TROPODEGRADABLE AND OTHER ENVIRONMENTALLY 

ACCEPTABLE FLAME EXTINGUISHANTS 

NGP ELEMENTS: 4D/14/1 AND 4B/6/23 

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

ABSTRACT 

In work sponsored by the National Institute of Standards and Technology and the NextGeneration Fire Suppression Technology Program, our current research effort is directed toward 

the continued study of known promising as well as several new chemical families with potential 

as sources of Halon 1301 replacement compounds for aircraft applications. This effort continues 

the study of tropodegradable alkenes and ethers as well as efforts to identify screening methods 

for cardiac sensitization. 

NIST Technical Note 1443, "Alternative Fire Suppressant Chemicals: A Research Review with 

Recommendations", provided the basis for this project through a systematic evaluation and 

prioritization of a broad range of chemical families for further study [1]. This survey resulted in 

several chemical families being classified as “High Priority” for future research efforts. 

Additional chemical families were identified as worthy of “Further Study” or “Quick Look” 

investigation. 

Identifying a compound whose cardiac sensitization properties approximate the LOAEL and 

NOAEL values of Halon 1301 is a fundamental progammatic goal; therefore, refinement in the 

methods employed in the estimation and ranking of a compound's cardiac sensitization properties 

continue to be of great interest. As preliminary screening methods, water-octanol partition 

coefficients and in vitro tissue methods offer hope of meeting near-term needs for screening 

compounds. These methods would not, however, be expected to supplant the formal dog 

exposure-based cardiac sensitization test; instead, these methods could be an aid in the 

preselection of compounds; serving to highlight and advance very promising candidates to 

consideration for the formal cardiac sensitization test. 

This NIST-funded project continues the study of tropodegradable candidates and also expands 

the search to the study of the promising chemical families identified in NIST Technical Note 

1443. The project is in the initial phase of work to select, acquire, and test promising candidates 

from a wide variety of chemical families. 

INTRODUCTION 

The research review conducted [1] covered five major chemical family types and individually 

evaluated fifty subgroups of compounds. While many of the chemical family subgroups were 

culled from further consideration, several were identified for continued research. The chemical 

families prioritized into “High Priority”, “Further Study”, and “Quick Look” categories are listed 
in Table 1. Compounds in the “Quick Look” category represent those that have not as yet been 

studied but appear to be promising based on chemical, toxicological, and physical data. 

Table 1. Summary of NGP Analysis of Chemical Families. 

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 

The research plan is initially focused on the compound families identified as "High Priority". 

Some candidate compounds from the “Further Study” chemical families will also be acquired 

during this period should resources permit. The primary families targeted for acquisition during 

this project’s initial year are the bromofluoro-alkenes, bromofluoro-ethers, bromofluoro-amines, 

hydrofluoroalkyl-amines, phosphorus acids and esters, and manganese compounds. 

SELECTION OF COMPOUNDS 

Compounds from the following chemical families are being sought. The actual numbers of 

compounds finally acquired will be a direct function of cost and availability. The potential 

sources for acquisition of these compounds include universities and institutes in the US, Japan, 

and FSU as well as commercial sources. 

• Bromofluoroalkenes - Prior research has demonstrated that members of this family of 

compounds are environmentally acceptable and toxicological testing thus far has been 

2
generally favorable. Compounds tested approach Halon 1301 in extinguishment 

performance but are considerably higher in boiling point. The primary challenge for 

future work in this chemical family is the identification of candidate compounds with 

cardiac sensitization LOAEL values approximating those of Halon 1301. To date 

selection of compounds for additional acquisition and testing has been hampered by a 

lack of a cardiac sensitization screening tool. Candidate methods being considered for 

use in future compound selection and cardiac sensitization screening will be described 

more fully later in this paper. 

• Bromofluoro-ethers: While limited cup-burner studies have demonstrated effective fire 

suppression performance, only a few of these compounds have actually been prepared 

and tested. Bromomethyl trifluoromethyl ether, CH2Br-O-CF3, (39-41o C) and 

bromomethyl difluoromethyl ether, CH2Br-O-CF2H, (70o C) have both been previously 

reported. Their cup-burner extinguishment values were 3.2 and 3.6 vol. %, respectively. 

While their boiling points are considerably higher than that desired, fluorination of the 

CH2Br group may drop the boiling points further toward a more acceptable range (25o to 

35o C). The additional fluorination may not improve cup-burner performance 

appreciably. 

• Bromofluoro-amines: Several bromofluoro-amines have been previously reported. 

N(CF3)2(CHFCF2Br) (boiling pt. 72o C), N(CF3)2(CF2CFHBr) (boiling pt. 72o C), and 

N(CF3)2(CH2CF2Br) (boiling pt. 80o C) all have cup-burner extinguishment values of 

2.4%. The principle drawback to the otherwise effective flame suppressants compounds 

tested are their high boiling points. Lowering the boiling point by changes in the degree 

of fluorination and/or use of substituted methyl substituents is a real possibility. 

Replacing several of the fluorines in N(CF3)3, boiling point -10o C, with hydrogens and a 

bromine might yield a compound of acceptably short atmospheric lifetime and low 

boiling point. Table 2 provides a brief listing of possible candidate bromofluoroamines. 

Table 2. Possible Bromofluoroamine Candidates 

Formula Boiling point, °C (°F) 

(CHF2)(CH2F)NCBrH2 NA

(CF3)2NCBrH2 NA

(CF3)2NCBrF2 40.6

(CF3)2NCF2CBrF2 59.5 to 60.5 

(CHF2)2NCBrF2 NA

• Fluoroalkyl-amines - Testing of perfluorinated alkyl amines, have yielded cup-burner 

values as low as 3.4% for compounds with boiling points in the low 20o to 22o C range. 

Perfluorinated alkyl amines (e.g., N(CF3)3, boiling point -10o C) are not under 

consideration, as they will have unacceptably high atmospheric lifetimes. 

3
Fluoroalkylamines in general are expected to exhibit low toxicity, and further acquisition 

and cup burner testing targeting additional low molecular weight fluorinated amines are 

planned. The unsaturated perfluorinated amine (CF3)2NCF=CF2 may well be 

tropodegradable due to its double bond and is under consideration as a candidate for 

acquisition and testing. 

Table 3. Possible Hydrofluoro and Fluoroamine Candidates 

Formula Boiling point, °C 

(CF3)2NCF=CF2 13.7

N(CH2F)(CF3)2 NA

(CF3)2NCF2CHF2 32.0

N(CHF2)3 NA

• Phosphorus Acids and Esters - These compounds were the subject of a recent NGP 

project just concluded [2]. The experimental determinations of compound flame 

extinguishment indicated cup-burner extinguishments, in general of over 3% with one 

significant exception. One of the compounds Bis(trifluoromethyl) 2,2,2-trifluoroethoxy 

Phosphine, P(OCH2CF3)(CF3)2 yielded a cup-burner extinguishment of 1.8%. The air 

reactivity of the compound suggests that it may not long survive in the air stream and that 

the actual active flame extinguishing species is its air oxidation product. This possibility 

is under study and may result in the identification of additional phosphorus compounds 

for study. A thorough review of future research directions investigating the fire 

suppression potential of this group of compounds is presented in a companion paper [2]. 

• Manganese compounds - Methylcyclopentadienyl manganese tricarbonyl (MMT) is a 

fuel additive that Ethyl Corporation and/or Albemarl (a spin-off of Ethyl) have 

developed. As fuel additives may have fire extinguishment effectiveness, we had 

thought, at one time, of looking into this. It may be that MMT is too flammable for use 

and that fluorinated derivatives are needed. Among the fluorinated compounds identified 

[3] are —pentacarbonyl(pentafluoroethyl)manganese(I), pentacarbonyl[tetrafluoro-1-

(trifluoromethyl)ethyl]manganese(I), pentacarbonyl(trifluoromethyl)manganese(I), and 

pentacarbonyl(heptafluoropropyl)manganese(I). While it is recognized, of course, that 

carbonyl derivatives are likely to have toxicity problems, these materials could provide 

starting points for additional concepts. Several of these compounds will be acquired and 

their cup-burner flame extinguishment performance evaluated. 

CUP-BURNER TESTING 

Cup-burner testing will utilize the same cup-burner design employed in prior projects, Figure 1. 

Due to the limited amount of compound to be prepared (5 to 10 grams), the cup-burner 

methodology employed will provide an upper bound extinguishment concentration which is 

expected to be slightly higher than the actual minimum extinguishment concentration. 

4
Figure 1. Cup-Burner and sample introduction equipment 

TROPODEGRADABLE BROMOFLUOROCARBONS AND CARDIAC 

SENSITIZATION PRESCREENING 

Past research firmly established the potential of tropodegradable bromocarbons as fire 

suppressants and resulted in preliminary lists of tropodegradable compounds ranked according to 

estimated toxicity and environmental acceptability [4, 5, 6, 7]. 

In the case of the bromofluoro alkenes, where cup-burner testing and limited toxicity testing 

have resulted in the identification of 2-bromo-3,3,3-trifluoropropene as a potential replacement 

for Halon 1201, there are many additional compounds that have yet to be tested, Table 4. 

Toxicity testing is of greatest concern for occupied space extinguishment agents. Exposure of 

aircraft maintenance workers, under normal operating circumstances, as well as accidental 

discharge incidents, is a concern. Methods for estimation of toxicity or low cost screening 

methodologies are very limited. Cardiac sensitization, a property of a wide number of 

compounds [8], is not well modeled at present; individual compound tests involve extremely 

expensive animal testing protocols. To aid in the final selection of compounds for animal testing 

screening, a test method will need to be developed and validated. 

The phenomenon of cardiac sensitization refers to the ability of certain un-substituted and 

halogenated hydrocarbons to make the mammalian heart abnormally reactive to epinephrine, 

resulting in cardiac arrhythmias and, potentially, sudden heart failure. The mechanisms

underlying the interaction of halogenated hydrocarbons and cardiac muscle resulting in cardiac 

arrhythmia are unknown. 

5
Dose-response data obtained from animal (dog) testing is the accepted method for determination 

of cardiac sensitization No Observable Adverse Effect Level (NOAEL) and Lowest Observable 

Adverse Effect Level (LOAEL) values. For reference, Halon 1301 LOAEL and NOAEL values 

are 7.4 and 4.5 vol.% respectively. The LOAEL value, in concert with situational risk models 

and evacuation time estimates, determines the mandated maximum acceptable air concentration 

for human exposure in fire suppression events. It is widely accepted that LOAEL data obtained 

from the dog exposure based cardiac sensitization testing are conservative and, in fact, deaths 

due to human exposure to halons are rare. 

Currently, halon replacement researchers are unable to evaluate and rank the cardiac 

sensitization potential of the large number of compounds being studied as possible halon 

replacements. This is due in part to the high cost of traditional dog exposure protocol test 

procedures and lack of usable models. This expense of standard dog exposure tests ($75,000. - 

not including the chemical) for determining a single compound’s cardiac sensitization potential 

is effectively a major impediment to progress. 

Quantitative Structure-Activity Relationships (QSAR) computational methods have been 

previously considered for estimating a chemical’s cardiac sensitization potential. The 

development of a QSAR-based method, due to the lack of sufficient applicable dog exposure 

cardiac sensitization data with which to develop correlations capable of providing reliable 

estimates of unknown substances, is not viewed as a viable approach.. Under more recent 

consideration are in vitro toxicity methods. 

A cardiac sensitization screen based on an in vitro method would involve the development of an 

experimental protocol capable of yielding an experimental ranking of known compounds that 

mirrors their LOAEL values. Even a general “best to worst” ranking capability applicable to the 

many halon replacement candidate compounds would provide a major step forward for the halon 

replacement research effort. 

To be of greatest use to the halon replacement community, an in vitro-based test protocol 

capable of differentiating between Halon 1301 (LOAEL 7.5 vol.%) and Halon 1211 (LOAEL 1.0 

vol.%) or trifluoromethyl iodide (LOAEL 0.4 vol.%) is the desired goal. This is due in part to 

the need to identify compounds whose fire suppression design air concentrations are expected to 

be in the range of 3 to 4 vol.% and whose LOAEL values are likely to be only two or three % 

higher. These tight air concentration constraints mandate the development of a protocol and test 

apparatus capable of closely controlling chemical exposure levels and durations. 

In addition to the potential application of in vitro toxicity testing methods, there is a strong 

possibility of near term use of water-octanol or water-membrane partition coefficient methods as 

a method of establishing a relative ranking of compounds providing, perhaps, at least tentative 

ranking of cardiac sensitization potential as reflected in LOAEL values. This possibility offers 

hope of providing indicators of cardiac sensitization LOAEL values applicable to the preliminary 

compound selection of compounds required by halon replacement researchers. Ultimately all 

compounds would still require formal dog exposure based cardiac sensitization testing. 

The status of in vitro toxicity options and partition coefficient approaches and applicability to the 

ranking of candidate compounds are discussed below. 

6
Table 4. Additional Bromofluoro-Alkenes 

Compound 

Formula 

Compound Name CAS Number 

CHBr=CHCF2H 1-Bromo-3,3-difluoropropene 691-46-3

CHBr=CFCFH2 1-Bromo-2,3-difluoropropene

CFBr=CHCFH2 1-Bromo-1,3-difluoropropene

CFBr=CFCH3 1-Bromo-1,2-difluoropropene

CH2=CBrCF2H 2-Bromo-3,3-difluoropropene

CHF=CBrCFH2 2-Bromo-1,3-difluoropropene

CF2=CBrCH3 2-Bromo-1,1-difluoropropene 51326-64-8

CH2=CFCFHBr 3-Bromo-2,3-difluoropropene

CF2=CHCH2Br 3-Bromo-1,1-difluoropropene 60917-29-5

CFH=CHCFHBr 3-Bromo-1,3-difluoropropene

CFH=CFCH2Br 3-Bromo-1,2-difluoropropene

CFH=CFCFBrH 3-Bromo-1,2,3- trifluoropropene 

CH2=CFCF2Br 3-Bromo-3,3,2-trifluoropropene 178676-13-6

CF2=CFCBrH2 3-Bromo-2,1,1-trifluoropropene

CFH=CHCBrF2 3-Bromo-3,3,1-trifluoropropene

CHBr=CHCF3 1-Bromo-3,3,3- trifluoropropene

CHBr=CFCF2H 1-Bromo-3,3,2- trifluoropropene

CBrF=CHCHF2 1-Bromo-1,3,3- trifluoropropene 

CFBr=CFCH2F 1-Bromo-1,2,3- trifluoropropene

CHBr=CFCHF2 1-Bromo-2,3,3- trifluoropropene

CH2=CBrCF3 2-Bromo-3,3,3- trifluoropropene

CF2=CBrCFH2 2-Bromo-1,1,3- trifluoropropene

CFH=CBrCF2H 2-Bromo-1,3,3- trifluoropropene 25602-04-4, 

25602-05-5 

7
IN VITRO TOXICITY TESTING METHODS 

In vitro toxicity testing methods have been identified as having the great future potential to guide 

a down-select to the “best” candidate compounds for further consideration and formal cardiac 

sensitization testing. Unfortunately, in vitro methods for this application are at an embryonic 

stage of development. Potential projects will require considerable effort to evaluate and select 

cell strains, determine the conditions of exposure, select observational methods, and identify 

those physical and physiological factors to be monitored. 

Fortunately, there appears to be strong current interest on the part of pharmaceutical companies 

in developing an in vitro screening test for cardiac sensitization to identify problematic chemical 

compounds earlier in the drug development process. This is an active area of interest and an in 

vitro method for evaluating the arrhythmia inducing potential of volatile halocarbons may well 

be identified at some future point. 

No in vitro method exists for evaluating the cardiac sensitization properties of compounds. 

Attempts are currently being made to obtain funding for the development of an in vitro method 

based on cardiomyocytes. The goal of this proposal is development of micro-scale in vitro 

testing systems, based on human or animal cardiomyocytes, with long-term viability of the cells. 

Cardiomyocyte-based systems are expected to outperform in vitro Purkinje fiber systems and 

unorganized cell cultures because cardiac cells will be the actual target of drug toxicity; 

endpoints from an in vitro test will be directly relatable to the abnormal clinical ECG patterns 

that define drug-induced arrhythmia 

Such in vitro testing systems could play an important role in evaluating a large number of 

compounds with potential to affect the electrophysiology of the myocardium in man. 

WATER – OCTANOL PARTITION COEFFICIENTS

In the near term, water-octanol partition coefficients may well offer the means to prescreen 

chemicals for their cardiac arrythmogenic properties. Water-octanol partition coefficients are 

recognized as correlating with biological activity [9]. Partition coefficients are typically used to 

describe the relative concentrations of a compound in two adjacent media (air/water and/or 

water/octanol or water/membrane). Water-octanol partition coefficients are frequently employed 

in quantitative structure activity relationships (QSAR) in the early stages of developing 

environmental risk assessments[10]. 

In fact, a wide range of compounds, including halogenated and unhalogenated alkanes, alkenes, 

and ethers, are known to induce cardiac arrhythmia. This situation has led some to speculate that 

the mechanism involved is not a chemical (reactivity based) toxicity, but instead, a generalized 

physical property effect that just happens to cause cardiac arrhythmia when sufficient chemical 

is absorbed into, or adsorbed onto, heart nerve and muscle cells and cell membranes [8]. 

Recent research has shown, using differential scanning calorimetry, that the inhalation anesthetic 

agent halothane (CF3CHClBr) destabilizes some proteins in aqueous solution with respect to 

thermal unfolding, presumably due to halothane binding to the native folded state [11]. The 

authors of this study reported that low millimolar concentrations of halothane produce significant 

destabilization of proteins. They reported that at 14 mM halothane concentrations, unfolding 

temperatures were reduced by up to 8.8 o

C in most proteins studied, and they concluded that 

8
destabilization of proteins by halothane can be attributed to mainly hydrophobic interactions of 

halothane with the proteins. 

Octanol-water partition coefficients are used in QSAR analysis and rational drug design as a 

measure of molecular hydrophobicity. Hydrophobicity is a key factor in drug absorption, 

bioavailability, hydrophobic drug-receptor interactions, metabolism of a compound, and toxicity. 

In addition, LogKOW values are key parameters in studies of the environmental fate of 

chemicals. 

Partition coefficients have also been employed in the past in the assessment of chemical toxicity. 

While they are widely accepted by the pharmaceutical industry as valuable indicators of drug 

effectiveness, they are typically just part of the data used to predict a compound’s overall toxic 

effect(s). 

PARTITION COEFFICIENT DETERMINATION BY RP-HPLC

Reverse phase high pressure liquid chromatography (RP-HPLC) is widely utilized for this 

determination. RP- HPLC employing compounds for which KOW values are known and 

accepted is used to develop relationships between measured chromatographic retention times and 

known partition coefficients. This method requires only mg’s of compound. This obviates many 

of the concerns over which calculation to employ, provides an easy means for 

identifying/modifying calculation methods that yield correct answers, and enables the use of the 

best calculation methods in the selection of additional promising compounds. 

PARTITION COEFFICIENT CALCULATION

Partition coefficients may be calculated (Molinspiration Cheminformatics website 

http://www.molinspiration.com and Syracuse Research Corporation http://esc.syrres.com). 

Generally, Log(KOW) values are calculated as a sum of the fragment-based contributions and 

correction factors. 

The calculated Log(KOW) values for a brief series of halogenated (brominated or iodinated) 

short chain fluorocarbons are listed, Table 5. While this data is by itself not all that convincing it 

does suggest a tentative relationship between the tendency of a compound to be hydrophobic and 

observed cardiac sensitization test results. There are doubtless other factors that influence the 

activity of a compound (possible size, shape, reactivity), and it is also possible that additional 

toxicological mechanisms are involved in certain types of cardiac arrhythmia. 

Table 5. Calculated Log(Kow) Comparison Of Bromofluoro-Carbons 

Compound Log KOW * 

(calculated) 

Log KOW 

(literature) 

LOAEL, vol. %

CF3Br (Halon 1301) 1.833 1.86 7.4 

CHBrF2 (FM-100) 1.849 NA 3.9 

CH2=CBrCF3 2.141 NA 1.0 

CF2ClBr (Halon 1211) 2.175 2.1 1.0 

CF3I 2.219 NA 0.4 

*Molinspiration Cheminformatics algorithm

9
Water-octanol partition coefficients were calculated for the difluorinated bromo-propenes using 

the Molinspiration Cheminformatics and Syracuse Research Corporation molecular fragment 

contribution-based methods, Figure 2. The plotted data points (the lines delineate points 

calculated by a particular method) are roughly comparable. Interestingly, the highest 

Log(KOW) value calculated for this series is for CH2=CHCF2Br, which proved highly toxic in 

inhalation toxicity tests. 

Difluorinated Bromopropene Log(KOW)calc.

0

0.5

1

1.5

2

2.5

3

CH2=CHCF2Br

CFBr=CHCFH2

CHF=CFCH2Br

CHF=CBrCFH2

CF2=CBrCH3

CFBr=CFCH3

CHBr=CFCFH2

Compounds

Log(K

O

W)

Molinspiration

Syrres

Figure 2. Comparison of two difluoro-bromopropene Log(KOW) calculation methods 

10
Predicted Log(KOW) values

0

0.5

1

1.5

2

2.5

3

CH2=CFCBrF2

CFH=CHCBrF2

CFH=CFCBrHF

CF2=CFCBrH2

CH2=CBrCF3

CF2=CBrCFH2

CHF=CBrCF2H

CHBr=CHCF3

CHBr=CFCF2H

CBrF=CHCHF2

CFBr=CFCFH2

Compound

Log(KO

W)

Molinspiration

Syrres

Figure 3. Comparison of two trifluoro-bromopropene Log(KOW) calculation methods 

Water-octanol partition coefficients were also calculated for the trifluorinated bromopropenes 

using the Molinspiration Cheminformatics and Syracuse Research Corporation molecular 

fragment contribution based methods, Figure 3. The plotted data points (line connecting data 

points from same method calculation) are also roughly comparable. 

The calculated values presented in Figures 2 and 3 point to the potential candidacy of several 

additional compounds from the difluorobromopropene and trifluorobromopropene subfamilies. 

Several of these compounds are currently being sought for RP-HPLC determination of their 

Log(KOW) values relative to 2-bromo-3,3,3-trifluoropropene. 

SUMMARY

The next step in the evaluation of the applicability of water-octanol partition coefficients will be 

the experimental determination of partition coefficients for the known halons, bromopropenes, 

and selected additional bromofluoropropenes, and application of these results to the 

identification of additional compounds for acquisition and testing. 

It is apparent that any additional information relating a chemical’s composition and structure to 

its cardiac sensitization properties will enhance future compound selection and reduce the 

number of cardiac sensitization tests required. It seems apparent that eventual identification and 

application of validated in vitro based prescreening methods to rank compounds with respect to 

induction of cardiac arrhythmia could greatly facilitate subsequent decisions to fund formal 

cardiac sensitization testing. 

11
The broad survey of promising chemical families conducted identified five “High Priority”, 

seven “Further Study”, and six “Quick Look” chemical families for investigation. While this 

project places its initial emphasis on the families of compounds past studies have shown to be 

most promising, compound acquisition and testing will include as many families as resources 

allow. 

The broad scope of the project may reasonably be expected to give additional basis upon which 

the study of several new compound families may be advanced and also provide further guidance 

in, and direction to, the search for effective fire extinguishants amongst the known promising 

families, such as the bromofluoropropenes. 

ACKNOWLEGEMENTS 

This research is sponsored by the National Institute of Standards and Technology. 

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

Program Officer: Dr. Richard Gann 

Building and Fire Research Laboroatory 

National Institute of Standards and Technology 

100 Bureau Drive, Stop 8664 

Gaithersburg, MD 20899-8664 

(301) 975-6866 

Richard.gann@nist.gov 

12
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13