4 times the vehicle fuel

capacity of an individual vehicle for fast fill operators. Therefore, for most CNG-fueled

fleets, where the number of vehicles would be relatively large, the total heat release potential

from a storage tank fire will be quite small compared to the other AMFs.
3-37

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 impact on

the potential for ignition include:

• FLASH POINT (applicable to fuels stored as a liquid) - at temperatures below this point,

a liquid will not produce sufficient vapors to form an ignitable mixture with air near

the surface of the liquid.

• FUEL VOLATILITY (applicable to fuels stored as a liquid at the referenced temperature)

- measured by Reid vapor pressure, i.e., the pressure exerted by the vapor over the liquid

in a closed container at 38 C (100 F).

• AUTOIGNITION TEMPERATURE - the minimum temperature required to cause selfsustained combustion in air due to heat alone, without any additional spark or flame. The

autoignition temperature is also known as the self-ignition temperature, or simply the

ignition temperature.

• FLAMMABILITY LIMITS - The range of fuel concentration in air, expressed as a

volume percentage, that will support combustion. A concentration below the lower

flammability limit will not propagate flame due to insufficient fuel, i.e., too "lean." A

concentration above the upper flammability limit will not propagate flame due to an

excess of fuels, i.e., too "rich."

• ELECTRICAL CONDUCTIVITY - the degree to which a fluid will conduct electricity

measured in microsiemens per meter (us/m). Materials with lower conductivity are more

likely to build up and experience static discharges due to sloshing (liquid fuels) or

flowing.

In order to provide some perspective on these different properties for each of the AMFs, a

series of figures have been prepared which illustrate the differences, and the effect on

ignition potential.

Figure 3-1 shows the flash point temperature for all of the liquid AMFs. Propane and LNG

are not shown because they are gases at ordinary temperatures and pressures. The figure

illustrates the fact that diesel and soy-diesel are inherently much less prone to ignition

because at normal temperatures, the liquid fuel is far below the flash point. Therefore, the

spilled or leaked fuel would have to come in contact with a heat source in order to elevate the

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 leak

will immediately have a vapor/air mixture generated. Methanol and ethanol are less prone to

ignition when the liquid temperature is quite cold, but once it gets above 10 C (50 F),

flammable vapors will be generated.
3-38

Figure 3-2 illustrates the fuel volatility for all of the liquid AMFs as measured by the Reid

vapor pressure in kPa (6.9 kPa - 1 psia). As would be expected, the liquid fuel with the

lowest flash point (gasoline) has the highest volatility. Propane is shown in this figure (not to

scale) simply to illustrate the fact that it is extremely volatile, and upon release of this

pressurized liquid, approximately one-third immediately flashes to vapor. Thus, a spill of

propane 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 of

interest to note that in this case, the reference fuels, diesel and gasoline actually have the

lowest autoignition temperatures. Fortunately, even for diesel which has the lowest

autoignition temperature of those shown in the figure (230 C or approximately 450 F) the

actual temperatures are quite high and not likely to be encountered unless a fire had already

been initiated, or unless the fuel vapors came into direct contact with some very hot engine

parts, e.g., the exhaust manifold.
3-39

It is very important to remember that the values for propane and for methane shown in Figure

3-3 are for the pure gases. The AMFs, natural gas and vehicular propane, are variable

mixtures of gases with autoignition temperatures that will be lower than the pure gas values

shown. For example, natural gas is estimated to have an autoignition temperature range of

450-500°C, compared to the value of 540°C for pure methane.

Figure 3-4 shows the flammability limits range for a number of AMFs. This range is an

important determinant of the likelihood of ignition. If the range is extremely wide, as it is for

hydrogen, then the likelihood of encountering a flammable mixture is higher for a given

volume 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 fuels

are much more prone to encountering an ignition source for a given volume of vapor than the

other AMFs. In order to demonstrate the effect of temperature on the flammability limits

range for ethanol and methanol, an intermediate line shows the maximum volume

concentration that can be achieved for a normal temperature of 22°C (70°F). This line

demonstrates that at this temperature, the "effective" flammability limits range for ethanol

and methanol are equivalent to, or less than, most other AMFs.
3-40

It is also necessary to note that ethanol and methanol are less volatile fuels such that it will

take a longer time for a leak or spill of liquid to create the same volume of vapor, compared

to the equivalent liquid volume of the more volatile fuels. If a leak of methanol or ethanol

occurs 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 heavierthan-air vapors such as propane, the wider flammability limits of ethanol and methanol create

a higher probability of ignition under equivalent conditions.

The electrical conductivity of the fuel is important, as explained in the definitions of

physical properties, in determining the effects of potential static electric discharges whenever

fuels are in rapid movement such as the discharge from a high pressure tank or line. In most

cases, adequate protection can be obtained by grounding the container or transfer line.

However, there have been some situations reported where compressed natural gas, which is

essentially non-conductive, escaping from a cylinder apparently ignited from a static electric

discharge. The same type of phenomena may also develop with a high pressure leak of

propane since the liquid fuel is quickly atomized while fuel flashes into vapor.
3-41

For the other liquid fuels, both gasoline and diesel have very low conductivities, with

gasoline having a value of 1 x 10 -6 μS/m and diesel having a value of 1 X 10-4 μS/m. Both

methanol (44 μS/m) and ethanol (0.14 μS/m) have much higher electrical conductivities

which will help to reduce static charge buildup. This is fortunate since both of these fuels in

storage 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 of

personnel and objects to thermal radiation outside the immediate area of the fire. There is

also the possibility of the explosive or detonation type of burning of a vapor cloud which can

cause an overpressure hazard.

The prediction of the actual consequences of the ignition of a leak or spill of an AMF is a

very complex process because it is dependent upon so many different physical variables. For

example, there are three basic scenarios for the burning of a liquid AMF.
3-42

• A pool fire in which a fire or fire plume is established on an evaporating (and burning)

pool of the liquid.

• A vapor fire in which the ignition of an established plume (or cloud) of vapor results 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 fuel

spilled is the most important factor. The size of potential spills during bulk transport and

storage have been discussed previously in this section. The next consideration is the thermal

radiation from fire.

A substantial amount of theoretical and experimental

work has been accomplished on the subject of pool

fires. Some of the experimental work included

measurements of the thermal radiation from pool fires

of LNG, propane, and kerosene (GRI, 1982).14 As

indicated in the box to the right, the relative thermal

radiation (kW/M2) at the initial stages (first five

minutes) of the fire normalized to kerosene

(approximately 30 kW/M2) are as shown.

The reduced radiation intensity for propane and

kerosene pool fires is attributed primarily to the soot

that is generated with these fires which tends to mask

the flames. Interestingly enough, these results do not

extend to the case of a vapor cloud fire. Experimental

results comparing the emissive power of LNG and

propane cloud fires showed that they were essentially

the same.14 The comparative data for cloud and pool

fires normalized to the emissive power of an LNG

pool fire (in the range of 200 Mm2) is illustrated in

the 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 of

equivalent volume occur-ring under similar weather conditions. However, since there are so

many variables associated with predicting the size, shape, and thermal radiation effects of an

AMF spill fire, it is not possible to make a relative assessment that would be valid for all

conditions. It can simply be stated that on an overall (equivalent volume) basis, the ignition

of either LNG or propane will have much greater consequences in terms of radiation intensity

than that associated with other AMFs such as methanol/blends and ethanol/blends.

Relative Radiation Intensity

Pool Fire

 Kerosene 1.0

 Propane 2.2

 LNG 5.5

Comparison of Relative Pool

and Cloud Fire Radiatoin

Intensity

Pool Fire Cloud Fire

LNG 1.0 0.85

Propane 0.21 0.85
3-43

One other way to assess the potential consequences of an AMF spill fire is to consider the

combustion energy released from a pool fire. There is some evidence to suggest that the

fraction of combustion energy radiated from many types of hydrocarbon fuel fires including

methane, natural gas, and propane is in the range of 20 to 25%. Therefore, some

approximation of the overall radiative effects of a pool fire can be estimated from the heat

release rate.

Figure 3-5 presents the relative heat release rate for liquid pool fires based on the mass rate

at which liquid fuel is consumed per unit area and the heat content of the fuel. The heat

release rate has been normalized to diesel, i.e., diesel pool fire heat release = 1.0. Since

Figure 3-5 provides a comparison for pools of equal size, it provides an indication of the

consequences of ignition of a complete spill of the contents of an AMF tank truck (assuming

they all carry approximately 10,000 gallons) for all of the fuels shown. The figure clearly

illustrates that the overall radiation effects resulting from a propane or LNG ignition and pool

fire will be much more severe than that of an equivalent diesel spill. Conversely, the heat

release and overall radiation effects from an ethanol or methanol spill fire will be a small

fraction (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 a

flame will spread across the surface of a liquid pool of fuel. This could be an important

factor in personal safety in that it defines the potential time that an individual has to move

away from the pool. Based on limited data available, the flame spread rate for gasoline is the

quickest at 4-6 meters/second (13-20 feet/second) while that for methanol is approximately

24 m/s (7-13 ft./s). A diesel pool fire, on the other hand, will spread very slowly at 0.02 0.08

m/s (0.8 - 3.2 inches/second)2

. This is due to the fact that the diesel fuel will have to be

heated up to its flash point before sufficient flammable vapor can be generated.

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 turbulence

such as that caused by wind in the flammable gas mixtures will tend to dramatically increase

the flame speed, therefore, it is likely that under most situations the flame will propagate very

quickly with very little chance for personnel to react. Maximum flame speeds of

approximately 10 to 15 m/s (33-50 ft./s) have been measured. One big problem with a CNG

fire is that it is absolutely essential to cut off the CNG supply before attempting to extinguish

it. Otherwise, there is the risk of another accumulation of flammable gas and subsequent

reignition.

The consequences of ignition of a major spill at the fleet operator's facility will depend upon

the volume of fuel stored. Using the volume equivalents to achieve the same energy

equivalent mileage range for the fleet, as indicated earlier in the text, it will be necessary to

store a greater volume of all liquid AMFs compared to diesel, ranging from 1.9 times for

propane to 2.7 times for methanol. However, it is not possible to make a direct link between

these increased volumes and increased fire hazards because the larger volumes are likely to

be stored in separate tanks with appropriate separation and protection to avoid the spill fire

from affecting adjacent tanks.
3-44

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 AMFs considered

(both primary and secondary); they can be ranked as follows:

High Pressure Hazards Ranking

CNG

Propane

LNG

Methanol

Ethanol

Biodiesel

Low Temperature Hazards Ranking

LNG

CNG

Propane

Methanol

Ethanol

Biodiesel
3-45

With regard to the high pressure hazard rankings, only CNG and propane are normally at

sufficiently high pressure to cause problems with personnel safety for those working in close

proximity. LNG is transported and stored at relatively low pressure but if there is some

malfunction in the venting and pressure relief system, there is some possibility of a rapid

pressure buildup due to thermal effects. The other AMFs are not subject to such pressure

buildup.

Low temperature hazards are typically associated with LNG due to its cryogenic storage

temperature. CNG and propane will become very cold when they expand from their

respective storage pressures to atmospheric pressure; therefore, there is some low

temperature hazard associated with these AMFs. The remaining fuels do not pose any

problems with regard to low temperature hazards.

 3.4.4 Assessment of Health Hazards

Most of the AMFs considered in this study are effectively nontoxic, particularly when they are compared to conventional

fuels such as gasoline. The relative ranking of the AMFs on

the basis of potential health hazards to personnel are indicated

in the box to the right.

Methanol and methanol blends are the most toxic AMFs for

inhalation- exposure with a threshold 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 ethanol 1,000 ppm, followed by natural

gas at a value of 10,500 ppm. In addition, there is an OSHASET personnel exposure time limit (PEL) of 1,000 ppm for

propane.

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 is

also more volatile with a vapor pressure (RVP) approximately 2.3 times greater than

methanol; therefore, personnel working in the presence of both of these fuels are more likely

to be exposed to gasoline vapors than methanol vapors.

There is a similar concern with regard to an extremely volatile fuel such as propane which

has a PEL of 1,000 ppm. Propane is generally required to be odorized such that a

concentration of 1/5th of the lower flammable limit is detectable, i.e., approximately 4,200

ppm. Therefore, leaks of propane may result in concentrations of propane vapors that are

well below the flammable limit and cannot be detected by odor, but still be in a concentration

range that could reach the OSHA PEL value. By contrast, gasoline is detectable by odor at a

concentration of 0.2 ppm; therefore, the same type of personnel health hazard does not apply

to gasoline.

Potential Health

Hazards to

Personnel Relative

Ranking

• Methanol/blends

• Ethanol/blends

• Propane

• Biodiesel

• CNG
3-46

The reported data on odor detectability of methanol is not consistent, with values from 100

ppm to nearly 6,000 ppm cited in the literature. Assuming that an average value of 2,000

ppm is correct, it would be possible for personnel to be exposed to concentration values well

above the TLV-TWA.

In all of these situations it is possible to use gas detectors (either fixed or portable) in areas

where 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 with

any particular AMF.

The ranking of biodiesel is based on the possibility of ingestion due to its vegetable oil

appearance and odor. The human body will break down the biodiesel into its original

components, e.g., soybean oil and methanol. This raises the potential of methanol toxicity

depending 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 normal

temperatures and pressures, shows that all of the liquid AMFs are biodegradable over a

reasonably short period of time (i.e., a period of several months or less). The major concern

is that the liquid AMF should be prevented from entering into any waterway or drainage

system. Aside from any consideration of aquatic toxicity, there is actually a potential

fire/explosion safety hazard situation created when a flammable or combustible liquid enters

a waterway where there are covered sections where vapors can accumulate.

 This above problem is particularly 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 for separating them out. In a fixed facility situation, it is necessary to

ensure that any AMF spill will not endanger any other portion of the facility or neighboring

environs, and that they will not enter into any drainage system. This is achieved through

various forms of impoundment systems (e.g., dikes) that are sized to handle any conceivable

spill. During bulk transport, a spill can occur anywhere, including an area adjacent to a

waterway or drainage system.

 
4-1

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, and

health hazards (dangers) for each alternative fuel. In each instance, the assessment of the

consequences of the hazards and of the state of knowledge concerning the hazards is based

on a comparison to diesel or gasoline fuel as currently used by fleet operators and transit

properties. This choice of a baseline was made to prevent the use of project resources to

merely document safety knowledge that is generally available to and already practiced by

transit 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

FTA staff, literature searches, telephone interviews, and site visits.

In order to place this summary list of hazards in context, the summary list is preceded by a

discussion of the distinctions between hazardous fuel properties, hazards, and risks. The

summary list of hazards is supplemented by case histories of actual incidents involving

alternative motor fuels. These case histories, though anecdotal in natural, can serve to

illustrate and extend the discussion of individual hazards.

In addition to organizing the substance of this part of the report, this summary list of

hazards will provide a checklist for fleet operators who are considering alternative fuels

and a guide to 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

use of 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 environmental

assessment of alternative fuel use.

• The report is not a risk assessment and does not evaluate hazard probabilities, so there

are no numerical ratings or rankings of fuels or hazards according to their overall risk.

Obviously, no list of hazards can be exhaustive. An attempt has been made to identify all

major hazards and to choose and/or emphasize those fuel-hazard combinations which were

judged to be most serious thereby focusing the available project resources on the most

significant hazards, while still meeting the objective of providing an overall survey of each

of the alternative fuels.
4-2

4.2.1 Fuels Included

In this report, safety, fire, and health hazards are reviewed for each of the following fuels

listed below. The number designation is the same as that used in the Summary List of

Alternative 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

listed fuels 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

of these fuels is likely to be further in the future. Reformulated gasoline and reformulated

diesel have not been included in the hazard list because they are so similar to fuels that are

already 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 are

considered:

(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
4-3

This list is not an exhaustive list of all possible hazardous properties but rather those

deemed to be most relevant to the use of alternative fuels in motor vehicles. For example,

radioactive materials, shock-sensitive materials, and vacuums all present hazardous

properties that can result in hazards, but these hazardous properties are not relevant in the

context of alternative fueled vehicles.

Some hazardous properties in the list are relevant only in the context of certain alternative

fuels or certain vehicle and/or fuel system designs. For example, some electric vehicles

may have batteries whose electrolyte is at a high temperature. Thus, the high temperature

hazardous property is relevant to this fuel, but not to other fuels which are stored and used

at normal temperatures or even to other battery designs, such as lead-acid cells, which do

not employ high temperatures.

4.2.3 Accident Events Included

The existence of these hazardous properties and their associated hazards is not sufficient to

cause an accident. Some type of accident event is necessary before the hazard and the

hazard consequences are realized. While the events which lead to accidents are many and

varied, 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 mentioned

hazardous properties. All discussion is in the context of the use of alternative fuels by motor

vehicles. The numbering of these hazards follows the numbering which is used in the

subsequent Summary List of Alternate Fuel Hazards - Tables 4-1 through 48 (sections a-h).
4-4

4.3.2 Safety Hazards Considered

 (a) Hazardous Property = Flammability

All conventional and alternative fuels are flammable. The flammability of these fuels may

result in:

• A pooled fuel fire

• A fuel vapor fire

• An explosion (if the hot products of combustion are confined and prevented from freely

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 vehicle electrical

system fire

 (b) Hazardous Property = Corrosivity

Most fuels are not particularly corrosive. However, some battery electrolytes are strongly

acidic or strongly basic. Also, materials compatibility problems may result in fuel leaks

that present 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 bums

 (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 may

result 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

processed so as to make them toxic:

• Ingestion
4-5

 (d) Hazardous Property = High Pressure

Pressure is defined as force per unit area. As many simple calculations and unfortunate

experiences have shown, even a seemingly modest pressure over a modestly large area

presents 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 high temperatures

 (f) Hazardous Property = Cryogenic Temperature

Cryogenic temperatures are generally regarded as those less than 150°C. The hazards of

such low temperatures are both obvious and subtle:

• Cryogenic bum 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

moving parts or the potential energy of a large mass at an elevation. The danger from

kinetic energy increases with the mass of parts and with the velocity, either linear or

rotational. The danger from potential energy increases with the mass and the height. The

mechanical energy hazardous property can cause:

• Separation or fragmentation of moving parts

• Crushing or impact from falling parts
4-6

 (h) Hazardous Property = Electrical Energy

Electricity presents a number of familiar hazards, especially electric shock. The severity of

these hazards depends on both the voltage and current available. While current flow is the

factor that causes the injury in electric shock, higher voltages lead to greater danger. In

general, voltages in excess of 50 volts are considered potentially lethal.

• Electric shock injuries

• Fire from electrical shorts

• Possible health effects from electromagnetic radiation
4-7

 4.4 SUMMARY LIST OF ALTERNATIVE FUEL HAZARDS

The summary list of alternative fuel hazards follows.
4-8
4-9
4-10
4-11
4-12
4-13
4-14
4-15
4-16
4-17
4-18
4-19
4-20
4-21
4-22
4-23
4-24
4-25
4-26
4-27
4-28
4-29
4-30
4-31
4-32
4-33
4-34
4-35
4-36
4-37
4-38
4-39
4-40
4-41
4-42
4-43
4-44
4-45
4-46
4-47
4-48
4-49
4-50
4-51
4-52
4-53
4-54
4-55
4-56
4-57
4-58
4-59
4-60

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 the case histories of safety

incidents that have 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

and fire. The situation was first noticed while the truck was on the freeway and the driver

noticed the check engine light on. Upon pulling over, the driver saw flames coming from

the engine compartment. He tried to extinguish the fire with a hand extinguisher, but was

not successful. 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 fuel

ignited, 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 extensively

damaged and the vehicle was a total loss. Ironically, the incident occurred in Southern

California 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 for

operation on LNG. The manufacturer's representative was repairing a natural gas fuel

system leak 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

inclement and 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 a

flammable methane- air mixture that had accumulated in the interior of the bus. The

resulting explosion 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, experienced

mechanics had loosened CNG fuel line fittings with as much as 60 psig pressure on the 0 

system. The pressure gages on the vehicles were faulty and often indicated zero even with

this much pressure. Thus, mechanics thought the system was at zero pressure even though it

was not. The result was fittings flying across the shop.
4-61

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 drain holes. In doing so he drilled into the propane tank. A large propane leak

ensued, but there was no fire.

4.5.5 Pressure Relief Device (PRD) Failure on CNG Bus

Several transit properties using CNG have experienced PRD failures. Large fleets of CNG

buses have experienced multiple such failures. These failures have resulted in the release of

one or more full tanks of CNG into the bus fueling area. One such failure occurred when a

recently fueled CNG bus with roof-mounted tanks was taken into the garage for light

maintenance. A PRD failure occurred and the gas-fired infrared heaters in use in the shop

ignited the escaping gas. Damage from fire and water used to fight the fire was 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

strong odor of natural gas in the parking lot. He traced it to the cascade and found a relief

valve stuck open on the top tank. He closed the valve on that cylinder in the cascade to

isolate the leak 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 procedure

involved filling a portable cylinder from the dispenser and weighing the portable cylinder to

ascertain the mass of gas dispensed. The portable cylinder is then vented and the process is

repeated. On this occasion, when the natural gas was being vented from 2,30 psig to 0 

atmospheric pressure, a fire occurred when the pressure was around 150 psig. Since the jet 0 

of gas was directed towards the dispenser, the dispenser was extensively damaged. The fire

was judged to have 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 a

morning run, but forget to disconnect the fueling hose. After driving about 12 feet there was

a loud pop at the rear of the vehicle. The driver walked to the rear of the bus and heard a

loud hissing sound of CNG escaping from the bus fuel system, which had just been
4-62

pressurized to 300 psig. The driver returned to the bus, shut off the engine and ran to a 0 

maintenance bay to tell a mechanic. About when the driver reached the maintenance shop,

the escaping 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 threads

on the body of the valve on the propane vehicle fuel tank. The valve had a threaded

connection which had not been tightened sufficiently. The leak was repaired by th upfittere 

who turned the fitting one more turn into the threaded tank connection.
A-1

APPENDIX A

SOURCES FOR ALTERNATIVE FUEL SAFETY INFORMATION

In addition to the specific references listed in "References - Section Three," the following

sources 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 and

Adrian 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-08-06-0060-94-1,

March 1994.

"Replacing Gasoline: Alternative Fuels for Light-Duty Vehicles, Office of Technology

Assessment report, September 1990.

"Safe Operating Procedures for Alternative Fuel Buses," Geoffrey V. Hemsley,

Transportation Research 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 Protection

Association 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 and

Michael G. Zabetakis, U.S. Bureau of Mines Report of Investigations 6099, 1962.
A-2

"Introduction to LNG Vehicle Safety," Delma Bratvold and David Friedman, Gas Research

Institute report GRI-92/0465, 1992.

"Introduction to LNG for Personnel Safety," Accident Prevention Committee of the

Operating Section, American Gas Association, 1973.

"Production, Storage, and Handling of Liquefied Natural Gas (LNG)," National Fire

Protection Association standard NFPA 59A, 1990.

Propane:

"An Assessment of Propane as an Alternative Transportation Fuel," R.F. Webb Corporation

report for the National Propane Gas Association, June 1989.

"Working with Propane, Dispensing Product," Propane Gas Association of Canada

publication 100-1-88.

Methanol:

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

May 1987.

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

1992.

"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 SoyDiesel

Development Board report, February 1994.

Hydrogen:

"Hydrogen Vehicles: An Evaluation of Fuel Storage, Performance, Safety, Environmental

Impacts, 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.
A-3/A-4

 Electricity:

"An Illustrated Guide to Electrical Safety," William S. Watkins, Editor, American Society of

Safety 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 of relevant 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.

R-1

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 Research Record 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 the ATA

Foundation, Inc., Trucking Research Institute by Battelle and Gannett Fleming, (November

1990).

4. "Safe Operating Procedures for Alternative Fuel Buses, A Synthesis of Transit Practice,"

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 Transportation

Operations," 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 Vehicle

Recommended Practice J1616, February 1994.

7. "An Introduction to LNG Vehicle Safety," Draft Report prepared for Gas Research

Institute 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 of

Energy report, DOE/PE/72013-2, pp. 2-29.

10. "Biodiesel - A Technology, Performance and Regulatory Overview," prepared for the

National Soydiesel Development Board by American Bio Fuels Association and

Information Resources, Inc. (February, 1994).

11. Industrial Toxicology, Edited by Phillip L. Williams and James L. Burson. Van Nostrand

Reinhold, New York, 1985. p. 248.

12. "Hydrogen as a Fuel," Congressional Research Service Report for Congress, 93-350 SPR,

prepared by Daniel Morgan (March, 1993).
R-2

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 and

Combustion," prepared for the Gas Research Institute by Technology & Management

Systems, (July, 1982).
R-3

REFERENCES - SECTION FOUR

1. "Evaluation of Aftermarket Fuel Delivery Systems for Natural Gas Vehicles and LPG

Vehicles," by B. Willson, NREL report NREL/TP-420-4892, (1992).

2. A pressure relief device (PRD) is connected to a compressed gas cylinder to relieve excess

pressure. PRDs may act from excess pressure through the use of a burst disk, or from

excessive temperature, through the use of a fusible plug. Most PRDs used on CNG vehicles

incorporate both types of protection.

3. "Natural Gas Fuel Tanks for Automobiles: Safety Problems," F.A. Jennings and W.R.

Studhalter, ASME paper 71-PVP-62, May 1971.

4. "Sparks from Steam," A.F. Anderson, Electronics and Power, January 1978. p. 50-53.

5. "Efflux of Gaseous Hydrogen or Methane Fuels from the Interior of an Automobile," J.M.

Arvidson, et al., National Bureau of Standards report COM-75-10288, March 1, 1975.

6. "Gas Quality Specifications for Compressed Natural Gas (CNG) Vehicle Fuel," in Gas

Quality, edited by G.J. van Rossum, (1986). p. 37.

7. "Determination of Arsenic and Arsenic Compounds in Natural Gas Samples," Kurt J.

Irgolic, Dale Spall, B.K. Puri, Drew Ilger, and Ralph A. Zingaro, Applied Organometallic

Chemistry, 5, 117-124 (1991).

8. "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.

9. "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.

10. See, for example, Fundamentals of Industrial Hygiene, Third Edition, National Safety

Council, (1988). p. 367.

11. "Guidelines for Visual Inspection and Requalification of Fiber Reinforced High Pressure

Cylinders, Compressed Gas Association publication CGA C-6.2-1988, (1988).

12. "Safety Information Profile Liquefied Natural Gas Usage in Industry," E.D. Pearlman and

G.W. Pearson, NIOSH report 124043, June 1981.
R-4

13. "LNG Safety Research in the U.S.A.," S. Atallah and A.L. Schneider, Journal of

Hazardous Materials, Vol. 8, pp. 25-42, 1983.

14. "Ignition Sources of LNG Vapor Clouds," D.J. Jeffres, N.A. Moussa, R.N. Caron, and

D.S. Allen, Gas Research Institute report GRI-80/0108, 1980.

15. See, for example, Fundamentals of Industrial Hygiene, Third Edition, National Safety

Council, (1988). P. 367.

16. "How Safe is the Storage of Liquid Hydrogen," by M.A.K. Lodhi and R.W. Mires,

International Journal of Hydrogen Energy, 14, 35, (1989).

17. "Tropane Over-filling Fires," Noel de Nevers, Fire Journal, September, 1987. p. 80.

18. "Evaluation of Aftermarket Fuel Delivery Systems for Natural Gas Vehicles and LPG

Vehicles," by B. Willson, NREL report NREL/TP- 420-4892, (1992).

19. See for example, Fundamentals of Industrial Hygiene, Third Edition, National Safety

Council, (1988). p. 367.

20. "Pressure Vessel Failure: Statistics and Probabilities," J.R. Engel, Nuclear Safety, Vol.

15, July 1974.

21. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A.

Machiele, SAE paper 901113 (1990).

22. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A.

Machiele, SAE paper 901113 (1990).

23. Fire rate data from "Heavy Truck Fuel System Safety Study," U.S. Department of

Transportation report DOT HS 807 484, September 1989. p. 52.

24. Perry's Chemical Engineers' Handbook, Sixth Edition, Robert H. Perry and Don Green, p.

23-29.

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

October 27, 1992.

26. "Automotive Methanol Vapors and Human Health: An Evaluation of Existing Scientific

Information and Issues for Future Research," Health Effects Institute report, May 1987.

27. "A Guide for Evaluating the Performance of Chemical Protective Clothing," Michael M.

Roder, NIOSH report, June 1990.

28. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A.

Machiele, SAE paper 901113 (1990).
R-5/R-6

 29. "Summary of the Fire Safety Impacts of Methanol as a Transportation Fuel," Paul A.

Machiele, SAE paper 901113 (1990).

30. Fire rate data from "Heavy Truck Fuel System Safety Study," U.S. Department of

Transportation report DOT HS 807 484, September 1989, p. 52.

31. Perry's Chemical Engineers' Handbook, Sixth Edition, Robert H. Perry and Don Green, p.

23-26.

32. Patty's Industrial Hygiene and Toxicology, 3rd revised edition, George D. Clayton and

Florence E. Clayton, (1982). p. 4541ff.

33. "Efflux of Gaseous Hydrogen or Methane Fuels from the Interior of an Automobile,"

J.M. Arvidson, et al., National Bureau of Standards report COM-75-10288, March 1, 1975.

34. Accident Prevention Manual for Industrial Operations, Ninth Edition, National Safety

Council, (1988). p. 377.

35. "Health Effects of Extremely Low-Frequency (50- and 60-Hz) Electric and Magnetic

Fields," Donald W. Zipse, IEEE Transactions on Industry Applications, 29, 447 (1993).

36. "Health Effects of Low-Frequency Electric and Magnetic Fields," Environmental Science

and Technology, 27, 42 (1993).

37. "Overview of Epidemiologic Research on Electric and Magnetic Fields and Cancer,"

David A. Savitz, American Industrial Hygiene Association Journal, 54, 197 (1993).

38. "Findings Point to Complexity of Health Effects of Electric, Magnetic Fields," Bette

Hileman, Chemical and Engineering News, July 18, 1994, p. 27.

 *U.S. GOVERNMENT PRINTING OFFICE: 1995-602-213/20010