NIST Technical Note 1443 

Alternative Fire Suppressant Chemicals: 

A Research Review with Recommendations

Robert E. Tapscott 

Ronald S. Sheinson 

Valeri Babushok 

Marc R. Nyden 

Richard G. Gann 
Alternative Fire Suppressant Chemicals: 

A Research Review with Recommendations

Robert E. Tapscott 

GlobeTech, Inc. 

Albuquerque, NM 

Ronald S. Sheinson 

Navy Technology Center for Safety & Survivability 

Naval Research Laboratory 

Washington, DC 20375 

Valeri Babushok 

Marc R. Nyden and Richard G. Gann 

Fire Research Division 

Building and Fire Research Laboratory 

National Institute of Standards and Technology 

Gaithersburg, MD 20899-8664

December 2001 

U.S. Department of Commerce 

Donald L. Evans, Secretary 

Technology Administration 

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology 

Arden L. Bement, Jr., Director

NIST Technical Note 1443 
National Institute of Standards U.S. Government Printing Office For Sale by the 

and Technology Washington: 2000 Superintendent of Documents 

Technical Note 1443 U.S. Government Printing Office 

Natl. Inst. Stand. Technol. Washington, DC 20402-9325

Tech. Note 1443 

84 pages (December 2001) 

CODEN: NTNOEF 
Table of Contents 

I. INTRODUCTION...............................................................................................................................1 

II. HALOGENATED ORGANIC COMPOUNDS...................................................................................3 

A. Alkanes4 

1. Iodine-containing alkanes ...................................................................................................4

2. Bromine-containing alkanes ...................................................................................................7 

3. Chlorine-containing alkanes ...................................................................................................9 

4. Fluorine-containing alkanes .................................................................................................10 

B. Alkenes ........................................................................................................................................12 

1. Iodine-containing alkenes ....................................................................................................12 

2. Bromine-containing alkenes .................................................................................................13 

3. Chlorine-containing alkenes .................................................................................................15 

4. Fluorine-containing alkenes .................................................................................................16 

C. Alkynes .......................................................................................................................................18 

D. Ethers ..........................................................................................................................................19 

1. Iodine-containing ethers ......................................................................................................19 

2. Bromine-containing ethers ...................................................................................................20 

3. Chlorine-containing ethers ...................................................................................................22 

4. Fluorine-containing ethers ...................................................................................................23 

E. Alcohols .....................................................................................................................................24 

1. Iodine-containing alcohols ...................................................................................................24 

2. Bromine-containing alcohols ................................................................................................25 

3. Chlorine-containing alcohols ................................................................................................27 

4. Fluorine-containing alcohols.................................................................................................28 

F. Aldehydes and Ketones ..............................................................................................................29 

1. Iodine-containing aldehydes and ketones..............................................................................29 

2. Bromine-containing aldehydes and ketones..........................................................................30 

3. Chlorine-containing aldehydes and ketones..........................................................................31 

4. Fluorine-containing aldehydes and ketones ..........................................................................32 

G. Aromatics ...................................................................................................................................34 

1. Iodine-containing aromatics .................................................................................................34 

2. Bromine-containing aromatics ..............................................................................................35

3. Chlorine-containing aromatics ..............................................................................................37 

4. Fluorine-containing aromatics...............................................................................................38 

III. NITROGEN-CONTAINING COMPOUNDS ...................................................................................39 

A. Nitriles .......................................................................................................................................39 

B. Nitro Compounds ........................................................................................................................41 

C. Organic Nitrates and Nitrites ......................................................................................................42 

D. Nitroso Compounds ...................................................................................................................44 

E. Fluoroalkyl Amines .....................................................................................................................45 
IV. SULFUR-CONTAINING COMPOUNDS ........................................................................................47 

A. Hexacoordinate Sulfur ................................................................................................................47 

B. Sulfides and Mercaptans .............................................................................................................48 

C. Difluorosulfur Compounds .........................................................................................................49 

D. Sulfoxides ...................................................................................................................................50 

V. PHOSPHORUS-CONTAINING COMPOUNDS ............................................................................51 

A. Phosphorus-containing Acids and Esters ...................................................................................51

B. Phosphonitriles.............................................................................................................................53 

C. Phosphorus Halides .....................................................................................................................54 

D. Phosphines...................................................................................................................................56 

E. Pentacoordinate Phosphorus ........................................................................................................57 

VI. METAL-CONTAINING COMPOUNDS .........................................................................................58 

A. Alkali Metal Compounds.............................................................................................................58 

B. Compounds of Alkaline Earths....................................................................................................60 

C. Boron and Aluminum Compounds ..............................................................................................61 

D. Copper-containing Compounds...................................................................................................62 

E. Titanium-containing Compounds ................................................................................................63 

F. Manganese-containing Compounds.............................................................................................64 

G. Antimony-containing Compounds ..............................................................................................65 

H. Germanium-containing Compounds............................................................................................66

I. Silicon-containing Compounds ...................................................................................................67 

J. Iron-containing Compounds ........................................................................................................68 

K. Tin-containing Compounds .........................................................................................................69 

VII. CONCLUSION ................................................................................................................................70 

VIII. ACKNOWLEDGMENTS ..............................................................................................................70 

IX. REFERENCES ..................................................................................................................................71 
I. INTRODUCTION

Since the signing of the Montreal Protocol on Substances that Harm the Ozone Layer in 1987 and its 

subsequent amendments, the use of the fire suppressant halon 1301 (CF3Br) has declined sharply to a 

limited number of essential applications. Production of this chemical in the industrialized world 

terminated in January 1994, and the supply of halon 1301 for these essential uses is being met by

established reserves. One of the essential uses is for fire protection in military and commercial aircraft. 

To enable relief from dependence on this environmentally harmful substance, researchers have examined 

a range of chemical compounds as alternatives. The Department of Defense (DoD) Next Generation Fire 

Suppression Technology Program (NGP) has been a principal contributor to this search. NGP projects 

have examined several families of compounds, have created or adapted methods to screen these 

chemicals, and are developing engineering methods for making the best use of less-than-perfect 

alternatives to halon 1301 in military aircraft.1,2,3

 

Supported by the DoD Strategic Environmental Research and Development Program (SERDP), the NGP 

is now in its fifth year, and planning is underway for the remaining years of this effort. The NGP 

Technical Coordinating Committee (TCC) deemed it timely to re-evaluate the world of chemistry,

identify which chemical families are unlikely to contain usable alternative chemicals, which have been 

examined sufficiently to know that the best candidates have been already identified, and which families 

are still in need of scrutiny. Studies of this last group would then be included in the research plans for the 

remainder of the NGP. This report summarizes the efforts of a task group to perform this re-evaluation. 

Such an examination requires a set of success criteria, and these have varied over time. Initially, some

looked for a true drop-in replacement; where all the properties of the replacement chemical were so 

similar to those of halon 1301 that compatibility with the platform was complete and no subsequent 

modification of the fire suppression system was needed. Others looked for unique products that their 

companies could market. Some focused on finding high fire suppression efficiency; others looked for

compounds that were free of any disqualifying property. As the field matured, several influencing factors 

emerged: 

 For the remaining essential uses, satisfactory and affordable solutions were hard to identify. It 

thus became reasonable to consider chemicals with some less-than-fully-desirable behavior if the 

drawback(s) could be overcome. 

 The list of attributes for a suppressant has evolved. For example, atmospheric lifetime has been 

added. Physiologically based pharmacokinetic (PBPK) modeling of the human body has shown 

that, for cardiac sensitization by halogenated chemicals, the toxic potency criterion need not be as 

limiting as had previously been thought. By contrast, there has been little resolution as to an 

acceptable minimal contribution to ozone depletion and global warming. 

 All new weapons systems are being designed free of ozone-depleting substances, and the U.S. 

Army has committed to retrofitting its ground vehicles with alternate fire suppressants. 

 

At present, the NGP is proceeding with its own set of screening criteria to define better where the search 

for alternative suppressants is most likely to be successful. These criteria are: 

 Fire suppression and reignition quenching efficiency comparable to halon 1301 and higher than

the hydrofluorocarbons (HFCs). 

 Atmospheric lifetime short, on the order of a month, to keep ozone depletion, global warming, 

and any future adverse contributions to a minimum. This is generally a result of such 

tropospheric processes as photolysis, reaction with water (hydrolysis), or raining (adherence to

water). 

1
 Toxic potency of agent and combustion byproducts sufficiently low that brief exposure to an

extinguishing concentration does not result in an unrecoverable injury; 

 No serious interaction of the agent or its byproducts with contacted aircraft materials; 

 Availability of compatible storage container components; 

 Boiling point sufficiently high that a suppressing volume fraction of 5 % (at thermal equilibrium) 

exists at -40 °C, the minimal design temperature for aircraft suppression system performance. 

This boiling point is about 25 °C. Consideration was given to agents that might require a smaller 

concentration for suppression; for example, this boiling point criterion rises to 35 °C for a 3 % 

suppression concentration. Even this is not an absolute criterion, since the engine heats the 

interior engine nacelle surfaces during flight and since it is often feasible to warm the agent 

storage container. The boiling point can be as high as 75 °C if the suppression takes place in an 

environment at 22 °C. Of course if the agent is dispensed as a mist/powder or via a solid 

propellant gas generator (SPGG), the concept of a limiting boiling point criterion is not 

applicable. 

Over the years, there has been testing and even commercializing of azeotropic blends of chemicals. Such 

mixtures can reduce the negative impact on people or the environment of one of the components. 

However, azeotropes maintain their special behavior over only a narrow range of pressure and 

temperature. Over the wider temperature range experienced during flight, a uniform mixture may not be 

maintained either within the storage container or during its discharge. In this situation, the container may

not fully empty or the emerging mixture may vary in composition during the discharge period, each of 

these resulting in a less-than-specified residence time for an extinguishing concentration. Thus, this 

project did not consider the use of chemicals in blends of any type. 

This document, then, reviews the state of knowledge of the fitness of chemicals as fire suppressants. In a 

number of cases, this has been supplemented by the judgment of the authors. Based on this compilation, 

the authors indicate chemical families that merit further research and, of those, the ones that are the most 

promising. 

2
II. HALOGENATED ORGANIC COMPOUNDS 

Compounds containing only carbon, hydrogen and oxygen, regardless of their chemical structure, are 

fuels rather than fire suppressants. However, when one or more halogen atoms are substituted into the 

structure, the compound gains the ability to quench flames. These halogenated hydrocarbons are 

commonly called halons. Bromine and iodine atoms are particularly effective at flame suppression, 

chlorine atoms less so. Remaining hydrogen atoms compromise the suppression efficiency by adding fuel 

to the fire. 

Bromine, iodine, and chlorine atoms are also potent depleters of stratospheric ozone. However, iodinecontaining compounds undergo rapid tropospheric photolysis and, therefore, have short atmospheric 

lifetimes, near-zero global warming potential (GWP) values, and low ozone depletion potential (ODP) 

values. Thus, iodine-containing compounds need no additional functionality to provide acceptable 

atmospheric environmental properties. On the other hand, compounds that contain no iodine, but that 

contain bromine and/or chlorine must possess functional groups that make the atmospheric lifetime 

sufficiently short to provide acceptable ODP values. 

We therefore used the following principles in considering halogenated hydrocarbons as potential 

alternates to halon 1301: 

 To obtain fire suppression performance similar to that of halon 1301, bromine or iodine (and 

perhaps chlorine) must be present. 

 When no iodine is contained in a halocarbon, some other functionality must be present to keep 

the atmospheric lifetime sufficiently low to provide acceptable ODP and GWP values. 

 The compounds must have some fluorine atoms to displace hydrogen in order to decrease or 

eliminate flammability and, in some cases, to decrease hepatotoxicity (harm to the liver). 

In this section, we consider all the families of organic compounds that contain only C, H, O, and/or 

halogen atoms: alkanes, alkenes, alkynes, ethers, alcohols, aldehydes and ketones, aromatics. We will 

discuss each of these in turn, starting with members of the family that contain iodine and may contain any

other halogen; then those that contain bromine and may contain fluorine and/or chlorine; then those that 

contain chlorine and may contain fluorine; and, finally, those that contain fluorine only. Thus, the term, 

for example, “bromine-containing” allows for compounds that may also contain chlorine and fluorine, but 

not iodine. Carboxylic acids and their esters are not considered in this report due to their expected low 

volatilities. 

3
A. ALKANES 

The alkanes are saturated hydrocarbons, i.e., they contain only single carbon-carbon bonds. 

1. Iodine-containing Alkanes 

The alkyl iodides are flammable and have high boiling points. They are thus not suitable as alternatives 

to halon 1301. At the other extreme of iodinated alkanes are those that are fully fluorinated except for the 

iodine. 

a. Fire Suppression Efficiency. The following table and figures show cup burner extinguishment 

concentrations for n-heptane fuel for a number of perfluorinated iodocarbons and for halon 1301 all 

determined with the same, non-standard, cup burner.4

 For reference, the n-heptane extinguishment 

volume and mass fractions for halon 1301 with the cup burner specified in the NFPA Standard on Clean 

Extinguishing Agents5

 are 3.4 % and 207 g/m3, respectively.

6

 Note that, generally, as the chain length 

increases, the extinguishment concentration expressed as volume fraction decreases, but the extinguishing 

concentration expressed as mass per unit volume increases. (See graphs.) The di-iodinated compound 

CF2ICF2CF2CF2I has a lower extinguishment concentration by volume than CF3CF2CF2CF2I, but when 

expressed as mass fraction, the performances of the di-iodinated and mono-iodinated compounds are 

almost identical. Testing with a 56 m3

 (2000 ft3) compartment fire indicates that the performance of CF3I 

was comparable to that of halon 1301, with any differences being due to distribution characteristics.7

0

0.5

1

1.5

2

2.5

3

3.5

1 2 3 4 5 6 7 8

Carbon Atoms

0

100

200

300

400

500

1 2 3 4 5678

Carbon Atoms

Extinguishment

Concentration, g/m3

Formula 

Ext. Volume 

Fraction 

(%) 

Ext. Mass 

Fraction 

(g/m3

) 

CF3Br 2.9 177

CF3I 3.0 240 

C2F5I 2.1 211

C3F7I 3.0 363

C4F9I 2.8 396

C6F13I 2.5 456

C8F17I 1.9 415

C4F8I2 2.1 390

b. Toxicity. The simplest and most volatile compound in this series, CF3I, has a very low cardiac 

sensitization LOAEL (Lowest Observable Adverse Effect Level), a volume fraction of 0.4 %,

8

 although 

the acute 4 hour rat ALC (Approximate Lethal Concentration, essentially an LC50) is much higher.9

 

Toxicities of a few other fluoroiodocarbons have been determined. Noteworthy is the fact that the 

toxicities are highly variable. For example, perfluoropropyl iodide (CF3CF2CF2I) has a 2 hour mouse 

LC50 of 3.3 % 10 whereas 2-iodo-2-(trifluoromethyl)-1,1,1,3,3,4,4,4-octafluorobutane 

(CF3C(CF3)ICF2CF3) has a 1 hour mouse LC50 of less than 0.005 %.

11 In spite of its relatively high LC50, 

the former compound has a very low cardiac sensitization LOAEL of 0.1 %10, and in this characteristic 

4
resembles CF3I. The only partially fluorinated fluoroiodocarbons for which toxicity data have been 

reported is 1,1,1-trifluoro-2-iodoethane (CF3CH2I), which has a 10 min mouse LC50 of 5 % and a 10 min 

mouse anesthetic volume fraction of 1.25 %.

12

c. Materials Compatibility. Anhydrous iodoalkanes show good compatibility with metals although 

there is some possible concern about their compatibility with copper. CF3I in particular showed no serious 

interaction with a number of alloys, although the interactions were an order of magnitude larger than with 

halon 1301.13 Severe corrosion can occur in the presence of water owing to hydrolysis, and this is more 

likely to occur with iodinated compounds than other organic halides. The compounds, of course, can 

react with organic polymers and elastomers may have to be carefully chosen to limit swelling and 

degradation. There are both elastomers and lubricants with which CF3I is compatible.14

d. Colligative Properties. As iodination increases, boiling point (BP) increases and volatility 

decreases, as expected. Volatility also decreases as fluorine is replaced by hydrogen. Eventually, 

however, one reaches a point when most or all of the fluorine atoms have been lost that the boiling point 

begins to decrease. The important thing is that the boiling point is approximately 35 °C higher for iodides 

than for the corresponding bromides. 

Formula BP (°C) MP (°C) ∆Hv (kJ/mol) Reference

CF3I -22.5 -110 22.0 5

CHF2I 21.6 -122 15

CH2FI 53.5 15

CH3I 42.5 -66.1 27.97 15

CF2I2 80 16

CHFI2 100.3 34.5 17

C2F5I 12 16

CF3CH2I 55 17

CHF2CF2I 39.4 16

C3F7I 41.2 -95.3 28 (est.)18 19

C4F9I 67 16

e. Atmospheric Impact. Iodocarbons have a strong tendency to decompose photolytically, resulting in 

very short atmospheric lifetimes. The atmospheric lifetime of CF3I is less than 1 day.

20 The atmospheric 

lifetime for releases at higher altitudes is thought to be significantly shorter. The estimated ODP for CF3I 

is less than 0.008 and more likely 0.0001 relative to CFC-11.20 If CF3I were released directly into the 

stratosphere from aircraft, the ODP would be considerably higher; however, analysis indicates that high 

altitude releases are not a significant threat to stratospheric ozone.21 (Based on figures compiled by the 

U.S. Air Force, U.S. Navy, and commercial aircraft industry, the current release of halon 1301 during 

flight is less than 500 kg annually, of which about 70 kg are released at altitudes above 27 km (30,000 ft). 

Because this quantity is so low, expected high altitude releases of CF3I, if used on aircraft, would not be 

considered a significant threat to the ozone layer.) 

f. Overall Assessment. Iodides are efficient fire suppressants with low atmospheric environmental 

impact. The only one known to have a sufficiently low toxicity and acceptable properties to be applied to 

fire protection needs is CF3I, and even this compound is unacceptable for use in normally occupied areas. 

There is a significant possibility that other iodides (e.g., hydrofluoroiodocarbons) could have acceptable 

toxicities; however, the cost to determine this may be unacceptably large. While CF3I has been well 

studied as a possible fire suppressant, little effort has been applied to others in this family. 

5
No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

6
2. Bromine-containing Alkanes 

Here we consider all brominated alkanes whether or not fluorine and chlorine atoms are also present. 

Example compounds include halon 1301 (CF3Br), HBFC-22B1 (CHF2Br), and methyl bromide (CH3Br). 

Bromoalkanes do not photolyze efficiently in the troposphere. Thus, hydrogen substitution (which makes 

the molecule susceptible to attack by atmospheric •OH) is needed to limit the atmospheric lifetime and 

the ozone depletion potential. However, if there are too many hydrogen atoms and/or carbon-carbon 

bonds relative to the number of halogen substituents, the compound will be an ineffective suppressant and 

may be flammable. This behavior is predictable.22

a. Fire Suppression Effectiveness. The fire extinguishment effectiveness of bromine-containing 

alkanes is well known. Some selected n-heptane cup burner values are shown in the accompanying table. 

Note that halon 1301 extinguishment volume fractions measured using acceptable equipment and 

procedures range from around 2.9 % to 3.4 %. The value given here is that determined in a review of 

data.6

 Hydrogenation decreases fire extinguishment effectiveness (higher extinguishment concentration); 

increased bromine content increases effectiveness (lower concentration). Methyl bromide is actually

flammable, but can suppress a flame.

Compound Formula 

Ext. Volume 

Fraction 

(%) 

Ref.

Halon 1301 CF3Br 3.4 6

BFC-12B2 CF2Br2 2.2 4

HBFC-22B1 CHF2Br 3.9 23

Methyl Bromide CH3Br 5.1 24

b. Toxicity. Halon 1301 appears to be the least toxic of the brominated alkanes whose toxicity has been 

reported. It is virtually non-toxic at design concentrations. Other brominated alkanes have varying 

analgesic, toxicity, and cardiotoxicity effects. The LC50 values in the accompanying table (all for 4 hour 

exposures of rats except BFC-12B2, which is a 2 hour exposure of mice, and methyl bromide, which is an 

8 hour exposure of rats) illustrate the range of toxicities encompassed by this family. In general, toxicity

of bromoalkanes increases with increasing bromine content and increasing hydrogen content. 

Compound Formula 

LC50 

(%) Ref.

Halon 1301 CF3Br >80 25

HBFC-22B1 CHF2Br 10.8 26

Methyl Bromide CH3Br 0.03 27

c. Materials Compatibility. In general, anhydrous bromoalkanes show excellent compatibility with 

metals; however, severe corrosion can occur in the presence of water owing to hydrolysis. The 

compounds, of course, can react with organic polymers.

d. Colligative Properties. In general, as the bromination increases, the boiling point (BP), melting 

point (MP), and heat of vaporization (∆Hv) increase. (See following table. The values are taken from the 

GlobeTech Chemical Database. References are available upon request.). In general, these properties also 

increase as fluorine is replaced by hydrogen. Eventually, however, one reaches a point when most or all 

of the fluorine atoms have been lost that these quantities start to decrease. Halon 1301 has the lowest 

melting point, boiling point, and heat of vaporization of any of the brominated alkanes. 

7
Compound Formula MP (°C) BP (°C) ∆Hv (kJ/mol)

Halon 1301 CF3Br -168 -57.8 16.53

BFC-12B2 CF2Br2 -110 24.5 25.9

HBFC-22B1 CHF2Br -145 -15.5 22.5

Methyl Bromide CH3Br -93 3.6 24.8 

-200

-150

-100

-50

0

50

CF3Br CHF2Br CH2FBr CH3Br

BP, °C

MP, °C

e. Atmospheric Impact. With one exception, the ODP values are long for the brominated alkanes, and 

the materials are regulated under the Montreal Protocol. The exception is the hydrobromocarbons 

(HBCs). Although methyl bromide, CH3Br, is regulated, the other HBCs are not. Moreover, some of 

these have relatively low toxicities and/or possibly adequate environmental properties. For example, npropyl bromide (CH3CH2CH2Br) has an ODP relative to CFC-11 of 0.006 and an atmospheric lifetime of 

about 11 days.

28 Although these compounds are flammable, they can be mixed with HFCs (or other 

halocarbons) to give nonflammable mixtures with good extinguishment properties.29

f. Overall Assessment. ODP concerns make these compounds unacceptable for use and thus for 

further study. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X 

Lightly studied 

Completely unstudied 

Estimated

8
3. Chlorine-containing Alkanes 

 

The fully halogenated chlorofluorocarbons have long atmospheric lifetimes and the chlorine atoms are 

potent ozone depleters. Elimination of use of these compounds was the principal reason for the Montreal 

Protocol. Thus, only the hydrochlorofluorocarbons (HCFCs), with at least one hydrogen atom to allow 

atmospheric •OH radical attack, can be considered. 

a. Fire Suppression Effectiveness. Chlorine atoms are distinctly less efficient at effecting flame 

suppression than bromine or iodine atoms. As examples, HCFC-123 (CHCl2CF3) has a cup burner 

extinguishing volume fraction of approximately 7.1 %, and HCFC 22 (CHClF2) has a value of 

approximately 11.6 % for n-heptane fuel.4

 With this reduced chemical effect, the physical effect of an 

HCFC is more important; larger molecules with higher molar heat capacity require a lower mole percent 

for suppression. However, all HCFCs are significantly less effective than halon 1301. The 

nonfluorinated materials are more likely to be flammable. 

b. Toxicity. Due to their applications in refrigeration, foam blowing, cleaning, and other processes to 

which CFCs were formerly applied, a large amount of toxicological work has been carried out on HCFCs. 

Overall, HCFCs have moderate to low toxic potencies. They are generally less toxic than 

bromofluorocarbons (CF3Br being a major exception) and more toxic than HFCs and PFCs. Toxicity is 

less a drawback than environmental characteristics. 

c. Materials Compatibility. Like all halocarbons, HCFCs can be corrosive toward metals in the 

presence of moisture. However, they are not generally corrosive when dry and are less likely to cause 

corrosion problems than either bromine-containing or iodine-containing compounds. Like other 

halocarbons, HCFCs may require careful selection of polymeric gasket materials to limit swelling and 

degradation. 

d. Colligative Properties. HCFCs are more volatile than corresponding bromine-containing 

compounds. Thus, suitable compounds can be found for most or all applications based on physical 

properties only. 

e. Atmospheric Impact. The major problem with HCFCs is that their ODP values, though low, are 

sufficiently large that the materials are regulated and their production will eventually be phased out. At 

best, they can be used only as transitional substitutes. 

f. Overall Assessment. HCFCs have unacceptable environmental properties without any redeeming 

suppression efficiency. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X 

Lightly studied 

Completely unstudied 

Estimated

9
4. Fluorine-containing Alkanes 

a. Fire Suppression Effectiveness. Both perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs) 

have been widely studied as fire suppressants, and there is a very large amount of extinguishment data 

available at all scales. PFCs and HFCs are only moderately effective as fire extinguishants on a volume 

basis (see the following table of n-heptane cup burner values), since fluorine atoms lack the catalytic 

suppression chemistry of the other halogen atoms. As expected, effectiveness decreases with increasing 

hydrogen content, with HFC-32 being flammable.

Compound Formula 

Ext. Volume 

Fraction (%) Ref.

FC-14 CF4 16 30

HFC-23 CHF3 12.3 31

HFC-32 CH2F2 8.8 4 

FC-116 C2F6 8.1 31 

HFC-125 C2HF6 8.7 31 

HFC-134a CH2FCF3 10 31

HFC-227ea CF3CFHCF3 6.3 31 

b. Toxicity. As a group, the PFCs are the least toxic of all halocarbons. In fact, many of these highly

stable compounds have no measurable toxicity. While the addition of hydrogen increases toxicity, HFCs 

still generally have low toxicity. Some HFCs have a sufficiently low cardiac sensitization that they are 

allowable for use in normally occupied areas. The accompanying table shows the important volume 

fractions for commercially available PFC and FC extinguishants and halon 1301 for comparison.25,32

Compound LC50 (%) NOAEL (%) LOAEL (%)

Halon 1301 5 7.5 

HFC-23 >65 50 >50

HFC-125 >70 7.5 10.0

HFC-227ea >80 9.0 10.5

HFC-236fa >18.9 10 15

FC-218 >81 30 >30

FC-3-1-10 >80 40 >40

c. Materials Compatibility. PFCs and HFCs are probably the least corrosive of any halocarbons. 

Problems can still exist with wet materials, but the high strength of the C-F bond makes hydrolysis 

difficult. PFCs are not compatible with some fluorinated polymers; but compatible elastomers exist. 

d. Colligative Properties. HFCs and PFCs have physical properties ideal for halon replacement. These 

compounds are more volatile than their bromine-containing counterparts. 

e. Atmospheric Impact. HFCs and PFCs have no significant ozone depletion, however, HFCs and, in 

particular, PFCs have long atmospheric lifetimes and high global warming. The following table shows 

the environmental properties of the HFC and PFC fire extinguishants now being commercialized with 

halon 1301 for comparison.33

10
Agent ODP GWP Atmospheric Lifetime (yrs) 

Halon 1301 12-16 5600 65 

HFC-23 0 1210 250

HFC-125 0 3200 36

HFC-227ea 0 3300 41

HFC-236fa 0 8000 250

FC-218 0 6100 3200

FC-3-1-10 0 5500 2600

f. Overall Assessment. These compounds have been well studied and are becoming widely marketed 

for a wide range of applications. However, for aircraft use, the relatively poor environmental properties 

and the mediocre extinguishment efficiencies suggest no further study is needed. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X 

Lightly studied 

Completely unstudied 

Estimated

11
A. ALKENES 

1. Iodine-containing Alkenes 

Iodoalkenes are a family that contains two functionalities, both of which are likely to contribute to lower 

stability relative to the alkanes. The carbon-iodine bond is rather weak and the carbon-carbon double 

bond is reactive. Iodine-containing compounds are also subject to hydrolysis. 

a. Fire Suppression Effectiveness. To the best of our knowledge, no extinguishment studies have been 

carried out on any iodoalkene. The effect of the double bond on extinguishment is uncertain; however, it 

is known that some highly halogenated, lower molecular weight alkenes are flammable.36

b. Toxicity. There are no published data. Due to their expected low stability and the possibility of 

alkylation, iodoalkenes are likely to be more toxic than many of the other halocarbons being considered.

c. Materials Compatibility. Because of their reduced stability and the potential formation of HI upon 

hydrolysis, it is expected that materials compatibility will be of concern with iodine-containing alkenes. 

d. Colligative Properties. Volatility is likely to be lower than the bromoalkenes. The boiling point of 

the simplest iodoalkene, vinyl iodide, is 56 °C, 40 °C higher than the comparable bromide. Fluorination 

could reduce these values. 

e. Atmospheric Impact. With expected rapid photolysis and the susceptibility of the double bond to 

attack by atmospheric •OH, iodine-containing alkenes are expected to have exceedingly short atmospheric 

lifetimes and near-zero GWP and ODP values. 

f. Overall Assessment. These compounds have been completely unstudied as fire suppressants. A 

screening study is recommended even though the compounds have possible stability and toxicity 

problems. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

 

12
2. Bromine-containing Alkenes 

 

a. Fire Suppression Effectiveness. A number of flame extinguishment studies have been carried out 

on bromofluoroalkenes and hydrobromofluoroalkenes. The cup burner values for n-heptane fuel in the 

following table have been taken from several sources.34,35,4,31

 Most of these compounds have 

extinguishment concentrations at least as low as halon 1301 on a volume basis. The substituted ethylenes 

appear to be significantly poorer extinguishing agents than the higher molecular weight materials. The 

effect of the double bond on extinguishment is uncertain; however, it is known that some highly

halogenated, lower molecular weight alkenes, e.g., CF2=CFBr, are flammable.36 Recent unreported work 

indicates that in larger scale testing, CH2=CBrCF3 greatly outperforms HFC-227ea.37 Testing using the 

Dispersed Liquid Agent Fire Suppression Screen (DLAFSS) apparatus developed by the National 

Institute of Standards and Technology indicates a fire suppression capability for CH2=CBrCF3

comparable to or possibly better than that of halon 130134, although precise comparison between the two 

agents is difficult with the DLAFSS apparatus because of differences in their dispersion. 

Bromoalkene 

Ext. Volume Fraction 

(%) 

CHBr=CHCF3 3.5

CH2=CHCBrF2 4.5

CH2=CBrCF3 2.6

CH2=CHCF2CBrF2 3.5

CH2=CHCClFCBrF2 4.5

CH2=CBrCF2CF3 3.8

CBrF=CF2 6.3

CHBr=CF2 6.0

CH2=CBrCF2CF2CF3 3.7

CH2=CBrCF(CF3)CF3 3.3

CH2=CBr(OCF3)CFCF3 3.8

(CF3)2C=CHBr 2.6

CF3CF2CH=CHBr 3.1

b. Toxicity. Acute inhalation toxicity testing has been performed on a limited number of 

hydrobromofluoroalkenes, as shown in the following table.35 The test exposure protocol used a 30 min 

exposure of 10 rats (5 male and 5 female) to each chemical at a volume fraction of 5 % in air. Following 

the exposure the animals were removed from the exposure apparatus, observed for 2 hours, and then 

sacrificed for examination of tissues. The compounds had much lower toxicity than expected. Other 

recent studies have shown negative results for chromosomal aberration tests38 and Ames tests35 on some

hydrobromofluoroalkenes. 

Bromoalkene Deaths Necropsy Result

CH2=CBrCF3 0 All tissues normal 

CHBr=CHCF3 0 All tissues normal 

CH2=CHCBrF2 7 Lungs mottled

CH2=CHCF2CBrF2 0 All tissues normal 

CH2=CBrCF2CF3 0 Lungs mottled

CH2=CBrCF2CF2CF3 1 Lungs mottled

CH2=CBrCF(CF3)2 10 Lungs marked mottling 

13
c. Materials Compatibility. Bromine-containing alkenes will generally be more reactive than the 

corresponding alkanes. Nevertheless, there is no reason to expect compatibility problems that cannot be 

overcome with suitable materials. As with all halocarbons, metal corrosion will be increased by the 

presence of water, which causes hydrolysis. 

d. Colligative Properties. The requirement for at least two carbon atoms (to allow formation of a 

carbon-carbon double bond), the probable need to use propene and higher molecular weight derivatives to 

obtain good fire suppression, and the requirement for at least one bromine atom, gives these compounds a 

higher molecular weight and therefore a lower volatility than some other halocarbon families. To date, 

the lowest boiling point material for which fire extinguishment testing has been performed has been 2-

bromo-3,3,3-trifluoropropene, CF3CBr=CH2, which has a boiling point of 34 °C. The fully halogenated 

propene CF2=CFCBrF2 has a boiling point of 28 °C39, and this may represent a lower limit for the 

compounds with three or more carbon atoms. Only a few heat of vaporization values have been reported 

or estimated for bromofluoroalkenes and hydrobromofluoroalkenes. These tend to be around 30 kJ/mol. 

e. Atmospheric Impact. Atmospheric lifetimes, GWP values, and ODP values are believed to be very

low for bromine-containing alkenes. Recent, yet unpublished work confirms this.40. Estimated lifetimes 

for three bromofluoroalkenes based on measured reactivity towards •OH are 3.2 days for CH2=CBrCF3, 

3.4 days for CH2=CBrCF2CF3, and 7.3 days for CH2=CHCF2CF2CBrF2. These values imply very low 

ODP and GWP values. 

f. Overall Assessment. Although the lower volatility will adversely affect the usage envelope, 

bromine-containing alkenes are probably the most promising halon replacements discovered to date. A 

fuller look at this family is thus warranted. There may be a higher probability of success for streaming 

agent substitutes. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X 

Lightly studied 

Completely unstudied 

Estimated

14
3. Chlorine-containing Alkenes 

 

a. Fire Suppression Effectiveness. No data are available on the extinguishing performance of 

chlorine-containing alkenes. It is expected that the higher energy content of the double bond will 

decrease performance relative to the corresponding alkane. A chlorine atom adds less effectiveness 

compared to that provided by bromine or iodine. 

b. Toxicity. No toxicity studies on chlorofluoroalkenes and hydrochlorofluoroalkenes have been 

reported. It is known that a number of nonfluorinated chlorine-containing alkenes are rather toxic. 

c. Materials Compatibility. Chlorine-containing alkenes will be, as a whole, less reactive than the 

corresponding bromine compounds, but higher in reactivity than the chlorine-containing alkanes. 

Nevertheless, there is no reason to expect compatibility problems that cannot be overcome with suitable 

materials. As with all halocarbons, metal corrosion will be increased by the presence of water, which 

causes hydrolysis. 

d. Colligative Properties. Little information is available on chlorofluoroalkenes and 

hydrochlorofluoroalkenes. The physical properties of these compounds are likely to be more suitable for 

total flood fire protection than the bromine-containing alkenes. 

e. Atmospheric Impact. Due to the presence of a double bond, chlorine-containing alkenes are 

expected to have very low atmospheric lifetimes, global warming potentials, and ozone depletion 

potentials. 

f. Overall Assessment. The chlorine-containing alkenes are not expected to have sufficient fire 

extinguishment capability to justify the studies required to better characterize these compounds as 

extinguishants. Toxicity also remains a major concern. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied 

Estimated X

15
4. Fluorine-containing Alkenes 

 

a. Fire Suppression Effectiveness. Only two compounds in this category have been investigated for 

flame suppression. Hexafluoropropene (CF2=CFCF3) has a heptane cup burner extinguishment volume 

fraction of 7.3 %31, and octafluoro-2-butene (CF3CF=CFCF3) is reported to have a cup burner 

extinguishment volume fraction of 4.9 %.

41 The latter value may be low since this determination is 

believed to have been made using an apparatus known to give low values in other cases. The analogous 

fully fluorinated saturated compounds are perhaps slightly more efficient, 6.1 % 42 and 5.3 %,

respectively.

31 

b. Toxicity. The toxicity of the few perfluoroalkenes and hydrofluoroalkenes whose toxicity has been 

studied is surprisingly high. CF3C(CF3)=CFCF2CF3 has a 1 hour mouse LC50 of 0.0175 %11; and in an 

anesthesia test, all mice exposed to a volume fraction of 0.8 % to 3.4 % of 

1-methylnonafluorocyclohexene died, as did all those exposed to 0.8 % to 1.5 % of

decafluorocyclohexene and to 3.0 % to 7.3 % (6 min) of octafluorocyclopentene43 On the other hand, the 

10 min LC50 for CH2=CHCF2CH3 is a moderately high 25 %, and the 4 hour LC50 for CF2=CFCF3 is 

1.12 %.

44 The very high molecular weight compound CF3CF2CF2CF2CH=CHCF2CF2CF2CF3 has been 

used as a blood substitute.18

c. Materials Compatibility. Although more reactive than the PFCs and HFCs, hydrofluoroalkenes and 

perfluoroalkenes are expected to have relatively good corrosion and compatibility properties. Again it is 

expected that fluoropolymers may be incompatible with these materials, but other elastomers are 

undoubtedly available. 

d. Colligative Properties. The accompanying table shows some of the important colligative properties 

of selected perfluoroalkenes and hydrofluoroalkenes. The ∆Hv values are at the normal boiling points. In

general, unsaturation leads to a very slight increase in boiling point when compounds are compared to 

saturated compounds with the same number of carbon atoms. The physical properties of the materials are 

suitable for total flood applications. 

Formula MP (°C) BP (°C) ∆Hv (kJ/mol)

CH2=CHCF2CH3 2412

CF2=CFCF3 -15618 -2918 2145

CH2=CHCF3 -2412 2418 (est.) 

CF2=CHCF3 -17 to -1639 2318 (est.) 

CF3CH=CHCH3 17.739

CF3CF=CFCF3 018 2118 (est.) 

CF3CH=CHCF3 618 2618 (est.) 

(CF3)2C=C(CF3)2 5518 2918

CF2=CF2 -142.515 -75.915

e. Atmospheric Impact. Unsaturation significantly reduces the atmospheric lifetime. For example, 

perfluoropropane has a lifetime of 2600 years46, while hexafluoropropene has a lifetime of only 5.8 

days.

47 Global warming and atmospheric persistence will not be problems with the fluorinated alkenes, 

and these materials have no ozone depletion potential. 

16
f. Overall Assessment. Perfluorinated alkenes and hydrofluoroalkenes have excellent atmospheric 

environmental properties, but they are expected to be no better than the perfluorocarbons and HFCs in fire 

protection and may be worse. The only reason to consider these materials is if environmentally superior 

HFC-like materials are required. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

17
B. Alkynes 

Alkynes contain carbon-carbon triple bonds. The bonds to adjacent atoms or groups are weakened and 

thus substituted alkynes should undergo react ion in the troposphere. The bond weakness may also lead 

to stability and manufacturing difficulties

a. Fire Suppression Effectiveness. Nothing is known of the fire suppression characteristics of 

haloalkynes. Bromine and iodine would impart some fire suppression capability, but the higher energy 

content of the triple bond will offset this. Compounds containing iodine or bromine directly attached to a 

triply bonded carbon are known to be unstable. Diiodoacetylene is explosive; some bromoalkynes are 

pyrophoric. The halogen could, of course, be attached to an alkyl substituent. 

b. Toxicity. Nothing is known of the toxicity of the haloalkynes. In view of the expected low stability,

however, toxicity is likely to be high. 

c. Materials Compatibility. It is likely that haloalkynes will have poorer material compatibility

properties than most other halocarbons discussed in this report; however, nothing concrete is known. 

d. Colligative Properties. Insufficient data are available on lower molecular weight haloalkynes to 

make any determination of physical property trends. More information is available on very large iodinecontaining alkynes, which are used in organic syntheses. 

e. Atmospheric Impact. Tropospheric reactions with tropospheric •OH (and photolysis) are likely to

limit atmospheric lifetimes and make contributions to ozone depletion and global warming negligible. 

f. Overall Assessment. Other than the expected good atmospheric environmental properties, there is 

no obvious advantage to haloalkynes. Their stability is likely to be low and there may also be 

manufacturing difficulties. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

18
C. Ethers 

These compounds contain a C-O-C grouping, which contributes to reactivity in the troposphere. 

1. Iodine-Containing Ethers

a. Fire Suppression Effectiveness. Nothing is known about the effectiveness of the iodinated 

derivatives. There is no reason to believe that the suppression capabilities will significantly differ from

those of the fluoroiodoalkanes, the hydrofluoroiodoalkanes, or the equivalent brominated compounds. 

b. Toxicity. Hydrofluoroethers and perfluoroethers can have low toxicity. The effect of iodine 

substitution is unknown, but it is expected that the toxicity will increase due to the low C-I bond strength. 

c. Materials Compatibility. The materials compatibility of iodine-containing ethers is unknown. It is 

possible that such compounds may exhibit slightly worse compatibility than the corresponding alkanes 

due to the small polarity induced by the oxygen atom.

d. Colligative Properties. Little information is available. The lightest iodine-containing ether, 

iodomethyl methyl ether (iodomethoxymethane) has a relatively high boiling point of 122 °C at 1 atm.

48 

It is expected that due to the higher molecular weight (all compounds must contain at least two carbon 

atoms and an oxygen atom) and the presence of iodine, compounds will have properties that are less than 

suitable for total flood application. 

e. Atmospheric Impact. The presence of iodine should lead to short atmospheric lifetimes, as with the 

other iodinated compounds. This would lead to very low ODP and GWP values. The ether linkage is 

likely a secondary contributor. 

f. Overall Assessment. If the iodine-substituted alkanes do not produce an acceptable candidate, this 

family might be worth screening. However, the high boiling point is a deterrent for total flooding 

applications. The only reason to use iodine-substituted ethers is to provide a way to modify the properties 

to improve toxicity, performance, stability, materials compatibility, or other characteristics. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied At present 

Estimated

19
2. Bromine-containing Ethers 

a. Fire Suppression Effectiveness. Some bromination of these compounds is needed to decrease 

flammability. Only two studies of fire suppression by of hydrobromofluoroethers (HBFEs) have been 

carried out. CH2=CBr(OCF3)CFCF3, which is unsaturated, has a cup burner extinguishment 

concentration of 3.8 volume percent.35 CH3-O-CF2CHBrF has been estimated to have a heptane cup 

burner volume fraction of 4.2 %.

36 These extinguishing concentrations seem high, given the presence of a 

bromine atom plus the physical cooling from the compounds’ relatively high molecular weights. The 

hydrobromochlorofluoroether CBrF2-O-CF2CHClF, has been suggested as an example of a chemical to be 

tested for fire suppression efficiency.

18

b. Toxicity. Some very limited toxicity results are available for HBFEs; however, much more work is 

needed to estimate the tolerability of the toxicity of this family. CH3-O-CF2CHBrF has been reported to 

be a good anesthetic at a volume fraction of 2.5 %.

49 CBrF2CF2-O-CH3 has been estimated to have a 2 

hour mouse LC50 of 0.84 % based on a quantitative structure-activity relationships (QSAR).50 A 

minimum anesthetic volume fraction of 0.8 % and a minimum lethal volume fraction of 1.5 % have been 

reported for CHFBrCF2CH2-O-CH3.

51 CHF2-O-CF2CHBrF has been reported to be a good anesthetic in 

mice at a volume fraction of 1.9 %52 and CH3-O-CF(CF3)CBrF2 has been reported to produce anesthesia 

in mice with excitation at a volume fraction of 5 %.

49 

c. Materials Compatibility. No information is available on material compatibility for the HBFEs; 

however, compatibilities better than the hydrobromofluoroalkenes and slightly worse than the HBFCs are 

expected. 

d. Colligative Properties. Boiling points for the HBFEs in the GlobeTech Database (references 

available on request) and for HFEs obtained from some HBFEs by substitution of fluorine for bromine 

are shown in the following table. Few data are available for low molecular weight HBFEs. 

Formula HBFE BP (°C) HFE BP (°C) 

CH3-O-CF=CBrF 67

CH3-O-CF=CBrF 59

CH3CH2-O-CF2CH2Br 70

CF3-O-CH2CH2Br 78.5

CH3-O-CF2CHBrF 88.8 37.2

CHFBrCF2CH2-O-CH3 125 66

CH3CH2-O-CF2CHFBr 106 57

CH2BrCH=CFCF2-O-CH3 74

CH3CH2CH2-O-CF2CHFBr 75.2

CHF2-O-CF2CHBrF 73 28.5

CH3-O-CF(CF3)CBrF2 80

CH3CH2-O-CF2CHBr2 65

CBrF2CF2CH2CH2CH2CH2-O-CH2CH3 185.7

CH3CH2CH2-O-CF2CHBr2 72.2

CH2=CBr(OCF3)CFCF3 75

CF3CHBrCH2-O-CH2CHBrCF3 167

CF3CHBrCH2-O-CH2-O-CH2CHBrCF3 195

CH3-O-CF2CHBr2 55.8

CF3CBrFCH2-O-CH2-O-CH2CBrFCF3 92

CH3-O-CF2CH2Br 54.7

20
The boiling point for CBrF2-O-CF3 (not an HBFE) has been estimated as -30 °C.18 This appears to be low. 

For four compounds (see table column marked HFE) substitution of Br for F causes an average boiling 

point increase of 52 °C. Since CF3-O-CF3 has a boiling point of -59 °C, CBrF2-O-CF3 is expected to have 

a boiling point of -8 °C. Similarly, CH3-O-CF3 has a boiling point of -24.2°C, and CH3-O-CBrF2 is 

predicted to have a boiling point of 28 °C. 3-carbon compounds (e.g., CH3-O-CF2CHBr2, BP = 55.8 °C) 

will have marginally acceptable boiling points for use as total flooding agents. The HBCFE CBrF2-OCF2CHClF has been estimated to have ∆Hv = 30.3 kJ/mol (115 kJ/kg) at the normal boiling point and a 

vapor phase heat capacity of 175 J/mol-K (664 J/kg-K) at 25 °C.49 

e. Atmospheric Impact. These compounds should have low environmental impact.34 Some hydrogen 

content is needed to provide sites for attack by atmospheric •OH since the C-O-C linkage is insufficiently 

polar to provide fast rainout. Only limited studies have been made of the kinetics of reactions of 

bromoethers with •OH.53 The lifetime of CH3-O-CF2CHBrF has been estimated as 14 and 50 days.

36 At 

this time, too few data exist to estimate ODP values, but the preceding lifetime estimates suggest the 

values would be low. 

f. Overall Assessment. These compounds may be sufficient, although not outstanding extinguishants. 

Before going further, it is essential that we have good information on atmospheric environmental 

properties. Below, we state that the compounds have been lightly studied; in fact, however, they are 

almost unstudied. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

21
3. Chlorine-containing Ethers 

a. Fire Suppression Effectiveness. No fire suppression testing has been carried out for a chlorinecontaining ether; however, the compounds 2-chloro-1,1,2-trifluoro-1-(difluoromethoxy)ethane (CHF2-OCF2CHClF) and 2-chloro-1,1,1-trifluoro-2-(difluoromethoxy)ethane (CHF2-O-CHClCF3) have been 

suggested as representative of chlorine-containing ethers for fire suppression testing.18 HCFEs are likely

to have fire suppression efficiencies greater than those of the hydrofluoroethers, but well below the 

efficiencies of bromine-containing compounds.

b. Toxicity. In general, fluorination is probably needed to keep the hepatic toxicity reasonable. Some 

chlorine-containing ethers have been considered as anesthetics and therefore have reasonable acute 

toxicities (although they may have anesthesia problems). Examples are 2-chloro-1-methoxy-1,1,2-

trifluoroethane (halomar), 2,2-dichloro-1,1-difluoro-1-methoxyethane (CH3-O-CF2CHCl2, methoxyflurane), CHF2-O-CF2CHClF (enflurane), and CHF2-O-CHClCF3 (forane). Methoxyflurane is reported to 

be anesthetic in mice at a volume fraction of 1.25 %54, and enflurane is reported to be a good anesthetic in 

mice at a volume fraction of 1.9 %.

52 It is expected that the presence of chlorine will make the toxicities a 

little worse than those of the corresponding hydrofluoroethers, some of which have reasonable toxicities.

c. Materials Compatibility. No information is available for the materials compatibility with HCFEs. 

These compounds are, however, expected to have no serious compatibility problems. They are likely to 

have compatibilities similar to, but a little more problematical, than those of the hydrofluoroethers. 

d. Colligative Properties. Data are available for a few chlorine-containing ethers, particularly since 

some have been considered as anesthetics. For methoxyflurane (with two Cl atoms), BP = 105 °C54; for 

enflurane, BP = 56.5 °C 52; and for forane, BP = 48.5 °C.55 Estimates of ∆Hv = 29.4 kJ/mol (159 kJ/kg) 

at the normal boiling point and vapor phase heat capacity = 162 J/mol-K at 25°C have been made for 

enflurane and, under the same conditions) of ∆Hv = 28.7 kJ/mol (156 kJ/kg) and vapor phase heat 

capacity = 167 J/mol-K for forane.18 The unsaturated 1-chloro-1,2-bis(trifluoromethoxy)ethene (CF3-OCH=CCl-O-CF3) has a boiling point of 54 °C.56 Three-carbon derivatives (e.g., forane) should have 

boiling points that are at the edge of acceptability as total flooding agents. The vapor pressures of fourcarbon HCFCs are likely to be too low.

e. Atmospheric Impact. In a number of cases, the presence of an ether linkage significantly increases 

reaction rates with tropospheric •OH; however, this is not true in all cases.57 It is likely that substitution 

of chlorine for fluorine will cause a decrease (though probably small) in atmospheric lifetime. Since 

some hydrofluoroethers are known to have atmospheric lifetimes, in the best of cases, of under a year, the 

HCFEs are likely to be, at best, marginally acceptable.

f. Overall Assessment. Since the HCFEs will operate mainly by heat absorption and are likely to be 

only marginally better than the hydrofluoroethers in fire suppression, and since these compounds are 

likely to have at best marginally acceptable environmental characteristics, it is recommended that no 

studies be performed. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

22 
4. Fluorine-containing Ethers 

a. Fire Suppression Effectiveness. These are primarily physical agents. Fluorine is needed primarily

to keep the flammability low and secondarily to control the physical properties. Cup burner flame 

suppression capabilities for three HFEs with n-heptane fuel are shown in the following table.41 In 

addition, flame suppression values for butane fuel using a micro cup burner have been reported for C4F9-

O-C2H5 (6.5 volume percent, 701 g/m3

) and CH3-O-C3F7 (7.5 volume percent, 613 g/m3).58 A mixture of 

hydrofluoropolyethers has been shown to have an n-heptane cup burner value of 5.1 volume percent.59 

Some larger scale testing of methyl perfluoro-n-butyl ether has been carried out. This agent can exceed 

halon 1301 efficiency if delivered as a mist, thus realizing the endothermicity of vaporization. 

Formula 

Ext. Vol. Fraction

(%) 

Ext. Conc. 

(g/m3

) 

CHF2-O-CF3 8.6 480

CHF2-O-CH2CF3 11.7 720

CH3-O-C4F9 (HFE-7100) 6.1 620 

b. Toxicity. Ethers have relatively low toxicities due to the low reactivity of the C-O-C functional 

group arising from the strength of the C-O bond. Several volatile ethers can affect the central nervous 

system. A substantial amount of data is available for HFCs since a number have been considered as 

alternative refrigerants and solvents. Most of the HFEs examined exhibit relatively low toxicities and are 

not mutagenic. A survey of toxicities for HFEs is available.60

c. Materials Compatibility. HFEs are expected to have compatibility properties at least as good as

those of halon 1301. Some limited results may be available from research being performed (primarily in 

Japan) on HFE refrigerants. 

d. Colligative Properties. A large amount of physical property data is available for the HFEs. The 

two-carbon compounds will, of course, have the lowest boiling points. The boiling point of CHF2-O-CF3

is –35 °C 61 and that of CHF2-O-CHF2 is 5 °C.62 The fully fluorinated material, CF3-O-CF3, has a boiling 

point of –59 °C.

e. Atmospheric Impact. Ethers that contain no iodine, bromine, or chlorine have no ODP; however, 

atmospheric lifetimes may still be a problem. In fact, perfluoroethers are expected to have atmospheric 

lifetimes similar to those of the perfluorocarbons and thus to be partially fluorinated to be acceptable. 

Lifetimes and GWP values as low as 0.3 years and 39 (100 year time horizon, relative to CO2) have been 

found for HFEs.57 However, some HFEs have considerably longer lifetimes and higher GWP values. 

f. Overall Assessment. There has been extensive examination of this family, and HFE-7100 has 

emerged as the optimal candidate.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X 

Lightly studied 

Completely unstudied 

Estimated

23 
D. Alcohols 

Alcohols contain one or more hydroxyl (-OH) groups attached to carbon atoms. 

1. Iodine-containing Alcohols. 

In this section, we consider alcohols that contain iodine and may contain other halogens. 

a. Fire Suppression Effectiveness. No extinguishment data have been reported for iodine-containing 

alcohols. Like other iodine-containing materials, these are expected to have good extinguishment 

properties. 

b. Toxicity. The toxicities of iodine-containing alcohols are unknown. It is expected that they will be 

more toxic than the iodine-containing alkanes, which in some cases to have very low cardiac sensitization 

levels.8,10

c. Materials Compatibility. Iodine-containing alcohols are expected to be more reactive toward metals 

than iodine-containing alkanes. There may be self reactions (e.g., CH2IOH → O=CH2 + HI or 

2CH2ICH2OH → CH2ICH2-O-CH2CH2OH + HI) forming highly corrosive hydrogen iodide.

d. Colligative Properties. A few iodine-containing alcohols have been reported and some of these are 

commercially available. Unfortunately, many of those commercially available have very large molecular 

weights (3-Perfluorohexyl-2-iodopropan-1-ol, MP = 49 °C, BP = 90 °C at 0.2 kPa; 3-(perfluoro-5-

methylhexyl)-2-iodopropanol, BP = 88 °C to 90 °C at 0.2 kPa.63 2-Iodoethanol has a relatively high 

boiling point of 85 °C at 3.3 kPa. 

e. Atmospheric Impact. Iodine-containing alcohols are expected to have exceedingly short 

atmospheric lifetimes. They should both rain out and photolyze rapidly. The GWP values and ODP 

values are expected to be near zero. 

f. Overall Assessment. An alcohol functionality is not needed when iodine is present in the molecule, 

and is expected to increase toxicity. There is no obvious advantage for consideration of iodine-containing 

alcohols. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

24
2. Bromine-containing Alcohols 

In this section, we consider alcohols that contain bromine and may also contain chlorine and/or fluorine. 

a. Fire Suppression Effectiveness. Little information is available; however, these compounds should 

be as effective as other brominated compounds. CF3CHOHCH2Br has been reported to have an n-heptane 

cup burner extinguishment volume fraction of 4.1 %, 323 g/m3

.

64 This compound has been reported to 

extinguish an H2/CH4 flame in an FID at a volume fraction of 3 %.65 An n-heptane cup burner 

extinguishment volume fraction of 4.87 %, 541 g/m3

, has been reported for the dibromo compound 

CF3CHOHCHBr2.

66

b. Toxicity. Almost no information is available; however, significant acute toxicity problems are 

expected. 2 hour mouse LC50 values of 0.38 % have been estimated by QSAR techniques for both 

CBrF2CH2OH and CBrF2CF2CH2OH.50 The estimate for CF3CHOHCH2Br was 0.46 % and that for 

CF3CBrFCH2OH was 0.23 %. CHFBrCF2CH2OH is reported to have a minimum anesthetic 

concentration of 100 to 500 mg/kg and a minimum lethal concentration >400 mg/kg, with poor 

anesthesia. 

c. Materials Compatibility. Bromine-containing alcohols are expected to be much more reactive

toward metals than bromine-containing alkanes. There may be self reactions (e.g., CH2BrOH → O=CH2

+ HBr or 2CH2BrCH2OH → CH2BrCH2-O-CH2CH2OH + HBr) forming highly corrosive hydrogen 

bromide. 

d. Colligative Properties. Some boiling points from the GlobeTech Chemical Options Database are 

shown in the adjacent table. Since some fluorination is required to keep the flammability down and since 

alcohols with fluorine atoms on the carbon attached to the hydroxyl group are unstable, brominecontaining fluoroalcohols will have to have at least two carbon atoms. The boiling points will be high. 

Compound BP (°C)

CBrF2CH2OH 67

CF3CHOHCH2Br 124

CHBrFCH(OH)CF3 124

CHFBrCF2CH2OH 149

CF3CBrFCH2OH 97

CF3CHBrCH2OH 108

CF3CH(OH)CHBrCH3 66

CF3CBrFCH(CH3)OH 112

CF3CBrFC(CH3)2OH 128

CF3CH(OH)CHBrCH2CH3 94

CF3CH(OH)CBr(CH3)CH3 68

CF3CBrClC(CH3)2OH 137

CF3CBr2C(CH3)2OH 152

CF3CHOHCHBr2 156

CBr2FCH2OH 85

e. Atmospheric Impact. Alcohols, even fluorine-containing alcohols, are expected to have a 

significant water solubility. For this reason, rainout is likely to be significant and the atmospheric 

lifetime small. Insufficient data are available to estimate what the ODP values might be. 

25
f. Overall Assessment. Although bromine-containing alcohols are likely to have good environmental 

properties and may have good extinguishing characteristics, they may have unacceptable toxicities and 

compatibility properties. Nevertheless, it is recommended that some additional investigation better define 

the ranges of the latter properties. This should be given low priority. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

26
3. Chlorine-containing Alcohols 

In this section we consider alcohols that contain chlorine and perhaps fluorine. 

a. Fire Suppression Effectiveness. No data are available. Hydrochlorofluoroalcohols are expected to 

extinguish flames primarily by physical cooling and to have extinguishment concentrations similar to 

those of the HCFCs. 

b. Toxicity. The toxicities of chlorine-containing alcohols are expected to be relatively high. 

c. Materials Compatibility. Chlorofluoroalcohols are expected to be more corrosive than HCFCs. 

d. Colligative Properties. Since some fluorination is required to keep the flammability down and since 

alcohols with fluorine atoms on the carbon attached to the hydroxyl group are unstable, chlorinecontaining fluoroalcohols will have to have at least two carbon atoms and will have to contain some

hydrogen atoms. Due to hydrogen bonding, the boiling points will be significantly higher than the 

corresponding HCFCs. 

e. Atmospheric Impact. Alcohols, even fluorine-containing alcohols, are expected to have a 

significant water solubility. For this reason, rainout is likely to be significant and the atmospheric 

lifetime, small. Insufficient data are available to estimate what the ODP values might be. 

f. Overall Assessment. Hydrochlorofluoroalcohols are likely to have good environmental properties; 

however, they are likely to have unacceptable toxicities and compatibility characteristics. There is no 

reason to expect their extinguishment characteristics to be sufficiently good to warrant investigation. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

27
4. Fluorine-containing Alcohols 

a. Fire Suppression Effectiveness. No data are available. Hydrofluoroalcohols are expected to 

extinguish flames primarily by physical cooling and to have extinguishment concentrations similar to 

those of the HFCs. Flammability may be of some concern; e.g., CF3CH2OH has a flash point.67

b. Toxicity. The toxicities of fluorine-containing alcohols are expected to be relatively high. 

c. Materials Compatibility. Chlorofluoroalcohols are expected to be more corrosive than HFCs. 

d. Colligative Properties. Since alcohols with fluorine atoms on the carbon attached to the hydroxyl

group are unstable, fluoroalcohols will have to have at least two carbon atoms and will have to contain 

some hydrogen atoms. Due to hydrogen bonding, the boiling points will be significantly higher than the 

corresponding HFCs. 

e. Atmospheric Impact. Alcohols, even fluorine-containing alcohols, are expected to have a 

significant water solubility. For this reason, rainout is likely to be significant and the atmospheric 

lifetime, short. CF3CH2OH has been estimated to have an atmospheric lifetime of 0.46 years based on 

reaction with •OH only68 and a 100 year GWP based on CO2 of 26.

62

f. Overall Assessment. Due to their expected high toxicities and poor extinguishment performance, 

there is no reason to consider these compounds further. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

28
E. Aldehydes and Ketones 

Aldehydes and ketones are saturated hydrofluorocarbons having the structure 

C

O

R1 R2

For aldehydes, at least one of the Rn substituents is hydrogen. Ketones have only carbon atoms directly

bonded to the carbonyl carbon. Carboxylic acids and their esters, which have an oxygen atom directly

bonded to the carbonyl carbon are not considered here. 

1. Iodine-containing Aldehydes and Ketones 

a. Fire Suppression Effectiveness. No extinguishment data have been reported for iodine-containing 

ketones and aldehydes. Like other iodine-containing materials, however, such compounds are expected to 

have good extinguishment efficiency. 

b. Toxicity. Lower aldehydes attack exposed moist tissue, especially eyes and mucous membranes. 

Higher aldehydes penetrate deeper into the respiratory tract and affect the lungs. Many members of the 

family are mutagens, and all have anesthetic properties. Ketones are less toxic but they can act as 

narcotics and as neurotoxins. The toxicities of iodine-containing ketones and aldehydes are unknown. It

is expected that such compounds will be even more toxic than the parent compounds. Compounds with 

halogen atoms on carbon atoms alpha to the carbonyl group are often strong lachrymators. 

c. Materials Compatibility. Carbonyl-containing compounds will be more corrosive than the 

corresponding alkanes. 

d. Colligative Properties. No data are available for iodine-containing aldehydes and ketones; however, 

since such compounds must contain a carbonyl group and avoid halogen atoms on the alpha carbon, 

structural requirements indicate relatively high molecular weights. 

e. Atmospheric Impact. Iodine is likely to be the controlling factor in determining the atmospheric 

lifetime, rather than the carbonyl group.

f. Overall Assessment. There is little to recommend this class. Iodine does not need the carbonyl

functionality to effect a short atmospheric lifetime. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

29
2. Bromine-containing Aldehydes and Ketones 

 

a. Fire Suppression Effectiveness. No extinguishment data have been reported for bromine-containing 

ketones and aldehydes. Like other bromine-containing materials, however, such compounds are expected 

to have good extinguishment properties. 

b. Toxicity. Lower aldehydes attack exposed moist tissue, especially eyes and mucous membranes. 

Higher aldehydes penetrate deeper into the respiratory tract and affect the lungs. Many members of the 

family are mutagens, and all have anesthetic properties. Ketones are less toxic but they can act as 

narcotics and as neurotoxins. The toxicities of bromine-containing ketones and aldehydes are unknown. 

It is expected that such compounds will be even more toxic than the parent compounds. Compounds with 

halogen atoms on carbon atoms alpha to the carbonyl group are often strong lachrymators. 

c. Materials Compatibility. Carbonyl-containing compounds will undoubtedly be more corrosive than 

the corresponding alkanes.

d. Colligative Properties. Few data are available for bromine-containing aldehydes and ketones; 

however, since such compounds must contain a carbonyl group and avoid halogen atoms on the alpha 

carbon, structural requirements indicate relatively high molecular weights. 

e. Atmospheric Impact. Carbonyl compounds can undergo photolysis and may also undergo physical 

removal, depending on their water solubility. Reaction with hydroxyl free radicals requires the presence 

of hydrogen atoms. Rate constants for reactions with hydroxyl free radicals and estimated quantum yields 

and absorption cross sections for photolysis indicate that aldehydes will have short atmospheric lifetimes, 

on the order of a few hours to approximately one month.69,70,71 The rate constants for reactions of nonhalogenated ketones with hydroxyl free radicals are relatively large, and the atmospheric lifetimes will be 

on the order of days. In addition, these compounds undergo photolysis in the troposphere. The method of 

Wuebbles and Connell72 used to estimate lifetimes due to hydrogen atom abstraction, however, shows that 

halogen substitution greatly increases the atmospheric lifetimes. Thus, halogenated ketones are suitable 

only if the photolytic lifetime is sufficiently short. Without absorption cross sections for compounds of 

interest, photolysis estimates cannot be made. 

f. Overall Assessment. Although the presence of a carbonyl group may give a sufficiently short 

atmospheric lifetime to allow use of the brominated compounds, the expected problems with molecular 

weight (high boiling points), toxicity, and, possibly compatibility cause us to recommend against 

investigations of this family.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

30
3. Chlorine-containing Aldehydes and Ketones 

a. Fire Suppression Effectiveness. No extinguishment data have been reported. These compounds are 

expected to be primarily physical extinguishants, and their effectiveness is unlikely to differ significantly

from those of HCFCs of the same molecular weight. 

b. Toxicity. Lower aldehydes attack exposed moist tissue, especially eyes and mucous membranes. 

Higher aldehydes penetrate deeper into the respiratory tract and affect the lungs. Many members of the 

family are mutagens, and all have anesthetic properties. Ketones are less toxic but they can act as 

narcotics and as neurotoxins. The toxicities of chlorine-containing ketones and aldehydes are unknown. 

It is expected that such compounds will be even more toxic than the parent compounds. Compounds with 

halogen atoms on carbon atoms alpha to the carbonyl group are often strong lachrymators. 

c. Materials Compatibility. Carbonyl-containing compounds will undoubtedly be more corrosive than 

the corresponding HCFCs. 

d. Colligative Properties. Since chlorine-containing aldehydes and ketones must contain a carbonyl

group and should avoid halogen atoms on the alpha carbon, structural requirements indicate relatively

high molecular weights. 

e. Atmospheric Impact. Carbonyl compounds can undergo photolysis and may also undergo physical 

removal, depending on the water solubility. Reaction with hydroxyl free radicals requires the presence of 

hydrogen atoms. Rate constants for reactions with hydroxyl free radicals and estimated quantum yields 

and absorption cross sections for photolysis indicate that aldehydes will have short atmospheric lifetimes, 

on the order of a few hours to approximately one month.69,70,69 The rate constants for reactions of nonhalogenated ketones with hydroxyl free radicals are relatively large, and the atmospheric lifetimes will be 

on the order of days. In addition, these compounds undergo photolysis in the troposphere. The method of 

Wuebbles and Connell72 used to estimate lifetimes due to hydrogen atom abstraction, however, shows that 

halogen substitution greatly increases the atmospheric lifetimes. Thus, halogenated ketones are suitable 

only if the photolytic lifetime is sufficiently short. Without absorption cross sections for compounds of 

interest, photolysis estimates cannot be made. 

f. Overall Assessment. There is nothing to recommend these physical extinguishants. They are likely

to be much more toxic than the HCFCs and to have materials compatibility and boiling point problems. 

There are better ways to decrease atmospheric lifetime than incorporation of a carbonyl group. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

31
4. Fluorine-containing Aldehydes and Ketones 

 

a. Fire Suppression Effectiveness. Fire suppression data are almost completely unknown for 

fluorinated carbonyl compounds. A major exception, however, is dodecafluoro-2-methylpentan-3-one, 

CF3CF2C(O)CF(CF3)2, which has a propane cup burner heptane extinguishment volume fraction of 

3.5 %.

73 This can be compared with values of 3.6 % for halon 1211 and 4.3 % for halon 1301 with the 

same fuel.73 Unfortunately, data for n-heptane extinguishment with this perfluorinated ketone have not 

been reported. Hexafluoroacetone, CF3COCF3, has a cup burner extinguishment volume fraction of over 

6 %.

b. Toxicity. Lower aldehydes attack exposed moist tissue, especially eyes and mucous membranes. 

Higher aldehydes penetrate deeper into the respiratory tract and affect the lungs. Many members of the 

family are mutagens, and all have anesthetic properties. Ketones are less toxic but they can act as 

narcotics and as neurotoxins. Hexafluoroactetone is known to be highly toxic; however, dodecafluoro-2-

methylpentan-3-one, CF3CF2C(O)CF(CF3)2 is reported to have a relatively low toxicity. The 4 hour LC50

value is greater than 10 %,and the cardiac sensitization NOAEL is 10 %.73

c. Materials Compatibility. Carbonyl-containing compounds will undoubtedly be more corrosive than 

the corresponding HFCs or PFCs. The fully fluorinated compound CF3CF2C(O)CF(CF3)2 is reported to 

show no reaction with a variety of metals at its boiling point.73 Some results for interactions with

elastomers have been reported; however, testing is still under way.

73

d. Colligative Properties. Since fluorine-containing aldehydes and ketones must contain a carbonyl

group and should avoid halogen atoms on the alpha carbon, structural requirements indicate relatively

high molecular weights compared to, e.g., the HFCs. There is one fluorinated ketone reported to be a fire 

extinguishant, CF3CF2C(O)CF(CF3)2. 

e. Atmospheric Impact. ODP is not a problem with these compounds; however, GWP values and 

atmospheric persistence must be considered. Carbonyl compounds can undergo photolysis and may also 

undergo physical removal, depending on the water solubility. Reaction with hydroxyl free radicals 

requires the presence of hydrogen atoms. Rate constants for reactions with hydroxyl free radicals and 

estimated quantum yields and absorption cross sections for photolysis indicate that aldehydes will have 

short atmospheric lifetimes, on the order of a few hours to approximately one month. 69,70,69

 The rate 

constants for reactions of non-halogenated ketones with hydroxyl free radicals are relatively large, and the 

atmospheric lifetimes will be on the order of days. In addition, these compounds undergo photolysis in 

the troposphere. The method of Wuebbles and Connell72 used to estimate lifetimes due to hydrogen atom

abstraction, however, shows that halogen substitution greatly increases the atmospheric lifetimes. Thus, 

halogenated ketones may have low GWP values only if the photolytic lifetime is sufficiently short. 

Without absorption cross sections for compounds of interest, photolysis estimates cannot be made. 

CF3CF2C(O)CF(CF3)2 is expected to have an atmospheric lifetime of 3 to 5 days and a 100 year GWP of 

1 (compared to CFC-11). 

f. Overall Assessment. In the absence of the recent results reported for CF3CF2C(O)CF(CF3)2, there 

was little to recommend the fluorinated ketones as extinguishants. This is still true for the aldehydes; 

however, at least some of the fully fluorinated ketones may have acceptable environmental and toxicity 

characteristics. Little is known about the fire extinguishing capabilities although studies are under way.

32
No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

33
F. Aromatics 

Aromatics are resonance-stabilized cyclic compounds. Owing to molecular weight considerations, the 

only compounds of interest here are derivatives of benzene, C6H6. 

1. Iodine-containing Aromatics 

a. Fire Suppression Effectiveness. No extinguishment studies have been made for any iodinecontaining aromatic. Although compounds containing iodine are usually good extinguishants, the large 

number of carbon atoms (at least six) may supply significant combustion energy and this may negate 

much of the suppression characteristics. 

b. Toxicity. No information is available on the toxicity of iodine-containing fluoroaromatics. It is 

expected that such compounds will have toxicities similar to those of the iodine-containing alkanes, some

of which are known to have very low cardiac sensitization levels.8,10 

c. Materials Compatibility. The materials compatibility properties are totally unknown; however, the 

iodine-containing aromatics are not expected to be significantly more corrosive than the iodine-containing 

alkanes. 

d. Colligative Properties. The iodine-containing aromatics will have very large molecular weights and 

high boiling points, even when fluorinated. 

e. Atmospheric Impact. Due to the presence of iodine, iodinated aromatics are expected to have very

short atmospheric lifetimes and low GWP and ODP values. 

f. Overall Assessment. These very large molecules carry a large fuel burden and have low vapor 

pressures. It is unlikely that suitable iodine-containing aromatics can be found for total flooding. In fact, 

the only reason to consider these compounds any further might be the slim possibility of finding a 

compound with low toxicity. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

34
2. Bromine-containing Aromatics 

 

a. Fire Suppression Effectiveness. Only one extinguishment study has been made for a brominecontaining aromatic: 1-bromo-2,3,5,6-tetrafluoro-4-(trifluoromethyl)benzene (n-heptane cup burner, 4.26

volume percent.64 Although compounds containing bromine are usually good extinguishants, the large 

number of carbon atoms (at least six) may supply significant combustion energy and this may negate 

much of the suppression characteristics. The compound expected to have the highest volatility,

bromopentafluorobenzene, is flammable (flash point 87 °C).74

b. Toxicity. Few data are available on bromine-containing fluoroaromatics. A 2 hour mouse LC50 of 

0.38 % has been estimated for bromopentafluorobenzene using QSAR methods.50 Exposure of mice to 

1.8 % to 2.4 % of this compound produced no anesthesia, and all survived. QSAR methods have also 

been used to estimate a 2 hour mouse LC50 of 0.5 % for 2-bromoheptafluorotoluene, 0.4 % for 3-

bromoheptafluorotoluene, and 0.4 % for 4-bromoheptafluorotoluene.

50 

c. Materials Compatibility. The materials compatibility properties are totally unknown; however, the 

bromine-containing aromatics are not expected to be significantly more corrosive than the brominecontaining alkanes. 

d. Colligative Properties. The boiling points for bromine-containing aromatics are very high. It is very 

unlikely that such agents could be used in total flooding applications, and the volatility may be too low 

even for streaming. 

Compound Formula BP (°C) Ref.

Bromopentafluorobenzene C6BrF5 134 75

2-bromoheptafluorotoluene C6BrF4CF3 154 76

3-bromoheptafluorotoluene C6BrF4CF3 153 77

4-bromoheptafluorotoluene C6BrF4CF3 152 78

e. Atmospheric Impact. Like the alkenes, hydroxyl free radicals can add to aromatics. At about room

temperature most •OH radical reactions studied to date proceed by addition to the aromatic ring rather 

than by abstraction of a hydrogen atom. Rate constants for the reaction of hydroxyl free radicals with 

aromatic compounds are similar to those observed for the alkenes.79 Of particular interest is the 298 K 

rate constant of kOH = 2.2 x 10-13 cm3

/molecule-s and approximately 3 x 10-12 cm3/molecule-s observed 

for reactions with hexafluorobenzene (C6F6) and n-propylpentafluorobenzene (CH3CH2CH2C6F5), 

respectively.

80 The reaction rates for the nonfluorinated analogs are somewhat faster: kOH = 1.59 x 10-12

for benzene and 7.8 x 10-12 cm3

/molecule-s for n-propylbenzene.80 Thus, fluorination of the aromatic ring 

decreases the reaction rate with •OH. One can calculate the first order rate constants for the two 

fluorinated compounds as k1 = kOH [•OH]. This gives k1 = 2.1 x 10-7 s-1 (t1/e = 1/k1 = 54 days) for 

hexafluorobenzene and k1 = 2.9 x 10-6 s-1 (t1/e = 1/k1 = 4 days) for n-propylpentafluorobenzene.

One can use the method of Wuebbles and Connell72 to estimate first-order rate constants and atmospheric 

lifetimes for a series of aromatic compounds of interest. The estimation method gives k1 = 8 x 10-8 s-1, 

(t1/e = 145 days) for hexafluorobenzene and k1 = 3 x 10-7 s-1, (t1/e = 39 days) for 

n-propylpentafluorobenzene. These rate constants are a little smaller than those determined from the 

experimental second-order rate constants above. These values indicate that aromatics have an excellent 

potential for environmental acceptability, even with bromine present. 

35
f. Overall Assessment. Despite the possibly good environmental characteristics, the exceedingly high 

molecular weights and fuel burden mitigate against further study of these compounds. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

36
3. Chlorine-containing Aromatics 

 

a. Fire Suppression Effectiveness. N-heptane cup burner extinguishment volume fractions have been 

reported4

 for 1,3-dichlorotetrafluorobenzene (6 %, 537 g/m3) and chloropentafluorobenzene (5.4 %, 447 

g/m3

). Much of this effectiveness is due to the large heat capacities of these heavy compounds. 

b. Toxicity. Some chlorine-containing aromatics are known to be carcinogens (e.g., chlorobenzene, 1,4-

dichlorobenzene, hexachlorobenzene); however, no toxicity data are available for chlorine-containing 

fluoroaromatics. There is little reason to believe that such compounds would have exceptionally high 

acute toxicities. 

c. Materials Compatibility. The materials compatibility properties are totally unknown; however, the 

chlorine-containing aromatics are not expected to be significantly more corrosive than the brominecontaining alkanes. 

d. Colligative Properties. The chlorinated aromatics are expected to have high boiling points and low 

volatilities, even when fluorinated. 1,3-Dichlorotetrafluorobenzene has a boiling point of 151 °C and a 

melting point of 73 °C.81 The normal boiling point of chloropentafluorobenzene is 117 °C. 

e. Atmospheric Impact. As with the bromine-containing aromatics, hydroxyl free radicals can add to 

these compounds, resulting in atmospheric lifetimes possibly within an acceptable range. 

f. Overall Assessment. Despite the possibly good environmental characteristics, the high molecular 

weights and fuel burdens mitigate against further study of these compounds. Besides, these compounds 

are not expected to be particularly outstanding fire suppressants. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

37
4. Fluorine-containing Aromatics 

 

a. Fire Suppression Effectiveness. No fire suppression testing has been carried out on fluorinecontaining aromatics; however, there is no reason to believe that these compounds will behave any 

different than other higher molecular weight physical agents. The large number of carbon bonds available 

upon reaction supply significant energy, which will negate in very large part the suppression effects. 

Pentafluorobenzene (C6HF5) and perfluorotoluene (C6F5CF3) are flammable in air. 

b. Toxicity. Some toxicity data are available for trifluoromethyl-substituted benzenes, which are being 

considered as solvents. All mice died in 6 hours after 10 min exposure to a volume fraction of 0.5 % to 

0.9 % of (trifluoromethyl)pentafluorobenzene; pentafluorobenzene produced anesthesia in mice with all 

surviving.43 

c. Materials Compatibility. The materials compatibility properties are unknown; however, the 

fluorine-containing aromatics are not expected to have compatibility problems. 

d. Colligative Properties. The boiling points are 85 °C for pentafluorobenzene and 103 °C for 

perfluorotoluene.43 (Trifluoromethyl)benzene has a boiling point of 104 °C.82

e. Atmospheric Impact. These compounds have zero ODP values. As with the iodine- and brominecontaining aromatics, hydroxyl free radicals can add to these compounds, resulting in atmospheric 

lifetimes that would mitigate any global warming contribution. 

f. Overall Assessment. Despite the possibly good environmental characteristics, the high molecular 

weights and fuel burdens mitigate against further study of these compounds. Besides, these compounds 

are not expected to be particularly outstanding fire suppressants. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

38
III. Nitrogen-containing Compounds 

A. Nitriles

Nitriles are organic compounds containing the -C≡N group. 

a. Fire Suppression Effectiveness. No fire suppression tests have been conducted on nitrile 

compounds, and there is no evidence or reason to believe that the nitrile group itself possesses an intrinsic 

fire suppression capability. Nonhalogenated nitriles are known or are expected to be flammable. 

Fluorination may well reduce this, and the resulting compounds would act mainly as physical 

suppressants. The addition of bromine or iodine would impart chemical flame inhibition to nitriles. 

b. Toxicity. Most nitriles are moderately to highly toxic. Propionitrile is quite toxic, apparently 

through metabolism of the cyanide ion. One-third of rats exposed to a volume fraction of 0.05 % (500 

ppm by volume) of propionitrile in air died.83 Similarly, butyronitrile and isobutyronitrile are highly toxic 

by skin contact or inhalation.84,85 There are no published data on the highly fluorinated nitriles or nitriles 

containing bromine or iodine. 

c. Materials Compatibility. Nitriles are not inherently highly corrosive toward metals. They do attack 

some polymeric materials. Nitriles are slowly hydrolyzed, particularly in the presence of acids or bases, 

to give carboxylic acids and ammonia; however, the net change in pH (indicative of corrosive tendencies) 

is nominally zero since both a weak base and a weak acid are formed. 

d. Colligative Properties. The following graph shows the variation of boiling point, melting point and 

heat of vaporization (at or near 25 °C) for linear nitriles containing 2 through 6 carbon atoms.86 The 

simplest nitrile, acetonitrile (methyl cyanide) has a boiling point of 81.6 °C and other nitriles have higher 

boiling points. The freezing points for compounds up to 6 carbon atoms are all below 80 °C except for 

acetonitrile, which is -43.8 °C. Halogenation is expected to cause significant property changes. For 

example, trifluoroacetonitrile has a surprisingly low boiling point of -64 °C.87

-150

-100

-50

0

50

100

150

200

2 3 456

Number of Carbon Atoms

BP, °C

MP, °C

∆Hv, kJ/mol

e. Atmospheric Impact. Nonhalogenated nitriles have no intrinsic ODP, and no estimate has been 

made of their GWP values; however, consideration of atmospheric chemistry (see below) indicates that 

GWPs should be negligible (assuming relatively rapid removal by rainout). Halogenated nitriles, 

however, could have significant ODP values and GWP values, depending on the degree of halogenation 

and the type of halogen atoms present. 

The approximate rate constant for reaction of •OH with acetonitrile at 298 K is 2 x 10-14

 cm3 molecule-1 s

-1

(recommended, estimated uncertainty ±40 %) and with propionitrile is 19 x 10-14 cm3 molecule-1 s

-1.79 

39
These compare with recommended values of 0.84 x 10-14 cm3 molecule-1 s

-1 for methane and 26.8 x 10-14

cm3 molecule-1 s

-1 for ethane, both at 298 K. Thus, the presence of a nitrogen atom in the nitriles does not 

appear to increase the reaction rate with •OH (compared with alkanes) significantly. Using a globally

averaged •OH concentration of 9.7 x 105

 molecule/cm3 88, one calculates an estimated lifetime for 

acetonitrile (three hydrogen atoms) based only on reaction with •OH of 1.53 years and for propionitrile (5 

hydrogen atoms) of approximately 2 months. 

The polarity induced by nitrogen causes nitriles to be completely (e.g., acetonitrile) or somewhat (e.g., 

propionitrile) water soluble. This greatly increases the probability for relatively rapid removal by rainout. 

Some atmospheric hydrolysis could also occur. This is expected to be negligible for homogeneous gas 

phase reactions, but could occur heterogeneously on atmospheric water droplets. 

The addition of fluorine atoms to decrease flammability will decrease the reaction rates with •OH and will 

also decrease the water solubility, both changes increasing the atmospheric lifetime. 

f. Overall Assessment. It appears unlikely that a nitrile could be designed to have desirable values of 

all the needed properties. However, it is suggested that a cursory examination of the possibility for 

inherent fire suppression capability of the nitrile group (possibly using CF3CN) be pursued. A positive 

result might stimulate a closer look at this family.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X

Estimated

40
B. Nitro Compounds 

Nitro compounds contain the -NO2 group. The simplest nitro compound is nitromethane (CH3NO2). 

a. Fire Suppression Effectiveness. Nitro compounds are often dangerously flammable and/or 

explosive. As a result, no fire suppression tests have been conducted using nitro compounds, and there is 

no evidence or reason to believe that the nitrile group itself possesses an intrinsic fire suppression 

capability. 

b. Toxicity. Most nitro compounds are highly toxic. 

c. Materials Compatibility. Nitro compounds generally have some materials compatibility problems. 

d. Colligative Properties. The following graph shows the variation of boiling point and freezing point 

(not melting point) for linear nitroalkanes containing 1 through 4 carbon atoms (nitro group on the first 

carbon atom in the butane and propane derivatives). The boiling points are high, in all cases over 100 °C. 

Fluorination would be expected to lower these boiling points. 

-150

-100

-50

0

50

100

150

200

1 2 3 4

Number of Carbon Atoms

BP, °C

FP, °C

e. Atmospheric Impact. Nitromethane reacts with •OH slightly faster than methane (1.58 x 10-14 cm3 

molecule-1 s

-1 versus 0.84 x 10-14 cm3 molecule-1 s-1 at 298 K) and nitroethane reacts slightly slower than 

ethane (7.2 x 10-14 cm3 molecule-1 s

-1 versus 27 x 10-14

 cm3 molecule

-1 s-1 at 298 K).89 The differences are 

negligible, and nitroalkanes are expected to have atmospheric lifetimes similar to those of the 

hydrocarbons. Nitro compounds have no intrinsic ODP.

f. Overall Assessment. Owing to the physical, toxicological, stability, and flammability problems of 

nitro compounds, examination of this group for fire suppression is not recommended.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

41 
C. Organic Nitrates and Nitrites 

Organic nitrates and nitrites are compounds containing, respectively, the groups -ONO2 and -ONO. The 

simplest organic nitrates and nitrites are methyl nitrate (CH3ONO2) and methyl nitrite (CH3ONO). 

a. Fire Suppression Effectiveness. The combustion properties of nitrates and nitrites are fairly well 

known, primarily because both types of compounds are often explosive. No fire suppression tests have 

been conducted using nitrates and nitrites, and there is no evidence or reason to believe that these groups 

possess any intrinsic fire suppression capability. It is not clear whether the addition of bromine or iodine 

would be sufficient to stifle the explosive tendencies. 

b. Toxicity. Nitrates and nitrites have relatively high toxicities. In the case of nitrates, methemoglobin 

formation is the primary toxicity cause. Nitrites are also known to induce methemoglobin formation and, 

have even caused human death by this route.90 (Methemoglobin is the oxidized form of hemoglobin in 

which the iron in the heme component has been oxidized from the ferrous (+2) to the ferric (+3) state. 

This renders the hemoglobin molecule incapable of effectively transporting and releasing oxygen to the 

tissues.) A 4 hour LC50 of 0.13 % has been reported for rats.91

c. Materials Compatibility. To date, no information has been obtained on general materials 

compatibilities of nitrates and nitrites. 

d. Colligative Properties. The following graphs show the variation of boiling point, melting point and 

heat of vaporization for some nitrates and nitrites with 1 through 3 carbon atoms. (These data are from a 

variety of sources, but primarily from the NIST Chemistry WebBook.) The boiling point data are very

uncertain due to the instability of the nitrates and nitrites. 

-150

-100

-50

0

50

100

150

123

Number of Carbon Atoms

BP, °C

MP, °C

∆Hv, kJ/mol

 Nitrates 

-40

-20

0

20

40

60

1 2 3

Number of Carbon Atoms

BP, °C

MP, °C

∆Hv, J/mol

 Nitrites 

e. Atmospheric Impact. Nonhalogenated nitrites and nitrates have no intrinsic ODP, and no estimate 

has been made of the GWP values. Halogenated nitriles, however, could have significant ODP values 

and GWP values, depending on the degree of halogenation and the type of halogen atoms present. 

A relatively large amount of data has been reported for reaction of nitrates and nitrites with •OH.79 The 

approximate rate constant at or near 298K for reaction with •OH is 3.4 x 10-14 cm3 molecule-1 s

-1 for 

methyl nitrate, 49 x 10-14 cm3 molecule-1 s

-1 for ethyl nitrate, and 62 x 10-14 cm3 molecule-1 s-1 for propyl

nitrate. Similarly, the approximate rate constant at or near 298 K for reaction with •OH is 12 x 10-14 cm3 

molecule-1 s

-1 for methyl nitrite (large unexplained experimental variation), 177 x 10-14 cm3 molecule-1 s-1

for ethyl nitrite, and 235 x 10-14

 cm3 molecule-1 s

-1 for propyl nitrite. These can be compared with 

recommended values of 0.84 x 10-14 cm3 molecule-1 s

-1 for methane, 27 x 10-14 cm3 molecule-1 s-1 for 

ethane, and 115 x 10-14 cm3 molecule -1s

-1 all at 298 K. Thus, the nitrates and especially the nitrites have 

42 
reaction rates with •OH somewhat higher than those of the corresponding alkanes. Using a globally

averaged •OH concentration of 9.7 x 105

 molecule/cm3 88, one calculates estimated lifetimes for methyl

nitrate, ethyl nitrate, and propyl nitrate of, respectively, 1 year, 24 days, and 19 days. For methyl nitrite, 

ethyl nitrite, and propyl nitrite the values are 3 months, 7 days, and 5 days. The addition of halogen 

atoms, such as fluorine, will decrease the reaction rates with •OH. 

The nitrates and nitrites are slightly water soluble, a property that increases the probability for removal by

rainout. 

f. Overall Assessment. While the nitrates and nitrites are expected to have low atmospheric lifetimes, 

the absence of any proven inherent fire suppression capabilities due to the nitrate and nitrite groups, the 

high toxicity, and, in particular, the explosive tendencies makes these compounds unacceptable for study.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

43 
D. Nitroso Compounds 

Nitroso compounds are organics containing the -NO group. The simplest nitrosoalkane is nitrosomethane 

(CH3NO); the simplest nitrosoarene is nitrosobenzene (C6H5NO). 

a. Fire Suppression Effectiveness. No fire suppression tests have been conducted on nitroso 

compounds, and there is no evidence or any reason to believe that the nitroso group itself possesses an 

intrinsic fire suppression capability. Bromination would probably be required to produce an inhibitor. 

Some nitroso compounds (e.g., 4-nitrosophenol) are explosive. 

b. Toxicity. Little is known of the toxicity of the nitrosoalkanes; however, these can react to form Nnitroso compounds, which are known to be strong carcinogens. A range of toxicities has been reported 

for the nitrosoarenes. 

c. Materials Compatibility. No information is available. 

d. Colligative Properties. No information is available for the nitrosoalkanes, but they are unstable, 

tending to rearrange, oxidize, and dimerize. The nitrosoarenes are solids at room temperature. 

e. Atmospheric Impact. Nonhalogenated nitriles have no intrinsic ODP, and no estimate has been 

made of the GWPs. No lifetimes or rate constants for atmospheric reactions have been reported. 

f. Overall Assessment. In view of the stability and toxicity problems associated with nitroso 

compounds, no further study is recommended. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

44 
E. Fluoroalkyl Amines 

Amines are derivatives of ammonia (NH3) and have the general formula NRR’R” where at least one of 

the nitrogen substituents is an alkyl group. The others can be hydrogen atoms. Due to toxicity concerns, 

the only compounds of interest are amines containing three alkyl groups. Moreover, to decrease toxicity

and corrosivity (by decreasing polarity) and to decrease flammability, the alkyl groups should be at least 

partially fluorinated. 

a. Fire Suppression Effectiveness. Research from the National Industrial Research Institute of Nagoya 

has focused on fluoroalkylamines, with an emphasis on perfluoroalkyl derivatives, as fire suppressants.92 

The inhibition effect of several bromine-free polyfluoroalkylamines including N(CF3CF2)3, 

N(CF3)2(CF2CF3), N(CF3)2(CF2CHF2), and N(CF3)2(CF=CF2) on flame propagation has been measured by 

determining the laminar burning velocity for a mixture of 9.5 % methane, 90.0 % air, and 0.5 % inhibitor, 

at an initial temperature of 298 K and a pressure of 101 kPa. All of the fluoroalkylamines inhibited 

flame propagation less efficiently than CF3Br, but more efficiently than HFC-227ea (CH3CHFCF3). 

Calculations showed that the inhibition effect of the fluoroalkylamines was caused not only by physical 

factors, but also by a chemical process in which fluorinated species capture combustion chain carriers 

(•H, •O, and •OH) to form stable HF molecules. The inhibition efficiencies of fluoroalkylamines were 

found to be higher than those of fluoroalkanes since fluoroalkylamine decomposes to reactive fluoroalkyl

radicals in the lower temperature region of each flame.93 Ab initio molecular orbital calculations indicate 

that fire suppression by perfluoromethylamines is due, in part, to reactions of the trifluoromethyl radical, 

which can be easily released from perfluoroalkyl-amine by dissociation of C-N bonds.94 Others had 

previously found that CF3 acts as a chemical inhibitor.30

b. Toxicity. Amines with at least partially fluorinated alkyl groups are the most likely to be considered 

as fire extinguishants. Fluorination will lower or eliminate flammability and is likely to decrease toxicity

by decreasing polarity. Some extremely limited toxicity data have been reported for partially fluorinated 

amines.62 The LCLO for mouse inhalation has been reported as 500 mg/m3

 for 2,2,2-trifluoroethylamine, 

(CF3CH2)NH2.

27 Some genotoxicity and cytotoxicity testing has been carried out on fluorinated amines 

using Chinese hamster lung cell cultures.95

c. Materials Compatibility. The perfluorinated amines are known to have excellent material 

compatibility. Some of the higher molecular weight perfluoroamines have been used as inert fluids in 

electronics testing. The more highly polar less fluorinated amines are known to attack metals.

d. Colligative Properties. The following table gives the boiling points for some fluorinated amines62,96 

The following )Hv values have been reported for fluorinated amines: 25.1 kJ/mol for N(CF3)3

18, 48 

kJ/mol for N(C4F9)3

97, 55 kJ/mol for N(C5F11)3 

97, 63 kJ/mol for (C3F7)2NC6F12N(C3F7)2 97, and 27 kJ/mol 

for N(CF3)2(CH2CH3) 98, all at the boiling point except for the last compound, where the conditions were 

not reported. 

45 
Compound Boiling Point (°C) 

N(CF3)3 -10

(CF3)2NCH3 11-12

(CF3)2NCF2CF3 20.5

(CF3)2NCH2CH3 33-34

(CF3)2NCH2CH3 33.3

(CF3)2NCH2CF3 38

N(CF3)(CF2CF3)2 46

(CF3)2NCH2CF2H 50-52

(CH3)2NCH2CF3 51.35

N(CF2CF3)3 70.3

e. Atmospheric Impact. A thorough assessment of the atmospheric impact of fluorinated amines and 

of bromofluoroamines (based on estimations and calculations) has been presented.60 For example, the 

compound (CBrF2)(CF3)NCH3 is estimated to have an atmospheric lifetime of 0.028 years (10 days) and 

an ODP of 0.006 relative to CFC-11.60

f. Overall Assessment. Fluoroamines and bromofluoroamines are undoubtedly the most promising of 

the nitrogen-containing compounds as potential halon replacements. There is evidence that some could 

have low atmospheric lifetime, low toxicity, and good fire extinguishment capability.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

46 
IV. Sulfur-containing Compounds 

A. Hexacoordinate Sulfur 

a. Fire Suppression Effectiveness. Cup burner results30 indicate that sulfur makes little if any 

chemical contribution to suppression by these compounds, a conclusions reached by others specifically

for SF6.

99,100 Note, however, that a sulfur dioxide cycle has been proposed to inhibit combustion by

removal of hydrogen atoms.101 Except for the brominated derivative, none of the compounds in this table 

exhibit a flame suppression capability approaching that of halon 1301. 

Compound Ext. Volume

Fraction (%) 

SF6 11

SF5Br 4.2

SF5Cl 13

SF5SF5 11

b. Toxicity. SF6 has an exceedingly low toxicity; however, the closely related compound S2F10 is highly

toxic. Of considerable concern is the toxicity of combustion products, such as SO2, that could form

during fire extinguishment. 

c. Materials Compatibility. SF6 is quite inert and has had extensive use as a dielectric fluid. Too little 

work has been performed on the derivatives to estimate their materials compatibility.

d. Colligative Properties. The data in the following table

,15,18,24,47 indicate that the properties of SF5X 

compounds are in the region needed as halon 1301 substitutes. 

Compound BP (°C) MP (°C) )Hv, 

kJ/mol 

SF6 -63.8 (subl) -50.7 (triple pt.) 

SF5Br 3.1 24 (est)

SF5Cl -21 21.7

SF5SF5 30 -52.7

SF5(CF3) -21

e. Atmospheric Impact. SF6 has a very long atmospheric lifetime of 3200 years and a calculated 100 

year GWP of 13,900 compared to CO2.

46 The lifetime and GWP of SF5(CF3) have been estimated as 

1000 years and 6741 compared to CO2

62; however, the method for making these estimations was not 

reported. 

f. Overall Assessment. Hexavalent sulfur has no significant chemical suppression contribution, nor 

does it lead to improved atmospheric environmental properties. Thus, no further study is recommended. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

47 
B. Sulfides and Mercaptans

Sulfides and mercaptans contain divalent sulfur not attached to an oxygen atom: R1-S-R2 and R-S-H. 

a. Fire Suppression Effectiveness. Since the nonhalogenated compounds are generally flammable, 

only the highly halogenated compounds are of interest. No fire suppression tests have been conducted on 

these, and there is no evidence indicating that the -S- group itself possesses an intrinsic chemical fire 

suppression capability. A sulfur dioxide cycle has been proposed to inhibit combustion by removal of 

hydrogen atoms.101 Added bromine or iodine would impart chemical flame suppression effectiveness. 

b. Toxicity. Most organic sulfides are toxic. Moreover, chlorine substitution in the beta position can 

give rise to highly toxic sulfur mustards (e.g., ClCH2CH2-S-CH2CH2Cl). No evidence of a similar 

toxicity with fluorine substituents has been reported. The mercaptans tend to be highly reactive. 

c. Materials Compatibility. Sulfides and particularly mercaptans are generally reactive toward metals, 

particularly copper and copper alloys. 

d. Colligative Properties. The following table includes some boiling points and heats of 

vaporization.102,103 Of particular interest is the decrease in boiling point with fluorination. 

Compound Boiling point ( °C) )Hv (kJ/mol) 

CH3-S-CH3 37.5

CF3-S-CF3 -22

CF3-S-C2F5 6.3 28.8

CF3-S-C3F7 38.6 27.7

e. Atmospheric Impact. Nonhalogenated sulfides have no intrinsic ODP, and no estimate has been 

made of the GWP values. A significant amount of kinetic data are available for reactions of sulfides and 

mercaptans with •OH79; however, no kinetic information is available for halogen-containing derivatives. 

The recommended rate constant for reaction of •OH with dimethyl sulfide is 460 x 10-14 cm3 molecule-1 

s

-1at 298 K. The value for ethane is 27 x 10-14 cm3 molecule-1 s-1. Thus, the presence of a sulfide atom

appears to increase the reaction rate with •OH significantly. Using a globally averaged •OH 

concentration of 9.7 x 105

 molecule/cm3 88, one calculates an estimated lifetime for dimethyl sulfide 

based only on reaction with •OH of 2.6 days. Higher molecular weight sulfides with more hydrogen 

atoms have larger rate constants with •OH and even lower atmospheric lifetimes. Thus, the sulfides 

appear to have intrinsically short atmospheric lifetimes. Halogenation will decrease the reaction rates 

owing primarily to removal of hydrogen atoms. 

f. Overall Assessment. The sulfides suffer from several drawbacks: no distinctive fire suppression 

efficiency and potential toxicity, reactivity, and materials compatibility problems. However, the 

possibility that atmospheric lifetimes could be very short for brominated compounds makes a screening 

study of the smaller bromofluorosulfides desirable. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied Limited screening 

Estimated

48 
C. Difluorosulfur Compounds 

These compounds contain tetravalent sulfur, with two of the bound ligands being fluorine atoms and the 

other two being partially halogenated alkyl groups. 

a. Fire Suppression Effectiveness. No flame suppression tests have been conducted on these 

tetravalent analogs of the sulfides. The expectations for suppression effectiveness are similar.

b. Toxicity. The toxicity of these compounds is unknown; however, fluorine on a sulfur(IV) compound 

may be highly labile. In particular, the compounds may undergo hydrolysis. 

c. Materials Compatibility. Materials compatibility is unknown. If the compounds do hydrolyze, 

metal corrosion is probable. 

d. Colligative Properties. The boiling points and heats of vaporization for a series of perfluorinated 

compounds are shown in the following table and graph.102

 All but the lowest boiling points are higher 

than optimum for halon 1301 substitutes. 

0

20

40

60

80

2 3 4

Number of Carbon Atoms

BP, °C

∆Hv, kJ/mol

Compound 

Boiling point

( °C)

)Hv

(kJ/mol)

CF3SF2CF3 21 28.8

CF3SF2C2F5 44.1 29.2

CF3SF2C3F7 69.3 32.8

C2F5SF2C2F5 69.5 32.2

e. Atmospheric Impact. No information is available on the lifetime or GWP for compounds of this 

type. Such compounds are expected to have no ODP in the absence of chlorine or bromine substitution. 

f. Overall Assessment. These sulfur(IV) compounds are likely to undergo hydrolysis giving rise to 

toxicity and materials compatibility problems. In the absence of information showing that this is not the 

case, it is recommended that no future studies of these compounds be carried out. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

49 
D. Sulfoxides 

These compounds contain tetravalent sulfur, with a double-bonded oxygen atom and two partially

halogenated alkyl groups. 

a. Fire Suppression Effectiveness. No fire suppression tests have been conducted on sulfoxides. 

Though there is little reason to believe that sulfur posses an inherent extinguishing ability, a sulfur 

dioxide cycle has been proposed to inhibit combustion by removal of hydrogen atoms.101

b. Toxicity. Extensive toxicological studies have been made on dimethylsulfoxide (DMSO), the 

simplest of the sulfoxide compounds and a widely used solvent. DMSO is one of the least toxic organic 

chemicals known. Its measured LD50 values (oral, dermal, and inhalation) show it to have a much lower 

acute toxicity than ethanol, acetone, and other common solvents. DMSO, however, does have the unique 

ability to penetrate human skin and this is some cause for concern. 

c. Materials Compatibility. Dimethylsulfoxide is known to attack most polymers; however, it has a 

relatively good compatibility with metals. Similar characteristics are expected for other sulfoxides. No 

compatibility studies have been carried out with the fluorinated sulfoxides.

d. Colligative Properties. The boiling points and heats of vaporization for a series of perfluorinated 

sulfoxides are shown in the adjacent table and graph.102

 As a whole, the boiling points are higher than 

desired for total flooding halon substitutes. 

Compound 

Boiling Point 

( °C)

)Hv

(kJ/mol)

CF3S(O)CF3 37.3 28.4

CF3S(O)C2F5 58.2 32.5

CF3S(O)C3F7 64 33.6

C2F5S(O)C2F5 62.7 35.1 0

20

40

60

80

2 3 4

Number of Carbon Atoms

BP, °C

∆Hv, kJ/mol

e. Atmospheric Impact. No information is available on the atmospheric lifetime or GWP values for 

sulfoxides. Such compounds are expected to have no ODP in the absence of chlorine or bromine 

substitution. 

f. Overall Assessment. There is insufficient information to make a truly informed judgment on the 

applicability of sulfoxides as halon 1301 substitutes. It is almost certain that bromination would be 

needed to prepare and acceptable extinguishant. It is recommended than a screening investigation be 

conducted. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied Limited screening 

Estimated

50 
V. Phosphorus Compounds 

A. Phosphorus Acids and Esters 

Phosphorus forms a very large number of acids and esters with a rather complicated chemistry. The 

primary single-phosphorus oxyacids of phosphorus are phosphoric acid, OP(OH)3 (also known as 

orthophosphoric acid); phosphonic acid, OPH(OH)2 (originally called phosphorous acid, a name now 

reserved for the hypothetical acid P(OH)3); and phosphinic acid, OPH2(OH) (originally called hypophosphorous acid, a name now used for the hypothetical alternative structure PH(OH)2). Phosphoric acid is 

triprotic, phosphonic acid is diprotic, and hypophosphonic acid is monoprotic. Phosphoric acid forms 

three phosphate esters: O=P(OH)2(OR), O=P(OH)(OR)2, and O=P(OR)3. Phosphonic acid gives two 

phosphonate esters: O=PH(OH)(OR) and O=PH(OR)2. These are often written as the “phosphite” forms 

P(OH)2(OR) and P(OH)(OR)2, where they can be considered as derivatives of the hypothetical 

phosphorous acid, P(OH)3; however, these two esters almost certainly exist only in the phosphonate forms 

with P=O and P-H bonds. A series of very common compounds includes the trialkyl and triaryl

“phosphites.” These materials appear to exist as two interconvertable forms: P(OR)3, which can be 

considered as derived from the hypothetical acid P(OH)3, and O=PR(OR)2, which can be considered as 

derived from phosphonic acid. In most cases, the stable compounds have the phosphonate structure with 

a P=O bond. For historical reasons, however, the compounds are still most often named as phosphites 

and given the structure P(OR)3 rather than being named as phosphonates, with the structure O=PR(OR)2. 

a. Fire Suppression Effectiveness. A significant amount of flame suppression testing has been carried 

out on a few esters of phosphorus-containing acids.104,105 Trimethyl phosphate ((O=P(OCH3)3) shows a 

more pronounced effect on flame velocity than Cl2 and Br2.

106 Phosphate esters are of particular interest 

as fire suppressants since they are difficult to ignite and will self-extinguish.107 Dimethyl

methylphosphonate (DMMP, O=P(CH3)(OCH3)2) is approximately 40 times more effective than nitrogen 

on a molar basis, and about 4 times more effective than halon 1301 at suppressing opposed flow diffusion 

flames.

108 It has been concluded that phosphorus-containing compounds are more efficient flame 

inhibitors than CF3Br, with the inhibition determined by the phosphorus content.

109 However, in 

suppressing cup burner flames, DMMP appears to be no more effective than CO2 on a mass basis.110 

b. Toxicity. The toxicities of the acids of phosphorus and their esters are highly variable. Nevertheless, 

this family of compounds generally has, on an average, a moderately low toxicity, at least for those 

compounds containing non-halogenated alkyl groups. The combustion products will include the 

phosphorus acids. 

c. Materials Compatibility. In the absence of hydrolysis, the phosphate esters have relatively good 

materials compatibility. The free acids will attack metals. 

d. Colligative Properties. Acids of phosphorus and their esters have low, often unacceptably low, 

volatilities and high boiling points. Some examples are given in the following table.15 It is anticipated 

that fluorination may help somewhat: P(OCH2CF3)3 has a boiling point of 131 oC compared with 156.5 oC

for the non-fluorinated compound. Additional fluorination is expected to further decrease the boiling 

point and increase the volatility.

51 
Compound Formula Boiling Point, °C 

Dimethyl methylphosphonate O=P(CH3)(OCH3)2 181

Trimethylphosphite P(OCH3)3 111.5

diethyl methylphosphonate O=P(C2H5)(OCH3)2 194

diethyl ethylphosphonate O=P(C2H5)(OC2H5)2 198

Triethylphosphite P (OC2H5)3 157.9

e. Atmospheric Impact. Some phosphorus compounds are known to be ozone depleters if released in 

the stratosphere. Moreover, stratospheric (and tropospheric) removal reactions of phosphorus are 

relatively unknown. One can propose reactions such as PO + O3 → PO2 + O2 coupled with PO2 + O →

PO + O2 that could deplete ozone. Nevertheless, it seems unlikely that phosphorus compounds would 

have any global environmental impact. 

f. Overall Assessment. Phosphorus compounds are highly effective at suppressing some types of 

flames, yet poor at suppressing others. Most work to date has emphasized alkyl phosphonates and related 

materials or phosphonitriles. Low volatility remains one of the major problems with phosphorus 

compounds as flame suppressants. Phosphorus compounds containing fluoroalkyl and hydrofluoroalkyl

groups, however, are often nonflammable and have higher volatilities; they should be given high priority

for additional study.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

52 
B. Phosphonitriles 

Phosphonitriles are compounds, possibly cyclic, containing the -P=N- unit. A common example is 

P3N3Cl6. 

a. Fire Suppression Effectiveness. As shown in the following table, attractively low cup burner flame 

extinguishment concentrations have been found for several phosphonitriles.104

 The first of these 

compounds was even more efficient at extinguishing an opposed flow diffusion flame.3

 A number of 

polyfluoroalkoxy-substituted compounds (e.g., P3N3(OCH2CF3)6) have shown very good extinguishments 

characteristics.111

Compound Ext. Vol. Fraction (%) 

P3N3F6 1.08 ± 0.07 

P3N3ClF5 0.91 ± 0.02 

P3N3Cl2F4 0.96 ± 0.08 

b. Toxicity. Except for those compounds containing phosphorus-halogen bonds, the phosphonitriles 

appear to have very low toxicities. 

c. Materials Compatibility. The phosphonitriles are expected to have very good materials 

compatibilities, due to some extent to their high molecular weights. 

d. Colligative Properties. The simple halogenated phosphonitriles (e.g., P3N3X6) are low volatility

materials. The alkoxy phosphonitriles have even higher boiling points; one of the simplest, 

P3N3(OCH2CF3)6, has a boiling point of 70 °C at 0.02 kPa. Blending with, e.g., hydrofluoroethers (HFEs) 

may give better distribution properties.104

e. Atmospheric Impact. As with the phosphorus acids and esters, it is unlikely that phosphonitriles 

would have any global environmental impact. This is particularly true due to their very low volatilities. 

f. Overall Assessment. A number of phosphonitriles have been shown to be excellent extinguishants in 

laboratory and carefully controlled field conditions; however, the exceedingly low volatilities make it 

unlikely that these could be practical total flooding extinguishants unless delivered as mists. To the 

extent misting is practical for suppressing aircraft fires, this family is worth a further look. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

53 
C. Phosphorus Halides 

a. Fire Suppression Effectiveness. The following table shows the high effectiveness of compounds 

containing direct phosphorus to halogen bonds in reducing the burning velocities of hexane flames 

relative to halon 1301 (CF3Br).109

 Multiple values for a particular compound are from different 

investigators as reported in the survey paper cited. Note that these results are true for low concentrations, 

where chemistry is believed to play a major role. At higher concentrations, the effects of heat capacity

and dilution may make the relative efficiencies smaller. POCl3 is about 10 times more effective than an 

equivalent amount of chlorine.112 Of particular interest is that there appears to be little difference between 

the chlorine-containing and the bromine-containing compounds. This may indicate that phosphorus plays 

a primary role. Flame inhibition results do not always translate to flame suppression efficiency. There is 

one report113 of PBr3 effectiveness on real-scale flames, indicating an effectiveness two orders of 

magnitude better than halon 1301. 

Compound Efficiency Relative to Halon 1301 

PCl3 6.7, 6.9

PBr3 4.6, 6.9

O=PCl3 5.2

S=PCl3 8

S=PBr3 6.7, 6.9

b. Toxicity. Compounds containing direct phosphorus to halogen bonds hydrolyze readily, forming 

injurious phosphorus-containing acids and halogen halides. For example, phosphorus tribromide will 

hydrolyze to give H3PO3 and HBr. Although there is some indication that hydrolysis is likely to be lower 

for fluorine-phosphorus bonds than for bonds of phosphorus with other halogens, 

hexafluorocyclotriphosphazene (P3N3F6) has been shown to be toxic in a manner consistent with 

hydrolytic formation of acids.114 Further study is needed to determine whether perfluorinated compounds 

will have a sufficiently low hydrolysis rate to give them an acceptable toxicity.

c. Materials Compatibility. Owing to ready acid formation from hydrolysis, compounds of 

phosphorus containing phosphorus-halogen bonds are expected to be highly corrosive toward metals. 

Materials compatibility may be less of a problem for such compounds as PF3 and O=PF3, where the rate 

of hydrolysis may be lower.

d. Colligative Properties. The adjacent table contains data for several phosphorus halides15,18

. As

expected, volatility decreases with decreasing fluorine content and increasing bromine content. In some

cases (e.g., PCl3 and PBr3), there are surprisingly large liquid ranges. 

Compound MP (°C) BP (°C) ∆Hv (kJ/mol)

PF3 -151.5 -101.5 16.5

PF2Br -16 23.9

PCl3 -112 76 30.5

PBr3 -40 173 38.8

O=PF3 -39.1a -39.7b 22.1

O=PF2Br 32 29.7

O=PCl3 1 105.5 34.4 a

 Triple point.

b

 Sublimation point. 

54 
e. Atmospheric Impact. These compounds should hydrolyze rapidly, giving products that would rain 

out. 

f. Overall Assessment. There are some enticing flame data on phosphorus halides. Thus, despite the 

expected or known high toxicities and corrosiveness, it would be valuable to verify the flame suppression 

data. Further, it would be useful to examine the possibly more stable, totally fluorinated compounds, PF3

and O=PF3.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

55 
D. Phosphines 

Phosphines have the general formula PR1R2R3, where the substituents are alkyl, aryl, and/or hydrogen. 

a. Fire Suppression Effectiveness. No flame suppression information is available on alkylphosphines, 

although the condensed phase chemicals are good flame retardants. Nonfluorinated phosphines are 

flammable, and it is not clear that fluorination will decrease this. For example, P(CF3)3 is reported to be 

spontaneously flammable.115 

b. Toxicity. PH3 is highly toxic. Few quantitative data exist on the toxicity of substituted phosphines. 

c. Materials Compatibility. Phosphines can react with metals. 

d. Colligative Properties. Phosphines will generally be more volatile than many of the other 

phosphorus compounds discussed here. This is due to their lower molecular weights and polarities. 

e. Atmospheric Impact. Though one can propose reactions such as PO + O3 → PO2 + O2 coupled with 

PO2 + O → PO + O2 that could deplete ozone, there is no evidence that such reactions would be effective 

in ozone depletion. There are no data on partially fluorinated phosphines. 

f. Overall Assessment. Even with the expected higher volatilities, toxicity and flammability

considerations indicate that phosphines are unlikely candidate fire suppressants. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

56 
E. Pentacoordinate Phosphorus 

a. Fire Suppression Effectiveness. Compounds containing bromine are expected to be good 

suppressants though probably no better than corresponding trivalent compounds. 

b. Toxicity. Only compounds where most or all of the groups are halogen atoms are stable. This is due 

to two factors. First, direct substitution stabilizes the higher oxidation state (+5). Second, there is 

decreased steric bulk from halogen atoms than from organic substituents. Halogen atoms attached to 

phosphorus are, however, subject to hydrolysis, leading to significant toxic hazard. 

c. Materials Compatibility. Owing to ready acid formation upon hydrolysis, compounds of 

phosphorus containing phosphorus to halogen bonds are expected to be highly corrosive toward metals 

except, possibly, in totally anhydrous conditions.. 

d. Colligative Properties. In general, due to their higher molecular weight (five groups attached to the 

central atom), the pentacoordinate compounds have relatively low volatilities. 

e. Atmospheric Impact. The pentacoordinate phosphorus compounds, all of which contain halogen 

directly bonded to the phosphorus, are expected to have very short atmospheric lifetimes due to 

hydrolysis and rainout and, therefore, low or zero GWP and ODP values. 

f. Overall Assessment. The expected high toxicities, low stabilities, and poor materials compatibilities 

make these compounds unattractive for study.

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied 

Completely unstudied X 

Estimated

57 
VI. Metal-containing Compounds 

A. Alkali Metal Compounds

Alkali metal compounds containing Na, K or Rb bound to inorganic or organic ligands are almost always

ionic solids. Consequently, their use is limited to applications where powdered fire suppressants and 

solutions are effective. 

a. Fire-Suppression Effectiveness. The inhibition effectiveness of compounds containing alkali metals 

is high. The approximate relative effectiveness of the potassium compounds K2SO4 and KHCO3 relative 

to CF3Br is 14 to 17 based on flame measurements in a methane flame..116 The literature contains 

numerous data on suppression concentrations of these compounds. Unfortunately, there is considerable 

scatter in these data. The results appear to depend on the size of the particles and the delivery procedure. 

Reported values for the suppression volume fractions (cup burner, n-heptane) of NaHCO3 and KHCO3

were 1.06 % 117 and 0.78 %118, respectively. The relative order of suppression effectiveness of alkali 

metal compounds is Rb>K>Na.119,120

Fire suppression studies have been conducted on the following compounds: K3AlF6, KF@2H2O, KI, KCl, 

KBF4, KBr, KF, Na3AlF6, Na2SiF6, NaCl, NaBr, NaBr in CaCl2, NaF, NaI, K2CrO4, K2SO4, Na2SO3, 

Na2S2O2@5H2O, K lactate (water solution), K acetate (water solution), NaAcAc, Na2C4H4O6@2H2O, 

KHO3@urea, KHCO3, K, K2CrO4, K2CO3, K2CO2, K2C2O4, K4Fe(CN)6@3H2O, KOH, KNO3, Na2CrO4, 

NaHCO3, Na, NaNO3, NaOH, NaC2H3O2@3H2O, Na2CO3, Na2C2O4, Na2[Fe(CN)5NO]@2H2O, 

Na4Fe(CN)6@10H2O, Na2B4O7@10H2O, RbCl, RbBr, RbI. 

b. Toxicity. The toxicities of the alkali metal cations range from very low to moderate. Sodium and 

potassium cations are normal physiological constituents and should therefore have minimal toxicity. 

Lithium salts are administered to humans suffering from bipolar personality abnormalities and are known 

to have toxic effects at doses exceeding about 2 g.121

c. Materials Compatibility. Alkali metal compounds can be very corrosive. 

 

d. Colligative Properties of Some Compounds

Compound BP (°C) MP (°C) 

KHCO3 Decomposes

KI 1420 723

K2SO4 1072

Na2CO3 Decomposes 851

Na2B4O7.10H2O (borax) 1575 741 

NaI 1300 651

e. Environmental Impact. Since alkali metal compounds are generally water soluble, they will rain 

out readily and their atmospheric impact would be small. The impact of the alkali metal cations on 

ground systems is minimal. Any concerns would be due to the accompanying anionic components.114

 

f. Overall Assessment . The fire suppression effectiveness of these compounds has already been 

established. The only research issue is how to effectively deliver them to the fire, which is being 

addressed in other NGP projects. 

58 
No Further Study Further Study 

High Priority for 

Further Study 

Well studied X 

Lightly studied 

Completely unstudied 

Estimated

59 
B. Compounds of Alkaline Earths 

Inorganic compounds of alkaline earths containing Mg, Ca, or Ba, are almost exclusively solids. 

Consequently, their use is limited to applications where dry chemical fire suppressants and solutions are 

effective. 

a. Fire-Suppression Effectiveness. Calcium- and magnesium- containing compounds were found to

be ineffective fire suppressants additives (CaCO3, Ca(OH)2, Ca2F6, CaSO4@H2O, MgCO3, MgSO4@4H2O, 

MgCl2).122,116, 123,124 Fire suppression properties of barium compounds are questionable. BaSO4 was found

ineffective for suppression of a methane flame.122 Ewing et al.118

 found that the suppression volume

fraction of BaSO4 is 1.5 % for an n-heptane flame. Bulewicz and Padley125 [6] found significant radical 

recombination rates for BaCl2@2H2O, BaSO4, Ba(OH)2.8H2O, and Ba(NO3)2. 

b. Toxicity. Toxicities of compounds containing the alkaline earth cations (Mg, Ca) are generally low. 

Magnesium and calcium are both required for physiologic functioning and are believed to cause no 

systematic poisoning.121 However, some MG salts (e.g., MG3(AsO3)2, MgCrO4, Mg(CN)2) are known to

be toxic. The soluble barium salts are poisonous when taken orally. The usual result of exposure to 

barium sulfide, barium oxide, and barium carbonate is irritation of the eyes, nose, mouth, and skin. 

c. Materials Compatibility. These compounds should be compatible with most materials. 

d. Colligative Properties

Compound BP (°C) MP (°C) 

BaSO4 1600, decomposes

BaCl2.2H2O 113 (the apparent MP caused 

by loss of crystal water) 

CaCl2 1935 772

CaSO4@H2O 1450

CaCO3 825, decomposes

Ca(OH)2 580, decomposes

MgSO4 200, decomposes

MgCl2 1412 708

e. Environmental Impact. The environmental impact of alkaline earth compounds (Mg, Ca) is 

expected to be minimal.114 

f. Overall Assessment. There is no evidence that these compounds are effective suppressants. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X (Ca) 

Lightly studied X (Ba,Mg) 

Completely unstudied 

Estimated

60 
C. Boron and Aluminum Compounds (Group III Elements) 

Inorganic and organic compounds of boron and aluminum generally have very low vapor pressures and 

are, therefore, only suitable for applications where suppression by dry chemicals or solution is effective. 

a. Fire-Suppression Effectiveness. There is little evidence of fire suppression capabilities of B- and 

Al-containing compounds. They were found to be ineffective in suppression of hydrocarbon 

flames.

114,126,116,124,127 Inhibition effectiveness of some compounds is due to the presence of other effective 

elements in the molecule. The list of studied compounds includes: K3AlF6, Na3AlF6, Al2Cl6, Al2O3, 

Al2(SO4)2@12H2O, BCl3, BF3, B(OCH3)3, KBF4, BBr3, Na2B4O7@10H2O 

b. Toxicity. Although borates and boric acid are widely used, boron-containing compounds are 

moderately toxic. The fatal oral dose of boric acid for an adult is approximately 15 g to 20 g.

114 Some 

aluminum compounds are irritants or toxic owing to the presence of the other constituents. Normally, 

aluminum compounds are of low toxicity. 

c. Materials Compatibility. Aluminum bromide and aluminum chloride exhibit corroding effects. 

 

d. Colligative Properties 

Compound BP (°C) MP (°C) ∆Hv (kJ/mol at BP)

AlCl3 183 190 (253 kPa)

Al2(SO4)3 770, decomposes

AlCl3 183 (100 kPa) 190 (252 kPa) 

BF3 -99.9 -126.8

B(OCH3)3 68 -29 37

e. Environmental Impact. Boron and aluminum compounds do not exhibit environmental impact 

since they are a common component of many soils and minerals. 

f. Overall Assessment. There is no evidence that these compounds are effective suppressants. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

61 
D. Copper-containing Compounds 

This includes inorganic and organic compounds containing divalent or monovalent Cu. 

a. Fire-Suppression Effectiveness. The existing data on the fire suppression efficiency of these 

compounds is contradictory. CuO was found to be ineffective for suppression of a methane flame128 and 

was characterized as a thermal inhibitor.124

 Cuprous chloride (CuCl), however, was found to be an 

effective inhibitor in methane flames. The inhibition effectiveness of CuCl relative to CF3Br is 4 to 12 

based on flame speed measurements in methane/air flames.

116

 Dolan and Dempster128 found that copper 

acetate monohydrate, copper carbonate, Cu2O, CuO, CuCl, and CuCl2 were all ineffective at suppressing 

the ignition of methane/air flames. 

b. Toxicity. Copper is one of several metals that are essential to life. Copper metal is non-toxic. The 

inhalation of dusts, fumes, and mists of copper salts, however, can cause congestion of the nasal and 

mucous membranes, occasionally producing perforation of the nasal septum. Toxicity (oral) of Cu2O is 

high: the LD50(rat) is 470 mg/kg.129 The LD50(oral, human) for CuCl is 200 mg/kg. Copper chloride and 

sulfate have been reported as causing irritation of the skin. Cuprous oxide is irritant to the eyes and upper 

respiratory tract. 

c. Materials Compatibility. There are no known issues. 

d. Colligative Properties. The inorganic salts are all solids and would need to be used as a dispersed 

aerosol. As shown in the following table, the boiling points of the organometallic compounds could be 

considerably lower. Whether fluorination would bring any of them into a useful range for dispersion as a

neat fluid remains to be seen. 

Compound BP (°C) MP (°C) 

CuO 1026, decomposes

Cu2O 1800, decomposes 1235

Cu(C2H3O2)2@H2O 214 200

CuCl2 498

CuCl 1366 422

e. Environmental Impact. Copper is both an essential and potentially toxic element.121 There are 

health related effects associated with either too little or too much in the environment. There are concerns 

that copper plays a role in the catalytic formation of chlorinated dioxins during incineration. Agricultural 

soils with a limit of 2 kg to 3 kg Cu per year are considered acceptable. In Switzerland, the limit for 

drinking water is 1.5 mg/kg Cu. 

f. Overall Assessment. The fire suppression effectiveness of copper-containing compounds is still 

open to question. A short set of screening tests would indicate whether further examination is warranted. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X

Completely unstudied 

Estimated

62 
E. Titanium-containing Compounds

These include compounds containing tetravalent Ti bound to inorganic or organic ligands. The +1 and +3 

oxidation states exist, but have not been studied. 

a. Fire-Suppression Effectiveness. Only one titanium-containing compound (TiCl4) has been 

investigated, and its fire suppression efficiency is high. The coefficient of effectiveness of TiCl4 relative 

to CF3Br is 5.5 based on flame speed measurements in hydrogen/air and hexane/air flames.106,126 Data on 

suppression concentrations are absent. Other common titanium compounds are high-melting solids, 

which make them unsuitable for use as fire suppressants. 

b. Toxicity. Titanium metal is non-toxic. Thus, the harmful effects of some of these compounds derive 

from products of the anion (e.g., hydrochloric acid in the case of titanium tetrachloride). Titanium is not 

absorbed or accumulated in the human body. The toxicity of TiCl4 is high (inhalation): the LC50(mice) is 

10 mg/m3

 for 2 hrs. 

c. Materials Compatibility. TiCl4 is highly reactive and corrosive. It liberates HCl on contact with 

H2O. 

d. Colligative Properties

Compound BP (°C) MP (°C) ∆Hv (kJ/mol at BP)

TiCl4 136 -30 39

e. Environmental Impact. It was suggested that titanium should not be considered within the scope of 

human monitoring. Titanium dioxide is classified as a nuisance dust.121 Monitoring may be necessary in 

the case of other titanium compounds as organic titanium derivatives. 

f. Overall Assessment. While TiCl4 is an effective suppressant and does have some volatility, it is not 

suitable for routine use as an extinguishant because of its tendency to liberate HCl. Other common Ti 

compounds, such as TiO2, are solids and do not appear to have properties that would make them more 

attractive candidates than other metallic compounds recommended in this report. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

63 
F. Manganese-containing Compounds

These are compounds containing Mn bound to inorganic or organic ligands. Manganese occurs naturally

in ionic salts as Mn+2. Synthetic compounds, however, are known in nearly all valences between –3 and 

+7. 

a. Fire-Suppression Effectiveness. There are practically no data on fire suppression properties of 

manganese-containing compounds. Manganese acetylacetonate is a very effective inhibitor based on data 

obtained from an ethanol/air counterflow burner experiments. It was found to be more effective than iron

pentacarbonyl on a molar basis.119

 Methylcyclopentadienyl manganese tricarbonyl (MMT) is well known 

as an antiknock fuel additive. 

 

b. Toxicity. Although inorganic manganese compounds tend to be low in toxicity, the more volatile 

organometallics (those containing metal to carbon bonds) are likely to be more toxic. Fumes and dust of

manganese compounds can cause central nervous system and pulmonary system damage. Chronic 

poisoning is possible for exposures over several months. LC50 (rat, inhalation, 7 hr) for MMT is 76 mg/m3

and LD50 (rat, oral) is 50 mg/kg.129

 

c. Materials Compatibility. There are no known issues. 

 

d. Colligative Properties.

Compound BP (°C) MP (°C) 

MMT 106 (1.6 kPa) -0.75 

MrBr2 1027 698

MnI2 1017 613

e. Environmental Impact. Manganese compounds do not present any known environmental risks.121

There are some regulations on the maximum allowable levels. The maximum allowable concentration at 

workplaces for an 8 hour day is up to 5 mg/m3

 in the U.S.121

f. Overall Assessment. There is a paucity of data on the fire suppression properties of these 

compounds, but what little there is points to a high degree of effectiveness. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

64 
G. Antimony-containing Compounds

Antimony may exist in oxidation states –3, +3, +4 or +5. More than 3000 organic antimony compounds 

are known. 

a. Fire-Suppression Effectiveness. The fire suppression efficiencies of antimony containing 

compounds are high. The coefficient of effectiveness of SbCl3 relative to CF3Br is 4.6 based on flame 

speed measurements in hydrogen/air and hexane/air flames.130,126 Data on extinction concentrations of 

antimony compounds are absent. Fire suppression data are available for the following antimony

compounds: SbCl3, SbCl5, and SbBr3. The corresponding iodides (SbI3 and SbI5) are also stable, but have

not been tested for fire suppression effectiveness. 

b. Toxicity. Most antimony-containing compounds are highly toxic via oral, inhalation and 

intraperitoneal routes. Locally, these compounds are irritant to the skin and mucous membranes. Toxicity

(inhalation) of SbCl3 is very high; the TCLO(human) is 73 mg/kg.129

 

c. Materials Compatibility. Antimony trichloride is highly reactive and corrosive. It liberates HCl 

upon contact with H2O. 

 

d. Colligative Properties.

Compound BP (°C) MP (°C) 

SbCl3 283 73

SbCl5 3 79

SbBr3 280 96.6

e. Environmental Impact. Some antimony compounds (e.g., SB2O3) are known to be carcinogenic. 

There are industrial standards limiting worker exposure to particulates.121 Zoller131 cites evidence for the 

introduction of Sb into the environment through incineration and dumping. There are industrial standards 

for limiting workplace exposure to Sb particulates, which range from 0.2 mg/ m3

 to 2 mg/m3.

f. Overall Assessment. The potential as fire suppressants is offset by concerns about the high toxicity

and environmental impact of these compounds. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

65 
H. Germanium-containing Compounds

These are compounds containing divalent or tetravalent Ge bound to inorganic or organic ligands. 

a. Fire Suppression Effectiveness. Although data on the interaction of germanium-containing 

compounds with flames is limited, there is some indication that some of these compounds may posses a 

high degree of fire suppression efficiency. The coefficient of effectiveness of GeCl4 relative to CF3Br is 

2.2 based on flame speed measurements in hexane/air flames.

106

 It is not clear whether the observed 

inhibition is due to the Ge itself or the ability of the GeCl4 to deliver Cl atoms into the reaction zone of 

the flame. 

b. Toxicity. Germanium compounds are considered to be of low toxicity. Little is known about the 

toxicity of organic germanium compounds; they may resemble other organometallics in having higher 

toxicity than inorganic forms. The toxicity of GeCl4 is moderate (irritation to skin, eyes).129

 

c. Materials Compatibility. Liberates toxic fumes of chlorides when heated or upon reaction with 

H2O [2].

d. Colligative Properties.

Compound BP (°C) MP (°C) ∆Hv (kJ/mol at BP)

GeF2 130 110

GeF4 -36.5

GeCl4 83 -49.5 35

GeBr2 150 143

GeBr4 186 26

e. Environmental Impact. Unknown. There are no air or occupational standards for germanium,

except germanes in the USA. The ecotoxicity of these compounds is also considered to be low.121

f. Overall Assessment. Although there is evidence that indicates the germanium halides are effective 

suppressants, this potential is offset by cost and materials compatibility issues. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

66 
I. Silicon-containing Compounds

These compounds contain tetravalent Si bound to inorganic or organic ligands. 

a. Fire-Suppression Effectiveness. Data on flame suppression demonstrate ineffectiveness of silicon 

containing compounds.124,128 Burning velocity measurements of inhibited n-hexane flame (SiCl4, 

Si(CH3)4) indicate that silicon compounds may have some inhibition effectiveness at low concentration 

additions.106

 List of studied compounds: SiCl4, SiHCl3, SiF4, Na2SiF6, SiO2, Si(CH3)4 . 

b. Toxicity. Compounds containing silicon directly bonded to halogens are highly toxic owing to rapid 

hydrolysis of the silicon-halogen bond. Limited testing of industrial chemicals indicates that stable silane 

derivatives have a low toxicity.

129

 A number of siloxanes used industrially have a low toxicity. Toxicity

of SiCl4 is moderate via inhalation route.

129

c. Materials Compatibility. The silicon halides, including SiF4 and SiCl4, liberate acid gases (HF and 

HCl) upon reaction with H2O. 

d. Colligative Properties.

Compound BP (°C) MP (°C) ∆Hv (kJ/mol at BP)

SiF4 -77 22

SiCl4 58 -70 32

Si(CH3)4 27 27

-65

e. Environmental Impact. Silicon is a common element and significant terrestrial environmental 

impacts due only to silicon itself are unlikely. There are industrial standards limiting worker exposure to 

particulates. Estimations reported indicate that silicon compounds containing bromocarbon substituents 

should have atmospheric lifetimes on the order of days and ODP values less than 0.02.114

f. Overall Assessment. Compounds containing a silicon-halogen bond are unacceptable due to their 

tendency to liberate HCl (or other acid gases) upon reaction with H2O; organosilicon compounds, such as 

TMS, are flammable. There do not appear to be any other members of this family of compounds having 

properties that would make them superior candidates to the other compounds recommended in this report. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

67 
J. Iron-containing Compounds

These compounds contain Fe bound to inorganic or organic ligands. 

a. Fire Suppression Effectiveness. The fire suppression efficiency of iron-containing compounds is 

high. The coefficient of effectiveness of iron pentacarbonyl and ferrocene relative to CF3Br is 50-100 

based on flame speed measurements in methane/air and hexane/air flames.

106,132,133 Measured extinction 

concentrations for iron pentacarbonyl are 1.7 % (ethanol flame

134) and 0.23 % for methane flame 

(0.01atm).135 Ewing et al., found 0.08 % to 0.1 % for K4Fe(CN)6.3H2O in an n-heptane flame.118 The 

list of iron containing compounds for which flame suppression and/or extinction data exists include: iron 

pentcarbonyl, ferrocene, iron acetylacetonate, K4Fe(CN)6.3H2O, K4Fe(CN)6, Na2[Fe(CN)5NO].2H2O, 

Na4Fe(CN)6.10H2O, Fe(CF3-CO-CH=CO-CF3)3

b. Toxicity. A number of iron compounds have relatively low toxicity. Highly volatile iron 

compounds are more likely to be toxic. Iron pentacarbonyl is highly toxic, a lung irritant, and causes 

damage to kidneys and liver.114

 The toxicity of ferrocene, however, is considered to be moderate (oral): 

LD50(rat) =1350 mg/kg.129

 

c. Materials Compatibility. We are not aware of any properties of these compounds that make them

incompatible with materials used in the construction of the weapons platform or storage/dispersion 

device. 

d. Colligative Properties.

Compound BP (°C) MP (°C) ∆Hv (kJ/mol at BP)

Ferrocene 174 (sublimes)

Fe(CO)5 103 -25 38

Iron acetylacetonate 69 (sublimes)

e. Environmental Impact. Not regulated. None of the transition metal compounds are expected to 

show global environmental impact due to the metal itself. 

f. Overall Assessment. The high flame inhibition effectiveness of these compounds has already been 

established, but no flames or fires have been suppressed by an iron-containing compound. There is also 

the issue of their effective delivery to the fire, which is being addressed in other NGP projects. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied X

Lightly studied 

Completely unstudied 

Estimated

68 
K. Tin Compounds

These compounds contain either divalent or tetravalent Sn bound to inorganic or organic ligands. 

a. Fire Suppression Effectiveness. The fire suppression efficiency of tin-containing compounds is 

expected to be high. The coefficient of effectiveness of SnCl4 relative to CF3Br is 5.7 based on flame 

speed measurements in hydrogen/air and hexane/air flames.106,126

 The fire suppression efficiencies of the 

following tin containing compounds have been investigated: SnCl2, SnCl4, Sn(CH3)4

b. Toxicity. The biological effects of tin compounds are almost exclusively determined by the nature 

and the number of groups bound to the tin atom.

121 Inorganic tin salts are of low order of toxicity. Tin 

halides, including SnCl2 and SnCl4, are known to undergo rapid hydrolysis forming acid halides, which 

are toxic by inhalation.129 Some organotin compounds exhibit acute toxicity that generally decreases in 

the order R3SnX > R2SnX2 > RSnX3, where R is a covalently bound organic ligand and X represents an 

anionic group attached to the tin via an electronegative atom such as a halogen or oxygen.121

c. Materials Compatibility. The tin halides are highly reactive and corrosive due to the formation of 

HCl and/or other acids upon contact with H2O.129

d. Colligative Properties.

Compound BP (°C) MP (°C) ∆Hv (kJ/mol at BP)

SnCl2 37

SnCl4 114 -33 37

Sn(CH3)4 78 -35

Sn(CH3CH2)4 -131

e. Environmental Impact. The environmental impact of water soluble, inorganic tin compounds is 

minimal. However, the aquatic toxicity of certain trialkyl and triaryl tin compounds is a concern. 

Tributyltin and triphenyltin, which are the active ingredients in antifouling paints for ships, appear to be 

highly toxic towards aquatic life.121

f. Overall Assessment. The existing data suggests a degree of high fire suppression efficiency and low 

environmental impact for these compounds. 

No Further Study Further Study 

High Priority for 

Further Study 

Well studied 

Lightly studied X 

Completely unstudied 

Estimated

69 
VII. CONCLUSION

As par of the search for fire fighting technologies alternative to halon 1301, the authors have reviewed the 

available data on the universe of chemical families. The search focused on fire-suppression effectiveness, 

toxicity, materials compatibility, colligative properties, and environmental impact. For each family, there 

is an evaluation of worthiness of further examination. The following table summarizes those families for 

which future examination was deemed valuable. 

Recommendation 

Chemical Family High Priority Further Study Quick Look 

Iodine-containing alkanes X

Iodine-containing alkenes X

Bromine-containing alkenes X 

Iodine-containing ethers X 

Bromine-containing ethers X

Bromine-containing alcohols X 

Fluorine-containing aldehydes and ketones X 

Nitriles X

Fluoro- and bromofluoroamines X 

Bromofluorosulfides

Sulfoxides X

Phosphorus-containing Acids and Esters X X 

Phosphonitriles X

Phosphorus halides X

Copper-containing Compounds X 

Manganese-containing Compounds X 

Iron-containing compounds X

Tin-containing compounds X 

VIII. ACKNOWLEDGMENTS 

This research is part of the Department of Defense's Next Generation Fire Suppression 

Technology Program, funded by the DoD Strategic Environmental Research and Development 

Program. The authors appreciate the contributions of Dr. Bradley Williams of the Naval Research 

Laboratory and Drs. Gregory Linteris, Robert Huie, and Wing Tsang of the National Institute of 

Standards and Technology. 

70 
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Highlights,” NISTIR 6366, National Institute of Standards and Technology, Gaithersburg, 11 p. 

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2. Gann, R.G., “Next Generation Fire Suppression Technology Program FY1999 Annual Report,” 

NISTIR 6479, 27 pages (2000). 

3. Gann, R.G., “FY2000 Annual Report: Next Generation Fire Suppression Technology Program

(NGP), NIST Technical Note 1436, National Institute of Standards and Technology, 48 pages 

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4. Moore, T. A., Weitz, C. A., and Tapscott, R. E., “An Update on NMERI Cup-Burner Test Results,” 

Proceedings, Halon Options Technical Working Conference, Albuquerque, New Mexico, 7-9 May 

1996, pp. 551-567. 

5. NFPA 2001 Standard on Clean Agent Fire Extinguishing Systems, 2000 Edition, National Fire 

Protection Association, Quincy, Massachusetts, 2000. 

6. Tapscott, R.E., “’Best Values’ of Cup Burner Extinguishing Concentrations,” Proceedings, 1999 

Halon Options Technical Working Conference, Albuquerque, NM, pp. 265-274, 1999. 

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9. Ledbetter, A., Acute Inhalation Toxicity Study of Iodotrifluoromethane in Rats, Final Report Project 

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New Mexico, May 1994. 

10. Tapscott, R. E., Skaggs, S. R., and Dierdorf, D. S., “Perfluoroalkyl Iodides and Other New 

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and W. Tsang, editors, American Chemical Society, Washington, DC, pp. 151-160, 1995. 

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12. Robbins, B. H., “Preliminary Studies of the Anesthetic Activity of Fluorinated Hydrocarbons,”

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13. Stoudt, M.R., Fink, J.L., Dante, J.F., and Ricker, R.E., “Compatibility with Metals,” in Gann, R.G., 

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14. McKenna, G.B., Horkay, F., Verdier, P.H., and Waldron, Jr., W.K., “Interactions of Agents with

Elastomers and Lubricants,” in Gann, R.G., ed., Fire Suppression System Performance of

Alternative Agents in Aircraft Engine and Dry Bay Laboratory Simulations, NIST Special

Publication SP 890, Volume 1, pp. 201-247, 1995. 

15. CRC Handbook of Chemistry and Physics, 78th Edition, Lide, D. R., and Frederikse, H. P. R., 

editors, CRC Press, Inc., Boca Raton, Florida, USA, 1997. 

71 
16. Nimitz, J. S., and Lankford, L., “Fluoroiodocarbons as Halon Replacements,” Proceedings, 

International CFC and Halon Alternatives Conference, Washington, D.C., 20-22 October 1993, pp. 

810-819. 

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