^^11err ^"'*^'' ^^^^es Department of Commerce

I Al 1^91 National Institute of Standards and Technology

A111D3 M31373

NIST Technical Note 1279

Construction of an Exploratory List of

Cliemicais to Initiate tiie

Search for Haion Alternatives

William M. Pitts, Marc R. Nyden, Richard G. Ganrt,

W. Gary Mallard, and Wing Tsang
NATIONAL INSTITUTE OF STANDARDS &

TECHNOLOGY

Research Information Center

Gaithersburg, MD 20899

DATE DUE

(^^l-^77U iny^9'.

Demco. Inc. 38-293
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NIST Technical Note 1279

Construction of an Exploratory List of

Cliemicals to Initiate the

Search for Halon Alternatives

William M. Pitts, Marc R. Nyden, and Richard G. Gann

Rre Measurement and Research Division Center for Rre Research

and W. Gary Mallard arKJ Wing Tsang

Chemic^ Kinetics Division Center for Chemical Technology

National Institute of Standards and Technology

Gaithersburg, MD 20899

Sponsored by: U.S. Air Force Engineering Laboratory

Air Force Engineering and Services Center

Tyndall AFB, FL 32403-6001

Contract 89CS8205

August 1990

*'i»rES o« ^

U.S. Department of Commerce

Robert A. Mosbacher, Secretary

National Institute of Standards and Technology

John W. Lyons, Director
National Institute of Standards U.S. Government Printing Office For sale by the Superintendent

and Technology Washington: 1990 of Documents

Technical Note 1279 U.S. Government Printing Office

Natl. Inst. Stand. Technol. Washington, DC 20402

Tech. Note 1279

206 pages (Aug. 1990)

CODEN: NTNOEF
TABLE OF CONTENTS

Section Title Page

EXECUTIVE SUMMARY 1

I INTRODUCTION 5

A. OBJECTIVE 5

B. BACKGROUND 5

1. Halogenated Hydrocarbon Fire Suppressants (halons) 5

a. Definition and Designation 5

b. A Brief History 5

c. Current Use of Halogenated Fire Suppression Agents 8

2. The Search for Halon Alternatives 9

C. SCOPE/APPROACH 9

1. Nature of the Problem 9

2. Structure of the Research Program 10

3. Search Strategy 10

4. Report Philosophy 12

a. Breadth of Coverage 12

b. Report Structure 12

5. Relation of This Work to Other Efforts 13

II CURRENT UNDERSTANDING 14

A. COMBUSTION AND FIRE CONCEPTS 14

1. Definitions of Combustion and Fire 14

2. The Fire TViangle 14

3. Combustion and Fire Classifications 14

a. Flaming Combustion and Smoldering 14

b. Fuel Types 15

c. Premixed and Diffusion Rames 15

d. Laminar and Tlirbulent Combustion 16

e. Lean, Stoichiometric, and Rich Combustion 16

4. Basic Combustion Concepts 16

a. Thermodynamics 16

111
TABLE OF CONTENTS

(CONTINUED)

Section Title Page

b. Chemical Kinetics 17

c. Combustion Chemistry 18

d. Thermal balance 21

e. Propagation Rates of Premixed Flames 21

f. Flame Structure 22

B. INTRODUCTION TO FIRE SUPPRESSION 22

1. Relevant Reviews 23

2. Fire Suppression Mechanisms 23

a. Physical Fire Suppression Mechanisms 23

b. Chemical Fire Suppression Mechanism 24

c. Chemical Fire Suppression and Physical Cooling 24

3. Characterizations of An Agent's Rame Suppression Capabilities 25

a. Flame Chemistry and Flame Structure of Premixed Flames 25

b. Agent Effects on Flame Speed of Premixed Flames 25

c. Agent Effects on Premixed Flame Flammability Limits and Peak

Concentrations 26

d. Full Kinetic Modeling of Premixed Flames 27

e. Types of Diffusion Flames Used for Inhibition Investigations 28

f. Flame Chemistry and Structure of Inhibited Diffusion Flames 29

g. Extinction of Laminar Diffusion Flames 30

h. Extinction of Tlirbulent Diffusion Flames 31

4. Agent Effectiveness, Tfesting Methods, and the Role of Different

Suppression Mechanisms 32

a. Agent Effectiveness and Tfesting Methods 32

b. Contributions of Physical and Chemical Mechanisms to Fire

Suppression Effectiveness 32

c. Conclusions Regarding a Chemical Mechanism for Fire

Suppression 36

C HALON STABILITY AND DEPLETION OF STRATOSPHERIC OZONE 37

1. Stability and Properties of Halons 37

IV
TABLE OF CONTENTS

(CONTINUED)

Section Title Page

2. Brief Introduction to Atmospheric Structure and Chemistry 37

3. Current Commercial Halons and Depletion of Stratospheric Ozone 38

4. Means for Reducing ODP Values of Effective Firefighting Agents 39

III FAMILIES AND COMPOUNDS INCLUDED ON THE LIST 41

A. INTRODUCTION 41

B.

' SATURATED HALOCARBONS 41

1. Justification for Consideration 41

2. Past Flame-Suppression Measurements 43

3. Recommendations 44

a. Perfluoro Compounds 44

b. Photosensitive Compounds 45

c. Hydrogen-Containing Compounds 45

C. HALOGENATED KETONES, ANHYDRIDES AND ESTERS 49

1. Justification for Consideration 49

2. Past Flame Suppression Measurements 52

3. Recommendations 52

D. UNSATURATED HALOCARBONS 54

1. Justification for Consideration 54

2. Past Flame Suppression Measurements 54

3. Recommendations 55

E. HALOGENATED ETHERS AND RELATED COMPOUNDS 55

1. Justification for Consideration 55

2. Past Flame Suppression Measurements 57

3. Recommendations 57

F. HALONS CONTAINING IODINE 59

1. Justification for Consideration 59

2. Past Flame Suppression Measurements 60

3. Recommendations 61
TABLE OF CONTENTS

(CONTINUED)

Section Title Page

G. SULFUR HALIDES 61

1. Justification for Consideration 61

a. Parent Properties 61

b. Chemical Analogs 61

2. Past Flame Suppression Measurements 63

3. Recommendations 63

H. COMPOUNDS CONTAINING PHOSPHORUS 63

1. Justification for Consideration 63

2. Past Flame Suppression Measurements 65

3. Recommendations 65

L SILICON AND GERMANIUM FLAME INHIBITORS 68

1. Justification for Consideration 68

a. Family of Chemicals 68

b. Properties 68

2. Past Rame Suppression Measurements 68

3. Recommendations ,

70

J. METALLIC FLAME INHIBITORS 70

1. Justification for Consideration 70

2. Past Flame Suppression Measurements 71

a. Alkali Metal Inhibitors 71

b. Heavy Metal Inhibitors 73

3. Recommendations 74

K INERT GASES 75

1. Justification for Consideration 75

2. Past Flame Suppression Measurements 75

3. Recommendations 75

VI
TABLE OF CONTENTS

(CONCLUDED)

Section Title Page

IV CONCLUSIONS AND RECOMMENDATIONS 78

REFERENCES 80

APPENDIX

A DATA SHEETS FOR SELECTED COMPOUNDS 95

Vll
LIST OF TABLES

Tkble Title Page

1. Compounds with no Bromine or Chlorine 46

2. Photosensitive Compounds '. 47

3. Compounds with no Bromine 48

4. Compounds Containing Bromine 50

5. Current Commercial Halons 51

6. Halogenated Ketones, Anhydrides and Esters 53

7. Unsaturated Halocarbons 56

8. Halogenated Ethers and Related Compounds 58

9. Recommended Halons Containing Iodine 62

10. Recommended Sulfur Halides 64

11. Phosphorous-Containing Gases and Liquids 66

12. Recommended Phosphorous-Containing Compounds 67

13. Silicon and Germanium Flame Inhibitors 72

14. Metallic Inhibitors 76

15. Inert Gases 77

16. Complete List of Recommended Compounds 79

viu
EXECUTIVE SUMMARY

The objective of this project is to initiate a systematic search for optimal halon replacements by

identifying approximately 100 gases and/or liquids, covering a range of chemical and physical principles thought

to affect flame suppression capability. This comprehensive report is designed to provide a basis for the search

for alternatives to the current commercial halons. As much detail as possible is provided for each of the 103

chemicals to aid researchers who might test or evaluate these chemicals in the future.

The current commercial halons have been identified as contributing to the depletion of the earth's stratospheric ozone. As a result, their manufacture has been limited to 1986 levels by the Montreal protocol,

and more severe limitations are anticipated in the near-future. This project is an early step in a

government/industry program to identify and qualify candidate replacements for halons 1301 and 1211 that

will satisfy the needs of the major users for existing applications. No such search has been conducted since

the late 1940s, when the U.S. Army conducted the study that led to today's predominant halogenated fire suppressants: halons 1301 (CFjBr) and 1211 (CF2ClBr). Halon 2402 (C^F^Brj) is in use to a lesser degree,

as are halons 1001 and 1011.

Replacements for the current halons must have a number of critical properties: fire suppression

efficiency, low residue level, low electrical conductivity, low metals corrosion, high materials compatibility,

stability under long-term storage, low toxicity (inhalation and contact) of the chemical and its combustion

products, and low (or zero) contributions to stratospheric ozone depletion and global warming. These

constraints are expected to complicate the search.

The search strategy selected by the National Institute of Standards and Technology (NIST) team

focusses on principles for efficient fire suppression and low contribution to stratospheric ozone depletion. The

widest range of chemical families were researched for their potential to test these principles. Some of these

families have not previously been considered for fire suppression. Compounds are discussed which are clearly

not candidates as alternatives, but which are included to test principles of fire suppression or ozone depletion.

As a basis for deriving these principles, this report begins with a compilation of state-of-the-art knowledge in flame suppression and ozone depletion chemistry. The means by which a chemical can quench

a flame fall under the following headings:

• Physical mechanisms

• smothering or blanketing

• cooling and dilution

• mechanical means (e.g., blowing out a match)

• flame radiation blockage

• Chemical action (interference with the chain reactions that propagate flames)

All agents have physical effects on a fire. Agents which also have a chemical mechanism, such as the

currently-used halons, are more effective due to the additional pathway for flame suppression. There have

been several studies of the effectiveness of specific chemicals. Very few of those separate the contribution of

physical and chemical mechanisms.

The means for altering a chemical to decrease its contribution to ozone depletion also fall under a few headings:
• Elimination of all bromine, chlorine, and iodine atoms;

• Increased reactivity in the lower atmosphere by

• enhanced reaction with OH radicals

• dissociation due to absorption of solar radiation

• enhanced rain out due to increased polarity

Assessment of ozone-depletion effectiveness is based on atmospheric modeling. The only experimental

work is the determination of possible reaction paths and their rates.

An extensive search was performed of the literature on combustion suppression, flame inhibition, and

fire retardancy. This led to the identification of nine families of chemicals with potential for workbench testing

of the above principles.

Saturated halocarbons or halons: (C„FqC1 Br I^ where o+p+q-l-r=2n+2). These are analogs

of the currently-used halons and include totally fluorinated compounds, photosensitive

compounds, and analogs to the HCFCs.

Halogenated ketones, anhydrides, and esters. These contain C=0 bonding and may be more

prone to solar dissociation in the troposphere.

Unsaturated halocarbons. These contain C=C bonding and may be more reactive with OH

in the troposphere.

Halogenated ethers. These contain an O-C-O linkage, which is thought to promote solar

dissociation in the troposphere.

Halons containing iodine. These are likely to be more reactive in the troposphere.

Sulfur halides. These are analogs to the halons.

Compounds containing phosphorus. These are non-ozone-depleting, possibly highly efficient

fire suppressants,

Silicon and germanium compounds. These are tropospherically-reactive analogs to the

halons.

Metallic compounds. These are extremely efficient fire inhibitors that are non-ozone-depleting.

Inert gases. These are baseline chemicals: less-efficient, only physically active agents with zero ozone-depletion potential.

While it is true that some of the chemicals which appear on this list can be considered candidates

themselves, others were chosen to test principles of fire suppression. The appendix contains data sheets for
A list of 103 chemicals which were selected from these families follows:

perfluoromethane

perfluoroethane

perfluoropropane

perfluoro-n-butane

perfluorocyclobutane trifluoromethane pentafluoroethane

1,1,1,2-tetrafluoroethane dibromodifluoromethane

2,2-dibromo-l,l,l,2-tetrafluoroethane chlorodifluoromethane

1 ,1 4-trichlorethane

2,2-dichloro-l,l,l-trifluoroethane 2-chloro-l ,1 ,1 ,2-tetrafluoroethane

1,1-dichloro-l-fluoroethane

l-chloro-l,l-difluoroethane

bromodifluoromethane

bromochlorofluoromethane

2-bromo-2-chloro-l ,1 ,1 -trifluoroethane 2-bromo-l -chloro-1 ,2,2-trifluoroethane

1 -bromo-1 ,1 ,2,2-tetrafluoroethane 2-bronio-l,l,l-trifluoroethane

1 ,2-dibromo-l ,1 ,2-trifluorc)ethane l,2-dibronio-l,l-<iifluoroethane

1 ,2-dibromo-l ,2-difluoroethane

l-bromo-l,l,2,3,3,3-hexafluoropropane

l,3-dibromo-l,l,3,3-tetrafluoropropane

2,2-dibromo-l ,1 ,3,3-tetrafluoropropane

l-bromo-l,l,3,3.3-pentafluoropropane

hexafluoracetone

trifluoroacetic anhydride

bis(perfluoroisopropyl) ketone

methyltrifluoroacetate

3-bromo-l ,1 ,1-trifluoropropanone

bromopentafluoroacetone

bromomethyltrifluoroacetate

perfluoropropene

perfluorobutene-2

perfluorotoluene

1,1,3,3,3-pentafluoropropene-l

3,3,3 trifluoropropene

1 ,2-bis(perfluoro-n-butyl)ethylene

3-bromoperfluoropropene

1 -bromoperfluoropropene

l,2-bis(perfluoromethyl)ethylene

l-bromoperfluoromethyl-2-perfluoromethylethylene

l-bromo-bis(pernuoromethyl)ethylene

tetris(perfluoromethyl)ethylene

tetrafluorodimethyl ether pentafluorodimethyl ether

2-chloro-l -(difluoromethoxy)-l ,1 ,2-trifluoroethane

isoflurane

perfluoro-2-butyltetrahydrofuran

bis(bromodifluoroethyl) ether

l-bromo-l,l,3,3,3-pentafluorodimethyI ether bromoenflurane

octafluorofuran 3-bromoperfluorofuran

bis(perfluoroniethyl) thioether

tris(perfluoroniethyl) amine

iodotrifluoromethane chlorodifluoroiodomethane

1 -bromo-1 ,1 ,2,2-tetrafluoro-2-iodoethane

l,l,2,2-tetrafluoro-l,2-diiodoethane

iodomethane

iodoethane 1-iodopropane

l,l,l,2,2,3,3-heptafluoro-3-iodopropane

sulfur fluoride

sulfur chloride fluoride

sulfur bromide fluoride phosphorous trifluoride phosphorous trichloride phosphorous bromide difluoride phosphoryl fluoride phosphoryl chloride phosphoryl bromide fluoride tetrachlorosilane

trichlorofluorosilane

tetrafluorosilane bromotrifluorosilane

tribromofluorosilane

tetramethylsilane

chlorotrimethylsilane

trichloromethylsilane

chloromethyltrimethylsilane

tetrachlorogermane

tetramethylgermane

sodium hydrogen carbonate sodium acetate potassium hydrogen carbonate

potassium oxalate potassium acetate potassium acetylacetonate

chromium acetylacetonate

chromyl chloride

tin (IV) chloride titanium (IV) chloride

tetraethyl lead

iron pentacarbonyl

nitrogen carbon dioxide argon
each of the selected compounds that include formulae, common names, classification numbers, physical properties, commercial sources and prices (if available), toxicity information, references to fire suppression results,

and additional relevant comments.

These compounds should be tested in a selective series of experiments based on the insights used in the development of the list. The study should determine the fire suppression effectiveness of these agents, and,

if possible, characterize their mechanisms of chemical flame inhibition. Such insights will provide the

knowledge base required for the intelligent design of alternative chemical fire suppressants with a full range

of desirable properties.

The authors appreciate the sponsorship of this project by the Engineering and Services Laboratory,

Air Force Engineering and Services Center, Capt. John M. Floden, Contract Monitor. The review provided

by the Halon Alternatives Research Corporation, chaired by Ms. Denise Mauzerall, was extremely helpful The

final copy of this report was prepared and edited by Ms. Paula Garrett
SECTION I

INTRODUCTION

A. OBJECTIVE

The objective of this project is to identify approximately 100 gases and/or liquids, covering a range

of chemical and physical principles thought to affect flame suppression capability. This project is part of an

overall effort to identify safe and effective fire suppression agents which are less detrimental to stratospheric ozone than thp current commercial halons. A major element in the choice of compounds is also understanding

the processes by which halons deplete stratospheric ozone. The list of compounds includes as much relevant

information as possible to aid researchers who will use the findings of this work in the search for new flame

suppressants.

B. BACKGROUND

1. Halogenated Hydrocarbon Fire Suppressants (halons)

a. Definition and Designation

Halogenated hydrocarbon fire suppressants refer to a group of chemical compounds

widely used for firefighting and inerting (creation of an atmosphere which does not support combustion). The

compounds denoted as halons contain one or more halogen atoms^ attached to a backbone of one or more

carbon atoms. Only straight chain, fully saturated (each carbon atom is bonded to four other atoms)

compounds are included.

A simple nomenclature developed by the United States Army Corps of Engineers is widely employed to designate halons [1]. A particular halon is assigned a "halon number" where, reading from

left to right, the first number is the number of carbon atoms and the remaining four numbers are the number

of each halogen atom in order of increasing atomic weight, i.e., F, CI, Br, and I. Any terminal zeros are dropped. As an example, trifluorobromomethane, CF3Br, is denoted as halon 1301. Note that some

inconsistencies are possible when two or more carbon atoms are present. Consider CBr2HCBr2H and

CBr3CBrH2. Both of these molecules would be designated as halon 2004.

b. A Brief History

Ford [2] has provided a brief perspective on the historical development of halons for

firefighting purposes. Carbon tetrachloride (halon 104) was the first halon to be used. Starting in the early

1900s and continuing until the mid-1960s, fire extinguishers containing this liquid were commercially available. In the late 1920s, methyl bromide (halon 1001) was found to be much more effective for fire-extinguishment.

Because of its high toxicity, this compound was never widely utilized in the United States. It was employed

^The five halogen atoms are: fluorine (F), chlorine (CI), bromine (Br), iodine (I), and astatine (At).

Astatine is very scarce and will not be considered further in this work.
militarily during Worid War II by the British (aircraft extinguishing systems) and Germans (aircraft

extinguishing systems and marine systems) [1].

During World War II the Germans developed a fire-extinguishing agent known as "CB," chlorobromomethane (halon 1011), which was as effective as halon 1001 and less toxic. This agent was

ordered to be installed on all German military aircraft, but apparently did not come into widespread use before

the end of the war [1].

Following the war, the German research efforts were reviewed by the United States

military; and, CB was extensively tested in this country [3]. CB was eventually adopted for use by the United

States Air Force [4]. Despite the improvements represented by CB, it was recognized that significant

toxicological problems remained and that fire suppression capabilities might be further refined. As a result,

the Air Force [1] and the U.S. Army Corps of Engineers [5,6] began extensive testing of a wide range of

possible compounds. These projects considered a number of possible firefighting agents, but the principal

focus was the halons.

The requirements for a new agent specified by the agencies are instructive because

they generally apply to so-called "clean" firefighting agents. Klein [1] lists the Air Force requirements as:

1. better extinguishing properties than CB over the temperature range of - 54°Cto7rC,

2. less toxic than CB,

3. less corrosive than CB,

4. suitable for class A, B, and C fires^, and

5. higher specific gravity than CB.

The Corps of Engineers' specifications [6] were similar. The agent was to be:

1. less toxic than carbon tetrachloride,

2. less corrosive than carbon tetrachloride,

3. a nonconductor of electricity,

4. stable when stored for five years in any climate, and

5. suitable for use over a temperature range of -54° C to Tl^C.

These investigations identified four halons as being particularly promising [2]: trifluorobromomethane (halon 1301), bromochlorodifluoromethane (halon 1211), dibromodifluoromethane

(halon 1202), and dibromotetrafluoroethane (halon 2402). Halons 1301 and 1211 have since been developed

and are utilized for a large number of applications. Halons 1202 and 2402 are also used, but less extensively.

^Fires are classified by the type of fuels and conditions present. Class A fires involve cellulosic materials

such as wood or paper. Class B fires refer to liquid fuels such as hydrocarbons and alcohols. Fires where

energized electronic components are present are denoted as Class C fires. If metal fuels such as sodium or aluminum are present, the fire is a Class D fire.
In this text these four halons will be denoted as "the current commercial halons" to differentiate them from

the broader halon and halogenated organic molecular families. In the literature, the current commercial

halons are often denoted simply as "halon."

Since the 1950s, the current commercial halons have come into widespread use for

firefighting and fire protection systems. The military uses these compounds extensively in a number of

mission-critical areas. Similarly, current commercial halon systems have been incorporated into a number of

civilian uses where costly or irreplaceable facilities, equipment, or items must be protected from fire. By 1985,

the production and use of these halons in the United States had reached 6.4 x 10^ kg [7]. Halon systems are

generally regarded as reliable, safe, and effective. As such, they have become an integral part of fire protection

practice.

Unfortunately, a major issue has arisen which threatens to curtail, if not eliminate use of the current commercial halons. This issue has been discussed extensively in the literature. A

chronological summary of major events in this area has been compiled by S. Daws [8]. Anderson [7] and

Grant [9] provide excellent histories of the problem and prospects for future halon usage. A brief history is provided here to illustrate the nature of the problem and the suddenness with which it arose.

In 1974, Molina and Rowland [10] hypothesized that the release of chlorine by

photolysis of manmade chlorofluorocarbons (CFCs) in the stratosphere would result in a reduction of the ozone concentration which shields the earth's surface from the sun's harmful ultraviolet radiation. By 1978,

the use of CFCs as propellants for aerosols was banned in the United States for all but essential uses.

From 1978 to 1985, the movement of the global community toward the control of

CFCs was very deliberate. This changed with the publication of results of ground-based observations indicating a 40 percent depletion of stratospheric ozone above the Antarctic at certain times of the year-the "ozone hole"

[11]. Satellite observations confirmed this to be a regional effect [12]. World-wide decreases in stratospheric ozone have since been detected [13]. By 1988, there was sufficient evidence for most scientists to conclude

that stratospheric ozone depletion has occurred as a result of ozone reactions with CI and Br atoms introduced

into the stratosphere by manmade CFCs and current commercial halons [13].

In September of 1987, the Montreal Protocol was signed by the United States,

Canada, members of the European Economic Community, and 23 other countries. This accord set limits on

the production of CFCs and halons 1211 and 1301 in an effort to limit further destruction of stratospheric ozone. Initial discussions had focused primarily on the CFCs, but in the final document, production of the

two halons is limited to their 1986 levels. Note that the limits require a cut in manufacture because

production has increased significantly since 1986. The protocol was effective as of January, 1989 and limits go into force in January, 1992.

Since the signing of the Montreal Protocol, evidence has continued to mount that halons contribute significantly to stratospheric ozone depletion. The current commercial halons are now

recognized as being 3 to 11 times more destructive of stratospheric ozone on a molecule-per-molecule basis

than the common CFCs due to the presence of bromine atoms in these fire suppressants [14]. It has been

hypothesized that Br atoms can have even larger effects on ozone levels through a synergistic interaction with more abundant CI atoms [15,16]. A recent study also suggests that atmospheric concentrations of halons 1211

and 1301 are increasing at annual rates of 12 percent and 5 percent, respectively [17]. These rates are much

higher than previously believed.

These recent findings suggest that future accords may demand larger cuts in halon

production than those mandated by the Montreal Protocol. During 1989, two bills were introduced in the

United States Senate designed to limit the production of current commercial halons to levels lower than called

for by the Montreal Protocol. The first mandates limiting production at 1986 levels as of July, 1989, with a
20 percent cut in 1992, a 50 percent cut in 1995, and a total ban in 1997. An exemption is provided for halon

uses essential to national security needs. The second bill would place a surcharge on halons in 1992 of $1.50

per pound multiplied by the chemical's ozone depletion potential. For halon 1301 this would amount to approximately $15 per pound [9].

Future fire protection will, at a minimum, be considerably more expensive and more

carefully controlled. It is also possible that all production of the current commercial halons will be halted and

that the world will be dependent on supplies which have been stored or "banked" for fire protection

requirements. Grant [9] refers to the current uncertainty concerning the future of halons as "one of the most

challenging problems ever to confront the fire protection community."

c. Current Use of Halogenated Fire Suppression Agents

The current commercial halons are rapid and effective fire inerting agents and

suppressants. They have low toxicity at ambient temperatures (note that the toxicity of combustion products

resulting from the use of halons is treated as a separate issue to be discussed in Section I-C-3) so that they can be effectively used in the presence of people. In addition, these compounds: are available as both liquids

and gases and can therefore be used either as streaming or flooding agents; they are clean, leaving little or no

residue (with the possible exception of combustion products); they are nonconductive, so that they can be

applied safely to energized electronic equipment; and they are compatible with a wide variety of plastics and

metals.

The three most commonly used halons, 1301, 1211, and 2402, have physical properties

which are compatible with two distinct modes of deployment. Halon 1301 is a gas at ambient temperatures

and is most often used in "total flooding" applications. The gas is introduced into an enclosure or space at

levels sufficient to suppress fires and prevent further ignition. Halon 2402 is a low-boiling-point liquid at normal room temperatures. As such, it is an ideal streaming agent for local application, which is its most

common use. Halon 1211 has physical properties which are intermediate between 1301 and 2402 and has been

used much the same as halon 2402.

The proceedings of a meeting held by the National Academy of Sciences cites many

examples of where halons have been used [18]. The most important of these are facilities where "clean" agents

are required and situations where personnel must remain during fire emergencies.

"Clean" fire extinguishing agents are often used when costly and/or irreplaceable

objects are present. Libraries, museums, and archives of important national documents are examples of

facilities which are currently protected by halon total-flooding extinguishment systems. Extinguishing agents

such as water or dry powders would be very damaging in these environments. Clean agents are also required

where other alternatives would interfere with important functions of a facility or device. Many computer

facilities, electronic record depositories, and telephone exchanges are protected by current commercial halon

total flooding systems. In this context, the lack of electrical conductivity is also crucial. Additional examples

include the mission-critical use of these halons on Air Force flight lines to combat aircraft and hangar fires and their use to fight nacelle fires in both civilian and military jet engines.

There are also circumstances when the evacuation of personnel during a fire emergency is not feasible. Control rooms of nuclear reactors and aircraft carriers are examples of facilities that must be staffed even after deployment of an extinguishing agent. Numerous mission-critical military

situations have the same requirement. Current commercial halon systems are employed to protect groundbased radar and military command and control centers, such as those on Navy ships, as well. Similar systems,

which are designed to suppress fires and explosions in armored vehicles during combat, are also in place.
The use of the current commercial halons for the requirements mentioned above, as well as numerous others, has become very widespread during the past two decades. Fixed suppression systems

number in the thousands. There are even more portable extinguishers in use, making halons an integral part

of fire protection engineering. As such, they currently play a crucial role in the protection of national resources and national security of the United States. The same is true for other industrialized countries.

2. The Search for Halon Alternatives

The discussion in the last section suggests that the manufacture of the current commercial

halons is likely to be phased out by the year 2000. On June 21, 1988, E.I. du Pont de Nemours & Co., a major

manufacturer of halon 1301, announced plans to initiate just such a phaseout [9]. Other companies have

announced that production will cease as soon as safe alternatives are available [19].

The fire protection community has recognized the seriousness of the situation. In 1987, an

International Halon Research Project (IHRP) was initiated under the auspices of the National Fire Protection

Research Foundation to conduct collaborative research [9]. The IHRP has released two reports [20,21]

designed to be first steps toward reducing releases of halon 1301 into the atmosphere. A project designated

as the "Best/Essential Use Project" was initiated by IHRP at the beginning of 1989. This project is designed

to identify applications where commercial halons are currently employed which can use alternative fire protection methods [9].

Some essential fire protection needs cannot be met by existing alternatives to the current commercial halons. Users of such systems have recognized the seriousness of the situation and have begun

to take action. Organizations are being formed to guide the search for alternatives which are effective fire suppression agents and have other desirable properties of the current commercial halons, but which do not

pose a significant threat to stratospheric ozone.

One of the first steps in this process was a meeting organized by the United States Air Force

and the Environmental Protection Agency, which was held at lyndall Air Force Base in late 1988 [22,23].

Numerous presentations were made delineating the problems faced, establishing the current understanding,

and identifying available resources. The participants recognized the need for the development of new agents

and a cooperative effort between private and public research interests was suggested as a mechanism for accelerating the development of new chemicals. Recommendations were provided for research areas to serve

as the basis of a comprehensive plan.

During the past year, the Halon Alternatives Research Corporation (HARC) was established

by the private sector to foster efforts to develop alternatives. A government working group has been formed

to serve as liaison between HARC and Federal agencies. Efforts are moving forward to implement an effective research plan. Reference [19] discusses these efforts.

In the meantime, a comprehensive research plan for identifying suitable replacements for the current commercial halons has been formulated by an ad hoc technical committee as an outgrowth of the

lyndall meeting [24]. The project described in this report is an element of this plan.

C. SCOPE/APPROACH

1. Nature of the Problem

The current commercial halons are likely to become prohibitively expensive or totally

unavailable for fire suppression and inerting purposes by the year 2000. There is a clear requirement for
replacement chemicals which have the following properties: fire suppression effectiveness, low toxicity, low

residue, favorable physical properties, low electrical conductivity, and materials compatibility. At the same

time, these chemicals must be far less destructive to stratospheric ozone than the halons which they are expected to replace. Unfortunately, since the current commercial halons were thought to possess ideal

properties, there have been very few research efforts since the late 1940s designed to identify alternatives. The

last wide-ranging study was that carried out by the Purdue Research Foundation [25] during the late 1940s

with support from the U.S. Army Engineers Research and Development Laboratories. (Even this study

focused primarily on fully halogenated compounds.) As a result, very little research infrastructure and

scientific expertise exists for the search.

As discussed in Section II.C.l, the unusual chemical stability of the halons contributes to their

effectiveness as fire extinguishing agents. Unfortunately, it is this same chemical stability which allows these

chemicals to pass unreacted through the earth's troposphere and penetrate the stratosphere. The culmination

of this process is the catalytic destruction of stratospheric ozone by bromine atoms which are produced in the

photolysis of halons (see discussion in Section II.C.3). The development of new fire suppression agents which

have the desirable properties of the current commercial halons but which are less harmful to stratospheric ozone will probably require careful balancing of chemical reactivity behavior. Principles need to be developed

to identify the best possible alternatives.

1\vo general search strategies for alternatives are immediately obvious. One approach is to consider chemical modifications of the commercial halons such that their fire suppression capability is maintained, but their atmospheric reactivity is increased to the point where transport to the stratosphere is minimized. The second approach is to identify completely different chemical families which offer the required

characteristics. A wide-ranging search must incorporate both approaches.

2. Structure of the Research Program

Under U.S. Air Force sponsorship, the National Institute of Standards and Tfechnology (NIST)

has undertaken to identify approximately 100 compounds covering a range of chemical and physical properties

believed to affect flame suppression capability. Following a thorough literature search, NIST staff members

have devised a strategy for identifying these compounds. This report serves to document the existing

knowledge of fire suppression, the search strategy employed, and the physical and chemical properties of the

compounds which have been chosen for consideration.

3. Search Strategy

The first priority of this project was to define the boundaries for the search. No systematic

search for new flame suppressants has been done since the late 1940s. We did a thorough literature search

to define the current understanding of flame suppression. This understanding serves as the foundation for the

remainder of the project.

The next task was the identification of chemical families to be considered. The decision was made to consider as wide a range of chemical families as possible. As a result, chemicals which have been

investigated in the past for fire suppression effectiveness were identified and assessed. The search was then

expanded to include classes of chemicals which have not been considered for fire suppression purposes

previously.

Several different approaches were possible for the search. One was to identify the compounds

offering the best possibilities as short-term alternatives for the current commercial halons. The project team

quickly realized that the existing knowledge of fire suppression, ozone depletion, toxicity, and other physical

propCTties was insufficient. An alternate strategy was to choose compounds in such a manner that the

10
principles necessary for the selection of alternatives for the current commercial halons would be tested. These

principles would then be available to guide future work. An intermediate path was ultimately chosen. As a

result, the final list of compounds contains members which are likely to be among those agents chosen in the near future for further testing as alternatives for the current commercial halons. At the same time, other

molecules which are definitely not suitable for replacing these halons are included to allow the development

of the principles required to guide the search for the best possible alternatives. This approach facilitates both

short- and long-term efforts to find the best possible alternatives for the current commercial halons. The

intention was to develop a broad base of knowledge to aide researchers and manufacturers in responding to future changes in the regulatory environment.

Next, we decided upon a method to weight the various properties which make the current commercial halons so effective for fire suppression purposes. These properties are listed in the first paragraph

of this section. We decided to focus on two:

• fire suppression and inerting, the principal functions of these agents; and

• stratospheric ozone impact, the principal reason the future of these chemicals has come into question.

The project team realized that the decision to focus on fire suppression and ozone depletion

required that several other important characteristics be deemphasized. Perhaps the most crucial of these is toxicity. Clearly, one of the most important characteristics of existing agents is that they can be deployed

effectively in the presence of people. This is a result of their relatively low toxicity. Unfortunately, toxicity

cannot be predicted confidently from chemical structure. Generally, the toxicity of a particular chemical is determined by a battery of expensive and time-consuming tests. The approach taken for this study is to report

existing toxicological data for compounds included on the final list, but not to attempt to predict the

toxicological behavior of compounds for which no previous studies are available.

Some general guiding principles for toxicological behavior are known (e.g., compounds

containing fluorine tend to be less toxic than their iodine analogs) and have been incorporated into discussions

of the chemical families which appear later in the report. Compounds which are known to be toxic, and in some cases highly toxic, are included on the final list. These compounds are not considered to be viable

alternatives for the current commercial halons (even though certain limited uses as fire suppressants are

possible for some) but are included to test principles of fire suppression or ozone depletion.

The toxicity referred to above is that for the chemicals themselves. Another important

consideration is the toxicity of decomposition products which results from the deployment of an agent on fires or in other heated environments. Numerous discussions of this topic (e.g., references [6,26,27,28,29,30,31,32])

with regard to the current commercial halons indicate that hydrogen halides, halogens, and other halogenated

compounds are formed. All of these compounds are noxious and toxic at relatively low levels. These species can also damage a wide range of materials and cripple electronic equipment.

These dangerous combustion products do not usually pose serious toxicological and materials

problems when the current commercial halons are deployed for fire suppression. This observation is traced

to the effectiveness of these fire extinguishment agents. If properly applied, the fire is extinguished so rapidly

that only small concentrations of these products are created [27,29,31]. Observed levels of fire products

attributable to the use of these agents are usually not dangerous. Certain situations involve exposure of the current commercial halons to deep-seated fires [28] or hot appliances [31] where high levels of noxious gases can be formed by decomposition of the agents. Conditions where the combustion products resulting from

usage of the current commercial halons pose a realistic danger have not been investigated extensively and no

quantitative results were identified during the literature search.

11
The combustion products generated by the application of alternative compounds are not likely to be more toxic than those generated by the use of the current commercial halons. It is further assumed that

any replacement agents will have roughly similar fire suppression effectiveness. On this basis, it can be

concluded that toxic products generated by the use of alternatives will not represent a more significant threat

than those resulting from the use of the current commercial halons. While recognizing that a potential

problem exists, the likelihood of producing toxic products during fire suppression has not been considered in choosing the chemicals included on the list.

Ideal alternatives for the current commercial halons would be "drop-in" agents. In other

words, the physical and materials compatibility of the replacements would be such that they could be used in existing halon suppression systems. This criterion is much too confining for a wide-ranging search for

alternatives. Some general selection of physical properties is enforced by requiring that compounds on the

list be gases or easily vaporizable liquids, but compatibility with current commercial halons is not included as a criterion. Even the simple requirement of being a liquid or gas is waived for a few compounds.

Generally, compounds which are gases or vaporizable liquids will leave no residue if pure. The electrical conductivity of most gases and liquids is low, but no attempt has been made to consider this property in the search strategy. Materials compatibility is very important for the design of practical fire suppression systems. Nonetheless, it was decided that consideration of this property should also be deferred

and it was not used as a criterion for including compounds on the list.

4. Report Philosophy

a. Breadth of Coverage

This project is intended to be comprehensive. The current understanding of fire suppression and ozone depletion is utilized to choose approximately 100 compounds for testing purposes. A

summary of this understanding is provided to give the reader the needed background to evaluate the basis for recommendations which are made. Large numbers of references to original literature are provided to allow

readers to obtain additional details. We have generated a detailed report which we hope will capture the current understanding of the problem, give clear explanations of approaches utilized in the study, and provide a comprehensive document which can serve as the basis of the search for alternatives to the current commercial

halons. As much detail as possible is provided for each chemical species included on the list to aid researchers

who might test or evaluate these chemicals in the future.

b. Report Structure

The report is divided into 4 major sections. This section began with a statement of

the objective of this study. Next, the properties of the current commercial halon fire extinguishing agents were enumerated with regard to their composition, historical development and uses. In the following subsection,

the relationship of this project to other ongoing efforts is discussed.

Section II is devoted to providing an overview of relevant areas of combustion science.

Included are descriptions of the current understanding of fire suppression mechanisms, various approaches

which are utilized for testing flame suppression effectiveness and a brief introduction to the mechanisms by

which the current commercial halons are thought to contribute to the depletion of stratospheric ozone.

Section III is divided into subsections corresponding to the chemical families which were considered in this investigation. Ajustification for including each chemical family, as well as a discussion

12
of previous tests of family members for fire suppression effectiveness, is presented. Recommended compounds

from each chemical family are tabulated, along with relevant properties, following each subsection.

The conclusions of this investigation are presented in Section IV along with the

complete exploratory list of chemical alternatives. Separate data sheets for each of the compounds on this

list are included in an appendix.

5. Relation of This Work to Other Efforts

The Engineering & Services Laboratory of the U.S. Air Force is funding a number of research

efforts related to usage of current commercial halons and alternatives. The goals are to provide a short-term

reduction in halon releases and a long-term solution to the problem by identifying appropriate alternatives

for training and use. An effort has been underway at the New Mexico Engineering Research Institute (NMERI) for several years [33]. This program has primarily considered means for reducing releases of the

current commercial halons to the atmosphere and the replacement of these halons with close chemical

relatives and mixtures.

The National Institute of Standards and Tfechnology (NIST) is performing three projects-

"Construction of an Exploratory List of Potential Replacements for halons 1211 and 1301," "Preliminary

Screening Procedures and Criteria for Replacements for halons 1211 and 1301," and "Halon Candidate Agent

Database." The team members of these three projects have interacted closely so there is a great deal of

coordination between these efforts.

It is anticipated that the compounds included on the master list will be passed through the

preliminary screening procedures under development at NIST. This initial screening will serve as a highly

effective test of the screening process and will generate initial information with regard to the relative ordering

of the compounds in terms of screen properties. Careful experimentation will be required to more fully

develop the fire suppression and ozone-depletion principles which the list of compounds has been explicitly

chosen to test and verify.

The database project has been the source for many of the physical properties included in this report. At the same time, many of the compounds identified in the current research effort will be included

in the database. Some of the findings of the literature search for this work will also be added to the database.

The United States Environmental Protection Agency is funding a project entitled

"Examination of Fire Types" which is being performed by Factory Mutual Research Corporation of Norwood,

MA. This project is designed to identify the classes of fires for which the current commercial halons are used

and recommend generic fires for testing purposes. The results of this project will be used for practical fire testing of compounds identified as the most likely candidates as alternatives for the current commercial halons.

13
SECTION II

CURRENT UNDERSTANDING

A. COMBUSTION AND FIRE CONCEPTS

This Section reviews the fundamental concepts of combustion and fire required for understanding the

discussion on fire suppression and inerting as well as the literature discussed during the remainder of the

report. The approach taken is intentionally introductory and many details are omitted. Any of several excellent texts on these subjects (e.g., [32,34,35,36,37]) can be consulted for more in-depth treatments.

1. Definitions of Combustion and Fire

"Combustion" and "fire" have general meanings which are recognized by everyone. At the same time it is difficult to provide specific definitions. For the purposes of this report, combustion will be

defined as "a rapid and persistent chemical reaction which combines fuel and oxygen to produce heat and

light." The quotation is adapted from an introductory book by Cottrell [38].

The above quotation was provided by the author to define fire and not combustion.

Generally, a more restrictive definition, such as that provided by Berl [39], is used for fire. Fires are "special cases of combustion where the addition of fuel and oxidizer to a flame is not under human control" [39]. The

class of fires of interest for this report are uncontrolled and unwanted fires. These fires are generally harmful,

destructive, and/or dangerous.

2. The Fire Ttiangle

The fire triangle is an introductory concept often employed to remind readers of the three

conditions which must be present simultaneously for combustion to take place and sustain itself. These

requirements are fuel, oxygen, and heat. These are often drawn along the sides of a triangle to emphasize that

all three are required.

The fire triangle also provides insights into how fires can be suppressed. If any of the sides

of the triangle is removed, the fire will be extinguished. This will become clearer in the section on

extinguishment mechanisms.

3. Combustion and Fire Classifications

Numerous methods are used to classify types of combustion and fire. A few of these are mentioned to provide background and nomenclature for the discussions which follow.

a. Flaming Combustion and Smoldering

1\vo types of combustion are common in fires. The first is known as flaming

combustion and involves chemical reactions occurring primarily in the gas phase. The name arises from the

fact that the combustion is characterized by the emission of visible and infi'ared (heat) electromagnetic

radiation by the fire. These emissions are the means by which a person often detects the presence of a fire. The visible radiation is either (a) emission from electronically excited chemical species formed as the result

14
of the chemical reactions or (b) thermal radiation from small particles (soot) located in regions of high

temperature which obey Planck's black body radiation law.

The second type of combustion is only important for burning solids such as wood or

plastics and involves chemical reactions occurring directly at, or near, the surface within a solid. These are heterogenous reactions since the solid surface reacts directly with oxygen from the surrounding gases. This

process is known as smoldering.

Flaming combustion is usually more vigorous and generates higher temperatures than

smoldering. As a result, flaming combustion is often more dangerous and poses a more immediate threat. On the other hand, smoldering can generate significantly higher concentrations of toxic gases than flaming

combustion (this depends on oxygen availability) and can be more difficult to extinguish. Smoldering often

evolves into flaming combustion.

b. Fuel Types

One example of fire classification based on fuel type is given in the footnote at the

bottom of page 2. This scheme is employed to allow people who must control these types of fires to rapidly

identify a fire class and to determine the best available means for fireflghting.

Combustion processes can also be classified based on the normal state-gas, liquid, or solid-of the fuel. This classification is important because it determines the mechanisms by which the fuel

is made available for flaming combustion. Note that liquids and gases do not support smoldering combustion

under normal conditions.

For gases, the fuel is provided directly to the combustion region. An example is the

flow of natural gas to a laboratory Bunsen burner. The supply of gaseous fuel is determined simply by the gas flow rate.

Liquid fuels are considerably more complex. Burning conditions for liquid fuels can

vary. As an example, consider the common configuration of flaming combustion occurring above a pool of

the liquid fuel. The gaseous fuel results from vaporization from the liquid surface, and the fuel supply rate

is determined by the rate of fuel vaporization and the surface area of the pool. The vaporization rate per unit area is highly sensitive to the liquid temperature and the radiation flux from the fire. Since flaming

combustion can heat the liquid by thermal conduction, convection, and radiation, it is possible for the flames

to affect the vaporization rate, and the fire can therefore influence its own behavior.

Combustion involving solid fuels is by far the most complicated. Here, the heat

feedback from the overhead flames is crucial for generating the gaseous fuels required for flaming combustion.

In some cases a solid fuel can simply melt and produce a vaporizable liquid which burns as a pool fire. More

generally, however, complex pyrolysis and chemical reactions occur near or at the solid surface resulting in the

release of gaseous products which serve as the fuel. These processes can result in even more complicated

behaviors in the solid such as charring. Wood burning is a common example of this type of combustion.

c. Premixed and Diffusion Flames

These terms refer to the means by which the fuel and oxidizer are mixed. When the

fuel and oxidizer are mixed before combustion the flames are known as premixed. A flame propagating down

a tube containing a mixture of a hydrocarbon fuel and air is an example of a premixed flame. A diflusion

flame is one where the fuel and oxidizer are not premixed, and the combustion and mixing take place at the same position(s). Common means for mixing are molecular or turbulent diffusion, hence the name. A candle

15
is an example of a diffusion flame, where the combustion is the result of molecular diffusion of fuel and

oxidizer species.

It is possible to have intermediate cases between premixed and diffusion flames. A

Bunsen burner allows partial premixing of fuel and air, but the amount of air provided by the burner may be

insufficient for complete combustion. In this case, additional reaction between excess fuel and ambient oxygen

occurs.

d. Laminar and l\irbulent Combustion

For gas-phase combustion, the behavior of the flow field is central to the flame

characteristics for both premixed or diffusion flames. Gas flows are typically characterized as laminar or

turbulent, and, while a complete discussion of these effects is beyond the scope of this report, a few general

comments are necessary. Here we follow the discussion of Fox and McDonald [40].

These classifications of flow are based on macroscopic behavior. In laminar flow,

there is no mechanical mixing between adjacent layers of the fluid. The flow is "smooth." The only dispersive

mechanisms are the result of molecular diffusion. By contrast, turbulent flow is characterized by the

generation of numerous and apparently random velocity fluctuations. These velocity fluctuations are the result of the formation of vortices extending over a wide range of size scales. These motions provide a mixing

mechanism for adjacent layers of fluid. As a result, transfer and mixing of momentum, heat, and mass is much

greater for turbulent flows than observed in laminar cases.

The type of flow which occurs is sensitive to a large number of system parameters.

In general, small area flows at low velocities will be laminar. An example of a laminar flame is a small candle.

As the area of the flow or its velocity increases a transition to turbulent behavior occurs. Most fires covering

areas greater than a few centimeters involve turbulent combustion.

As might be expected, the behaviors of combustion systems involving laminar and

turbulent flows are different because of large variations in the rates of temperature, chemical species, and

momentum mixing.

e. Lean, Stoichiometric, and Rich Combustion

These terms refer to the relative amounts of fuel and oxidizer available for combustion. When the amount of oxidizer is exactly that needed to convert all fuel to final products (CO2

and H2O for most fuels) the combustion is said to be stoichiometric. If excess air is available, the combustion

is lean, and in the opposite case, (fuel in excess), the combustion is rich.

4. Basic Combustion Concepts

The attempt to understand combustion is a part of the earliest of modem scientific research

[41]. The complex nature of the interaction between the flow fields and the chemistry made progress difficult. However, today the major elements of the problem are understood and modeling calculations provide

reasonable results for simple combustion systems.

a. Thermodynamics

Combustion occurs when a fuel and an oxidizer (typically air) mix and are ignited.

The resulting reaction generates heat and light. Thermodynamics provides the tools to calculate the amount

of heat which can be released for any given fuel. It also allows the calculation of the maximum possible

16
temperature which can be generated by a flame and the equilibrium concentrations of species which are produced. As an example, consider the combustion of the simplest hydrocarbon-methane. The overall

reaction of methane with oxygen can be written as

CH4 + 2O2 -» 2H2O + CO2.

The heat of reaction at room temperature is calculated as the sum of the standard heats of formation for the

products minus that for the reactants. The net heat release for the above reaction is 802 kJ/mole of CH4

consumed. This quantity, the heat of reaction of fuel with oxygen to produce water and carbon dioxide, is called the heat of combustion. Similar calculations can be made for any fuel, whether it is a simple gas (as

above) or a complex fuel such as wood.

The heat of combustion can be used to estimate the maximum temperature a flame can achieve. .This is called the adiabatic flame temperature, lb calculate this quantity, it is necessary to know

both the heat of combustion of the fuel and the composition of the reaction mixture. When methane is burning in air, this means that we must account for the nitrogen, which does not take part in the reaction. In addition, it must be assumed that all of the heat released by the combustion reaction goes into heating the

product gases and the nitrogen. Calculation of the adiabatic flame temperature also requires input of the heat

capacities of all product and inert gases. The heat capacity of a gas is simply the number of joules that are required to increase the temperature of one mole of the gas one Kelvin. In general, the heat capacity of a molecule increases with increasing molecular complexity-the more atoms in the molecule, the more energy

required to heat the molecule.

The calculation of equilibrium composition of the reaction mixture depends on the

estimated flame temperature and requires knowledge of the heats of formation of stable species (such as CO),

as well as, the heats of formation of the radicals having the highest concentrations in the flame (for example,

hydrogen atoms, H; hydroxyl radicals, OH; oxygen atoms, O; hydroperoxide, HO2; and methyl radical, CH3).

Finally, data on the entropy of formation for all of these species is needed. This process is iterated until convergence. These calculations can be extended to include other additives, such as inhibitors, provided that adequate thermodynamic data are available. The approximation of adiabaticity is generally good, but always

produces an upper limit for the temperature. Equilibrium composition calculations are generally adequate

if soot concentrations are not high. The data necessary for these calculations are, for the most part, well- known [42] and the calculations are readily performed.

Thermodynamics can be used to predict the amount of heat and the composition of

the gases produced, but it does not address the question of how fast the reaction occurs. Tb do this it is necessary to examine the kinetics of combustion processes.

b. Chemical Kinetics

Combustion can be described as rapid oxidation. The yellowing of a piece of paper

over time is an oxidation process as well, but it is slow. When a flame is touched to the same piece of paper,

the resulting oxidation is much more rapid. The difference is the result of variations in the overall rates of

reaction for the processes or, in other words, the kinetics. In the methane/air example given above, the fuel and oxidizer could have been mixed in a cylinder at room temperature and there would have been no reaction.

On the other hand, even a small spark passing through the mixture would have initiated a rapid, indeed almost

explosive, reaction.

lb understand these differences in reaction behavior it is necessary to examine

chemical kinetics in general, and, more specifically, the kinetics of ignition and propagation of flames. Overall

reactions, such as the combustion of methane, generally occur by a number of individual reaction steps

involving molecular species. These reaction steps are characterized by the reactants, the products, and the rate

17
at which they occur. The reaction of H atoms and O2 molecules to produce OH radicals and O atoms, an

extremely important combustion reaction, is written as H + O2 -* OH + O.

The rate at which the reaction occurs can be defined in terms of the rate of loss of

a reactant, -d[H]/dt or -d[02]/dt, or the rate of production of a product, d[OH]/dt or d[0]/dt. (The notation

[X] denotes the concentration of X in molesA'olume.) The reaction rate is equal to the product of the

reactant concentrations times a rate constant, k.

Rate = k[H][02],

where the rate constant is usually expressed as

k = AT"exp(-Ea/RT).

The energy of activation,E3, is a measure of the energy barrier that the reactants must overcome to produce

products. The preexponential factor, AT", incorporates the rate of collision between the reactive species in the gas phase and the probability that if the reactants have sufficient energy, reaction will occur. In general,

most of the temperature dependence for a reaction step is the result of the energy of activation since it appears in an exponent. The form of the equation is such that for E^ > 0, the reaction rate increases with

temperature, lb understand why the methane/air mixture does not undergo combustion when mixed at room

temperature, it is necessary to examine the details of the chemistry of combustion.

c. Combustion Chemistry

Combustion chemistry is primarily the chemistry of free radicals-their production,

reaction, and destruction. A free radical is a molecular species that is very reactive because it contains

unpaired electrons. These species are not generally thermodynamically stable at room temperatures - they

recombine to form stable molecules. At flame temperatures, typically > 800 K, their recombination (loss) processes are not as fast as their generation rate. Thus, the radicals' concentrations are relatively large, and

their high reactivity dominates flame chemistry.

The most important ft-ee radicals in most practical flame systems are H and OH. In

addition, CH3, HO2, and O are important in some situations. Beyond these species, dozens of other radicals

play a role in the combustion of complex fuels. The chemistry of combustion is complex because of the very

large number of species and because, at different temperatures and different ratios of fuel to oxidizer, different

reactions among these species will dominate. We can characterize the major types of reactions in terms of

their role in the overall chemistry. The usual classifications are:

• Initiation Reactions. These are reactions that provide the first radicals to start the

combustion process for the fuel and oxidizer.

• Branching Reactions. These are reactions that increase the number of radicals and therefore

the overall reaction rate. The most important of these reactions consume the oxidizer.

Propagation Reactions. These reactions usually consume fuel or oxidizer with no net change

in the number of radicals.

Termination Reactions. These reactions reduce the net number of radicals or produce

unreactive radicals from reactive radicals.

18
The branching reactions are common to all practical combustion systems. This is especially true for the branching reaction H + O2 -» OH + O discussed above. The individual initiation and

propagation reactions often depend on the ftiel. The important termination reactions are common to many

systems.

Initiation reactions are typically like these:

H2 + O2 — HO2 + H

CH4 + O2 — CH3 + HO2

^2^6 -* 2CH3.

In these reactions, stable molecules react to generate radicals such as H and CH3. These reactions typically

have activation energies greater than 200 kJ/mol. These are the only reactions that produce radicals directly

from the stable ftiel and oxidizer. The high activation energies of these reactions mean that the rate constants,

k, vary by over 30 orders of magnitude between room temperature and combustion temperatures. Even at combustion temperatures, these are typically slow reactions with rate constants below all of the other reactions we will discuss, lb illustrate how slow these processes are, the reaction between H2 and O2 will produce less than one H atom per century at room temperature. Combustion does not occur unless the temperature is very high or there is some other source of radicals. Once the radicals are produced, the initiation reactions are completely unimportant; and the rate of reaction is set by the rates of the branching and propagation

reactions.

The most important branching reaction for practical combustion systems is: H + O2 — OH + O.

This reaction has an activation energy of 69 kJ/mole and an average pre-exponential factor. At combustion

temperatures this reaction occurs about one in every hundred collisions. Most importantly, this reaction

produces two reactive radicals, OH and O, for each radical (H atom) which is consumed. Reactions of O

atoms with the fuel such as: O + H2 - OH + H

O + CH4 - OH + CH3

are also important. The OH free radicals produced by these reaction steps react primarily with fuel molecules

in propagation reactions.

The propagation reactions are highly variable since they depend on the fuel type.

Some examples are:

H2 + OH — H2O + H

CH4 + OH — H2O + CH3

CO + OH - CO2 + H.

In each of these cases, the OH radical reacts with a fuel molecule (H2,CH4,CO) to produce a stable end

product (H20,C02) and another radical (H,CH3). All of these reactions have low activation energies (5-20

kJ/mol), although the third is an unusual reaction and is slower than the first two at flame temperatures. The

19
propagation and branching reactions are typically fast reactions that, once started, will rapidly consume all of

the available fuel or oxidizer.

The termination reactions either produce a radical with greatly reduced reaaivity or produce stable products from two radicals. Examples are: H + O2 + M — HO2 + M

H + OH + M -> H2O + M

CH3 + CH3 + M -»• €2^6 + M

where in each case M is some third body that does not participate in the reaction, e.g, N2. These reactions are typically slower than branching or propagation reactions at flame temperatures, but have negative

activation energies, so that they become faster at lower temperatures.

It is possible to understand very simple combustion systems, such as H2/O2 within

the context of a manageable set of reactions; and, for special cases, algebraic solutions of the rates of growth

for the species involved can be found. In general, the reaction systems are so complex that computer modeling

is essential just to understand the kinetics. When the effects of flow fields, mixing, and di^sion are included, even the simplest system must be modeled.

It is nevertheless possible to use the simple ideas discussed here to understand the

general principles of combustion. For example, the stability of combustible materials at room temperature

is a result of the high activation energies for their initiation reactions. The discussion thus far is only strictly

applicable to simple gaseous fuels, but the same general features pertain to more complex fuels; that is, the

initiation reactions which involve the creation of radicals from stable species will be slow at room temperature.

In addition, the rate of combustion, once initiated, can be understood in terms of the branching and

propagation reaction rates. The rates for branching reactions increase with temperature and are reasonably

fast, and the radical attack on the fuel molecules is generally fast and has low activation energy. As a result,

the overall reaction rate is sufficient to maintain combustion for high temperatures.

The same kind of analysis can be applied to the role of suppressants in the flame,

lb stop a combustion process one must either remove the radicals faster than the chain branching process can produce them (note that the propagation steps only maintain the number of radicals) or reduce the

temperature so that the chain termination steps can dominate. These are really the same idea: in both cases the radicals are removed faster than the branching process can create them.

Consider, for example, the primary chain branching reaction

H + O2 - OH + O.

This reaction has an alternate channel,

H + O2 + M - HO2 + M.

Both of these channels are always present. The second channel is pressure-dependent, that is the second order

rate constant increases with pressure. The rate expressions of these two processes are such that at atmospheric

pressure, the rates are roughly equal at 1000 K. Below this temperature the recombination channel (producing

HO2) dominates, while above this temperature the branching channel dominates. The H + O2 reaction is also important since it is the predominant path for O2 consumption in combustion. If there is competition for the

20
H atoms by other reactions, these will correspondingly reduce the net rate of the chain branching reaction by

reducing the concentration of H atoms.

Using the ideas expressed here, it is also possible to see what role an ignition source

plays in the combustion process. The rate of radical production by the initiation reactions is so slow that, at room temperature, the termination reactions will soak up any radicals faster than the branching reactions.

If a sudden, concentrated local source of radicals is introduced, the branching and propagation reactions will produce enough excess energy to heat the gas locally and start the combustion. This local radical source could

be a spark or a small flame. Once the combustion has been started, the problem of flame inhibition goes back

to the same ideas discussed above. For simple combustion systems, H2/O2 or CH4/O2, the kinetic data is well

enough established that modeling is a useful tool for analyzing the combustion process. Although there is some kinetic data on halocarbons and other halogens, it is inadequate for computer modeling of the flame

suppression process.

d. Thermal balance

All of the concepts discussed above can be incorporated into the idea of thermal

balance. The discussion above can be simply summarized as follows: the energy released in the combustion

process must be sufficient to keep the temperature high enough so that the branching reactions can stay ahead

of the termination reactions. The thermal losses, heating up new fuel and oxidizer and breaking the initial bonds, are made up by the thermal gains, exothermic production of combustion products. In a practical system

there are other loss mechanisms such as radiation, conduction and convection that the exothermic processes must also make up. The heating of new fuel will, in a diffusion flame, also include the loss of H atoms to the

fuel. This loss of H atoms can be viewed as a mechanism for self-extinction and is responsible for rich combustion limits.

These ideas can be translated into some simple rules of thumb for the limits of

combustibility. For most organic fuels the heat of combustion is found to be approximately 425 kJ/(mole-02)

[43,44,45,46,47]. Note that the mole-02 means per mole of O2 consumed. Flammability limits, both rich and

lean, and the limits in the presence of inerts have empirically been found to be expressed in terms of a limiting

heat capacity for the reacting mixture (fuel/oxidizer/inert) of 210 J/(mole-02 K). That is, the mixture will not

sustain combustion if the heat capacity of the mixture is greater than 210 J/K for each mole of oxygen present

in the mixture [44,48]. Note that excess oxygen or fuel acts simply as an inert gas that adds to the heat

capacity of the system. Thus, the addition to the heat capacity of the mixture can be accomplished by the

addition of an inert, excess fuel, or excess oxidizer. The heat production is constant per mole of Oj consumed,

so the increase in heat capacity must correspond to a decrease in the final temperature of the flame. The

result is again the dominance of the recombination processes over the branching process.

The use of the ideas of chemical kinetics can provide a qualitative understanding of

the rationale behind thermal balance, but the results depend on the fluid mechanical details of the combustion

and must be determined either from experiments or from models that mimic the system under consideration,

lb the extent that there are other loss mechanisms for the radicals needed for the branching reaction, the

simple ideas developed from the thermal balance will not hold. Thermal balance concepts have been extended

to include the definition of a limit temperature. That is mixtures having an adiabatic flame temperature below some lower limit will not support combustion. These temperatures have been found to be greater than that

for which the rates of the branching and recombination channels of the H + O2 reaction intersect for a wide

variety of combustion systems. This suggests that additional radical loss mechanisms are operant.

e. Propagation Rates of Premixed Flames

An important property for a burning fuel/oxidizer system is its flame speed. This

property is generally only meaningful for gaseous and liquid fuels for which flammable gaseous mixtures can

21
be formed. There are a number of experimental methods available for flame spread measurements [49], but

all attempt to report the one-dimensional flame propagation rate of the combustion front into the fuel/oxidizer

mixture.

Flame speed measurements vary with a number of system parameters. As expected,

flame speeds depend strongly on the concentrations of the fuel and oxidizer as well as the total pressure. Flame speeds are generally found to increase with the temperature of the unburned fuel/oxidizer mixture. In turbulent mixtures, flame speeds are proportional to both the turbulence intensity and the laminar flamespread rate [50]. The majority of all flame speed measurements are reported for fuel/air mixtures at ambient

atmospheric conditions.

f. Flame Structure

The term "flame structure" refers to the details of the velocity, temperature, and

concentration fields in the vicinity of the combustion reaction zone. The structures for both premixed and

diffusion flames are characterized on the basis of experimental measurements. Usually, well-defined systems

are investigated in which the combustion region can be assumed to be one-dimensional. Thus far, most

interest has focused on laminar flames. Interactions of the heat release of combustion with the turbulent

motion of fluids, along with temporal fluctuations of properties, makes flame structure determinations in turbulent flames very difficult. It is significant that the most widely accepted theoretical treatment of turbulent

combustion~the laminar flamelet approach [51,52]-treats the local flame structure in a turbulent flame as being a laminar flame.

Modeling of combustion and diffusion flames involving full-kinetic treatments of

major chemical reactions [53] and realistic treatments of molecular diffusion transport [54] allows flame

structures to be calculated for simple laminar fuel/oxidizer systems. In general, excellent agreement is obtained

between experimental and calculated results.

B. INTRODUCTION TO FIRE SUPPRESSION

This Section is intended to serve three purposes.

• First, the current understanding of fire suppression is summarized. The goal is to help the

reader to understand why and how choices were made concerning the compounds included on the final listing.

• Second, the types of experiments used to characterize fire suppression effectiveness are summarized. This discussion provides the understanding necessary to evaluate past measure- ments of the fire suppression capabilities for compounds included on the list.

• Third, the results of past measurements are used to determine whether (or not) chemical fire suppression is a general phenomenon. This is important since many of the chemicals

included on the final list are intended to test various principles concerning chemical

mechanisms for flame suppression. Experimental findings strongly suggest that combustion

suppression can occur by chemical pathways.

22
1. Relevant Reviews

There are numerous literature reviews and critical analyses of fire suppression. These should

be consulted by any reader interested in developing a basic understanding of the field. Some of these reviews are mentioned here as a guide for the reader.

An excellent review of early work was provided by Fryburg [55]. This work considers fire suppression mechanisms in general, but focuses on the possibility of chemical suppression. A contemporary

report prepared by Malcolm [56] is not a review article per se, but it does provide an invaluable summary of

a number of investigations dealing with fire suppression and halogenated suppressants. In 1957, a thorough

review of flame suppression mechanisms by Friedman and Levy [57] appeared. This review was followed by

two shorter efforts designed to summarize the literature appearing during interim periods [58,59] and two

additional short reviews [60,61]. Other authors have contributed to the interim reviews and a continuous

record can be traced up through 1969 [62,63,64,65,66]. The monograph edited by Gann is an invaluable source

of information on various aspects of flame suppression and the halogenated fire suppressants in particular [67]. A bibliography of halon literature up through 1976 has been prepared by Miller and Kenney [68].

More specialized reviews are also relevant. Workers at the U.S. Bureau of Mines have

provided extensive reviews and critical analysis of flammability data for gases and vapors [69,70]. A later review dealing with the same subject includes a section on flame inhibition [71]. TVvo authors have provided

extensive reviews with a focus on the reactions important for flame suppression chemistry [72,73].

No reviews of this field have appeared since 1976 because very little new data have been

reported after this date. Most of these additional studies will be discussed during the following sections. The

dearth of recent studies can be traced directly to the success of the current commercial halons as fire suppressants. Their properties have been so well-suited to their use that there has been little incentive for improvement; as a result, research funding for this area had dried up.

The lack of recent research in fire suppression suggests that it may be possible to make rapid

progress. During the past 15 years, significant gains have been made in the understanding and modeling of

combustion systems. These advances are available to researchers and should be directly applicable to the

problem of flame suppression.

2. Fire Suppression IVfechanisms

The possible mechanisms of flame suppression can be categorized in various ways. Here we

follow the discussion of Friedman and Levy [57], but their discussion is typical of other authors. TWo general

classes-physical and chemical~for flame extinguishment mechanisms are recognized.

a. Physical Fire Suppression Mechanisms

There are 4 types of physical fire suppression mechanisms. Brief introductions to each are provided. Reference to the fire triangle discussed earlier in section II.A,3 provides immediate insights

into the physical basis for these processes.

• Smothering or Blanketing. This physical mechanism operates by separating

the fuel and air. Covering a small fire with a blanket to extinguish it is a common example. Application of appropriate gases and liquids can also smother a fire. Carbon dioxide fire extinguishers are recognized as operating

primarily by blanketing.

23
• Cooling and Dilution. These processes absorb heat from the combustion zone and lower the temperature. As discussed in section II.A,4.d, it is possible to extinguish a flame when sufficient heat is extracted. There are a number of physical means by which heat can be absorbed by agents added

to a fire. These include simple heating of the agent (proportional to the

heat capacity), phase changes such as vaporization or sublimation, and

endothermic decomposition. One might also expect that the rate of heat

transfer from the combustion zone, as well as the heat capacity, might be an

important parameter for cooling mechanisms. The physical property which

characterizes heat transfer behavior is thermal conductivity. The results of

experiments suggest that the dominant physical property is heat capacity and

that thermal conductivity plays only a minor role in flame inhibition.

• Mechanical Means. This term refers to mechanisms by which the fuel, heat,

and/or air are forcibly separated. For example, blowing on a match removes

the heated gases and soot necessary for sustaining combustion from the

flame zone and extinguishes the flames.

• Flame Radiation Blockage. Friedman and Levy [57] also discuss a mechanism by which flame suppression occurs when an agent is interposed

between the surface of a liquid or solid fuel and the flames which absorbs

the thermal radiation which is necessary for the generation of gaseous fuel. Very little discussion of this process is found in the literature.

b. Chemical Fire Suppression Mechanism

This classification refers to an agent, which either by itself or through its decomposition products, interferes with the combustion chemistry to a degree sufficient to inhibit (or suppress)

combustion. Based on the current understanding of combustion as consisting of chain reactions, the most

effective chemical inhibitors would be expected to be those which remove chain carriers in, or near, the

reaction zone.

c. Chemical Fire Suppression and Physical Cooling

When a chemically active agent is added to a combustion system the agent will have

both physical and chemical effects. The concept of chemical fire suppression was suggested when agents were

identified which were more effective fire suppressants than expected based simply on their physical properties.

Only very recently have efforts been made to quantify the contributions of physical and chemical modes of fire suppression for an agent. Such studies are discussed in Section II.B.4.b.

The relative effects of cooling and chemical effects on the suppression of a fire are

difficult to ascertain, in part, because the details of the heat removal processes are not well defined. Consider

a diffusion flame. Based on existing combustion models it is expected that the location where temperatures

must be lowered in order to cause flame suppression is in the vicinity of the high-temperature flame zone. This zone transfers heat to its immediate surroundings, and the process continues until the temperature

reaches that for the surroundings. No definitive prescriptions are available for handling the diflierent heat

transfer processes implied by this discussion. For instance, room temperature heat capacities are sometimes

used for correlating flame suppression efficiencies, while others use an integrated heat capacity from room

temperature to some assumed flame temperature. For evaporation or endothermic decomposition, the

location of the process relative to the combustion region might be expected to be very important. No analyses are available which treat this problem. Similar considerations will apply to premixed flames.

24
A concept which has been used implicitly in the discussions above requires further

explanation. Simple endothermic thermal decomposition has been treated as a heat extraction mechanism

capable of cooling a flame. It is therefore classed as a physical mechanism for flame suppression, despite the

fact that thermal decomposition is recognized as a chemical process. Thermal decomposition is defined to contribute to chemical flame suppression only if it generates a chemical species which interferes with the

combustion chemistry. TWo hypothetical examples serve to illustrate this point. Consider an agent capable

of undergoing endothermic decomposition to produce two inert molecular species. The flame would be cooled

by the heat capacity of the agent as it is heated, the heat absorbed during the thermal decomposition of the

agent, and any additional heat absorbed by the inert species which are generated. Since the species which are generated by the thermal decomposition are inert, only a physical mechanism is considered to be active. The

alternative case occurs when thermal decomposition produces one or more molecular species which are

reactive and capable of interfering with combustion intermediates and inhibiting the flame chemistry. Both

physical and chemical mechanisms are active in this case. Heat absorbed from the flame system by the agent,

the agent's thermal decomposition, and the decomposition products would be classed as a physical mechanism.

Only the infiibition of the flame chemistry as the result of the active species generated by the decomposition

is classed as a chemical mechanism of fire suppression. Fire suppression in the latter case is the result of both

physical and chemical mechanisms.

3. Characterizations of An Agent's Flame Suppression Capabilities

There are fundamental justifications for investigating flame suppression, but for the purposes

of this report, the principal objective is to identify agents which are effective as fire suppressants for unwanted

fires. As a result, the ultimate test of an agent is its ability to extinguish fires which are characteristic of real unwanted fires. Note that these will usually be relatively large, turbulent diffusion flames.

Cost, material, and time limitations prevent testing every possible agent on a full-scale fire. As a result, numerous procedures have been developed which are designed to provide guidance to researchers

in characterizing fire suppression behavior. These tests range from observations of flame structure changes

in premixed flames to full-scale fire tests. The descriptions which follow provide the necessary background to understand the significance of previous tests of fire suppression agents. The methods are listed in a rough

order such that their relevance to actual fire situations is increasing. Note that measurements in premixed

flames are directly applicable to situations where the agent is employed to inert fuel-air mixtures. Nonetheless,

diffusion flame investigations are deemed more relevant for extinguishment of unwanted fires.

a. Flame Chemistry and Flame Structure of Premixed Flames

In these experiments, the fuel and oxidizer are premixed and burned in the presence

and absence of an added agent. It is possible to monitor the combustion products of the reaction and see if the agent undergoes a chemical transformation. An example of such an investigation is the work of Burdon

et al. [74], who found that bromine and hydrogen bromide were produced when hydrogen and carbon

monoxide were burned in the presence of methyl bromide.

In a series of benchmark papers, Biordi and coworkers [75,76,77] have reported

detailed concentration profiles for low-pressure premixed flames of methane, oxygen, and argon in the absence

and presence of low concentrations of CF3Br. These investigations have provided important insights into the

chemical mechanisms of fiame suppression.

b. Agent Effects on Flame Speed of Premixed Flames

Flame speed, or burning velocity, is the rate at which the combustion front moves

into a premixed fuel and oxidizer mixture. Burning velocities are experimentally determined in a variety of

25
ways [49]. The velocities observed are sensitive to parameters such as the fuel/air ratio, temperature and

pressure. The addition of fuel additives also modifies the burning velocity. A decrease in burning velocity

with the addition of varying amounts of flame suppressants is sometimes employed as a measure of flame

suppression capability.

An early example of such an investigation is the work of Rosser et al [78]. These

researchers reported the effects of a variety of agents on the flame speed of methane-air flames. Several of

these compounds contained bromine atoms. A very good correlation was found of the effect of an agent on

the flame speed and the number of bromine atoms contained in the agent. Ratios of inhibition effectiveness

for Cl:Br:I were reported as 1:7:7.

Lask and Wagner [79] reported the effects of a number of additives on hydrogen and

hydrocarbon flames. Data are reported graphically for flame velocity versus percentage of added agent as well

as in tables with the percentage of additive required to reduce measured flame speeds by 30 percent. One of

the most interesting observations was that bromine-containing molecules reduced flame velocities much more

efficiently than those containing chlorine. Limited measurements on species with iodine suggested that this atom was still more effective. This observation was confirmed by Halpern [80]. A comparison of the effects of several halogenated hydrocarbons on the flame speed of methane/air mixtures showed that compounds

containing bromine were considerably more effective than those containing chlorine.

Homann and Poss [81] measured the flame speed of ethylene/air flames inhibited with

a series of compounds as a function of pressure. Pressure was varied from 18 kPa to 101 kPa (101 kPa is one

atmosphere). As expected, flame speeds varied substantially with pressure. However, when data for inhibited

flames were normalized by the flame speeds for uninhibited flames, the results for different pressures collapsed

into a single curve. An interesting observation of this work was that CH3I was slightly more effective as a suppressant than CH3Br at both high and low pressures.

c. Agent Effects on Premixed Flame Flammability Limits and Peak Concentrations

Flammability limits refer to the relative amounts of fuel and oxidizer in the mixture

necessary to sustain combustion. These measurements are often made in a device called an explosion burette. The mixture to be tested is placed in a long tube, open to the atmosphere with sufficient diameter to ensure

that the walls have a minimal effect. A spark or small flame is used to ignite the gases. The mixture is considered to be flammable when the combustion propagates to the end of the tube and nonflammable when

propagation does not occur. By varying the concentrations of the gases it is possible to map out the

flammability curve. Other devices utilized for determining flammability diagrams are discussed by Ford [2].

The effect of an agent on combustion behavior is often characterized in terms of the

lean and rich flammability limits as the concentration of the additive is increased. Usually the concentration

range of fuel and air capable of supporting combustion decreases as the agent is added. Extensive

compilations of flammability results are available [69,70]. The work of Moran and Bertschy is also of interest

since they investigated the flammability limits of pentane/air mixtures for a number of halogenated

hydrocarbons [82].

As the agent concentration is increased, a point is reached where the lean and rich

limits coincide. The agent concentration at this point is called the flammability peak concentration or, more

simply, the peak concentration. Further increases in agent concentration lead to a situation where the fuel and air will not support combustion for any fuel to air ratio. Peak concentrations are often used to rate agent

effectiveness. The most extensive series of measurements have been provided by the Purdue Foundation [25]. Results are provided for 56 compounds.

26
d. Full Kinetic Modeling of Premixed Flames

In recent years, it has become possible to model important aspects of laminar flames. This does not imply that complete modeling of combustion systems is feasible. Soot formation, for example,

remains an intractable problem. However, equations which include realistic treatments of mass, momentum,

and heat transfer, and which incorporate complex kinetic mechanisms to treat the chemical reactions, can be

solved. Frequently, these calculations are simplified by considering only one- or two-dimensional flames.

Numerous comparisons have shown that it is possible to accurately calculate laminar

flame speeds and flame structures for a number of fuel/oxidizer systems. The significance of this advance

cannot be overstated. It is now possible to make useful predictions concerning practical combustion systems on the basis of measured chemical properties (e.g., thermal conductivities and rate constants for individual

reaction steps). Such understanding offers great possibilities for tailoring and modifying combustion systems

to meet specific engineering goals.

A few workers have attempted to utilize these techniques for investigating flame

inhibition. An early example of such an approach is a paper by Dixon-Lewis [83] in which the structure and

properties for uninhibited and inhibited hydrogen/air premixed flames were investigated. These authors

concluded that the primary mechanism of flame inhibition was the catalyzed removal of H atoms to form less reactive Br atoms by the reactions

H + HBr 5* H2 + Br

H + Br2 55 HBr + Br.

Interestingly, the first of these reactions was found to be very close to partial equilibrium (i.e., equal reaction

rates in forward and reverse directions), but the second was shifted far to the right of equilibrium (as written).

The second reaction is primarily responsible for removing H atoms which are necessary to sustain combustion.

As recognized by Day et al. [84], it is necessary to include recombination reactions such as

Br -I- Br -I- M 5i Br2 + M

to explain the observed flame suppression effectiveness of Br. Day et al. [84], suggests that the greater flame

suppression efficiency of Br atoms as compared to CI atoms results from the higher Br atom concentrations

possible when H atoms and the hydrogen halide are in equilibrium.

Westbrook reported similar calculations for organic fuels in a series of three papers

[85,86,87]. In the first paper, he considered the inhibition of methane and methanol-air flames by HBr [85]. Calculated flame behaviors were found to be in agreement with available experimental data. The inhibitor was predicted to be more effective for lean flames than stoichiometric or rich flames. Flame inhibition was

primarily the result of the catalytic removal of H atoms via the mechanism discussed above.

In the second paper [86], the calculations were extended to include inhibition effects of HCl, HBr, HI, as well as, halogenated hydrocarbons formed by single substitution of CI, Br, and I in methane, ethane, and ethylene. Preliminary findings for halon 1301, CF3Br, were also discussed. The catalytic

removal of H atoms was found to be the principal inhibition mechanism for each molecule. The only

additional suppression reactions included beyond those for the hydrogen/air system discussed above were

27
H + RX ^ HX + R

X + RX 5i X2 + R,

where RX is the halogenated hydrocarbon and X represents the halogen atom.

The calculations agreed with experimental observations in that compounds containing

iodine were predicted to be slightly more effective inhibitors than their bromine analogs, while both were

considerably more effective than the corresponding chlorine compounds. In the case of the halogenated

hydrocarbons, variations in the fuel content of the parent species led to variations in inhibition efficiency with

equivalence ratio. Effects of pressure changes were also characterized.

The final paper in the series by Westbrook [87] includes detailed numerical modeling

results for CF3Br-inhibited flames of hydrogen, methane, methanol, and ethylene. Good agreement between

computed flame structures and the experimental determinations of Biordi et al. [75,76,77] was found.

Rammability limits and burning velocities for the laminar flames were predicted and compared with

experimental findings. The effects of variations in pressure, ambient temperature, and equivalence ratio were

characterized.

The calculations described above must be considered as preliminary attempts to model

fire suppression effectiveness. Our analysis has identified serious deficiencies with regard to some of the rate constants utilized in the calculations. On the other hand, these calculations are valuable because they indicate

that flame modeling can provide important insights into flame suppression mechanisms. State-of-the-art calculations of this type are capable of modeling simple diffusion flames. Characterization of suppression

behavior in flames of this type should be particularly illuminating.

e. Types of DifTusion Flames Used for Inhibition Investigations

Tvo types of configurations have been used to investigate the flame structure of

inhibited diffusion flames. The first is the diffusion flame typical of a flowing fuel entering an ambient or coflowing oxidizing atmosphere. We will refer to this configuration as a "standard" diffusion flame. Normally

these flames are stabilized at the mouth of the burner, and there is a region near the mouth where the flames

are quenched. For certain fuels and burner configurations stable lifted flames can be created, while for other

conditions blow out occurs. Note that it is possible to have some fuel and oxidizer mixing in the cool regions

between the burner outlet and the flame base.

The second type is known as a counterflow diffusion flame. As the name implies,

these flames are formed at positions where head-on flows of fuel and oxidizer meet. TWo configurations are common. One involves flows moving in opposite directions. The second utilizes a porous cylinder placed in a flowing oxidizer (or less often, fuel) stream. Fuel (or sometimes oxidizer) is passed through the walls of the

cylinder and a diffusion flame is stabilized around the cylinder. A stagnation point for the flow exists on the

upstream side of the cylinder.

Since counterflow diffusion flames are located at positions removed from solid

surfaces they are less subject to heat loss effects and premixing of fuel and oxidizer. For these reasons, measurements in counterflow diffusion flames tend to be more reproducible between different facilities. When

the velocities of the fuel and/or oxidizer are increased, these diffusion flames are eventually quenched. This

quenching occurs first at the flow-stagnation point in the center of the flame sheet. The flow velocity required

to "open up" a diffusion flame provides a reproducible measure of diffusion flame extinction known as the

flame strength.

28
f. Flame Chemistry and Structure of Inhibited DifTusion Flames

Most investigations of changes in flame structure due to the addition of an inhibitor

have been made for standard diffusion flames. Several examples are discussed to provide insight into the types

of measurements and understanding which have been achieved.

Simmons and Wolfhard [88] used spectroscopic techniques to investigate the flame

structure of di^usion flames of ethane and carbon monoxide in air, bcth with and without, methyl bromide

added to the fuel or oxidizer. A startling change in flame structure was found when the agent was added to the air. In the primary combustion zone emission intensities of continuum radiation (indicating increased soot

concentration) and C2 emission were observed as the inhibitor concentration was increased. Most unusual was the formation of a second reaction zone on the oxidizer side of the flame which showed considerable

emission from excited bromine atoms. It was emphasized that reaction at this secondary location was not

expected in the absence of the agent. Further tests demonstrated that this reaction zone was the result of the

addition of the agent, which acted like a fuel. These results provided strong evidence that chemical reactions are responsible for flame inhibition.

Creitz [89] utilized gas chromatography to measure stable chemical species in the

region outside of the flame zone for a propane diffusion flame. He observed that when CF3Br was added to the oxidizer, the agent disappeared at positions outside of the flame where temperatures were too low for thermal decomposition. This observation is consistent with the observations of Simmons and Wolfhard [88]

and suggests that chemical species generated by the flame interact with the agent.

Noda et al. [90] employed electron-spin resonance to measure the relative H atom

concentrations within a methane Bunsen-type flame. Such a flame burns partly as a premixed flame and partly as a diffusion flame. The effects of adding a series of halogen-containing compounds on the H atom

concentration were reported. For relatively low concentrations of the agents, H atom concentrations were

decreased by amounts linearly related to the amount of agent added to the secondary air. The decreases were

quite dramatic. For instance, the addition of 2 percent of methyl bromide to the air decreased the H atom

concentration by 60 percent. The decreases in H atom concentrations were roughly correlated with inhibition

efficiency with the amount of decrease increasing in the series F < CI < Br.

Relatively few flame structure characterizations of counterflow diffusion flames are

available. Ibiricu and Gaydon [91] reported spectroscopic results for ethylene-air and hydrogen-air flames to which inhibitors (methyl bromide, bromine, carbon tetrachloride, chlorine, or phosphorous oxychloride) were

added. Their observations are similar to those of Simmons and Wolfhard [88]. They concluded that the

inhibitors result in the removal of OH fi-ee radicals from the flames.

A method for stabilizing counterflow diffusion flames for liquid fuels was used by

Kent and Williams [92] and Seshadri and Williams [93] to investigate flame structures for several organic fuels. Gases added to the oxidizer stream included N2, CO2, He, and CFjBr. Some differences in the behavior of

major species were found when these authors compared their findings to those of Creitz [89]. However, the

rapid disappearance of CF3Br as the flame zone is approached was observed in both types of diffusion flames.

Tfemperature measurements have also been reported for counterflow diffusion flames

[92,93]. It was concluded that flame temperatures for conditions close to extinction are much higher when

CF3Br is added to the oxidizer than for nitrogen dilution. This is taken as support for a chemical mechanism

for CF3Br inhibition since N2 is believed to inhibit flames only as the result of heat capacity effects.

29
g. Extinction of Laminar Diffusion Flames

The relative effectiveness of agents can be quantified by comparing the amounts which

must be added to either the fuel or oxidizer in order to extinguish a diffusion flame. Both standard and

counterflow diffusion flames have been widely used for such studies.

Early investigations involving standard diffusion flames are those of Simmons and

Wolfhard [88] and Creitz [94]. Simmons and Wolfhard reported the percentages of methyl bromide which

must be added to the fuel or air to extinguish flames of four organic fuels and hydrogen. In all cases the

percentage of agent which had to be added to the fuel was much greater than required for the oxidizer. Extinction percentages were compared with measurements for premixed flames utilizing both the peak agent

concentration and the percentage required for a stoichiometric mixture. The percentage of agent required for the oxidizer varied in similar ways as a function of fuel and, while larger for the diffusion flames, were of

comparable magnitude to those necessary to prevent flame propagation in stoichiometric premixed flames. This is consistent with the view that the flame sheet in diffusion flames lies near positions of stoichiometric

mixing.

Creitz reported similar measurements for a variety of fuels utilizing nitrogen, methyl

bromide, and halon 1301 as inhibitors [94]. In this investigation, the concentration of oxygen in the

surrounding atmosphere was also varied. As found by Simmons and Wolfhard [88], a considerably higher

percentage of agent was required for extinction when added to the fuel than when added to the oxidizer. Creitz concluded that the mechanism of inhibition is different for the two cases. It is not clear whether he

treated his data in terms of concentrations for stoichiometric combustion. One interesting conclusion was that

for nitrogen/oxygen mixtures containing more than 25 percent oxygen, methyl bromide became a fuel and was

entirely ineffective as a suppression agent. This compound burned as a diffusion flame in 32 percent oxygen.

Early measurements of percentages of inhibitor required to extinguish laminar

diffusion flames were for gaseous fuels only. The results had a great deal of scatter for given fuel and inhibitor

combinations [95,%]. This scatter was most likely due to variations between experimental apparatus and

techniques. In response to this situation, Bajpai [96] developed an apparatus for determining the

concentration of agents required to extinguish small pool fires of liquids. The device has come to be known

as a "cup burner" after the shape of the vessel holding the liquid fuel. A coflow of oxidizer flows by the cup. In Bajpai's device the fuel surface had a diameter or 25.4 mm. Hirst and Booth have described a very similar

apparatus having a cup diameter of 28 mm [97]. It is unclear if the flame will be strictly laminar for these

conditions, but it is also true that the flame is unlikely to be fully turbulent. These devices will be discussed

in greater detail because of their widespread use for testing suppression agents.

The percentage of agent required to extinguish a flame has been found to be a

function of the oxidizer flow velocity, first increasing and then falling with increasing velocity [%,97]. Bajpai

reported values of the peak percentages of halons 1301 and 1211 in air required to extinguish a wide variety

of liquid fuels [96]. He found that his results agreed with the then-unpublished measurements made with a

similar apparatus at Imperial Chemical Industries [97]. Hirst and Booth reported results for halons 2402,

1202, 1011, and 113 as well as halons 1301 and 1211. Bajpai [96] also compared his cup burner results with

the findings of other researchers who measured percentages of agents required for extinguishment of much

larger pool fires in enclosures [98,99,100]. Generally, peak percentages of agents for the two types of

experiments were comparable, but values for the large-scale fires were smaller. Hirst and Booth made similar

observations [97].

Sheinson and coworkers have reported peak percentages for a number of agents

utilizing heptane and 2-propanol as fuels [45,46]. The results of these measurements are discussed in more

detail in Section II-B-4-b.

30
Petrella and Sellers [101] had previously used a similar apparatus to investigate the

extinction of propane diffusion flames. The gaseous fuel flowed from a round tube into the oxidizer coflow.

Experimental results were reported in terms of the lowest oxygen index (LOI). This is simply the lowest

oxygen concentration in air diluted with the agent which allows combustion to occur. Values of LOI were shown to be nearly independent of propane flow rate and to have only a mild dependence on the oxidizer flow

rate. LOI values are reported for halons 1001, 1011, 1211, 1202, 1301, and 2402 as well as nitrogen. All of

the brominated species gave LOI values of approximately 0.205 as compared to that for nitrogen of roughly

0.16.

Measurements have also been reported for percentage of agents in fuel or air required

to extinguish opposed flow diffusion flames. One of the first investigations of this type is the study of

Friedman and Levy [102]. These authors report the concentrations of various gaseous agents which must be

added to the methane to open a hole in the flame sheet formed between counterflow jets of fuel and air. The

effectiveness of various agents was ranked in the order CH3CI < CCI4 < CHjBr < CF3Br, which is the same

ordering reported by Rosser et al. [78] for the inhibition effects on flame speeds of premixed methane/oxidizer

mixtures,

Milne et al. [103] used the counterflow geometry of TSuji and Yamaoka [104] to

investigate inhibition. In this configuration, fuel is supplied by a porous cylinder and the oxidizer flows by the

cylinder. Extinction occurs at the stagnation point in front of the cylinder. Measurements are reported for agents added to both fuel and air for methane, propane and butane. Agents tested were CFjBr, CF2ClBr,

CH3Br, CO2, At, and N2. The ordering of agent effectiveness was consistent with measurements by other

techniques.

Kent and Williams [92] and Sheshadri and Williams [93] report the amounts of CF3Br

and nitrogen in the oxidizer which are required to extinguish counterflow flames for liquid fuels.

h. Extinction of Ibrbulent DifTusion Flames

Tfests of the ability of agents to extinguish turbulent diffusion flames are expected to most closely resemble the agents' use in the field to fight fires. At this point it is necessary to distinguish two

common uses of halons: total flooding and local application. Tbtal flooding is employed for firefighting in enclosures. The aim here is to create an environment in which the fire cannot exist by adding the agent to the entire atmosphere in the room at a concentration sufficient to inhibit combustion. Usually the enclosure

is designed to be relatively airtight so that the agent concentration can be maintained above a specified level for several tens of minutes. Gaseous agents are employed for total flooding. Local application involves

spraying the agent directly on, or near, the fire in order to induce extinguishment. Since liquids are more

easily applied, agents used for this purpose are usually liquids which evaporate near room temperature or gases which condense just below room temperature.

Tfests have been developed to assess agent effectiveness in both types of applications.

These tests are usually less standardized than the tests previously described and utilize fire systems which are

subject to a great deal of variability. As a consequence, these results show more variation so that reproducibility between different laboratories tends to be poor. Since they are the final step in the

development of firefighting agents, many large-scale tests have been performed. Only a few are mentioned

to provide a flavor of the types of studies which have been carried out.

Ford [2] discusses a number of large-scale fire tests which have been utilized to test the effectiveness of halon 1301. Results for both class A and class B fires are described. Three published

examples of such tests were mentioned earlier [98,99,100]. The results of McKee et al. [105] and Alvares [106] for the extinguishment of pool and spray fire by halon 1301 and halon 1211 are also of interest. Investigations

31
have shown that deep-seated smoldering fires in solid fuels often require considerably higher agent

concentrations for extinguishment [28,107,108].

Fire tests involving direct application to fires in the open are less numerous. Ford

[2] again provides a short review of previous tests. Malcolm describes some very early tests in which various

halons were tested for their ability to extinguish Class B fires and cotton waste saturated with gasoline [6]. An editor's note in this paper (see Tiible XV, p. 128) points out many of the difficulties associated with this type of testing. Breen [109] has investigated the effectiveness of various mixtures of halons 1211 and 1301 for extinguishing heptane fires. A slight dependence of fire suppression efficiency on mixture fraction beyond a simple summation was identified. The author attributed this observation to differences in thermophysical

properties between the two agents. Problems of reproducibility for this type of measurement are discussed.

The results of practical studies are usually published as internal reports and are sometimes difficult to access. An example of such work is a report which appeared as a Wright Air

Development Division technical report [110]. Results for tests on a number of different size pool fires are

discussed. Halons 1011, 1211, 2402, 1202, and 1301 were tested. Difficulties with reproducibility are discussed.

4. Agent Effectiveness, Testing IVlethods, and the Role of Different Suppression

IVfechanisms

a. Agent EfTectiveness and Testing Methods

Many of the test methods which have been used to characterize the flame suppression

capability of agents were discussed in the previous section. It is important to consider whether these tests are

true predictors for fire suppression efficiency when the agents are utilized in real fire situations.

The effectiveness of an agent utilized as a total flooding agent is usually well

correlated with its behavior in any of the several small-scale tests (e.g., explosion burette or cup burner). This

is not surprising since cooling, dilution, and chemical flame suppression mechanisms (see the discussion in Sections II.B.2.a and .b) are expected to be most important in total flooding applications. In contrast, the

performance of local application-agents does not correlate nearly as well with small-scale tests. This is due

to the fact that these tests are insensitive to certain physical effects, such as evaporative cooling, smothering

and mechanical blow off, which contribute to the effectiveness of streaming agents. Only test methods

involving the direct application of these agents to fires (as liquids) will be able to account for these additional

physical mechanisms.

b. Contributions of Physical and Chemical Mechanisms to Fire Suppression

Effectiveness

Thus far, little mention has been made of the relative contributions of the various

physical and chemical mechanisms to the flame suppression capability of an agent. This point is discussed here

with reference to the published literature and the previous discussion.

As noted in the last section, very few of the tests used to characterize agents for fire suppression effectiveness screen for smothering or mechanical suppression. Perhaps as a result of this, the

understanding of these processes remains very poor. No literature has been identified which attempts to quantify the contributions of these processes to flame suppression. The possibility of flame radiation blockage

is even less well understood. These physical mechanisms will not be discussed further.

The majority of tests utilized for agent suppression efficiency characterization are expected to be sensitive to the physical processes of cooling and dilution and to any chemical mechanisms for

32
flame suppression. Even for these mechanisms, the relative contributions of each to total agent suppression

effectiveness are not well characterized.

Early studies focused on the role of inert agents in the extinction of flames. These

studies are important since these gases are believed to play no chemical role in inhibiting combustion. As a

result, their effectiveness can only be due to cooling and dilution. Therefore, these gases provide examples

of flame suppression behavior where the mechanism can be characterized as well known.

Coward and Hartwell [111] reported on the extinction of methane flames by carbon

dioxide, nitrogen, helium, and argon. These workers showed that the "extinctive action" of CO2, Ar, and N2

were nearly in the inverse ratio of their heat capacities and concluded that heat removal from the reaction zone was the principal mechanism of flame inhibition. Helium was found to be more effective than predicted,

based on heat capacity effects alone. This was attributed to the high thermal conductivity of this low

molecular weight gas and suggests that thermal heat transfer plays a minor, but detectable, role in an agent's

effectiveness.

In 1925 White [112] suggested that flame temperatures for a given fuel-air mixture were nearly constant at the lower flammability limit and were independent of the initial temperature of the

mixture. The limiting temperature did vary from fuel to fuel. An experimental investigation by Simmons and

Wolfhard [113] for a number of fuel-air mixtures diluted by nitrogen supports this conclusion. Many authors

have applied the idea of a well-defined limit temperature to the understanding of the effects of inert gases on

the flammability limits of fuel-oxidizer mixtures.

Egerton and Fowling [114] calculated adiabatic flame temperatures for hydrogen and

methane flames at their lower flammability limits when the nitrogen in air was replaced with CO2, Ar, and

He. With the exception of added helium, the calculated flame temperatures were roughly the same. The

limiting temperature with helium was higher which is consistent with the findings of Coward and Hartwell

[111] concerning the importance of the high thermal diffusivity of this light gas.

Flame temperatures for methane flames at their fuel and oxidizer extinction limits were measured by Ishizuka and TSuji [115] in a counterflow diffusion flame. The oxidizer used for the

experiments was oxygen mixed with N2. Ar, or He. For N2 and Ar, the flame temperatures were very close

(± 30 K) to 1500 K- In the cases where the oxidizer contained helium, flame temperatures were roughly 1640

K. The slightly higher temperatures which were observed for helium mixtures are consistent with previous

conclusions concerning the limited role thermal conductivity plays in the determination of extinction limits.

Ewing et al. [116] have also considered the effects of inert diluents on temperatures

at flame limits. They calculated adiabatic flame temperatures and concluded that the limit temperatures were

functions of the molecular weight of the inert extinguishants. Both diffusion flames of heptane in air and

premixed flames of methane/air were considered. An explanation was not provided as to why the limit flame

temperature behavior they find differs from that reported by other authors.

There is widespread agreement that the fire suppression effectiveness of certain agents

is beyond what would be expected on the basis of their ability to extract heat. Much of the literature discussed

in Section II.B is based on the hypothesis that chemical mechanisms are active. Fryburg [55] provides a good

review of the justifications for a chemical mechanism based on work published prior to 1950. The following

paragraph quoted from this work is typical of the literature.

"The importance of the chemical actions are indicated by the greatly enhanced

extinguishing effectiveness of the gaseous and liquid halogen-containing compounds, as determined in inflammable-limits studies. These compounds have larger specific heats than the inert gases and the cooling

action would therefore be increased, but the increase is not large enough to account for the much greater

33
effectiveness of many of the compounds investigated by Jorissen." (See references [117,118,119].) "In addition,

there is no relationship between extinguishing effectiveness and specific heat among the halogen compounds.

This effect therefore must be derived fi-om strong chemical actions."

Additional evidence for a chemical mechanism of flame suppression is available in results for the effect of suppressants on the flame temperature at limit concentrations. It has been shown

earlier that physical suppression does not change limit temperatures significantly. Burdon et al. [74]

investigated the effect of methyl bromide on H2-air and CO-air flames. As part of the investigation adiabatic

flame temperatures were calculated for limit mixtures. These limit temperatures were found to increase

substantially as the methyl bromide concentration was raised and the authors concluded that the temperature

rise "may be attributed to the chemical intervention of methyl bromide in the flame reactions" [74].

Simmons and Wolfhard [88] reached an identical conclusion based on measurements on methane-air mixtures inhibited with bromine and methyl bromide. Simmons and Wright [120] considered

the system of propane-air-hydrogen bromide. Adiabatic flame temperatures increased from 1590 K at the lean

limit with no hydrogen bromide to 2100 K for a mixture containing a concentration of HBr which was just

short of the peak percentage.

As part of a study which argues that extinction of hydrocarbon flames can be

understood based solely on heat-absorption processes (even for the "chemical" suppressants), Ewing et al. [116]

found that for certain classes of suppressants the calculated limit flame temperature was raised considerably

above that observed for inert suppressants. Even though it is not the aim of the authors, this observation

provides additional support for a chemical mechanism.

Section II.A4.d noted that, for flames in which only heat loss mechanisms are important, roughly 210 J/K per mole of O2 are required to suppress a flame, flicker et al. [47] used this idea

to analyze the effects of inert diluents and halon 1301 on various fuel-oxidizer combinations. Based on the

nitrogen results, predictions were made for the heat capacity contributions required from CO2, He, and CF3Br.

The experimental amount of CO2 was predicted within 10 percent, but the amounts of He and CF3Br required were greatly overpredicted. We have seen previously that helium gas results in higher heat losses fi-om the

combustion zone due to its unusually high thermal conductivity and therefore more easily extinguishes flames

than heavier molecules. Tlicker et al. [47] concluded that the overprediction of the amount of CF3Br required

is due to a chemical effect of this halon on the flame chemistry.

Using a cup burner test with n-heptane as the fuel Sheinson et al. [45,46] have

determined the amounts of various agents required for extinguishment. They have analyzed their results in terms of the heat capacity of the flame gases per mole of oxygen. Inert agents are found to require roughly

210 J/K for extinguishment. Certain agents such as CF3Br and CF3I require considerably less heat capacity

for the gas mixture. This decrease in the required heat capacity is attributed to a chemical mechanism for flame suppression.

As we have seen, chemical mechanisms of flame suppression have been hypothesized

and tested for many decades. Despite this, until recently there have been no attempts to quantify the relative contributions of physical and chemical mechanisms to the flame extinguishment process. The first attempts,

of which we are aware, are those of Larsen [121,122,123] and Ewing et al. [116]. These authors reached the

somewhat startling conclusion that flame suppression is the result solely of a physical mechanism. This was

argued to be true even for the so-called chemical suppressants.

In the earliest of these papers [121] Larsen found that the effectiveness of halogen

atoms for fire suppression was directly proportional to their atomic weights. It was argued that this supported

a physical mechanism for their extinguishment capabilities, but no hypothesis was made as to why fire suppression effectiveness should scale with atomic weight. It is very likely that some other physical property

34
which scales with atomic weight (e.g., hydrogen halide bond energies decrease with increasing halogen

molecular weight) is the source of the observed correlation.

In another paper [122], it was demonstrated that the flame suppression capabilities

of inert agents could be understood in terms of heat capacity effects. Larsen argued that a similar analysis of

peak concentration data for a number of halons suggested that the effectiveness of these agents was also due

to exclusively heat capacity [123]. Instead of calculating the total heat capacity of the gases at the flame limit,

Larsen reported values for three ratios (Kjq, Kjp, KC ) of heat capacities. Kjq is the ratio of the heat

capacity of the agent to the total heat capacity of a mixture of oxygen and inert which is chosen such that,

when the fuel is added, the mixture passes through the peak concentration. Kjp is a similar ratio for a fuel- agent mixture. KC is the ratio of the total heat capacities of the inerts and the total heat capacity for all gases. All heat capacities are for a temperature of 298 K. Values of Kjq and Kjp were found to be roughly

constant. Larsen argued that this observation supports his contention that only heat capacity effects are important for flame suppression effectiveness.

The monograph [123] where Larsen's paper appeared includes comments from the

participants of the conference [124]. Many of them questioned the analysis and conclusions which Larsen

reached. Perhaps the most important critique was offered by J. W. Dehn. In his comment, Dehn noted that the ratios of heat capacities employed were determined primarily by the heat capacities of nitrogen and air. Variations in other additives would have minor effects on their values. Consequently, these ratios would not be expected to be very sensitive indicators of fire suppression efficiency.

Sheinson et al. [45,46] and Ewing et al. [116] have performed analyses based on the

total heat extraction capabilities of combustion product gases which seem to be more realistic than those

employed by Larsen [122,123]. Sheinson et al. calculated the heat capacities available per mole of O2 for n- heptane diifiusion flames burning at their limit in air/agent mixtures. Seven agents which are expected to be

inert in the flame gave values covering a range of 180-205 J/K(mole-02). The lowest value was for helium

which is expected to have a lower value due to its high thermal conductivity. Values for agents which are expected to take part in the chemistry of the flame (CF3Br and SF^Br) required only on the order of 155

J/K(mole-02). This is taken as strong evidence for a chemical mechanism of flame suppression [45,46].

A different type of analysis was provided by Ewing et al. [116]. These authors

calculated the heat extraction behaviors for a number of fuel/air combustion systems in the presence of various

agents (including solids) and made the assumption that extinction occurs for well-defined flame temperatures.

In this way they were able to correlate the findings for a wide variety of suppressants added to flames. As

discussed above, inert species gave limit temperatures which varied little and are relatively low. This behavior was not observed for those agents which are traditionally considered to be chemically active [116]. The total heat extraction capability of these agents was too low to be the sole source of extinction. Note that this conclusion is at variance with Larsen's [123] contention that only heat capacity effects need be considered.

Ewing et al. noted that agents such as CF3Br can absorb additional heat by decomposing. Even though

decomposition is a chemical process, this is classified as physical extinction since there is no direct interaction

with the combustion chemistry (this viewpoint is consistent with that discussed in Section II.B.2.C). Better agreement was obtained when these additional heat extraction mechanisms were taken into account. The

major conclusion of this work was that "for most substances the extinguishing capacity is related to heatextraction and that many of the effects previously attributed to chemical mechanisms may be thermodynamic

in nature rather than kinetic."

Interestingly, these authors had to assume that the limit temperature varied for different types of agents [116]. For agents which in the past have been classed as chemically active, including some solids, the limit temperatures were considerably higher than for inert gaseous species. As discussed

above, such changes in the limit temperature can be taken as evidence for a chemical mechanism. This work

is important because it emphasizes that all mechanisms for heat removal must be considered in assessing the

35
physical effects of an agent. Furthermore, it provides a prescription for accomplishing this. On the other hand,

the conclusion that only physical processes are responsible for extinguishment is not consistent with the

increases in limit temperatures which are required in order to obtain correlations of flame suppression

effectiveness for different chemical families.

Sheinson et al. [46,125] incorporated some of the ideas of Ewing et al. [116] into a model which attempts to quantify the roles of physical and chemical mechanisms on agent effectiveness. Their

model assumes that physical and chemical effects are additive. Physical contributions are determined by

calculating the heat which can be extracted from the flame by the heat capacity and chemical decomposition

of the agent. As discussed above, a total of roughly 210 J/K(mole-02) are required to inert a mixture.

Cup burner measurements of extinguishing agent concentrations for an n-heptane

pool fire were used for the analysis by Sheinson et al. If the mixtures required less than 210 J/K(moles-02)

the difference was attributed to chemical suppression effects. The assumption of a linear relationship allowed

the relative fractions of physical and chemical suppression to be reported. Interestingly, two agents tested,

SF5CI and S2Fio» seemed to enhance the fire. In agreement with past investigations, it was concluded that CF3CI, CF3Br, CF3I, and SF5Br act as chemical flame suppressants. As an example, these authors conclude

that the suppressant effects of CF3Br are 20 percent physical and 80 percent chemical [46,125].

The analysis of Sheinson et al. [46,125] is recent, and considerably more development

and testing are required. However, the work does provide the first steps toward quantifying the contributions

of physical and chemical mechanisms to flame suppression. If ideas of this type can be further developed, it may become possible to tailor molecules to maximize physical and chemical contributions to flame suppression

behavior.

c. Conclusions Regarding a Chemical Mechanism for Fire Suppression

There is widespread agreement that combustion reactions can be interrupted by the

application of certain fire suppression agents. Most researchers conclude that interference with the flame

chemistry increases the effectiveness of such agents significantly as compared to that expected based on heat

extraction effects alone. The modern understanding of combustion chemistry and kinetics identifies the most

likely chemical mechanism for fire suppression as an interruption of the important free radical chain reactions

responsible for maintaining the high heat release rate. The most likely species for attack by a chemical agent or its products is the H atom.

The fact that some uncertainty remains concerning the chemical mechanism of flame

suppression can be traced to the relatively poor characterization of the process. Recent attempts have been

made to quantify the relative contributions of physical and chemical mechanisms to the effectiveness of fire suppression agents. The tools available to modern combustion scientists should allow these uncertainties to be resolved in the near future.

Based on the extensive literature review discussed above, we have concluded that chemical fire suppression does occur and that chemical mechanisms contribute significantly to the fire suppression capabilities of many agents. For this reason, the ability to develop principles of chemical fire suppression has played a major role in selecting compounds for the exploratory list.

36
C. HALON STABILITY AND DEPLETION OF STRATOSPHERIC OZONE

1. Stability and Properties of Halons

As discussed above, the current commercial halons used for fire suppression have many

desirable properties. In almost every case, these favorable properties can be traced to the unusual chemical

stability of these molecules. In many systems, including the atmosphere and living organisms, the species most

likely to be responsible for chemical attack on a given molecule is the highly reactive hydroxyl free radical,

OH. Due to the relative strength of carbon-halogen bonds compared to the relatively low bond energies of

possible products, OH reactions with fully halogenated species are slow. In contrast, for molecules containing

carbon-hydrogen bonds, OH free radicals can abstract the hydrogen atom rapidly to create a new carbon-based

free radical and a water molecule. The resulting free radical reacts rapidly with O2 and is ultimately destroyed.

The lack of significant reactions and the low polarity of the current commercial halons mean

these molecules are nonconducting and thus safe for use on electrical equipment. The nonreactivity of the

molecules is the principal reason why the species have low toxicity. The normal processes which cause toxic

responses in organisms do not take place. The low reactivity of totally halogenated species also means that they do not react easily with other materials and, therefore, have good compatibility properties.

In combustion, molecules can be destroyed by unimolecular decomposition or attack by H and

OH radicals. Commercial halons such as CF3Br (halon 1301) are unreactive towards OH. They tend to be

about as reactive towards H atoms as are more typical fuel molecules (via H -I- CF^Br -* CF3 + HBr), but

are more likely to undergo unimolecular decomposition (to CF3 -I- Br). These reactions release Br and HBr

which are thought to play important roles in the mechanism of chemical fire suppression. The subsidiary

question, which will be addressed in the course of testing the candidate compounds, is whether the details of

the mechanism and the rate of halogen release affect fire suppression activity. This can be addressed through

experimental work coupled with chemical kinetic modeling. It may well be that there is only a narrow

"window" for effective chemical suppressant activity. If this can be established, it will open the way to designing molecules for specific fire suppression situations.

2. Brief Introduction to Atmospheric Structure and Chemistry

The earth's atmosphere is a dynamic and complicated physical system. In this section, we

introduce some very simple descriptions of the structure and chemistry of two regions of the atmosphere, the

troposphere and the stratosphere, to provide a background for the following discussion on depletion of

stratospheric ozone by the current commercial halons. Details can be found in a number of textbooks (e.g., [126,127]). A report describing the outcome of the Alternative Fluorocarbon Environmental Acceptability

Study (AFEAS) [128] is also relevant. It contains an excellent discussion of these topics including an

examination of compounds designed to replace the widely-employed chlorofluorocarbons (a subclass of halons). Dr. John Herron discusses many of the concepts of atmospheric chemistry related to the current commercial

halons in the companion report "Preliminary Screening Procedures and Criteria for Replacements for halons

1211 and 1301 [129]."

The troposphere is the region of the atmosphere extending from the earth's surface to a height denoted as the tropopause. The tropopause separates the troposphere and the stratosphere. The

height of the tropopause varies with location and season, but is on the order of 11 km [126]. The stratosphere

lies above the tropopause and extends to a height of roughly 50 km where the stratopause is located. The next region of the atmosphere is known as the mesosphere.

37
The troposphere is a region of rapid air movements and intense mixing. As a result, it is reasonably uniform; and chemical species released here are dispersed and mixed within the layer quite rapidly

(on the order of a few weeks). Air pollution in urban areas is the result of chemical processes occurring in

this region of the atmosphere. The chemistry is very complex [127] and no attempt is made here to discuss

it. It is worthwhile to reiterate that hydroxyl free radicals are by far the most important species responsible

for chemical attack in the troposphere.

There are a number of processes by which a molecule can be removed from the troposphere:

• Reactive molecules undergo chemical transformation in the troposphere and in most

cases eventual removal from the atmosphere.

• The troposphere is subject to sunlight having wavelengths greater than 290 nm. If a molecule absorbs at these wavelengths, it is possible that photolysis may occur. Photolysis creates reactive species and eventually leads to the removal of the

molecule from the troposphere.

• If the molecule is water-soluble or capable of hydrolysis, it can interact with moisture

in the troposphere and eventually "rain out."

• If the molecule survives long enough it can eventually diffuse into the stratosphere.

Temperatures generally fall with height in the troposphere. This trend is reversed in the

stratosphere where temperatures begin to increase with altitude. This temperature rise occurs as the result of absorption of the sun's radiant energy at wavelengths shorter than 300 nm by ozone, O3 [126]. As a result of the change in temperature behavior with height, mixing across the tropopause is very slow. Chemical

species released in the troposphere require several years to diffuse into the stratosphere.

Ozone is formed in the stratosphere as the result of photolysis of oxygen by sunlight to create oxygen atoms followed by recombination of the atoms with oxygen molecules to form ozone. These reaction processes can be written as:

O2 + hv ^ 20

O + O2 + M -* O3 + M,

where hv represents a photon having a wavelength shorter than 220 nm and M is a third body required to remove excess thermal energy.

There are also chemical processes taking place in the stratosphere which remove ozone

molecules. The equilibrium concentration of ozone in the stratosphere is the result of a balance between these

destruction and formation processes. O3 is found throughout the stratosphere with a maximum concentration

at a height of approximately 25 km.

3. Current Commercial Halons and Depletion of Stratospheric Ozone

In section I.B.l.b it was pointed out that the current commercial halons are generally

recognized as contributing to the depletion of ozone in the stratosphere. It is now possible to discuss the reasons for this conclusion in more detail.

38
Current commercial halons have been, and continue to be, released into the atmosphere by

a variety of mechanisms. These include discharges during firefighting, training, testing of total flooding systems

(efforts are underway to limit this activity), and leaks [7]. In the vast majority of cases these releases take

place in the troposphere. The current commercial halons have very long tropospheric lifetimes due to their

unusual chemical stability. As a result, they eventually diffuse to the stratosphere. As the molecules rise in the stratosphere they are exposed to shorter wavelength light. Eventually, a height is reached where the

current commercial halons begin to absorb this higher energy light and undergo photolysis which releases bromine atoms. The bromine atoms are highly reactive and initiate a catalytic chain reaction which converts ozone to oxygen molecules in the following manner:

Br + O3 -» BrO +O2

BrO + O -» Br + O2 Net: O3 + O -* 2O2.

As a consequence of this mechanism, the rate of destruction of ozone is increased. This leads to a reduction

of the equilibrium concentration of ozone in the stratosphere. Once introduced into the stratosphere, bromine

atoms have very long lifetimes; and the destruction of ozone can continue for decades. Chlorine and iodine

atoms also catalytically destroy ozone in the stratosphere. Fluorine atoms are recognized as being relatively

unimportant, since effective mechanisms are available for chain termination.

A widely used concept to characterize the ability of a specific type of molecule to catalytically

destroy ozone is the ozone depletion potential (ODP). Several parameters must be considered in deriving this number. These include: tropospheric lifetime, diffusion time from the troposphere to the stratosphere,

effectiveness in destroying ozone, and possible sinks (removal processes) for the reactive species created from

the molecule in the stratosphere. Such calculations are subject to a great degree of uncertainty and are thus

difficult to quantify. As a consequence, values are usually reported relative to the results for CFC-11, CCI3F,

as first suggested by Wuebbles [130]. This ratio has come to be known as the ODP value. As noted above,

ODP values for two of the current commercial halons are estimated to be 2.7 (halon 1211) and 11.4 (halon

1301).

As discussed in Section I.B.l.b reductions of stratospheric ozone have been observed which

are attributed to the release of manmade halons (both current commercial halons and CFCs) into the

stratosphere. The production of these chemicals has been limited by the Montreal Protocol. It is ironic that the chemical stability of the current commercial halons, which makes them so useful for fire suppression, is responsible for their ability to destroy stratospheric ozone, and will ultimately limit their use.

4. Means for Reducing ODP Values of Effective Firefighting Agents

The use of current commercial halons will be strictly limited or curtailed entirely in the future. The challenge is to find replacements which are effective and safe as fire suppression agents and which are less harmful to stratospheric ozone than the current commercial halons. In this section possible means for identifying fire suppression agents which are safe for stratospheric ozone are discussed.

The present understanding suggests that there are two general mechanisms for limiting the

destruction of stratospheric ozone by molecules which are effective as fire suppressants. The first is to employ

agents which contain no chlorine, bromine, or iodine. This requires that agents which are recognized as being

the most effective fire suppression agents, including the current commercial halons, cannot be employed. The

second approach is to use agents which are destroyed over short time scales within the troposphere and thus

do not have time to diffuse to the stratosphere.

39
For the first approach it is necessary to utilize only perfluorinated organics or other classes of molecules which do not contain CI, Br, or I. This approach severely limits the number of possible agents

and removes large classes of molecules which have been shown to be effective fire suppression agents.

The second approach, employing molecules which are effectively destroyed in the troposphere,

might allow some molecules containing the heavier halogens to be used. The discussion in Section II.C.2 provides insights as to how halons might be destroyed in the troposphere. These destruction mechanisms Avill be discussed by considering the possibility of modifying one of the current commercial halons to dramatically

reduce its lifetime in the troposphere. Keep in mind that the discussion is general, and similar considerations

will apply to the entire halon family.

Possible modifications to current commercial halons for reducing tropospheric lifetimes

include:

• providing a site for OH free radical attack,

• extending the absorption region of the molecule toward the red so that solar wavelengths reaching the troposphere can photolyze the molecule, and

• increasing the solubility or susceptibility to hydrolysis so that the molecule will rain

out of the atmosphere.

As examples of these concepts, consider some possible molecular modifications for halon

1301. Keep in mind that these modifications are provided only to demonstrate principles. No claim is made

that these particular molecules will be appropriate alternatives for halon 1301. The susceptibility of halon

1301 to chemical attack by OH can be increased by substituting an H atom for one of the fluorines to give

CF2HBr (halon 1201). The lifetime of this molecule in the troposphere will be reduced compared to that for CF3Br. A second approach is to red-shift the absorption spectrum of the CF3Br. One means of doing this

is to replace the bromine atom with iodine-yielding CF3I (halon 1301). CF3I should be an effective fire suppression agent. Its absorption spectrum is red-shifted from that for CF3Br which should increase the

probability that it will photolyze in the troposphere. Since the solubility of a molecule in water and its susceptibility to hydrolysis both increase with molecular polarity, it is possible that tropospheric lifetimes might

be decreased by increasing the polarity of CF3Br. For example, halon 1201 is more polar than halon 1301 and

would, therefore, be expected to have a shorter tropospheric lifetime.

Modifications discussed here are designed to increase the reactivity of the molecular species.

Such changes are also likely to result in variations in physical properties and characteristics (e.g., fire suppression effectiveness, toxicity, and materials compatibility) which make the molecule less likely to be useful

as a fire suppressant. It is certain that a careful balancing of properties will be required to provide an effective and safe fire suppression agent which is also less harmful to stratospheric-ozone than current commercial

halons. This is the primary challenge to the fire protection community.

40
SECTION III

FAMILIES AND COMPOUNDS INCLUDED ON THE LIST

A, INTRODUCTION

This section describes the development of the list of compounds. The discussion is broken down into a series of chemical families. A discussion is provided as to why these families were chosen, as well as, a summary of previous measurements of fire suppression effectiveness for representative compounds fi^om each

family. The subsections conclude with a tabulation of the names and relevant properties for the family

members which are included in the final list.

B. SATURATED HALOCARBONS

1. Justification for Consideration

The saturated halocarbons or halons (C^FqCI Br I^ where o+p+q+r=2n+2) are well

established as flame suppressants [66]. Halons containing iodine are treated as a special case and are discussed

later. Their mechanism for suppression is not fully resolved between two proposals:

• first, chemical action via catalytic recombination of chain carriers [55]; and

• second, physical action via increasing the capacity of the system to absorb heat

[121,122,123].

In either case, a large number of halocarbons exist that would provide the necessary recombination agent (CI or Br) or adequate stability and heat capacity. The appeal of the current commercial halons was primarily

their relative safety and lack of residue. The safety allowed compounds such as halons 1301, 2402, and 1211

to be used without the need for alternative life support systems in a large number of environments. The lack

of residue and the nonionic character of the compounds also made them ideal for dealing with fires in sensitive

electrical equipment. All of these compounds are very stable to reaction, and this very stability makes them

such a threat to the ozone layer. The halons used in fire suppression are not destroyed in the troposphere,

but are reactive in the stratosphere. In addition, all of the species listed above contain bromine, which has

proven to be much more destructive to the ozone on a per mole basis than chlorine.

The strategy for dealing with the relatively high ozone depletion potentials of the current commercial halons is to provide alternative compounds that either do not reach the stratosphere or, if reaching

the stratosphere, do not participate in catalytic destruction of ozone. In the case of the CFCs (a subclass of

halons) used in refi^igeration and for solvent applications, this has meant a fairly simple modification - adding

a hydrogen to the molecule. The resulting molecule will be destroyed in the troposphere in a time that is short relative to its tropospheric residence time by reactions with atmospheric hydroxyl radicals. It is also

possible to design molecules that will react in sunlight and be destroyed in the troposphere. Finally, within

the halocarbons we may seek molecules that do not destroy stratospheric ozone.

The difficulty in designing such molecules does not come from the requirement that it put

out a fire, or even fi-om the requirement that it not destroy ozone, but rather from the requirement that these

compounds have low toxicity, Tb see this, one need simply to look at the effects of addition of H atoms to any brominated compound. As an example we can use halon 2402, CF2BrCF2Br, which can be hydrogenated

41
in a number of ways. The simplest for this discussion would produce CF2HCF2Br. This molecule would be

expected to react reasonably rapidly in the atmosphere, since the H atom is available for reaction with OH.

At the same time, it may be expected to undergo hydrolysis in an ionic medium to produce HBr and C2F4 more rapidly, and, since it would be expected to have a larger dipole moment, to be more soluble in an ionic

medium. Hydrolysis in rain droplets would be faster and thus aid in the destruction of the compound; but

solubility in blood and subsequent reaction could make the compound more toxic.

Even in cases where the halon is not acutely toxic, it may have side effects that must be

considered. For example, one of the compounds listed below as a candidate, halothane (BrClHCCF3), is an

anesthetic. Halothane has been in clinical use for over 30 years so there is a substantial body of data on its side effects [131]. It is not especially toxic, but there is evidence, as there is for other halocarbons, that cardiac

sensitization does occur. In addition, the very fact that the compound is an anesthetic makes it necessary to

exercise caution in using it as a general replacement for the current commercial halons. While these

precautionary comments must be noted, it is also true that, with regard to toxicity, very small changes in the

structure of the compound can greatly change the physiological effect [132]. The compounds suggested should

be viewed as a starting point for further work and not as a final list. As studies on the toxicity and the fire suppression effectiveness of these compounds are extended, new, closely related compounds may well suggest

themselves for study.

In producing a list of compounds, two basic criteria were applied:

• the compound should have some feature that suggests it would not be as destructive

to the ozone layer as the current commercial halons,

• it should test the basic ideas as to how halocarbons affect flames.

In addition, wherever possible, compounds with low toxicity were sought. In many cases, however, the toxicity

data was not available.

The result of applying the first criterion was that only compounds containing a hydrogen atom,

compounds containing no chlorine or bromine, or compounds that might be photoactive were included. The

first alterative has been discussed briefly above. It simply states that if there is an H atom in the molecule,

the rate of reaction with atmospheric OH might be fast enough to destroy the molecule in the troposphere

before it reaches the stratosphere. The second alternative requires that the molecule be fully fluorinated.

(Iodine-containing halons are discussed separately in Section III.E) The final alternative can be stated as requiring either that the molecule have more than one Br/Cl on a single carbon, or that there be some other

feature in the molecule that shifts the absorption cross section toward the red enough that the solar radiation

flux in the troposphere would be sufficient to photolyze the molecule in a time short compared to the time

expected for the molecule to reach the stratosphere.

The second alternative~the fully fluorinated compounds-is the simplest to discuss and so we

shall begin with it. There has been extensive work on the use of perfluoroalkanes as fire suppressants, partly

as a result of the desire to create atmospheres that would sustain life and not combustion [44,48,133]. In

addition, the fluorinated analog of cyclobutane has been suggested as a possible fire suppressant. The

inclusion of these compounds has the further benefit of testing one of the two proposed mechanisms of fire suppression and thus satisfies the second criterion for selection. The perfluorinated compounds are less reactive than other halocarbons. It is generally assumed that CF4 is inert and thus differences between it and

Cj (single carbon) halocarbons containing Br or CI may be analyzed in terms of the difference between the

chemical and physical effects. The larger perfluorinated compounds are less reactive than the corresponding

bromine-substituted compounds, but since the C-C bonds are about the same strength as those of

hydrocarbons they are not totally inert in a flame.

42
The third alternative-photoactive compounds-requires data that are difficult to measure. The solar flux in the troposphere starts to increase dramatically at exactly the point that most of the current

fire suppressants have steep decreases in their photoabsorption cross sections [134,135]. However, by putting

two bromines or a bromine and a chlorine on the same atom, the absorption cross section shifts toward the

red and the resulting tropospheric lifetime is decreased. In addition, the cross section will shift toward the

red if the molecule is made larger. Going from C1-C2-C3 provides a steady, but small shift toward the red

[136]. Data for most molecules is difficult to find in the literature, and because the absorption cross sections are small, the measurements are subject to impurity effects.

The first alternative - adding H to the halocarbon - is essentially that being followed by the

research leading to alterative refrigerants and solvents. For these compounds, all hydrogenated chlorofluorocarbons, the problem of hydrolysis, discussed above, is much less acute because of the increased C-X bond

strength of Cl/F compounds relative to Br compounds. Thus one mode of toxicity is reduced. Beyond the

toxicity effects there are also the effects on the physical properties of the molecule. In general, if one of the

fluorines is replaced with a hydrogen, the boiling point of the compound will increase due to increased

polarity. This is slightly offset by the decrease in boiling point due to decreased molecular weight, but, in general, the boiling point will increase upon H substitution. Replacing chlorine by hydrogen generally results in a decrease in boiling point. Most other physical properties show similar predictable variations with

substitution. The hydrogen-substituted compounds also offer the greatest scope for examining some of the

proposals for understanding fire suppression.

The idea of endothermicity affecting fire suppression is at the heart of the argument that fire suppressants work by adding to the heat loss mechanisms in the fire. While the suggestion that endothermic

processes are important is not new [116], it has not been systematically explored. In a theoretical calculation one could increase the heat capacity of an additive species indefinitely and at some point the fire would no

longer propagate. Curiously, this has not been done within the context of modern flame modeling calculations. In practice, the larger the molecule, the greater its heat capacity. There are, however, other ways of increasing

the heat-absorbing potential of a molecule. One of these is to find molecules that undergo endothermic

reactions to produce stable products. A simple example of this sort of process would use a hydrogensubstituted analog of halon 2402. In this case, like the example earlier, one of the bromines would be replaced

with an H atom, resulting in CF2HCF2Br. This molecule could eliminate HBr to form CF2=CF2 [137] in a reaction that was estimated by functional group contributions to be about 138 kJ/mole endothermic. The

reaction rate has not been measured, but can be estimated to occur readily in a temperature range of 300-

800" C. The 138 kJ/mole exothermicity is converted to a heat absorbed per gram, it corresponds to about 760

J/g. This should be compared to a total heat absorbed by halon 1301 in going from room temperature to 500° C of about 230 J/g. The reaction endothermicity is in addition to the heat capacity of the starting

material, which would be expected to be larger than that of halon 1301. Even if only 20 percent of the halon

underwent this reaction, it would still represent an addition of 150 J/g to the heat extraction capability of the

system.

There are other important endothermic pathways; one is simple bond breaking. The C-Br

bond strength in CF3-Br is 290 kJ/mole, but the rate constant for bond dissociation is too small for this process to have an effect at temperatures below about 700" C [138]. If the bond energy were lower by about

40 kJ/mol, there might be substantial effects from bond breaking processes of this type. There has been very

little exploration of this class of reactions as an explanation of fire suppression effectiveness.

2. Past Flame-Suppression Measurements

The literature on halogenated hydrocarbons is extensive (see Section II.B). A note of caution

must be included in any survey of fire test results. First, the results are often indicative, not predictive: small

changes in the test configuration will change the results dramatically. Second, there are two approaches that

43
are often in conflict: the "full-scale test" and the "research project." An experiment using a premixed flame

and suppressant added to the fuel gas before combustion is likely to yield different results than an experiment

with a diffusion flame with the suppressant added in the oxidizer stream. Both of these would probably be

classed as "research projects" and might correspond to the results of spraying a suppressant agent at a fuUy

turbulent pool fire. Each of these experiments has value, and all need to be done. However, the

interpretation of the results for each kind of experiment relative to another must be made with extraordinary

care. The role of chemical and heat-capacity effects is best determined with the more controlled research scale

tests, but the final choice as to which of otherwise equally effective agents should be used must be made with

a clear understanding of how the material will be used in practical applications. In general, when trying to

assess data, it is best to find a single experiment done on a large number of compounds—even if the experiment

is not ideal.

The earliest, and, in many ways, the most complete, of the tests of fire suppression agents is the Purdue Foundation Study [25]. In this study over 50 compounds were tested. In the most extensive set of tests, the compounds were added to n-heptane/air mixtures and the amount of the test compound required

to suppress combustion for all heptane/air mixture ratios was reported. The data were taken under reduced

pressure conditions - typically 0.4 - 0.8 atm, and generally over a range of stoichiometric conditions (1-6

percent heptane, corresponding to stoichiometric ratios of 0.5 to 6 in the absence of inhibitor). Not every

inhibitor had the full range of coverage (2-5 percent was the most common), and in most cases only about 16- 20 separate experiments were preformed.

There is no comparable body of data on diffusion flames, or oxygen index type tests. For

these tests, one would use a diffusion flame and add suppressant to the oxidizer stream. The results from such

a test more nearly simulate the effects of a total flooding system. In broad outline, the results would be

expected to be similar, but not identical, to the results of the flame propagation experiments from the Purdue

Study. Very few experiments have been done along these lines, although the work of Creitz [89,94] examined

not only the effect of agent addition to the fuel and oxidizer, but also the effect of different fuels. Unfortunately, only two inhibitors were investigated. Simmons and Wolfhard [88] did similar experiments in a different burner configuration. (The cup burner test series discussed above studied a diversity of fuels, but

focussed on halons 1211 and 1301.)

3. Recommendations

The saturated halocarbons chosen for inclusion on the list will be subject to revision. Small

changes in the structure - moving a hydrogen from the end to an interior carbon, replacing a bromine with

a chlorine, switching the position of a fluorine and a bromine - can have very large effects on toxicity, with

possibly only minor effects on the fire suppression effectiveness. The recommendations are broken up into

three groups based on the rationale for believing the molecule will not deplete the ozone layer. The first group is selected because they have no chlorine or bromine in the molecule. The chemicals in the second are probably photoactive and are more likely to be destroyed by sunlight in the troposphere. In the third group,

all the chemicals contain hydrogen.

a. Perfluoro Compounds

The fluorinated analogues of methane, ethane, propane, n-butane and cyclobutane

are initially considered. In addition, it may prove useful to examine the fluorinated analog of neo-pentane.

The choice among these compounds is based largely on physical properties. Some work on these compounds

indicates a relative effectiveness in fire suppression of C^Fg > €2^6 ^ ^^4 l^]- ^^^ ^^^ straight-chain

perfluoro compounds the boiling points are -128,-78,-37,-2 for CI - C4 respectively (temperatures in °C), so

that all of them might be considered for total flooding applications. The corresponding heat capacities are

63, 105, 146, 188 J/(K-mole). Data are not available on neo-C5Fj2, but the heat capacity should be in the

44
region of 230 J/(K-mole) and the boiling point in the range of 0-10°C. Cyclooctafluorobutane (C4Fg) has a

boiling point of -6*'C and a heat capacity of 156 J/(K-mole). (The heat capacity per mole is the proper value

to be using for a total flood agent since these compounds will be designed to replace a given volume of room

air, and thus a defined number of moles of gas will be delivered. Fbr streaming agents, comparing heat

capacity per unit weight, or possibly per unit volume may be more useful.)

In general, the toxicity of the perfluorocarbons is not a serious issue - the primary

toxic effect is that of asphyxia; that is, it simply replaces the air. Fbr at least some of the fluorinated

compounds, there are other possible problems, cyclooctafluorobutane has been investigated for mutagenic

effects, and one of larger fluorinated hydrocarbons, n-CyPj^, has been reported to be mildly toxic via

inhalation [139]. Tkble 1 summarizes the relevant physical property data on the recommended compounds.

b. Photosensitive Compounds

The photon flux in the troposphere falls off dramatically at wavelengths below 300

imi [127] due to the absorption of ozone in the upper atmosphere. For the current commercial halons, this

is about the point at which they begin to absorb. The net effect is that photolysis is not an important factor

in the destruction of these halons. However, small shifts of the absorption cross section toward the red

(longer wavelength) would provide substantial increases in total rates of solar photolysis. Research for refrigerant substitutes has resulted in data indicating that solar photolysis is significant when there are two or more chlorine atoms on the same carbon atom [140]. This can be generalized to say that solar photolysis is important as a destruction pathway whenever there are any two halogens larger than fluorine on the same

carbon atom. Only for some methane derivatives - CI compounds - would the absorption spectrum be shifted

far enough toward the red for photolysis to be effective. The suggested compounds are CBrClF2, CBr2F2,

CF3CFBr2. Note that the last is an isomer of halon 2402 which is CF2BrCF2Br. Halon 2402 should be

carefully re-investigated since it is on the edge of having a tropospheric lifetime short enough to be acceptable.

CBrClF2 is classed as an asphyxiant and is thus not toxic in the normal sense of the

word. It has a boiling point of -4°C. The other two compounds suggested are higher in boiling point and

thus likely substitutes for the liquid halons. CBr2F2 has a boiling point of 22° C and a room temperature

vapor pressure of 1.15 atm. These physical properties are almost ideal for a liquid agent, since they insure

that there will be a minimum of time for evaporation of the extinguishant after its use. The lifetime for solar

pyrolysis in the troposphere for these two compounds has been estimated: for the chloro compound the

lifetime is 14-21 years; for the bromo compound 0.9-1.4 years. The ethane derivative CF3CFBr2 will probably

have a lifetime in the 1 year range also, and its physical properties will be similar to those of halon 2402. A

summary of the relevant physical data for these compounds is given in Tbble 2.

c. Hydrogen-Containing Compounds

This group logically divides into two subgroups. The first contains those compounds

which are under active consideration as refrigerant substitutes; the second, bromine-containing compounds.

Brominated halocarbons were never used as refrigerants or solvents since the solvation or refrigerant

properties that were desired could be achieved without bromination, which adds to the cost and in general

reduces the chemical stability. There is, however, a broad body of evidence that bromine adds to the fire suppression capability, so brominated compounds were used for this application. In addition, there are special uses for brominated halocarbons, such as halothane, which is used as an anesthetic. The majority of uses for the halocarbons did not require bromine; and so when non-ozone depleting compounds were sought, simple

hydrogen substitution was used. The current set of possible replacement compounds for refrigerants should

all be tested for fire suppression potential. These compounds are listed in Tbble 3 along with relevant physical

property data.

45
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47
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48
The second group, containing bromine, are chosen to try to examine the role of HBr

elimination, to provide H atoms for OH attack, and to examine a range of compounds for toxicological effects. The range of compounds includes some that are simple substitutions of H for F or Br in the current commercial compounds, and some that are extensions in that they are derivatives of propane. These have been

chosen so that the properties could later be better adjusted. The compounds are:

CI: CHF2Br and CHFBrCl

C2: CF3CHBrCl,CF2BrCFHCl,CF2BrCF2H,CH2BrCF3,CF2BrCFHBr,CF2BrCH2Br,CHBrFCHBrF

C3: CF2BrCHFCF3,CF2BrCH2CF2Br,CF2HCBr2CF2H,CBrF2CH2CF3.

This list contains a bias, in that most of these compounds are commercially available. Other isomers may turn out to be important when toxicity is considered, but those listed above provide a framework for examining the fire suppression and physical properties of the molecules. Physical property data

are given in Tkble 4.

For comparison purposes, a list of properties for the current commercial halons is included in Tkble 5. While these compounds are not included explicitly on the final list of potential

replacements, it is anticipated that they will be tested concurrently with the compounds appearing on the final

list.

C. HALOGENATED KETONES, ANHYDRIDES AND ESTERS

1. Justification for Consideration

Fluorinated carbonyl compounds (with appropriate bromine or chlorine substitution) are considered for the present application because the insertion of a carbonyl group into an organic framework

shifts the absorption spectrum of the molecule towards the red. The consequence is that the molecule is more

likely to be photolyzed in the troposphere (see section II.C). A typical case is the contrast between the

absorption spectra of €2^5 ^nd CH3COCH3 [141]. For the alkane, absorption does not occur for wavelengths

above 155 nm. Acetone, however, has an absorption maximum near 280 nm. Thus, it is not surprising that the absorption spectrum of hexafluoroacetone peaks at 313.0 nm [141]. The mechanism and quantum yields for the photolysis of hexafluoroacetone have been studied by many workers [142,143,144,145]. In order to mimic as closely as possible the fire suppressant properties of compounds such as halon 1301 or halon 2402, a bromine group must be substituted for a fluorine in the structure. This will have the effect of moving the

absorption spectrum further into the red.

Spectroscopic information on fluorinated esters and anhydrides does not appear to be

available. However the similarities between the absorption and photochemical data for 1,1,1- trifluoroacetone

and acetone [145] suggest that the photochemical processes are dominated by the presence of the carbonyl

group. Thus the data on the hydrogenated esters and anhydrides indicate that their absorption spectra will not be shifted as much towards the red as the ketones. It will be necessary to verify that photolysis will in fact destroy these compounds in the troposphere. All of these compounds are quite soluble in water. This

provides another possible mechanism for destruction or removal of these compounds in the troposphere.

In comparison to compounds without the carbonyl group (ethers and alkanes), the biggest

changes in physical properties are lower vapor pressures and correspondingly higher boiling points. There will also be a small increase in the heat capacity. A thorough discussion of the chemical consequences under

49
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capacity (J/K-mol

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pressure (atm) (298 K •1-o o o

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50
1 .^O CL

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fM <s

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51
combustion conditions will be presented later. At the simplest level the introduction of small amounts of CO

from the carbonyl group into a flame is expected to have minimal effects.

2. Past Flame Suppression Measurements

Compounds with a carbonyl group have not been used as fire suppressants [146]. In the

Purdue report [25], mention was made of the synthesis of ethyltrifluoroacetate. However, no results on flame

suppression properties were given. As can be inferred from the earlier discussion, the exact nature of the fire suppression process is not well characterized. In the following some of the issues will be discussed. The

mechanism for the decomposition of the suppressant in a fire situation may be an important property when

there is a chemical basis for such activity. Although there are no direct measurements on the mechanisms and

rates for the decomposition of these compounds, some estimates can be made [147,148,149]. If the suppressant

molecule contains no hydrogen atoms, the general decomposition process will involve the cleavage of the

weakest bond [147] and/or hydrogen atom attack on the bromine or chlorine substituent [150,151]. The

gradation of bond strengths for the present discussion is C-F > C-Cl = C-C > C-Br [149]. Thus carbonbromine bonds are the most readily broken in fire situations. Alternatively, hydrogen atoms can abstract chlorine and bromine, leading directly to the formation of the hydrogen halides. This is a much less selective process. At lower temperatures, this is undoubtedly the prime mechanism for removing halides from the

organic moieties. The uncertainty regarding the temperature at which chemical suppressant action is effective prevents a definitive choice between these alternatives. Interestingly, it is usually assumed that hydrogen atoms

will not abstract fluorine atoms. However, there are almost no experimental tests of this assumption.

The consequence of these considerations is that, if one starts with halon 2402 and inserts a carbonyl group between the carbon-carbon bond, the chemical kinetic stability properties (in terms of

unimolecular decomposition to form bromine or hydrogen atom attack leading to hydrogen bromide

formation) will not be greatly changed. There are, however, differences from halon 2402 in the nature of the

perfluorinated fragments. For halon 2402, perfluoroethylene is formed almost immediately upon removal of

the first bromine, whether by radical attack or thermal decomposition. For the carbonyl compounds listed here, their chemical structures suggest the rapid formation of a large variety of perfluorinated compounds and

radicals. It is usually assumed that these properties will have no effect on fire suppression capabilities. On

the other hand, as noted earlier, Sheinson and coworkers [46,125] claim that the CF3 radical acts as a chemical

flame suppressant. Because some of these compounds are toxic, probably the most important reason for investigating the fire suppressant power of this type of compound is to elucidate the role of the organic

fluorine species generated during fire situations.

3. Recommendations

In the absence of any data on the fire suppression properties of compounds containing

carbonyl groups, it is worthwhile to examine these compounds in some detail. Tkble 6 includes the compounds

which are recommended for testing along with relevant physical properties. The first five compounds in Tlible 6 are commercially available. Only one of these compounds contains a bromine group; thus, a true comparison to halons 1301 and 2402 will require custom synthesis of the last two compounds in the table,

which contain bromine atoms. Synthesis of these compounds from common materials should not be

particularly difficult [152]. Direct comparison of the fire suppression properties of these compounds when

bromine is substituted for hydrogen and with the suppression effectiveness of alkanes and ethers should be

especially interesting.

All of these compounds have a considerable degree of toxicity. This is probably the chief

constraint to their use [139]. It is for this reason that fluorinated acids, aldehydes and acyl compounds have

not been included in the list. It may be possible to tise these compounds in dilute mixtures in the presence

of nonchemical suppressants, such as the perfluorinated compounds. It is suspected that the situation with

52
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53
regard to toxicity will not improve appreciably with bromine substitution. Furthermore, bromine substitution

will increase the boiling point by 50-60° C.

D. UNSATURATED HALOCARBONS

1. Justification for Consideration

Hydroxyl radicals add readily to double bonds [153] near ambient temperatures to form a

hydroxyl-alkyl radical. The newly-formed radical readily reacts with the oxygen in the troposphere and can

therefore be destroyed before it is transported into the stratosphere where formation of chlorine and bromine

atoms through photolysis will destroy ozone. Rate constants for OH attack on totally halogenated ethylenes

are, however, much smaller than for ethylene itself [153]. An important issue will be whether this decrease

will move it out of the range necessary for destruction of these molecules in the troposphere. The presence

of the double bond and a bromine atom may shift the absorption spectrum of a particular species further

toward the red and thus give photolysis [141] a chance to destroy the gas before it migrates into the

stratosphere.

The introduction of a double bond leaves physical properties relatively unchanged. There are small decreases in the boiling point and heat capacity; however, profound changes in the possible chemistry can be expected. These are discussed in a subsequent section.

2. Past Flame Suppression Measurements

The Purdue report [25] mentioned that perfluorinated ethylene is combustible and that, in general, unsaturated compounds are ineffective in decreasing the flammability of air and n-heptane mixtures.

However, the exact nature of the unsaturated compounds investigated was not specified; and it was found that 2,2-difluorovinyl bromide had suppression properties similar to methyl bromide. Aside from this cursory mention, Larsen [154] has published a table containing data on lower explosion limits for a variety of

halogenated organics with possible application as anesthetics. These include a number of olefins. Although

exact comparisons are difficult, inspection of the data suggests that the presence of a double bond lowers the

flammability limit.A large number of fluorinated olefins are available. Assuming a special role for bromine in

fire suppression, custom synthesis will be necessary to place bromine in a variety of positions and exploit the

special effects introduced with the presence of a double bond. A very interesting aspect of these compounds

is that, depending on the site of bromination, one can have molecules where the strength of the C-Br bonds

will cover a range of nearly a 100 kJ/mol [138,148,149]. This can be contrasted with the situation for halon

1301 and halon 2402 where the difference in bond energies is only 18 kJ/mol. For example, a bromine in the

allylic position in a compound such as 3-bromoperfluoropropene will have a carbon-bromine bond strength

about 45 kJ/mol lower than that for halon 2402. The bond strength will in fact approach that of the CF3-I

bond. Such a compound can therefore be expected to release bromine atoms through a thermal mechanism

with great rapidity.

Even more interesting is the introduction of possible new reaction pathways. Although

carbon-bromine bond energies adjacent to double bonds are greatly increased, hydrogen atoms can add to double bonds; and thermodynamics dictates that it will displace all halogens except fluorine atoms [155].

Thermochemistry suggests that OH can displace bromine atoms [156,157]. Alternatively, after addition, the

hydrogen halide may be eliminated directly. It is well known that in the pyrolysis of hydrocarbons the

formation of olefins is responsible for the observed self-inhibiting nature of most of these systems [158]. The

fire suppression capability of difluorovinylbromide can be rationalized in terms of the displacement of the

54
bromine atom by a hydrogen atom. This provides a rapid means of releasing bromine into the combustion

region.

3. Recommendations

Tkble 7 lists the names, formulas, and relevant properties for those compounds which are recommended for study. The first six compounds are commercially available. None contains a bromine group.

Therefore, custom synthesis will be necessary to widen the range of possibilities. Based on the earlier comments, the molecules which have been added to Tiible 7 will be particularly interesting.

Bromine substitution will increase the boiling point. Some of the compounds contain

hydrogen. This will render the double bond redundant. The possibility that under certain conditions they may

be inflammable must also be considered [25,154].

Many of these compounds are mildly toxic [139] and therefore compare unfavorably with

halon 1301. Perfluorinated isobutene is an extremely dangerous poison. It may well be necessary to consider

the possibility of its formation during the use of some of the other perfluorinated olefins. Unsaturated olefins

such as l,2-bis(perfluoro-n-butyl)ethylene or bis(di-n-butyl)ethylene have been used as blood substitutes

[159,160]. This would seem to assure that these compounds are not toxic. As blood substitutes, these

molecules must have low vapor pressures or, equivalently, high boiling points. Thus the boiling point for 1,2- bis(perfluoro-n-butyl)ethylene is 132" C and would seem to disqualify this compound on purely physical

grounds. Compounds such as 1,2- bis(perfluoromethyl)ethylene, tetris(perfluoromethyl)ethylene, and those

where there is bromine for fluorine or hydrogen substitution will probably have more reasonable boiling

points. The important issue is whether such molecules will retain the favorable toxicity profiles. Bagnall and

coworkers [161] have synthesized a number of partially-fluorinated butenes with chlorines in the allylic and

vinyl positions in order to investigate possible anaesthetic properties. It appears that a vinyl CF2CI group

leads to unfavorable toxic effects.

The main reason for studying these compounds is to define the role of the double bond. It should be noted that the experimental observations regarding self-inhibition and the lowered explosion limits appear to be contradictory. There are clearly fundamental issues that are not understood. Particularly

important experiments are those that involve studies with bromine in a variety of positions. For example, for perfluorinated propene, studies with bromine substitution in the 1 and 3 positions may well lead to the

determination of whether the manner or rate by which bromine atoms are released into a fire situation is of

any consequence.

E. HALOGENATED ETHERS AND RELATED COMPOUIVDS

1. Justification for Consideration

The addition of an oxygen between two carbon groups in an alkane moves the absorption

spectra about 30 nm toward the red [141]. This suggests that for a compound such as CF2BrCF2Br or CF3CFClBr, oxygen insertion may be sufficient to make it photochemically active [136]. The chances of ethers

with only one bromine or chlorine atoms being photochemically active in the appropriate spectral region is much less likely. The addition of an extra CF2 group is not expected to improve the situation. The effect of

hydrogen substitution will probably be similar to that in the current commercial halons with respect to

reactivity towards OH attack.

Some of the compounds in this class are well known anesthetics [162,163,164,165]. These

include methoxyflurane (CHCI2CF2OCH3), enflurane (CHF2OCF2CHFCI),and isoflurane (CF3CHCIOCHF2).

55
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It is claimed that they are non-flammable. This is however only with reference to their specific application.

Larsen [154] has shown that their lower flammability limits for oxygen are only at the 5 to 7 percent level. This can be compared with a value of 10 percent for methyl bromide. The large number of studies on the use of fluorinated compounds as anesthetics provides a very important initial source of toxicity data

[154,161,164,165,166,167]; however, these data should be used with care, since much of the focus is on shortterm effects. A disturbing property of the ethers is their wide range of (generally unpredictable) biological responses. Hexafluorodiethyl ether, for example, is an extremely potent convulsant. Perfluorodiethyl ether

is, however, only mildly toxic. Of course, a good anesthetic is an undesirable fire suppressant. Indeed, the

ratio of concentrations necessary for satisfactory anesthesia and lethal dosage is rarely an order of magnitude

[154]. Perfluorinated n-butyltetrahydrofuran has been used as a blood substitute. Certainly this application

should provide a very satisfactory guarantee of safety. A high priority should be assigned to the bromination

of the perfluorotetrahydrofuran.

Physical properties of the ethers are quite favorable. The boiling points appear to be little changed with the substitution of the oxygen.

The above discussion has focused on C, F, H, and O compounds. Some consideration has

also been given to halogenated organic systems involving sulfur and nitrogen atoms. The specific compounds

are the perfluorinated thioethers and amines. Although the absorption spectra of these compounds probably

do not extend sufficiently far toward the red for photolysis to be an effective destruction mechanism in the

troposphere [141], a particularly interesting aspect of their behavior is the possibility of addition of OH to the

sulfur or nitrogen moiety followed by reaction with oxygen and subsequent removal from the troposphere.

The evidence for such a process is quite strong for the organic sulfides [168] and less compelling for the

amines where there are insufficient data.

The sulfur analog of the well known anaesthetic methoxyflurane has been synthesized and it appears to be a much more powerful anaesthetic. This suggests that sulfur substitution may well have

deleterious toxic effects in comparison to the ether. However it is known that bis(trifluoromethyl) sulphide

resembles a perfluoro ether in its stability to heat and attack by strong acids and bases [169]. 'n-is(perfluorinated propyl) amine is used as a blood substitute. It can therefore be assumed that there will be no

toxicity problems. It also suggests that smaller members of this group will have similar properties. This is borne out by the inertness of tris(perfluoromethyl) amine [170].

2. Past Flame Suppression Measurements

Malcolm [6] has noted rough flame suppression studies with octadecafluoroperdibutyl ether. On a relative basis it is only half as effective as carbon dioxide. This is difficult to understand since the heat

capacity of the perfluoro compound is much larger than that for CO2. There does not appear to have been

any other prior work using halogenated species containing ether linkages as fire suppressants [25]. The

strengths of the carbon-bromine bonds are expected to be in the same range as halon 1301 and halon 2402.

Perfluorinated phosgene as well as various fluorinated carbenes and methyl radicals are expected to be formed

quite readily. Experimental studies will therefore bear on the question of the importance of such substitutions

for the CF3 and C2F4 from halon 2402 and halon 1301 decomposition. Although it has been noted earlier that the three anesthetic ethers are not really non-flammable in the general sense, it may well be that bromination will improve this property.

3. Recommendations

The compounds listed in Tkble 8 are recommended for study. The first five compounds are commercially available and may also be useful as possible reactants for subsequent synthetic work. With EPA

support, bis(bromodifluoromethyl) ether and l-bromo-1,1,3,3,3- pentafluorodimethyl ether are now being

57
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58
synthesized. The same procedures should lead to the bromination of the enflurane and isoflurane. Perfluoro2-butyltetrahydrofuran is included because of its use as a blood substitute. This is a large compound and its boiling point and vapor pressure are unfavorable. Thus it will be important to test the tetrafluorofuran and

3-bromotetrafluorofuran.

The first prerequisite will be to establish that the simplest brominated ethers can in fact be

photolytically decomposed. Comparison of these compounds with the purely fluorinated analogs will be

extremely interesting not only for the immediate problem, but to develop a better understanding of fire suppression mechanisms. For example, comparisons of the behavior of bis(bromodifluoromethyl) ether with

halon 2402 and l,3-dibromo-l,l,2,2,3,3-hexafluoropropane should yield a great deal of information on

mechanistic issues. It is interesting that enflurane (CHF2OCF2CHFCI) has apparently lower toxic effects in comparison to halothane (CF3CHClBr) and has overtaken the use of the latter as the most used volatile anesthetic agent in many institutions, despite the higher cost [162]. It is possible that the greater toxicity of

the halothane is due to the presence of the bromine group. This is an issue that should be investigated.

For the nitrogen and sulfur compounds, it will be extremely interesting to investigate

bis(perfluoromethy) sulfide and tris(perfluoromethyl) amine, and, should the initial results be favorable, to go on to compounds where bromine is substituted for fluorine. These compounds are not available from

commercial sources. However, the standard electrochemical method (Simons process) [171] is probably

suitable for their preparation. This process has, in fact, been used to prepare some of the amines [170,172].

It is also very convenient that fluorination is not complete. There will, therefore, be a few hydrogens

remaining for bromination. The sulfide can also be prepared from the pyrolysis of the disulfide [173].

F. HALONS CONTAINING IODINE

1. Justification For Consideration

Current commercial flame suppressants such as halons 1211 and 1301 include bromine atoms. Many experts in the field (e.g., [57,72,146] have reported the efficiency of halogen atoms for fire suppression

as follows:

I > Br > CI > F

Some compounds containing iodine were investigated in the Purdue study [25]. Malcolm [6] used these findings to assign "apparent atomic values of firefighting effectiveness" for the halogens. His results were: fluorine, 1; chlorine, 2; bromine, 10; and iodine, 16. Later work showed that extinguishing

concentrations of halons containing F, CI, and Br were correlated accurately in terms of scores obtained simply

by summing the products of the number of each halogen atom in the molecule by its firefighting effectiveness

[97]. Unfortunately, no molecules containing iodine were tested during the development of this correlation.

Despite the apparent effectiveness of iodine atoms for flame inhibition, no compounds

containing iodine have been widely used or tested for flame extinguishment purposes. References in the early

literature of the field [1,5] suggest that halons containing iodine were not considered primarily due to the

scarcity and cost of iodine; it is also clear that the recognition that iodine compounds are generally more toxic

played a role [1].

In general, iodine-containing halons are more reactive and have longer wavelength absorptions

than analogs containing lower molecular weight halogens. These characteristics suggest that molecules

containing iodine will be more easily destroyed in the troposphere than the corresponding bromine

59
compounds. As a result, they are less likely to reach the stratosphere where they would contribute to the

destruction of ozone.

Based on the above discussion, it is considered likely that halons containing iodine will have

good fire suppression capabilities while being less damaging to stratospheric ozone than the current commercial halons. In addition to this practical reason for including a number of compounds containing

iodine on the final list, it is also likely that new principles for the understanding of chemical fire suppression

will emerge following the testing of a number of these species.

2. Past Flame Suppression Measurements

One very short, but intriguing reference, suggests that iodine-containing compounds may be

very effective extinguishment agents for real fires [174]. de C. Ellis refers to early work of R.V. Wheeler and

H.B. Dixon who, it is claimed, discovered "the combustion-inhibiting influence of the iodides" [174].

Measurements were made to test the effectiveness of methyl iodide as compared to carbon tetrachloride, the

commonly-used chemical fire extinguisher of the day. Results indicated that only one fifth of the quantity of

CH3I was required to extinguish a fire. Tfests are described for petrol burning on water with an indication that burning areas greater than 1.3 m^ were used. Carbon tetrachloride sprayed on the fires failed to extinguish;

but when methyl iodide was used, the flames were quickly quenched.

Some common measurements of suppression effectiveness have been reported for iodinecontaining compounds. In 1932 Jorissen et al. [118] reported the flammability limits for methane-air mixtures

inhibited by ethyl iodide. The peak concentration was slightly greater than 5 percent. Flammability peak

concentrations for CH3I (6.2 percent) and C2H5I (6.2 percent) in n-heptane/air mixtures were determined

during the Purdue investigation [25]. Both agents required considerably lower concentrations to inert n- heptane/air mixtures than the corresponding species with bromine. The peak concentrations were somewhat

higher than for fuUy-halogenated alkanes. Lask and Wagner reported the effects of CF3I on the flammability

limits of n-hexane/air mixtures [79]. The peak concentration for this compound was roughly 3.5 percent.

Rosser et al. [78] have reported measurements of reductions in flame speeds for methane/air

mixtures due to the addition of a number of compounds including CH3I and C3H-7I. Their results indicated

that the compounds containing iodine are roughly equivalent to their analogs containing bromine in fire suppression effectiveness. Homann and Poss measured reductions in flame speed as various additives were added to ethylene/air mixtures [81]. Measurements were recorded as a function of pressure. Direct

comparisons were made for CH3I and CH3Br acting as inhibitors. For a range of pressure, the methyl iodide was found to inhibit the flame slightly more efficiently.

name speeds for a one-dimensional ethylene/air premixed flame with 1 percent concentrations

of various agents added have been calculated by Westbrook utilizing a detailed chemical kinetics model [86]. Agents included were HCl, HBr, HI, and methyl, ethyl, and vinyl radicals combined with CI, Br, or I. The

addition of the agents to the fuel/air mixture resulted in significant reductions in calculated flame speeds, with

the relative reductions increasing in the order I = Br > CI. These results suggest that species containing

iodine should be effective fire suppressants.

Sheinson et al. [46,125] have reported cup burner results for heptane fuel in which the

concentrations of agent in air required to extinguish the flame were measured for a number of compounds

including CF3Br (3.1 percent) and CF3I (3.2 percent). These two compounds yielded the lowest percentages

of the compounds tested in this study. As is clear from the values reported, the effectiveness of these two

similar compounds were nearly identical with perhaps a slight edge going to the agent containing bromine.

60
A few workers have investigated the effects of agents containing iodine on fires. The work

of de C. Ellis [174] was described above. Malcolm [56] quotes the results of two relevant studies. One

investigation was performed by the Civil Aeronautics Authority in Indianapolis, IN (See Appendix E, Exhibit

1 in Malcolm [56]). Fires in a model aircraft engine were extinguished by a variety of agents and the amount

required for extinguishment reported as a weight. On a per mole basis, the amounts of methyl iodide and

methyl bromide required were identical. The second study quoted was work performed at the Minnesota

Mining and Manufacturing Company and is summarized in Malcolm's Appendix E, Exhibit 2 [56]. In this study flaming cotton was inserted into a small enclosure in which the inhibitor had been mixed with air and

the amount of agent required for extinguishment measured. One of the gases tested in this way was methyl

iodide. On a per mole basis the most effective agent tested was the halon with iodine. The agent CB (halon

1011) was one of the molecules included in this investigation. The methyl iodide was roughly 10 percent more

effective than this agent.

3. Recommendations

The fire suppression properties, as well as other relevant properties of halons with iodine

atoms, have not been well-characterized despite indications that such compounds are very effective flame

suppressants. A wide range of such compounds is included on the list in order to provide insight into fire suppression mechanisms and to investigate whether such compounds might be used as replacements for existing clean firefighting agents. Appropriate testing of these compounds is likely to provide significant

insights into the effects of replacing bromine with iodine on the ODP and toxicity behaviors of halons.

As a direct test of the effectiveness of compounds containing iodine compared to the three

widely employed halons (1211, 1301, and 2402), four analogs of these compounds with iodine substituted for one or more of the bromine atoms are included on the list. In order to characterize the behavior of

hydrocarbons with a single substituted iodine atom, the homologous series with 1-3 carbons has been added.

Finally, a perfluorinated propyl iodide has been included to characterize the effect of substituting fluorines

for hydrogens on the alkyl iodides fire suppression characteristics. The resulting list of compounds is given

in Tkble 9, along with appropriate physical properties.

G. SULFUR HALIDES

1. Justification for Consideration

a. Parent Properties

Sulfur halides are identified as possible fire suppressants, based principally on the

properties of one member of this class of compounds ~ SF^. This gas has many desirable properties for a chemical fire suppressant. It is colorless, odorless, tasteless, nontoxic, and nonflammable [175]. Since SF^

contains numerous fluorine atoms, the molecule might be expected to have significant fire suppression

capability.

b. Chemical Analogs

SFg is a unique molecule due to its high symmetry and strong bonds. The other

sulfur halides are toxic, reactive, and thermally unstable. As noted above, this is not the case for SF^. Normal

nucleophilic reagents cannot attack the highly symmetric octahedral structure [175].

One might hope that it would be possible to exchange one or more of the fluorine

atoms on SFg for chlorine or bromine to create a gas with properties similar to SF^, but with improved fire

61
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62
suppression capabilities. Unfortunately, this does not turn out to the case. Only two analogs, SF5CI and

SF5Br, are stable. The molecular properties of these species differ dramatically from those of the parent

molecule. SF5CI is stable up to 400" C while SFsBr decomposes at 150° C [176]. Both are easily hydrolyzed.

SF5CI has been reported in rat studies as a strong lung irritant and as being as toxic as phosgene [177],

2. Past Flame Suppression Measurements

Three references were identified which report the mole fraction of SF^ at the flammability

peak (concentration just sufficient to limit flame propagation for all concentrations) for hydrocarbon/air

flames. The Purdue study [25] found that a mole fraction of 0.205 was required to inhibit n-heptane/air flames. This was one of the higher limit concentrations reported of the 56 compounds investigated. A similar

investigation for pentane/air mixtures yielded a mole fraction of 0.158 [82]. Compared to the levels of CO2

necessary for these cases, SF^ appears to be slightly more effective for pentane combustion than for n-heptane,

but relatively high mole fractions of SF^ are required for extinguishment with each fuel. A low-pressure premixed CH4/air flame only required a mole fraction of 0.057 SF^ to cause extinguishment [178]. This mole fraction is somewhat lower than found in the atmospheric-pressure flame

studies, but it is difficult to reach conclusions since the amounts of other gases required to extinguish the lowpressure flame were also smaller than found for the corresponding atmospheric-pressure flames.

Sheinson et al. [45,46] have investigated the effectiveness of SF^ as a flame extinguishment

agent in a cup burner apparatus with n-heptane fuel. Their results and analysis indicate that the only

mechanism responsible for flame suppression with SF^ is the physical effect based on the molecular heat

capacity.

The only fire suppression investigation of halogen-substituted SF^ compounds identified was

the work of Sheinson et al. [45,46] These workers measured the amount of SF5CI and SF^Br required to extinguish n-heptane flames. Their analysis suggests that SF5CI has no chemical suppression capability and

may actually enhance combustion. On the other hand, SF5Br appears to have a definite flame suppression

capability.

3. Recommendations

SF^ is readily available commercially. SF5CI is also produced by specialty manufacturers. No

commercial source of SF^Br has been identified, but an effective procedure for its preparation has been

published [179] and it should be possible to synthesize this molecule at a reasonable cost for testing purposes.

Since a consensus does not exist on the fire suppression capabilities of SF^, this molecule

should definitely be included on the list for testing. Clearly, SF5CI and SF^Br are not suitable as replacements

for the current commercial halons. However, it seems likely that the understanding of fire suppression

mechanisms can be significantly enhanced if these compounds are included in the testing protocol. It is recommended that SF5CI, SF^Br and SF^ be included on the list of test compounds. Relevant properties are included in Thble 10.

H. COMPOUNDS CONTAINING PHOSPHORUS

1. Justification for Consideration

Phosphorus-containing compounds are widely used as fire retardants for natural and man- made polymers [146]. This suggests that gas-phase phosphorus compounds could prove to be effective flame

63
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64
extinguishment agents. It is generally believed that antimony halides are effective radical traps [146] and thus

act as flame suppressants. Since phosphorus and antimony are both group V elements, a similar behavior

might be expected for phosphoriis trihalides.

2. Past Flame Suppression Measurements

An immense literature exists which deals with the use of phosphorus-containing compounds

as flame retardants in solids [146]. However, only a few references have been identified in which the effective- ness of a phosphorus-containing liquid or gas as a flame suppressant has been tested. Phosphorus trichloride was included as one of a large number of compounds tested for fire-suppression capabilities during the study

carried out at Purdue University [25]. Results for this study are reported in terms of the volume percent of

the tested molecule required to prevent flame propagation in heptane/air mixtures. PCI3 required one of the

highest volume fraaions, 22.5 percent, of any species studied during this investigation. Of the 56 compounds

considered in the Purdue study, only CO2, CF4, and HCl required higher volume fractions to prevent flame

propagation.

Lask and Wagner [79] measured the concentrations of a variety of species required to reduce

the flame velocity of a n-hexane/air flame by 30 percent. Included in the tests were PCI3, PBr3, PSCI3, and

PSBr3. These compounds were all found to be considerably more effective inhibitors than CI2, Br2, or CCI4.

These authors concluded that the phosphorus compounds inhibit flames by a second chemical mechanism

which occurs in conjunction with the mechanism responsible for flame inhibition due to halogen molecules.

POCI3 was one of the molecules Miller tested for extinguishment of low-pressure premixed

flames of methane [178]. A considerably lower mole fraction of POCI3 than Br2, which is recognized as an

effective suppressant, was required for extinguishment. Jorissen et al. [118] also noted that POCI3 is a very powerful flame inhibitor. They claimed that less than 1 percent of this compound is sufficient to prevent flame

propagation in methane/air mixtures.

The papers summarized above suggest that some phosphorus-containing molecules may be

very efficient fire suppression agents. At the present time, the fire suppression behavior of this family of

molecules must be classed as poor. Investigation of the fire suppression behavior of phosphorus-containing

molecules is certain to result in an improved understanding of chemical fire suppression mechanisms and

might point the way to possible replacements for the current commercial halons.

3. Recommendations

Only a relatively few liquids and gases containing phosphorus are known [180,181]. These

compounds are the hydrides, trihalides, pentahalides, and oxo-halides. In addition, the phosphonium halides

have been observed. Most of the compounds are highly toxic and hygroscopic. For this reason they are poor

candidates for widespread replacement of existing halons. However, it is possible that one or more of these

compounds may provide important tests for the screens being developed or new insights into flame

extinguishment mechanisms. A choice of appropriate compounds for screen testing is aided by the information

in Tkble 11 [181,182,183,184]. Only a few of these compounds are available commercially. These include

PCI3, PBr3, POCI3, PSCI3, PH3, and PCI5.

Based on previous results of fire suppression investigations and the information shown in

Tlible 11, the compounds included in T^ble 12 have been chosen for inclusion on the final list of compounds.

These compounds should allow conclusions concerning the role of phosphorus in fire suppression effectiveness to be formulated. Comparison between the results for the phosphorus halides and the phosphoryl halides will allow the fire suppression effectiveness of these two families of phosphorus compounds to be characterized.

Finally, by comparing findings for cases where different halogen atoms are substituted on the phosphorus, the

65
TABLE 11. PHOSPHOROUS-CONTAINING GASES AND LIQUIDS

Compound m.p. CC) b.p. cc) Comments

PH3 -209 -126 Highly flammable, can form explosive mixtures

PH4CI 28 subl This compound is very unstable

PH4Br «30 subl This compound is very unstable

PH4I «19 39 This compound is very unstable

PF3 -152 -102 Complexes with hemoglobin, hydrolyses slowly

PCI3 -112 76 Violently hydrolyzed by water

PBrg -40 173 Violently hydrolyzed by water

PF2CI -165 -47

PFCI2 -144 14

PF2Br -134 -16

PFBr2 -115 78.4

PF5 -136 -121 Very hazardous due to hydrolysis by water

POF3 -39 -40

POF2CI -96 3

POFCI2 -80 53

POF2Br -85 32

PSF3 -149 -52

PSCI3 -35 125

PSF2Br -137 36

66
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67
importance of chemical flame suppression due to halogen molecules to the overall suppression efficiency of

this class of molecules can be assessed.

I. SILICON AND GERMANIUM FLAME INHIBITORS

1. Justification for Consideration

a. Family of Chemicals

The focus of this section is on the compounds of silicon (Si) and, to a lesser extent, on some germanium (Ge) analogs. TWo of the other Group IVA elements, tin (Sn) and lead (Pb), are more

appropriately classified as metals. Accordingly, compounds involving these elements will be considered in the

section on metallic flame inhibitors (Section J).

b. Properties

The position of silicon directly below carbon in the periodic table suggests that the

chemistry of these elements will be similar. Like carbon, silicon has a valency of four. There do not appear

to be any compounds derived from the divalent state (3s^p^) which are stable at room temperature [188].

However, the tendency to form divalent compounds increases with atomic weight so that Sn(II) and Pb(II) are

relatively common. The Group IVA elements, other than carbon, do not form strong bonds with like atoms. The Si-Si bond, for example, is notably weaker (213 kJ/mole) than the Si-C bond (301 kJ/mole).

All of the Group IVA elements form stable halides. The silicon and germanium

analogs of the halons, in particular, would be expected to be effective flame inhibitors. This hypothesis was

confirmed very early, at least with respect to silicon tetrachloride (SiCl^), which was one of the chemicals

tested in the Purdue Research Foundation study [25].

Obviously, if both families of chemicals behaved similarly with respect to all properties, including ozone depletion and global warming potentials, there would be no reason to continue

this discussion. There are, however, significant differences in the behavior of these compounds in the

atmosphere. Unlike the halons, all of the halosilanes readily hydrolyze in moist air [185]. An important

consequence is that these compounds will undergo rapid decomposition in the troposphere and would

therefore be expected to have correspondingly low potentials for ozone depletion and global warming.

Unfortunately, this beneficial property is offset by the fact that hydrogen halides are produced in the hydrolysis

of halosilanes. This effect is so pronounced that the presence of a single silicon-halogen bond in a molecule

is sufficient to make its vapors corrosive and dangerous to breathe [185].

On the basis of this consideration, it is clear that along with fire suppression

effectiveness, the propensity for hydrolysis will be the critical factor in determining whether any of the

halosilanes will be viable candidates for the replacement of halons. The strategy, therefore, is to examine the

chemical properties of these molecules in an effort to identify structural permutations which result in a balance

between toxicity and tropospheric lifetime, while at the same time retaining their ability to inhibit flames.

2. Past Flame Suppression Measurements

A list of the results obtained by the Purdue Research Foundation [25] is duplicated in Lyon's

book on fire retardants [146] and in a review article by McHale [66]. The tabulated values are the volume

percent of inhibitor corresponding to the peak in the flammability curve for a premixed n-heptane flame. The

value reported for SiCl4 was 9.9 percent. On the basis of this criterion, the flame suppression efficiency of

68
SiCl4 is between those for halon 1301 (CF3Br) and carbon tetrachloride (CCI4), which were found to have

peak values of 6.1 percent and 11.5 percent, respectively.

In an independent study, Lask and Wagner conducted flame velocity measurements for a series of additives including some halosilanes and related compounds [79,186,187]. The figure of merit was the

volume percent of inhibitor required to reduce the burning velocity of a premixed (stoichiometric) n-hexane

flame by 30 percent. On this basis, it was determined that the flame inhibition activity of SiC^ (0.56 percent) was comparable to BT2 (0.7 percent) but considerably higher than CCI4 (1.38 percent).

It is difficult to make quantitative comparisons between data obtained fi"om flammability curve and flame velocity measurements; however, the relative rankings of the inhibitor efficiencies would appear to be consistent. Thus, in addition to the compounds cited above, both sets of measurements have been made

on chloroform (CHCI3). The Purdue Research Foundation reported that the peak in the CHCI3 flammability curve occurred at 17.5 percent. This implies that it is a less efficient inhibitor than either SiCl4 or CCI4. The

data on flame speeds justify a similar ranking. Lask and Wagner found that it took 1.97 percent of CHCI3

(in the mixture of fuel and oxidizer) to reduce the velocity by 30 percent of the value obtained for the clean

flame. This was considerably more than the amounts of SiCl4 and CCI4 which were required to achieve the same velocity reduction.

A smaller effect was observed for the silicon analog of chloroform - trichlorosilane (SiHCl3).

It required 2.9 percent of this halosilane to reduce the flame speed by 30 percent. Although this is considerably larger than the values obtained for some of the other halogenated compounds, it still indicates a significant degree of flame inhibition. Mixtures of 6.8 percent CO2, which is widely used as fire extinguishing

agent, and 8 percent of N2, were needed to produce the same degree of inhibition.

Flame velocity measurements were also reported by Lask and Wagner on two additional

tetrachlorides of the Group IVA elements. The values of 0.50 percent and 0.19 percent were reported for GeCl4 and SnCl4, respectively. The hierarchy for inhibition: SnC^ > GeCl4 > SiCl4 > CCI4 was also found

to apply to increases in the ignition temperatures of hydrocarbon/(02 + N2) mixtures [187]. No explanation

for this trend has been found; however, it may have some relevance to the problem of interest. It is known

that the susceptibility to hydrolysis of compounds involving Group IVA elements decreases with increasing

atomic weight [188]. Thus, the most potent inhibitors may, in fact, be the least corrosive. Unfortunately, the

drop-off may not be fast enough to yield practical benefits. Thus, SnCl4 readily hydrolyzes and, as a consequence, it is highly corrosive [139]. On the other hand, lead chloride (PbCy, which does not hydrolyze,

is a solid. The toxicity of this compound is probably due more to the presence of a heavy metal than to HCl.

The possibility that some of the mixed halogermanes may be more suitable, however, should not be dismissed

out of hand.

The mechanism by which the halosilanes affect flame inhibition is probably similar, if not

identical, to the halons (vide-supra). The same mechanism, however, cannot explain the flame inhibition which

has been observed for tetramethykilane (Si(CH3)4) [79,186,187]. This compound, which is commonly referred

to as TMS, is routinely used as a standard in nuclear magnetic resonance (NMR) spectroscopy. Although

TMS does have a large heat capacity, the effect is considered to be insufficient to explain the degree of flame

inhibition exhibited by this compound [189]. The magnitude of flame inhibition suggests, instead, that a chemical mechanism is operant One possibility is that the alkyl groups play a role in promoting radical

recombination of H and OH radicals in the flame. Lask and Wagner reported that a mixture of 1.5 percent

of TMS was required to reduce the velocity of their stoichiometric n-hexane flame by 30 percent. This

indicates that the inhibiting effect of TMS is comparable to that of CCI4. The possibility that halogenation

of alkyl groups may increase the ability of alkysilanes to inhibit flames should be examined further.

69
3. Recommendations

Many compounds of the Group IVA elements, including the halosilanes, halogermanes and

alkylsilanes are effective flame inhibitors. The possibility that some of these compounds may be viable

candidates for the replacement of halon fire extinguishing agents warrants further consideration.

A variety of halogenated and alkylated compounds of silicon and germanium are listed, along

with some of their relevant properties in Tkble 13 [190,191]. These particular compounds were selected

because they were thought to represent structural permutations which are likely to affect susceptibility to

hydrolysis and flame-inhibition activity. We recommend conducting corrosion and fire suppression efficiency

testing of these compounds. This information will be useful in identifying silicon and germanium compounds

which are viable alternatives for the existing halon extinguishing agents.

J. METALLIC FLAME INHIBITORS

1. Justification for Consideration

The ability of alkali metal compounds to extinguish fires has been recognized for over 100

years [32]. Sodium hydrogen carbonate (NaHC03) was probably the first dry chemical extinguishing agent.

In addition to NaHCOg, formulations based on potassium hydrogen carbonate (KHCO3), potassium chloride

(KCl) and potassium oxalate (K2C2^4^2^) ^^^ ^^^ ^^ widespread use as extinguishing agents. More

recently, it was discovered that certain heavy metal compounds, including tin chloride (SnCl4), titanium

chloride (TiCl4), tetraethyl lead (Pb(C2H5)4)» chromyl chloride (Cr02Cl2) and iron pentacarbonyl (Fe(CO)5)

are extremely effective flame inhibitors [189].

Metallics have physical and chemical properties which would seem to disqualify them fi'om

consideration as candidates for the replacement of halons. Since these compounds are usually not volatile,

they would be expected to leave a residue, which in many cases, would be highly corrosive. Commercial

extinguishing agents such as "Purple-K" and "Super-K," which are based on KHCO3 and KCl, respectively,

leave a sticky residue which is destructive to electronics and other delicate equipment. Tbxicity is also a

concern, particularly with heavy metals. The vapor pressure of Fe(CO)5 is about 30 Tbrr, while SnC^ has a vapor pressure of about 20 Tbrr at ambient temperature. Thus, although relatively volatile, both compounds

are highly toxic [139] and could not be deployed in the presence of people.

The high degree of activity exhibited by metallic flame inhibitors is the basis for their further

consideration. In one study, Hayes and Kaskan determined that NaHC03 was 20 times more effective than

CH3Br, on a weight percent basis, in inhibiting premixed CH4/air flames [192]. Milne, Green and Benson

arrived at a similar conclusion regarding the relative effectiveness of alkali metals and the halons after studying

inhibition of CH4/air counterflow diffusion flames with CF3Br and "Purple K" [103]. Three of the heavy metal

compounds, Fe(CO)5, Cr02Cl2 and Pb(C2H5)4, are measurably more effective than the alkali metals and may

be as much as two orders of magnitude more efficient than the halons in suppressing hydrocarbon flames

[79,189]. Thus, it is conceivable that a solution containing a small amount of a metallic inhibitor dissolved

in a volatile low toxicity solvent may result in a viable alternative to the halon extinguishing agents. F\irther

elucidation of the operant principles of metallic flame inhibition will also serve to provide additional guidance

in the search for halon replacements.

70
2. Past Flame Suppression Measurements

a. Alkali Metal Inhibitors

The fire suppression properties of alkali metal salts are well established. They are used as extinguishing agents in a wide variety of situations ranging from small household fires to large aircraft fuel fires. A large number of flame velocity and extinction measurements on these compounds have been

reported in the literature [102,193,194,195,1%,197,198,199,200,201].

The consensus which has developed on the basis of these experiments is that flame

inhibition by the alkali metals is the result of a chemical, rather than a thermal process. The distinction

between chemical and thermal suppression is clarified in Section II.B.4.b. Support for this hypothesis was

obtained in early investigations of heptane and gasoline fires conducted by McCamy, Shroud and Lee [193]

and independently by Lee and Robertson [194]. A major conclusion of both studies was that there was no

correlation between heat capacity and fire suppression effectiveness of the alkali metal salts.

The effects of decomposition of the metallic extinguishing agents were not considered

in these early studies and have yet to be fully resolved. Decomposition of alkali metal salts is a highly

endothermic process and might be expected to facilitate suppression by reducing flame temperatures. This

possibility was considered in a paper by Dodding, Simons and Stephens [195]. Their calculations indicated

that the reduction in flame temperatures (at extinction) due to the presence of NaHCOj, varied from about

35 to 75° C, depending on the average particle size of the powder. They went on to conclude that this was

insufficient to account for the observed inhibition. Unfortunately, these results are open to interpretation.

Ewing, Hughes and Carhart performed a similar analysis of the data for a wide variety of extinguishing agents,

including some compounds of the alkali metals [116]. They arrived at just the opposite conclusion - that the

data is consistent with thermal suppression, provided that the energy requirements for decomposition of the

extinguishing agents are taken into account. At the present time, the chemical hypothesis seems to be more

widely accepted. However, the alternative point of view, that the dominant mode of suppression is thermal

in nature, cannot be dismissed out of hand. (See the discussion in Section II.B.4.b.)

The dependence of flame suppression effectiveness on particle size is an important concern because it has a critical impact on the design of efficient delivery systems. Dolan observed that the

surface area of powders was a major factor in determining the ability of alkali metal salts to inhibit explosions

in methane/air mixtures [196]. More recently, Birchall demonstrated that in some alkali metal salts, there is an optimal particle size for reduction in the velocities of town gas/air diffusion flames [197]. Birchall's explanation for this behavior was based on the argument that small particles will decompose before penetrating

the flame front, whereas large particles will pass through before they can volatilize. In the same study, Birchall

confirmed earlier observations reported by Friedrich [198] and by Lee and Robertson [194] that the oxalates

of the alkali metals are particularly effective. It is now generally recognized that the order of eff^ectiveness for a specified alkali metal is: oxalate > cyanate > carbonate > iodide > bromide > chloride > sulfate >

phosphate, whereas the hierarchy for the metals is Rb > K > Na > Li [189].

The elucidation of the chemical mechanisms of alkali metal flame inhibition is a focal point of the research effort in this area. DeWitte, Vrebosch and van Tiggelen observed that alkali metal salts were incompletely volatilized in their downward burning CH4/(N2 + O2) premixed flames [199]. On this basis,

they reasoned that the observed reduction in flame velocities was due to the recombination of combustion

radicals on surfaces of the alkali metal particulates. Although a mechanism based on catalytic radical

recombination seemed very likely, there was considerable debate over whether this occurs on particles

(heterogeneous) or in the gas phase (homogeneous). Evidence supporting a homogeneous mechanism was

obtained from measurements of temperature changes in Na-inhibited premixed CH4/air flames by lya,

WoUowitz and Kaskan [200]. On the basis of spatially resolved concentration measurements, these researchers

71
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72
were able to demonstrate that the degree of inhibition depended only on the concentration of Na atoms that had penetrated the reaction zone and was independent of initial particle size distribution and the nature of

the ligand. This is compelling evidence in favor of a homogeneous mechanism as the efficiency of a heterogeneous catalyst would be expected to increase with the average size of the particles.

Further progress in determining the mechanism of alkali metal flame inhibition was made by Friedman and Levy [102]. They observed that the introduction of elemental potassium in the fuel stream of their counterflow diffusion burner had no effect on the strength of CH4/air flames. (See the

discussion of flame strength in Section II.B.3.e.) This observation could be cited in support of the thermal

suppression mechanism discussed above. Thus, it may be argued that elemental potassium has no effect on

flame speeds because it does not decompose (as do potassium salts) and, therefore, does not withdraw heat

from the flame. Friedman and Levy, however, reasoned that this would also be expected if there was a critical intermediate that could not be produced from elemental potassium in sufficient concentrations to inhibit the

flame. The /esults of thermochemical calculations suggested that KOH was a good possibility. Potassium

salts, for example carbonates and oxalates, decompose by forming K2O which readily reacts with H2O to give

KOH. Friedman and Levy attributed the failure of elemental potassium to inhibit the flame to the slow rate of conversion of K to KOH via the termolecular reaction K + OH + X -» KOH + X. The third body, X,

is needed to dissipate the kinetic energy generated in the collision [202]. Independent results obtained by lya,

WoUowitz and Kaskan support the contention that this termolecular reaction is too slow to have a significant

effect on the chemistry of alkali metal-inhibited flames [200]. Calculations made by these researchers using a kinetic model indicated that the reaction Na + OH + X ^ NaOH + X could not account for the observed

OH concentration profiles. They went on to propose the alternative: Na + H2O - Na-H20; Na-H20 +

OH -* H2O + NaOH. Although this mechanism removes the discrepancy between predicted and observed

OH concentrations, it is inconsistent with Friedman and Levy's original observation that elemental K, and by

implication the other alkali metals as well, is not an effective flame inhibitor.

The details of the mechanism of alkali metal flame inhibition, and in particular

whether the catalysis is homogeneous or heterogenous, have not been fully resolved. Advocates of a homogeneous mechanism tend to agree that the critical intermediate is the alkali metal hydroxide (MOH).

Flame inhibition is thought to result from removal of hydrogen radicals via the reaction MOH + H -» M +

H2O [102,197,200,201]. Note that the inhibitor does not regenerate itself in this mechanism. It has been

postulated, however, that a single functioning of each inhibitor molecule may be sufficient because of the low

concentration of hydrogen radicals in hydrocarbon flames [102]. This mechanism also accounts for the

surprising observation that halide salts are amongst the least effective alkali metal inhibitors [79,189]. The

poisoning effect is due to the tendency of the halogen to tie-up the metal, thereby reducing the concentration

of MOH in the flame.

b. Heavy Metal Inhibitors

Bulewicz and Padley demonstrated that low levels (ppm) of a wide range of metallic

elements including Mg, Cr, Mn, Sn, U and Ba have a measurable effect on the recombination of hydrogen

radicals in premixed H2/(02 + N2) flames [203]. Despite this observation, which would appear to be good

evidence that the ability to inhibit flames is widespread in metals, the data on metallic compounds which do

not contain either Na or K is very limited.

A paper by Lask and Wagner appears to be the first serious attempt to investigate

the influence of heavy metals on flames [79]. The effects of a wide range of additives on the flame velocities of premixed (stoichiometric) n-hexane flames were measured. These additives included TiCl4, SnCl4, Fe(CO)5,

Pb(C2H5)4, Cr02Cl2, as well as a series of phosphorous and silicon compounds. The halogens, Br2 and CI2,

and halogenated hydrocarbons like CH3CI and CCI4 were tested as well. An extended list which was compiled

for a report [186] appears in a later paper by Morrison and Scheller [187]. Lask and Wagner reported that the flame inhibition exhibited by Fe(CO)5, Pb(C2H5)4 and Cr02Cl2 was at least an order of magnitude greater

73
than what was observed with any of the other compounds that were tested. It required less than 0.02 percent

(by volume) of these compounds in the fuel mixture to reduce the flame speed by 30 percent. The other two

metallics, TiCl4 and SnCl4, were also effective requiring about 0.2 percent to achieve a 30 percent velocity

reduction. Fbr comparison, it took a mbrture of 0.7 percent of Br2 and almost 1.4 percent of CCI4 to produce

the same results.

The high degree of flame suppression activity exhibited by Fe(CO)5 had been

previously reported by Jost, Bonne and Wagner [204]. At the same time, it was noted that the catalytic

efficiency depends on the concentration Fe(CO)5 in the flame. This suggests that there may be two distinct mechanisms. A heterogeneous process may be operant at concentrations which exceed the saturation pressures of iron containing species (e. g. FeO) in the flame, whereas at lower concentrations of Fe(CO)5 a homogeneous reaction predominates [205]. Hastie cites the observed fall-off in activity at higher concentrations as an indication that heterogeneous recombination may be less efficient [189].

There is, however, no direct evidence that any of these metallics exhibit homogeneous

flame inhibition. Arguments for a heterogeneous mode have cited the streaky white appearance (indicative

of the presence of nonvolatile oxides) and luminosity which are evident in transition metal inhibited flames

[203]. It is known that Fe(CO)5, in particular, produces finely divided oxides in flames [73,206]. In addition,

particle temperatures in considerable excess of the adiabatic flame temperature (by as much as 400 k) have

been observed [189,203]. This effect has been attributed to the heat released during surface recombination

reactions [203,207,208]. Further evidence of heterogeneous inhibition was presented by Miller [209] and by

Miller and Vree [210]. These investigators assigned continuum emission bands which were observed in low

pressure methane flames (both diffusion and premixed) inhibited by Fe(CO)5 and Cr02Cl2 to hot particles.

In a more recent study, Vanpee and Shirodkar examined the inhibition exhibited by

a wide variety of metal chlorides, acetates and acetylacetonates using a counterflow diffusion burner with an

ethanol/(air + N2) flame [211]. After dissolving the compounds in ethanol, the solutions were atomized in a sonic nozzle and the resulting mist was mixed with the oxidizer. In all cases, with the exception of aluminum

acetylacetonate, the solutions were effective inhibitors. The figure of merit was the increase in oxygen

concentration in the oxidizer stream per unit concentration of the additive at extinction. The transition metal

compounds were most effective when compared on a molar basis. However, when compared on a mass basis

the alkali metal compounds were superior. Surprisingly, Fe(CO)5 was rated comparatively low using either

criterion.

3. Recommendations

Compounds of the alkali metals, as well as some heavy metals including Sn, Ti, Pb, Cr and

Fe are flame inhibitors. Some of these compounds, for example Fe(CO)5, Pb(C2H5)4, Cr02Cl2, may be as much as two orders of magnitude more effective than the halons in inhibiting hydrocarbon flames. As is also the case with the halons, the dominant mechanism of metallic flame inhibition is thought to be chemical - involving the catalytic recombination of hydrogen and hydroxyl radicals, rather than thermal in nature. Although inconclusive, the evidence favors the hypothesis that the catalytic action of alkali metal inhibitors

is homogeneous, whereas a heterogeneous mechanism appears to predominate in heavy metal inhibited flames.

The efficiency of metallic inhibitors depends on the physical states and relative stabilities of the intermediates

(for example metal oxides and hydroxides) which perform the catalytic function. Properties, such as volatility

and average particle size, are also important because they determine the ability of the agent to penetrate the

flame front.

An intensive search has not been successful in identifying low toxicity, high volatility, metallic

flame inhibitors. The unfortunate conclusion is that pure metallic compounds are not acceptable halon

replacements. This does not, however, preclude the possibility that a solution consisting of a small amount

74
of a metallic inhibitor dissolved in a volatile solvent may make an effective fire extinguishing agent The

prospect of using Fe(CO)5 as a fire suppression additive was first considered by Jost, Bonne and Wagner [204].

Mixtures consisting of halogenated fire inhibitors adsorbed on metal powders have also been examined [212].

A list of the metallic flame inhibitors recommended for further study is presented in Tkble

14 along with some of their relevant properties [190,191,213,214]. All of these chemicals, with the exception

of Pb(C2H5)4, are listed in the 1990 - 1991 Aldrich Catalogue. Many of these compounds, including the alkali metal acetates, Fe(CO)5, and both potassium and chromium acetylacetonates, are soluble in ethanol. Flame

inhibition measurements conduaed by Vanpee and Shirodkar [211] suggest that these solutions might be

effective as fire extinguishing agents. Additional experiments, involving solvents which are themselves flame

inhibitors, are warranted.

K EVERT GASES

1. Justification for Consideration

In the present context, gases are considered to be inert if they do not undergo chemical

transformation when they pass through a flame. As a result, these compounds can have no chemical effect on the flame chemistry and therefore must effect suppression by purely physical mechanisms. This point is disoissed extensively in Section II-B. Comparitive studies involving inert and chemical agents should help to further elucidate the differences between physical and chemical suppression.

2. Past Flame Suppression Measurements

There are numerous flame inhibition and suppression investigations utilizing inert species.

These will not be disctissed in detail. Several were disoissed in Section II.B. It should suffice to point out

that CO2 fire extinguishers are widely employed for local firefighting and that their effeaiveness has been the

subject of a great deal of investigation. Nitrogen has been proposed as an inerting agent [215,216,217] but

has not been widely used. The third agent to be recommended here, argon, has not been tested as a practical

firefighting agent

3. Recommendations

The primary reason for including inert compounds on the list is to establish a baseline for purely physical fire suppression and to provide a basis for the comparison of chemical agents. It is recognized

that these agents will not be suitable as replacements for all situations where the current commercial halons

are used.

Three inert agents, N2, CO2, and Ar, have been chosen for inclusion on the list. These

compounds are relatively inexpensive and have a range of heat capacities and densities. Tkble 15 summarizes

the molecular properties of these three species.

As discussed in Section III.B.l carbon tetrafluoride is also included on the list. This species

is believed to be inert at flame temperatures and will th\is provide an example of a still more complicated inert

species for comparison purposes.

75
OSg

QQXzo C ^-v o a. S JO tS^ S "= re re re re re re re 1-H r~ 0\ ^ 00 = 11 c c '^ c B c c «r CO (^ >o > ^

Heat

apacity

/K-mol 298 K)

§8 § rec

rec srecrec

rec

so

1-H

rec u —> ^-^

Vapor

ressure (atm) 298 K)

4-O o ^ % % rec

rec i 1 o o o o o ^ d

Dm ^-^ o

(/a (A

_ ,—

^ S^ S 3^

u

3^

Norma Boiling Point ibp°C E E E E E E o so

<s s o o o c<-, T—

1-H i-H «

t—

Cj tj

y o uu

T3 •o tr T3

5^

:o !2 T3 S "O ."2 3 12 :2 r2 :g ."2 = <«M 3 3 3 3 3 K i s s i s 1 1 .g- .2" .cr .O" .2" CUZu

«9

rr ?5

00

OS SO

00 9o 00 1

rH T-H (S 1—

CO o o n M

(N fS (S

X «* E ouXre omXnU 8

a:•9^

OX

6'

Si• 9-

a:u

B

•I- UP Xu

1/^ ou

u. z re Z u 1^

Xu

u XI £

i>d

(AUO

JS3

4> re

u 1

2^ iz sC

<u sC2

1)

re§

re 1S> 1o1 ou 31 u

TM £

•a 3 IE E E E 1E 1 oo g

,2 -p E3 E 3 3 3 3 3E t E3 c

21 « 2 E =

re « 1

re o O

'5 re

BO

'5 " 1 1 8. 8. i x:u

.c

re

U re »- B

76
COaCO<

O

w

1 .2 ex

-2 ^

Heat of oriza atn

>—

5d

2 § Soo ON

o\

o

K§-^a (S f^ <M

v_^

u f^ S5c^ CQ On

CO

Vap

press (ati (298 c 0\

r4 c

'4-' c ^^ /"^ 00in w-5

Nor

oiling (nbp

On w-> 00

1 00

1—1

1

x>

ulyj (/3 V3 W3 W M « CO 43 &0 00 00

Cl,

ON

1 o\ 1 Z r^

1

r- ^

^t^

CO u

t^

i2"3 <^ o

u

^

tu

_« u z

S o

CO

CO •o "S z, § >

CO B

•3 o

^« f3 C3 2

O e

o II 4-1 k. oo

'2 n CO

COc

77
SECTION rv

CONCLUSIONS AND RECOMMENDATIONS

A total of 103 compounds are included on the list which has been generated during the course of this study. Tkble 16 list the names of these compounds.

A quick review of these compounds reveals that a wide range of chemical families has been

recommended for study. A more careful check reveals that the list meets the goals of the project by including

species which are likely to be considered as immediate replacements for the current commercial halons, while

at the same time, allowing the development of principles for fire suppression and ozone depletion which can be applied to a long-term search for replacements.

It is recommended that these compounds be tested in a very selective series of experimental

investigations chosen to maximize the knowledge to be gained using the insights which have been used in the

development of the list. For instance, certain halons are included on the list to characterize their behavior

in the troposphere. Particular emphasis should be focused on whether or not these molecules will be attacked

by OH radicals or undergo photolysis at wavelengths greater than 300 nm. The effects of changes in chemical

stmaure on fire suppression and toxicity behavior must also be characterized. Similarly, compounds

containing phosphorous and the metal compounds have been added to the list because literature reports

indicate that these compounds are unusually effective fire suppressants. Efforts should be made to characterize

the fire suppression effectiveness of these agents, and, if possible, charaaerize their mechanisms of chemical

flame inhibition. Such insights will provide the knowledge base required for the intelligent design of alternative chemical fire suppressants.

The literature review performed as part of this investigation suggests that there has been no systematic

search for new fire suppressants since the early 1950s. For this reason the review of the literature and

recommendation of initial chemicals to investigate was a necessary and appropriate early step in the search

for suitable alternatives. It is unlikely that this search will be easy, and the effort may not even lead to chemicals which are as effective and safe as the current commercial halons. On the other hand, the need for

effective agents is so great that alternatives will be necessary for certain critical applications. The authors

believe that this document will serve as the guidepost in the important effort to develop alternative chemicals

for use in place of the current commercial halons.

78
TABLE 16. COMPLETE LIST OF RECOMMENDED COMPOUNDS

perfluoromethane

perfluoroethane

perfluoropropane

perfluoro-n-butane

perfluorocyclobutane trifluoromethane pentafluoroethane

1 ,1,1 ,2-tetrafluoroethane dibromodifluoromethane

2,2-dibromo-l,l,l,2-tetrafluoroethane chlorodifluoromethane

1,1,1 -trichlorethane

2,2-dichloro-l,l ,1 -trifluoroethane

2-chloro-l,l ,1 ,2-tetrafluoroethane

1 ,1 -dichloro-1 -fluoroethane

1 -chloro-1 ,1 -difluoroethane bromodifluoromethane

bromochlorofluoromethane

2-bromo-2-chIoro-l ,1 ,1 -trifluoroethane 2-bromo-l -chloro-l ,2,2-trifluoroethane 1-bromo-l ,1 ,2,2-tetrafluoroethane

2-brontio-l ,1 , 1 -trifluoroethane 1,2-dibromo-l ,1 ,2-trifluoroethane

1 ,2-dibromo-l ,1 -difluoroethane

1 ,2-dibromo-l ,2-difluoroethane

l-bromo-l,l,2,3,3,3-hexafluoropropane

l,3-dibromo-l,l,3,3-tetrafluoropropane

2,2-dibromo-l,l,3,3-tetrafluoropropane

l-bromo-1,l,3,3,3-pentafluoropropane

hexafluoracetone

trifluoroacetic anhydride

bis(perfluoroisopropyl) ketone

methyltrifluoroacetate

3-bromo-l ,1 ,1 -trifluoropropanone

bromopentafluoroacetone

bromomethyltrifluoroacetate

perfluoropropene

f)erfluorobutene-2

perfluorotoluene

1,1,3,3,3-pentafluoropropene-l

3,3,3 trifluoropropene

l,2-bis(perfluoro-n-butyl)ethylene

3-bromoperfluoropropene

1 -bromoperfluoropropene

1 ,2-bis(perfluoromethyl)ethylene

l-bromoperfluoromethyl-2-perfluoromethylethylene

l-bromo-bis(perfluoromethyl)ethylene

tetris(perfluoromethyl)ethylene

tetrafluorodimethyl ether

p)entafluorodimethyl ether

2-chloro-l-(difluorometho}ty)-l,l,2-trifluoroethane

isoflurane

perfluoro-2-butyltetrahydrofuran

bis(bromodifluoroethyl) ether l-bromo-l,l,3,3,3-pentafluorodimethyl ether bromoenflurane

octafluorofuran 3-bromoperfluorofuran

bis(perfluoromethyI) thioether

tris(perfluoroniethyl) amine

iodotrifluoromethane chlorodifluoroiodomethane

l-bromo-l,l,2,2-tetrafluoro-2-iodoethane

l,l,2,2-tetrafluoro-l,2-diiodoethane

iodomethane

iodoethane 1-iodopropane

1 ,1 ,1 ,2,2,3,3-heptafluoro-3-iodopropane

sulfur fluoride

sulfur chloride fluoride

sulfur bromide fluoride phosphorous trifluoride phosphorous trichloride phosphorous bromide difluoride phosphoryl fluoride phosphoryl chloride phosphoryl bromide fluoride tetrachlorosilane

trichlorofluorosilane tetrafluorosilane bromotrifluorosilane

tribromofluorosilane

tetramethylsilane

chlorotrimethylsilane

trichloromethylsilane

chloromethyltrimethylsilane

tetrachlorogermane

tetramethylgermane

sodium hydrogen carbonate sodium acetate potassium hydrogen carbonate

potassium oxalate potassium acetate potassium acetylacetonate

chromium acetylacetonate

chromyl chloride

tin (IV) chloride titanium (IV) chloride

tetraethyl lead

iron pentacarbonyl

nitrogen carbon dioxide argon

79
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[207] Tischer, R. L. and Scheller, K., "The Behavior of Uranium Oxide Particles in Reducing Flames," Combustion and Flame, vol. 15, pp 199-202, 1970.

[208] Bulewicz, E. M. and Padley, P. J., "Metal Oxide Particle Tfemperatures in Flames," Combustion and

Rame. vol. 15, pp. 203-205, 1970.

[209] Miller, W. J., "Rame Ionization and Combustion Inhibition," Fire Research Abstracts and Reviews.

vol. 10, p. 191, 1968.

[210] Miller, W. J. and Vree, P. H., "Rame Ionization and Combustion Reactions," Fire Research Abstracts

and Reviews, vol. 10, pp. 190-191, 1968.

92
[211] Vanpee, M. and Shirodkar, P. P., "A Study of Rame Inhibition by Metal Compounds," Seventeenth

Symposium (Intemationan on Combustion, pp. 787-793, The Combustion Institute, Pittsburgh, 1978.

[212] Fristrom, R. M., "Combustion Suppression," Fire Research Abstracts and Reviews, vol. 9, pp. 125-152,

1967.

[213] The Sigma-Aldrich Library of Chemical Safety Data, First Edition (Lenga, R.E., Editor), SigmaAldrich, 1985.

[214] W^gman, D. D., Evans, W. H., Parker, V B., Schamn, R. H., Halow, E, Bailey, S. M., Chumey, K.

L. and Nuttall, R. L., Journal of Physical and Chemical Reference Data, vol. 11, supplement No. 2.

[215] Tlitem, P.A., Gann, R.G., and Carhart, H.W., "Pressurization with Nitrogen as an Extinguishant for Fir^ in Confined Spaces," Combustion Science and Tfechnology. vol. 7, pp. 213-218, 1973.

[216] Iktem, P.A., Gann, R.G., and Carhart, H.W., "Pressurization with Nitrogen as an Extinguishant for Fire in Confined Spaces. II. Cellulosic and Fabric Fuels," Combustion Science and Tfcchnologv. vol.

9, pp. 255-259, 1974.

[217] Gann, R.G., Stone, J.P, Tktem, F.W., and Carhart, H.W., "Suppression of Fires in Confined Spaces

by Nitrogen Pressurization: III. Extinction Limits for Liquid Pool Fires," Combustion Science and

Tbchnology. vol. 18, pp. 155-163, 1978.

93

APPENDIX A

DATA SHEETS FOR SELECTED COMPOUNDS

This Appendix contains data sheets for each of the selected compounds that include formulae,

common names, classification numbers, physical properties, commercial sources and prices (if available),

toxicity information, references to fire suppression results, and additional relevant comments.

95
Name: perfluoromethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CF4

halon 14, cfc 14

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

75-73-0

-128

Pressure greater than critical pressure. 61

11.6 PCR, Inc., Gainesville, PL 32602, (800)-33 1-63 13

$65/50g

Tbxicity: Essentially non-toxic. CF4 can be view as a simple asphyxiant, that is its action is only to replace air.

Comments: There is a substantial body of evidence to indicate the effectiveness of CF^; however, it will require a much larger concentration than halon 1301 and it may be a significant greenhouse

gas.

Fire suppression studies:

Ewing, C.T., Hughes, J.T. and Carhart, H.W., "The Extinction of Hydrocarbon Flames based on the Heat-absorption Processes which Occur in them," Fire and Materials, vol. 8, pp 148-

156, 1984.

McHale, E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

96
Name: perfluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2F6

halon 26, cfc 116

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

76-16-4

-78 Pressure greater than critical pressure. 106

16.1 PCRJnc, Gainesville,FL 32602, (800)-331-6313

$40/100g

Tbxicity: Very low, also primarily an asphyxiant.

Comments: A more effective fire suppressant than CF4, less effective than C3Fg, also possible problems

with greenhouse effect.

Fire suppression studies:

McHale,E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

97
Name: perfluoropropane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CgFg

halon 38, cfc 218

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

76-19-7

-36

8.69

148

19.7 PCR, Inc., Gainesville, PL 32602, (800)-331-6313

$75/50g

Tbxicity: Sax and Lewis give inhalation data for rats and mice. Rated as mildly toxic by inhalation.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Comments: This compound has the right range for physical properties for a replacement for halon 1301.

As with the other perfluorinated compounds it is likely to be a problem as greenhouse gas.

98
Name: perfluoro-n-butane

Compound group:

Fbrmula:

Alternate Names:

Halogenated hydrocarbons

^4^10

Outside of halon naming conventions.

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

355-25-9

-22.63

189

23.2

PCR, Inc., Gainesville, FL 32602, (800)-331-6313

$50/25g

Tbxicity: As the perfluorinated saturated hydrocarbons become larger, there are increasing toxicity concerns. There has been very limited long term study of these compounds.

Comments:

Previous fire suppression studies:

McHale, E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

99
Name: perfluorocyclobutane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C4F8

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

115-25-3

-63.07

156

23.0

PCR, Inc., Gainesville, FL 32602, (800)-331-6313

$75/25g

Tbxicity: Tbxicity suspect. Decomposition products may be exceptionally toxic. There is some

anecdotal evidence that this compound will decompose in a flame or on hot surfaces to produce perfluoroisobutene which is very toxic. This report does not attempt to cover combustion product toxicity, but the toxicity of the perfluoroisobutene has been reported to be so high that some caution needs to be advised with regard to this compound. Sax and

Lewis give only limited data to indicated low direct toxicity.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Comments: Except for its toxic effects, this compound would be an interesting candidate for the

investigation of chemical energy absorption since it breaks down into two C2F4 molecules in the gas phase.

Fire suppression studies:

McHale, E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

100
Name: trifluoromethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CHF3

halon 13, cfc 23

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

75-46-7

-82

46.7

51

16.7 Aldrich Chemical, Milwaukee, WI 53201, (800)-558-9160

$120/200g

Tbxicity: Tbxicity is expected to be very low. Clayton has reported data showing no fatalities in a 2

hour exposure of guinea pigs at 20% trifluoromethane.

Clayton, J.W., "Fluorocarbon Tbxicity and Biological Action," Ruorine Chemistry Reviews

(ed. Thrrant, P.), vol. 1, 197-252, 1%7.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

Fire suppression studies:

McHale, E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

101
Name: pentafluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2HF5

halon 25, cfc 125

CASN:

Normal boiHng point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

354-33-6

-48.5 10+

94

20+

PCR, Inc., Gainesville, FL 32602, (800)-331-6313

$120/50g

Tbxicity: DuPont has given a value for toxicity of > > 100,000 ppm for rats exposed for 4 hrs. In the same note the stated toxicity of CF3Br was 400,000 - 800,000 ppm. This data comes from

Clayton who reports essentially the same value (Clayton was at Haskell Labs - a branch of

DuPont).

Clayton, J.W., "Fluorocarbon Tbxicity and Biological Action," Ruorine Chemistry Reviews

(ed. Tirrant, R), vol. 1, 197-252, 1967.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

In addition DuPont has recently announced that it will be making C2HF5 available for testing as a fire suppressant.

Estimated for this report by authors.

102
Name: l,l,l>2-tetrafluoroethane

Compound group:

Formula:

Alternate names:

Halogenated hydrocarbons

C2H2F4

halon 24, cfc 134

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

881-97-72

-26.5 7t

87+

22+

PCR, Inc., Gainesville, PL 32602, (800)-331-6313

$195/100g

Tbxicity: Data was not found for this compound, but the 1,1,1 trifluoroethane was reported to have

anesthetic dose for 50% of the mice tested of 50-60% and no fatal dose was reported. In general the more highly fluorine substituted the molecule, the lower its toxicity, so that this compound would be expected to be at least as safe as the 1,1,1 trifluoro compound.

Robbins, B.H., "Preliminary studies of the anesthetic activity of fluorinated hydrocarbons," J. Pharmacology & Experimental Therapeutics, vol. 86, pp 197-204, 1946.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

Note that only compounds with small numbers of H atoms were considered among the

alternative cfc's. As the number of H atoms increases and the corresponding halogen content of the molecule decreases, the fire suppression effectiveness of the molecule will decline.

+ Estimated for this report by authors.

103
Name: dibromodifluoromethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CBr2F2

halon 1202, cfc 12B2

CASN: 75-61-6

Normal boiling point (nbp "C): -58

Vapor pressure (atm at 298 K): 15.8

Heat capacity (J/K-mol at 298 K): 69

Heat of Vaporization (kJ/mol at nbp): 17.5 Source: PCR, Inc., Gainesville, PL 32602, (800)-331-6313

Price: $35/100g

Tbxicity: Clayton reports LC50 in rats of 5.5% for a 15 min exposure.

Clayton, J.W., "Ruorocarbon Tbxicity and Biological Action," Fluorine Chemistry Reviews

(ed. Thrrant, P.), vol. 1, 197-252, 1%7.

Comments: This compound will probably be destroyed by solar photolysis in the troposphere.

Fire suppression studies:

Ewing, C.T., Hughes, J.T. and Carhart, H.W., "The Extinction of Hydrocarbon Flames based on the Heat-absorption Processes which Occur in them," Fire and Materials, vol. 8, pp 148-

156, 1984.

McHale, E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

104
NAME: 2,2-dibromo-l,14)2-tetrafluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2Br2F4

1,1 dibromotetrafluoroethane, FC-114aB2

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

27336-28-8

50t

0.4+ 116+

29+

PCRJnc, Gainesville,FL 32602, (800)-331-6313

$160/100g

Tbxicity: No data found. This is probably more toxic than the symmetric analog since it is less stable.

Comments: This compound is the asymmetric form of halon 2402, and as such could also be called halon

2402, to avoid confusion this name is not used. Because of the two bromine atoms on a

single carbon, this compound should be very sensitive to solar photolysis in the troposphere.

+ Estimated for this report by authors.

105
Name: chlorodifluoromethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CHCIF2

halon 121, cfc 22

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

75-45-6

-41

10.1 57

20.2

Aldrich Chemical, Milwaukee, WI 53201, (800)-558-9160

$30/100g

Tbxicity: This compound has been tested as an anesthetic and the reported AD50 (the dose at which

50% of the test animals are anesthetized) is 20%. No data on fatality was found.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

106
Name: l,l)l-trichloroethane

Compound group:

Fbrmula:

Alternate Names:

Halogenated hydrocarbons

CoH'iCl'i

halon 203, cfc 14

CASK:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

71-55-6

74

0.16

93

29.8

Aldrich Chemical, Milwaukee, WI 53201, (800)-558-9160

$8/100ml

Tbxicity: Sax and Lewis give extensive data and conclude that the compound is moderately toxic by

inhalation. In addition it is an experimental teratogen and sensitizes the heart. Lowest

effective concentration in humans for an effect on central nervous system is reported at 200ppm over a 4H exposure.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

107
Name: 2,2-dichloro-l,l,l-trifluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

halon 2302, cfc 123

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

306-83-2

24

1+102

26t

PCR, Inc., Gainesville, FL 32602, (800)-331-6313

$75/lkg

Tbxicity: Sax and Lewis report 14% in 4 min for mouse toxicity. Robbins reports an LD50 of 7.7%.

Both Robbins and Davies et al. report AD50 of about 2.5%.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Robbins, B.H., "Preliminary studies of the anesthetic activity of fluorinated hydrocarbons," J. Pharmacology & Experimental Therapeutics, vol. 86, pp 197-204, 1946.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

^ Estimated for this report by authors.

108
Name: 2-chloro-l,l,l>2-tetrafluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2HCIF4

halon 241

CASN: 2837-89-0

Normal boiling point (nbp "C): -12

Vapor pressure (atm at 298 K): 4^

Heat capacity (J/K-mol at 298 K): lOl"'" Heat of Vaporization (kJ/mol at nbp): 23^

Source:

Price: PCR, Inc., Gainesville, PL 32602, (800)-331-6313$48/100g

Tbxicity: Davies et al. report an AD50 of 15% in mice.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

^ Estimated for this report by authors.

109
Name: 1,1-dichloro-l-fluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2ri'3Cl2F

halon 212

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

1717-00-6

32

0.5+ 89+

27+

PCR, Inc., Gainesville, PL 32602, (800)-331-6313

$65/250g

Tbxicity: Robbins reports an AD50 of 2.5% and an LD50 of 5% in mice. Davies et al. report an AD50

of 6% in mice.

Robbins, B.H., "Preliminary studies of the anesthetic activity of fluorinated hydrocarbons," J. Pharmacology & Experimental Therapeutics, vol. 86, pp 197-204, 1946.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

+ Estimated for this report by authors.

110
Name: l-chloro-l,l-difluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CUHiCIFt

halon 221

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

75-68-3

-10

3.33

82

22.4

Aldrich Chemical, Milwaukee, WI 53201, (800)-558-9160

$40/100g

Tbxicity: Davies et al. report AD50 of 23% for mice, Rabbins'^ reported AD50 of 25% and no

fatalities.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Robbins, B.H., "Preliminary studies of the anesthetic activity of fluorinated hydrocarbons," J. Pharmacology & Experimental Therapeutics, vol. 86, pp 197-204, 1946.

Comments: This compound is undergoing tests as an alternative cfc for uses other than fire suppression.

Ill
Name: bromodifluoromethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CHBrF2

halon 1201

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

1151-62-2

-15

4.4 59

23+

Great Lakes Chemicals will be selling this in the near future. na

Tbxicity: Tbxicity, as reported by Great Lakes Chemicals, is greater than halon 1211 and much greater

that halon 1301. Cardiac sensitization not reported.

Comments: Great Lakes Chemicals has recently announced that they will be making this compound

available as a commercial fire suppressant.

Fire suppression studies:

McHale, E.T., "Survey of Vapor Phase Chemical Agents for Combustion Suppression," Fire

Research Abstracts and Reviews, vol. 11, pp 90-104, 1969.

+ Estimated for this report by authors, na = not available.

112
Name: bromochlorofluoromethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CHBrClF

halon nil

CASK: 593-98-6

Normal boiling point (nbp "C): 36

Vapor pressure (atm at 298 K): 0.5+

Heat capacity (J/K-mol at 298 K): 63

Heat of Vaporization (kJ/mol at nbp): 28+

Source: No commercial source was identified

Price: na

Tbxicity: Davies et al. report an AD50 of 1% for mice. This compound may be expected to be

substantially more toxic than many of the other halons.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound will have a relatively short lifetime due to solar photolysis as well as reacting

with OH.

+ Estimated for this report by authors, na = not available.

113
Name: 2-bromo-2-chloro-l,l)l-trifluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2HBrClF3

halothane, narcotane

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

151-67-7

50

0.4 104

27.3

PCR, Inc., Gainesville, PL 32602, (800)-331-6313

$25/100g

Tbxicity: Sax and Lewis give extensive data on this molecule since it is widely used as an anaesthetic.

Human toxicity over 3-hour periods starts to occur at about 7000 ppm. In addition it is a

sever eye irritant which may make it undesirable as a suppressant where continued occupation

of the site is necessary. Davies et al. report AD50 in mice of less than 1%, Robbins does not

report data on this compound but has data on the 2-bromo-l-chloro-l,l-difluoro ethane and

gives AD50 of 0.8% and LD50 of 3.7%.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Robbins, B.H., "Preliminary studies of the anesthetic activity of fluorinated hydrocarbons," J. Pharmacology & Experimental Therapeutics, vol. 86, pp 197-204, 1946.

Comments: This compound is included as a research topic. As an anaesthetic it is not appropriate as a

general fire suppressant but it represents an important class of compounds that can undergo

HBr elimination.

114
Name: 2-bromo-l-chloro-l,2,2-trifluoroethane

Compound group:

Fbrmula:

Alternate Names:

Halogenated hydrocarbons

C2HBrClF3

CASN: 354-06-3

Normal boiling point (nbp "C): 53

Vapor pressure (atm at 298 K): 0.4''' Heat capacity (J/K-mol at 298 K): 103

Heat of Vaporization (kJ/mol at nbp): 29^

Source:

Price: PCR, Inc., Gainesville, FL 32602, (800)-331-6313

$25/100g

Tbxicity: Sax and Lewis give data for mice. Lowest toxic concentration reported is 35 ppt over 17

minutes. Davies et al. give an AD50 of 1.1% for mice.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound is more interesting from the point of view of undergoing HBr elimination

since the H and Br are on adjacent carbon atoms rather than on the same carbon atom.

Estimated for this report by authors.

115
Name: l-bromo-l,l)2,2-tetrafluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2HBrF4

halon 2401

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

354-07-4

-5

3.1 86+

23.8

No commercial sources identified. R. Du Boisson of PRC states that this should be easy to make but

start up costs alone will make the cost in the range of $2000-1-

(amount does not matter greatly)

Tbxicity: Davies et al. give an AD50 of 7%. Based on the average value of the AD50/LD50 observed

for bromo-fluoro compounds the LD50 might be estimated to be in the range of 20%.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This is the most ideal candidate for undergoing HBr elimination. The resulting perfluoroethene is not stable and would probably take up radicals in the flame adding to its effectiveness. This molecule should be given high priority in testing and is a strong candidate

for fundamental research since data on the elimination reaction does not exist and estimation

techniques for this class of reactions are not very accurate. The relatively low toxicity also makes this a strong candidate.

+ Estimated for this report by authors.

116
Name: 2-bromo-l,l,l-trifluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

^H2BrF3

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

421-06-7

26

it

91+

27+

Aldrich Chemical, Milwaukee, WI 53201, (800)-558-9160

$28/25g

Tbxicity: Robbins reports AD50 of 2.8% and LD50 of 11.7%

Robbins, B.H., "Preliminary studies of the anesthetic activity of fluorinated hydrocarbons," J. Pharmacology & Experimental Therapeutics, vol. 86, pp 197-204, 1946.

Comments: See comments on previous molecule. Increasing the fluorine content raised the AD50 from

2.8% in this molecule to 7% in the previous molecule. These small differences in the

molecules may change the toxicity a great deal and possibly only marginally affect the fire suppression. Note that in this case the increase in F atom content would be expected to increase the fire suppression.

+ Estimated for this report by authors.

117
Name: l,2-dibromo-l,l,2-trifluoroethane

Compound group:

Fbrmula:

Alternate Names:

Halogenated hydrocarbons

C2HBr2F3

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

354-04-1

76

0.2+

106^' 31+

PCR, Inc., Gainesville, FL 32602, (800)-33 1-63 13

$145/250g

Tbxicity: Davies et al. report AD50 of 0.6%, so that this molecule must be considered more toxic than

most in the halogenated hydrocarbon group.

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: Also a candidate for HBr elimination. Vapor pressure may be too low for many applications,

but in adverse environments where wind shear of the suppressant stream is a factor,

compounds with higher boiling points and therefore greater resistance to dispersion of the

stream may be advantageous.

+ Estimated for this report by authors.

118
Name: l,2-dibromo-l,l-difluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C2H2Br2F2

CASN: 75-82-1

Normal boiling point (nbp "C): 93

Vapor pressure (atm at 298 K): 0.1+

Heat capacity (J/K-mol at 298 K): 95^

Heat of Vapori2ation (kJ/mol at nbp): 33+

Source: PCR, Inc., Gainesville, PL 32602, (800)-33 1-63 13

Price: $25/100g

Tbxicity: Sax and Lewis rate this as mildly toxic by inhalation. Data given indicate toxicity in rats at the 5 ppt level for long exposure.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Conmients: May also eliminate HBr. Boiling point is very high.

Estimated for this report by authors.

119
Name: l,2-dibromo-l,2-difluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

halon 2202

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

20705-29-7

102+

o.oe''' 97+

33+

R. Du Boisson of PRC indicated that this compound is very difficult to make. na

Tbxicity:

Comments:

+ Estimated for this report by authors, na = not available.

120
Name: l-bromo-l,l,2,3,3,3-hexafluoropropane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

CgHBrF^

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

2252-78-0

35.5

0.5+

145+

29+

PCR, Inc., Gainesville, PL 32602, (800)-331-6313

$85/100g

Tbxicity: Sax and Lewis have data on a related compound 3-bromo-l,l,2,2-tetrafluoropropane (CASN

679-84-5) : human lowest toxic concentration was given as 40 ppt. Generally increasing the

fluorine content at the expense of the hydrogen reduces toxicity so this compound may be

expected to be less toxic. Davies et al. report an AD50 of <2% for the 1 -bromo-1,1,3,3,3-

pentafluoro compound. Again, increasing the fluorine content should increase the safety of

the compound. The data does seem to indicate that for the larger halocarbons the ratio of

AD50 to LD50 is lower, but the data are not conclusive.

Sax, N.I.; Lewis, R.J.; "Dangerous Properties of Industrial Materials," Van Norstrand

Reinhold, New York (1987).

Davies, R.H., Bagnall, R.D., Jones, W.G.M., "A Quantitative Interpretation of Phase Effects

in Anaesthesia," Int. J. Quantum Chem: Quantum Biology Symp. No. 1, pp 201-212, 1974.

Comments: This compound is one of the test cases for the HBr elimination.

Estimated for this report by authors.

121
Name: l,3-dibromo-l,l,3,3-tetrafluoropropane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C3H2Br2F4

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

460-86-6

118+

0.04+

138''" 35+

No commercial source was identified na

Tbxicity: Tbxicity probably much greater that the 1-bromo-hexafluoropropane discussed above.

Comments: Vapor pressure probably eliminates this compound as a practical suppressant, but it is included as an example of the propanes which may be capable of delivering much higher heat

capacities.

Estimated for this report by authors, na = not available.

122
Name: 2,2-dibromo-l,l)3,3-tetrafluoropropane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C3H2Br2F4

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

na

120+

0.03+

137+

35+

No commercial source was identified na

Ibxicity: Probably greater than 1-bromo-hexafluoro propane discussed above.

Comments:

+ Estimated for this report by authors, na = not available.

123
Name: l-bromo-l,l,3,3,3-pentafluoropropane

Compound group:

Formula:

Alternate Names:

Halogenated hydrocarbons

C3H2BrF5

CASN:

Normal boiling point (nbp **C): Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

460-88-8

5lt

133+

29+

No commercial source was identified na

Tbxicity: Probably greater than the 1-bromo-hexafluoro propane discussed above.

Comments:

+ Estimated for this report by authors, na = not available.

124
Name: hexafluoracetone

Compound group:

Formula:

Alternate Names:

Halogenated Ketones, Anhydrides and Esters CF3COCF3

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

684-16-2

-26

6.65

118

20.9

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$175.00/100g

Tbxicity: Hexafluoroacetone is given a hazard rating of 3 in Sax and Lewis.

Sax, N. I., and Lewis, R. J. Dangerous Properties of Industrial Materials 7th Edition, Van

Nostrand Reinhold, 1989

Comments: A detailed description of the physics and chemistry of hexafluoroacetone can be found in a

review by Krespan and Middleton

Krespan, C. G. and Middleton, W. J., "Hexafluoroacetone" in Fluorine Chemistry Reviews.

1, 145-196, 1%7

125
Name: trifluoroacetic anhydride

Compound group: Halogenated Ketones, Anhydrides and Esters Formula: CF3COOCOCF3

Alternate Names:

CASN: 407-25-0

Normal boilifig (nbp "C): 40

Vapor pressure (atm at 298 K): .4^ Heat capacity at (J/K-mol at 298 K): ISS"*" Heat of Vaporization (kJ/mol at nbp): 28^

Source: PCR Incorporated, Gainesville, FL 32602 800-331-6313

Price: $125.00/lkg

Tbxicity: Trifluoroacetic anhydride has a hazard rating of 2 in Sax and Lewis. It is a severe skin and

eye irritant.

Sax, N. I., and Lewis, R. J. Dangerous Properties of Industrial Materials 7th Edition, Van

Nostrand Reinhold, 1989

Comments:

^Estimated for this report by authors.

126
Name: bis (perfluoroisopropyl) ketone

Compound group: Halogenated Ketones, Anhydrides and Esters Formula: (iC3F7)2CO

Alternate Names:

CASN: 813-44-5

Normal boiling (nbp "C): 73

Vapor pressure (atm at 298 K): .IS**^ Heat capacity at (J/K-mol at 298 K): 280''' Heat of Vaporization (kJ/mol at nbp): 29.7^

Source: PCR Incorporated, Gainesville, PL 32602 800-331-6313

Price: $160.00/25g

Tbxicity: There are no toxicity data on this compound. Note however the toxic properties of

hexafluoroacetone.

Comments: Comparison of the fire suppressant capacity of this compound with hexafluoroacetone will highlight heat capacity effects.

^Estimated for this report by authors.

127
Name: methyltrifluoroacetate

Compound group:

Formula:

Alternate Names:

Halogenated Ketones, Anhydrides and Esters CF3COOCH3

CASN:

Normal boiling (nbp " C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

431-47-0

44

.4+ 113+

32+

PCR Incorporated, Gainesville, PL 32602 800-331-6313

$130.00/100g

Tbxicity: There are no toxicity data on this compound. From Sax and Lewis one notes that fluorinated

esters have a general lower toxicity rating, 2, than the ketones

Sax, N. L, and Lewis, R. J. Dangerous Properties of Industrial Materials 7th Edition, Van

Nostrand Reinhold, 1989.

Comments: This compound is selected with the view that it will be studied in tandem with the brominated

compound.

^Estimated for this report by authors.

128
Name: 3-bromo-l,l>l-trifluoropropanone

Compound group:

Formula:

Alternate Names:

Halogenated Ketones, Anhydrides and Esters CF3COCH2Br

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

431-35-6

86

.08+

113"^

32"^ PCR Incorporated, Gainesville, FL 32602 800-331-6313

$140.00/100g

Tbxicity: There are no toxicity data,

hexafluoroacetone.

Tbxicity properties should not be any better than the

Comments: 1,1,1 trifluoroacetone can be purchased and it should be possible to brominate this compound. Comparison with the non-brominated compounds should be extremely interesting.

^Estimated for this report by authors.

129
Name: bromopentafluoroacetone

Compound group:

Formula:

Alternate Names:

Halogenated Ketones, Anhydrides and Esters BrCF2COCF3

CASN:

Normal boiling (nbp " C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

815-23-6

31

.9+ 126+

26.4

No commercial source was identified na

Tbxicity: There are no toxicity data on bromopentafluoroacetone. However there is no reason to think

that the reactivity of hexafluoroacetone will be decreased by bromination.

Comments: Bromopentafluoroacetone can be prepared from the reaction ofbromine with pentafluoropropenol-2 following by beta-dehydrobromination of the pentafluoro-l,2ibromopropanol-2 by

heating in N-methylpyroUidone. It is a liquid with an unpleasant odor, soluble in common

solvents. In water it forms a hydrate. It is a lachrymator.

This compound is selected for comparison with hexafluoroacetone and will give direct

information on the effect of bromine.

Belenki, G. G., Fokin, A. V, Rondarev, D. S., Ryazanovam R. M., Sokolov, S. V, Sterlin, S. R., Voronkov, Zeifman, Y. V. "Fluoroaliphatic Compounds" in Synthesis of Fluoroorganic

Compounds. (Knunyants, I. L. and Yakobson, I. L, Editors) Springer-Verlag, New York, pp

3- 108, 1985

^Estimated for this report by authors, na = not available

130
Name: bromomethyltrifluoroacetate

Compound group:

Fbrmula:

Alternate Names:

Halogenated Ketones, Anhydrides and Esters CF3COOCH2Br

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

116478-92-4

105+

.03+ 126+

33.7+

No commercial source was identified na

Tbxicity: There are no toxicity data. Tbxic properties may be similar to other esters.

Comments: It should be possible to brominate the methyltrifluoroacetate. Studying the brominated and

non-brominated compounds will lead to important information on the effect of bromine.

+Estimated for this report by authors, na = not available

131
Name: perfluoropropene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

C3F6

Hexafluoropropene

CASN:

Normal boiling (nbp ° C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

116-15-4

-29

6.42

116

21

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$105.00/lkg

Tbxicity: Sax and Lewis assign a hazard rating of 3. It is rated as mildly toxic by inhalation, ihl-rat LC50:11200mg/m^/4H, ihl-mus LC50: 750 ppm/4H

Larsen has summarized findings on the possible uses of this compound as an anaesthetic.

With mixtures in the 50-75% range anaesthetic effects were mild. However convulsions and

delayed death also occurred.

Sax, N. I., and Lewis, R. J. Dangerous Properties of Industrial Materials 7th Edition, Van

Nostrand Reinhold, 1989

Larsen, E. R. "Fluorine Compounds in Anaesthesiology" in Fluorine Chemistry Reviews.

(Tbrrant, P, Editor.) Marcel Dekker, New York, 1%9

Comments: This compound is selected to determine the effect of double bonds on fire suppressant

activity. It is a base for comparisons with various brominated compounds.

132
Name: perfluorobutene-2

Compound group:

Fbrmula:

Alternate Names:

Unsaturated Halocarbons

C4F8-2

l,l,1.2,3A4,4,octafluorobutene

CASN: 360-89-4

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K): 2.62

Heat capacity at (J/K-mol at 298 K): 138''' Heat of Vaporization (kJ/mol at nbp): 21^

Source: PCR Incorporated, Gainesville, FL 32602 800-331-6313

Price: $200.00/100g

Tbxicity: Sax and Lewis assign a hazard rating of 1. It is mildly toxic by inhalation; ihl-rat LCLo:6100

ppm/4H

Sax, N. I., and Lewis, R. J. Dangerous Properties of Industrial Materials 7th Edition, Van

Nostrand Reinhold, 1989

Comments: The isomer perfluoroisobutene is a deadly poison by inhalation. In studies with this compound some thought should be given to the possibility of conversion to this toxic isomer.

^Estimated for this report by authors.

133
Name: perfluorotoluene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

CF3C6F5

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

434-64-0

104

.03+ 207+

34+

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$156.00/50g

Tbxicity: Perfluorotoluene is given a hazard rating of 1 by Sax and Lewis and is stated to be mildly

toxic by inhalation. Larsen has summarized studies on the possible use of this compound as an anaesthetic and reported delayed death at levels as low as 0.5-0.9%

Sax, N. I., and Lewis, R. J. Dangerous Properties of Industrial Materials 7th Edition, Van

Nostrand Reinhold, 1989

Larsen, E. R. "Fluorine Compounds in Anaesthesiology" in Fluorine Chemistry Reviews.

(Tkrrant, P, Editor.) Marcel Dekker, New York, 1969

Comments: This compound has been selected in order to test the effects arising from a fully fluorinated

aromatic structure.

+Estimated for this report by authors.

134
Name: l,l>3,3,3-pentafluoropropene-l

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

CF3CH=CF2

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization at nbp (kJ/mol):

Source:

Price:

690-27-7

-21

5+

109+

23+

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$500.00/100g

Tbxicity: There are no toxicity data.

Comments: This compound has been selected for comparison with the fully fluorinated propene.

Important information will also be obtained through comparison with the compound where

the hydrogen is replaced by bromine.

^Estimated for this report by authors.

135
Name: 3,3,3-trifluoropropene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

CF•! CH.^Cri2

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

677-21-4

-17

4t

92+

24+

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$220.00/500g

Tbxicity: There is no toxicity data.

Comments: This compound has been selected for comparison with the fully fluorinated propene.

Important information will also be obtained through comparison with the compound where

the hydrogen is replaced by bromine.

^Estimated for this report by authors.

136
Name: 1,2-bis (perfluoro-n-butyl) ethylene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

(nC4F9)CH=CH(nC4F9)

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

84551-43-9

132

.006+

377+

36+

Produits Chimiques Ugine Kuhlmann, France na

Tbxicity: This compound has been used as a blood substitute. Short-term toxic properties should

therefore be satisfactory

Comments: The boiling point is probably too high for use as a fire suppressant. However the ready

availability means that tests can be made immediately. The data summarized by Larsen

indicate that flammability limits are lowered by the presence of the double bond. It will be

very interesting to see how this is carried over to this compound which is extremely inert. A particularly interesting property is that it is readily emulsified. This may prove to be an

interesting way of delivering the suppressant.

Riess, J. G. and LeBlanc, M. "Perfluoro Compounds as Blood Substitutes" Anpewandte

Chemie. International Edition, 9, 621-634, 1978

Larsen, E. R. "Fluorine Compounds in Anaesthesiology" in Fluorine Chemistry Reviews.

(Tkrrant, P, Editor.) Marcel Dekker, New York, 1969

+Estimated for this report by authors, na = not available

137
Name: 3-bromoperfluoropropene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

BrCF2CF=CF2

CASK:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-moI at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

431-56-1

28

it

121"'' 27+

No commercial source was identified na

Tbxicity:

Comments: This compound is selected for comparison with the fully and partially fluorinated propenes.

3-Bromoperfluoropropene can be synthesized through the reaction of

dibromodifluoromethane in the presence of benzoyl peroxide at 100° C. The major product,

3-dibromo-l,l,2,3,3-pentafluoropropane can be dehydro-brominated in the presence of KOH

to form the desired compound.

Tkrrant, P. Lovelace, A. M. and Lilyquist, M. R. "Free Radical Additions Involving Fluorine

Compounds," Journal of the American Chemical Society, 77, 2783-2787

Cocia, A. T, "Free Radical Addition to TVifluoroethylene," Journal of Organic Chemistry.

2995-2996, 26, 1%1

^Estimated for this report by authors, na = not available

138
Name: 1-bromoperfluoropropene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

CF3CF=CFBr

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

14003-53-3

14003-61-3

30+

it

ni''' 27+

No commercial source was identified na

Tbxicity: There are no toxicity data.

Comments: This compound has been selected for comparison with the fully and partially fluorinated

substances that are also recommended for study.

^Estimated for this report by authors, na = not available

139
Name: 1,2-bis (perfluoromethyl) ethylene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

CF3CH=CHCF3

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

66711-86-2

6

1.6+ 130+

26+

No commercial source was identified na

Tbxicity: There are no toxicity data for this compound. The perfluorobutyl analogy is a blood

substitute and it may well be that the properties of this compound will also be favorable. However, it is known that the reactivity of these compound decreases as the size of the

perfluorinated alkyls are increased. It may well be that there is an optimum size for fire suppression purposes.

Riess, J. G. and LeBlanc, M. "Perfluoro Compounds as Blood Substitutes" Anpewandte

Chemie. International Edition, 9, 621-634, 1978

Comments: This compound is proposed in the expectation that the brominated analog will also be

studied. Larsen has shown that the presence of a double bond generally lowers the

flammability limit. It is expected that bromination will raise this value. Comparisons with

perfluorinated butene-2, as well as, 1,1,1,2,3,4,4,4-octafluorobutane will provide an extremely

important set of results regarding the role of double bond in flame suppression.

This compound has been synthesized via the fluorination of fumaric acid by SF4 at 130" C. An alternate synthetic path is telomerization of perfluoroethylene with methyl iodide.

Larsen, E. R. "Fluorine Compounds in Anaesthesiology" in Fluorine Chemistry Reviews.

(Tkrrant, P., Editor.) Marcel Dekker, New York, 1969

Hasek, W. R., Smith, W. C. and Engelhardt, V A., "The Chemistry of Sulfur Tfetrafluoride.

II. The Fluorination of Organic Carbonyl Compounds" Journal of the American Chemical

Society. 82, 543-551, 1960

+Estimated for this report by authors, na = not available

140
Name: l-bromoperfluoromethyl-2-perfluoromethylethylene

Compound group: Unsaturated Halocarbons

Formula: CF2BrHC=CHCF3

Alternate Names:

CASN: na Normal boiling (nbp "C): 51'^ Vapor pressure (atm at 298 K): .1^ Heat capacity at (J/K-mol at 298 K): 138''' Heat of Vaporization (kJ/mol at nbp): 30^

Source: No commercial source was identified

Price: na

Tbxicity: There are no toxicity data.

Comments: This compound has been selected for comparison with 1,2 bis(perfluoromethyl)ethylene.

^Estimated for this report by authors, na = not available

141
Name: 1-bromo-bis (perfluoromethyl) ethylene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

CF3BrC=CHCF3

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

400-41-9

65+

.06t 143+

33+

No commercial source was available na

Tbxicity: There are no toxicity data.

Comments: This compound is selected with the expectation that it will be studied with the non- brominated analog. The comparison of the results from the two studies will yield information on the effect of bromine on fire suppression properties.

It should be possible to synthesize this compound through the hydrobromination of

perfluorobutyne-2.

^Estimated for this report by authors, na = not available

142
Name: tetris (perfluoromethyl) ethylene

Compound group:

Formula:

Alternate Names:

Unsaturated Halocarbons

(CF3)2C=C(CF3)2

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

360-57-6

55

.28+ 180

29

No commercial source was available na

Tbxicity: The tetris(perfluoro-n-butyl)ethylene version of this molecule is a blood substitute. This

molecule is proposed for study in the expectation that it will have similar favorable

properties.

Geyer, R. P., "Perfluorochemicals as Oxygen Transport Vehicles" in Blood Substitutes

(Chang, T M. S. and Geyer, R. R, Editors) Marcel Dekker, New York, pp31-49, 1989

Comments: Possible synthesis routes are outlined in the paper by Bell et al.

Bell, A. N., Fields, R. and Haszeldine, R. N., "Fluoro-olefin Chemistry. Part 13. A Further

Route to Perfluoro-2,3-dimethylbut-2-ene and the Photochemical Rearrangement of Some

Perfluoro-Alkyl Olefins," J. Chem. Soc. 487, 1980

"'^Estimated for this report by authors, na = not available

143
Name: tetrafluorodimethyl ether

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

CF2HOHCF2

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

1691-17-4

2

2+

92+

24.5+

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$150.00/100g

Tbxicity: There are no toxicity data.

Comments: This is the starting material for bromination. Comparison with the brominated compound

can lead to important mechanistic information on chemical fire suppressant mechanisms.

^Estimated for this report by authors.

144
Name: pentafluordimethyl ether

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

CF2HOCF3

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

3822-68-2

-35

7t

109+

21.2+

PCR Incorporated, Gainesville, FL 32602 800-331-6313

$150.00/100g

Tbxicity: There are no toxicity data.

Comments: This is the starting material for bromination. Comparison with the brominated compound

can lead to important mechanistic information on chemical fire suppressant mechanisms.

^Estimated for this report by authors, na = not available

145
Name: 2-chloro-l-(difluoromethoxy)-l,l>2-trifluoroethane

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

CHF2OCF2CHFCI

enflurane, enthrane, methylfluorether

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

13838-16-9

56.5

.29

162''' 29.4+

Anaquest, 2005 West Beltline Highway, Madison Wisconsin 53713-

2318

$400.00^50 cm^

Tbxicity: This compound is a widely used anaesthetic. Health effects are well documented. It is considered to be mildly toxic by inhalation, ingestion and subcutaneous routes and is given

a hazard rating of 2 by Sax and Lewis

Comments: As a successful anaesthetic it is disqualified as a fire suppressant. We have selected this compound in order to study it in tandem with the brominated version.

^Estimated for this report by authors.

146
Name: isoflurane

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

CF3CHCIOCHF2

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

26775-46-7

48.5

.32 167+

28.7''" Anaquest, 2005 West Beltline Highway, Madison Wisconsin 53713-

2318

$400.00/750 cm^

Tbxicity: This is a well known anaesthetic. A great deal of toxicity data exists.

Comments: As an anaesthetic this is not an acceptable fire suppressant. However, it is known to be non- flammable in anaesthetic contexts and since it is readily available it will be interesting to compare this compound with its structural isomer, 2-chloro-l-(difluoromethoxy)- 1,1,2-

trifluoroethane or enflurane (see other data sheet).

^Estimated for this report by authors.

147
Name: perfluoro-2-butyltetrahydrofuran

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

C4F9C4F7O

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

335-36-4

103

.033+ na

33.5'^ PCR Incorporated, Gainesville, FL 32602 800-331-6313

$85.00/500g

Tbxicity: This compound has been used as a blood substitute. It should not have any short term health

effects.

Comments: The vapor pressure of this compound is probably too low for fire suppressant use. However,

its availability and favorable toxic properties suggest that studies be carried out as a preliminary to further test with the side chain removed and with bromine substitution.

^Estimated for this report by authors, na = not available

148
Name: bis(bromodifluoroethyl) ether

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

BrCF20CF2Br

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

na

25+

it

117''' 26.7+

No commercial source was identified na

Tbxicity:

Comments: This is one of the compounds that is being synthesized for EPA. First priority should be

assigned to determining whether this compound can be photolyzed in the troposphere.

^Estimated for this report by authors, na = not available

149
Name: l-bromo,l,l,3,3,3-pentafluorodimethyl ether

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

CF2BrOCF3

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

na

-30''' 6+

104+

No commercial source was identified na

Tbxicity: There are no toxicity data.

Comments: The compound is being synthesized through an EPA-supported program. An important issue

is whether the addition of the bromine will change the photolytic property sufficiently.

^Estimated for this report by authors, na = not available

150
Name: bromoenflurane

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

CBrF20CF2CHFCl

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

na

67+

.2t 175+

30.3+

No commercial source was identified na

Tbxicity: There are no toxicity data. The nonbrominated version of the compound is the well known

anaesthetic enflurane. One does not expect that toxicity will decrease with behavior.

Comments: The nonbrominated compound is easily obtainable. Bromination should be straightforward.

Studies on the fire suppressant capabilities of the pair of compounds should be extremely

informative.

+Estimated for this report by authors, na = not available

151
Name: octafluorofuran

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

C4F8O

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

773-14-8

50t

.33+ 151+

28.8+

No commercial source was identified na

Tbxicity: There are no toxicity data. The perfluorobutyl substituted compound is a blood substitute. This may mean that the toxic properties of this compound will be within acceptable limits.

Comments: It may be possible synthesize this compound through the electrofluorination of tetrahydrofuran.

+Estimated for this report by authors, na = not available

152
Name: 3-bromoperfluorofuran

Compound group:

Formula:

Alternate Names:

Halogenated Ethers

BrC4F70

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

na

105+

.03+ 159+

33.7+

No commercial source was identified na

Tbxicity: There are no toxicity on this compound.

Comments: It may be possible to synthesize this compound through the electrofluorination of

tetrahydrofuran and then brominating the incompletely fluorinated compounds.

+Estimated for this report by authors, na = not available

153
Name: bis(perfluoromethyl) thioether

Compound group:

Formula:

Alternate Names:

Miscellaneous

CF3SCF3

CASN:

Normal boiling (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

371-78-87

-22.2

6.1 126+

25.1+

No commercial source was identified na

Tbxicity: No toxicity data are available. However, note that the thio-analog of the well known

anaesthetic methoxyflurane has been synthesized and tested and showed enhanced properties.

This general trend may hold for all such substitutions.

Le Blanc, M. and Riess, J. G., "Artificial Blood Substitutes Based on Perfluorochemicals" in Preparation. Properties and Industrial Applications of Organofluorine Compounds. (Banks,

R. E., Editor.) Halsted Press, New York, pp 83-138 ,1982

Comments: Bis(perfluoromethyl)thioether is not available from any commercial source. It should be

possible to synthesize the compound via electrochemical fluorination (Simons Process)

starting with dimethyl ether. The process is not complete. Thus it should also be possible to recover thioethers with one or more hydrogens. These should be convenient starting products

for bromination, if these compounds are necessary for subsequent study.

This compound has also been prepared via the photolysis of the disulfide.

Brandt, G. A. R., Emeleus, H. J., and Haszeldine, R. N., "Organometallic and Organometalloidal Fluorine Compounds," Journal of the Chemical Society. 2198-2205, 1952

^Estimated for this report by authors, na = not available

154
Name: tris(perfluoromethyl) amine

Compound group:

Formula:

Alternate Names:

Miscellaneous

(CF3)3N

CASN:

Normal boiling (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity at (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

432-03-1

-10.1 3.9 167+

25.1 No commercial source was available na

Tbxicity: No toxicity data are available. Higher members of this series are used as blood substitutes. This may be an indication that there will be no serious health effects at least in the short term.

Comments: 'll-is(perfluoromethyl) amine is not available from any commercial source. It is readily

prepared from trimethyl amine via electrochemical fluorination (Simons Process). Should

initial tests on these compounds prove to be satisfactory the next step will be to replace one

or two of the fluorine by bromine. This can be accomplished by brominating the hydrogens

from the incomplete fluorination of the trimethyl amine.

Pawelke, G., Heyder, F. and Burger, H., "Halogen Exchange of Fluoroalkyl Amines , Synthesis of Polychloro- and Bromo-TVialkylamines Journal of Fluorine Chemistry. 20, 53-63,

1982.

^Estimated for this report by authors, na = not available

155
Name: iodotrifluoromethane

Compound group:

Formula:

Alternate Names:

Halons Containing Iodine

CF3I

perfluoromethyl iodide, trifluoromethyl iodide, halon 13001

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

2314-97-8

-22.5 na

70.9

22+

Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

$255.90/100 g

Tbxicity: No published data were identified for this compound. Researchers should use caution.

Comments: Fire suppression references:

Lask, G. and Wagner, H.Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eight Symposium (International) on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1962.

Sheinson, R.S., Gellene, G.I., Williams, F.W., and Hahn, J.E., "Quantification of Fire

Suppression Action on Liquid Pool Fires," Abstract for paper presented at the 1978 Fall Tbchnical Meeting of the Eastern Section of the Combustion Institute, Miami, FL, 29

November- 1 December 1978.

Sheinson, R.S., Penner-Hahn, J.E., and Indritz, D., "The Physical and Chemical Action of Fire

Suppressants, Fire Safety Journal, accepted for publication.

^Estimated for this report by authors, na = not available

156
Name: chlorodifluoroiodomethane

Compound group:

Fbrmula:

Alternate Names:

Halons Containing Iodine

CF2CII

halon 12101

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

420-49-5

33

na

76t

No commercial source was identifled. na

Tbxicity: No published data were identifled for this compound. Researchers should use caution.

Comments: A preparative procedure is available in the literature.

Burton, D.J., Shin-Ya, S., and Kesling, H.S., "Preparation of Halo-F-Methanes via Potassium

Fluoride-Halogen Cleavage of Halo-F-Methylphosphonium Salts," Journal of Fluorine

Chemistry, vol. 20, pp. 89-97, 1982.

No fire suppression measurements were identified for this compound.

^Estimated for this report by authors, na = not available

157
Name: l-bromo-l,l,2,2-tetrafluoro-2-iodoethane

Compound group: Halons Containing Iodine

Formula: CFjBrCFjI

Alternate Names: l-bromo-2-iodotetrafluoromethane, halon 24011

CASN: 471-70-5

Normal boiling point (nbp "C): 78

Vapor pressure (atm at 298 K): na Heat capacity (J/K-mol at 298 K): 124"'' Heat of Vaporization (kJ/mol at nbp): 31^

Source: PCR Incorporated, Gainesville, FL 32602, 800-331-6313

Price: $195/100 g

Tbxicity: No published data were identified for this compound. Researchers should use caution.

Comments: No fire suppression measurements were identified for this compound.

^Estimated for this report by authors, na = not available

158
Name: l,l,2,2-tetrafluoro-l,2-diiodoethane

Compound group:

Fbrmula:

Alternate Names:

Halons Containing Iodine

CF2ICF2I

halon 24002

CASN:

Normal boiling point (nbp " C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

354-65-4

112 na

126+

34t

PCR Incorporated, Gainesville, FL 32602, 800-331-6313

$165/100 g

Tbxicity: No published data were identified for this compound. Researchers should use caution.

Comments: No fire suppression measurements were identified for this compound.

^Estimated for this report by authors, na = not available

159
Name: iodomethane

Compound group:

Formula:

Alternate Names:

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

Halons Containing Iodine

CH3I

methyl iodide, halon 10001

74-88-4

42.4

0.53

44.1

27.4

Aldrich Chemical Company, Milwaukee, WI, 53233, 800-0558-9160

$74.70/500 g

Tbxicity: Sax and Lewis: HR:3, High toxic, fire, or reactivity hazard Poison, suspected carcinogen, a human skin irritant, human mutagenic data.

Sigma Aldrich: Carcinogen, highly toxic, vesicant, mutagen

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials. 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Lenga, R.E., The Sigma-Aldrich Library of Chemical Safety Data, Sigma-Aldrich Corporation,

1985.

Comments: Fire suppression references:

de C. Ellis, O.C, "Extinction of Petrol Fires by Methyl Iodide," Nature, vol. 161, pp. 402-403,

13 March 1948.

"Final Report on Fire Extinguishing Agents for the Period September 1, 1947 to June 30,

1950," Purdue Research Foundation and Department of Chemistry, Purdue University, West

Lafayette, IN, July 1950.

Rosser, W.A., Wise, H., and Miller, J., "Mechanism of Combustion Inhibition by Compounds

Containing Halogen," Seventh Symposium (International) on Combustion, pp. 175-182,

Butterworths, London, 1958.

Homann, K-H. and Poss, R., "The Effect of Pressure on the Inhibition of Ethylene Flames,"

Combustion and Flame, vol. 18, pp. 300-302, April 1972.

Westbrook, C.K., "Inhibition of Hydrocarbon Oxidation in Laminar Flames and Detonations

by Halogenated Compounds," Nineteenth Symposium (International) on Combustion, pp. 127-141, The Combustion Institute, Pittsburgh, 1982.

160
Name: iodoethane

Compound group:

Formula:

Alternate Names:

Halons Containing Iodine

CH'jCri2l

ethyl iodide, halon 20001

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

75-03-6

72.3

0.18

67.8

29.4

Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

$107.50/5 g

Tbxicity: Sax and Lewis: HR:3, High toxic, fire, or reactivity hazard

Sigma Aldrich: Tbxic, severe irritant, vesicant

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials. 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Lenga, R.E., The Sigma-Aldrich Library of Chemical Safety Data, Sigma-Aldrich Corporation,

1985.

Comments: Fire suppression references:

Jorissen, W.P., Booy, J., and van Heiningen, J., "Reaction-Regions XXII. On the Prevention

of Explosive Reactions in Gas and Vapour Mixtures by Small Amounts of Various

Substances," Recueil des TVavaux Chimiques des Pay-Bas, vol. 51, pp. 868-877, 15 July 1932.

"Final Report on Fire Extinguishing Agents for the Period September 1, 1947 to June 30,

1950," Purdue Research Foundation and Department of Chemistry, Purdue University, West

Lafayette, IN, July 1950.

Westbrook, C.K., "Inhibition of Hydrocarbon Oxidation in Laminar Flames and Detonations

by Halogenated Compounds," Nineteenth Symposium (International) on Combustion, pp. 127-141, The Combustion Institute, Pittsburgh, 1982.

161
Name: 1-iodopropane

Compound group:

Formula:

Alternate Names:

Halons Containing Iodine

CH-iCH^CHoI

propyl iodide, halon 30001

CASK: 107-08-4

Normal boiling point (nbp "C): 102.4

Vapor pressure (atm at 298 K): 0.6 Heat capacity (J/K-mol at 298 K): 88.3

Heat of Vaporization (kJ/mol at nbp): 32.1 Source: Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

Price: $47.30/500 g

Tbxicity: Sax and Lewis: HR:3, High toxic, fire, or reactivity hazard

Poison by intraperitoneal route, experimental neoplastigen, very mildly toxic by inhalation

Sigma Aldrich: Harmful if swallowed, inhaled, or absorbed through skin; may cause

irritation; chronic effects: carcinogen.

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials, 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Lenga, R.E., The Sigma-Aldrich Library of Chemical Safety Data, Sigma-Aldrich Corporation,

1985.

Comments: Fire suppression references:

Rosser, W.A, Wise, H., and Miller, J., "Mechanism of Combustion Inhibition by Compounds

Containing Halogen," Seventh Symposium (International) on Combustion, pp. 175-182,

Butterworths, London, 1958.

162
Name: l,l,l,2,2,3,3-heptafluoro-3-iodopropane

Compound group:

Formula:

Alternate Names:

Halons Containing Iodine

CF3CF2CF2I

perfluoropropyl iodide, halon 37001

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

754-34-7

40

na

197+

28+

Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

$76.70/25 g

Tbxicity: No published data were identified for this compound. Researchers should use caution.

Comments: No fire suppression measurements were identified for this compound.

^Estimated for this report by authors, na = not available

163
Name: sulfur fluoride

Compound group:

Formula:

Alternate Names:

Sulfur halides

sulfur hexafluoride

CASN:

Normal boiling point (nbp **C): Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

2551-62-4

-63.8 (sublimes)

21.8

97.0

23.6

Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

$%.40/227 g

Tbxicity: Sax and Lewis: HR:1, Low toxic, fire, or reactivity hazard

Chemically inert and considered to be physiologically inert as well.

Sax, N.L and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials, 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

"Final Report on Fire Extinguishing Agents for the Period September 1, 1947 to June 30,

1950," Purdue Research Foundation and Department of Chemistry, Purdue University, West

Lafayette, IN, July 1950.

Moran, Jr., H.E. and Bertschy, AW., Rammability Limits for Mixtures of Hydrocarbon Fuels,

Air, and Halogen Compounds, NRL Report 4121, Engineering Research Branch, Chemistry

Division, Naval Research Laboratory, Washington, DC, 25 February 1953.

Miller, W.J., "Inhibition of Low Pressure Flames," Combustion and Flame, vol. 13, pp. 210-

212, April 1969.

Sheinson, R.S., Penner-Hahn, J.E., and Indritz, D., "The Physical and Chemical Action of Fire

Suppressants, Fire Safety Journal, accepted for publication.

164
Name: sulfur chloride fluoride

Compound group:

Fbrmula:

Alternate Names:

Sulfur halides

SF5CI

sulfur chloropentafluoride

CASN:

Normal boiling point (nbp **C): Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

13780-57-9

-21 na

104

21.7

PCR Incorporated, Gainesville, FL 32602, 800-331-6313

$175/25 g ($110 cylinder charge)

Tbxicity: Sulfur chloride fluoride has been cited as being as toxic as phosgene by Gage. Phosgene is given a HR rating of 3 (high toxic, fire, or reactivity hazard) by Sax and Lewis and is described as a human poison.

Gage, J.C, "Subacute inhalation toxicity of 109 Industrial Chemicals," British Journal of

Industrial Medicine, vol. 27, pp. 1-18, 1970.

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials. 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Sheinson, R.S., Penner-Hahn, J.E., and Indritz, D., "The Physical and Chemical Action of Fire

Suppressants, Fire Safety Journal, accepted for publication.

na = not available

165
Name: sulfur bromide fluoride

Compound group:

Formula:

Alternate Names:

Sulfur halides

SFsBr

sulfur bromopentafluoride, pentafluorosulfur bromide

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

15607-89-3

3.1 na

107

24+

No commercial source was identified. na

Tbxicity: No toxicity data were identified in the literature. By analogy with sulfur chloride fluoride,

this compound is likely to be at least as toxic as phosgene.

Comments: A preparative procedure is available in the literature.

Kovacina, T.A., Berry, A.D., and Fox, W.B., "Improved Preparation and Purification of

Pentafluorosulfur Bromide," Journal of Fluorine Chemistry, vol. 7, pp. 430-432, 1976.

Fire suppression references:

Sheinson, R.S., Penner-Hahn, J.E., and Indritz, D., "The Physical and Chemical Action of Fire

Suppressants, Fire Safety Journal, accepted for publication.

^Estimated for this report by authors, na = not available

166
Name: phosphorus trifluoride

Compound group:

Formula:

Alternate Names:

phosphorus-containing compounds

PF3

phosphorous fluoride

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

7783-55-3

-101

66

58.7

14.6

Pfaltz and Bauer, Inc., Waterbury, CT, 203-574-0075

$539.50/100 g plus refundable $95 cylinder charge

Tbxicity: Sax and Lewis: HR:3, High toxic, fire, or reactivity hazard

Moderately toxic by inhalation; a severe eye, skin, and mucous membrane irritant.

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials, 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: No fire suppression measurements were identified for this compound.

The commercial material is nominally 98% pure. A procedure for its purification has been

published.

Liang, S. and TVenary, M., "An Infrared Study of the Symmetric P-F Stretch of PF3

Chemisorbed on the Pt(lll) Surface," Journal of Chemical Physics, vol. 89, pp. 3323-3230,

September 1988.

167
Name: phosphorus trichloride

Compound group:

Formula:

Alternate Names:

phosphorus-containing compounds

PCI3

phosphorous chloride, chloride of phosphorous

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

7719-12-2

76

0.16

71.6

30.5

Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

$75.70/100 g

Tbxicity: Sax and Lewis: HR:3, High toxic, fire, or reactivity hazard Poison by inhalation; moderately

toxic by ingestion; a corrosive irritant to skin, eyes, and mucous membranes.

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials. 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

"Final Report on Fire Extinguishing Agents for the Period September 1, 1947 to June 30,

1950," Purdue Research Foundation and Department of Chemistry, Purdue University, West

Lafayette, IN, July 1950.

Lask, G. and Wagner, H.Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eight Symposium (International) on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1962.

168
Name: phosphorus bromide difluoride

Compound group:

Formula:

Alternate Names:

phosphorus-containing compounds

PFzBr

bromodifluorophosphine

CASN:

Normal boiling point (nbp " C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

15597-40-7

-16

4.5 64+

23.9

No commercial source was identified. na

Tbxicity: No toxicity information was identified for this compound. By analogy with other phosphorous halides it is very likely that it would be assigned a HR rating of 3 using the Sax and

Lewis (high toxic, fire, or reactivity hazard) system.

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials, 7 Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: This compound is included on the list to test mechanisms for fire suppression. It is a dangerous and unstable species. Particular care must be exercised in its synthesis and testing.

A standard preparative procedure is available in the literature.

Morse, J.G., Cohn, K., Rudolph, R.W., and Parry, R.W., "3B Phosphorous. 22. Substituted

Difluoro- and Dichlorophosphines," Inorganic Syntheses, vol. 10, pp. 147-156, 1967.

No fire suppression measurements were identified for this compound.

^Estimated for this report by authors, na = not available

169
Name: phosphoryl fluoride

Compound group:

Fbrmula:

Alternate Names:

phosphorus-containing compounds

POF,

CASN:

Normal boiling point (nbp °C):

\^por pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of \^porization (kJ/mol at nbp):

Source:

Price:

13478-20-1

-40

13.2 68.8

22.1

Atomergic Chemetals Corporation, Plainview, NY 11803,

516-349-8800

$400/200 g

Ibxicity: No toxicity information was identified for this compound. By analogy with other phosphoryl

halides it is very likely that it would be assigned a HR rating of 3 using the Sax and Lewis

(high toxic, fire, or reactivity hazard) system.

Sax, N.I. and Lewis, Sr., RJ., Dangerous Properties of Industrial Materials. 7 Ed., \^

Nostrand Reinhold, New York, 1989.

Comments: No fire suppression measurements were identified for this compound.

170
Name: phosphoiyl chloride

Compound group:

Formula:

Alternate Names:

phosphorus-containing compounds

POCI3

phosphorus oxychloride, phosphorous oxytrichloride

CASN: 10025-87-3

Normal boiling point (nbp "C): 106

Vkpor pressure (atm at 298 K): 0.05

Heat capacity (J/K-mol at 298 K): 84.9

Heat of Vaporization (kJAnol at nbp): 33.7

Source: Aldrich Chemical Company, Milwaukee, WI, 53233, 800-558-9160

Price: $207.05/100 g

Ibxicity: Sax and Lewis: HR:3, High toxic, fire, or reactivity hazard

Poison by inhalation and ingestion; a corrosive eye, skin, and mucous irritant.

Sax, N.I. and Lewis, Sr., RJ., Dangerous Properties of Industrial Materials. 7th Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

MUler, W.J., "Inhibition of Low Pressure Flames," Combustion and Flame, vol. 13, pp. 210-

212, April 1969.

Jorissen, W.P., Booy, J., and van Heiningen, J., "Reaction-Regions XXII. On the Prevention

of Explosive Reactions in Gas and Vapour Mixtures by Small Amounts of Various

Substances," Recueil des Thivaux Chimiques des Pav-Bas. vol. 51, pp. 868-877, 15 July 1932.

171
Name: phosphoryl bromide fluoride

Compound group:

Formula:

Alternate Names:

phosphorus-containing compounds

POF2Br

CASN:

Normal boiling point (nbp **C): Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:.

Price:

14014-18-7

32

0.77

75t

29.7

No commercial source was identified. na

Tbxicity: No toxicity information was identified for this compound. By analogy with other phosphoryl

halides it is very likely that it would be assigned a HR rating of 3 (high toxic, fire, or

reactivity hazard) using the Sax and Lewis system.

Sax, N.I. and Lewis, Sr., R.J., Dangerous Properties of Industrial Materials. 7 Ed., Van

Nostrand Reinhold, New York, 1989.

Comments: This compound is included on the list to test mechanisms for fire suppression. It is a dangerous and unstable species. Particular care must be exercised in its synthesis and testing.

A preparative procedure is available in the literature.

Bernstein, PA., Hohorst, F.A., Eisenberg, M., and DesMarteau, D.D., "Preparation of Pure

Difluorophosphoric Acid and ii-Oxo-bis(phosphoryl difluoride)," Inorganic Chemistry, vol. 10, pp. 1549-1551, July 1971.

No fire suppression measurements were identified for this compound.

^Estimated for this report by authors, na - not available

172
Name: tetrachlorosilane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

SiCl4

Silicon tetrachloride

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price (per kg):

10026-04-07

58

0.31 145

32

Liquid Carbonic, Corporation, Chicago, IL, 60603,

312-855-2500

$11

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials, Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

"Final Report on Fire Extinguishing Agents for the Period September 1, 1947 to June 30,

1950," Purdue Research Foundation and Department of Chemistry, Purdue University, West

Lafayette, IN, July 1950.

Lask, G. and Wagner, H. Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eighth Symposium (International) on Combustion, pp. 432-438, Williams and >\^lkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

173
Name: trichlorofluorosilane

Compound group:

Fbrmula:

Alternate Names:

Silicon and Germanium

SiCljF

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mole at 298 K):

Heat of Vaporization (kJ/mole at nbp):

Source:

Price:

14965-52-77

15

1.46

92

26

No commercial source was identified na

Tbxicity: High. Halosilanes hydrolyze in moist air - forming hydrogen halides in the process.

Rochow, E. G. in Comprehensive Inorganic Chemistry, vol. 11, Pergamon Press, New York,

1973.

Comments: No fire suppression measurement data was uncovered.

References pertaining to the synthesis of this compound can be found in:

Ebsworth, E. A. V, Volatile Silicon Compounds. Academic Press, New York, NY, 1975.

na = not available.

174
Name: tetrafluorosilane

Compound group:

Fbrmula:

Name:

Silicon and Germanium

SiF4

Silicon tetrafluoride

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price (per kg):

7783-61-1

-65

1510

74

22

Liquid Carbonic, Corporation, Chicago, IL, 60603,

312-855-2500

$250

Tbxicity: Sax and Lewis assign a hazard rating of 3 (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: No fire suppression measurement data was uncovered.

175
Name: bromotrifluorosilane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

SiBrF,

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price (per kg):

14049-39-9

-42

10.5 80+

18

No commercial source was identified na

Tbxicity: High. Halosilanes have a tendency to hydrolyze in moist air - forming hydrogen halides in the

process.

Rochow, E. G. in Comprehensive Inorganic Chemistry, vol. 11, Pergamon Press, New York,

1973.

Comments: No fire suppression measurement data was uncovered.

References pertaining to the synthesis of this compound can be found in:

Ebsworth, E. A. V, Volatile Silicon Compounds, Academic Press, New York, NY, 1975.

tEstimated for this report by authors, na = not available

176
Name: tribromofluorosilane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

SiBrjF

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298):

Heat of Vaporization (kJ/mole at nbp):

Source:

Price (per kg):

18356-67-7

84

0.11 150+

34

No commercial source was identified na

Tbxicity: High. Halosilanes have a tendency to hydrolyze in moist air - forming hydrogen halides in the

process.

Rochow, E. G. in Comprehensive Inorganic Chemistry, vol. 11, Pergamon Press, New York,

1973.

Comments: No fire suppression measurement data were uncovered. References pertaining to the synthesis

of this compound can be found in:

Ebsworth, E. A V, Volatile Silicon Compounds. Academic Press, New York, NY, 1975.

tEstimated for this report by authors, na = not available

177
Name: tetramethylsilane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

Si(CH3)4

TMS

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mole at nbp):

Source:

Price (per kg):

75-76-3

27

0.95

204

27

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$185

Tbxicity: High.

The Sigma-Aldrich Library of Chemical Safety Data, First Edition (Lenga, R. E., Editor),

Sigma-Aldrich, 1985.

Comments: Fire suppression references:

Lask, G. and Wagner, H. Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eighth Symposium (International) on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

178
Name: chlorotrimethylsilane

Compound group:

Fbrmula:

Alternate Names:

Silicon and Germanium

Si(CH3)3Cl

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price (per kg):

75-77-4

57

0.31

175+

32

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$39

Tbxicity: Sax and Lewis assign a hazard rating of 3 (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: No fire suppression measurement data was uncovered.

tEstimated for this report by authors

179
Name: trichloromethylsilane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

Si(CH3)Cl3

CASH:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price (per kg):

75-79-6

66

0.23

100+

31

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$29

Tbxicity: Sax and Lewis assign a hazard rating of 3 (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: No fire suppression measurement data was uncovered.

tEstimated for this report by authors

180
Name: chloromethyltrimethylsilane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

Si(CH3)CH2Cl

CASN:

Normal boiling point (nbp " C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price (per kg):

2344-80-1

98

na

200+

na

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$1246

Tbxicity: High.

The Sigma-Aldrich Library of Chemical Safety Data. First Edition (Lenga, R. E., Editor),

Sigma-Aldrich, 1985.

Comments: No fire suppression measurement data was uncovered.

fEstimated for this report by authors, na = not available.

181
Name: tetrachlorogermane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

GeCl4

Germanium tetrachloride

CASN:

Normal boiling point (nbp "C):

V^por pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of \^porization (kJ/mol at nbp):

Source:

Price (per kg):

10038-98-9

83

0.11

150+

35

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$1652

Ibxicity: Sax and Lewis assign a hazard rating of 3 (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, \^n

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Lask, G. and A^gner, H. Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eighth Symposium (IntemationaH on Combustion, pp. 432-438, 'y^lliams and >^lkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Ojgrgen-Nitrogen Mixtures," Combustion and Rame. vol. 18, pp. 3-12, 1972.

fEstimated for this report by authors.

182
Name: tetramethylgermane

Compound group:

Formula:

Alternate Names:

Silicon and Germanium

Ge(CH3)4

CASN:

Normal boiling point (nbp "C):

\^por pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of VEiporization (kJ/mole at nbp):

Source:

Price (per kg):

865-52-1

44

0.52

200+

30

No commercial source was identified na

Tbxicity: No information on the toxicity of this specific chemical was found. However, related

compounds are not particularly toxic.

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: No fire suppression data have been reported for this compound.

References pertaining to the synthesis of this compound can be found in:

Glockling, E, The Chemistry of Germanium. Academic Press, New york, NY, 1969.

tEstimated for this report by authors, na = not available.

183
Name: sodium hydrogen carbonate

Compound group:

Formula:

Alternate Names:

Metallic

NaHCOj

Sodium bicarbonate

CASK:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

144-55-8

decomposes

ot

na

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$16

Tbxicity: Low. Sax and Lewis assign a hazard rating of 1.

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Birchall, J. D., "On the Mechanism of Flame Inhibition by Alkali Metal Salts," Combustion

and Flame, vol. 14, pp 85-%, 1970.

Friedman, R. and Levy, J. B., "Inhibition of Opposed - Jet Methane - Air Diffusion Flames.

The Effects of Alkali Metal Vapors and Organic Halides," Combustion and Flame, vol. 7, pp. 195-201, 1%3.

tEstimated for this report by authors, na = not available.

184
Name: sodium acetate

Compound group:

Formula:

Alternate Names:

Metallic

NaC2H302

Acetic acid, sodium salt

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price:

127-09-3

decomposes

ot80

na

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$36 (per kg)

Tbxicity: Medium. Sax and Lewis assign a hazard rating of 2.

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials, Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Dewitte, M., Vrebosch, J. and van Tiggelen, A, "Inhibition and Extinction of Premixed Flames

by Dust Particles," Combustion and Flame, vol. 8, pp. 257-266, 1964.

tEstimated for this report by authors, na = not available.

185
Name: potassium hydrogen carbonate

Compound group:

Fbrmula:

Alternate Names:

Metallic

KHCO3

Potassium bicarbonate

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

298-14-6

decomposes

otna

na

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$24

Tbxicity: Low.

Comments: Fire suppression references:

Birchall, J. D., "On the Mechanism of Flame Inhibition by Alkali Metal Salts," Combustion

and Flame, vol. 14, pp 85-96, 1970.

Friedman, R. and Levy, J. B., "Inhibition of Opposed - Jet Methane - Air Diffusion Flames.

The Effects of Alkali Metal Vapors and Organic Halides," Combustion and Flame, vol. 7, pp. 195-201, 1963.

tEstimated for this report by author, na = not available.

186
Name: potassium oxalate

Compound group:

Formula:

Alternate Names:

Metallic

K2C204.H20

Potassium oxalate monohydrate

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

6487-48-5

decomposes

otnana

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$46

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Friedrich, M. "Extinguishment Action of Powders," Fire Research Abstracts and Reviews, vol.

2, pp. 132-135, 1960.

Dewitte, M., Vrebosch, J. and van Tiggelen, A, "Inhibition and Extinction of Premixed Flames

by Dust Particles," Combustion and Flame, vol. 8, pp. 257-266, 1964.

tEstimated for this report by authors, na = not available.

187
Name: potassium acetate

Compound group:

Formula:

Alternate Names:

Metallic

Acetic acid, potassium salt

CASK:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

127-08-2

decomposes

otna

na

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$39

Tbxicity: Medium. Sax and Lewis assign a hazard rating of 2.

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials, Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Dewitte, M., Vrebosch, J. and van Tiggelen, A., "Inhibition and Extinction of Premixed Rames

by Dust Particles," Combustion and Flame, vol. 8, pp. 257-266, 1964.

tEstimated for this report by authors, na = not available.

188
Name: potassium acetylacetonate

Compound group:

Formula:

Alternate Names:

Metallic

KC5H702«ViH20

Potassium acetylacetonate hemihydrate

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

57402-46-7

decomposes

na

nana

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$300

Tbxicity: High.

Comments: No fire suppression measurement data were uncovered.

na = not available

189
Name: chromium acetylacetonate

Compound group:

Formula:

Alternate Names:

Metallic

Cr(C5H702)3

CASN:

Normal boiling point (nbp °C):

Vapor pr^sure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

21679-31-2

340 na

nana

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$120

Tbxicity: High.

Comments: Fire suppression references:

Vanpee, M. and Shirodkar, P. P., "A Study of Flame Inhibition by Metal Compounds,"

Seventeenth Symposium (Internationan in Combustion, pp 787-793, 1978.

na = not available.

190
Name: chromyl chloride

Compound group:

Fonnula:

Alternate Names:

Metallic

Cr02Cl2

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

14977-61-8

116

0.024 na

41

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$2216

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials, Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Lask, G. and ^^gner, H. Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eighth Symposium (International) on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

na = not available.

191
Name: tin (IV) chloride

Compound group:

Formula:

Alternate Names:

Metallic

SnCl4

Stannic chloride

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

7646-78-8

114

0.030

165

37

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$45

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials, Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Lask, G. and Wagner, H. Gg., "Influence of Additives on the Velocity of Laminar Rames,"

Eighth Symposium (InternationaH on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

192
Name: titanium (TV) chloride

Compound group:

Fbrmula:

Alternate Names:

Metallic

TiCL

CASN:

Normal boiling point (nbp **C): Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

7550-45-0

136

0.015

145

39

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$40

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Lask, G. and "WagneT, H. Gg., "Influence of Additives on the Velocity of Laminar Rames,"

Eighth Symposium (International) on Combustion, pp. 432-438, Williams and A^^lkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

193
Name: tetraethyl lead

Compound group:

Formula:

Alternate Names:

Metallic

Pb(C2H5)4

CASN:

Normal boiling point (nbp °C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

78-00-2

200

0.00055 na

54

Alfa Products, Danvers, MA, 01923, 800-342-0660

$15500

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression references:

Lask, G. and Wagner, H. Gg., "Influence of Additives on the Velocity of Laminar Flames,"

Eighth Symposium (International) on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1962.

Morrison, M. E. and Scheller, K., "The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

na = not available

194
Name: iron pentacarbonyl

Compound group:

Fbrmula:

Alternate Names:

Metallic

Fe(CO)5

Iron carbonyl

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of vaporization (kJ/mol at nbp):

Source:

Price (per kg):

13463-40-6

103

0.040

241

38

Aldrich Chemical Company, Milwaukee, WI, 53233,

800-558-9160

$79

Tbxicity: Sax and Lewis assign a hazard rating of 3. (high toxic, fire, explosive, or reactivity hazard).

Sax, N. I. and Lewis, R. J., Dangerous Properties of Industrial Materials. Seventh Edition, Van

Nostrand Reinhold, New York, 1989.

Comments: Fire suppression data references:

Lask, G. and Wagner, H. Gg., "Influence of Additives on the Velocity of Laminar Rames,"

Eighth Symposium (International) on Combustion, pp. 432-438, Williams and Wilkins,

Baltimore, 1%2.

Morrison, M. E. and Scheller, K., The Effect of Burning Velocity Inhibitors on the Ignition

of Hydrocarbon-Oxygen-Nitrogen Mixtures," Combustion and Flame, vol. 18, pp. 3-12, 1972.

Vanpee, M. and Shirodkar, P. P., "A Study of Flame Inhibition by Metal Compounds,"

Seventeenth Symposium (International in Combustion, pp 787-793, 1978.

195
Name: nitrogen

Compound group:

Formula:

Alternate Names:

inert gases

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:.

Price:

7727-37-9

-195.8 na

29.3

5.6 Matheson Gas Products, Baltimore, MD 21227, 301-796-0517

(99.998%) $42/8.3 kg

Tbxicity: Sax and Lewis: HR:1, low toxic, fire, or reactivity hazard.

Low toxicity; in high concentrations it is a simple asphyxiant.

Comments: The effects of nitrogen on flames have been investigated extensively. A few representative

references are provided.

Coward, H.F. and Hartwell, F.J., "Extinction of Methane Flames by Diluent Gases," Journal

of the Chemical Society, pp. 1522-1532, 1926.

Simmons, R.F. and Wolfhard, H.G., "Some Limiting Oxygen Concentrations for Diffusion

Flames in Air Diluted with Nitrogen," Combustion and Flame, vol. 1, pp. 155-161, 1957.

Tiitem, P.A, Gann, R.G., and Carhart, H.W., "Pressurization with Nitrogen as an Extinguish- ant for Fires in Confined Spaces," Combustion Science and Ibchnologv. vol. 7, pp. 213-218,

1973.

Ishizuka, S. and Tiuji, H., "An Experimental Study of Effect of Inert Gases on Extinction of

Laminar Diffusion Flames," Eighteenth Symposium (Internationa^ on Combustion, pp. 695-

703, The Combustion Institute, Pittsburgh, 1981.

Tbcker, D.M., Drysdale, D.D., and Rasbash, D.J., "The Extinction of Diffusion Flames Burning

in Various Oxygen Concentration by Inert Gases and Bromotrifluormethane," Combustion and

Flame, vol. 41, pp. 292-300, 1981.

na = not available.

196
Name: carbon dioxide

Compound group:

Formula:

Alternate Names:

inert gases

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heat capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

124-38-9

-75.8 (sublimes)

29.9

37.7

15.3 Matheson Gas Products, Baltimore, MD 21227, 301-796-0517

(99.99%) $95/27.2 kg

Tbxicity: Sax and Lewis: HR:1, Low toxic, fire, or reactivity hazard

An asphyxiant; an experimental teratogen.

Comments: The effects of carbon dioxide on flames have been investigated extensively,

representative references are provided.

A few

Coward, H.F. and Hartwell, F.J., "Extinction of Methane Flames by Diluent Gases," Journal

of the Chemical Society, pp. 1522-1532, 1926.

Egerton, A and Powling, J., "The Limits of Flame Propagation at Atmospheric Pressure. II. The Influence of Changes in the Physical Properties," Proceedings of the Royal Society of

London, vol. A197, pp. 190-209, May 27, 1948.

TVicker, D.M., Drysdale, D.D., and Rasbash, D.J., "The Extinction of Diffusion Flames Burning

in Various Oxygen Concentration by Inert Gases and Bromotrifluormethane," Combustion and

Flame, vol. 41, pp. 292-300, 1981.

197
Name: argon

Compound group:

Formula:

Alternate Names:

mert gases At

CASN:

Normal boiling point (nbp "C):

Vapor pressure (atm at 298 K):

Heal capacity (J/K-mol at 298 K):

Heat of Vaporization (kJ/mol at nbp):

Source:

Price:

7440-37-1

-185.4 na

20.9

6.5 Matheson Gas Products, Baltimore, MD 21227, 301-796-0517

(99.998%) $77/13.5 kg

Tbxicity: Sax and Lewis: HR:1, low toxic, fire, or reactivity hazard

A simple asphyxiant gas.

Comments: The effects of argon on flames have been investigated extensively. A few representative

references are provided.

Coward, H.F. and Hartwell, F.J., "Extinction of Methane Flames by Diluent Gases," Journal

of the Chemical Society, pp. 1522-1532, 1926.

Egerton, A. and Powling, J., "The Limits of Flame Propagation at Atmospheric Pressure. II. The Influence of Changes in the Physical Properties," Proceedings of the Royal Society of

London, vol. A197, pp. 190-209, May 27, 1948.

Ishizuka, S. and 'Ruji, H., "An Experimental Study of Effect of Inert Gases on Extinction of

Laminar Diffusion Flames," Eighteenth Symposium (International) on Combustion, pp. 695-

703, The Combustion Institute, Pittsburgh, 1981.

na = not available.

198
NIST-114A

(REV. 3-89) U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

BIBLIOGRAPHIC DATA SHEET

TITLE AND SUBTITLE

1. PUBUCATION OR REPORT NUMBER

NIST/TN-1279

2. PERFORMING ORGANIZATION REPORT NUMBER

3. PUBUCATION DATE August 1990

Construction of an Exploratory List of Chemicals to Initiate the Search for Halon

Alternatives

5. AUTHOR(S) William M. Pitts, Marc R. Nyden, Richard C. Gann, W. Gary Mallard, and Winq Tsang

6. PERFORMING ORGANIZATION (IF JOINT OR OTHER THAN NIST, SEE INSTRUCTIONS)

U.S. DEPARTMENT OF COMMERCE

NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY

GAITHERSBURG, MD 20899

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (STREET, CITY, STATE, ZIP) U.S. Air Force Engineering Laboratory

Air Force Enqineering & Services Center

Tyndall AFB, FL 32403-6001

7. CONTRACT/GRANT NUMBER

Contract 89CS8205

8. TYPE OF REPORT AND PERIOD COVERED

Final

10. SUPPLEMENTARY NOTES

DOCUMENT DESCRIBES A COMPUTER PROGRAM; SF-185, FIPS SOFTWARE SUMMARY, IS ATTACHED.

11- ABSTRACT (A 200-WORD OR LESS FACTUAL SUMMARY OF MOST SIGNIFICANT INFORMATION. IF DOCUMENT INCLUDES A SIGNIFICANT BIBUOGRAPHY OR

LITERATURE SURVEY, MENTION IT HERE.)

Production of the currently-used halogenated fire suppressants (halons) will be curtailed

because of their contribution to stratospheric ozone depletion. This report, one of the

first efforts toward identifying alternatives, documents the rationale for and selection

of a set of approximately one hundred gases and/or liquids, covering a range of chemical

and physical principles thought to affect flame suppression capability and stratospheric

ozone depletion. An Appendix provides extensive information on each of the selected

chemicals. Also included in the report are an introduction to combustion concepts, fire

suppression mechanisms, test approaches for flame suppression effectiveness, and the

mechanisms by which the current commercial halons can decrease stratospheric ozone.

12. KEY WORDS (6 TO 12 ENTRIES; ALPHABETICAL ORDER; CAPITALIZE ONLY PROPER NAMES; AND SEPARATE KEY WORDS BY SEMICOLONS)

fire suppression; halons

13. AVAILABIUTY UNUMITED

FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE TO NATIONAL TECHNICAL INFORMATION SERVICE (NTIS).

X

X

ORDER FROM SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE,

WASHINGTON, DC 20402. ORDER FROM NATIONAL TECHNICAL INFORMATION SERVICE (NTIS), SPRINGFIELD, VA 22161.

14. NUMBER OF PRINTED PAGES

206

15. PRICE

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