ENVIRONMENTALLY ACCEPTABLE FLAME EXTINGUISHANTS 

J. Douglas Mather, Ph. D. 

Chemical Development Studies, Inc. 

7636 William Moyers Ave. NE 

Albuquerque, NM 87122 

505-797-9706 

DougMather@speakeasy.net 

Robert E. Tapscott, Ph.D., 

GlobeTech, Inc. 

8200 Montgomery Blvd. NE, #218 

Albuquerque, NM 87109 

505-883-9399 

GlobeTech@speakeasy.net

INTRODUCTION 

Research geared to the identification and testing of environmentally friendly 

extinguishants – specifically compounds with low boiling points suitable for use in cold 

environments - is sponsored by the National Institute of Standards and Technology and 

the Next Generation Fire Suppression Technology Program. 

Low temperature conditions are a characteristic of aircraft in-flight at higher altitudes. 

Fire suppression agents with lower boiling points are expected to disperse more rapidly 

and uniformly than higher boiling agents. 

A broad review of chemical families identified many with potential to meet the restrictive 

list of requirements for a suitable halon replacement. This subsequent chemical selection 

effort builds on several prior projects and guidance from in depth assessment of a wide 

range of chemical families [1, 2., 3, 4, 5, 6] 

Chemical families examined as potential sources of halon 1301 alternatives covered a 

broad range of elements, chemical functionalities. Information relating to environmental 

persistence, toxicity, flame suppression, reactivity and a number of other factors were 

considered. The resulting list of chemical families presented as being worthy of 

continued or initial consideration ranged from brominated carbon based compounds to 

metal containing compounds. 

The current focus on low boiling compounds eliminated many of theses down-selected 

chemical families. The remaining chemical families were reexamined and the higher 

boiling members eliminated from further consideration. Additional chemical families 

with structural properties indicating shorter atmospheric lifetime were identified and 

subsequently added to the list of potential low boiling chemical families to be considered, 

Table 1. 

Table 1. Current Down Select of Chemical Families 

Bromofluoro alkenes 

Bromofluoroethers 

Bromofluoroalkylamines 

Fluoroalkylamines 

Bromofluoro Oxiranes 

Bromofluoro & Fluoro Nitriles 

Bromofluoro vinylethers 
BRIEF OVERVIEW OF THE CHEMICAL FAMILIES UNDER 

CONSIDERATION 

The bromofluoroalkenes continue to receive considerable attention. The amount of 

toxicity, atmospheric lifetime, and flame extinguishment data for members of this family 

dwarfs that accumulated for the remaining families. The relatively higher availability of 

the alkenes offers continued hope that optimal low toxicity compounds may eventually be 

identified once a concerted toxicity testing program is initiated. The chemical acquisition 

focus is on the tetrafluorinated bromopropenes and on one difluorinated bromoethylene. 

Bromofluoroethers are more challenging synthetically than the aforementioned alkenes. 

The favorable toxicities of some brominated fluoro ethers (i.e., roflurane) suggest that the 

overall family might well yield some of the lowest toxicity halon replacement candidates. 

With the emphasis on low boiling points only the simplest two and three carbon ethers 

are under consideration. Efforts to develop synthetic approaches to the 2 carbon ethers 

are still being pursued. 

Bromofluoropropene oxides represent a new addition to the chemical families to be 

considered. The low boiling point of the parent propene oxide and potential for reactivity 

with OH radical and therefore possible shorter atmospheric lifetime warranted a closer 

look at this family to obtain baseline data on flame suppression and boiling points. 

Bromofluoronitriles and fluoronitriles also represent new chemical families for 

consideration. Representative compounds for both of these families are relatively easily 

to acquire and test. The low boiling point of the bromofluoronitrile CF2BrCN and the 

extremely low boiling point of the fluoronitile analogue CF3CN offered hope of 

identifying compounds with the potential to address the needs of low temperature 

extinguishment applications such as those encountered in aircraft. 

Bromofluorovinyl ethers are a family of compounds whose potential as flame 

suppressants was untested. The presence of an ether linkage and a site of unsaturation 

had suggested possibly poor flame extinguishment performance. 

Brominated fluoroamines have long been sought for testing. The expected low toxicity 

of the fluoroalkyl amines makes the brominated analogue to this family of great interest. 

Past work has only resulted in the testing of three compounds from this family. Recently 

a possible source for additional compounds and critical intermediates with the potential to 

lead to a wide number of low molecular weight and possibly low boiling point 

bromofluoroamines has been identified. This has led to renewed efforts in this area of 

chemical acquisition and testing. 

N-Brominated fluoroalkyl amines and imines are of interest as well. These compounds 

may well exhibit short atmospheric lifetimes through hydrolysis of the Br-N and imine 

bonds. Boiling point information suggests the likelihood of several of these compounds 

boiling in the range of 10 to 25 °C. 

COMPOUND SELECTION, ACQUISITION AND TESTING 

Bromofluoroalkenes: The emphasis in compound selection is on low boiling points and 

short atmospheric lifetime. Unfortunately, the uncertainty in atmospheric lifetime and 

boiling point estimates for unknown compounds is large however and practical 

limitations of compound availability from contract synthesis sources often leave few real 
choices. The choices made though do help to establish boiling point and structure 

information and confirm or not the acceptability of flame extinguishment performance. 

As unacceptably high extinguishment values are disqualifying the information gathered is 

of immediate use in the further selection of compounds within that family. 

Past acquisition and testing of alkenes took a broad look at a range of compounds 

including propenes, butanes, pentenes and branched compounds. Toxicity testing of 

several initially available compounds indicated considerable promise, Tables 2 – 5 Of 

the alkenes studied the boiling points of the propenes were the only ones low enough to 

justify continued consideration. The present focused acquisition efforts are primarily of 

tetrafluorinated and remaining pentafluorinated bromopropenes. 

The atmospheric lifetime evaluations of alkenes confirm short lifetimes. Calculated Log 

KOW values for the 35 possible penta-, tetra- and trifluorinated bromofluoropropenes 

ranged from 1.4 to 2.5. Using experimental KOW values of 1.84 for Halon 1301 and 2.3 

for Halothane (CF3CHBrCl) as guides, a list of compounds whose low calculated values 

predicted a possibly equivalent or higher LOAEL was prepared and promising 

compounds selected for acquisition. Of particular interest are the 

bromotetrafluoropropenes listed as these compounds are generally of lower boiling point 

and may well have higher LOAEL values. 

A sample of CHF2CBr=CF2 was acquired. Tb was estimated to be about 30 °C. The cup 

burner extinguishment value was 3.3 vol. %, as expected for a bromine-containing 

compound with only one hydrogen atom. 

Table 2. Acute inhalation toxicity tropodegradable bromofluoroalkenes 

Compound Formula Deaths* 

1-Bromo-3,3,3-trifluoropropene CF3CH=CHBr 0 

2-Bromo-3,3,3-trifluoropropene CF3CBr=CH2 0 

4-Bromo-3,3,4,4-tetrafluorobutene CF2BrCF2CH=CH2 0 

2-Bromo-3,3,4,4,4-pentafluorobutene CF3CF2CBr=CH2 0 

2-Bromo-3,3,4,4,5,5,5-heptafluoropentene CF3CF2CF2CBr=CH2 0 

*30-minute exposure at 5% v/v air concentration 

Table 3. Ames mutagenicity test results 

Compound Formula Ames Test 

Result 

2-Bromo-3,3,3-trifluoropropene CF3CBr=CH2 Negative 

4-Bromo-3,3,4,4-tetrafluorobutene CF2BrCF2CH=CH2 Negative 

2-Bromo-3,3,4,4,4-

pentafluorobutene 

CF3CF2CBr=CH2 Negative 
Table 4. Chromosomal aberration test results 

Compound Formula Test 

Result 

2-Bromo-3,3,3-trifluoropropene CF3CBr=CH2 Negative 

4-Bromo-3,3,4,4-tetrafluorobutene CF2BrCF2CH=CH2 Negative 

Table 5. Cardiac sensitization data for bromofluoropropenes 

Compound Name Formula NOAEL LOAEL 

2-Bromo-3,3,3-trifluoropropene CH2=CBrCF3 0.5 vol. % 1.0 vol.% 

A very large number of potential penta tetra and tri fluorinated propene candidates exist. 

Compound acquisition and testing efforts have provided data for only a fraction of these, 

Table 6. 

Table 6. Penta, tetra and tri fluorinated propenes 

Formula Chemical Name 

CF2=CBrCF3 2-bromo-1,1,3,3,3-pentafluropopene 

CFBr=CFCF3 1-bromo-1,2,3,3,3-pentafluropopene, (E) (Z) 

CF2=CHCF2Br 3-bromo-1,1,3,3-tetrafluropopene 

CFH=CBrCF3 2-bromo-1,3,3,3-tetrafluropopene, (E) (Z) 

CHBr=CFCF3 1-bromo-2,3,3,3-tetrafluropopene, (E) (Z) 

CH2=CBrCF3 2-bromo-3,3,3-trifluropopene 

CFH=CHCBrF2 3-bromo-1,3,3-trifluropopene, (E) (Z) 

CHBr=CHCF3 2-bromo-3,3,3-trifluropopene, (E) (Z) 

CFBr=CFCF2H 1-bromo-1,2,3,3-tetrafluropopene, (E) (Z) 

CFBr=CHCF3 1-bromo-1,3,3,3-tetrafluropopene, (E) (Z) 

CHF=CFCF2Br 3-bromo-1,2,3,3-tetrafluropopene, (E) (Z) 

CF2=CFCFHBr 3-bromo-1,1,2,3-tetrafluropopene 

CF2=CBrCF2H 2-bromo-1,1,3,3-tetrafluropopene 

CF2=CBrCFH2 2-bromo-1,1,3-trifluropopene 

CFH=CBrCF2H 2-bromo-1,3,3-trifluropopene, (E) (Z) 

CF2=CFCBrH2 3-bromo-1,1,2-trifluropopene 

CFH=CFCFBrH 3-bromo-1,2,3-trifluropopene, (E) (Z) 

CF2=CHCFBrH 3-bromo-1,1,3-trifluropopene 

CH2=CFCF2Br 3-bromo-2,3,3-trifluropopene 

CF2=CFCF2Br 3-bromo-1,1,2,3,3-pentafluropopene 

CHBr=CFCHF2 1-bromo-2,3,3-trifluropopene, (E) (Z) 

CFBr=CFCFH2 1-bromo-1,2,3-trifluropopene, (E) (Z) 

CBrF=CHCHF2 1-bromo-1,3,3-trifluropopene, (E) (Z) 

Many of these higher boiling compounds might still be useable as extinguishants, Table 

7, in the more intermediate temperature ranges of interest. 
Table 7. Maximum Boiling Point and Ambient Temperature Relationship 

Conc. Ambient Temperature, °C

% -60 -50 -40 -30 -20 -10 

0 10 20 30 

1 33 47 61 76 90 105 119 133 148 162 2 19 33 46 60 74 87 101 115 128 142 3 11 24 37 51 64 77 91 104 117 130 4

5 18 31 44 57 70 83 96 109 122 

5 

0 13 26 39 52 65 77 90 103 116 

10 -14 -1 11 23 35 47 59 72 84 96 15 -22 -10

2 14 25 37 49 61 73 84 

20 -28 -16 -5

7 19 30 42 53 65 76 

Example: To achieve a 5 vol. % concentration at -20 °C, the calculated maximum boiling point is 52 °C. 
Finally, the intriguing observation that 1-chloro-1,2-difluoroethylene, bp -5 °C, has no 

flash point and that its structural isomer 1-chloro-2,2-difluoroethylene, bp -18 °C, is 

flammable has led to interest in the acquisition and testing of the brominated analogue of 

1-chloro-1,2-difluoroethylene. Initial literature searches for 1-bromo-1,2-

difluoroethylene yielded no information and no indication that it had ever been prepared. 

Subsequently, efforts to develop a synthesis have been successful and the compound is 

now on order. 

Bromofluoroalkylethers: These compounds are expected to have relatively low toxicity 

and good flame extinguishment properties but unless they prove sufficiently polar they 

will require some degree of hydrogenation to achieve a short atmospheric lifetime and 

minimize ODP impact. Two of the simplest brominated ethers are CBrH2-O-CF3 (39 oC) 

and CBrF2-O-CF3, (boiling point estimated between -30 °C and -8 °C). The 

tetrafluorinated C2 bromoethers CBrHF-O-CF3 (bromofluoromethyl trifluoromethyl 

ether) and CBrF2-O-CHF2 (bromodifluoromethyl difluoromethyl ether) are predicted to 

boil in the range 5 °C to 15 oC and are still being sought for testing. 

The bromofluoro ethers CF2HCFBrOCF3 and CFBrHCFHOCF3 were successfully 

sourced and acquired. Boiling point values are estimated as 42 °C and 37 °C, 

respectively. Cup-burner values are below 4.5 volume % for both compounds.

Bromofluorovinyl ethers: A sample of the bromofluorovinyl ether CF2BrCF2OCF=CF2

(boiling point aprox 55 °C) was acquired and a cup-burner value 4.5 vol. % determined. 

Other compounds will be acquired only if they have lower boiling points. Changes in the 

bromination site might help.

Bromofluoropropene oxides: A sample of this compound was acquired, with boiling 

point estimated to be 20 °C. The measured cup burner value was a marginal 4.9 vol. %. 

A low atmospheric lifetime was expected. 

Fluoro nitriles: The commercially available compound CF3CN, was of great interest 

due to its boiling point -64 °C. As no data on the effects of a CN group on cupburner 

flame extinguishment existed a sample was obtained and the cup burner value determined 

to be 9.0 vol. %. Thus, there is no chemical activity from the CN group. The compound 

is no better than HFC-125. 

Bromofluoro nitriles: The commercially available compound CBrF2CN, was of great 

interest due in part to its low boiling point of 3 °C and the presence of bromine in the 

structure. Cup-burner extinguishment testing indicates a value less than 4.0 vol. %. This 

compound should have a short atmospheric lifetime due to OH reactivity. The rumored 

existence of unpublished toxicity test data indicating CF2BrCN was highly toxic has 

currently halted further consideration of this compound. Attempts to identify the source 

of this toxicity data and verify the findings have so far been unsuccessful.

Bromofluoroalkyl amines, n-bromo-fluoroalkyl amines and imines: Discussion of 

these chemical families has been combined for the purpose of achieving a more efficient 

presentation of the efforts to identify synthetic approaches, identify sources and 

ultimately obtain and test representative chemicals. To aid in following this discussion a 

table follows which lists these families and provides an typical or generic example of 

each. 
Table 7. Bromofluoro amines and imines 

Chemical familiy Example(s) 

Bromofluoroalkyl amines (CF3)(CF2Br)NH, (CF2Br)NH2, 

n-bromo-fluoroalkyl amines (CF3)2NBr 

n-bromo-fluoroalkyl imines CF2=NBr 

Attempts to source two compounds that due to their low boiling points are of particular 

interest have made significant progress. Published syntheses for (CF3)2NBr, boiling 

point 22 C, and CF2=NBr, boiling point 14.7 C indicated that preparation of these 

compounds is feasible in relatively high yield [7, 8, 9] . The synthesis of both 

compounds is underway. Should this effort be successful the availability of the useful 

intermediate, perfluoro-2-azapropene, could provide access to a variety of possibly low 

boiling n-bromofluoroalkylamines and bromofluoroalkyl amines such as those listed in 

Table 7. 

The Preparation of N-Bromo bis(trifluoromethyl) amine, (CF3)2NBr, (Eq. 1 – 3) 

CF3NO + CF2=CF2 Æ CF3-N=CF2 Eq. 1 

CF3-N=CF2 + HgF2 Æ (CF3)2N-Hg-N(CF3)2 Eq. 2 

(CF3)2N-Hg-N(CF3)2 + Br2 Æ (CF3)2NBr Eq. 3 

and preparation of N-Bromodifluoromethanimine, CF2=NBr, are both describe as being 

fairly straight forward, (Eq. 4,5). 

FCN + KF + CsF Æ CF2=N- K+ Eq. 4 

CF2=N- K+ + Br2 Æ CF2=NBr Eq. 5 

FUTURE CARDIAC SENSITIZATION SCREENING OPTIONS 

There are simply no current options for screening compounds for the purpose of 

identifying the most promising or least cardiac sensitizing compounds for continued 

testing. The only choice for developers of halogenated and or fluorinated fire 

extinguishants has been to perform the tremendously expensive formal dog exposure 

testing. This approach has exhausted available funds (and interest) rapidly. 

Only limited research targeting the development of cardiac sensitization screening 

methods for compounds is in progress. It seems these efforts are still only in their 

infancy. Methods based on in-vitro cell cultures do offer hope of an eventual solution to 

the screening problem as well as some hope of valuable insight into the cellular and 

biochemical mechanism(s) involved in the cardiac arrhythmia observed. 

As described earlier an alternative method with the potential for more immediate use in 

compound selection and testing is the use of hydrophobic hydrophilic partition 

coefficients. In particular Reverse Phase High Pressure Liquid Chromatography (RPHPLC) based determination appears to have potential to serve as a means of evaluating 

the relative tendencies of a series of compounds to induce arrhythmia. Correctly ordering 

compounds would be in itself a tremendous boost to the selection process. Relationships 

between partition coefficients and cardiac events and arrhythmia has received some 
attention in the past though experimental data is limited. Anesthesia agent and 

chlorofluorocarbon effects on cardiac muscle studies in some cases provide some reason 

to consider a physiochemical mechanism [10, 11, 12, 13, 14., 15] 

Partition coefficients are a measurement of lipophilicity and substances having high 

negative partition coefficient values dissolve better in fats and oils than in water. This 

enhances their ability to enter lipid membranes in the body and enhances their potential 

for interaction with ion channel performance and cell membrane processes of absorption. 

Cardiac arrhythmia induced by clinical anesthetics, Table 9 appear to follow a trend . 

More precise Log(KOW) experimental method applied to evaluating the link between 

compounds with known LOAEL values and their experimental Log(KOW) values is 

desirable. 

Table 9. Anesthesia Compounds – Partitioning and Arrhythmia Properties 

Property Halothane Enflurane Isoflurane Desflurane Sevoflurane 

Formula CF3CHBrCl CF3-OCF2CHFCl 

CF3-OCHCl-CF3CHF2-OCHF-CF3CH2F-OCH(CF3)2

Blood-gas 

Ratio a 2.5 1.9 1.4 0.42 0.6 

Oil-water 

Ratio b 220 120 170 19 55 

Arrhythmia c +++ + + ~ ~ 

MAC d 0.74 % 1.68 % 1.15 % 6.3 % 2.0 % a

 Ratio - (blood anesthesia agent concentration)/(air concentration). 

b

 The "oil" phase is commonly, but not exclusively, octanol. c

 The symbols "+++," "+," and "~" reflect, in order, a decreasing tendency of the 

anesthetic to induce PVC’s in human patients during anesthesia. “~” indicates only 

a slight tendency. 

d

 Minimum Alveolar (air) Concentration (MAC) is a measure of the anesthetic 

potency of the compound, i.e., the air concentration where 50 % of patients don't 

have a motor response to a pain stimulus. 

Reverse Phase High Pressure Liquid Chromatography (RP-HPLC) based determination 

appears to have potential to serve as a means of evaluating the relative tendencies of a 

series of compounds to induce arrhythmia. The chromatographic method yield high 

precision data for retention time – data that is reproducible within 0.1 second on a 

consistent basis. 

The great chemical separation power of the capillary gas chromatography method is 

illustrated in Figure 1. A single RP-HPLC analysis of a broad series of compounds is 

expected to cost between $5,000 and $10,000 to set up and execute. The results could 

well point reliably to compounds with the lower tendencies to induce cardiac arrhythmia. 

Formal dog exposure cardiac testing would still be a necessity but the need to test many 

compounds could well be greatly reduced. 
Figure 1. Illustration of RP-HPLC characterization of chromatographic retention 

times for use in estimating Log(KOW) values (x-axis is time).[16] 

SUMMARY 

With efforts concentrated on identifying and obtaining the lowest boiling tropodegradable 

bromocarbons for application to aircraft fire suppression work to further develop the 

higher boiling compound applications has diminished. Of the many compounds 

identified it will require toxicity testing to identify those with potential for use in 

occupied areas. Cardiac sensitization screening and testing remains the greatest hurdle to 

progress. 

ACKNOWLEDGEMENTS 

This research is sponsored by the US Department of Defense’s Next Generation Fire 

Suppression Technology Program and funded by the DoD Strategic Environmental 

Research and Development Program. The Project Leader is Richard G. Gann, Ph.D., 

Senior Research Scientist - Building and Fire Research Laboratory, National Institute of 

Standards and Technology, Gaithersburg, MD. 

REFERENCES 

 

1 Mather, J.D., and Tapscott, R.E., "Tropodegradable Bromocarbon Extinguishants 

II," Final Report to SERDP, 2004. 

2 Tapscott, R.E., Sheinson, R.S., Babushok, V., Nyden, M.R., Gann, R.G., 

"Alternative Fire Suppressant Chemicals: A Research Review with Recommendations," 

NIST Technical Note 1443, National Institute of Standards and Technology, 

Gaithersburg MD, December 2001. 
 

3 Brabson, G.D., Garcia, M.M., Heinonen, E.W., Juarez, G., “Main Group 

Compounds as Extinguishants”, Final Report May 2001, NMERI 98/8/33380. 

4 Shreeve, J.M., Singh, R.P., Tapscott, R.E., and Mather, J.D., Fluoroalkyl 

Phosphorus Compounds, Final Report to SERDP, Report 2003/1/34501, New Mexico 

Engineering Research Institute, Albuquerque, NM, 2003. 

5 Riches, J., Grant K., and Knutsen L., “Laboratory Testing of Some PhosphorusContaining Compounds as Flame Suppressants,” Proceeding’s, Halon Options Technical 

Working Conference, Albuquerque, NM. pp. 444-452, 1999. 

6 Takahashi, K., Inomata, T., Fukaya, H., and Abe, T., “New Halon Replacements 

Based on Perfluoroalkylamines. An Approach from the Other Side of Fluorine 

Chemistry,” in Halon Replacements Technology and Science, ACS Symposium Series 

611, Miziolek, A. W., and Tsang, W., editors, American Chemical Society, Washington, 

DC, Chapter 13, pp. 139-150, 1995. 

7 DesMarteu, D., O’Brien, An Efficient Synthesis of N-Bromo perhalo-1-

alkanimines, J, Org. Chem., 49, 1467-1469, (1984). 

8 Bauknight, C. W., DesMarteau, D., Reactions of N-Bromodifluoromethanimine, 

J. Org. Chem., 53, 4443-4447, (1988). 

9 O’Brien, B., Thrasher, J., Bauknight, C., Robin, M., DesMarteau, D., NBromodifluoromethanimine, J. Am. Chem. Soc., 105, 4266-4267, (1984). 

10 Clark, D.G., Tinston, D.J.,“Correlation of the Cardiac Sensitizing Potential of 

Halogenated Hydrocarbons With Their Physicochemical Properties”, British Journal of 

Pharmacology, Vol.49, 355-357, 1973. 

11 Hemmings, H. Jr., and Hopkins, P., Foundations of Anesthesia - Basic and 

Clinical Sciences, Chapters 20, 22, 24 and 41, Harcourt Publishers Ltd., 2000. 

12 An excellent tutorial website (virtual-anaesthesia-textbook.com/vat/volatile.htm) 

provides detailed discussions of a wide variety of anesthesia agents including clinical 

human exposure and cardiac effects information as well as further reference citations. 

13 Larsen, E. R., “Fluorine Compounds in Anesthesiology,” in Fluorine Chemistry 

Reviews, P. Tarrant, editor, Marcel Dekker, New York, pp. 1-44, 1969. 

14 www.virtual-anaesthesia-textbook.com/vat/volatile.htm . A tutorial website with a 

wide variety of anesthesia agents clinical human exposure and cardiac effects information 

as well as further reference citations. 
 

15 Eger EI; Ionescu P; Laster MJ; Gong D; Hudlicky T; Kendig JJ; Harris RA; 

Trudell JR; Pohorille A., “Minimum alveolar anesthetic concentration of fluorinated 

alkanols in rats: relevance to theories of narcosis,”Anesthesia and Analgesia, 1999 Apr, 

88(4):867-76. 

16 The reader is directed to the following internet site for additional examples and 

discussion of the application of RP-HPLC to comparison of compound retention times 

www.limathon.com/