NGP SEARCH FOR NEW CHEMICALS - ENVIRONMENTALY 

ACCEPTABLE FIRE SUPPRESSANTS 

J. Douglas Mather Robert E. Tapscott 

Chemical Development Studies, Inc. Vice President - GlobeTech, Inc. 

7636 William Moyers Ave, NE 3812 Palomas Drive NE 

Albuquerque, NM 87122 Albuquerque, NM 87110 

Tel: 505-707-9706 Tel: 505-881-7863 

DougMather@Speakeasy.net GlobeTech@Speakeasy.net 

HALON REPLACEMENT PROGRAM EFFORTS 

As the NGP program began in the mid 1990’s it is useful to include a limited review of 

knowledge gained as a result of efforts that occurred in the years prior to the NGP. Changes in 

thinking occurred frequently in the early 1990’s amongst those involved in identifying and 

evaluating new fire suppressant compounds. Realization that instead of a single drop-in 

replacement being identified for halon 1301 (as well as halon 1211) the world of fire suppression 

applications was going to see a broad range of new agents and technologies. Criteria for 

environmental acceptability changed significantly during this period, risk assessment based 

toxicity tests and limits were identified, and understanding of situational toxicological 

constraints underwent considerable evolution. 

Halon 1301 is unique as a brominated fluorocarbon. Its -58 °C boiling point is the lowest of the 

bromofluoroalkane chemical family. Its toxicity is quite low and it is an excellent fire 

suppressant and explosion inertant. Its low boiling point and excellent fire suppression 

properties give it great dimensionality (space filling), tolerance to less than optimal discharge 

technique, and excellent long term chemical stability. As a consequence the search for 

alternatives based on higher boiling compounds (basically all other conceivable chemical 

extinguishants) faced a considerable challenge to even come close to matching the overall 

performance of halon 1301. 

With the emphasis on dramatic reductions in both stratospheric ozone depletion effects and 

atmospheric global warming potentials one research focus has been on identifying short 

atmospheric lifetime molecules. Short atmospheric compounds incorporate structural 

components that are reactive with atmospheric constituents of the atmosphere or are 

photochemically reactive, Table 1. 
TABLE 1. TROPOSPHERIC REMOVAL MECHANISMS 

Primary removal mechanism Example families 

Photodegradation Iodides, Carbonyls, Bromides 

Reaction with Hydroxyl Alkenes, Aromatics, Hydrogen-Containing Amines, 

Hydrogen-Containing Ethers, Carbonyls 

Physical Removal Ketones, Alcohols, Esters 

Reaction with Tropospheric Ozone Alkenes 

In the 1970’s work on fire suppressants performed at the Naval Research Laboratory studied a 

variety of fire suppression related topics and potential chemicals agents including SF5/CH4 and a 

number of other compounds.1,2 Research at NRL also studied CF3I flame extinguishment3,4 and 

conducted studies of hydrogen fluoride (HF) byproduct formation resulting from halon 1301 fire 

extinguishment.5,6

Efforts funded by the US Air Force at NMERI sought replacements for halon 1211. Early 

NMERI work on streaming agent replacements for halon 1211 funded research led to 

development of methods of estimating atmospheric lifetime and ozone depletion,7 laboratory 

scale test methods,8

 methods for evaluation of materials compatibility and operational 

validation,9 and preliminary lists of advanced agents (chemically active suppressants).10

Early U. S. Air Force (USAF) sponsored research at NMERI on “first-generation” (CFCs and 

HFCs) halon replacement candidates focused on chemicals that were or soon would be readily 

available and that had a significant amount of known toxicological information.11 

HCFCs will eventually be phased out of production due to their non-zero ODP, and some 

restrictions are already in place in parts of Europe (and to a limited extent in the USA). The 

European Community (EC) regulation 3093/94, which entered into force on 1 June 1995, does 

not allow the use of HCFCs for fire protection. HFCs had been prominent as replacements for 

ozone depleting substances but, in 1996 Denmark announced that they planed to phase out all 

hydrofluorocarbons (HFCs) within the next 10 years due to global warming.12

Under US Air Force sponsorship the National Institute of Standards and Technology published 

in August 1990 NIST Technical Note 1279.13 This report is titled “Construction of an 

Exploratory List of Chemicals to Initiate the Search for Halon Alternatives.” This report was the 

first systematic survey since late 1940’s of chemical families potentials as halon replacements. 

The report identified a range of specific chemical families with potential as sources of halon 

replacement and provided listing of 103 compounds of immediate interest for further testing in 

flame extinguishment and explosion suppression. 

2
TABLE 2. NIST LIST OF RECOMMENDED CHEMICAL FAMILIES (1990) 

Chemical family recommendation Justification for further consideration - Environmental 

advantage and flame suppression estimates 

Halogenated ketones, anhydrides, esters Carbonyl red shift contributes to photolysis 

Unsaturated halocarbons Reactivity of alkenes to atmospheric OH 

Halogenated ethers and related compounds Absorption red shift due to C-O-C linkage aides in photolysis 

Halons containing iodine Iodinated halogenated compounds more photochemically 

reactive and a higher fire suppression efficiency 

Sulfur halides Desirable attributes - Low toxicity, possible significant fire 

suppression properties 

Phosphorus containing compounds Established fire suppression properties (expected free radical 

trap mechanism) needs a more volatile or gaseous compound 

Silicon and germanium compounds Silicon in particular (possibly germanium) expected flame 

suppression effectiveness and short atmospheric lifetime 

Metallic compounds Established flame suppression properties, likely alternative 

compounds of great interest 

Inert gases Physical suppressant options 

Guiding attributes required of a replacement halon included: fire suppression effectiveness, low 

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

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

combustion products, and low (or zero) contributions to stratospheric ozone depletion and global 

warming. The report summarized the various mechanisms of flame extinguishment and listed 

approaches to altering a chemical to decrease its contribution to ozone depletion including 

enhancement of agent/chemical reactivity with atmospheric •OH radicals. 

This study provided a useful guide for halon researchers in the early 1990’s. In fact, several of 

the chemical families identified as well as approaches to selecting environmentally acceptable 

short atmospheric lifetime compounds identified were successfully employed in later studies. 

The Halon Options Technical Working Conference held its first annual meeting in the spring of 

1991. The conference continues to the date of this publication as a forum for presentation of 

research related to halon replacements and as such routinely covers topics ranging from new 

agents and fire suppression equipment to atmospheric science and chemical and suppression byproduct toxicology. 

The DoD’s Technology Development Plan (TDP) was initiated to identify alternatives for fire 

extinguishment in occupied spaces by 1997 under Technical Plans I-VI. The plans covered 

RDT&E activities performed by the Navy and one by the Air Force with the goal of identifying 

alternative chemicals, processes and/or techniques for extinguishment fires in occupied 

compartments. 

The AAWG was formed in August 1994 by representatives of most DoD services, NIST, EPA, 

several fire suppression industry representatives, private consultants, and the New Mexico 

3
Engineering Research Institute (NMERI). The AAWG in work funded some of the initial efforts 

to determine the probability of identifying clean advanced agents for use in normally occupied 

areas. A listing of specific chemicals was developed for study which emphasized estimated short 

atmospheric lifetime and the presence of bromine in the chemical structure. Toxicological and 

physical property reviews of this list of compounds were performed. Little cardiac sensitization 

data could be identified at this point and models in existence did not address essential 

toxicological end points such as cardiac sensitization. U.S. Army Center for Health Promotion 

and Preventative Medicine (CHPPM) employed TOPKAT to model QSAR toxicity 

predictions.14 British Ministry of Defence (MOD) DERA employed DEREK (Deductive 

Estimation of Risk from Existing Knowledge version 15.1)15, to evaluate the same list of 

compounds. 

ght bromofluoro alkenes 

demonstrated no adverse effects in the five of the tested compounds.16 

TABLE 3. ACUTE INHALATION TOXICITY TROPODEGRADABLE 

BROMOFLUOROALKE

Inhalation exposure acute toxicity testing at 5 vol. percent, Table 3, of ei

NES 

Deathsa Compound Formula during 

(post) exposure 

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 (1) 

3-Bromo-3,3-difluoropropene CH2=CHCBrF2 7 

2-Bromo-3-trifluoromethoxy-3,4,4,4-tetrafluorobutene CH2=CBr(OCF3)CFCF3 10 

2-Bromo-3-trifluoromethyl-3,4,4,4-tetrafluorobutene CH2=CBrCFC(CF3)2 10 

a 10 rats and a 30-minute exposure at 5% v/v agent air concentrations 

ompound may well be able to serve as a halon 1211 

replacement, usable in unoccupied areas. 

The surprisingly good results from this round of acute inhalation testing provided impetus for a 

greatly expanded program of testing for selected bromofluoroalkenes. The AAWG provided the 

funding for this and many of the other toxicity testing efforts mentioned here. The Ames 

Mutagenicity test results17 on the more promising compounds selected based on boiling point 

were equally reassuring as were the results of the chromosomal aberration tests.18 Cardiac 

sensitization testing of two bomofluoropropenes was performed.19,20 While the 1 % LOAEL 

value observed for 2-bromo-3,3,3-trifluoropropene is disappointingly low and the compound not 

useable as a halon 1301 replacement, the c

While the limited toxicity data are promising, increased fluorination of these molecules is 

desirable in order to obtain reduced boiling points. It is unclear where the optimum in degree 

and pattern of fluorination and site of bromination lies. Given the many additional compounds 

that have yet to be tested hope that at least one will have acceptable cardiac sensitization and 

4
other toxicity properties to be acceptable for use in occupied areas does not seem entirely 

unreasonable. 

The status of alternative agents and development of selection criteria prior to the start of NGP 

research efforts was dominated by non-brominated fluorocarbons and dry powder extinguishants. 

An almost universal goal of all researchers was the demand by the halon user community for a 

drop-in replacement agent. This goal is defined as the identification of a new environmentally 

acceptable agent that enabled users to retain all their current halon systems (storage bottles, 

ggressive dog exposure based agent and epinephrine challenge for 

assessment of cardiac sensitization was questioned. Overall though the lack of a useable 

 atmospheric moisture, or simply polar enough to 

dissolve in rain in a process referred to as rain out were reviewed extensively. In all cases 

ar structures in order to achieve nonflammability and to reduce boiling points. 

in need of scrutiny as potential flame suppressants and halon 

replacements, to list those chemical families for which sufficient knowledge exists to select the 

bly higher boiling points than agents whose 

dispersion requires vaporization under ambient temperatures. The conclusion of the review was 

a categorization into “High Priority”, “Further Study”, and “Quick Look” classifications for the 

Chemical families found to be of interest, Table 4. 

piping, valves, and nozzles) while matching or exceeding halon 1301 in it low toxicity and 

superior fire suppression performance and fire fighting dimensionality. 

The development of CF3I reached a critical point prior to the start of the NGP with the 

announced results of cardiac sensitization LOAEL performance far lower than that of even halon 

1211. Use of CF3I was questioned and additional risk assessments performed. The broad 

applicability of the highly a

screening method for cardiac sensitization represented a major financial barrier to the candidate 

chemical selection process. 

Incorporating bromine in short atmospheric lifetime (tropodegradable) compounds as a means of 

achieving more aggressive flame suppression and hopefully reducing agent weight requirements 

was a well recognized option. Potentially tropodegradable compounds possessing molecular 

features susceptible to attack by atmospheric •OH or •H radicals or tropospheric ozone, 

photolysis by solar radiation, hydrolysis by

compounds considered retained fluorine in their molecul

NGP PROGRAM – NEW CHEMICALS SCREENING 

A very broadly scoped review and analysis of chemical family’s potential and known suitability 

for study is summarized in NIST Technical Note 1443.21 The goal of this review was to identify 

chemical families still 

best candidates and finally to identify those families unlikely to contain useable alternative fire 

suppressing chemicals. 

Compounds with particularly good flame extinguishment characteristics as reflected by their 

having low extinguishment concentration requirements can have proportionately higher boiling 

points. Flame suppression enhancing compounds amenable to use in high temperature 

dispersion systems such as pyrogenically generated aerosols or solid propellant gas generator 

types of fire suppression systems can have considera

5
TABLE 4. CHEMICAL FAMILIES SELECTED FOR CONSIDERATION 

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 

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 

All families studied were evaluated in terms of predicted fire suppressant properties, toxicity, 

colligative properties, environmental and atmospheric impact, and materials compatibility. 

These families in some cases had been well characterized and no additional study of their 

properties was needed. Other chemical families exhibited toxicities that were clearly outside all 

reasonable limits. In some cases the chemical families colligative properties rendered the 

likelihood of dispersion remote or there was simply no reason to suspect that the chemical family 

possessed chemical flame extinguishment properties that were significant that would justify the 

cost and effort involved in further consideration. 

CHEMICAL PROPERTIES AND ENVIRONMENTAL SUITABILITY ESTIMATION 

The toxicities, physical properties, Ozone Depletion Potentials (ODP), and Global Warming 

Potentials (GWP) of chemical that might be appropriate for halon 1301 applications were 

reviewed and/or estimated. Reference 22 gives an overview of global environmental problems 

and presents a detailed discussion of ODP, GWP, the various tropospheric removal mechanisms, 

and approximation methods. Estimation techniques included Quantitative Structure Activity 

Relationships for toxicity; estimated or known hydroxyl free radical rate constants with globally 

averaged atmospheric hydroxyl radical concentrations for lifetimes; estimation methods for 

conversion of lifetimes to ODP and GWP based on data fitting to known values; and estimation 

of physical removal and photolytic removal based on chemical and physical properties. Sources 

6
of toxicity and safety data employed in these efforts included Sax and Lewis and the Registry of 

Toxic Effects of Chemical Substances (RTECS).23,24

Down-selecting chemicals benefits greatly from the existence of low cost readily available test 

methods as well as the chemical(s) of interest. Unfortunately neither of these was the case. 

Cardiac sensitization testing proved extremely expensive and no screening method was ever 

proven through testing. Candidate methods were identified. These included reverse phase high 

pressure liquid chromatography (RP-HPLC) and gas chromatography mass-spectrometry 

methods which are employed in the assessment of environmental toxicity and pharmaceutical 

activity and effect. The RP- HPLC (and GCMS) method employs compounds for which KOW 

values are known and compares chromatographic retention time data for unknown compounds to 

that of the known compounds. KOW values for unknowns are derived directly form this data. 

Both methods require only nanogram or milligram quantities of compound. These methods 

require only mg of compound and provide easy means for the selection of additional promising 

compounds. 

The approach may provide a method for estimating cardiac sensitization for a series of 

compounds. The result could be a ranking of compounds, identification of compounds with 

expected higher LOAEL values and facilitation of compound acquisition.22,25

NGP - CHEMICAL FAMILY SURVEYS 

The search for alternative fire suppressants and in particular, replacements for halon 1301, was 

broad in scope. To ensure that the most optimal chemicals were identified a comprehensive 

search and assessment of a broad array of chemical families and elements was performed. 

• Main Group Elements of Groups IA, IIA, IIIB, IVB, VB, VIB, VIIB, and VIIIB 

• Bromofluoro-Alkenes 

• Fluoroalkoxide and Fluoroalkyl Phosphorus Compounds 

• Bromofluoro Amines 

• Bromofluoro Ethers 

NGP LOW BOILING POINT - FOCUSED STUDIES OF CHEMICAL FAMILIES 

The focus on aircraft applications necessitated a strong emphasis on identifying low boiling 

suppressant chemical families and individual chemicals. Consideration for possible superior 

extinguishment performance broadened the search by inclusion of some chemical families 

thought to be potential sources of highly effective suppressant compounds. The chemical 

families studied and specific chemicals identified and in some cases acquired and evaluated by 

cup-burner are described. 

Fluoroalkoxide and Fluoroalkyl Phosphorus Compounds 

A focused study of fluoroalkyl phosphorus compounds in which eight compounds were 

identified and seven ultimately acquired and tested provided detailed information on flame 

suppression, air reactivity, boiling point trends and also aided in the identification of additional 

compounds which were estimated to be effective extinguishants. Unfortunately, as the observed 

7
flame extinguishment performance was not indicative of an enhanced performance (< 3vol.%) 

and because the boiling points for these compounds were above the cut-off they were not 

included in the continued search for low boiling environmentally acceptable extinguishants. 

Low Boiling Environmentally Acceptable Extinguishants 

The low temperature conditions experienced by aircraft whether located in extreme climates or 

in flight at altitude greatly impact selection of chemical agents and their methods of discharge. 

Identifying new chemical agents for aircraft necessitated a focused study of low boiling 

compounds with the potential to serve as replacements. An extensive research evaluation was 

performed in order to identify specific chemical families and chemicals for further study and 

development.26 While earlier studied had also identified and characterized several low boiling 

compounds most of their efforts were confided to the bromofluoroalkenes and ethers. 

Employing NIST Technical Note 1443 as guidance, Table 4, chemical families that were likely 

to represent low boiling candidate compounds were selected for study. Additional chemical 

families were included based on structural or functional similarities to known flame 

extinguishing compounds where examination indicated the possible tropodegradability. The 

combined list of chemical families served as the focus of compound acquisition and 

extinguishment testing. 

TABLE 5. POTENTIALLY LOW BOILING CHEMICAL FAMILIES 

Chemical family 

Bromofluoro propenes and ethenes 

Bromofluoro dimethyl ethers and methyl ethyl ethers 

Bromofluoromethylamines and n-Bromofluoromethylamines 

Bromofluoroimines 

Bromofluoropropene oxides (oxiranes) 

Bromofluoro acetonitriles 

While some estimates of fire suppression application needs are as low as -60 °C more recent 

analysis seem to suggest that application temperatures in the -20 °C range could be more 

representative of actual aircraft fire suppression application needs. 

Regardless of the chemical family under consideration low boiling points are easiest achieved by 

keeping molecular weight to a minimum while avoiding flammability of the compound. These 

goals are somewhat in opposition as non-flammability can only be achieved through sufficient, 

usually 50%, substitution of fluorine for hydrogens in the molecular structure. Too much 

fluorination in a molecule, while generally but not always imparting a lower boiling point and 

decreased flammability can result in increased atmospheric lifetimes. This is an issue that 

affects ethers in particular. 

Low Boiling - Bromofluoro Alkenes 

With the focus on the lowest boiling alkenes the direction of compound acquisition and testing 

focused primarily on the tetrafluoro and pentafluoro bromopropenes and selected isomers of 

8
brominated difluoroethenes thought based on the chlorinated analogues to not be flammable. 

The chemical family of bromofluoropropenes represents an extensive array of structural 

possibilities. The tetrafluorinated and pentafluorinated bromopropenes alone represent 17 unique 

compounds some of which are cis (Z) and trans (E) isomers of one another. Extinguishment 

studies also included the nonflammable compound 1-bromo-1,2-difluoroethene, CFBr=CFH. 

Several of these compounds were acquired and their cup-burner extinguishment evaluated, 

 1-bromo-1,2-difluoroethene cup-burner extinguishment performance of 8.4 vol.% is outside 

the desired range for continued consideration and as such completes the study of the low boiling 

bromofluoroethenes. The tetra and pentafluoro bromopropenes are clearly the lowest boiling 

chemical suppressants in the alkene family. 

Table 

6

TABLE 6. LOW BOILING BROMOFLUORO ALKENE CUP-BURNER VALUES 

Compound Boiling Point (°C) Cup-Burner 

Extinguishment 

(vol.%) 

1-Bromo-pentafluoropropene 27 3.1 

2-Bromo-pentafluoropropene 25 3.5 

3-Bromo-1,1,3,3-tetrafluoropropene 33 3.3 

2-Bromo-1,3,3,3-tetrafluoropropene 29 3.5 

2-Bromo-1,1,3,3-tetrafluoropropene 29 3.3 

1-Bromo-2,3,3,3-tetrafluoropropene 30 (est.) 3.3 

2-Bromo-3,3,3-trifluoropropene 32-34 3.1 

1-Bromo-1,2-difluoroethene 20 – 24 (est.) 8.4 

Trifluorinated, tetrafluorinated and pentafluorinated bromopropenes all are good extinguishants 

with no indications of flammability. 

Low Boiling Bromofluoro Ethers 

Two early studies of fire suppression by of the higher boiling hydrobromofluoroethers (HBFEs) 

have been carried out. CH2=CBr(OCF3)CF2CF3 which is unsaturated, has a cup burner 

extinguishment concentration of 3.8 volume percent. CH3-O-CF2CHBrF (also known as the 

anesthetic Roflurane) has been estimated to have a heptane cup burner volume fraction of 4.2 % 

and a short atmospheric lifetime.,27

With the focus on low boiling compounds consideration shifted to a limited number of 

bromofluoro methyl ethyl ethers, 

With the focus on low boiling compounds brominated fluorodimethyl ethers were of greatest 

interest. These compounds have been sought on several occasions with limited success. 

Following a review of prior attempts and literature and unpublished synthetic details both 

bromomethyltrifluoromethyl ether and bromomethyldifluoromethyl ether were eventually 

obtained. Extingusihement testing of both compounds by cup-burner provided flame 

extinguishment data characteristic of chemically active agents. Cup-burner performance and 

9
boiling points for CH Br-O-CF , (39-41 °C) 3.2% and bromomethyl difluoromethyl ether, 

CH Br-O-CF H, (70 °C) 3.6% are promising, 

2 3

2 2

Table 8. Substituting additional fluorine for a hydrogen on CH Br-O-CF may yield a compound 

(two structural isomer are possible) with a boiling point in the vicinity of 20 to 30 °C suggesting 

that additional fluorination is worth a try. Ethers may well have superior long term materials 

stability with respect to the alkenes. 

2 3

Table 7, and dimethyl ethers, 

Table 8. 

With the focus on low boiling compounds brominated fluorodimethyl ethers were of greatest 

interest. These compounds have been sought on several occasions with limited success. 

Following a review of prior attempts and literature and unpublished synthetic details both 

bromomethyltrifluoromethyl ether and bromomethyldifluoromethyl ether were eventually 

obtained. Extingusihement testing of both compounds by cup-burner provided flame 

extinguishment data characteristic of chemically active agents. Cup-burner performance and 

boiling points for CH2Br-O-CF3, (39-41 °C) 3.2% and bromomethyl difluoromethyl ether, 

CH2Br-O-CF2H, (70 °C) 3.6% are promising, 

Table 8. Substituting additional fluorine for a hydrogen on CH2Br-O-CF3 may yield a compound 

(two structural isomer are possible) with a boiling point in the vicinity of 20 to 30 °C suggesting 

that additional fluorination is worth a try. Ethers may well have superior long term materials 

stability with respect to the alkenes. 

Table 7. Bromofluoro methyl ethyl ether Cup-Burner Testing Summary 

10
Compound, Formula Boiling 

point, (°C) 

Cup-Burner 

Extinguishment 

(vol.%) 

1-Bromo-1,2,2-trifluoroethyl trifluoromethyl ether, CF3OCFBrCF2H < c 42 4.5

2-Bromo-1,1,2-trifluoroethyl trifluoromethyl ether, CF3OCHFCF2Br 37 < 4.5 

TABLE 8. BROMINATED FLUORO DIMETHYL-ETHER FLAME EXTINGUISHMENT 

DATA 

Compound Formula Boiling 

Point, °C 

CupBurner 

Bromomethyl trifluoromethyl ether CH2Br-O-CF3 39 3.2% 

Bromomethyl difluoromethyl ether CH2Br-O-CF2H 70 3.6% 

Bromodifluoromethyl difluoromethyl ether CF2Br-O-CF2H 20-24 (est.) a 3.7 (2.4)b

a Impure sample 65% bromodifluoromethyl difluoromethyl ether, 25 % bisdifluoromethyl ether, 10% other ethers 

b Estimated extinguishment value based on a 65% purity 

c < signify upper limit extinguishment value. 

The cup-burner extinguishment performance of the sample of 65% bromodifluoromethyl 

difluoromethyl ether was ether was initially calculated as if the sample were 100% pure. If the 

observed 3.7 % extinguishment value is corrected for the actual 65% purity of the sample an 

extinguishment value of 2.4% is obtained. It is unlikely that the major impurity in this sample 

(bisdifluoromethyl ether) contributes significantly to extinguishment at its effective low 

concentration of 0.9%. The remaining impurities in this sample included predominantly 

chlorinated analogues to the desired product. 

Based on these results the ether bromofluoromethyl trifluoromethyl ether (CFHBr-O-CF3) 

would also be of interest unfortunately however sources of the required fluoroether starting 

material (CFH2-O-CF3) could not be located. 

Bromofluoro ethers exhibit some of the lowest boiling points of any of the compounds tested. 

The toxicity of ethers is relatively low and the ether linkage has a relatively low biological and 

chemical reactivity. There are an abundant number of structural isomers and boiling points to a 

low of 20 to 24 °C appear to be possible. Limited atmospheric lifetime estimates suggest the 

possibility of acceptable performance over a range of many of these compounds. 

27

Low Boiling Bromofluoro Propene Oxides 

The propene oxides (or oxiranes) were expected to be low boiling compounds. As carriers of 

bromine there was potential for them to exhibit acceptable flame extinguishment properties as 

well. Testing indicates that perfluoropropene oxide has a cup-burner value of 9.6 vol.%. 

Toxicity is unknown. These compounds are expected to be stable under storage and may be 

readily attached by OH radicals. Their atmospheric lifetimes may well be short, but this is 

28

11
unconfirmed. Synthesis of 3-bromopentafluorooxirane has been reported.29, 30 CF2(O)CBrCF3 

(2-bromo-1,2-perfluoropropene oxide) was successfully sourced and flame extinguishment of 4.9 

vol.% determined Given the unspectacular cup-burner results further investigation of the 

bromofluoropropene oxides was halted. 

Low Boiling Bromo and N-Bromo fluoro Amines, Imines and Nitriles 

Bromofluoro amines have been studied previously however the boiling points of acquired 

compounds representing bromine and fluorine substituted dimethyl ethyl amines were well 

outside acceptable volatility limits, Table 9. 

Table 9. Bromofluoroamine Cup-Burner Flame Extinguishment Data 

Compound, Formula Boiling 

point °C 

Cup-burner 

(%) 

Bis(trifluoromethyl)-2-bromo-1,2,2-trifluoroethyl amine, 

N(CF3)2(CHFCF2Br) 

72 

2.4a

Bis(trifluoromethyl)-2-bromo-1,1,2-trifluoroethyl amine, 72 

N(CF3)2(CF2CFHBr) 

Bis(trifluoromethyl)-2-bromo-2-fluoroethylamine, 80 2.4 

N(CF3)2(CH2CF2Br) 

a Results of a 60/40 blend of N(CF3)2(CHFCF2Br) and N(CF3)2(CF2CFHBr) 

Bromofluoro nitriles as well as the related n-brominated amines, imines and nitriles were until 

recently unstudied. This is in large measure due to a lack of availability of starting materials and 

facilities willing to attempt the chemistry. Synthetic approaches to some compounds have been 

developed and reported.31, , 32 33 Several compounds from these chemical families may well have 

boiling points low enough to warrant further study confirmation. Two of the compounds have 

been reported and their boiling points determined. The two reported compounds nbromobistrifluoromethylamine, ((CF3)2N-Br, 22 oC) and N-bromo-difluoromethanimine, 

(CF2=NBr, boiling point 14 oC) have attractively low boiling points as does the compound 

bromodifluoroacetonitrile, (CF2BrCN, boiling point 3 oC). These compounds may be 

unacceptable toxic but that is as yet unconfirmed. As possibly environmentally acceptable 

compounds with boiling points lower than 30 C are rare, interest in pursuing the synthesis of 

these two compounds as well as other related bromofluoro and n-brominated amines, imines, and 

nitriles, was attempted. 

The related and readily available compounds bromodifluoroacetonitrile (CF BrCN), boiling 

point 3 oC) and trifluoroacetonitrile, ((CF CN), boiling point -64 oC) were also of interest due to 

their rather low boiling points and utility as a means of evaluating the effects of triple bonds on 

flame extinguishment. 

2

3

12
TABLE 10. CUP-BURNER EXTINGUISHMENT OF NITROGEN BASED 

EXTINGUISHANTS 

Compound Boiling point, 

 (°C) 

Cup-burner 

Extinguishment 

(vol. %) 

N-Bromo-difluoromethanimine, CF2=NBr 14 a 

N-Bromobistrifluoromethylamine, (CF3)2N-Br 22 a 

Bromodifluoroacetonitrile, CF2BrCN 3 < 4% 

Trifluoroacetonitrile, CF3CN -64 9% 

a Compound synthesis incomplete 

It was considered unlikely that nitriles would have an intrinsic (chemical) fire suppression 

capability and this was verified in these studies. Nonhalogenated nitriles are known or are 

expected to be flammable. Fluorination is likely to reduce flammability and these compounds 

are likely to be physical suppressants. The addition of bromine or iodine would impart a 

chemical flame suppression property. 

CF3CN has an extremely low boiling point and might possibly be a tropodegradable compound. 

CF2BrCN is also a low boiling brominated compound and potentially tropodegradable. Cupburner testing of both compounds was performed. 

CF2BrCN demonstrated the enhanced extinguishment expected of a brominated compound and 

indicated little adverse effect from the presence of the CN group however it should be 

emphasized that it may be quite toxic. The high required exitinguishment concentreation of 

CF3CN precluded any further consideration of the non-brominated nitriles. 

CHEMICAL FAMILY DOWN-SELECTION REVIEW AND CONSIDERATIONS 

The search for replacements for halon 1301 has been broad based with commercial sources 

offering several fluorocarbon products from different chemical families. Some efforts focused 

on finding high fire suppression efficiency agent while others sought replacement compounds 

that were free of any of the generally recognized disqualifying properties. The general list of 

desired properties includes a boiling point requirement: 

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. 

Boiling point maxima were not rigidly applied as a general selection criteria in the compound 

selection and testing program. Consideration including chemical heats of vaporization, agent 

storage bottle temperature, nozzle design, pressurization and new technologies and methods of 

producing atomized or misted agent discharges were as likely to result in significantly increased 

volatilization and effectively a higher upper boiling point limit. 

13
With the focus on aircraft application the limits of temperatures experienced in flight were a 

prime consideration and fire related agent discharge characteristics at these temperature of great 

interest. Dispersion testing of CF I at -40 °C was performed with results that were not 

reassuring. These tests indicated that even with its relatively low boiling point CF I (-22.5 °C) 

lacks sufficient volatilization under conditions of the testing to give assurance that a uniform 

extinguishment concentration would be obtained. 

3

3

The potential for new agent distribution and application methods to greatly affect the 

performance and ultimately the usability of an agent as a fire suppressant should be kept in mind 

in view of the limited choices available. 

CHEMICAL FAMILY OPTIONS SUMMARY 

Demonstrated clearly identified chemicals and or chemical family options for application to 

aircraft remain unmet. No chemical studied thus far satisfactorily addresses aircraft applications 

demanding and unique combination of high flame suppression efficiency, low boiling point, 

acceptably short atmospheric lifetime, and acceptable toxicity. Should any of these constraining 

attributes, particularly boiling point, be relaxed it is likely that some chemical families options 

may well be applicable. New agent dispersion methods may facilitate use of chemicals whose 

boiling points are in the 25 to 35 °C range. 

This extensive review and evaluation of chemical families and chemical testing has yielded a 

limited list of candidate chemical families that might be useable should boiling point limits be 

relaxed. Some of these chemical families, particularly the bromofluoroalkenes and 

bromofluoroethers may well include compounds with toxicity low enough to allow consideration 

for use in occupied areas. Chemical families such as the bromofluoronitriles, bromofluoroimines, 

and the n-brominated amines and imines should include relatively low boiling compounds whose 

applictions will likely be restricted to unoccupied areas. Additional study and testing might also 

allow inclusion of selected fluoroalkyl phosphorus compounds in this listing however at this 

point no such justification exists. 

14
TABLE 11. CHEMICAL FAMILIES ASSESSMENT SUMMARY 

Chemical Family 

(Example) Overall Candidacy Assessment - Conclusions/Recommendations

Many brominated fluoro- ethenes, propenes, butenes and some pentenes 

of which program allowed study of only a few examples. Effective fire 

suppression performance, acceptable acute inhalation toxicity in some 

cases, and demonstrated short atmospheric lifetimes. Inability to easily 

screen for cardiac sensitization a major hurdle to progress. Boiling 

points are generally higher than 25 °C for the bromo fluoro propenes. 

Bromo-tetrafluoroalkenes may have the best mix of toxicity, flame 

suppression, and boiling point. 

Brominated fluoro 

alkenes 

(CH2=CBr-CF3) 

Demonstrated fire suppression effectiveness, lower boiling points, 

possible shorter atmospheric lifetimes if sufficient hydrogen’s in 

structure. Toxicity may in some cases to be acceptable for some 

applications. Synthetic pathways converting fluoromethyl ethers to 

their brominated congeners provide ready approaches to other members 

of this family. 

Brominated fluoro 

ethers 

CF2Br-O-CF2H 

Bromofluoroamines may eventually offer significant promise if sources of these compounds can 

be located. The toxicity of this class of compounds is expected to be low and there are numerous 

compounds that in theory might well be considered if available. Compounds such as 

N(CFH ) (CF Br) could provide short atmospheric lifetimes and chemical suppression. The 

primary barrier to progress remains compound availability. 

2 2 2

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17