Chapter 7: SEARCH FOR NEW FIRE

SUPPRESSANT CHEMICALS

TABLE OF CONTENTS

7.1 Fire Suppressant Replacement Knowledge Prior to the NGP .........................................612 

7.1.1 Overview of Early Halon Replacement Efforts ....................................................612 

7.1.2 Fire Suppressant Research – 1974 Through 1993.................................................613 

7.1.3 DoD Technology Development Plan (1993 to 1997)............................................615 

7.1.4 Advanced Agent Working Group (AAWG) .........................................................616 

7.1.5 Summary: Alternative Agents and Selection Criteria Prior to the NGP ...............622 

7.2 The NGP Approach to New Chemicals Screening..........................................................612 

7.3 NGP Surveys of Inorganic Chemical Families................................................................612 

7.3.1 Main Group Elements - Group I............................................................................626 

7.3.2 Main Group Elements - Group II ..........................................................................627 

7.3.3 Main Group Elements - Group III.........................................................................627 

7.3.4 Main Group Elements - Group IV.........................................................................628 

7.3.5 Main Group Elements - Group V..........................................................................634 

7.3.6 Main Group Elements - Group VI.........................................................................645 

7.3.7 Main Group Elements - Group VIII (Noble Gases)..............................................646 

7.3.8 Transition Metal Based Compounds.....................................................................646 

7.3.9 Inorganic Chemicals - Conclusions.......................................................................647 

7.4 NGP Surveys of Organic Compounds.............................................................................647 

7.4.1 Highly Efficient Thermal Agents..........................................................................647 

7.4.2 Tropodegradable Candidate Compounds..............................................................658 

7.4.3 Bromofluoroalkenes..............................................................................................662 

7.4.4 Fluoroalkoxide and Fluoroalkyl Phosphorus Compounds....................................665 

7.4.5 Fluoroalkyl Nitrogen-based Candidates................................................................680 

7.4.6 Bromofluoroalkyl Nitrogen-based Candidates......................................................685 

7.4.7 Fluorinated Ethers .................................................................................................687 

7.4.8 Bromofluoroethers.................................................................................................691 

7.4.9 Bromofluorooxiranes.............................................................................................694 

7.4.10 Bromofluoro / Fluorinated Aldehydes and Ketones..............................................695 

7.4.11 Bromofluoro Alcohols...........................................................................................695 

7.4.12 Iodinated Hydrocarbons........................................................................................696 

7.5 Chemical Family Options and Replacement Issues.........................................................700 

7.5.1 Suppressant Criteria and Selection Constraints.....................................................700 

7.5.2 General Conclusions..............................................................................................701 

7.6 References........................................................................................................................702 

J. Douglas Mather, Ph.D. 

Chemical Development Studies, Inc. 

Robert E. Tapscott, Ph.D. 

GlobeTech, Inc.
612 Search for New Fire Suppressant Chemicals 

7.1 FIRE SUPPRESSANT REPLACEMENT KNOWLEDGE PRIOR TO THE NGP 

7.1.1 Overview of Early Halon Replacement Efforts 

As described in Chapter 1 of this book, in the years following the Army-Purdue study, there was 

extensive scientific and engineering research that led to the commercialization and widespread use of 

halon 1301. Following the adoption of the Montreal Protocol on Substances That Deplete the Ozone 

Layer in 1987, organized efforts to identify replacements were initiated by a broad range of governmental 

and non-governmental groups. These efforts were hastened in the United States by the planned phase-out 

of production of halon 1301 (CF3Br) and halon 1211 (CF2ClBr) by the end of 1993. 

The replacement of halon 1301 presented some daunting challenges. Halon 1301 is unique as a 

brominated halocarbon. Its -58 °C boiling point is the lowest of the bromofluoroalkane chemical family, 

and its toxicity is quite low. It is an efficient fire suppressant and explosion inertant. It has great 

dimensionality (space filling), high tolerance to less than optimal discharge technique, and excellent 

chemical stability. Early results showed that a small change in the molecule could lead to large and 

conflicting effects on key performance properties. For example, the replacement of a fluorine atom by a 

hydrogen atom to produce halon 1201 (CF2HBr) reduced the estimated atmospheric lifetime from 

65 years to 15 years, but raised the boiling point to -15 °C. 

Nonetheless, the search for alternatives to the firefighting halons began as a quest for a "drop-in," a 

chemical that would fit into existing fire suppression systems and perform just like or better than the 

halon it was replacing. During the early years of this research, there were frequent changes in thinking 

among those involved in identifying new chemicals. For instance, it was realized 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. Furthermore, the criteria for 

environmental acceptability changed. With the emphasis on dramatic reductions in both stratospheric 

ozone depletion effects and atmospheric global warming potentials, the research focus shifted to 

identifying short atmospheric lifetime molecules. These compounds incorporate structural components 

that are reactive with atmospheric constituents of the atmosphere or are photochemically reactive, as 

shown in Table 7–1. 

Table 7–1. Tropospheric Removal Mechanisms. 

Primary Removal Mechanism Example Families 

Photodegradation Iodides, carbonyls, bromides 

Reaction with hydroxyl radicals Alkenes, aromatics, hydrogen-containing amines, hydrogencontaining ethers, carbonyls 

Physical removal Ketones, alcohols, esters 

Reaction with tropospheric ozone Alkenes 

Risk assessment based toxicity tests and limits were identified, and understanding of situational 

toxicological constraints underwent considerable evolution. Some chemical options considered for halon 

replacement (e.g., the perfluorocarbons) were at first embraced, but later discarded as understanding of 

global warming impact issues developed. 

By the time NGP research began in 1997, these efforts had resulted in the birth of new fire 

extinguishment technologies, a broader view of the chemical options available, and emerging 
Fire Suppressant Replacement Knowledge Prior to the NGP 613

understanding of the dynamics of fire suppression under the adverse conditions encountered during the 

suppression of in-flight fires in aircraft. The following is a brief summary of these activities and their 

outcomes. 

7.1.2 Fire Suppressant Research - 1974 Through 1993 

Scientists at the Naval Research Laboratory had begun investigation of the principles of fire suppression 

by halon 1301 as early as 1974. This was driven by the Naval Air System Command's desire for a more 

efficient agent for suppressing in-flight fires. The outcome of this and the few contemporary efforts are 

summarized in Reference 1. As Rowland and Molina's finding that such compounds could deplete 

stratospheric ozone became well-known, this research broadened to a variety of fire suppression related 

topics and potential chemical agents.2,3 Research at NRL also studied CF3I flame extinguishment4,5 and 

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

extinguishment.6,7

Beginning in the mid-1980s, the U.S. Air Force (USAF) sponsored research at the New Mexico 

Engineering Research Institute (NMERI) on “first generation” halon replacement candidates focused on 

chemicals that were or soon would be readily available and that had a significant amount of known 

toxicological information.8

 This strategy was adopted for two reasons: 

1. Available chemicals could be tested at relatively low cost to determine effectiveness in 

firefighting scenarios, and 

2. Toxicological testing of candidates was expensive and time consuming. 

Chemicals developed primarily as chlorofluorocarbon (CFC) replacements were the major focus as firstgeneration replacements. Relatively large quantities of these chemicals were available, and 

manufacturers were supporting toxicological testing, as these chemicals were often being considered for 

applications as refrigerants, solvents, and foam blowing agents, in addition to fire suppression. This 

strategy proved successful in that a number of halon replacement candidates were identified that were 

readily available for testing that had a significant amount of toxicity testing already performed.9,10,11,12,13 

Evolving understanding of likely global warming and ozone depletion restrictions as well as the desire for 

greater agent effectiveness in fire suppression led to a de-emphasis on “first generation” chemicals. 

The first generation agents were all halocarbons: hydrochlorofluorocarbons (HCFCs), perfluorocarbons 

(FCs or PFCs), and hydrofluorocarbons (HFCs). Hydrobromofluorocarbons (HBFC) were also evaluated 

very early in the program, but were dropped when it became apparent that they would be regulated due to 

their still significant Ozone Depletion Potentials (ODP). Although the first generation program was 

successful in identifying available candidates that did not require toxicological testing, the first generation 

halocarbons were not as effective as the in-use halons and required approximately two to four times more 

agent. Moreover, some had toxicological and environmental drawbacks. In particular, environmental 

concerns led to the following restrictions: 

• HCFCs would 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. 
614 Search for New Fire Suppressant Chemicals 

• Under the Significant New Alternatives Policy (SNAP), the U.S. Environmental Protection 

Agency (EPA) has applied narrowed limits to the use of perfluorocarbons. PFCs are fully 

fluorinated compounds, unlike HCFCs or HFCs, and have several attractive features. They 

are nonflammable, have low toxicity, and do not contribute to stratospheric ozone depletion. 

The environmental characteristics of concern, however, are their high Global Warming 

Potentials (GWPs), which are as much as 12,500 times that of carbon dioxide (for a 100 year 

time horizon), and their long atmospheric lifetimes of up to 50,000 years for CF4.

14 Although 

the actual contributions to global warming depend upon the quantities emitted, the long 

lifetimes make the warming effects of PFCs irreversible. The EPA is allowing the use of 

PFCs for only selected applications where no other substitute would meet performance or 

safety requirements. 

• HFCs have been prominent as replacements for ozone depleting substances. Nevertheless, 

they are receiving increasing attention from environmental organizations. The National 

Institute of Public Health and Environmental Protection, The Netherlands, has projected a 

significant increase in greenhouse gas emissions due to the use of HFCs to replace CFCs and 

HCFCs.15 Moreover, in 1996 Denmark announced that they planed to phase out all 

hydrofluorocarbons (HFCs) within the next 10 years due to their contributions to global 

warming.16

Early NMERI research on streaming agent replacements for halon 1211 led to the development of 

methods of estimating atmospheric lifetime and ozone depletion,17 laboratory scale test methods,18

methods for evaluation of materials compatibility and operational validation,19 and preliminary lists of 

advanced agents (chemically active suppressants).20

In 1989, a number of companies involved in the manufacture, sale, and installation of fire suppressant 

chemicals formed the Halon Alternatives Research Consortium (HARC, which would evolve into the 

Halon Alternatives Research Corporation). This group's Technical Committee formulated a research plan 

that would lead to the identification of alternatives to halon 1301 and halon 1211. The first (and only) 

projects were sponsored by the USAF at the National Institute of Standards and Technology (NIST). The 

output was two reports: 

1. Preliminary Screening Procedures and Criteria for Replacements for Halons 1211 and 1301, 

which was discussed in Chapter 6 of this book. 

2. Construction of an Exploratory List of Chemicals to Initiate the Search for Halon 

Alternatives.

21 This report is the first systematic survey since the late 1940s of chemical 

families and their potentials as halon replacements. Table 7–2 presents the chemical family 

recommendations resulting from this analysis. 

Guiding attributes required of a replacement for halon 1301 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 chemical reactivity 

with atmospheric •OH radicals. Finally, the report listed 103 compounds of immediate interest for further 

testing in flame extinguishment and explosion suppression. 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. 
Fire Suppressant Replacement Knowledge Prior to the NGP 615

Table 7–2. 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 absorption max. red shift contributes to photolysis 

Unsaturated halocarbons Reactivity of alkenes to atmospheric •OH radicals 

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 

The Halon Options Technical Working Conference held its first annual meeting in the spring of 1991. 

The conference became the premier forum for presentation of research related to halon replacements and, 

as such, routinely covered topics ranging from new agents and fire suppression equipment to atmospheric 

science and chemical and suppression by-product toxicology. The compiled papers are available on CD 

from NIST22 and at the HOTWC web site, www.bfrl.nist.gov/866/HOTWC. 

As early as the first HOTWC, research papers were presented describing the synthesis of compounds 

which to the present are topics of intense interest. For example, a 1991 paper presented by Dr. J. Adcock 

of the University of Tennessee detailed his synthesis, under funding by the Electric Power Research 

Institute, of the low molecular weight brominated fluoroethers that remain of intense interest today.23 

Papers presented by EPA staff covering toxicology and regulatory and toxicological issues provided 

guidance to the fire research community and those involved in the search for new chemicals. Researchers 

from private industry presented numerous papers detailing the results of their halon replacement efforts. 

Many papers detailing agent and equipment development and testing as well as basic extinguishment 

science were presented by researchers from the military services in the U.S. and overseas. 

7.1.3 DoD Technology Development Plan (1993 to 1997) 

The Technology Development Plan (TDP) was initiated to identify feasible, commercially available 

alternatives to ozone depleting substances or use in existing weapons systems.24 The work was divided 

among seven Technical Plans. Those involving fire fighting were: 

• Technical Plan I. Alternative chemicals, processes and/or techniques for extinguishment of 

slow growth fires in manned spaces of ships and critical command and control facilities. The 

best chemical for retrofit was identified as HFC-227ea (C3HF7). Fine water mist was noted as 

a candidate for future platforms. 

• Technical Plan II. Alternative chemicals, processes, and/or techniques for extinguishment of 

slow growth fires in engine nacelles and dry bays of fixed wing aircraft and helicopters. 

HFC-125 (C2HF5) was identified as the optimal chemical for engine nacelle fires. Solid 
616 Search for New Fire Suppressant Chemicals 

propellant gas generator technology was promoted for dry bay applications. Perfluorohexane 

was identified as a streaming agent to replace halon 1211. 

• Technical Plan III. Alternative chemicals, processes, and/or techniques for extinguishment of 

fast growth fires and explosion suppression in unmanned spaces of fixed wing aircraft engine 

nacelles and dry bays of fixed wing aircraft and helicopters. Completion of this work was 

deferred. 

• Technical Plan IV. Alternative chemicals, processes, and/or techniques for explosion 

suppression in crew occupied compartments of ground armored vehicles. 

All but one of these compounds was less efficient than the halon it would replace, requiring more mass 

and higher storage volume to achieve comparable performance. Trifluoromethyl iodide (CF3I) was found 

to be as effective as the existing halons. However, cardiac sensitization at levels well below the 

extinguishing concentration restricted further consideration. 

There was, therefore, an increasing incentive to look at compounds other than the usual, saturated 

halocarbons. These compounds are the non-halocarbon candidates, known as “advanced agents.” The 

most promising of these were the phosphorus compounds (particularly, the phosphorus nitrides (which 

include phosphazenes and phosphonitriles), metal compounds, and silicon compounds. In addition, the 

broad family of tropodegradable bromocarbons included promising candidates. 

7.1.4 Advanced Agent Working Group (AAWG) 

On August 23, 1994 representatives of the North Slope Oil Producing and Transmission Companies met 

with members of the “CF3I Working Group.” The AAWG was formed in the course of this meeting with 

participating representatives of most of the U.S. military services, NIST, EPA, several fire suppression 

industry representatives, private consultants, and NMERI. The AAWG funded some of the initial efforts 

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

work was largely performed at NMERI. Questions posed included: 

• What chemically active agent mechanisms were available for protection against fire and 

explosion? 

• What chemical families could provide a replacement for halon 1301 (including preliminary 

assessments of manufacturability, global environmental impact, and toxicity for these 

families)? 

• What were the prospects for a halon 1301 replacement without major hardware changes? 

A listing of specific chemicals was developed for study (Table 7–3). The compounds listed emphasized 

estimated short atmospheric lifetime and the presence of bromine in the chemical structure. Additional 

efforts to estimate toxicity, physical properties and more accurately determine fire extinguishment 

performance through selective testing of some of the compounds listed were initiated. 

NMERI assembled physical and toxicological information on the compounds and identified sources and 

in some cases synthetic methods for these compounds. Toxicological and physical property reviews of 

this data related toxicity modeling data were performed. Little cardiac sensitization data could be 

identified at that point and models in existence did not address this particular toxicological end point. 
Fire Suppressant Replacement Knowledge Prior to the NGP 617

Table 7–3. AAWG Preliminary List of Compounds. 

Chemical Formula Chemical Name CAS No./Availability 

Alkenes 

CH2=CHCF2Br 3-bromo-3,3-difluoropropene 420-90-6/Commercial 

sources 

CF2BrCH=CHCF3 cis- and trans-1-bromo-1,1,4,4,4-pentafluoro-2-butene 

CF2BrCF2CH=CH2 4-bromo-3,3,4,4-tetrafluorobutene 18599-22-9/Commercial 

sources 

CF2BrC(CF3)=CH2 3-bromo-3,3-difluoro-2-(trifluoromethyl)propene 

Alcohols 

CF2BrCH2OH 2-bromo-2,2-difluoroethanol 420-94-0 

CF3CFBrCH2OH 2-bromo-2,3,3,3-tetrafluoropropanol 94083-41-7 

CF2BrCF2CH2OH 3-bromo-2,2,3,3-tetrafluoropropanol 

CF3CHOHCH2Br 3-bromo-1,1,1-trifluoro-2-propanol Research chemical only 

Ethers 

CF2H-O-CFHBr (bromofluoromethyl)(difluoromethyl)ether no CAS Number 

CF2Br-O-CH3 (bromodifluoromethyl)(methyl)ether 

CF2BrCH2-O-CF3 (2-bromo-2,2-difluoroethyl)(trifluoromethyl)ether 

CF2BrCF2-O-CH3 (2-bromo-1,1,2,2-tetrafluoroethyl)(methyl)ether 13749-39-8 

-CH2CF2CBrFCH2-O- 3-bromo-2,2,3-trifluorooxolane 

Amines 

(CBrF2)(CHF2)2N bis(difluoromethyl)(bromodifluoromethyl)amine no CAS Number 

(CBrF2)(CF3)(CH3)N (bromodifluoromethyl)(trifluoromethyl)(methyl) 

amine 

no CAS Number 

(CF3)2(CH2CBrF2)N bis(trifluoromethyl)(2-bromo-2,2-difluoroethyl)amine 

(CBrF2)(CF3)2N bis(trifluoromethyl)(bromodifluoromethyl)amine 

Carbonyl Compounds 

CBrF2CH2C(O)H 3-bromo-3,3-difluoropropanal 

CH3C(O)CH2CF2Br 4-bromo-4,4-difluoro-2-butanone 

CBrF2CH2C(O)OCH3 methyl 3-bromo-3,3-difluoropropionate 99953-33-0 

CBrF2CH2C(O)OCF3 trifluoromethyl 3-bromo-3,3-difluoropropionate 

Aromatics 

C6F5Br bromopentafluorobenzene 344-04-7/Commercial 

sources 

C6F5CBrF2 (bromodifluoromethyl)pentafluorobenzene 35523-39-8 

C6BrF4CF3 bromoheptafluorotoluene 

2-bromoheptafluorotoluene 

3-bromoheptafluorotoluene 

4-bromoheptafluorotoluene 

113601-46-0 

66820-64-2 

5360-80-5 

17823-46-0 

A toxicological quantitative structure-activity relationship (QSAR) relies on the establishment of a 

statistically significant mathematical correlation between chemical toxicity and a particular chemical, 

structural, or physical property of a group of similar compounds in order to be used to predict the toxicity 

of untested chemicals. Further, the predictive accuracy of values and trends is greatest for only for 

compounds in the same group or very similar groups. QSAR models also included proprietary models for 

halon property estimation which attempted the estimation of cardiac sensitization LOAEL values.25 
618 Search for New Fire Suppressant Chemicals 

QSAR modeling of 25 brominated compounds was performed by the U.S. Army Center for Health 

Promotion and Preventative Medicine (CHPPM) and the British Ministry of Defence (MOD) DERA. 

U.S. Army CHPPM employed TOPKAT to model QSAR toxicity predictions of acute LD50, LC50, eye 

sensitization and chronic LOAEL, mutagenicity, DPT, and carcinogenicity.26 The results of this study are 

presented in Table 7–4. 

Table 7–4. TOPKAT Toxicity Predictions. 

Chemical Formula Acute Toxicitya Chronic Toxicitya 

LD50 LC50 Eye LOAEL Mut. DTP Carc. 

Alkenes 

CH2=CHCF2Br o o o X o (X) 

CF2BrCH=CHCF3 o o X o o o X 

CF2BrCF2CH=CH2 o o o o o o X 

CF2BrC(CF3)=CH2 o X o X o (X) 

Alcohols 

CF2BrCH2OH o o o o o X (X) 

CF3CFBrCH2OH o o o o o X X 

CF2BrCF2CH2OH o o o o o X X 

CF3CHOHCH2Br o X X X (X) 

Ethers 

CF2H-O-CFHBr X o X 

CF2Br-O-CH3 o o o X 

CF2BrCH2-O-CF3 o o X 

CF2BrCF2-O-CH3 o o o o X 

-CH2CF2CBrFCH2-O- X X o X 

Amines 

(CBrF2)(CHF2)2N o o 

(CBrF2)(CF3)(CH3)N o o (X) 

(CF3)2(CH2CBrF2)N o o X 

(CBrF2)(CF3)2N o X 

Carbonyls 

CBrF2CH2C(O)H o o 

CH3C(O)CH2CF2Br o X o o X 

CBrF2CH2C(O)OCH3 o o o (X) 

CBrF2CH2C(O)OCF3 o o (X) 

Aromatics 

C6F5Br X o X o 

C6F5CBrF2 o X o 

C6BrF4CF3 X* X o 

o meaningful estimates X possibly unacceptable toxicity levels 

* moderate confidence ( ) mixed results on different models 

Eye eye irritation Carc carcinogenicity 

Mut mutagenicity 

DERA employed DEREK (Deductive Estimation of Risk from Existing Knowledge), version 15.1,27 to 

evaluate the same list of compounds. DEREK is a rule-based software system designed for qualitative 

prediction of potential toxicity hazards by a chemical based on known structure-activity relationships. 
Fire Suppressant Replacement Knowledge Prior to the NGP 619

The program does not estimate cardiac sensitization.28 Four endpoints were evaluated by DEREK, as 

shown in Table 7–5: carcinogenicity, mutagenicity, sensitization (presumably respiratory) and skin 

sensitization. In addition, the “rules” incorporated into model skin sensitization (where the program has a 

tendency to predict false positives) as well as respiratory sensitization, irritation and corrosivity. Acute 

toxicity is of the highest concern for halon alternatives, but unfortunately is not addressed by the program. 

These estimation methods are both highly dependent on the existence of a “training set” of data for 

similar chemical structures and chemical functional groups in order to establish the correlations and 

weightings needed to be predictive. Such information is limited, rendering this approach of little use. 

Table 7–5. DEREK Toxicity Predictions. 

Chemical Family Chemical Formula DEREK Prediction

Alkenes CH2=CHCF2Br Skin irritation 

CF2BrCH=CHCF3 Skin irritation 

CF2BrCF2CH=CH2 Skin irritation, mutagenicity 

CF2BrC(CF3)=CH2 Skin irritation 

Alcohols CF2BrCH2OH Skin irritation 

CF3CFBrCH2OH Skin irritation, mutagenicity 

CF2BrCF2CH2OH Skin irritation, mutagenicity 

CF3CHOHCH2Br Skin irritation, mutagenicity 

Ethers CF2H-O-CFHBr Skin irritation 

CF2Br-O-CH3 Skin irritation 

CF2BrCH2-O-CF3 Skin irritation 

CF2BrCF2-O-CH3 Skin irritation 

-CH2CF2CBrFCH2-O- Skin irritation, mutagenicity 

Amines (CBrF2)(CHF2)2N Skin irritation 

(CBrF2)(CF3)(CH3)N Skin irritation 

(CF3)2(CH2CBrF2)N Skin irritation, mutagenicity 

(CBrF2)(CF3)2N Skin irritation 

Ethers CBrF2CH2C(O)H Skin irritation, mutagenicity 

CH3C(O)CH2CF2Br Skin irritation 

CBrF2CH2C(O)OCH3 Skin irritation 

CBrF2CH2C(O)OCF3 Skin irritation 

Aromatics C6F5Br None 

C6F5CBrF2 Skin irritation, skin sensitization 

C6BrF4CF3 (ortho, meta, para isomers) None 

As an alternative approach, Tapscott and Mather identified some general toxicity trends for alkanes, based 

on non-quantitative structure activity relationships (SARs) and published toxicity information, from 

comprehensive reviews of toxicity literature.29 The identified trends are shown below in rows, with the 

compound formula followed by ln(LC50) values in mice for 30 min exposures. General trends relating the 

number of fluorine or hydrogen atoms needed to impart favorable toxicity were not identified. This study 

indicated that location of substituents appeared to play a more important role than the number of fluorine 

or hydrogen atoms. 

• Toxicity increases in the order F < Cl < Br, for example: 
620 Search for New Fire Suppressant Chemicals 

CHF2CH2Cl, 2.00 CHF2CH2Br, 1.52 CF3CHBrCl, 0.18 

CF3CHFCl, 3.8 CF3CHCl2, 2.00 

• For haloethanes, H adjacent to a –CF3 group increases toxicity, therefore, CF2XCHFX is 

preferred over CF3CHX2 (the X’s can be identical or dissimilar halogens and follow the same 

trend as outlined above). For example: 

CF2ClCHFCl, 2.20 CF3CHCl2, 2.00 CF3CHBrCl, 1.10 

CF2BrCHFBr, 0.45 CF3CHBr2, 0.18 

CF2ClCHFBr, 1.42 CF2BrCHFCl, 1.22 

• For halopropanes, the –CH3 group reduces toxicity (at least when opposite a –CF3 group); 

therefore, CF3CXRCH3 is preferred over CF3CRHCH2X, where R can be either a halogen or 

H. For example: 

CF3CCl2CH3, 2.30 CF3CH2CHCl2, 0.88 CF3CHClCH2Cl, 0.79 

CF3CHBrCH3, 2.03 CF3CH2CH2Br, 1.50 

• For halopropanes, -CH2- groups are favored over –CF2- groups, for example: 

CHF2CH2CClF2, 3.00 CHF2CF2CH2Cl, 1.62 

CF2ClCH2CH3, 2.77 CH2ClCF2CH3, 2.13 

To decrease the toxicity, it is essential that carbon atoms alpha to the carbonyl group contain no halogen 

atoms. Carbonyl compounds exhibit a range of toxicities depending on whether the carbonyl group is in 

an aldehyde, ketone, carboxylic acid, or ester. 

Toxicity Studies of Tropodegradable Bromofluoroalkenes 

Extremely promising inhalation exposure acute toxicity testing at 5 volume %, Table 7–6, of eight 

bromofluoroalkenes demonstrated no adverse effects in five of the tested compounds.30 The surprisingly 

good results from this round of initial testing provided impetus for a greatly expanded program of testing 

for selected bromofluoroalkenes. The AAWG provided a large part of the funding for this exposure 

study. 

The Ames Mutagenicity test results31 on the more promising compounds selected based on boiling point 

were equally reassuring, Table 7−7, as were the results of the chromosomal aberration tests, Table 7−8.32

Cardiac sensitization is a property that has been associated with both halogenated and non-halogenated 

compounds. It has surfaced as a prime consideration in the development of solvents, fire suppressants, 

and propellants for medical inhalers. It was observed as a cause of cardiac arrest in substance abuse by 

inhalation of solvents used in spray paints, lubricants, glues and hairsprays, and it has been associated 

with some pharmaceuticals and volatile surgical anesthesia agents. Known cardiac sensitizing or 

arrhythmogenic compounds are represented by a wide range of chemical families including alkanes, 

alkenes, ethers, fluorocarbons, iodocarbons, and bromocarbons. 
Fire Suppressant Replacement Knowledge Prior to the NGP 621

Table 7–6. Acute Inhalation Toxicity Tropodegradable Bromofluoroalkenes. 

Chemical Name Chemical Formula Deathsa

 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 min exposure at 5 volume % agent in air 

Table 7–7. Ames Mutagenicity Test Results. 

Chemical Name Chemical 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 7–8. Chromosomal Aberration Test Results. 

Chemical Name Chemical Formula Test Result 

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

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

The cardiac sensitization test data presented in Table 7–9 represent the only two such tests attempted on 

bromofluoropropenes.33,34 While the 1 volume % LOAEL value observed for 2-bromo-3,3,3-

trifluoropropene was disappointingly low, making the compound not usable as a halon 1301 replacement, 

the compound may well be able to serve as a halon 1211 replacement, usable in unoccupied areas. 

Testing of 1-bromo-3,3,3-trifluoropropene was terminated due to severe adverse effects including tremor. 

Table 7–9. Cardiac Sensitization Testing of Bromofluoropropenes. 

Chemical Name Chemical Formula NOAEL LOAEL 

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

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

a Determination aborted due to adverse effects on dogs 

Further fluorination of these molecules was desirable to reduce boiling points. However, it was unclear 

where the optimum in degree and pattern of fluorination and site of bromination lay. Given the many 

additional compounds that had yet to be tested, it was hoped that at least one would have acceptable 

cardiac sensitization and other toxicity properties to be acceptable for use in occupied areas. 

Significant Toxicity Data Source – Inhalation Anesthetic Development 

Early compound toxicity efforts were greatly aided by research in anesthesiology, where limited testing 

results on halogenated alkenes had been reported (Table 7–10).35 Where provided, the concentrations 
622 Search for New Fire Suppressant Chemicals 

used were high. The observations in the comments section provided useful compound selection guidance 

and indicated that study of the related brominated alkenes was worthwhile. 

Table 7–10. Anesthesiology Testing of Fluoroalkenes. 

Chemical 

Formula Animals Anesthesia Comments 

F F 2 2 

F 2 

C l

C l 2 rats no 

Extreme depression, analgesia, respiratory depression and 

failure. Death within 18 hours. 

CClF=CClCF3 4 dogs yes 

Induction quiet, recovery uneventful, heart slowed with no

fall of blood pressure. Brachycardia. 

CF2=CClCF3 1 dog no 

Concentration of 75 %. Marked struggle, gasping, respiratory

arrest, revived by artificial respiration.

CCl2=CClCF3 1 dog no Muscular rigidity, pulmonary edema, death after a few hours. 

CHCl=CClCF3 2 rats no Respiratory depression and failure, one rat died, the other

recovered quickly.

CCl2=CClCF3 3 rats a

no/yes Depression, pulmonary edema, eye irritation, convulsions and

death within 1 hour. 

CF2=CFCF3 2 dogs no 

Concentrations of 50 % and 75 %. No demonstrable effect. 

Tremors, respiratory irritation. 

CH2=CHCF3 2 dogs no Tremors, lack of coordination. 

a Anesthesia observed for one rat at a higher concentration.

2-Bromo-3,3,3-trifluoropropene, CH2=CBrCF3, was reported to be an excellent anesthetic with a rapid,

uneventful recovery.

36 As the concentrations used were unknown, it was difficult to determine the 

potency of this chemical as an anesthetic; however, that no adverse effects were observed indicated that

this material may have a low toxicity. Studies of 3-chloro-3,3-difluoropropene, CF2ClCH=CH2, as an 

anesthetic in dogs showed cardiac arrhythmia with ventricular extra systole, blood pressure decrease, and

tremor. Interestingly, inhalation studies later demonstrated that the brominated analogue, CF2BrCH=CH2, 

was quickly lethal to rats at an air concentration of 5 volume %.30

Overall, the reported live animal toxicity testing performed in the course of anesthesia research provided 

useful guidance in evaluation candidate compound acute inhalation toxicities and aided early efforts to 

down-select and target compounds for further synthesis and testing. Efforts to identify suitable anesthesia 

agents confronted challenges similar to those of interest to the halon replacement community. Suitable

anesthesia agents for inhalation needed to be non-flammable and also have low acute toxicity. Low acute

toxicity attributes would preferably have included little tendency to induce cardiac arrhythmia. 

7.1.5 Summary: Alternative Agents and Selection Criteria Prior to the NGP 

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. In addition,

blends of HFCs and HCFCs, combinations of dry powders and fluorocarbons including jelled, agents 

were in various stages of either commercialization or SNAP approvals. The use of brominated 

compounds with short atmospheric lifetimes was under consideration for use in streaming applications 
The NGP Approach to New Chemicals Screening 623

and as replacements for halon 1301 in massive fire suppression applications such as protection of 

petroleum production facilities. An almost universal goal of all researchers was the demand by the halon 

user community for a drop-in replacement agent. 

The history of halon replacement development through the mid 1990s reflected concurrent progress in fire 

technology and basic environmental and atmospheric research areas. In a very real way, halon 

alternatives development in this era has the appearance of a sequential process of research-based 

discovery, environmental selection criteria revision followed by rejection of developed alternatives, and a 

resumption of applied research. 

The non-brominated and non-iodinated compounds under consideration were often in commercial use for 

other purposes. They all suffered from various shortcomings. While they were not ozone depleters 

because they did not have bromine or iodine in their structures, they did not have short atmospheric 

lifetimes, and in some cases had significant global warming potentials. Other common weaknesses 

included significantly higher boiling points, higher toxicity, and high flame extinguishment 

concentrations. The functional fire suppression related shortcomings were generally highlighted through 

comparison to halon 1301. 

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 limited risk assessments were performed. The applicability of the test involving 

epinephrine-challenged dogs was challenged, and the resulting discussion continues. Further, the lack of 

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

chemical selection process. 

Toward the end of the pre-NGP period, the concept arose of incorporating bromine in short atmospheric 

lifetime (tropodegradable) compounds as a means of achieving more aggressive flame suppression and 

hopefully reducing agent weight requirements. This desire lead to preliminary lists of potentially 

tropodegradable compounds. These incorporated molecular features susceptible to attack by atmospheric 

•OH or •H radicals or tropospheric ozone, photolysis by solar radiation, hydrolysis by atmospheric 

moisture, or sufficient polarity to dissolve in rain water. Retaining fluorine in the molecule in order to 

achieve non-flammability and to an extent to reduce boiling point was deemed essential. 

7.2 THE NGP APPROACH TO NEW CHEMICALS SCREENING 

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

broad in scope, covering nominally the world of chemistry. To ensure that the most optimal chemicals 

were identified efficiently, a comprehensive search and assessment of a broad array of chemical families 

and elements was performed. 

The 1997 statement of objectives of the nine-year NGP effort was to develop and demonstrate, by 2005, 

replacements for halon 1301 that were, retrofitable, economically feasible, environmentally acceptable 

and user-safe processes and techniques and fluids that meet the operational requirements currently 

satisfied by halon 1301systems in aircraft, ships, land combat vehicles, and critical mission support 

facilities. The results were to be specifically applicable to fielded weapons systems. By FY2000 this 

comprehensive goal was restructured and focused on aircraft alone. This change in targeted systems 

refocused chemical selection efforts on chemical families with the capability to address fire suppression 
624 Search for New Fire Suppressant Chemicals 

needs in the extreme low temperature conditions experienced by in-flight aircraft. As part of this 

refocused effort, NGP evaluations of agent low temperature dispersion, aircraft fire incidence and fire risk 

assessment were conducted. These studies are detailed in Chapters 2 and 8, and they significantly 

reduced the sole chemical selection boiling point criterion at a midway point in the Program. 

As noted in Chapter 6, these surveys typically began with an assessment of available literature 

information on physical properties, toxicity, and flame suppression. A second step involved estimation of 

these properties, where possible. Promising chemical families were subject to increased scrutiny, and in 

some cases representative compounds were obtained and flame suppression tests run. Where unusually 

interesting, and especially previously unexamined, chemical families were identified, limited mechanistic 

studies were performed and often individual projects were largely dedicated to their study. 

The criteria for further serious consideration of a compound as a candidate for suppression for in-flight 

aircraft fires were delineated in Chapter 6: 

• Cup burner flame extinguishment level measured or estimated to be below 5 volume %. To 

better this 5 volume % limit, a compound had to catalytically suppress combustion or have a 

high heat capacity. 

• Boiling points below about 20 °C. For fluids with slightly higher boiling points, similar 

fluids were considered to see if there might be a lower boiling member of the chemical 

family. 

• Inclusion of a chemical feature that rendered the chemical tropodegradable, i.e., likely to have 

a short atmospheric lifetime. 

• Absence of any toxicological data showing that serious effects on people could occur at a 

concentration lower than that needed to effect flame extinguishment. 

As the early NGP research progressed, some chemical families were found unsuitable, while others of 

promise were identified.37,38 About one-third of the way into the Program, the NGP performed a detailed 

analysis of the state of knowledge of the chemical families.39 The goal of this review was to identify 

chemical families still in need of scrutiny as potential flame suppressants and halon replacements, to list 

those chemical families for which sufficient knowledge existed to select the best candidates, and to 

identify those families unlikely to contain useable alternative fire suppressing chemicals. Allowance for 

otherwise desirable candidates with somewhat elevated boiling points was made. The available data for 

each family was reviewed and a consensus reached on chemicals for further investigation and those for 

which further study was not warranted. Priorities were divided into three groups, as shown in 

Table 7–11: 

• High Priority: Families that had not been extensively studied and for which there was high 

promise to yield one or more candidates. 

• Further Study: Families for which limited data indicated promise to yield one or more 

candidates. 

• Quick Look: Families that were relatively unstudied and whose potential was unclear or for 

which the cost of the compounds might prohibit a full study. 

Table 7–12 lists the wide range of chemical families for which further study was not recommended and 

the primary reasons for those decisions. 
The NGP Approach to New Chemicals Screening 625

Table 7–11. Chemical Families Selected for Further Study. 

Recommendation 

Chemical Family High Priority Further Study Quick Look 

Iodine containing alkanes and 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 

Phosphonitriles and Phosphorus halides X 

Copper containing Compounds X 

Manganese containing Compounds X 

Iron containing compounds X 

Tin containing compounds X 

Table 7–12. Chemical Families Not Pursued Further. 

Major Disqualifying Finding 

Chemical Family Well Studied 

Toxicity, Colligative 

Property or Other 

Drawback 

Suppression 

Efficiency or 

Flammability 

Brominated, chlorinated and fluorinated alkanes X 

Chlorinated alkenes X X 

Fluorinated alkenes X 

Alkynes X 

Iodinated ethers X 

Chlorinated ethers X 

Fluorinated ethers X 

Iodinated or chlorinated alcohols X 

Fluorinated alcohols X X 

Iodinated or brominated aldehydes & ketones X 

Chlorinated aldehydes & ketones X X 

Halogenated (I, Br, F) aromatics X 

Nitro compounds X X 

Nitrates, nitrites, nitroso compounds X 

Hexavalent sulfur X X 

Difluorosulfur compounds X 

Phosphines or pentacoordinate Phosphorus X 

Alkali metal or alkaline earth compounds X 

Boron and aluminum compounds X 

Titanium, antimony, germanium or silicon -

containing compounds X 
626 Search for New Fire Suppressant Chemicals 

A summary of the several broad survey efforts to identify chemical families with the potential to yield 

suitable effective and environmentally acceptable halon replacements is presented in the following 

sections. The material presented describes selection approaches, chemical family evaluations, and the 

limited testing done to confirm extinguishment performance. 

Separate presentations of the focused studies of fluoroalkyl phosphorus compounds and low boiling 

tropodegradable chemical families of flame suppression performance are located in Section 7.4. A 

limited presentation of work on phosphorus halide extinguishants such as PBr3 is discussed later in 

Section 7.3.5. A broad discussion of phosphorus and metal fire extinguishment chemistry is presented in 

Chapter 3 of this book. 

7.3 NGP SURVEYS OF INORGANIC CHEMICAL FAMILIES 

7.3.1 Main Group Elements - Group I 

The term “main group elements” is used to denote any elements other than transition metals. Figure 7–1 

represents a periodic table with the elements being considered in boldface. Note that carbon, oxygen, and 

the halogens may be (in some cases, are likely to be) present; however, such elements do not form the 

primary structural features of the compounds considered here. As noted earlier, some nitrogen 

compounds were examined in earlier work; others are discussed in section 7.4. Helium, neon, and argon 

were considered in their elemental form. Due to their toxicity, the radioactive elements were excluded. 

Though they were included, the Group I and Group II elements were unlikely to have utility as defined 

here since most compounds of these are solids. 

Group I elements comprise the alkali metals: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), 

cesium (Cs), and francium (Fr). The last element is radioactive and was not considered. Compounds of 

the alkali metals, in particular potassium and sodium salts, have long been used as fire extinguishing 

agents. A thorough review of the literature on fire extinguishment by compounds of the Group I elements 

has been prepared,40 and these elements have also been discussed in a report prepared for the USAF.20

These compounds were highly effective extinguishants but the suppression mechanism was uncertain. 

Extinguishment may be due to heat absorption, free-radical recombination on particulate surfaces, or 

homogeneous free-radical removal. Heat extraction did not account for the high extinguishment 

efficiencies of these elements. 

I II III IV V VI VII VIII

He

Li Be B C N O F Ne

Na Mg Al Si P S Cl A

K Ca Ga Ge As Se Br Kr

Rb Sr Transition Metals In Sn Sb Te I Xe

Cs Ba Tl Pb Bi Po At Rn 

Fr Ra

Figure 7–1. Groups and Elements Studied. 

Nearly all compounds of the Group I elements are solids at room temperature, and, therefore, past work 

has been on either dry chemical powders or aqueous solutions. Exceptions are some of the lithium alkyls, 
NGP Surveys of Inorganic Chemical Families 627

which are flammable. Some eutectic mixtures of alkali metal salts have melting points near room 

temperature; however, the vapor pressures are negligible. Studies have shown that aqueous solutions of 

some alkali metal compounds are extremely effective fire extinguishants,41 as are alkali metal powders 

(Chapter 4). However, these have been rejected for aircraft application due to their corrosion threat. 

Given the more mature state of knowledge and demonstrated effectiveness of sodium, potassium, and 

phosphorus based powders, any less efficient powders of other elements did not warrant consideration. 

7.3.2 Main Group Elements - Group II 

No flame extinguishment data have been found for compounds of beryllium. However, compounds of the 

other Group II elements (excluding, of course, radium) have been shown to have lower fire extinguishing 

efficacies than those of the Group I compounds. Since these Group II compounds are also solids, 

compounds of the Group II elements were not considered further. 

7.3.3 Main Group Elements - Group III 

Boron 

A number of boron compounds are gases or liquids; however, apparently without exception all are either 

flammable, highly toxic, or act merely as carriers where, as a part of the molecule, they bring halogen 

atoms into the combustion zone. The known gaseous and liquid boranes (boron hydrides) are flammable. 

Many of the simple halides, such as BF3, B2Cl6, etc., are highly unstable in the presence of moisture and 

are all highly toxic. 

Fire extinguishment testing using standard handheld extinguishers had shown that finely divided borax 

(Na2B4O7, degree of hydration not specified) was approximately equal to sodium bicarbonate in fire 

extinguishment effectiveness.42 The fire suppression efficiency of this compound may be due to the 

presence of sodium. 

Common flame retardants for fabrics and plastics are sodium borate pentahydrate (borax pentahydrate, 

Na2B4O7•5H2O), boric acid (B(OH)3, boric oxide (B2O3), disodium octaborate tetrahydrate 

(Na2B8O13•4H2O), ammonium pentaborate octahydrate [(NH4)2B10O16•8H2O], and the zinc borates (e.g., 

Zn4B12O22•7H2O).43 In an extensive study of boron compounds, sodium tetrafluoroborate (NaBF4), a 

solid, was the most effective single compound for reducing fabric flammability.44 These flame retardants 

are all solids. 

In this study, no liquid or gaseous boron compounds were found that have a reasonable toxicity and that 

are nonflammable. There was also no evidence that boron has any catalytic fire suppression capability. 

Aluminum 

Aluminum oxide trihydrate (Al2O3•3H2O) is a widely used fire retardant in elastomers,45 where it operates 

primarily by endothermic release of water to provide cooling. Gaseous aluminum chloride had been 

shown to be an effective inhibitor of premixed methane/air flames,46 and the dispersed powder effectively 

inhibited spark ignition of methane/air mixtures.47 This activity was probably due to the presence of 

chlorine rather than to the aluminum itself. To date, no evidence that aluminum has any catalytic fire 
628 Search for New Fire Suppressant Chemicals 

suppression capabilities has been presented. Moreover, the few gaseous or liquid aluminum compounds 

that exist have serious drawbacks (toxicity, flammability, and/or stability). 

Gallium, Indium, and Thallium 

No fire extinguishing studies have been reported for these three relatively rare elements. This may be due 

to the realization that toxicity would present a serious barrier to use of any thallium or indium compounds 

as extinguishants. 

7.3.4 Main Group Elements - Group IV 

Carbon 

Carbon is the structural core of organic compounds, which are discussed in Section 7.4. There is no 

reason to expect that solid carbon particles are effective fire suppressants, as they would act as fuel and 

oxidize to CO and CO2. It is possible that flame radiation absorption by particulate carbon may aid in 

suppression, but no evidence exists that carbon imparts any catalytic fire suppression capability. 

Silicon 

Silicon compounds have been examined in several projects,37,38,48,49 and there is little evidence that silicon 

offers any inherent fire suppression capabilities. The presence of silicon may, in some cases, offer 

desirable environmental (improved rain-out due to hydrolysis to polar species) and toxicological (through 

chemical decomposition) characteristics or physical properties. 

The chemistry of silicon compounds related to compounds of interest in the development of fire 

suppressants has been reviewed in detail.49

Due to the complexity of the syntheses, no attempt was made to prepare fluoroalkyl-containing silicon 

compounds during the NGP. Table 7–13 lists those silicon compounds selected for testing to obtain at 

least some baseline data.49 

Table 7–13. Silicon-containing Compounds. 

Chemical Name Formula Tb (°C) Flash Point, °C 

Silicon tetrachloride SiCl4 57.6 None 

Bromotrimethylsilane SiBr(CH3)3 79 32 

Silicon tetrabromide SiBr4 153 None 

Silicon tetrachloride (SiCl4) has a relatively low boiling point; however, this compound caused problems 

with the Standard NMERI Cup Burner. During the first test, the metering valve on the cup burner 

apparatus became increasingly difficult to adjust and finally froze. Upon disassembly, the valve and line 

leading to the valve were found to be clogged with particulate matter. It is likely that silicon dioxide was 

formed by hydrolysis. No further testing was attempted; however, with care, it is likely that the Modified 

NMERI Cup Burner could be used for this or similar compounds in the future. 
NGP Surveys of Inorganic Chemical Families 629

Bromotrimethylsilane (SiBr(CH3)3) was tested using the Modified NMERI Cup Burner. With a boiling 

point of 79 °C, this compound was relatively easily volatilized; however, the material is flammable. Two 

tests gave cup burner extinguishment concentrations of 2.3 volume %. As the flow of the compound was 

increased, there appeared to be some effect on the flame, although no distinct lifting of the flame off the 

fuel cup was observed. The flame wandered around, occasionally falling down the side of the cup. When 

the flow reached 0.043 g/s, the flame behaved erratically and traveled to the bottom of the chimney (to the 

glass beads). The flame in the fuel cup was extinguished, but the compound continued to burn on the 

surface of the glass beads. A small amount of the compound was found to sustain a flame. 

Silicon tetrabromide (SiBr4), as expected, was more effective than the other silicon compounds tested. 

The first test with the Modified NMERI Cup Burner gave an extinguishment concentration of 

2.0 volume %. During subsequent testing, however, serious problems with clogging of the syringe pump 

were encountered. Cleaning the syringe completely and repeating the test resulted in the same problem. 

This cast doubt on the extinguishment value of 2.0 volume % obtained in the first test. If the syringe 

were sticking, the measured flow would have been less than the actual flow, because the syringe pump 

was allowed to slip for safety. This would have resulted in a low cup burner value. 

Silicon Compound Fire Suppression Mechanism 

A past review of the chemistry and fire suppression properties of silicon compounds had been presented 

in Reference 49. Except as otherwise stated, all of the information presented here was newly acquired or 

is an expansion of information contained in that source. Of particular interest as fires suppressants were 

silicon-containing compounds with fluorinated alkyl groups. Fluoro-organosilicon polymers have been of 

some commercial interest.50

Many organosilicon materials are relatively stable, inert, have a low toxicity, and have lower atmospheric 

lifetimes than do closely related carbon compounds. This allows the incorporation of bromine in silanes 

and siloxanes without having unacceptably large ODP values. While silicon compounds without bromine 

do not appear to have significant fire suppression capabilities, the addition of bromine could provide a 

compound with good fire suppression capability while maintaining good environmental characteristics. 

Overall, there was little evidence that silicon itself plays a significant role in flame extinguishment, even 

though one could propose combustion free radical recombination cycles such as those in Reactions 

7-1 and 7-2, similar to those proposed for other metals.51

SiO• + •H + X → SiOH + X* (7-1)

SiOH + •H → H2 + SiO• (7-2)

The combustion and explosive properties of dichlorosilane (SiH2Cl2) have been thoroughly studied.52 

Polyorganosiloxanes and inorganic silicates have been examined as potential flame retardants.53 The 

major mode of reaction is the formation of protective surface coatings during a fire. The flammability of 

silicone polymers has been reduced through addition of fluorine, bromine, and CCl3 groups.54
630 Search for New Fire Suppressant Chemicals 

Claims have been made that liquid fire extinguishing compositions containing haloalkanes and cyclic 

polysiloxanes increase penetration and throw distance.55 However, there has been no claim that the 

silicon-containing compounds actually increase the intrinsic fire suppression capability. 

Silicon Compound Atmospheric Lifetime, ODP, and GWP 

Silicon, and other metalloids and metals, are known to be deposited in the upper atmosphere by meteors; 

however, it is believed that only the more polar metal oxides (e.g., sodium oxide) are likely to have any 

direct homogeneous chemical effect on atmospheric chemistry since these compounds have weak 

metal-oxygen bonds and can regenerate free atoms through photolysis and reactions with •O and •OH.56 

On the other hand, it must be recognized that silicon-containing particulates could play a significant role 

in heterogeneous atmospheric chemistry.57 The silicon-oxygen bond is quite strong compared with the 

sodium-oxygen bond in the simple diatomics (Si-O, 799.6 kJ/mole; Na-O, 256.1 kJ/mole).58 Thus, 

reactions proposed for ozone depletion by sodium (Reactions 7-3 and 7-4) are unlikely for ozone 

depletion by silicon.59 Sodium atoms generated in the atmosphere may also enhance ozone depletion by 

chlorine60 although it is not known whether similar enhancement by silicon takes place. Note, however, 

that since approximately 40 metric tons to 300 metric tons of metals are deposited daily by meteorites61

and since silicon is one of the more abundant elements in meteorites60 it is unlikely that anthropogenic 

silicon would produce a significant atmospheric effect in comparison to other sources. 

•Na + O3 → •NaO + O2 (7-3)

•NaO + •O → •Na + O2 (7-4)

Rate constants for reactions of some silicon compounds with •OH free radicals and estimated lifetimes 

based on those rate constants are presented in Table 7–14. 

Methane (CH4) has a rate constant of 0.0836 x 10-12 cm3

/molec-s at 298 K62, a value considerably smaller 

than that found for silane (SiH4). This is, however, undoubtedly due to the lower Si-H bond strength in 

SiH4 (bond strengths: H-SiH3, 384.1 kJ/mole; C-CH3, 438.9 kJ/mole).58 Of greater interest are rate 

constants for silicon-containing molecules with no Si-H bonds. 2,2-Dimethylpropane (C(CH3)4) has an 

•OH rate constant of 0.875 x 10-12 cm3

/molec-s at 298 K, which is slightly smaller than that of 

tetramethylsilane (Si(CH3)4). Unfortunately, other data allowing a direct comparison between C-H bond 

rate constants for carbon and silicon compounds were unavailable. Thus, there appeared to be no reason 

to assume that, in the absence of Si-H bonds, silicon compounds were inherently more reactive toward 

•OH than are carbon compounds. 

Maximum rate constants (no reaction observed) on the order of 10-21 cm3

/molec-s have been determined 

for the reaction of O3 with silicon-containing compounds.63 These data gave minimum estimated 

lifetimes of the order of 2500 days. Thus, there would be little, if any, removal by tropospheric ozone. 

In general, silicon compounds are considerably more unstable toward hydrolysis than are carbon 

compounds, and this property may provide an effective removal route for many of these materials. The 

Si-halogen bond hydrolyzes readily; however, the rapidity of this hydrolysis (and the resulting formation 

of toxic products) eliminates the consideration of compounds containing halogens bonded directly to 
NGP Surveys of Inorganic Chemical Families 631

silicon as fire suppressants (other than for basic laboratory studies). Compounds containing Si-H bonds 

also hydrolyze relatively easily when the pH is greater than 7, but are relatively stable in acidic solution. 

The alkoxy-Si bond is subject to hydrolysis and cleavage can cause condensation to higher polymers. 

Note, however, that this is highly dependent on the absence of steric hindrance. Alkoxy-substituted 

silanes with larger alkoxy groups are much more stable toward hydrolysis.64 Silanes containing only 

carbon bonded to silicon are relatively hydrolytically stable. 

Table 7–14. •OH Rate Constants for Silicon Compounds. 

Chemical Formula kOH, cm3/molec-s Atmospheric Lifetime, daysa

SiH4

b 12.2 x 10-12 0.97 

Si(CH3)H3

b 34.3 x 10-12 0.35 

Si(CH3)2H2

b 44.8 x 10-12 0.27 

Si(CH3)3Hb 26.7 x 10-12 0.45 

Si(CH3)4

b 1.09 x 10-12 10.9 

SiH4

c d

12.4 ± 1.9 x 10-12 0.96 

Si(C2H5)4

c e

75 x 10-12 0.16 

Si(CH3)4

f d

1.00 ± 0.09 x 10-12 11.9 

(CH3)3SiOSi(CH3)3

f d

1.38 ± 0.09 x 10-12 8.6 

[(CH3)2SiO]3

f d

5.2 ± 1.1 x 10-13 22.9 

[(CH3)2SiO]4

f d

1.01 ± 0.20 x 10-12 11.9 

[(CH3)2SiO]5

f d

1.55 ± 0.30 x 10-12 7.7 

(CH3)3SiOSi(CH3)2OHf d1.89 ± 0.36 x 10-12 6.3 

a Lifetimes estimated using globally averaged •OH model. 

b Personal communication from Dr. Paul Marshall, Department of Chemistry, University of North Texas, Denton, to Dr. Robert 

E. Tapscott, 27 May 1997. Values are at 295 K. 

c Reference 62 

d Value at 297 K 

e Value at 793 K 

f Reference 63 

Silicon compounds are expected to be more susceptible to photolysis than are the corresponding carbon 

compounds. The laser-induced photodissociation of silanes is one method used for vapor deposition of 

silicon films in the production of microelectronics.65

A few, scattered, and, in some cases suspect, lifetime and GWP data have been reported for siliconcontaining compounds.49 Siloxanes have been reported to have atmospheric lifetimes of from 10 days to 

30 days.66

It was concluded that silicon compounds are unlikely sources of stratospheric ozone depletion due to the 

presence of silicon only. When hydrogen atoms are present, limited data indicated effective removal by 

tropospheric •OH and short atmospheric lifetimes. Insufficient data were available to judge tropospheric 

removal and atmospheric lifetimes for silicon compounds containing no hydrogen, with one exception. 

Silicon compounds containing direct Si-halogen bonds hydrolyze rapidly and give short atmospheric 

lifetimes; however, such compounds were unsuitable for halon substitutes due to their expected high 

toxicity. Photolysis may be a potential route to atmospheric removal in some cases. Of particular interest 

was possible photolytic “synergism” when both silicon and bromine were present; however, no data 

existed to evaluate such “synergism.” Unfortunately, there were no atmospheric data for fully 

halogenated organosilicon compounds containing no Si-H or Si-halogen bonds (and, in particular, 
632 Search for New Fire Suppressant Chemicals 

compounds containing primarily fluorine as the halogen). Such compounds are unlikely to be removed 

rapidly by hydrolysis, rainout, or other processes, with the possible exception of photolytic 

decomposition. In summary, although there was no evidence that silicon compounds will have 

unacceptable global atmospheric environmental properties (e.g., unacceptable ODP, GWP, or lifetime), 

this may not be true for fully halogenated silicon compounds containing no Si-H or Si-halogen bonds. 

Finally, silicon compounds were expected to have few if any global atmospheric impacts. This may be 

the case even when bromine is present. There is, however, a real need for studies of the photochemistry 

of bromine-containing silicon compounds. 

Silicon Compounds - Toxicity 

Compounds containing silicon bonded to halogens are highly toxic owing to rapid hydrolysis of the 

silicon-halogen bond, although the inhalation toxicity of SiCl4 is moderate.67 Limited testing of industrial 

chemicals indicated that stable silane derivatives have a low toxicity. A number of siloxanes used 

industrially have a low toxicity.67

One paper not presented in Reference 39 reported that no toxic signs were found for four male rats to a 

single 6-hour exposure at 8000 μL/L or to 15 6-hour exposures at 1000 μL/L for tetramethylsilane, 

Si(CH3)4.

68 In the same study, 20 6-hour exposures of four female rats to diphenyldimethoxysilane, 

Si(C6H5)2(OCH3)2, at its saturation vapor pressure showed no adverse effects. 

A recent EPA final action on significant new uses listed potential toxicity hazards for a number of silicon 

compounds.69 The final rule stated that alkoxysilanes can cause lung toxicity and severe irritation to skin, 

eyes, and mucous membranes. Of particular interest is the finding that “Based on analogy to 

alkoxysilanes and perfluoro compounds,” Si(OCH3)3(CH2CH2CF2CF2CF2-CF2CF2CF2CF2CF3) may cause 

lung toxicity, irritation to mucous membranes, liver toxicity, blood toxicity, immunosuppression, and 

reproductive toxicity. In part, this finding may have been due to the analogy between the fluoroalkyl 

chain and some HFCs; it may have had little or nothing to do with the silicon atom. 

There is only a relatively small amount of toxicity data available for the silicon compounds of primary 

interest here (compounds containing halogenated alkyl groups and no direct Si-halogen bonds). In 

general, siloxanes have moderately low toxicities. Alkoxy-containing silicon compounds could cause 

irritation to skin, eyes, and mucous membranes. The presence of Si-halogen bonds is expected, in all 

cases, to cause severe toxicity problems due to hydrolysis with formation of hydrohalic acids. Such 

compounds are probably unacceptable as halon substitutes. 

Silicon Compound Chemistry 

Silicon chemistry has been the subject of a number of relatively recent reviews (e.g., the papers in 

Reference 70); however, the number of nonflammable silicon compounds that can be considered for 

halon replacement is small. 

Silicon compounds offer relatively little promise. The silicon itself contributes little to fire suppression 

effectiveness, and many of the most interesting compounds (e.g., those containing bromofluoroalkyl 

and/or fluoroalkyl groups) have been difficult to synthesize. Of particular concern was the instability of 

compounds containing -CF3 groups immediately adjacent to the silicon atom, and such compounds were 
NGP Surveys of Inorganic Chemical Families 633

not considered further. Compounds in which -OR and/or -OCF2Br groups are attached to the silicon atom 

have low volatility and high viscosity. 

A series of bromoalkylsilanes were prepared in a two-step synthesis from a halomethane and a 

bis(trimethylsilyl)amide.71 The preparation is shown in Reactions 7-5 and 7-6, where “M” is sodium or 

potassium and “R” is a nonfluorinated (compounds containing fluorine on a carbon atom adjacent to 

silicon are usually unstable) haloalkyl group. 

(M+ [(CH3)3Si]2N-) + RH → [(CH3)3Si]2NH + (M+ R-) (7-5)

(M+ R-) + (CH3)3SiCl → (CH3)3SiR + MCl (7-6)

The reaction of trialkylchlorosilane (SiClR3) with chlorotrifluoroethene (CClF=CF2) allowed the 

synthesis of a number of trifluorovinylsilanes (CF2=CFSiR3).72 Bromination or hydrobromination of the 

double bond may permit the formation of the compounds CBrF2CBrFSiR3, CBrF2CHFSiR3, and 

CHF2CBrFSiR3. 

A series of tetra(fluoroalkoxy)silanes (Si(OR)4) have been prepared by reaction of the appropriate 

fluorinated alcohol with silicon tetrafluoride (SiF4).73 All of the compounds are liquids at room 

temperature, Table 7−15; the melting points are low, (less than -68 °C except for Si(OCH2CF3)4). 

However, the boiling points and viscosities are high. One major problem with such alkoxy compounds is 

that they hydrolyze readily and then polymerize. 

Table 7–15. Tetra(fluoroalkoxy)silanes. 

Chemical Name Formula Tb °C (kPa) 

Liquid 

density 

g/mL (°C) 

Liquid 

viscosity, 

20 °C (cp)

Tetrakis(2,2,2-trifluoroethoxy)silane Si(OCH2CF3)4 155.5 to 157 

(99) 

1.5107 

(20) 

2.2089 

Tetrakis(2,2,3,3-tetrafluoropropoxy)silane Si(OCH2CF2CHF2)4 117 to 118 

(0.5) 

1.5927 

(20) 

18.92 

Tetrakis(2,2,3,3,4,4,4-

heptafluorobutoxy)silane 

Si(OCH2(CF2)2CF3)4 96 to 97 

(0.5) 

1.5740 

(71.1) 

7.613 

Tetrakis(2,2,3,3,4,4,5,5-

octafluoropentoxy)silane 

Si(OCH2(CF2)3CHF2)4 156 to 159 

(0.3) 

1.8150 

(20) 

42.75 

Tetrakis(2,2,3,3,4,4,5,5,6,6,7,7-

dodecafluoropentoxy)silane 

Si(OCH2(CF2)5CHF2)4 201 to 204 

(0.4) 

1.7181 

(71.1) 

108.8 

Tetrakis(2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9-

hexadecafluorononoxy)silane 

Si(OCH2(CF2)7CHF2)4 a

235 to 240 

(0.3) 

Not 

reported 

Not 

reported 

a With decomposition. 

Overall it was determined that there was insufficient basis for continued consideration of silicone-based 

compounds as halon replacements.39
634 Search for New Fire Suppressant Chemicals 

Germanium, Tin, and Lead 

The only germanium compound studied as a fire extinguishant was germanium tetrachloride, GeCl4,

74

whose extinguishing capability was primarily due to the presence of the chlorine atoms. On the other 

hand, there is evidence of strong chemical inhibition for compounds of tin and lead (Chapter 3). Thus, 

lead tetra-acetate (Pb(CH3COO)4) and lead acetylacetonate, Pb(CH3C(O)CHC(O)CH3)2), neither of which 

contain halogens, are effective extinguishants.75 A catalytic mechanism has been proposed for fire 

extinguishment by tin.76 A recent paper presented results indicative of a weak catalytic flame suppression 

action by tin compounds.77

Despite the scattered indications of catalytic effects for compounds of the heavier Group IV elements, 

germanium is too costly to be considered, and tin and lead are environmentally unacceptable as well as 

toxic to animals. Heavy metal toxicity is a well recognized and extensively documented environmental 

concern. 

7.3.5 Main Group Elements - Group V 

Inorganic Nitrogen 

The chemistry and flame suppression of nitrogen compounds (with an emphasis on fluoroalkyl amines) 

was discussed in earlier work performed under the NGP.37,38 One cycle that has been proposed to 

catalyze recombination of hydrogen atoms and hydroxyl free radicals is given in Reactions 7-7 through 

7-9.78 The NO cycle, however, appears to be relatively inefficient.79

H + NO + M → HNO + M* (7-7)

H + HNO → H2 + NO (7-8)

HNO + OH → H2O + NO (7-9)

Inorganic Phosphorus 

A search of the Chemical Abstracts Database for the key words “flame,” “fire,” and “flammable” coupled 

with “phosphonitriles” and related terms yielded 366 references, nearly all of which were for fire 

retardants for polymers. These included reviews of cyclo- and polyphosphazenes as fire retardants and as 

fire resistant materials.80,81

The mechanisms of fire retardancy of solids by phosphorus-containing compounds have been studied for 

decades.82 Depending on the specific compound and the host polymer, these additives act in the gas 

and/or condensed phases.83 The details of the mechanism are still debated, as evidenced in papers 

presented at the annual Business Communications Company (BCC) Conference on Flame Retardancy. 

Phosphorus and bromine behave as synergistic flame retardants, and the greatest synergism appears to be 

when the two elements are combined in the same molecule.84,85 It has been proposed that in polyesters, 
NGP Surveys of Inorganic Chemical Families 635

compounds containing both phosphorus and bromine act in two separate roles as flame retardants.86 The

work cited indicated that the phosphorus induced formation of aromatic residues and char, which reduced

the transport of gases to the flame. The bromine was believed to reduce the overall oxidation rate, 

reducing the heat transported back to the solid. 

The preparation of halogenated triaryl phosphines as flame retardants has been reported.87 An example is 

shown in Reactions 7-10 and 7-11 for tris(parachlorophenyl)phosphine (solid, melting point 106 °C). A 

number of phosphonium salts have also been prepared, as shown in Reaction 7-12, where R1, R2, and R3

are various alkyl and aryl groups. All of these materials are solids. 

Cl Br ⎯⎯ → ⎯, ⎯2 ⎯( ⎯⎯⎯⎯⎯)

2

Mg Et O anhydrous

N atmosphere

Cl MgBr

(7-10)

Cl MgBr + PCl3 → P

3

Cl (7-11)

BrH2C CH2Br

CH2

Br

 + P(R1R2R3)3 → 3Br

-

CH2PR1R2R3

+

CH2PR1R2R3

+

+

R1R2R3PCH2

(7-12)

Resorcinol bis(diphenyl phosphate) (Figure 7–2, n = 1 to 8), a polymeric material containing no halogen,

has been reported to act as a flame retardant additive.88 The material, which is made from phosphorus 

oxychloride, resorcinol, and phenol, is a colorless to light yellow liquid with a viscosity of 600 cp at room

temperature and 100 cp at 55 °C. 

Figure 7–2. Resorcinol. 

n 

P P 

O O 

O O 

P h O 

P h O O Ph

O P h 

Phosphorus-containing groups have been incorporated directly onto polymeric molecules rather than 

using phosphorus additives to provide flame retardancy. Fire resistant organosilicon polymers have been

prepared by incorporation of phosphazenes.89 Resins containing melamine combined with

triethylphosphate and dimethylmethylphosphonate have been reported as flame retardants.90 A number of 

compounds containing vinyl groups attached to phosphorus have been prepared to permit copolymer 

formation (e.g., Figure 7–191). It is believed that when incorporated directly into a polymer, these 

materials provide flame retardancy primarily by char formation. 
636 Search for New Fire Suppressant Chemicals 

O O

P

O

O O

P

O

Figure 7–3. Vinyl Phosphonates. 

The large variability in toxicity of phosphorus compounds and the possibility of cholinesterase inhibition

raised toxicity concerns with these compounds. In general, their toxicity decreases as the oxidation state 

of the phosphorus increases, i.e., phosphines are generally the most toxic and phosphates are the least 

toxic. Phosphonitriles appear to have relatively low toxicities, but mutagenicity may be of concern. 

Compounds with phosphorus-halogen bonds are probably unacceptable as halon substitutes. Phosphorus 

chemistry has been the subject of a number of relatively recent reviews (e.g., the papers in Reference 92); 

however, most of this work has been on nonvolatile or flammable chemicals. 

Chapter 3 and Reference 93 provide good overviews of phosphorus chemistry as it applies to chemicals of 

interest as fire suppressants. A review of NGP testing of phosphorus compounds is consolidated in 

Section 7.4.4.

Phosphonitriles 

Among the phosphorus compounds, phosphonitriles have been of primary interest as replacement fire 

suppressants in the past; however, there are relatively few that have sufficiently high volatility to replace 

halon 1301. There may, however, be some interest in using these materials in carriers for some 

applications. 

The linear phosphonitriles, for which preparations have been reported,94 are considerably more reactive 

than the cyclic compounds, particularly toward hydrolysis.95 This makes them somewhat less attractive 

than the cyclic materials for study as halon 1301 replacements. The reactivity of the 3-membered ring

system P3N3Cl6 toward chloride exchange is lower than that of the four-membered and larger cyclics.96

Of particular interest are the fluorinated phosphonitriles. Fluorination normally occurs as geminal 

substitution; however, procedures for making nongeminal derivatives have been reported.97 Although a

number of chloro- and fluoro-substituted bis(dimethylamino)-cyclotriphosphonitriles have been reported98

most of these are solids. The fluoro-substituted bis(dimethylamino)cyclotriphosphonitriles compound,

Figure 7–4, is however, a liquid. 

Bromine-containing phosphonitriles are of some interest due to the potential for fire extinguishment 

contribution by bromine and for possible synergism between bromine and phosphorus. The fully

brominated compounds are solids or oils

99 and are, therefore, unlikely to be appropriate for investigation

as fire extinguishants, though they may have other uses (e.g., flame retardants). Crown ether complexes

have been used to prepare the highly colored solid compound NP2Br9 from KBr and

hexachlorocyclotriphosphonitrile (P3N3Cl6).100 This compound can then be heated to form the more 

stable NP2Br7. Structures have not been published for either of these materials. The preparation of mixed
NGP Surveys of Inorganic Chemical Families 637

fluorine- and bromine-substituted phosphonitriles by reaction of silver fluoride with P3N3Br6 have been 

reported,101 but the chemical and physical properties were not given.

N

P 

N

P 

N

P 

C l 

F F 

N(CH3)2

C l 

(CH3)2N 

Figure 7–4. Example of a Fluoro-substituted 

Bis(dimethylamino) Cyclotriphosphonitrile. 

Mixed methyl- and fluorine-substituted phosphonitriles have been prepared by reaction of 

octafluorocyclotetraphosphonitrile with methyl lithium.

102,103 The compounds are high boiling liquids and

solids. Derivatives with tert-butyl and n-butyl substituents104,105 and with 1- and 2-propenyl substituents

106

have also been reported. 

Acquired phosphonitriles were reported to have attractively low cup burner flame extinguishment 

concentrations (Table 7–16).93 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 also shown very good extinguishments characteristics. 

Table 7–16. Phosphonitrile Flame Extinguishment 

Chemical Formula Cup Burner Extinguishing (volume %)

P3N3F6 1.08 ± 0.07

P3N3ClF5 0.91 ± 0.02

P3N3Cl2F4 0.96 ± 0.08

Phosphoranes 

A number of fluorophosphoranes (pentacoordinate phosphorus(V) compounds), including some aminosubstituted products have been described.107,108 Although all of these contain phosphorus-fluorine bonds

(making them unlikely candidates as halon replacements), the boiling points are in the acceptable range 

for a number of compounds. Unfortunately, none of the alkyl derivatives in the sources cited was

fluorinated. 

Phosphorus Halides 

As shown in Table 7–17, some of these compounds are four to eight times as efficient as halon 1301 as 

flame suppressants. However, the boiling points are too high for aircraft use, except perhaps PF3. 

Moreover, the toxicity and corrosiveness of these compounds is expected or known to be high. 

Nonetheless, it would be useful to examine the possibly more stable, totally fluorinated compounds, PF3

and O=PF3. 
638 Search for New Fire Suppressant Chemicals 

Table 7–17. Phosphorus Halide Flame Extinguishment. 

Chemical Formula Tb (°C) Efficiency Relative to Halon 1301 

PCl3 75 6.7, 6.9 

PBr3 173 4.6, 6.9 

PF2Br 23.9 

PF3 16.5 

O=PCl3 34.4 5.2 

O=PF2Br 32 

S=PCl3 8 

S=PBr3 6.7, 6.9 

Phosphorus-containing Compounds – Atmospheric Lifetime, ODP, and GWP 

The effect of phosphorus on stratospheric ozone has not been reported. A general cycle that may enable 

ozone depletion by phosphorus is shown in Reactions 7-13 and 7-14. Note, however, that the large 

stability and expected reluctance to add additional oxygen atoms make •PO3 and higher oxides unlikely 

candidates for direct participation in ozone depletion. •NO3 is known to photolyze sufficiently rapidly 

that at least some possible reactions are believed to be insignificant in atmospheric chemistry, and the 

higher oxides of phosphorus are likely to photolyze even more rapidly.109

•POx + O3 → •POx+1 + O2 (7-13)

•POx+1 + •O → POx + O2 (7-14)

Nitrogen oxides are believed to deplete stratospheric ozone by the reactions shown in Reactions 7-15 

through 7-17.110 Here and elsewhere in this chapter, enthalpies of reaction (∆Hr) and free energies of 

reaction (∆Gr) were calculated from standard enthalpies of formation (∆Hf) and standard free energies of 

formation (∆Gf) at 298.15 K taken from Reference 111 unless otherwise indicated. By analogy, one 

might propose Reactions 7-18 and 7-19 for ozone depletion by phosphorus. Reaction 7-18 is highly 

exothermic and has been proposed as the cause for the chemiluminescence observed for the reaction of 

ozone with phosphine.112 Here, however, the relatively large O-PO bond dissociation enthalpy 

(calculated as 540 kcal/mol from the standard enthalpies) compared to the O-NO bond dissociation 

energy (306 kJ/mole) makes the second reaction in the cycle (Reaction 7-19) unfavorable at 298.15 K. 

The higher stability of phosphorus dioxide can be seen from the total enthalpy of 1129 kJ/mole for 

dissociation of PO2 into its constituent atoms compared with the calculated value of 938 kJ/mole for NO2. 

•NO + O3 → •NO2 + O2, ∆Hr = -200 kJ/mole, ∆Gr = -199 kJ/mole (7-15)

•NO2 + •O → •NO + O2, ∆Hr = -192 kJ/mole, ∆Gr = -196 kJ/mole (7-16)

Net: •O + O3 → 2O2, ∆Hr = -392 kJ/mole, ∆Gr = -395 kJ/mole (7-17)
NGP Surveys of Inorganic Chemical Families 639

•PO + O3 → •PO2 + O2, ∆Hr = -435 kJ/mole, ∆Gr = -433 kJ/mole (7-18)

•PO2 + •O → •PO + O2, ∆Hr = 42 kJ/mole, ∆Gr = 38 kJ/mole (7-19)

An alternative mechanism is described in Reactions 7-20 and 7-21, where the second reaction is again 

distinctly unfavorable. This cycle is similar to the chlorine ozone depletion cycle in Reactions 7-22 and 

7-23. Here, again, the large phosphorus-oxygen bond strength is an obstacle. The bond strength in 

diatomic PO is 599.1 kJ/mole compared with 269 kJ/mole for •ClO.58

•P + O3 → •PO + O2, ∆Hr = -483 kJ/mole, ∆Gr = -490 kJ/mole (7-20)

•PO + •O → •P + O2, ∆Hr = 91 kJ/mole, ∆Gr = 95 kJ/mole (7-21)

•Cl + O3 → •ClO + O2, ∆Hr = -163 kJ/mole, ∆Gr = -171 kJ/mole (7-22)

•ClO + •O → •Cl + O2, ∆Hr = -229 kJ/mole, ∆Gr = -224 kJ/mole (7-23)

Bromine and chlorine jointly provide a highly effective mechanism for stratospheric ozone depletion 

through a cycle of Reactions 7-17 and 7-24 through 7-26.113 Here, ∆Hf and ∆Gf for •BrO were taken from 

Reference 58. A similar cycle can be proposed for phosphorus by coupling Reactions 7-20, 7-24, and 

7-27. The free energy change for Reaction 7-27, however, is very large, positive, and, thus, unfavorable. 

•Br + O3 → •BrO + O2, ∆Hr = -129 kJ/mole, ∆Gr = -137 kJ/mole (7-24)

•ClO + •BrO → •Cl + •Br + O2, ∆Hr = 6 kJ/mole, ∆Gr = -18 kJ/mole (7-25)

Net: 2O3 → 3O2, ∆Hr = -285 kJ/mole, ∆Gr = -326 kJ/mole (7-26)

•PO + •BrO → •P + •Br + O2, ∆Hr = 326 kJ/mole, ∆Gr = 301 kJ/mole (7-27)

The analysis presented above provides a strong indication that any ozone depletion must involve reaction 

of O3 with •PO (e.g., Reactions 7-18 and 7-19). The phosphorus-oxygen bond in this diatomic molecule 

is too strong to allow formation of significant concentrations of atomic phosphorus. As noted above, 

however, the second reaction in the cycle (Reaction 7-19) is unfavorable at 298.15 K. The minimum 

stratospheric temperature (at the tropopause) varies from approximately 193 K to 223 K depending on the 

latitude, and the maximum stratospheric temperature (at the mesopause) is approximately 285 K 

depending on the season and latitude.114 Data from the JANAF tables111 indicate that the reaction 

becomes even less favorable (∆Hr and ∆Gr both become more positive) as the temperature decreases from 

298.15 K. A major question is how fast •PO is removed by reaction with O3 (Reaction 7-18) before it 

reacts with O2 (the reverse of Reaction 7-19). Ozone concentrations vary widely in the stratosphere; 

however, we can take the concentration of ozone in the stratosphere to be approximately 
640 Search for New Fire Suppressant Chemicals 

1010 molecules/cm3 to 1011 molecules/cm3 compared to a maximum of around 109 molecules/cm3 for 

•O(3

P).i,115,116 Thus, the mixing ratio (the ratio to air) for •O(3P) is calculated as approximately 1 μL/L in 

the stratosphere. This implies that Reaction 7-19 would lie far to the left and that the concentration of 

•PO would be small. 

Missing, of course, from this analysis is an assessment of kinetics for Reactions 7-18 and 7-19. Also 

missing is any discussion of other reactions of •PO and •PO2, both of which are highly polar and are 

likely to be absorbed onto ice crystals. Despite the shortcomings of this analysis, it is obvious that 

stratospheric ozone depletion by phosphorus-containing compounds is very unlikely. 

Relatively few data are available on atmospheric lifetimes for phosphorus compounds. Atkinson has 

reported the rate constants for several phosphorus compounds,117 and these are shown in Table 7–18 

along with atmospheric lifetimes estimated from the globally averaged tropospheric •OH concentration. 

Very limited data indicate that the presence of a phosphorus atom increases •OH reactivity. Thus, for 

example, methane (CH4) has a rate constant of 0.0836 x 10-12 cm3

/molec-s at 298 K,117 a value 

considerably smaller than that found for phosphine (PH3), even though methane has one more reactive 

site (i.e., one more hydrogen atom). The activation energy for hydrogen atom abstraction decreases (as 

expected) with decreasing dissociation energy of the M-H bond, and this undoubtedly explains the higher 

rate constant for PH3 (bond strengths: H-PH2, 351.0 kJ/mol; C-CH3, 438.9 kJ/mol).58,118,119 It is difficult 

to compare compounds with and without phosphorus and containing hydrogen bonded only to carbon, 

since there are no isostructural compounds. The rate constant of 3.92 x 10-12 cm3

/molec-s at 298 K for 

2,2-dimethoxypropane (C(CH3)2(OCH3)2) is smaller than that of trimethylphosphate ((CH3O)3PO), which 

has three fewer hydrogen atoms. The rate constant of 11.7 x 10-12 cm3

/molec-s at 298 K for 

2,2-diethoxypropane (C(CH3)2(OC2H5)2) is smaller than that of triethyl phosphate ((C2H5O)3PO), which 

has nearly the same number of hydrogen atoms.117 Since the predominant mechanism for reaction with 

the compounds in Table 7–18 appears to be hydrogen atom abstraction117 it may be that a decreased bond 

strength accounts for the possibly higher reactivity for phosphorus-containing compounds; however, bond 

strength data to confirm this are lacking. 

Table 7–18. Rate Constants •OH Reactions With Phosphorus Compounds. 

Chemical Formula k2 at 297 K, cm3/molec-s Estimated Tropospheric Lifetime, days 

PH3 13 ± 3 x 10-12 0.9 

(CH3O)3PO 7.37 ± 0.74 x 10-12 1.6 

(C2H5O)3PO 55.3 ± 3.5 x 10-12 0.2 

(CH3O)2P(O)SCH3 9.29 ± 0.68 x 10-12 1.3 

(CH3S)2P(O)OCH3 9.59 ± 0.75 x 10-12 1.2 

(CH3O)3PS 69.7 ± 3.9 x 10-12 0.2 

(CH3O)2P(S)SCH3 56.0 ± 1.8 x 10-12 0.2 

(CH3O)2P(O)N(CH3)2 31.9 ± 2.4 x 10-12 0.4 

(CH3O)2P(S)N(CH3)2 46.8 ± 1.4 x 10-12 0.3 

(CH3O)2P(S)NHCH3 233 ± 15 x 10-12 0.05 

(CH3O)2P(S)NH2 244 ± 9 x 10-12 0.05 

(CH3O)2P(S)Cl 59.0 ± 3.8 x 10-12 0.2 

 

i

 The concentration of oxygen atoms in other than the 3P ground state would be even smaller. 
NGP Surveys of Inorganic Chemical Families 641

Phosphorus compounds studied to date are quite unreactive toward ozone. An upper limit of 

6 x 10-20 cm3

/molecules has been determined for reaction of trimethylphosphate ((CH3O)P=O) with ozone 

at 296 K.120 Using a globally averaged tropospheric ozone concentration, one estimates from this value a 

minimum lifetime of 386 days for reaction of trimethylphosphate with tropospheric ozone. Atkinson has 

reported rate constants with upper limits on the order of 10-19 at 296 K to 298 K for gas-phase reactions of 

O3 with phosphorus-containing compounds, giving estimated minimum lifetimes of around 200 days. In 

none of these cases was a reaction observed.121

It is likely that many phosphorus compounds are sufficiently polar that rainout is an important 

tropospheric removal mechanism. Atmospheric hydrolysis is possible for phosphonitriles containing 

direct P-halogen bonds even when the halogen is fluorine, and this is likely to be an effective tropospheric 

removal mechanism for such compounds. Photolysis is more important for compounds containing 

phosphorus than for corresponding carbon compounds; however, insufficient data are available to 

determine whether photolysis provides effective atmospheric removal. 

No rigorous calculations of atmospheric lifetimes or GWPs of phosphorus-containing compounds have 

been reported. A 3 day lifetime has been estimated for trimethylphosphate based on the rate constant for 

reaction with •OH.120 This value differs slightly from that given in Table 7–18 due to the use of a slightly 

different globally averaged •OH. 

In summary, phosphorus compounds are unlikely sources of stratospheric ozone depletion due to the 

presence of phosphorus only. When hydrogen atoms are present, limited data indicate effective removal 

by tropospheric •OH and short atmospheric lifetimes. Insufficient data are available to judge tropospheric 

removal and atmospheric lifetimes for phosphorus compounds containing no hydrogen; however, it is 

likely that rainout and/or hydrolysis will give short atmospheric lifetimes. In summary, there is no 

evidence to suggest that phosphorus compounds will have unacceptable global atmospheric 

environmental properties (i.e., unacceptable ODP, GWP, or lifetime). 

Toxicity of Phosphonitrilic Compounds 

A general review of the toxicity of phosphorus compounds is also accessible in Reference 93. One 

concern is that a number of phosphorus compounds (particularly phosphite esters) are cholinesterase 

inhibitors. The following summarizes results from tests of this particular class of compounds. 

Hexakis(2,2,2-trifluoroethoxy)cyclotriphosphazene toxicity: An acute oral toxicity assessment utilizing 

male and female Fischer 344 rats and genotoxicity testing utilizing the Ames assay has been performed on 

hexakis(2,2,2-trifluoroethoxy)cyclotriphosphazene (P3N3(OCH2CF3)6).122 No deaths or signs of toxic 

stress were observed in any of the rats orally dosed at the limit test value of 5 g of P3N3(OCH2CF3)6 per 

kg body weight. Body weights of the male rats during the subsequent 14 day observation period appeared 

unaffected by treatment. In the Ames assay, P3N3(OCH2CF3)6 produced no mutagenicity (base-pair 

substitution or frameshift mutation) in the bacterial (Salmonella) system. In summary, P3N3(OCH2CF3)6

produced no toxicity via the oral route of administration and was determined not to be genotoxic. 

Phosphonitrilic Chloride Compounds (Chlorophosphazene): In 1979, Ethyl Corporation submitted to the 

U. S. Environmental Protection Agency (EPA) the results of in vitro and in vivo studies on two similar 

phosphonitrilic chloride compounds, each with the same CAS (Chemical Abstracts Service) No. 

(25034-79-1). In all, there were 16 reports, each covering a separate toxicological test for each compound: 
642 Search for New Fire Suppressant Chemicals 

a. In vitro mammalian cell transformation assay.123,124

b. In vitro mammalian cell transformation assay in the presence of exogenous metabolic 

activation assay.125,126 

c. In vivo mammalian cell point mutation assay.127,128 

d. In vitro mammalian cell point mutation assay in the presence of exogeneous 

metabolic activation assay.129,130 

e. In vivo cytogenetic assay in rodents for mutagenicity.127

f. Salmonella/Microsomal assay for bacterial mutagenicity assay.131,132 

g. Differential inhibition of repair deficient and repair competent strains of Escherichia 

Coli: DNA (deoxyribonucleic acid) repair assay.133,134 

h. Dominant lethal assay in rodents for mutagenicity assay.135,136

Table 7–19 paraphrases the results of the eight toxicity tests for each compound. Due to the limited 

solubility of the test compounds in vehicles compatible with mammalian cell culture systems, it was 

difficult to establish the exact concentration of the chemical in solution for the in vitro tests, a problem 

noted in the reports cited. 

Table 7–19. Toxicity Studies of Chlorophosphazenes. 

3899-A 3899-B 

In Vitro Mammalian Cell Transformation Assay

a. Although the cytotoxicity tests were not 

reproducible in showing the toxic effects of the test 

compound with target cells, a dose response effect 

was observed in each of the cytotoxicity studies. 

b. The test compound was incapable of inducing 

morphological transformants (Type III foci) in the 

BALB/3T3 clone A31 cell system. 

a. The cytotoxicity studies demonstrated a dose 

response effect. 

b. The test chemical was demonstrated to be positive 

in producing a Type III foci at 60 μg/mL 

concentration. Relative to solvent (acetone), the 

number of morphologically transformed (Type III) 

foci present at this concentration was statistically 

significant (P<0.05). 

In vitro Mammalian Cell Transformation Assay in the Presence of Exogenous Metabolic Activation

a. Cytotoxic effects of the test agent appeared to 

increase in the presence of an exogeneous source of 

metabolizing activity (S-9). 

b. The test chemical was effective in inducing 

morphological transformation (Type III foci) at the 

30 μg/mL concentration. Relative to the negative 

control, the number of morphologically 

transformants per number of cells at risk at the 30 

μg/mL concentration was not statistically 

significant (P>0.05). 

a. Cytotoxic effects of the test agent appeared to 

increase in the presence of an exogeneous source of 

metabolizing activity (S-9). 

b. The test chemical was effective in inducing 

morphological transformation (Type III foci) in the 

BALB/3T3 Clone A31 cell system at all 

concentrations employed. 

In Vitro Mammalian Cell Point Mutation Assay

a. Although the cytotoxicity tests were not 

reproducible in showing the toxic effects of the test 

compound with target cells, a dose response effect 

was observed in each of the cytotoxicity studies. 

b. The test compound was incapable of inducing 

ouabain-resistant colonies at all of the doses tested. 

a. The cytotoxicity tests demonstrated a dose response 

effect. 

b. The test chemical was incapable of inducing 

ouabain-resistant colonies at all concentrations. 
NGP Surveys of Inorganic Chemical Families 643

3899-A 3899-B 

In Vitro Mammalian Cell Point Mutation Assay with Exogenous Metabolic Activation

a. Cytotoxic effects of the test agent appeared to 

increase in the presence of an exogenous source of 

metabolizing activity (S-9). 

b. The test chemical was ineffective in inducing 

ouabain-resistant colonies in the BALB/3T3 Clone 

A31 cell system at all concentrations employed. 

a. The cytotoxic effects of the test agent appeared to 

increase in the presence of an exogenous source of 

metabolizing activity (S-9). 

b. The test chemical was ineffective in inducing 

ouabain-resistant colonies at all concentrations 

employed. 

In Vitro Cytogenetic Assay in Rodents for Mutagenicity

 The test compound exhibited little or no clastogenic 

activity. No dose response was observed. Under 

the conditions of this test, the data suggest that the 

test compound exhibits little or no mutagenic 

activity. 

 The test compound exhibited moderate clastogenic 

activity. A dose response was observed. Under the 

conditions of this test, the data suggest that the 

compound exhibits mutagenic activity. 

Dominant Lethal Assay in Rodents for Mutagenicity

 Test compound appeared to exhibit minimal 

activity in total implantations, number of live 

implantations per pregnant female, and preimplantation losses. No significant dose response 

was observed and little or no mutagenic activity in 

the dominant lethal test. 

 Test compound appeared to exhibit minimal 

activity in total implantations, number of live 

implantations per pregnant female, and preimplantation losses. No significant dose response 

was observed and little or no mutagenic activity in 

the dominant lethal test. 

Salmonella/Microsomal Assay for Bacterial Mutagenicity

a. The test agent did not induce a significant increase 

in the number of point mutations in Salmonella

typhimurium strains in the absence of activating 

system for strains TA1535, TA1537, TA1358, 

TA100, and TA98. 

b. It did not induce a significant increase in the 

number of point mutations with the addition of an 

exogenous source of liver enzymes for metabolic 

activation in strains of TA1535, TA1537, TA1358, 

TA100, and TA98. 

a. Test agent did not induce significant increase in 

number of point mutations in Salmonella

typhimurium strains in the absence of activating 

systems for TA1535, TA1537, TA100, TA98. 

b. Induced a significant increase in the number of 

point mutations in the absence of the activating 

system for strain TA1538. 

c. Did not induce a significant increase in the number 

of point mutations with the addition of an 

exogenous source of liver enzymes for activation. 

Differential Inhibition of Repair Deficient and Repair Competent Strains of 

Escherichia Coli (E. coli): DNA Repair

 The test chemical did not produce a statistically 

significant difference in its ability to produce cell 

death between repair deficient (polA-

) and repair 

competent (polA+

) strains in E. coli. 

 Test chemical produced statistically significant 

difference at 2 μL per plate in production of cell 

death between repair deficient (polA-

) and repair 

competent (polA+

) strains in E. coli. 

The fact that a positive effect was obtained in a number of in vitro tests indicates that the material may be 

a potential mutagen, and thus this class of materials may be mutagenic. Note that compound 3899-B (the 

less refined compound) generally appeared more toxic. This indicated that impurities and other chemicals 

may increase toxicity to an unacceptable level even if the pure compounds are not unacceptably toxic. 

Other Phosphorus Compounds: In a study of a number of phosphorus compounds, no toxic signs were 

observed following 15 6 h exposures of two male and two female rats to 200 μL/L tributyl phosphite, 

P(OC4H9)3.

137 The blood, urine, and organs (upon autopsy) were normal. The same study showed that 

tris(hydroxymethyl)propane bicyclic phosphite, Figure 7–5, has an unexpectedly high toxicity and was 

stated to be “one of the most toxic compounds handled in this laboratory.” All rats died following a 1 h 
644 Search for New Fire Suppressant Chemicals 

exposure to 10 μL/L. The action on the central nervous system was probably due to its sufficient stability 

to penetrate cell membranes as a non-ionized molecule, possibly with subsequent hydrolysis. Note, 

however, that its hydrolysis product, dihydroxybutylphosphonic acid, has a low oral and parental toxicity. 

Figure 7–5. Tris(hydroxymethyl)propane Bicyclic 

Phosphite. CH3

CH2C P

CH2

CH2O

CH2

O

O

Phosphorus Tribromide (PBr3) 

In spite of its contact toxicity and corrosive hazards, documented in material safety data sheets67,138, the

attraction of a reactive molecule containing four catalytic atoms (three bromine atoms and a phosphorus

atom) led to several studies of the efficacy of phosphorus tribromide (PBr3) molecule as a fire 

extinguishant.

84,85,92 The high boiling point (173 °C) and low vapor pressure (1.3 kPa @ 48 °C) of PBr3

indicated that in fire suppression applications the compound would have no dimensionality, and unless 

the compound were applied in sufficient quantity directly on the burning surface, it was unlikely that 

complete and reliable flame extinguishment would be obtained. These physical properties led to the

conclusion that PBr3 had no promise as a total flooding agent. The alternative study of low boiling

bromine carriers such as the alkenes and ethers was judged more likely to yield a more toxicologically

and environmentally acceptable halon replacement with greater dimensionality, and therefore no further

effort to study PBr3 was made. 

Nonetheless, studies continued. In the 1990s, there were limited press releases of some studies of PBr3, 

along with poster session presentations at the annual Halon Options Technical Working Conferences in

the 1990s. A report to the Air Force conveyed some technical documentation.139

Recently, it was announced that a commercial aircraft engine nacelle fire extinguishment system would 

employ this chemical, in very small quantity relative to halon 1301.140 The described approach utilized

focusing a spray of the PBr3 onto a location where the fire was assumed to occur. This approach gained

its advertised agent mass and volume advantage because halon 1301 is typically discharged to flood the 

entire engine nacelle. Total flooding mitigates the risk that the fire might start in an obstructed location 

and not be extinguished. In addition, the discharge of HFCs and halons is accompanied by significant 

cooling of hot surfaces in and around the flame zone. This is credited with diminishing or even 

eliminating the potential for relight of hot liquids and vapors present in the burn zone. There was no

presentation of same-test-fixture comparison of the PBr3 system to halon 1301 extinguishment. 

Arsenic, Bismuth, and Antimony

Antimony has been extensively used in flame retardants, usually in conjunction with bromine-containing 

compounds.48 No studies on fires suppression by arsenic or bismuth compounds have been found.

Arsenic and antimony compounds are too toxic to meet that screening criterion. 
NGP Surveys of Inorganic Chemical Families 645

7.3.6 Main Group Elements - Group VI 

Oxygen 

Oxygen compounds are included under other headings and are not covered here. The use of water (H2O) 

as an extinguishant dates to before the earliest historical written records. There is no indication that 

simple inorganic oxygen compounds provide any type of catalytic fire suppression capability. 

Sulfur 

A sulfur dioxide cycle (Reactions 7-28 and 7-29) has been proposed to inhibit combustion by removal of 

hydrogen atoms.79

H + SO2 + M → HSO2 + M* (7-28)

H + HSO2 → H2 + SO2 (7-29)

However, no fire suppression tests have been conducted on these compounds, and there is no evidence 

indicating that the sulfur atom imparts any chemical fire suppression capability. The nonhalogenated 

sulfur-containing compounds are generally flammable. Thus, attention was directed at highly 

halogenated compounds. 

It appeared possible that brominated fluorosulfur compounds could be efficient fire suppressants and have 

short atmospheric lifetimes. However, no affordable sources of these compounds could be located, and 

there was also expectation that their volatility would be insufficient. 

The perfluoroalkyl sulfur compounds have relatively high oxidation and hydrolysis stability. 

Bis(trifluoromethyl)sulfide (CF3-S-CF3) is prepared by heating bis(trifluoromethyl)disulfide 

(CF3-SS-CF3) at 425 °C for 3 days to 4 days.141 This and other perfluoroalkylsulfides can also be 

prepared by heating or photolysis of RfOC(O)Rf, where Rf is a perfluoroalkyl group.142,143 The ester is 

prepared by reaction of Rf -S-Cl and silver perfluorocarboxylates (AgOOCRf). The derivatives Rf-SF2-Rf, 

are prepared by fluorination of the corresponding sulfide with ClF or F2, followed by hydrolysis to give 

Rf-S(O)-Rf

144,145 These compounds are generally hydrolytically and oxidatively stable.141,143,144

As can be seen in Table 7–20, only the first two sulfides are sufficiently volatile to meet the screening 

criterion for aircraft use. 

A major drawback of sulfur compounds is the expected formation of toxic sulfur oxides or hydrogen 

sulfide during fire extinguishment. Toxicity concerns, a lack of availability of test chemicals, and likely 

long atmospheric lifetime of the fully fluorinated thioalkanes resulted in further examination of this 

family being abandoned. 
646 Search for New Fire Suppressant Chemicals 

Table 7–20. Perfluoroalkyl Sulfur Compounds. 

Chemical Name Formula Tb (°C) 

1,1,1,3,3,3-hexafluoro-2-thiopropane CF3-S-CF3 a-22 

1,1,1,3,3,4,4,4-octafluoro-2-thiobutane CF3-S-CF2CF3 b6.3 

1,1,1,3,3,4,4,5,5,5-decafluoro-2-thiopentane CF3-S-CF2CF2CF3 b38.6 

1,1,1,2,2,3,3,3-octafluoro-2-thiopropane CF3SF2CF3 b21.0 

1,1,1,2,2,3,3,4,4,4-decafluoro-2-thiobutane CF3SF2CF2CF3 b44.1 

1,1,1,2,2,3,3,4,4,5,5,5-dodecafluoro-2-thiopentane CF3SF2CF2CF2CF3 b69.3 

1,1,1,2,2,3,3,4,4,5,5,6,6,6-dodecafluoro-3-thiopentane CF3CF2SF2CF2CF3 b69.5 

1,1,1,3,3,3-hexafluoro-2-oxo-2-thiopropane CF3S(O)CF3 b37.3 

1,1,1,3,3,4,4,4-octafluoro-2-oxo-2-thiobutane CF3S(O)CF2CF3 b58.2 

1,1,1,3,3,4,4,5,5,5-decafluoro-2-oxo-2-thiopentane CF3S(O)CF2CF2CF3 b64.0 

a Reference 141. 

b Reference 143. 

Selenium and Tellurium 

The only compound containing one of these elements for which fire extinguishment capabilities have 

been reported is perfluoroselenolane.146 There was no indication that selenium or tellurium compounds 

exhibited catalytic flame inhibition or that such compounds would have particular utility as halon 

replacements. Selenium toxicity was of great concern.67,138

7.3.7 Main Group Elements - Group VIII (Noble Gases) 

Of the non-radioactive Group VIII elements (helium, neon, argon, krypton, and xenon), only xenon and, 

to a much lesser extent, krypton are known to form compounds. These compounds are strong oxidizing 

agents and would probably act to increase flame intensity rather than decrease it. At any rate, these are 

not stable at ordinary temperatures, so only the atoms would reach the flame. Like nitrogen, the noble 

gases extinguish flames by dilution and cooling. They thus did not meet the efficiency screening 

criterion. 

7.3.8 Transition Metal Based Compounds 

The 2001 NGP review39 of the status of knowledge of fire suppressants recommended a further look at 

compounds of copper, iron, manganese, and tin. A more detailed and more current review (including 

extensive NGP research) of the chemistry of transition metal compounds appears in Chapter 3 of this 

book. That chapter notes data supporting high flame inhibition efficiency for a longer list of metals, 

adding chromium, cobalt, lead, molybdenum, and tungsten. Unfortunately, most metal-containing 

compounds from this larger set have the potential to lose their ability to quench flames due to 

condensation of the active species. There was no direct evidence for salts of cobalt, copper, molybdenum, 

and tungsten to lose their flame quenching potential. 

All compounds containing these metals are solids or dense liquids at flight temperatures and are thus not 

sufficiently volatile for total flooding as gases. Thus, the NGP did not perform a systematic flame 

extinguishment study of these compounds. They could be dispensed by incorporation in a solid 

propellant fire extinguisher, as described in Chapter 9. The addition of K2CO3 has significantly improved 
NGP Surveys of Inorganic Chemical Families 647

the performance of a prototype device, and salts of these metals would need to be at least as beneficial for 

further consideration. 

7.3.9 Inorganic Chemicals - Conclusions 

Nearly all of the inorganic compounds are insufficiently volatile and/or have not shown even moderate 

fire suppression efficiency. They thus do not meet primary screening requirements for replacing halon 

1301 in aircraft applications. A few compounds are moderately volatile, but are toxic or corrosive. Some 

phosphorus halides have boiling points that might be sufficient for use should the operational temperature 

criterion be raised significantly above the -40 oC extreme at which halon 1301 alternatives are expected to 

perform. 

7.4 NGP SURVEYS OF ORGANIC COMPOUNDS 

7.4.1 Highly Efficient Thermal Agents 

Screening 

The NGP conducted extensive research to determine whether other organic compounds could be as 

efficient at flame extinguishment as halon 1301 simply by absorbing heat from the flames, i.e., without 

any chemical or catalytic activity.147 A number of reports by Pitts et al. describe specific aspects of and 

the conclusions resulting from this research.148,149,150,151,152,153,154 In this effort, two existing 

thermodynamic databases maintained by NIST were searched in order to identify chemical compounds 

predicted to extract large amounts of heat from a combustion zone: 

• Design Institute for Physical Properties database (DIPPR), which contains 1458 compounds 

from 83 chemical families (Table 7–21) and 

• REFPROP, which contains 43 compounds tailored to alternate refrigerant applications, 

including many candidates for replacing HCFCs. 

This search also included representative compounds from some families of chemicals not well 

represented in existing thermophysical property databases. These were compounds having high heat of 

vaporization, liquid phase heat capacity, total heat absorption due to a phase change, and/or heat needed 

to raise the liquid or gas to combustion temperatures. Fluorinated ethers were important to consider, since 

their atmospheric lifetimes may be significantly lower than those of chlorofluorocarbons,155 and some of 

these had been identified as possible replacements for blowing agents, refrigerants, fire suppression 

agents, and solvents.21,156,157,158,159,160 Additional compounds were several cyclic fluorinated ether 

compounds (fluorinated oxiranes, oxetanes, and furans), some non-cyclic methyl ethers (HFE-116, 

HFE-125), fluorinated methyl ethyl ethers with two or fewer hydrogen atoms (HFE-227me, HFE-236me), 

and some larger fluorinated ethers (methoxy-nonafluorobutane, C4F9OCH3, HFE-7100; 

perfluorodimethoxymethane, CF3OCF2OCF3; perfluoropropyltrifluoromethyl ether, CF3OCF2CF2CF3; and 

heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, CF3CHFOCF2CF2CF3). Lastly, the list of compounds 

considered included two fluorinated amines, the alternative refrigerant HFC-338mccq (CH2FCF2CF2CF3), 

and the fluorinated alcohol 2,2,3,3,3-pentafluoropropanol (CF3CF2CH2OH). 
648 Search for New Fire Suppressant Chemicals 

Table 7–21. Family Types in the DIPPR Database 

# Family Type # Family Type # Family Type 

1 n-Alkanes 29 Cycloaliphatic alcohols 57 Other amines, imines 

2 Methylalkanes 30 Aromatic alcohols 58 Nitriles

3 Dimethylalkanes 31 Polyols 59 C,H,NO2 compounds

4 Other alkanes 32 n-Aliphatic acids 60 Isocyanates/diisocyanates 

5 Cycloalkanes 33 Other aliphatic acids 61 Mercaptans

6 Alkylcyclopentanes 34 Dicarboxylic acids 62 Sulfides/theophenes

7 Alkylcyclohexanes 35 Aromatic carboxylic acids 63 Polyfunctional acids 

8 Multi-ring cycloalkanes 36 Anhydrides 64 Polyfunctional esters

9 1-Alkynes 37 Formates 65 Other polyfunctional C,H,O

10 2,3,4-Alkenes 38 Acetates 66 Polyfunctional nitriles

11 Methylalkenes 39 Propionates & Butyrates 67 Nitroamines

12 Ethyl and higher alkenes 40 Other saturated aliphatic esters 68 Polyfunc. amides/amines 

13 Cycloalkenes 41 Unsaturated aliphatic esters 69 Polyfunctional C,H,O,N

14 Dialkenes 42 Aromatic esters 70 Polyfunctional C,H,O,S

15 Alkynes 43 Aliphatic ethers 71 Polyfunc. C,H,O,halides

16 n-Alkylbenzenes 44 Other ethers and diethers 72 Polyfunc. C,H,N,halides

17 Other alkylbenzenes 45 Epoxides 73 Other polyfunc. organics

18 Other monoaromatics 46 Peroxides 74 Elements

19 Napthalenes 47 C1/C2 aliphatic chlorides 75 Silanes/siloxanes

20 Other condensed rings 48 C3 & higher aliphatic chlorides 76 Organic-inorganic 

21 Diphenyl/polyaromatics 49 Aromatic chlorides 77 Inorganic acids

22 Terpenes 50 C,H,Br compounds 78 Inorganic bases

23 Other hydrocarbon rings 51 C,H,I compounds 79 Organic salts

24 Inorganic gases 52 C,H,F compounds 80 Sodium salts

25 Aldehydes 53 C,H multihalogen compounds 81 Other inorganic salts 

26 Ketones 54 n-Aliphatic primary amines 82 Inorganic halides 

27 n-Alcohols 55 Other aliphatic amines 83 Other inorganics 

The research approach involved developing a figure of merit for evaluating each compound based on the

total enthalpy absorbed by the compound as it was heated from room temperature to flame temperature, 

represented by 1400 K. The total heat absorbed consists of three contributions (Equation 7-30), 

, l v g

Total ∆H =∆H +∆H +∆H (7-30)

where the first contribtion, H1, is the heat involved in taking the liquid from room temperature up to 

the normal boiling point, T

∆

b, 

∆ =∫

Tb

K

liquid H Cp T 1 298 d . (7-31)

The value of the liquid heat capacity (Equation 7-31) at the normal boiling point was used, since the heat 

capacity of a liquid does not change significantly over a small temperature range. If this was unavailable, 

the liquid phase heat capacity at 20 °C was estimated using the method of Chueh and Swanson.

161162

The second term, ∆Hv, is the latent heat of vaporization at the normal boiling point. If not available, these 

were estimated using the approach of Fishtine.163
NGP Surveys of Organic Compounds 649

The third contribution, ∆Hg, is the integral, [Equation 7-32] of the gas-phase heat capacity from the 

normal boiling point to 1400 K, 

∆ =∫ K

g T p b

The gas phase heat capacities were estimated using the method of Rihani and Doraiswamy,

164 which was

based on structural contributions. For agents with boiling points below 298 K, the total heat involved is

just the contribution ∆H . 

gas C T 1400 d .

v

H (7-32) 

Table 7–22 summarizes the results of this computation, comparing the best of the examined chemicals, 

along with some reference compounds. The listing is in order of their ∆HTotal expressed on a molar basis 

(kJ/mol). 

Table 7–22. Compounds with High ∆HTotal (Molar Basis).

Tb (°K) ∆HTotal (kJ/mol)

perfluoro-2-butyltetrahydrofuran, C8F16O 375.2 608.4

heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether 315.2 421.9 

methoxy-nonafluorobutane, HFE-7100 334 407.6 

perfluoropropyltrifluoromethyl ether,CF3OCF2CF2CF3 279.9 336.3

perfluoroisobutane, C4F10 252.5 321.2

1,1,1,2,2,3,3,4-octafluorobutane, HFC-338mccq 301 321.0 

decafluorobutane, C4F10 271 318.5

octafluorocyclobutane, C4F8 267 303.2

perfluorotrimethylamine, C3F9N 264 293.8

lactic acid, C3H6O3 455 292.9

perfluorodimethoxymethane, CF3OCF2OCF3 263 286.8

octafluorofuran, C4F8O 272.4 289.8

2,2,3,3,3-pentafluoropropanol, C3F5H3O 353.15 280.8

octafluoro-2-butene 270 261.9

tris(difluoromethyl)amine, C3H3F6N 275 256.5

trifluoromethyl-1,2,2,2-tetrafluoroethyl ether, HFE-227me 263.6 255.3 

octafluoropropane, FC-218 236.4 250.8 

difluoromethyl-1,2,2,2-tetrafluoroethyl ether, HFE-236me 296.5 239.4 

1,1,1,2,3,3,3-heptafluoropropane, HFC-227ea 257.5 236.5 

1,1,1,2,3,3-hexafluoropropane, HFC-236ea 279.7 222.2 

bis(trifluoromethyl)ether, HFE-116 257 196.2 

pentafluorodimethylether, HFE-125 235 183.8 

hexafluoroethane, FC-116 194.95 181.1 

1,1,2,2-tetrafluorodimethylether, HFE-134 279.4 170.2 

pentafluoroethane, HFC-125 225.2 166.8 

1,1,1,2-tetrafluoroethane, HFC-134a 247 156.8 

1,1,2,2-tetrafluoroethane, HFC-134 250 152.8 

bromotrifluoromethane, halon 1301 215.26 110.9

Water, H2O 373.1 87.5

carbon dioxide, CO2 N/a 56.2

Nitrogen, N2 77.4 34.7

Argon, Ar 87.3 22.9 
650 Search for New Fire Suppressant Chemicals 

Table 7–23 gives the same quantity, but expressed on a mass basis (kJ/kg). Compounds that were 

identified as flammable or toxic, or that had known ozone depletion problems, have been eliminated. The 

DIPPR database does not contain any information on toxicity or other health effects. This information 

came from manufacturers’ safety data sheets and Hawley.165 Since the information on toxicity was 

incomplete, further investigation of some chemicals would be needed. The web site at 

http://chemfinder.camsoft.com/ provided OPD and GWP information. Perfluorocarbons are included for 

reference, although the EPA has indicated they may be used only when all other compounds are 

inappropriate. Halon 1301 and HFC-125, two reference compounds, are shown in boldface. 

Table 7–23. Compounds with High ∆HTotal (Mass Basis). 

Chemical Name, Formula Tb (°K) ∆Htotal (kJ/kg) 

Water, H2O 373.1 4855.7 

lactic acid, C3H6O3 455 3251.6 

2,2,3,3,3-pentafluoropropanol, C3F5H3O 353.15 1872.0 

methoxy-nonafluorobutane, HFE-7100 334 1630.4 

1,1,1,2,2,3,3,4-octafluorobutane, R338mccq 301 1588.7 

1,1,1,2-tetrafluoroethane, HFC-134a 247 1536.8 

tris(difluoromethyl)amine, C3H3F6N 275 1535.5 

octafluorocyclobutane, C4F8 267 1515.8 

1,1,2,2-tetrafluoroethane, HFC-134 250 1497.6 

heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether 315.2 1475.0 

perfluoro-2-butyltetrahydrofuran, C8F16O 375.2 1462.3 

1,1,1,2,3,3-hexafluoropropane, HFC-236ea 279.7 1461.4 

1,1,2,2-tetrafluorodimethylether, HFE-134 279.4 1442.0 

difluoromethyl-1,2,2,2-tetrafluoroethyl ether, HFE-236me 296.5 1424.7 

1,1,1,2,3,3,3-heptafluoropropane, HFC-227ea 257.5 1390.9 

pentafluoroethane, HFC-125 225.2 1389.8 

trifluoromethyl-1,2,2,2-tetrafluoroethyl ether, HFE-227me 263.6 1372.4 

pentafluorodimethylether, HFE-125 235 1351.3 

perfluoroisobutane, C4F10 252.5 1349.6 

octafluorofuran, C4F8O 272.4 1341.5 

decafluorobutane, C4F10 271 1338.2 

octafluoropropane, FC-218 236.4 1333.8 

perfluorotrimethylamine, C3F9N 264 1329.3 

perfluoropropyltrifluoromethyl ether, CF3OCF2CF2CF3 279.9 1323.9 

hexafluoroethane, FC-116 194.95 1312.2 

octafluoro-2-butene 270 1309.2 

perfluorodimethoxymethane, CF3OCF2OCF3 263 1303.5 

carbon dioxide, CO2 n/a 1276 

bis(trifluoromethyl)ether, HFE-116 257 1273.9 

nitrogen, N2 77.4 1238.3 

bromotrifluoromethane, halon 1301 215.26 744.7 

Argon, Ar 87.3 573.2 
NGP Surveys of Organic Compounds 651

The results of Table 7–22 indicate that the top candidates for use in moderate (ground level) ambient 

temperature environments or as streaming agents (defined here as having boiling points higher than 

293 K), on a molar basis, are perfluoro-2-butyltetrahydrofuran, methoxy-nonafluorobutane, 

heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, and 1,1,1,2,2,3,3,4-octafluorobutane. 

Table 7–23 indicates that methoxy-nonafluorobutane (HFE-7100) is also high on the list when expressed 

on a mass basis. It is available commercially.166 The others are not, but have been synthesized and used 

for research.167. 168,169 The top total-flooding candidates (defined as having boiling points lower than 

293 K) are perfluoropropyltrifluromethyl ether, perfluoroisobutane, decafluorobutane, and 

octafluorocyclobutane. Of these, the last two are available commercially.170 The latter three are 

perfluorocarbons and thus not reasonable to consider further. 

HFE-7100 was developed as a replacement for ozone-depleting chemicals used in a variety of 

applications. It has been estimated to have a zero ozone depletion potential, a relatively low global 

warming potential, low toxicity, and good materials compatibility.166 It has been approved under the 

Significant New Alternatives Policy (SNAP) of the United States Environmental Protection Agency. 

There is an existing patent dealing with use of HFE-7100 as a fire-extinguishing agent. Based on these 

favorable properties, it was decided to characterize the extinguishing capability of HFE-7100 

experimentally. 

The data included in Table 7–23 indicate that lactic acid is predicted to be highly effective as a thermal 

agent. Clearly, this compound is not a potential candidate as a replacement for halon 1301 for in-flight 

fires due to its high boiling and melting points and caustic nature. It is also an organic compound and 

may be combustible. However, based solely on its ability to extract heat, it is predicted to be nearly twice 

as effective on a mass basis as any of the other potential thermal agents considered, except water. Its 

ability to extract heat is predicted to be roughly two-thirds of that of water on a mass basis and 3.5 times 

greater on a molar basis. Since lactic acid is soluble in water, it was deemed worthwhile to investigate the 

suppression characteristics of mixtures of these two polar liquids. 

Effectiveness of Thermal Agents 

In order to understand the effectiveness of thermal agents better, experimental and modeling 

investigations were performed for flame extinguishment by water, lactic acid, and HFE-7100. Prefatory 

measurements and calculations for simpler, gaseous thermal agents (nitrogen, carbon dioxide, argon, and 

helium) were used to establish the viability of the approach.147

Figure 7–6 shows the relative contributions of the various heat extraction mechanisms in Equation 1 for 

the seven agents in terms of heat extraction per mole of agent and per mass of agent. On a molar basis 

HFE-7100 is predicted to be the most effective, with lactic acid a close second. The contribution of liquid 

processes to the total heat extraction is relatively small for HFE-7100. Liquid water is predicted to be the 

next most effective due primarily to the relatively high heat absorbed during evaporation. The four 

gaseous agents are predicted to be relatively ineffective and are ordered CO2 > N2 > Ar = He. 

On a per mass basis, the plot has a very different appearance. The most effective agent in these terms is 

helium followed by water and lactic acid. On this plot the role of heat extraction by heating and 

vaporization of the liquid agents is clear. It can be seen that for water, over half of the heat extraction 

arises from the liquid processes. For lactic acid, the contribution of liquid vaporization to the total heat 
652 Search for New Fire Suppressant Chemicals 

extraction is significant, but greatly reduced as compared to water. The large differences between the 

HFE-7100 and lactic acid and water are due to hydrogen bonding that exists in water and lactic acid. This 

bonding significantly increases the amount of heat energy required to vaporize liquids when it is present. 

Figure 7–6. Relative 

Contributions of Liquid 

Heating, Vaporization, and Gas 

Heating to 1400 K to the Total 

Heat Absorbed by Various 

Thermal Agents. 

(top: mole basis; bottom: mass 

basis)

Estimated Total Heat Extraction (kJ/kg)

∆HTotal (kJ/kg)

0 1000 2000 3000 4000 5000

∆Hl

∆Hv

∆Hg

N2

Ar

CO2

HFE7100 (C5F9H3O)

Lactic Acid (C3H6O3)

H2O

He

Estimated Total Heat Extraction (kJ/mol)

∆HTotal (kJ/mol)

0 100 200 300 400

∆Hl

∆Hv

∆Hg

N2

Ar

CO2 HFE7100 (C5F9H3O)

Lactic Acid (C3H6O3)

H2O

He
NGP Surveys of Organic Compounds 653

Nitrogen and carbon dioxide were predicted to extract roughly the same amount of heat per kg, while the 

amount extracted by gaseous HFE-7100 was only slightly higher. In fact, it has been found that for a 

number of gaseous species expected to act primarily as thermal agents the mass required to extinguish a 

fire is roughly constant.171 However, it is clear from these plots that this criterion should only be used to

provide guidance and that it is not generally applicable to a wide range of molecular species. 

The performance of HFE-7100 and lactic acid was evaluated using the Dispersed Liquid Agent Fire 

Suppression Screen (DLAFSS, Chapter 8). Despite lactic acid's expected ability to withdraw significant 

levels of heat from a flame zone, it is flammable. Thus, there will be competitive effects between the heat 

release and heat extraction in the suppression processes. To mitigate the effect of the heat release, lactic

acid was mixed with water, also a good thermal agent, but nonflammable. Both the ether and the aqueous 

solution were introduced as droplets. 

Figure 7–7 shows the test results for three lactic acid solutions. The undiluted stock solution was not

tested because it was so viscous it caused the syringe pump, used to deliver the liquid to the nebulizer, to

stall. Each data point represents an average of five or more tests; the error bars represent one standard 

deviation. The blow-off velocity decreased with increasing liquid application rate. In other words, as 

more of the acid mixture was delivered to the flame, less airflow was required to induce extinction. 

igure 7–7. Air

xtinguishment of the

LAFSS Flame as a 

id

for

he slopes of the lines in Figure 7–7 are a measure of the effectiveness of a liquid in suppressing a flame.

more effective is the liquid. The three lactic acid/water mixtures showed no 

provement of fire suppression effectiveness over neat water. In fact, the fire suppression effectiveness 

decreased as the lactic acid mass fraction was increased. Given that no chemical effects were expected

F

Velocities at 

E

D

Function of Liqu

Application Rate

Lactic Acid/water 

Mixtures. 

T

The steeper the slope, the

im

for fire suppression with lactic acid, it was concluded that the increased heat extraction due to lactic acid 

was being overwhelmed by heat release due to its combustion. 

Liquid application rate (m L/m in)

0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8

Blo

w-off vel

ocity (cm/s)

60

80

100

120

140

160

180

200

220

240

260

5.4 % lactic acid

Linear regression line

13.7 % lactic acid

Linear regression line

22.4 % lactic acid

Linear regression line

W ater

Linear regression line
654 Search for New Fire Suppressant Chemicals 

Figure 7–8 is a similar plot for HFE-7100. The shallower slope indicates a less efficient agent than water. 

HFE-7100 was also studied in the Transient Application Recirculating Pool Fire (TARPF) facility 

(Chapter 8) to understand its performance under flow condition

-3 3

s typical of those present in aircraft engine 

nacelles. The airflow in the tunnel was fixed at 6.67 Η 10 m /s. The porous burner was operated with a 

duration was varied from 1 s to 10 s. The hot surface used to investigate re-ignition was not activated. 

r was observed when water was tested. 

The difference is almost certainly associated with agent distribution and entrainment in the TARPF. It is

igure 7–8. Air Velocities 

LAFSS Flame as a 

pplication Rate for HFE100.

propane flow of 33 mL/s. The mist nozzle had a flow of 1.9 mL/s at 1.03 MPa. The mist discharge

The only heating of this surface came from the impinging flame. 

For these operating conditions, it was found that the pool fire stabilized behind the backward-facing step

could not be completely suppressed by the HFE-7100 mist. Furthermore, the nominal effective mass 

fraction of the HFE-7100 for the TARPF experiments was more than twice as high as that required to

extinguish a propane flame in the DLAFSS. A similar behavio

likely that droplets of agent dispersed in the high-speed air flow had sufficient momentum to pass above 

the recirculating zone without being entrained. In this way, it would be possible to have an extinguishing

concentration of liquid agent in the air above the flame, but a lower concentration in the actual location

where the flame is stabilized. In either case, the results demonstrated the importance of agent distribution

for effective flame extinguishment. 

F

at Extinguishment of the 

D

Function of Liquid 

A

7

Liquid Application Rate (mL/min)

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0

Blow-Off Velocity (cm/s)

180

190

200

210

220

240

HFE7100

Linear regression line

230
NGP Surveys of Organic Compounds 655

Chemical Kinetic Modeling of Thermal Agents 

o obtain further insights into the effectiveness of thermal agents and their mechanisms of flame 

extinguishment, detailed chemical-kinetic computations were performed in which various thermal agents 

ere added to the air side of laminar opposed-flow diffusion flames.147 The flames were simulated using 

OPPDIF,172 a computer code developed by Sandia National Laboratories. OPPDIF is built on a number 

HEMKIN-III.173 GRI-Mech 1.2, which had been 

developed with the support of the Gas Research Institute, provided the detailed kinetics for the 

mechanism was not optimized using diffusion flame results. The extinction 

behavior for the propane/air flame was calculated using the mechanism of Babushok and Tsang.175 

gent, 

criterion was adopted which defined the extinction velocity as that for which a burning solution was still 

cases. The new solution then became the starting point for cases 

involving further changes in the controlling parameters. For a given set of initial conditions (fuel, agent 

so 

close at 500 s ± 6 s . Other reported calculations show similar results, while reported experimental 

tween the (consistent) calculated values and the 

(consistent) measured values results from the particular chemical kinetic mechanism used. The 

T

w

of general purpose subroutines, collectively known as C

methane/air flame.174 

GRI-Mech 1.2 consisted of 32 chemical species undergoing 177 reactions. One- and two-carbon species 

were included. Thermodynamic and transport data were provided as separate files. The mechanism was 

created by starting with appropriate estimates for the rate constants and then optimizing to provide the 

best agreement with experimental measurements in such systems as premixed flames, shock tubes, and 

flow reactors.174 The 

In the simulations, the goal was to identify the flow conditions just sufficient to cause extinction of a 

flame formed by fuel and either air or air with added agent. The approach was based on the hypothesis 

that the maximum flame temperature at extinguishment for a given fuel is a unique value as long as the 

agent is non-reactive in the flame. Most of the calculations were for methane/air flames, but some were 

performed for the computationally more intensive propane/air flames. An arbitrary, but strin

obtained, but for which an increase of only 0.01 cm/s in the fuel and air initial velocities either resulted in 

(a) a failure to find a solution or (b) a non-burning solution. Additional small increases in velocity always 

resulted in non-burning solutions. 

The general procedure was to find a solution for a given type of diffusion flame by first solving an 

isothermal case and using the solution as the input for a calculation in which the energy equation was 

added. Once that solution was available, it was used as the starting point for calculations in which such 

parameters as the oxidizer and flow velocities were changed. Only the formulation including the energy 

equation was solved for the “restarted” 

fraction, etc.), higher and higher flow velocities were used until the above extinction criterion was met. 

Checks against later GRI-Mech releases 2.11 and 3.0 showed no more than a minimal effect of the 

specific release on the calculated results. 

Figure 7–9 shows the similarity of the calculated maximum flame temperatures at extinction, which were 

uniform at 1794 °C ± 7 °C. The three calculations of the strain rate of the flame at extinction were al

-1 -1

values from seven laboratories averaged 384 s-1 ± 21 s-1.

147 Since all the calculations invoke similar 

chemistry, it is presumed that the difference be

uncertainties in the rate constants could readily account for the roughly 20 % difference. 
656 Search for New Fire Suppressant Chemicals 

For the propane/air flames, the calculated strain rate at extinction was 621 s-1. The three reported values

were 510 s-1, 583 s-1, and 721 s-1.

147

 This range of measured values is wider than that for the methane/air

flames and encompasses the calculated value for the propane/air flame. 

Table 7–24 lists the added volume fractions of inert gases calculated to extinguish a buoyancy dominated, 

ncluded in Reference 147. Table 

7−25 is a similar table for propane/air flames. 

h DLAFSS values, as expected since the extinguishing 

concentrations are tied to the experimental values for porous burners in opposed flow

lame Temperatures as a

nd Air Velocity

methane/air diffusion flame. Previously published and NGP-measured values for each of the inert gases

are included. Note that prior to the NGP, there was just one published value for flame extinguishment by

the inert gases other than nitrogen. Details of all the measurements are i

The following observations follow from the above data: 

• For both fuels, the extinguishment values show some dependence on the type of burner. 

• The calculated values agree wit

configurations. 

• The helium results are consistently lower than the predicted values. 

• Detailed chemical kinetic modeling, combined with the concept of a limit temperature, does a 

good job of capturing the relative effectiveness of thermal agents for extinguishing diffusion 

flames as well as the effects of using different fuels. 

Methane/Air Diffusion Flame

Figure 7–9. Maximum 

F

Function of the Equal Fuel 

a

Magnitudes for a 

Flow Velocities (cm/s)

0 50 100 150 200 250 300

Maximum Flame Temperature (K) 1750

1800

1850

1900

1950

2000

2050

2100

GRIMech 1.2

GRIMech 2.11

GRIMech 3.0

Methane/Air OpposedFlow Diffusion Flame for 

Three Versions of the GRIMech Mechanism. 
NGP Surveys of Organic Compounds 657

Table 7–24. Extinguishing Volume Fractions of Inert Gases for CH4/Air Diffusion Flames. 

Burner N2 Ar He CO2 Reference 

Calculated 0.33 0.43 0.33 0.22 147 

Counterflow 0.34 179 

Counterflow 0.32 176 

Opposed Jet 0.29 177 

Opposed Jet 0.30 0.19 178 

Coflow 0.27 181 

DLAFSS 0.33 0. 0 0. 47 .21 24 147 

Coflow 0.23 0. 0 0. 31 .20 13 147 

Table 7–25. Extinguishing Volume Fractions of Inert Gases for C3H8/Air Diffusion Flames. 

Burner N2 Ar He CO2 Re ce feren

Calculated 0.39 0.50 0.39 0.28 147 

Counterflow 0.39 179 

Opposed Jet 0.35 177 

Coflow 0.32 171 

Coflow 0.33 0.20 180 

Coflow 0.33 181 

DLAFSS 0.26 0. 0 0. 55 .22 26 147 

Coflow 0.28 0. 0 0. 37 .28 18 147 

Chemical Kinetic Modeling of HFE-7100 

 order to obtain some idea of the concentrations that might be required for extinguishment by a more 

general thermally acting agent, a series of calculations was carried out for HFE-7100. This calculation 

action was the heat capacity of the gaseous agent, even 

though significant heat could also be removed by evaporation if the agent were released as a liquid at 

it a particularly effective thermal agent in molar terms. 

If liquid vaporization and chemical effects improved its effectiveness still further, this species might 

In

assumed that the only mechanism for heat extr

room temperature. This molecule was likely to decompose upon entering the high temperature region of 

the flame and then react to form final products. Reaction of the agent was not modeled. Due to the 

presence of a large number of fluorine atoms, it was also likely that the extinguishing efficiency would 

include a small chemical component.182,183,184,185 On this basis, the result of this calculation was an upper 

limit for the required extinguishing concentration. 

It is noteworthy that a relatively small volume fraction of C4F9OCH3, 0.055, was required to lower the 

maximum flame temperature to the extinguishment temperature of 1550 K. The high heat capacity of this 

molecule, due to its large number of atoms, makes 

approach the effectiveness of halon 1301, which has an extinguishing volume fraction of 0.029 % on a 

molar basis.186 On a mass basis, this fluorinated ether is less effective, based on the molecular weights of 

148.9 g/mol for halon 1301 and 250 g/mol for C4F9OCH3, but not dramatically so. It might be expected 

that the mass fraction of C4F9OCH3 that must be added would be similar to other agents that do not have a 

strong component of chemical effectiveness.171
658 Search for New Fire Suppressant Chemicals 

Two experimental measurements of the volume fractions of this compound required to extinguish 

diffusion flames have been identified. Unpublished measurements from the New Mexico Engineering 

Research Institute using a standard cup burner with heptane fuel yielded an extinguishing volume fraction 

of 0.061.187 In a patent disclosure, Flynn and Scott also reported that a volume fraction of 0.061 was 

blish this equilibrium would depend on the 

particular fire scenario. For example, in the event of an office building fire, there might well be time for 

eous chemicals that achieve a flame extinguishing efficiency comparable to 

halon 1301 purely through absorption of heat from flames. There may well be some liquid chemicals 

gment the other thermal effects and achieve the desired 

efficiency. 

ature is sufficiently high that it might be applicable for fires in enclosed spaces. As will be 

seen in Chapter 8, its high boiling point probably precludes its consideration for timely extinguishment of 

hat of halon 1301, ensures superior low temperature 

dispersion. There is thus no clear reason to replace it with another compound that has no chemical fire 

 and Tropodegradable Processes 

hemical to travel from the earth’s surface to the 

stratosphere where it is fragmented by ultraviolet radiation. The bromine atom then catalyzes ozone 

cy of the bromine catalysis was to 

search for replacement fire suppressants that were bromine-free. 

as a carrier or base structure. To this, a 

sufficient to extinguish a butane flame in a “micro-cup burner.”188 Given the limitations of the chemical 

kinetic simulation, there was reasonably good agreement. 

At 300 K and atmospheric pressure, the saturation volume fraction of the ether in air was calculated to be 

0.29. Thus, the saturation pressure at room temperature should be more than sufficient to extinguish a 

diffusion flame. Whether there would be time to esta

sufficient evaporation to occur. Conversely, for an in-flight fire in an aircraft engine nacelle, the air flow 

through the nacelle would likely flush the agent faster than evaporation could establish an extinguishing 

concentration (Chapter 8). 

Summary of Thermally Active Agents 

There appear to be no gas

whose enthalpies of vaporization could au

HFC-7100 (methoxy-nonafluorobutane (C4F9OCH3) appears to be the best of these liquid compounds. Its 

high boiling point suggests it would show promise as a streaming agent. Its equilibrium vapor pressure at 

room temper

in-flight fires in cold engine nacelles and dry bays. 

HFC-125 was a key reference compound due to its selection as the best commercially available agent 

under the TDP. On a mass basis, it is in an effectiveness class with the better non-aqueous thermal 

suppressants. Its boiling point, nearly as low as t

suppression activity. 

7.4.2 Tropodegradable Candidate Compounds 

Atmospheric Chemistry

The long atmospheric life of CF3Br allows time for this c

conversion to molecular oxygen. The initial reaction to the poten

Early in the 1990s, a halon replacement strategy emerged to reintroduce the chemical suppression 

effectiveness of bromine. This approach employed a “carrier molecular structure” with intrinsically very 

low atmospheric lifetime (on the order of days or weeks) to act 
NGP Surveys of Organic Compounds 659

bromine atom was added, resulting in a tropodegradable brominated fire extinguishant or tropodegradable 

bromocarbon. Since, in general, GWP and ODP values decrease with decreasing atmospheric lifetime, 

tropodegradable bromocarbons potentially solved the environmental problems (global warming and ozone 

depletion) while providing efficient fire suppression. Tropodegradable compound atmospheric lifetimes 

had in some cases been measured, but generally were estimated based on data generated for functional 

groups such as sites of unsaturation, numbers of C-H bonds, and substitution patterns. Early estimates of 

atmospheric lifetime for alkenes, which were as low as a few days, have since been demonstrated to be 

accurate. 

The carrier compounds selected were generally partially fluorinated and incorporated chemical features 

that are reactive with atmospheric -OH or O3, are photochemical reactive, or are inherently polar and 

therefore subject to atmospheric removal by the rainout process (Table 7–26). 

Table 7–26. Tropodegradable Brominated Candidates. 

Tropodegradable Base Structure Corresponding Tropodegradable Bromocarbon 

CF3-O-CF2H CF3-O-CF2Br 

CF3-O-CFH2 CF3-O-CFBrH 

CF2H-O-CF2H CF2H-O-CF2Br 

CH2=CHCF3 CH2=CBrCF3, CHBr=CHCF3

CH2=CFCF3 CHBr=CFCF3

CH2=CFCF2H CH2=CHCF2Br, CHBr=CFCF2H 

CHF=CHCF3 CFBr=CHCF3, CHF=CBrCF3

The reactions ospheric decomposition of' a ers, and amines, 

as summariz –1. For alkenes, reaction with ith tropospheric or 

round level ozone target the double bond, while ethers and amines are subject to hydrogen abstraction 

s, NOx, nitric acid, and peroxy species. Such reactions are 

relatively minor tropospheric sinks for the chemicals considered here.189

 tropospheric ozone. These rate 

constants vary not only with the chemical being removed from the troposphere, but are also a function of 

 that cause atm molecule differ for alkenes, eth

ed in Table 7 hydroxyl free radicals or w

g

reactions by the -OH radical. Photolysis of the C-I bond is the predominant reaction pathway for 

iodinated fluoroalkanes such as CF3I. Direct physical removal of alcohols through rainout is not 

contingent on the reactivity of the compound. 

Compounds can also be degraded by reaction with a number of other atmospheric species, including 

oxygen atoms in the 3

P and 1D electronic state

A rate constant can be assigned to each of these processes: kOH for reaction with hydroxyl free radicals, 

kphysical for physical removal, kphoto for photolysis, and kO3 for reaction with

the atmospheric position (which determines the hydroxyl free radical concentration, temperature, and 

solar flux). As an approximation, one can use, for all but kphoto, the globally averaged rate constants. An 

overall pseudo first-order rate constant k1 can be written, where k1 = kOH[•OH]+ kphysical + kphoto + kO3[O3], 

[•OH] is a globally averaged tropospheric hydroxyl free radical concentration (9.7 x 105 cm3

/molec-s),190

and [O3] is the globally averaged tropospheric ozone concentration (5.0 x 1011 cm3

/molec-s).191
660 Search for New Fire Suppressant Chemicals 

Hydroxyl Free Radical Hydrogen Atom Abstraction 

All compounds containing a hydrogen atom (e.g., hydrocarbons, HFCs, and HCFCs) are subject to 

reaction with tropospheric •OH. The organic free radical •R formed rapidly reacts with diatomic oxygen 

(O2) to form a peroxy radical (ROO•), which further reacts to give a series of products. In most cases, 

these final products are rapidly removed by physical processes so that they do not contribute significantly

to ozone depletion or global warming. For most saturated haloalkanes, this process is too inefficient to be 

considered as giving tropodegradable compounds. 

For the compounds of interest here, a hydroxyl free radical can abstract a hydrogen atom and/or add to an

unsaturated molecule to yield products (Reaction 7-33). The effectiveness of •OH reactions in removing 

compounds from the atmosphere depends on the reaction rate constant (kOH) and the atmospheric 

concentration of •OH. The rate constant kOH gives the time rate of change of the concentration of a 

compound C in the atmosphere due to reaction with •OH only (Equation 7-34) and can be written as the 

sum of the rate constants for hydrogen atom abstraction ( ) and for hydroxyl addition to an

unsaturated compound ( k OH

2 ). The atmospheric half-life of a chemical for which the sole removal

mechanism is reaction with •OH is given by Equation 7-35, which can be rewritten to yield the 

atmospheric lifetime (i.e., the e-folding lifetime), Equation 7-36. 

k OH

1

C +•OH → products (7-33) 

k OH

d[C] = −k C[ ][•OH] (7-34) dt OH

t

k OH 1/ 2

OH

= •

ln

[ ]

2 (7-35) 

t

1

k [ OH] OH • 1/ e = (7-36) 

e to potential manufacturing difficulties and stability problems, 

alkynes (compounds containing triple bonds) are not considered as halon replacement candidates; 

however, aromatic compounds are. 

Addition of •OH Free Radicals to Unsaturated Chemicals 

Addition of •OH free radicals to unsaturated chemicals is a highly effective removal process. For

alkenes, the •OH adds to give a highly energetic product radical (Reaction 7-37), where the asterisk

indicates an activated species.). If it does not lose another group, the energetic product can then either 

revert back to reactants, or it can be stabilized by collision with another molecule (M), which can carry 

off the excess energy (Reaction 7-38). The reverse reaction is probably not important below 100 oC, 

higher than temperatures found in the troposphere. Hydroxyl free radicals can also add to a triple bond 

(Reaction 7-39) and to aromatics. Du
NGP Surveys of Organic Compounds 661

C C + OH C C

OH *

(7-37)

C C + C C

OH

OH + M

*

C C

OH

+ M

* (7-38)

C C + OH C C

HO *

(7-39)

d infrared (IR). Photolysis of a 

molecule depends on two parameters, the absorption cross section (σ) (which determines how much of

the available light is absorbed) and the quantum yield (φ) (the fraction of the absorbed photo

affects photolysis). If every photon absorbed produced a reaction, φ = 1. 

the

stratosphere. For example, the CFCs (chlorofluorocarbons) absorb little if any of the solar radiation 

sis: (1) the absorption cross section (how well it 

absorbs electromagnetic radiation encountered in the troposphere) and (2) the quantum yield. Both of 

Photolysis 

Photolysis (also called photodegradation and photolytic decomposition) requires absorption of

electromagnetic radiation with resulting molecular decomposition. The photodecomposition reactions 

have the form shown in Reaction 7-40, where the products are fragments of the original reactant 

molecule. Planck’s constant (h) multiplied by the frequency of the electromagnetic radiation (ν) gives the 

energy of a single photon of radiation with that frequency, and “hν” is often used as a symbol for a

photon in a chemical equation (e.g., Reaction 7-40). As the frequency of the electromagnetic radiation 

increases and the wavelength (λ) decreases, the energy per photon increases. Thus, shorter wavelength

electromagnetic radiation, such as ultraviolet (UV), is usually more effective in effecting

photodegradation than is longer wavelength radiation, such as visible an

ns that 

Reactant + hν → Products (7-40) 

Most organic compounds exhibit decreasing absorption cross sections as the radiation wavelength 

increases (at least for the ultraviolet and visible spectral regions). Since much of the lower wavelength, 

higher energy solar radiation is removed by stratospheric ozone before sunlight reaches the troposphere 

(particularly UV-B radiation, with wavelengths between 180 nm and 320 nm many molecules do not

encounter electromagnetic radiation of a sufficiently short wavelength for absorption until they reach

required for photolytic decomposition as they pass through the troposphere. However, in the stratosphere, 

where short wavelength UV radiation is intense, the CFCs photodecompose to release chlorine atoms. 

Photodissociation in the troposphere requires that a compound absorb radiation in the wavelength range 

from 299 nm to 700 nm. The photodissociation rate constant kphoto is determined by Equation 7-41, where 

σ(λ) is the absorption cross section as a function of the wavelength, λ, I(λ) is the solar intensity as a 

function of λ, and φ(λ) is the photodissociation quantum yield. Thus, a chemical compound has two 

characteristics that determine the importance of photoly
662 Search for New Fire Suppressant Chemicals 

these are a func

photodissociation only is then given by Equation 7-42.

= σ λ( ) ( ) λ φ( ) λ dλ (7-41) 

t1/e = 1/kphoto (7-42) 

In general, halocarbons require one of the groups shown in Figure 7–10 to be present for significant

absorption and photodissociation in the troposphere (i.e., absorption for λ = 299 nm to 700 nm). 

tion of the electromagnetic radiation wavelength. The atmospheric lifetime for 

k I photo

nm

∫

290

700nm

R

C O

R C C

C C

C C

Carbonyl, R ≠ OH or OR Conjugated Double Bonds Double Bond Conjugated to

Aromatic 

NO2

Polynuclear Aromatic Nitro-Substituted Benzene Bromine or Iodine 

Figure 7–10. Groups Required for Significant Tropospheric Photodissociation. 

Only the ketones and iodides were of major interest; however, compounds with co

-Br or -I 

njugated double bonds 

(i.e., double bonds that allow some delocalization of the π electron cloud) and compounds containing a 

atic could form the basis for more “exotic” fire suppressants, albeit 

with likely higher boiling points. In addition, photolysis of bromine compounds assists in lowering the 

mine-containing compounds (those proposed herein). 

e listing and assessment of structural options, including structural 

isomers a

From the ov

for screenin

west boiling points were likely to be found among 

toms) and those with the fewest carbon 

double bond conjugated to an arom

atmospheric lifetimes for bro

7.4.3 Bromofluoroalkenes 

Criteria for Acquisition 

The chemical family of bromofluoroalkenes represents an extensive array of structural possibilities. The 

examination began with an exhaustiv

. T ble 7–27 shows the range of variety just for C3 compounds with 3, 4, or 5 fluorine atoms. 

erall list, the following were concepts used to determine which compounds would be acquired 

g:

• Lowest boiling points in a given subgroup. Ideally, a compound’s boiling point was

published; some were estimated. The lo

the more heavily fluorinated compounds (3, 4 or 5 a

atoms (2 or 3). 
NGP Surveys of Organic Compounds 663

• Variation in chemical structure. This helped develop guidance for isomeric effects on flame 

extinguishment efficiency and volatility. 

Estimation of tendency to cause cardiac arrhythmia. 

Availability and cost from a commercial supplier or laboratory synthesis. 

•

•

• Expected flame sup tom is always released in the 

flam uish flame

was expected increasing fluorination and 

wever, some flu ere reported to be spontaneously 

), complicating selection and prediction of effectiveness. 

7–27 Bromofluo

pression efficiency. Since the bromine a

e zone, all the bromofluoroalkenes were

lume %. This 

 expected to exting

 to be improved by

s at 3 volume % to

4 vo estimate 

decreasing hydrogenation. Ho oroalkenes w

flammable (e.g., CF2=CFBr192

Table ropropenes. 

Chemical Name Chemical Formula cis/tran omers s Is

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

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

1-bromo-1,2,3,3,3-pentafluoropropene CFBr=CFCF3 Y 

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

2-bromo-1,3,3,3-tetrafluoropropene CFH=CBrCF3 Y 

1-bromo-1,2,3,3-tetrafluoropropene CFBr=CFCF2H Y 

1-bromo-1,3,3,3-tetrafluoropropene CFBr=CHCF3 Y 

3-bromo-1,2,3,3-tetrafluoropropene CHF=CFCF2Br Y 

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

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

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

3-bromo-1,3,3-trifluoropropene CFH=CHCBrF2 Y 

2-bromo-3,3,3-trifluoropropene CHBr=CHCF3 Y 

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

2-bromo-1,3,3-trifluoropropene CFH=CBrCF2H Y 

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

3-bromo-1,2,3-trifluoropropene CFH=CFCFBrH Y 

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

3-bromo-2,3,3-trifluoropropene CH2 2 =CFCF Br 

1-bromo-2,3,3-trifluoropropene CHBr=CFCHF2 Y 

1-bromo-1,2,3-trifluoropropene CFBr=CFCFH2 Y 

1-bromo-1,3,3-trifluoropropene CBrF=CHCHF2 Y 

1-bromo-2,3,3,3-tetrafluoropropropene CHBr=CFCF3 Y 

ric lifetimes would be short. In the case of the halogenated propenes, 

atmospheric lifetimes are limited primarily by atmospheric OH radical reactions and estimated to be on 

evaluated. As the first of the tropodegradable families examined, two groups were investigated. 

It was presumed that the atmosphe

the order of a week. For example, 2-bromo-3,3,3-trifluoropropene was estimated to have an atmospheric 

lifetimes of 4 days.193

Cup Burner Extinguishment 

Several of these compounds were acquired in small (5 g) quantities and their cup burner extinguishment 
664 Search for New Fire Suppressant Chemicals 

Table 7–28 includes chemicals with a range of carbon content (3 atoms to 5 atoms) and structural 

variation, and three or more fluorine atoms. While these differences had significant impact on the boiling 

points, there was essentially no effect on the concentration needed to extinguish a cup burner 

henes eliminated further consideration of 

these lowest boiling alkenes. Table 7–29 shows the cup burner values and boiling points of the most 

volatile p . There 

was no effect of stru uishing concentrations

fluoropropene Cup Burner Flame Extinguishment Data. 

flame.194,195,196 The values were as expected and acceptable, given the presence of a bromine atom and 

some hydrogen fuel in each molecule. 

The second group involved the most volatile compounds. Flammability, air reactivity, or markedly 

higher cup burner extinguishment values in the fluorinated et

ropenes (and one ethene). None of the substituted propenes met the volatility criterion

cture on the exting . 

Table 7–28 Bromo

Compound Name Chemical Formula Tb (°C) V ol. %

1-Bromo-3,3,3-trifluoropropene CF3CH=CHBr 40 3.5 a

3-Bromo-3,3-difluoropropene CBrF2CH=CH2 42 4.5 

2-Bromo-3,3,3-trifluoropropene CF3CBr=CH2 34 2.6 

4-Bromo-3,3,4,4-tetrafluorobutene CF2BrCF2CH=CH2 54 3.5 

2-Bromo-3,3,4,4,4-pentafluorobutene CF3CF2CBr=CH2 56 3.8 a

2-Bromo-3-trifluoromethyl-3,4,4,4-tetrafluorobutene CF3C(CF3)FCBr=CH2 78 3.3 a

1-Bromo-2-trifluoromethyl-3,3,3-trifluoropropene (CF3)2C=CHBr 63 2.6 a

1-Bromo-4,4,4,3,3-pentafluorobutene CF3CF2CH=CHBr 58 3.1 a

2-Bromo-3,3,4 3.7 a ,4,5,5,5-heptafluoropentene CF3CF2CF2CBr=CH2 78 

2-Bromo-3- tr 3.8 a ifluoromethoxy)-3,4,4,4-tetrafluorobutene CF3 3 CF(CF O)CBr=CH2 75 

a Testing performed /air mixtures 

ow Boiling Bromofluoroalk Cup Burner Values

 using premixed agent

Table 7–29 L ene . 

Compound Name Tb (°C) Vol % ume

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 to 24 (est.) 8.4 

The cup burner extinguishment performance of the substituted ethene was outside the range for continued 

consideration. The isomeric compound (1-bromo-2,2-difluoroethene, CHBr=CF2) is flammable. This 

demonstrated the potential for strong effects of structural isomerism on flammability in these very small 

at all are 

good extinguishants with no indications of flammability. However, bromofluoropropene boiling points 

molecules. While 1-bromo-1,2-difluoroethene serves as a bromine carrier, this was clearly not sufficient 

to assure an acceptable cup burner value. 

In summary, there are trifluorinated, tetrafluorinated and pentafluorinated bromopropenes th
NGP Surveys of Organic Compounds 665

lower than 25 °C are extremely unlikely. If the low temperature limit were raised, these compounds 

could prove useful in aircraft applications, subject to atmospheric lifetime and toxicity testing. 

7.4.4 Fluoroalkoxide and Fluoroalkyl Phosphorus Compounds 

ever, 

there were multiple toxic effects, rather than a focus on cardiac arrhythmia. The substitution of F atoms 

s was expected to lower the boiling point and increase flame suppression efficiency. Syntheses 

for many of the compounds were complex or untried, and this was a limiting factor in the research. 

ns of 

mutagenicity. The presence of P-halogen bonds can cause severe irritation and lung damage owing to 

o phosphorus atoms are poor candidates as halon substitutes. 

Table 7–30 c g chemicals 

relate interest here

le 7–30 Phosphorus Compound Toxicity (S mation. 

Criteria for Acquisition 

The approach to compound selection was similar to that for the bromocarbons in Section 7.4.3. How

for H atom

Toxicity 

There is a large amount of toxicity data available for phosphorus compounds. In part, this is because a 

number of phosphorus compounds (particularly phosphite esters) are cholinesterase inhibitors. The 

toxicity of phosphorus compounds is highly variable. Thus, toxicity must be given careful consideration. 

There is limited information indicating that toxicity may increase from phosphates to phosphites to 

phosphines. Phosphonitriles appear to have relatively low toxicities, but some show indicatio

hydrolysis with formation of phosphorus-containing and hydrohalic acids. For this reason, compounds 

containing direct halogen atom bonds t

ontains information on the toxicity and safety of some phosphorus-containin

d to compounds of . 

Tab afety) Infor

Compound Name Formula CAS No. Observations a 

Bis(trifluoromethyl)-

chlorophosphine 

PCl(CF3)2 650-52-2 [BLO280] Ignites spontaneously in 

air. HR = 3. 

Dibutylphosphate O=P(OH)(OC4H9)2 107-66-4 {RTECS HS630000} [DEG600] 

LD50 (rat, oral) = 3200 mg/kg. 

Moderately toxic by ingestion. HR = 

2. 

Dibutylphosphonate O=PH(OC4H9)2 1809-19-4 

0

. 

{RTECS HS6475000} [DEG800] 

LD50 (rat, oral) = 3200 mg/kg, LD5

(rabbit, skin) = 1990 mg/kg. 

Moderately toxic by ingestion, skin 

contact. Severe eye irritant. HR = 2

Diethylphosphonate O=PH(OC2H5)2 762-04-5 00} [DJW400] 

0

{RTECS TG78750

LD50 (rat, oral) = 3900 mg/kg, LD5

(rabbit, skin) = 2165 mg/kg. 

Moderately toxic by ingestion, skin

contact. HR = 2. 
666 Search for New Fire Suppressant Chemicals 

Compound Name Formula CAS No. Observations a 

Diisopropyl 

methylphosphonate 3)2]2

kin 

O=P(CH3)-[OCH(CH 1445-75-6 {RTECS SZ9090000} [DNQ875] 

LD50 (rat, oral) = 826 mg/kg, LD50

(mouse, oral) = 1041 mg/kg. 

Moderately toxic by ingestion, s

contact. HR = 2. 

Diisopropylphosphonate O=PH[OCH(CH3)2]2 1809-20-7 TECS SZ7660000} [DNQ600] 

 = 

{R

LD50 (rat, oral) = 3100 mg/kg, LD50

(rabbit, skin) = 5700 mg/kg. 

Moderately toxic by ingestion. 

Mildly toxic by skin contact. HR

2. 

Dimethyl(1,2-dibromo-2,2-

dichloroethyl) phosphate 

O=P(OCH3)2-

(OCHBrCBrCl2) 

300-76-5 

rat, 

 (rabbit, 

{RTECS TB9540000} [DRJ600] 

LD50 (rat, inh) = 7700 μg/kg, LD50

(mouse, inh) = 156 mg/kg, LD50 (

oral) = 250 mg/kg, LD50

skin) = 1100 mg/kg. Poison by 

ingestion, inhalation. Moderately

toxic by skin contact. Skin irritant. 

Insecticide of the cholinesterase 

inhibitor type. HR = 3. 

Dimethyl(2,2-

dichloroethenyl)-phosphate 

O=P(OCH3)2-(CH=Cl2) 62-73-7 

m3, 

, 

{RTECS TC0350000} [DRK200] 

LC50 (rat, inh, 4 hr) = 15 mg/

LC50 (mouse, inh, 4 hr) = 13 mg/kg, 

LD50 (rat, oral) = 25 mg/kg, LD50

(rabbit, skin) = 107 mg/kg. Poison

by ingestion, inhalation, skin contact

intraperitoneal, intravenous, 

subcutaneous. Experimental 

teratogen, suspected carcinogen 

Cholinesterase inhibitor. HR = 3. 

Dimethylphosphonate O=PH(OCH )2 868-85-9 600] 

0

gen. 

 3. 

3 {RTECS SZ7710000} [DSG

LD50 (rat, oral) = 3050 mg/kg, LD5

(rabbit, skin) = 2400 mg/kg. 

Moderately toxic by ingestion, skin 

contact. Experimental carcino

Skin, eye irritant. HR =

Hexaethyltetraphosphate OP(OC2H5)2-

[OP(O)(OC H )] -

757-58-4 

t, 

. 

2 5 2

OP(O)(OC2H5)2

{RTECS XF1575000} [HCY000] 

LD50 (rat, oral) = 7 mg/kg, LD50

(mouse, oral) = 56 mg/kg, LDLO (ra

skin) = 15 mg/kg. Poison by 

ingestion, skin contact, 

intraperitoneal, subcutaneous, 

intravenous, intramuscular. HR = 3

Tris(2-chloroethyl) O=P(OCH2CH2Cl) - 140-08-9 000] 

. Poison 

. 

phosphite 2(CH2CH2Cl) b 

{RTECS KK2810000} [PHO

LD50 (rat, oral) = 100 mg/kg, LD50 

(rabbit, skin) = 810 mg/kg

by ingestion, intraperitoneal. 

Moderately toxic by skin contact

Severe eye irritant. HR = 3. 
NGP Surveys of Organic Compounds 667

Compound Name Formula CAS No. Observations a 

Tris(2-fluoroethyl)

phosphite 

H2F)2-

ouse, inh, 10 

O=P(OCH2C

(CH2CH2F) b 

63980-61-0 {RTECS KL1925000} [PHO250] 

LCLO (rat, inh, 10 min) = 

500 mg/m3, LCLO (m

min) = 1000 mg/m3. Poison by 

inhalation. HR = 3. 

Triethylphosphite O=P(C2H5)(OC2H5)2 122-52-1 0] 

kin, 

 2. 

b {RTECS TH1130000} [TJT80

LD50 (rat, oral) = 3200 mg/kg. 

Moderately toxic by ingestion. S

eye irritant. HR =

Tris(1-bromo-3-

chloroisopropyl)-phosphate 

O=P[OCBr-

(CH3)(CH2Cl)]3

7328-28-1 {RTECS TC8600000} [TNE500] 

Mutagenic data. HR = D 

(insufficient data). 

Triisooctylphosphite O=P[(CH ) CH-(CH3)2]- 25103-12-3 KT000] 

act. 

2 5

[O(CH2)5CH(CH3)2]2

b

{RTECS TH1150000} [T

LD50 (rat, oral) = 9200 mg/kg, LD50

(rabbit, skin) = 3970 mg/kg. 

Moderately toxic by skin cont

Mildly toxic by ingestion. Skin 

irritant. HR = 2. 

Triisopropylphosphite O=P[CH(CH3)2]-

2

b

116-17-0 

on 

R = 3. 

[OCH(CH3)2]

{RTECS TH2800000} [TKT500] 

LD50 (rat, oral) = 167 mg/kg. Pois

by ingestion. Moderately toxic by 

intraperitoneal. H

Trimethylphosphite

 

in, eye irritant. HR = 2. 

O=P(CH3)(OCH3)2b 121-45-9 {RTECS TH1400000} [TMD500] 

LD50 (rat, oral) = 1600 mg/kg, LDLO

(rabbit, skin) = 2200 mg/kg. 

Moderately toxic by ingestion, skin 

contact. Experimental teratogen.

Severe sk

Tributylphosphine 

oxide 

O=P(C4H9)3 814-29-9

e 

{RTECS SZ1575000} [TNE750] 

Poison by intravenous route. Ey

irritant. HR = 3. 

Tritolylphosphate 

(tricresylphosphate) 

O=P(OC6H5CH3)3 1330-78-5 

 mg/kg. Poison 

{RTECS TD0175000} [TNP500] 

LD50 (rat, oral) = 5190 mg/kg, LD50

(mouse, oral) = 3900

by ingestion. Moderately toxic by

skin contact. Eye, skin irritant. 

HR = 3. 

Tri-2-tolylphosphate 

(tri-o-cresylphosphate) 

O=P(OC6H5CH3)3 78-30-8 

, oral) = 1160 mg/kg. 

by 

{RTECS TD0350000} [TNP750] 

LD50 (rat

Poison by ingestion, subcutaneous, 

intramuscular, intravenous, 

intraperitoneal. Moderately toxic 

ingestion. HR = 3. 

Dimethylfluorophosphate C4H10 3 FO P 358-74-7 {RTECS TE5600000} [DJJ400]

LC50 (rat, inh, 10 min) = 7 g/m3, 

LC50 (mouse, inh, 10 min) = 500 

mg/m3. Poison by inhalation, skin. 

HR = 3. 
668 Search for New Fire Suppressant Chemicals 

Compound Name Formula CAS No. Observations a 

Dimethylfluorophosphate C2H6FO3P 5954-50-7 {RTECS TE6125000} [DSA800] 

LC50 (rat, inh, 1 min) = 1800 mg/m3, 

LC50 (mouse, inh, 10 min) = 290

mg/m3. Poison by inhalation, skin

contact, intravenous. HR = 3. 

2-Ethyl-2(hydroxymethyl)-

phosphate (1:1) 

C6H11O4P 1005-83-2 000} [ELJ500] 

1,3-propane-diol, cyclic 

{RTECS TX6475

LC50 (rat, inh, 1 hr) = 30 mg/m3. 

Poison by ingestion, inhalation, skin 

contact, intraperitoneal and 

intravenous routes. HR = 3. 

Ethyl isopropyl 

fluorophosphonate 

C5H12FOP None 

assigned 260 mg/m3, 

{RTECS SZ8552000} [ELX100] 

LC50 (rat, inh, 10 min) =

LC50 (mouse, inh, 5 min) = 245 

mg/m3. Poisonous by inhalation, 

skin contact, and subcutaneous 

routes. HR = 3. 

Hexamethyl phosphoramide C6H18N3OP 680-31-9 

ous by 

 

nic data. HR = 3. 

{RTECS TD0875000} [HEK000] 

TCLO (rat, inh, 52 wk continuous) = 

50 ppb, carcinogenic. An 

experimental carcinogen and 

tumorigen. Moderately poison

ingestion, skin contact, 

intraperitoneal, intravenous. 

Experimental reproductive effects.

Human mutage

Triphenylphosphite 6H5)2b

ison 

O=P(C6H5)(OC 101-02-0 {RTECS TH1575000} [TMU250] 

LD50 (rat, oral) = 1600 mg/kg, LD50

(mouse, oral) = 1333 mg/kg. Po

by intraperitoneal, subcutaneous. 

Moderately toxic by ingestion. 

Severe skin irritant. HR = 3. 

Tris(2-bromoethyl) O=P(OCH2CH2Br)]3 27568-90-7 

c 

phosphate 

{RTECS TC8480000} [TNE600] 

LCLO (rat, inh) = 260 mg/m3. 

Poison by inhalation. Mutageni

data. HR = 3. 

Isopropyl methyl 

fluorophosphonate 

C4H10FO2P 107-44-8 

50 mg/m3, 

3 

oison by 

= 3. 

{RTECS TA8400000} [IPX000] 

LD50 (rat, inh, 10 min) = 1

LD50 (mouse, inh, 30 min) = 5 

mg/m3, TCLO (man, inh) = 90 μg/m

(eyes), LC50 (human, inh) = 70

mg/m3. Deadly human p

skin contact and inhalation. HR 

Mevinphos 

methylvinyl dimethyl 

phosphate) 

C H O P 7786-34-7 

(2-carbomethoxy-1- 7 13 6 {RTECS GQ5250000} [MQR750] 

LC50 (rat, inh, 1 hr) = 14 ppm. 

Poison by ingestion, inh, skin 

contact, subcutaneous, intravenous, 

intraperitoneal. HR = 3. 
NGP Surveys of Organic Compounds 669

Compound Name Formula CAS No. Observations a 

Monocrotophos 

(3-hydroxy-N-methyl-ciscrotonamide, dimethyl 

phosphate) 

4 

. 

C7H14NO5P 6923-22- {RTECS TC4375000} [MRH209]

LC50 (rat, inh, 4 hr) = 63 mg/m3. 

Poison by ingestion, inh, skin 

contact, intraperitoneal, 

subcutaneous, and intravenous 

routes. Mutagenetic data. HR = 3

Tetraethylpyrophosphate P(O)(OC2H5)2-

OP(O)(OC2H5)2

107-49-3 

 (rat, oral) = 500 μg/kg, LD

, 

, other. 

 = 3. 

{RTECS UX6825000} [TCF250] 

LD50 50

(mouse, oral) = 7 mg/kg, LD50 (rat

skin) = 2400 μg/kg. Poison by 

ingestion, skin contact, 

intraperitoneal, intramuscular

Cholinesterase inhibitor. HR

Triethylphosphate O=P(OC2H5)3 78-40-0 {RTECS TC7900000} [TJT750] 

LDLO (rat, oral) = 1600 mg/kg, LDLO

(mouse, oral) = 1600 mg/kg. 

Moderately toxic by ingestion, 

intraperitoneal, and intravenous. 

Reproductive effects. Mutagenic 

data. Cholinesterase inhibitor. HR = 

2. 

1,1,1-Trishydroxymethylpropane bicyclic 

phosphite 

C6H11O3P 824-11-3 {RTECS TY6650000} [TNI750] 

LCLO (rat, inh, 4 hr) = 10 ppm. A 

poison by ingestion, inhalation, skin 

contact, intraperitoneal, and 

intravenous routes. HR = 3. 

a The SAX No. (Reference 67) is given in brackets followed by information from that reference; the RTECS No. (Reference 

 OCl3 was due to the chlorine and that its 

197

ning b

)3) showed a more pronounced effect on 

flame 201 MMP, 

O=P(C at 

H2/O2/Ar flam MMP acted as a flame pro No cup burner n 

d ould be diffic s because of its ve ling 

point ( ow vapor pressure (160 Pa at 2 ). 

w

138) is given in braces. “HR” denotes the SAX Hazard Rating. 

b The most probable (phosphonate) structure is given for these compounds, which can also be assigned the phosphite structure 

(P(OR)3). Both forms may exist. 

Flame Chemistry and Flammability 

A description of the inhibition chemistry of phosphorus appeared in Chapter 3, and Section 7.3.5 of this 

chapter described the behavior of largely inorganic phosphorus-containing compounds. Over 40 years 

ago, it was proposed that the flame extinguishment action of P

high efficiency was due to ready formation of HCl in the flame. Subsequent research found that POCl3

was about 10 times more effective than an equivalent amount of chlorine.198 

Liquid halocarbons contai oth phosphates and phosphites had been claimed as fire extinguishants.199 

Phosphates and phosphate esters had been of particular interest as fire suppressants since they are difficult 

to ignite and self-extinguish.200 Trimethylphosphate ((O=P(OCH3

velocity than Cl2 or Br2. In an opposed-jet burner, dimethylmethylphosphonate (D

H3)(OCH3)2) was about 4 times more effective than halon 1301.202 However, studies on fl

 values have bee

r i

es indicated that D

P, and it w

moter.203 

etermined for DMM uch value

181 °C 58) and l

ult to obtain s

5 °C 204

y high bo

The estimated extinguishment concentrations of a broad range of organophosphates and phosphonates

ere estimated using a screening method based on the Flame Ionization Detector (FID) response of each 
670 Search for New Fire Suppressant Chemicals 

c 6,ii The data pre 7–31 indicate that in general the nonf phosphonates may extinguishants. However, many of the

c ey all have hig

ishment E s Acids and Est

ompound (Table 7–31).

205,20 sented in Table

luorinated phosphates and well be efficient

ompounds are flammable, and th h boiling points. 

Table 7–31. FID Extingu stimates of Phosphoru ers.

Compound Name Structure 

FID Extinguish. 

(volume %)

Trimethyl phosphate O=P(OCH3)3 0.6 – 2.8 

Dimethyl methylphosphonate O=P(OCH3)2CH3 0.7 

Diethyl methylphosphonate O=P(OC2H5)CH3 0.9

Dimethyltrifluoroethyl phosphate O=P(OCH3)2OCH2CF3 0.7

Diethyltrifluoroethyl phosphate O=P(OC2H5)2OCH2CF3 0.7

Diethylpentafluoropropyl phosphate O=P(OC2H5)2OCH2CF2CF3 0.7 

Diethylhexafluoroisopropyl phosphate O=P(OC2H5)2OCH(CF3)2 0.7

Diethylheptafluorobutyl phosphate O=P(OC2H5)2OCH2CF2CF2CF3 0.6 

Diethyloctafluoropentyl phosphate O=P(OCH2H5)2OCH2CF2CF2CFCF2H 1.1

Bis(2,2,2-trifluoroethyl)-2.2,3.3,3-

pentafluoropropyl phosphate O=P(OCH2CF3)2OCH2CF2CF3 0.7

Tris(2,2,2-trifluoroethyI) phosphate O=P(OCH2CF3)3 0.8

Tris(2,2,3.3,3-pentafluoro-l-propyl) phosphate O=P(OCH2CF2CF3)3 1.0

Tris(2,2,3,3,4,4,4-heptafluoro-l-butyl)

phosphonate O=P(OCH2CF2CF2CF3)3 1.8

Laboratory studies had also found that decomposition of organophosphorus compounds could generate 

additional fuel. Gas phase studies in nitrogen found that diethylmethylphosphonate (DEMP, 

O=P(CH3)(OCH2CH3)2) pyrolyzed to form ethene (CH2=CH2), ethanol (CH3CH2OH), and

ethylmethylphosphonate (O=P(OH)(CH3)(OCH2CH3)).207 Formation of ethene may have resulted from

formation of a six-membered ring transition state or by scission of a PO-CH2CH3 bond with subsequent

l (•CH2CH3). Similar results have been found in pyrolysis

pene (CH =CHCH

loss of a hydrogen atom from the ethyl radica

(DIMP), which generated pro 2 3), 2-propanol

(CH3CH(OH)CH3), isopropylmethylphosp onate (IMP, O=P(OH)(CH3)(OCH(CH3)2)), and 

methylphosphonic acid (MPA, O=P(OH)2(CH3)).208 A six-membered ring transition state (Figure 7–11)

was proposed for formation of 2-propene. s

spectrometry has identified DMP, (dimet OH)(OCH3)2), monomethylphosphate

(O=P(OH)2(OCH3)), MPA, orthophosphoric acid (O=P(OH)3), phosphorous acid (P(OCH3)3), and

phosphonic acid (O=PH(OH)2) as combustion products in a CH4/O2/N2 flame doped with DMMP.209

embered Ring

Transition State. 

studies of diisopropylmethylphosphonate

h

Derivatization followed by gas chromatography-mas

hylphosphate (O=P(

Figure 7–11. Formation of a Six-m

 

ii The FID extinguishment values are quite different from those obtained using a cup burner. This is because the gas 

chromatograph FID technique enables estimation of relative extinguishment performance for a small hydrogen flame. This is 

not equivalent to the extinguishment of a heptane pool. 

C2H5

H3C O C H

H

P

O

H
NGP Surveys of Organic Compounds 671

Attempts to determine a cup burner extinguishment value for a high volatility, nonfluorinated compound, 

trimethylphosphite (P(OCH3)3) have also been unsuccessful, due to its flammability. Each of the 

phosphorus compounds discussed above is, in fact, flammable at some concentration. 

rus-containing 

he flammability 

The NGP examined both of 

these approaches using the 

Preliminary Fluoroalkoxide Phosphorus Flame Suppression Testing 

E r studies and ma ties indicat osphonitriles were not ideal 

for testing owing to their low volati p o hine too toxic to cons 

p studies. Tab en available phosphorus-conta nds 

s ting, along ties. 

Table 7–32 Properties of Phosphorus-C Compounds. 

Nonetheless, there was good reason to expect efficient flame suppression from a phospho

compound (PCC), as long as (a) it decomposed to release the phosphorus atom and (b) t

was mitigated. This expectation led to extensive NGP examination of a range of families of PCCs in 

which a significant portion of the molecule was organic. 

There are two ways around the flammability problem. One is to blend the material with a nonflammable 

carrier; the other is to work with fluorinated alkyl derivatives of phosphorus. 

cup burner. 

xamination of prio terials proper ed that alkylph

lity, and that h sp s were likely 

le 7–32 presents sev

ider, except

ossibly for mechanistic ining compou

elected for preliminary tes with key proper

ontaining 

Compound Name Formula Tb , °C (kPa) Flash Point, °C 

Dimethylmethylphosphonate O=P(CH3)(OCH3)2 181 (101) 210 68 210

Trimethylphosphate O=P(OCH3)3 197 (101) None 

Trimethylphosphite P(OCH3)3 111-112 (101) 27 

(Bromodifluoromethyl) 

diethylphosphonate 

O=P(CBrF2)(C2H5)2 99-102 (2.1)211

220 (101) a

Not available 

Hexamethylphosphoramide O=P(N(CH3)2)3 230-232 (98) Not available 

Bis(2,2,2-trifluoroethyl)phosphite O=PH(OCH2CF3)2 43-44 (0.26) 210

190 (101) 210

76 210

Tris(2,2,2-trifluoroethyl)phosphite P(OCH2CF3)3 130-131 (99) 210 >110 210

a Estimated using pressure-temperature nomograph. 

Testing of dimethylmethylphosphonate (O=P(CH3)(OCH3)2) was attempted using the Standard NMERI 

cup burner but due to its high boiling point, the material was difficult to volatilize. The elevated 

temperature caused some decomposition to a black, tarry substance. A single test gave an extinguishing 

value of 5 volume %. This was considered a maximum value because not all the compound was available 

to extinguish the fire. 

)3) was also difficult to test due to its high boiling point. The 

extinguishment value of 6.6 volume % is high, as it was observed that a small amount of the compound 

Trimethylphosphate (O=P(OCH3

did not volatilize in the mixing chamber. With a higher chamber temperature (328 °C), an 

extinguishment value of 6.8 volume % was obtained; however, again, some of the compound in the 

mixing chamber did not volatilize. At a mixing chamber temperature of 344 °C, a cup burner value of 

5.3 volume % was obtained. This value was also suspect, since the n-heptane in the fuel cup boiled and 

was difficult to control. 
672 Search for New Fire Suppressant Chemicals 

Trimethylphosphite (O=P(OCH3)3) was flammable and ignited. Complete extinguishment of the nheptane flame was not achieved. 

Only a small amount of (bromodifluoromethyl)diethylphosphonate (O=P(CBrF2)-(C2H5)2) was available. 

During the first test, the flame extinguished readily at a value of 4.7 volume %. The second test 

employed approximately one-third that of the first test. Even though the temperature of the heated 

he compound after the syringe 

pump was turned off, which indicated that the compound in the mixing chamber continued to volatilize 

ared to volatilize, but n-heptane boiling was observed at the 

extinguishment point of 1.4 volume %. Thus, the extinguishment concentration was estimated to be 

Testing of hexamethylphosphoramide (O=P[N(CH3)2]3) was difficult due to its high boiling point and low 

va

Tris(2,2,2-tr tested at a chamber ure of 200 °C. uishing 

v

T blended with either HFC-227ea or HFC-125 to form a nonflammable 

m ent co determined (Table 3). These 

ixtures were 1 % to 2 % lower in extinguishment concentration than the respective pure HFC. 

chamber at the base of the cup burner was 250 °C, it appeared that the compound did not volatilize 

completely. The flame continued to show some extinguishment from t

even after the agent supply was stopped. The temperature of the heated chamber was therefore increased 

to 300 °C and the compound appe

between 1.4 volume % and 4.7 volume %. A test with an increased flow and a slightly lower chamber 

temperature (270 °C) resulted in an extinguishment value of 3.3 volume %. 

por pressure. An extinguishment value of 8.7 volume % was obtained. 

ifluoroethyl)phosphite was temperat An exting

alue of 1.8 volume % was obtained. 

rimethylphosphite was also

ixture, and cup burner flame extinguishm ncentrations were 7–3

m

Table 7–33. Flame Extinguishment Values for Trimethylphosphite Blends with HFCs. 

Compound Name (/Blend) Formula 

Extinguishment Value, 

volume % 

1,1,1,2,3,3,3-Heptafluoropane (HFC-227ea) CF3CHFCF3 6.2 

Trimethylphosphite/HFC-227ea (7.2 %/92.8 %) P(OCH3)3/CF3CHFCF3 5.1 

Pentafluoroethane (HFC-125) CHF2CF3 8.7 

Trimethylphosphite/HFC-125 (12.2 %/87.8 %) P(OCH3)3/CHF2CF3 6.8 

From these data, it was concluded that highly fluorinated PCCs in this family can have flame 

extinguishment efficiencies comparable to halon 1301. While blending flammable PCCs with an HFC 

might reduce the flammability hazard, the flame extinguishment concentration was dominated by the 

HFC, and the mixture concentration offered little advantage over the HFC alone. Moreover, during the 

discharge process, disproportionation of the mixture is likely, potentially creating a zone in which a 

flammable PCC concentration exists. 

Second Series Compound Availability and Synthesis 

toxicity. The selected compounds represented a range of related structures and included both phosphine 

This first set of results led to the selection of a second set of phosphorus-containing compounds for 

examination. In this process, compounds such as PH3 or P(CH3)3 were ruled out as being flammable, 

while compounds involving P-F bonds were ruled out due to expected hydrolysis and unacceptable 
NGP Surveys of Organic Compounds 673

and phosphonate compounds. Including both P(III) and P(V) phosphorus oxidation states, as well as 

incorporating, where possible, similar fluorinated substituents increased the probability of identifying 

promising chemical families. Promising compounds would serve as guides to future research and 

Phosphites (Phosphonates) and Phosphates 

tris(trifluoromethyl)phosphite (P(OCF3)3) and tris(trifluoromethyl)phosphate 

(O=P(OCF3) ). 

The phosph

unsuccessfu

alcohols tha

oxygen are 

carbonyl co

undertake th

•

y. ∆H was 

e reaction may provide a pathway for decomposition. This is particularly likely since 

the entropy of the decomposition reaction would almost certainly be positive due to the 

• Reaction of phosphorous acid with trifluoromethyl iodide: P(OH) + 3CF I → P(OCF3)3 + 

3H

A synthesis for the phosphate has been published, based on oxidation of tris(tri osphine 

(P(C I iling nd a me oint of -86 ssure, 

p, in kPa can be fit to the equation log10p = -1445/T + 4.45, where T is in K, yielding a vapor pressure of 

40 kPa (0.4 atm) at 25 °C. This vapo is sufficient for cup burner testing, b at -40 oC 

of 0.02 kPa is far too low for aircraft GP attempt to produce this compound was unsuccessful. 

compound synthetic efforts. 

Each of the selected compounds needed to be synthesized for the NGP. This was accomplished using 

utilizing bench top and vacuum line procedures. Each of the products was purified and then 

characterized, as needed for structure verification, by 19F, 31P and 13C NMR, infrared and mass spectral 

measurements and by elemental analysis. The syntheses performed, as well as relevant literature 

references, are briefly described below. Table 7–37, at the end of the section, summarizes the results. 

The most problematic features of these families of PCCs were high boiling points and flammability. 

Fluorination reduced both. Thus, the most promising additional compounds have formulas such as 

P(ORf)3 or O=P(ORf)3, where Rf is a fluorinated group, which should have as low a molecular weight and 

as high a degree of fluorination as possible. Based on this, two logical compounds for further 

examination were 

3

ite was not commercially available, and efforts to obtain a custom synthesized sample were 

l. Protonated phosphites can be synthesized by reaction of PCl3 with ROH. Unfortunately, 

t could be used to prepare esters containing fluorine bound to the carbon atom adjacent to 

inherently unstable, breaking down by a 1,2-elimination of hydrogen fluoride (HF) to give 

mpounds. Alternative synthetic processes were proposed, but with no laboratory willing to 

e effort. 

Reaction of trifluorophosphine with carbonyl fluoride: PF3 + 3 O=CF2 → P(OCF3)3. The 

enthalpy of reaction (∆Hr) was estimated based on published bond energy values.212,213,214 

Table 7–34 provides data used in these calculations. The column marked “Basis” indicates 

the type of compound or types of compounds used to determine the bond energ r

estimated as 92 kJ/mol (22 kcal/mole). Thus, the reaction is slightly endothermic, and the 

revers

increase in the number of moles of gas. (Were the material to be formed as the phosphonate 

structure, O=P(CF3)(OCF3)2, the reaction is less endothermic, with ∆Hr estimated as to be 

58 kJ/mol (14 kcal/mole). Again, however, the reverse reaction should have a positive 

entropy change. Even though the reactions are predicted to be endothermic, one must 

recognize that the use of average bond energies is highly suspect.) 

3 3

I. 

fluoromethyl)ph

F3)3).215 t has a bo point of 52 °C at 101 kPa a lting p °C. The vapor pre

r pressure ut the value

use. An N
674 Search for New Fire Suppressant Chemicals 

Ta e 7–34. Enthal ction for P bl py of Rea F3 + 3 O=CF2 → P(OCF3)3. 

Bond

∆H, Total for Bond Formation 

or Dissociation 

Type Number Energy, cal/mol) kJ/mol (k Basis kJ/mol (kcal/mol) 

Reactants 

P-F 3 498 (119) PF3 1500 (360) 

C-F 6 490 17) CF (1 4 2900 (700) 

C=O 3 749 (179) Ketones 2200 (550) 

Sum 6 700 (1600)

Product, Phosphite Structure 

P-O 3 368 (88) P4O6 1 100 (260)

C-F 9 490 (117) CF4 4400 (1050) 

C-O 3 358 (85.6) Organics 1070 (260) 

Sum 6600 (1600) 

Product, Phosphonate Structure 

P-O 2 368 (88) P4O6 740 (180) 

P=O 1 456 (109) O=PCl3 460 (110) 

P-C 1 306 (73) 310 (70) 

C-F 9 490 (117) CF4 4490 (1100) 

C-O 2 358 (85.6) Organics 720 (170) 

 Sum 6600 (1600) 

Attention then focuse

• Tris(trif 37). This two-step 

synthesis (Reactions 7-43 and 7-44) involved reaction of red phosphorus with CF3I, forming 

 yield) (7-43)

3 3 2 2 3 3

7-45. 

3 2 2 3 3 

3

hesis of Compound l. The NO was removed under vacuum. 

This reaction is summarized in Reaction 7-46. 

 

d on four phosphite/phosphonate compounds.iii

luoromethyl) Phosphonate, O=P(CF3)3 (Compound 1, Table 7–

the flammable intermediate (CF3)3P. This was followed by an oxidation insertion reaction 

with nitrous oxide and nitrogen dioxide to form the phosphonate, (CF3)3P=O.38

Red Phosphorus + CF3I (232 °C, 60 hr) —h P(CF3)3, (52 %

P(CF ) —— (N O, NO )—h (CF ) P=O (100 % yield) (7-44)

• Tris(2,2,2-trifluoroethoxy) Phosphite, P(OCH2CF3)3 (Compound 2, Table 7–37). This 

synthesis was carried out by adding trifluoroethanol dropwise into a vigorously stirred 

solution of phosphorus trichloride (slight excess) at 0  ̊C. After 5 h, fractional distillation 

gave the desired product. This reaction is summarized in Reaction 

PCl3 + CF CH OH—————hP(OCH CF ) (100 % yield) (7-45)

• Bis(trifluoromethyl) trifluoromethoxy Phosphonate, O=P(OCH3)(CF3)2, (Compound 3, 

Table 7–37). The (CF3)2POCF intermediate was oxidized with a slight molar deficiency of 

nitrogen dioxide as in the synt

iii Rearrangements can occur between the phosphite form, e.g., P(OR)2R, and the phosphonate form, e.g., O=P(OR)R2. 
NGP Surveys of Organic Compounds 675

3 —— (O)OC

ethyl) 2,2,2-trifluoroethoxy Phosphonate, (CF3)2P(O)OCH2CF3, (Compound 4, 

 similar to that for Compound 3. This reaction is 

—————h 3 2 2 3

Fluoroalkyl Phosphines 

Fo earned fro revious family of com amination of the s 

focused on the smallest, heavily fluorinated mole published data for some of the 

s ully fluorinated organ . 

Tab . Perfl hosphines. 

(CF3)2POCF (NO2)——h(CF3)2P H3 (100 % yield) (7-46)

• Bis(trifluorom

Table 7–37). This synthesis is very

summarized in Reaction 7-47. 

(CF3)2POCH2CF3

NO2

—— (CF ) P(O)OCH CF (7-47) 

llowing the lessons l m the p pounds, ex phosphine

cules. Table 7–35 shows

implest f ic phosphines

le 5 7–3 uoroalkyl P

Compound Formula Tb (°C) Properties Reference 

(CF3)3P 17 Spontaneously flammable 216 

(CF3P)4 Not available Solid, melting point 66.4 °C 220 

(CF3P)5 190 Not available 220 

(CF3)2PP(CF3)2 83 to 84 Flammable 216 

(C2F5)3P 70 Not available 211 

The simplest perfluorinated trialkyl compound is tris(trifluoromethyl)-phosphine ((CF3)3P), which has 

been prepared as a mixture with trifluoromethyldiiodophosphine, (CF3)PI2, and bis(trifluoromethyl)-

iodophosphine, (CF3)2PI, by reaction of phosphorus with trifluoroiodomethane (CF3I),216 and also by 

reaction of tris(diethylamino)phosphine, P(N(C2H5)2)3, with trifluoromethyl bromide (CBrF3, halon 1301) 

and triphenylphosphite, O=P(OC6H5)3, in tris(dimethylamino)phosphine oxide, OP(N(CH3)2)3, 

hexamethylphosphor-amide, HMPA).217 Unfortunately, this material (like some of its complexes218) is 

spontaneously flammable (Table 7–35). The iodide derivatives are exceedingly useful precursors for a 

atives are likely to be more stable than the methyl 

pounds having the general formula 

have 

been synthesized as bidentate ligands starting with (CF3)2PP(CF3)2. It has been stated that these 

number of compounds of interest here; however, even with optimized procedures,219 the syntheses are 

difficult, and the reactants and products are hard to handle. Reaction of (CF3)2PI with mercury gives the 

flammable compound tetrakis(trifluoro-methyl)diphosphine (CF3)2PP(CF3)2

 216 and the tetrameric and 

pentameric cyclic compounds (CF3P)4 and (CF3P)5

220 (Table 7–35). The compounds (CF3)PF2 and 

(CF3)2PF are also known.221

The higher molecular weight perfluoroalkyl deriv

compounds. Tris(pentafluoroethyl)phosphine ((C2F5)3P), with a boiling point of 70 °C, has been prepared 

by reaction of phosphorus trichloride (PCl3) with ethyl lithium (C2F5Li), which can be prepared by 

reaction of chloropentafluoroethane (C2F5Cl) with n-butyl lithium (C4F9Li).211 The procedure, however, 

has not been published. It has proven impossible to prepare the tris(heptafluoropropyl)-phosphine 

((C3F7)3P), apparently due to steric hindrance.222

A large number of trifluoromethyl-substituted diphosphorus com

(CF3)2PRP(CF3)2, where “R” represents a branched or linear hydrocarbon or fluorocarbon chain, 

223,224
676 Search for New Fire Suppressant Chemicals 

compou s

similar com

The primary

Based on th

• Bis(trifluoromethyl)methoxy Phosphine, (CF3)2POCH3, (Compound 5, Table 7–37). The 

intermed n 

and red phosphorus, was reacted at 25  ̊C with AgCl to form (CF3)2PCl at an approximately 

(C 3OH F3)2P

2 N 

) 2,2,2-trifluoroethoxy Phosphine, (CF3)2POCH2CF3, (Compound 7, 

Table 7–37). This synthesis, very similar to Reaction 7-49, is summarized in Reaction 7-50. 

sphine ((C3F7)2PNH2), a high boiling liquid (Table 7–36), has been 

prepared by reaction of (C3F7)2PCl with anhydrous ammonia.222 As is typical for all of these reactions, 

e starting material was prepared by reaction of heptafluoropropyl iodide with phosphorus at high 

temperature and pressure followed by replacement of the iodide with chloride using silver chloride. 

Th e simplest of these compounds was insu ircraft use, and t l 

f t examined f . 

nd are difficult to prepare owing to difficulty in synthesis of the diphosphine precursor.211 A 

pound has also been prepared: (C2F5)2PCH2CH2P(C2F5)2, boiling point 105 °C at 11 kPa.225 

 interest in these compounds is as bidentate ligands.226 

is information, the following three compounds were synthesized for further examination. 

iate, (CF3)2PI, formed as one of the products in 25 % yield from the reactio of CF3I 

100 % yield. The chloride was subsequently reacted with methanol in the presence of 

triethylamine, substituting the methoxide for the iodine. 38 This reaction is summarized in 

Reaction 7-48. 

F3)2PCl + CH /(CF3CH2)3N —h (C OCH3, (85 % yield) (7-48)

• Bis(2,2,2-trifluoroethoxy) trifluoromethyl Phosphine, (CF3)P(OCH2CF3)2, (Compound 6, 

Table 7–37). This synthesis is very similar to the synthesis of Compound 5. This reaction is 

summarized in Reaction 7-49. 

(CF3)PCl2

2eq CF3CH2OH 

———————h

eq (CF3CH2)3

(CF3)P(OCH2CF3)2 (7-49) 

• Bis(trifluoromethyl

CF3)2PCl 

CF3CH2OH 

 ———————h 

(CF3CH2)3N 

(CF3)2POCH2CF3 (7-50) 

Amino Fluoroalkylphosphines 

Aminobis(trifluoromethyl)phosphines ((CF3)2PNR2, R= -H, -CH3) have been prepared by reaction of 

chlorobis(trifluoromethyl)phosphine ((CF3)2PCl) with the appropriate amine.227 Though these materials 

are relatively stable liquids (Table 7–36), they are readily oxidized in air. The simplest amino compound 

is spontaneously flammable, as is the (CF3)2PCl starting material. Amines containing two and three 

bis(trifluorophosphine) groups228 and compounds of the type [(CF3)2N]nP(CF3)3-n, n = 1 to 3 (the latter 

discussed further in Reference 93) have also been prepared (Table 7–36). The starting materials, 

however, are also spontaneously flammable: (CF3)2PCl or tris(trifluoromethyl)phosphine ((CF3)3P). 

Aminobis-(heptafluoropropyl)-pho

th

e volatility of even th fficient for a his chemica

amily was no urther
NGP Surveys of Organic Compounds 677

Table 7–36. Amino Fluoroalkylphosphines. 

Compound Formula Tb (°C)a Properties Re ce feren

(CF3)2PNH2 67.1 Spontaneously flammable 227 

(CF3)2PNH(CH3) 72.3 Not available 227 

(CF3)2PN(CH3)2 83.2 Not available 227 

((CF3 2 2 ) P) NH Not available Vapor pressure 6.2 kPa at 23.9 °C 228 

((CF3)2P)2NCH3 Not available Vapor pressure 2.3 kPa at 25.0 °C 228 

((CF3)2P)3N Not available Solid, melting point 36.5 oC to 36.8 °C 228 

(CF3)2NP(CF3)2 51 Stable at room temperature 229 

((CF3)2N)2P(CF3) 92.5 Stable at room temperature 229 

((CF3)2N)3P 135 Stable at room temperature 229 

(C2F7)2PNH2 143 Not available 222 

a 101 kPa (nominal) pressure. 

Reactivity in Air 

Upon breaking open their respective glass sealed vials, Compounds 5 and 7 reacted extremely vigorously 

(i.e., fumed) as air entered and contacted the liquid agent. Some fuming was also noted for Compounds 3 

and 6. It may be that compound 7 underwent air oxidation to yield a phosphonate structure, 

O=P(OCH2CF3)(CF3)2, or oxygen insertion reactions at the P-CF3 bonds. 

Cup Burner Flame Extinguishment Testing 

In view of the wide range of boiling points represented by the compounds synthesized, a means was 

required for preventing the condensation on cooler surfaces and countering the evaporative cooling 

d 55 oC counteracted the evaporative cooling effects of the misted agent at the tip of 

rization. On mixing with the cooler, nebulized agent/air stream, 

perature dropped to between 45 oC to 50 oC. The preheated air was also employed to 

Observations 

Only Compound 4 approached the desired boiling point range. In the trade-off between higher degree of 

effects of the nebulized agent as they dispersed into the air stream of the cup burner. Heating the inlet air 

to between 50 oC an

the nebulizer and enhanced droplet vapo

the column tem

warm the entire cup burner chimney prior to a test run, and as a result no condensation of agent was 

observed during or following extinguishment testing. 

Due to the limited quantities of some agents, each was tested no higher than the screening concentration 

of 5 % by volume. 

It is possible that phosphonates having multiple -CF3 groups are too stable for the phosphorus atom to be 

released into the cup burner flame. When Compound 1 was tested at 5 volume %, no evidence of flame 

lift-off was observed. Compound 3, with two -CF3 groups, showed lift-off and flame extinguishment just 

below 5 volume %. Compound 4, also with two -CF3 groups, showed lift-off but no flame 

extinguishment at 5 volume %. 

fluorination to reduce the boiling point and moderate hydrogenation for efficient fire suppression, there 

may be limited further promise in this family of compounds. This conclusion must be tempered by the 

observed low cup burner test value (1.8 %) of compound 7 and the possibility that air reaction is 

converting it to a very efficient flame suppressant. It cannot, however, be concluded at this point that the 
678 Search for New Fire Suppressant Chemicals 

air oxidation produces a complete conversion to a single compound or that the reaction is complete by the 

time the products enter the flame zone. 

In earlier work, Compound 2 had been reported to have a cup burner extinguishment value of 

1.78 volume % for n-heptane fuel.39 This value is much lower than that measured subsequently and 

reported here. Differences in manner of sample vaporization could well be responsible. In the earlier 

studies, a hot sand bath (>250 oC) was employed to volatilize the compound as it was introduced into the 

base of the cup burner. It is possible this method induced thermal decomposition and air reaction of the 

test compound, yielding a more effective flame suppressant. 

Compound 7, though air reactive, yielded an impressively low cup burner value. It is possible this low 

ropellant fire extinguishers or powder panels (Chapter 9) might be achieved. The 

nature and toxicity of compound 6 air decomposition products needs to be determined. 

higher effectiveness, make this compound a prime target for further 

research and testing. 

they can be ruled out as candidates 

 compounds were identified that met needed criteria for volatility, stability, and 

flame suppression efficiency. Some may be useful flame suppressants at temperatures above the current 

perature criterion. Given the high flame suppression efficiency of a chemically liberated 

phosphorus atom, a well chosen PCC could enhance the effectiveness of solid propellant fire 

 Determination of the decomposition rates and combustion products could further that 

choice. Some of the phosphorus compounds are polar or reactive (to hydrolysis) and thus are likely to 

have short atmospheric lifetimes. The environmental fate of their decomposition products fate would 

need to be assessed. 

value might have been due to a breakdown product whose air concentration was even lower than 

1.8 volume %. Identification and study of Compound 7 (or Compound 5) air reaction products might lead 

to significant advancements in phosphorus-based suppressants for aircraft dry bays and other unoccupied 

areas. If the extinguishing concentration were 1 volume % or lower, significant improvements in the 

efficiencies of solid p

The synthesis attempted of (tris(trifluoromethoxy) phosphonate, O=P(OCF3)3) had been reported in the 

literature. While the NGP was unable to obtain this compound, a realistic expectation of its synthesis still 

exists. Its similarity to the structures thought to be the breakdown products from compound 7, that may 

be contributing to its demonstrated

Phosphines provide good materials for mechanistic studies; however, 

owing to their inherent low stability (many are flammable, sometimes spontaneously, even with 

fluorinated substituents) and high toxicities. Though it is possible to obtain fire extinguishment 

(sometimes very efficient) with phosphazenes, these compounds have inherently high molecular weights 

and, therefore, very low volatility. 

Fluoroalkyl (alkoxide) Phosphorus Compounds - Summary 

No phosphorus-containing

low tem

extinguishers.
NGP Surveys of Organic Compounds 679 Table 7–37. Phosphorus-containing Compound Performance. Compound Name Formula Mass Available(g) Tb (oC)a Ext. Conc. (vol. %) Exposure of Agent to Air 1 Tris(trifluoromethyl) Phosphonate O=P(CF3)3 7.3 32 None @ 5 % No fumes or ignition 2 Tris(2,2,2-trifluoroethoxy) Phosphite P(OCH CF 2 3)3 50.0 130 (est.) 3.1 No fumes or ignition 3 Bis(trifluoromethyl) trifluoromethoxy Phosphonate O=P(OCH3)(CF3)2 5.5 42 4.6 Fumes, no ignition 4 Bis(trifluoromethyl) 2,2,2- trifluoroethoxy Phosphonate O=P(OCH CF 2 3)(CF3)2 7.0 130 None @ 5 % No fumes, did not ignite cloth 5 B e 5.3 55 is(trifluoromethyl)methoxy Phosphin P(OCH3)(CF3)2 Ignited on air exposureb Ignited spontaneously 6 Bis(2,2,2-trifluoroethoxy) trifluoromethyl Phosphine P(OCH CF 2 3) CF 2 3 7.2 111 3.0 Fumes, no ignition 7 Bis(trifluoromethyl) 2,2,2- trifluoroethoxy Phosphine P(OCH CF 2 3)(CF3)2 6.5 25 8 1. Ignited cloth, fumed strongly a. Determined at nominally 100 kPa, except Compound 7 at 7 kPa. b. In view of the low cup burner test value of Compound 7, the structurally similar Compound 5 was preserved in order to provide a future opportunity to identify the product of its reaction with air.
680 Search for New Fire Suppressant Chemicals 

7.4.5 Fluoroalkyl Nitrogen-based Candidates 

Atmospheric Lifetime, ODP, and GWP 

The fact that nitrogen oxides could be direct depleters of stratospheric ozone was recognized earlier than 

that halocarbons posed an environmental threat.230 The first concerns were about direct injection of 

nitrogen oxides into the stratosphere by high altitude aircraft.231 Nitrogen compounds, however, play 

other roles in atmospheric chemistry involving ozone depletion. The ozone chemical balance depends 

directly on the total amount of active nitrogen species.232 Nitric oxide (NO) releases chlorine from 

chlorine monoxide (Reaction 7-52).233 Nitrogen oxides can also decrease stratospheric ozone depletion 

by the formation of the chlorine nitrate (ClONO2) reservoir (Reaction 7-53)233 and by the removal of •OH 

(Reactions 7-54 through 7-56).234 Hydroxyl free radicals convert HCl and HBr to free chlorine and 

bromine atoms, which are potent depleters of stratospheric ozone. Removal of nitric acid by 

condensation is believed to play a major role in the Antarctic ozone hole.234

•NO + •ClO→ Cl + •NO2, ∆Hr = -37 kJ/mole, ∆Gr = -28 kJ/mole (7-52)

•NO2 + •ClO→ ClONO2 (7-53)

•OH + HNO3 → H2O + •NO3 (7-54)

•NO3 + hν → •NO2 + •O (7-55)

•OH + •NO2 + M → HNO3 + M*, ∆Hr = -206 kJ/mole, ∆Gr = -159 kJ/mole (7-56)

Since some highly fluorinated amines have long atmospheric lifetimes, it is possible that anthropogenic 

amines of interest in this research could deplete stratospheric ozone. 

A relatively large amount of data are available for reactions of atmospheric •OH radicals with nitrogencontaining compounds; however, few experimental data (as opposed to estimations) are available for 

compounds that might be useful as halon 1301 replacements, i.e., those containing fully or partially 

fluorinated alkyl groups (to improve toxicity and flammability characteristics). Amines containing no 

hydrogen atoms are expected to be inert to attack by •OH, which can be seen in the absence of reaction 

observed with N,N-bis(pentafluoroethyl)penta-fluoroethanamine (N(CF2CF3)3), for which an •OH rate 

constant k2 < 6 x 10-16 cm3

/molec-s has been reported.235 This rate constant corresponds to an estimated 

atmospheric lifetime of greater than 55 years. 

A relatively large amount of data is available for hydrogen-containing, nonfluorinated amines. 

Nitroalkanes (RNO2) have been relatively well studied,236 but these have little resemblance to amines, 

which are the most promising of the nitrogen-containing halon replacements. As a result of concerns 

about health impacts, the atmospheric chemistry of N-nitrosodimethylamine ((CH3)2N-NO) and 

dimethylnitramine ((CH3)2N-NO2) has been examined.237 Table 7–38 presents rate constants for hydroxyl 

free radicals reactions with several nonfluorinated amines.119 Where several values were given, the first 

value cited at or near 298 K was used for consistency. These values were calculated at or near the high 
NGP Surveys of Organic Compounds 681

pressure limit. Atmospheric lifetimes in Table 7–38, calculated from a globally tropospheric •OH 

concentration of 9.7 x 105

 molecules/cm3, are on the order of a few days or less. The reactions of all of 

the compounds in Table 7–38 probably involve hydrogen atom abstraction from the alkyl groups. Since 

all of these compounds are highly polar, rainout would also be an effective removal mechanism. 

Rate constants have been compiled for gas-phase reactions of O3 with a number of nitrogen-containing 

compounds,238 and the data for amines are shown in Table 7–39. The rate constants increase and lifetimes 

(estimated from the globally averaged tropospheric O3 concentration) decrease with increasing alkyl 

substitution. This is also the direction of increasing proton affinity (-∆H for the reaction B + H+ → BH+, 

where B is a base).239

Table 7–38. •OH Rate Constants for Nitrogen-containing Compounds. 

Compound Name kOH, cm3/molec-s Temperature (K) 

Atmospheric 

Lifetime (days)a

Methylamine, NH2(CH3) 22.0 ± 2.2 x 10-12 299 0.5 

Ethylamine, NH2(CH2CH3) 27.7 ± 2.8 x 10-12 299.6 0.4 

Dimethylamine, NH(CH3)2 64.5 ± 6.6 x 10-12 298.5 0.2 

Trimethylamine, N(CH3)3 60.9 ± 6.1 x 10-12 298.7 0.2 

Diethylhydroxylamine 

N(CH2CH3)2OH 101 x 10-12 308 0.1 

2-(Dimethylamino)ethanol 

CH2(N(CH3)2)CH2OH 47 ± 12 x 10-12 300 ± 2 0.3 

2-Amino-2-methyl-1-propanol 

CH3C(CH3)(NH3)CH2OH 28 ± 5 x 10-12 300 ± 2 0.4 

N-Nitrosodimethylamine 

(CH3)2N-NO 02.53 ± 0.21 x 10-12 298 ± 2 4.7 

Dimethylnitramine, (CH3)2N-NO2 03.84 ± 0.15 x 10-12 298 ± 2 3.1 

a Based only on reaction with •OH. 

Table 7–39. Rate Constants for Reactions of O3 With Amines. 

Compound Formula 

k2 at 296 K, 

(cm3/molec-s) 

Estimated Tropospheric 

Lifetime (days) 

Proton Affinity 

(kJ/mole) 

NH2(CH3) 2.13 ± 0.29 x 10-20 1087 896 

NH2(CH2CH3) 2.76 ± 0.34 x 10-20 839 908 

NH(CH3)2 2.61 ± 0.30 x 10-18 008.9 923 

N(CH3)3 9.73 ± 1.02 x 10-18 002.4 938 

The reactions appear to proceed by addition of O3 to the nitrogen to give R3N+-O-O-O-, which then 

decomposes by uncertain mechanisms. Data for reactions involving halogen-substituted alkyl amines 

have not been reported; however, it is likely that the reaction rates will decrease with increasing halogen 

substitution, which makes the nitrogen atom less electron rich. 

Rate constants have also been reported for reaction of O3 with pyridines (approximately 

5 x 10-20 cm3

/molec-s to 50 x 10-20 cm3/molec-s) and for unsaturated nitriles (< 1 x 10-19 cm3/molec-s to 

1.38 x 10-19 cm3

/molec-s for acrylonitrile CH2=CHCN and 3.52 x 10-19 cm3/molec-s for methacrylonitrile 

CH2=C(CH3)CN).121 Ozone is known to react with alkene derivatives, and the results for the acrylonitriles 
682 Search for New Fire Suppressant Chemicals 

probably have little to do with the presence of nitrogen. The pyridines, which are, at best, distantly related to 

the amines of interest, have calculated lifetimes for reaction with tropospheric ozone of approximately 1 year 

or less. The maximum values of the rate constants for reaction of N-nitrosodimethylamine (CH3)2N-NO and 

dimethylnitramine (CH3)2N-NO2 with tropospheric ozone are 1 x 10-20 cm3

/molec-s and 3 x 10-21 cm3/molec-s 

(calculated lifetimes of 6 years and 21 years, respectively) and could be less than this.237 Photolysis is probably 

the primary removal mechanism for N-nitrosodimethylamine. 

Of particular interest for fire suppression are alkyl-substituted amines, with one or more alkyl groups 

containing bromine atoms. The primary problem is that fluorination is needed to decrease both the 

flammability and toxicity of amines. As fluorination increases, both the polarity and the flammability are 

expected to decrease (for different reasons). The polarity is directly related to toxicity, since highly polar 

amines are strong bases and therefore irritants. The polarity is, however, also directly related to the 

effectiveness of atmospheric removal. Nonfluorinated amines are expected to undergo significant rainout. 

Reported lifetimes and GWPs were reviewed for several fluoroalkyl amines in Reference 240. However, 

the values are highly suspect. For example, the lifetime of (CH3)2NC2F5 is reported as 250 years, while 

that of the much less hydrogen-rich compound (CF3)2NCF2CF2H is given as 2.10 years.241 Moreover, the 

estimation methods for the lifetimes and GWPs were not reported. Eliminating the highly questionable 

value of 250 years gives estimated lifetimes for hydrofluoroamines (HFAs) of around 0.3 years to 

3 years.241 

While there is nothing inherent in nitrogen compounds that would lead to atmospheric lifetime or GWP 

problems, individual compounds may have significant effects. Replacement of fluorine atoms with 

bromine atoms would tend to reduce HFA lifetimes by a factor of 10 in some compounds. Data indicate 

that for bromine-containing alkanes, each 10-year increase in the atmospheric lifetime increases the ODP 

by approximately a factor of 2. Therefore, hydrofluorobromoamines should have low ODPs. Any impact 

from nitrogen on stratospheric ozone would be negligible compared to that from bromine. 

Research from the National Industrial Research Institute of Nagoya has focused on fluoroalkylamines, 

with an emphasis on perfluoroalkyl derivatives, as fire suppressants.242 All of their fluoroalkylamines 

inhibited flame propagation less efficiently than CF3Br, but more efficiently than HFC-227ea. A 

thorough assessment of the atmospheric impact of fluorinated amines and of bromofluoroamines (based 

on estimations and calculations) has been presented.240 For example, the compound (CBrF2)(CF3)NCH3 

is estimated to have an atmospheric lifetime of 10 days and an ODP of 0.006 relative to CFC-11.240 The 

amine N(CF3)2CF=CF2 is expected to have a lower atmospheric lifetime due to the presence of its -F=CF2

group. 

Toxicity 

The acute inhalation toxicities of some hydrofluoroamines (HFAs) are given in Table 7–40.29 These have 

also been reviewed in Reference 240; however, here the LC50 values are also given as volume percent. 

Although these lower bounds do not cause any concern, measurements at higher concentrations are 

needed. In addition to the compounds shown in Table 7–40, the LCLO for mouse inhalation has been 

reported as 0.0123 volume % for 2,2,2-trifluoroethylamine (CF3CH2)NH2,

67 a value that appears rather 

low; however, this compound contains hydrogen atoms directly bonded to the nitrogen. 
NGP Surveys of Organic Compounds 683

Table 7–40. Acute Inhalation Toxicity of Hydrofluoroamines. 

Compound Formula 

Exposure Time, 

Subject LC50 (mg/L) 

Molecular 

Weight LC50 (volume %) 

(CF3)2NCH3 3 h, rat >20 113.99 >0.43 

(CF3)2NCF2CF2H 3 h, rat >20 253.04 >0.19 

(CF3)2NCFHCF3 3 h, rat >20 253.04 >0.19 

(CF3)2NCH2CF3 3 h, rat >20 235.05 >0.21 

(CF3)2NCH2CF2H 4 h, rat >20 217.06 >0.23 

(CF3)2NCH2CH3 4 h, rat >20 181.08 >0.27 

A review of Reference 67 identified inhalation toxicity data for over 120 compounds containing both 

nitrogen and fluorine; however, inhalation data are available for only 6 of these (Table 7–41). Nearly 

every compound in this limited set is given a SAX HR of 3, signifying the worst hazard level. However, 

none of these compounds is closely related to amines, and most contain groups known to lead to toxicity. 

Many N-nitroso compounds, such as the nitrosocarbamates, are carcinogens. 

Table 7–41. Toxicity and Safety Information for Selected N, F Compounds. 

Compound Name Formula CAS No. Observations a

fluoroacetanilide C8H8FNO 330-68-7 {RTECS AE2975000} [FFH000] LCLO (mouse, inh, 

10 min) = 480 mg/m3. Poison by ingestion, 

intraperitoneal, and possible other routes. 

Moderately toxic by inhalation. HR = 3. 

beta-fluoroethyl-N-

(beta-chloroethyl)-Nnitrosocarbamate 

C4H8ClFN2O3 63884-92-4 {RTECS EZ2275000} [IH000] LCLO (guinea pig, 

inh, 10 min) = 300 mg/m3

. Poison by inhalation. 

HR = 3. 

2-fluoroethyl-Nmethyl-Nnitrosocarbamate 

C4H7FN2O3 63982-15-0 {RTECS FC6475000} [FIS000] LCLO (guinea pig, 

inh, 10 min) = 100 mg/m3, LCLO (mouse, inh, 10 

min) = 500 mg/m3

. Poison by inhalation. HR = 3. 

3-nitrobenzotrifluoride C7H4F3NO2 98-46-4 RTECS XT3500000} [NFJ500] LC50 (rat, inh) = 

870 mg/kg, LC50 (mouse, inh, 2 hr) = 880 mg/m3

. 

Moderately toxic by ingestion, inhalation, and 

subcutaneous routes. HR = 3. 

(alpha, alpha, alphatrifluoro-mtolyl)isocyanate 

C8H4F3NO 329-01-1 RTECS NR200000} [KJ250] LC50 (rat, inh) = 3600 

mg/m3

, LC50 (mouse, inh) = 3300 mg/m3. 

Moderately toxic by ingestion, inhalation, 

intraperitoneal routes. HR = 2. 

2,4,6-trifluoro-s-triazine C3F3N3 675-14-9 {RTECS XZ1750000} [TKK000] LC50 (rat, inh, 4 

hr) = 3.1 μL/L. Poison by skin contact, inhalation. 

HR = 3. 

a The SAX No. (Reference 67) is given in brackets followed by information from that reference; the RTECS No. (Reference 

138) is given in braces. “HR” denotes the SAX Hazard Rating. 

No generalities on the toxicity of nitrogen compounds can be made. Amines range in toxicity from 

poisons to only slightly toxic. In fact, fully fluorinated alkyl amines show no toxicity. Some amines are 

skin irritants while others are sensitizers.67 Although LC50 values have been determined for some 

hydrofluoroamines (HFA), the test levels are very low and measurements at higher concentrations are 

needed. ((CH3)2NCF2CBrF2) has tested negative for genotoxicity and cytotoxicity.243
684 Search for New Fire Suppressant Chemicals 

Volatility 

Generally 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. This chemical family represents a 

very broad range of fluorination patterns and alkyl substitution patterns. Table 7–41 indicates that there 

are some such fluoroalkylamines with boiling points below and near the screening criterion. 

Flame Extinguishment 

As the primary question to be addressed was extinguishment performance, and little change in 

performance was expected amongst the fully fluorinated ethyl and methyl amines, three low boiling 

compounds were selected for examination. 

Table 7–42. Fluoroalkylamine Boiling Points. 

Compound Formula Tb (°C) 

N(CF3)3 -10 

N(CF3)2CF=CF2 13.7 

N(CF3)2CH3 11 to12 

N(CF3)2CF2CF5 20.5 

N(CF3)2CF2CHF2 32.0 

N(CF3)2CH2CH3 33 to 34 

N(CF3)2CH2CH3 33.3 

N(CF3)2CH2CF3 38 

N(CF3)(CF2CF3)2 46 

• N,N-bis(trifluoromethyl)pentafluoroethanamine ((pentafluoroethyl)bis(dimethyl)-amine,

N(CF3)2(C2F5)), obtained from Dr. Takashi Abe, National Industrial Research Institute 

(NIRI), Japan was the product of electrochemical fluorination.244 This synthetic approach is 

generally not amenable to the preparation of partially fluorinated compounds. Three cup 

burner tests were run to give an average extinguishment value of 3.8 volume %. 

• Trifluoroacetonitrile, CF3CN, is a commercially available compound.170,192 It has very low 

boiling point of -67 °C and seeming potential tropodegradability resulted in an interest in 

further study. Cup burner tests yielded flame extinguishment at 9 volume %, suggesting that 

there is no chemical effect from the nitrile group. 

• N,N-bis(trifluoromethyl)-trifluoro-methanamine (tris(trifluoromethyl)amine, N(CF3)3), 

synthesis was attempted unsuccessfully using the procedure shown in Reaction 7-57. No cup 

burner value therefore was obtained. 

NH3 + 3CF3I → N(CF3)3 + 3HI (7-57)
NGP Surveys of Organic Compounds 685

Summary 

There is no indication that the presence of a nitrogen atom in a compound significantly improves the fire 

suppression efficiency relative to other thermally active flame suppressants. The fully fluorinated 

compounds, which have the lower boiling points, are also likely to have long atmospheric lifetimes. 

While partially fluorinated amines are likely to have relatively short atmospheric lifetimes, it is difficult to 

determine whether the lifetime would be sufficiently short to allow bromine substitution (to increase 

flame suppression efficiency). Toxicity appears to be problematic for the partially fluorinated 

compounds. 

7.4.6 Bromofluoroalkyl Nitrogen-based Candidates 

There are three families of this type that were considered: amines, imines, and nitriles. 

In general, the atmospheric lifetimes of bromofluoro nitrogen-based compounds were expected to be 

similar to those of analogous non-brominated nitrogen-based compounds. There is no indication that the 

nitrogen alkyl linkage provides any significant contribution to rainout. The polarity of the nitrogen lone 

pair may be too small. Perfluorinated saturated amines are expected to have atmospheric lifetimes similar 

to those of the perfluorinated alkanes, a property that generally makes their use as halon replacements 

questionable. The atmospheric lifetimes for partially fluorinated amines are much shorter. Atmospheric 

lifetimes of imines are unknown but may well be limited by their unsaturated bond, though this has not 

been confirmed. Bromination of the amine or imine structures is not expected to alter this assessment. 

Cup burner flame extinguishment results suggested that a wide number of these compounds would likely 

meet extinguishment performance needs. 

The toxicity of bromofluoro nitrogen based compounds was expected to be higher than those of 

analogous non-brominated nitrogen-based compounds. 

Bromofluoroamines 

Amines offer significant promise, particularly as a result of research underway in Japan on the 

applications of fluoroalkyl amines as halon and CFC replacements.244 Much of this research appears to be 

headed toward perfluoroalkyl amines, which are likely to have long atmospheric lifetimes. Nevertheless, 

the work provides synthetic routes and property evaluations. Incompletely halogenated compounds, such 

as N(CF3)(CHF2)(CF2Br), could provide short atmospheric lifetimes and chemical suppression. 

Bromofluoro amines have a wide range of structures, as indicated by the examples in Table 7–43. 

Table 7–43. Bromofluoroamine Candidate Compounds. 

Chemical Formula 

N(CF3)2CFHBr N(CF2H)(CF2H)(CFHBr) N(CFH2)(CFH2)(CF2Br) 

N(CF3)(CF2H)CF2Br N(CFH2)(CF3)(CFHBr) N(CFH2)(CF2H)(CFHBr) 

N(CF3)(CF2H)CFHBr N(CF3)(CF2H)(CH2Br) N(CH3)(CF3)(CFHBr) 

N(CF2H)(CF2H)CF2Br N(CH3)(CF3)(CF2Br) N(CH2F)(CF3)(CH2Br) 

N(CFH2)(CF3)CF2Br N(CH3)(CF2H)(CF2Br) 
686 Search for New Fire Suppressant Chemicals 

There are synthetic pathways to many of these. For instance, N-bromobistrifluoromethylamine 

(CF3)2NBr adds to the unsaturated compounds tetrafluoroethene CF2=CF2, trifluoroethene CHF=CF2, 

1,1-difluoroethene CH2=CF2, cis-1,2-difluoroethene CHF=CHF, ethene CH2=CH2, hexafluoropropene 

CF2=CFCF3, chlorotrifluoroethene CClF=CF2, and 1,2-dichlorodifluoroethene CClF=CClF under mild 

conditions, to give the 1:1 adducts in high yield. The (CF3)2N attaches only to the CH2 group of 

1,1-difluoroethene, whereas trifluoroethene gives the isomers (CF3)2NCHFCF2Br (78 %) and 

(CF3)2NCF2CHFBr (22 %). Hexafluorocyclobutene and octafluorobut-2-ene require more drastic 

conditions, and give the olefin dibromide and tetrakistrifluoromethylhydrazine rather than addition of the 

N-bromo-compound.245

The boiling points of bromofluoroamines range only as low as 22 o C, as indicated in Table 7–44. In the 

last three rows, the flame extinguishment values for the two compounds and their mixture indicate that 

the value of the bromine atom and the thermal effects of the complex molecule were both realized. 

However, because of the N-Br linkage, the lowest boiling of these compounds may be unacceptably toxic. 

Table 7–44. Bromofluoroamine Boiling Points and Flame Suppression Results. 

Chemical Formula Tb (°C) 

Cup Burner Flame Extinguishment 

(Volume %) 

(CF3)2N-Br 22 --- 

(CF3)2NCBrF2 40.6 --- 

(CF3)2NCF2CBrF2 59.5 --- 

N(CF3)2(CHFCF2Br) 72 2.4 

60 % N(CF3)2(CHFCF2Br), 40 % N(CF3)2(CF2CFHBr) 72 2.4 

N(CF3)2(CH2CF2Br) 80 2.4 

Imines 

Bromofluoroimines 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.246,247,248

The simplest of these, N-bromo-difluoromethanimine, CF2=NBr, has an attractively low boiling point of 

14 oC. However, it too has an N-Br linkage and may be unacceptably toxic. 

Nitriles 

As seen in the prior section for CF3CN, it is unlikely that nitriles would have an intrinsic chemical fire 

suppression capability. The addition of bromine or iodine should impart a chemical flame suppression 

contribution. 

Bromodifluoroacetonitrile (CF2BrCN) was the sole brominated fluoroalkyl nitrile obtained for 

examination. Its boiling point is uniquely low, 3 oC, which is also the lowest boiling potentially 

tropodegradable brominated compound identified. Cup burner testing of CF2BrCN indicated an upper 

bound flame extinguishment value of 4 volume %, consistent with the effect of the bromine atom and 

confirming the minor impact of the triple bond on flame extinguishment efficiency. There was an 
NGP Surveys of Organic Compounds 687

unconfirmed report that this compound is toxic. Should the minimum in-flight temperature requirement 

be relaxed, toxicity and atmospheric lifetime determinations for this compound would be in order. 

7.4.7 Fluorinated Ethers 

Fire Suppression Properties 

Hydrofluoropolyethers (HFPE) are being introduced into the market, and there is some evidence for 

relatively good fire suppression performance.249 A large amount of research has been performed on 

fluoroethers as CFC replacements. 

Atmospheric Lifetimes, ODP, and GWP 

The presence of the ether linkage increases reactivity toward hydrogen abstraction, though fluorine 

substitution decreases the enhancement.250 Hydrofluorocarbons show an approximately linear correlation 

between kOH and the highest-occupied molecular orbital (HOMO) energies.251 Rate constants, many 

estimated, reported for reaction of hydrofluoroethers (HFE) with •OH are shown in Table 7–45. In the 

absence of a hydrogen atom, fluorinated ethers exhibit no reaction with •OH, significantly increasing the 

atmospheric lifetime. 

Very little work has been done on reactions of ethers with ozone, primarily due to their low reactivity. 

The rate constants for reaction with furan (2.42 x 10-18 cm3

/molec-s) and 2,5-dihydrofuran 

(1.61 x 10-17 cm3

/molec-s) are relatively large, owing to the presence of a double bond.238 For saturated 

ethers, however, rate constants are expected to be extremely slow, ≤ 10-20 cm3

/molec-s, at room 

temperature.238

The energy of the HOMO has been used to estimate atmospheric lifetimes for a number of HFEs.252 A 

list of atmospheric lifetimes reported for halogenated ethers, most of which are estimated, Table 7–46. 

The degradation products resulting from the alkoxy radicals formed after initial hydrogen atom 

abstraction from hydrofluoropolyethers (HFPE) have been studied.253 Chlorine-atom initiated 

photooxidations of the HFPEs in air (HCF2OCF2OCF2OCF2H, HCF2OCF2CF2OCF2H and 

HCF2OCF2OCF2H) produced COF2 as the only carbon-containing product, with observed average COF2

molar formation yields of 4.73, 3.77, and 2.82, respectively. In the early stages of the reaction, the COF2

molar formation yields are close to the number of carbon atoms in each parent HFPE. Based on current 

knowledge of degradation pathways of hydrofluorocarbons (HFC) and hydrochlorofluorocarbons 

(HCFC), it is expected that COF2 will also be produced with near-unit yield per carbon atom from the 

above HFPEs in the troposphere, where loss processes would be initiated primarily by reaction with •OH 

radicals. 

Toxicity 

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

reactivity. 
688 Search for New Fire Suppressant Chemicals 

Table 7–45. Rate Constants for Hydrofluoroether Reactions with •OH. 

Halocarbon No. Formula kOH, cm3/molec-s Reference 

a

2.51 x 10-15 HFE-CE225ea -O-CF2CHFCF2- 250 a

2.4 x 10-15 250 

HFE-E CH3-O-CF(CF3)2 a,b1.6 x 10-14 254 

HFE-E CH3-O-CH(CF3)2 a,b2.2 x 10-13 254 

HFE-E CHF2-O-CH(CF3)2 a,b1.8 x 10-14 254 

HFE-E CH2F-O-CH(CF3)2 7.3 x 10-14 255 

HFE-E125 CHF2-O-CF3 a3.38 x 10-15

a

3.56 x 10-15

c

4.2 x 10-16

250 

250 

249 

HFE-E134 CHF2-O-CHF2 a2.53 x 10-14

a

2.41 x 10-14

a,b3 x 10-15

c

2.3 x 10-15

2500 

250 

254 

249 

HFE-E143a CH3-O-CF3 a2.14 x 10-14 250 

HFE-E227ca1 CHF2-O-CF2CF3 b,d1.95 x 10-15 251 

HFE-E227ca2 CHF2CF2-O-CF3 b,d4.5 x 10-15 251 

HFE-E227ea1 CF3CHF-O-CF3 a,b5.1 x 10-15

b,d3.5 x 10-15

254 

251 

HFE-E236ca1 CHF2-O-CF2CHF2 b,d1.15 x 10-14 251 

HFE-E236ca12 CHF2-O-CF2-O-CHF2 1.3 x 10-15 249 

HFE-E236ea1 CHF2-O-CHFCF3 a,b9.5 x 10-15

b,d7 x 10-15

254 

251 

HFE-E236ea2 CHF2CHF-O-CF3 b,d3 x 10-14 251 

HFE-E236mf1 CF3CH2-O-CF3 a,b1.5 x 10-14 254 

HFE-E245ca2 CHF2-O-CF2CH2F b,d7 x 10-15 251 

HFE-E245cb1 CH3-O-CF2CF3 c1.07 x 10-14

a,b4.6 x 10-14

b,d5.5 x 10-14

256 

254 

251 

HFE-E245cb2 CH3CF2-O-CF3 b,d1.5 x 10-15 251 

a 296 K 

b Estimated from HOMO energy. 

c 298 K 

d Average 

Table 7–46. Atmospheric Lifetimes for Fluorine-containing Ethers. 

Halocarbon No. Chemical Formula 

Atmospheric 

Lifetime ( years) Reference 

FE-CE216 -O-CF2CF2CF2- a >330 250 

HCFE-E235ca2 CHF2-O-CF2CHClF a6 255 

HCFE-E235da1 CHF2-O-CHClCF3 a5 255 

HFE-CE225ea -O-CF2CHFCF2- b,c26 250 

HFE-E CHF2-O-CH(CF3)2 a3.8 257 

HFE-E CH3-O-CF(CF3)2 4.9 

b,c3.5 

257 

250 
NGP Surveys of Organic Compounds 689

Halocarbon No. Chemical Formula 

Atmospheric 

Lifetime ( years) Reference 

4.3 258 

HFE-E CH3-O-CH(CF3)2 b,c0.25 254 a HFE-E CH2F-O-CH(CF3)2 1.4 255 

b,c3.1 254 

HFE-E HF2CO(CF2O)n(CF2CF2O)mCF2H e8 f 

HFE-E125 CHF2-O-CF3 82 

19 

b,c156 

259 

250 

249 

8 259 

b,c2.6 250 

b,c19 250 

HFE-E134 CHF2-O-CHF2

b,c35 249 

HFE-E143a CH3-O-CF3 b,c3 250 

b,e,f HFE-E227ca1 CHF2-O-CF2CF3 16.05 252 

b,e,f33 251 

CHF2-O-CF2CHF2 b,e,f HFE-E236ca1 5.95 252 

b,e,f8.5 251 

HFE-E236cb1 CH2F-O-CF2CF3 b,e,f5.9 252 

b,e,f HFE-E227ca2 CHF2CF2-O-CF3 12.1 252 

b,e,f17.5 251 

HFE-E227ea1 CF3CHF-O-CF3 b,c11 250 

20 258 

b,e,f23.5 251 

b,e,f14.9 252 

HFE-E236cb2 CH2FCF2-O-CF3 b,e,f6.7 252 

HFE-E236ea1 CHF2-O-CHFCF3 a4.04 257 

b,e,f6.5 251 

b,e,f7.5 252 

HFE-E236ea2 CHF2CHF-O-CF3 b,e,f5.1 252 

b,e,f4.55 251 

HFE-E236mf1 CF3CH2-O-CF3 b,c3.7 250 

b,e,f4.75 252 

HFE-E245ca1 CH2F-O-CF2CHF2 b,e,f3.5 252 

HFE-E245ca2 CHF2-O-CF2CH2F a2.18 257 

b,e,f6.5 251 

b,e,f4.4 252 

HFE-E245cb1 CH3-O-CF2CF3 6.5 256 

b,c1.2 250 

b,e,f0.85 251 

b,e,f1.4 252 

HFE-E245ea1 CHF2-O-CHFCHF2 b,e,f2.75 252 

HFE-E245eb1 CH2F-O-CHFCF3 b,e,f2.2 252 

HFE-E245eb2 CH2FCHF-O-CF3 b,e,f3.35 252 

HFE-E254ea1 CH2F-O-CHFCHF2 b,e,f1.3 252 
690 Search for New Fire Suppressant Chemicals 

Halocarbon No. Chemical Formula 

Atmospheric 

Lifetime ( years) Reference 

HFE-E254ea2 CH2FCHF-O-CHF2 b,e,f1.75 252 

HFE-E254eb1 CH3-O-CHFCF3 b,f0.5 252 

HFE-E254ca1 CH2F-O-CF2CH2F b,e,f3.1 252 

HFE-E245cb2 CH3CF2-O-CF3 b,e,f11.2 252 

b,e,f27.5 251 

HFE-E245fa1 CHF2-O-CH2CF3 b,c5.2 250 

b,c1.7 251 

b,e,f1.15 251 a

4.7 257 

b,f1.9 252 

HFE-E245fa2 CF3-O-CH2CHF2 c2.2 251 

b,e,f1.45 251 

b,e,f2.65 252 

HFE-E254cb1 CH3-O-CF2CHF2 a0.47 257 

b,c0.85 251 

b,e,f0.35 251 

b,e,f0.95 252 

HFE-E254cb2 CH3CF2-O-CHF2 b,e,f3.85 252 

b,e,f6 251 

HFE-E254eb2 CH3CHF-O-CF3 b,e,f2.45 252 

HFE-E254fa1 CHF2-O-CH2CHF2 b,e,f1.05 252 

b,e,f0.45 251 

HFE-E356mcf2 CF3CH2-O-CF2CH2F a1.8 257 

HFE-E356mec1 CH3-O-CF2CHFCF3 b,c0.94 251 

HFE-E356mff2 CF3CH2-O-CH2CF3 a0.5 257 

HFE-E356pcc1 CH3-O-CF2CF2CHF2 b,c0.93 251 

HFE-E356pfc1 CHF2-O-CH2CF2CHF2 b,c1.3 251 

HFE-E356pfc2 CHF2CH2-O-CF2CHF2 b,c2 251 

HFE-E365mc1 CH3-O-CH2CF2CF3 b,c0.11 251 

HFE-E365sf2 CH3CH2-O-CF2CF3 a0.3 257 

HFE-E374pcf2 CH3CH2-O-CF2CHF2 b,c0.43 251 

HFE-E4-3-10pccc124 CHF2-O-CF2-O-CF2CF2-O-CHF2 b,c7 249 

HFE-E254fb1 CH2F-O-CH2CF3 b,f0.5 252 

HFE-E254fb2 CH2FCH2-O-CF3 b,e,f1.6 252 

b,e,f0.7 251 

HFE-E263fb1 CH3-O-CH2CF3 b,c0.1 251 

b,f<0.1 251 

b,c0.1 251 

HFE-E263fb2 CH3CH2-O-CF3 b,f0.3 251 

HFE-E329p2 CHF2CF2-O-CF2CF3 b,c6.8 251 

HFE-E338mf2 CF3CH2-O-CF2CF3 b,c4.3 251 

HFE-E347pf1 CHF2-O-CH2CF2CF3 a1.62 257 

HFE-E347pf2 CF3CF2-O-CH2CHF2 b,c2.8 251 

HFE-E347s1 CH3-O-CF2CF2CF3 6.4 241 
NGP Surveys of Organic Compounds 691

Halocarbon No. Chemical Formula 

Atmospheric 

Lifetime ( years) Reference 

b,c1.3 251 

5.6 258 

HFE-E449s1 CF3CF2CF2CF2-O-CH3 4.1 260 

HFE-E569sf2 CF3CF2CF2CF2-O-CH2CH3 1.2 261 

a Estimated 

b For reaction with •OH only. 

c Non-rigorous calculation. 

d See Reference 

e Average 

f Estimated from HOMO energy. 

Extinguishment Testing 

1-Methoxynonafluorobutane, HFE-7100, was obtained from 3M Company. Hydrofluoropolyether was 

obtained as an experimental product from Ausimont S.p.A. in Milano, Italy. As expected and indicated in 

Table 7–47, neither of these compounds exhibited extinguishment performance suggesting a chemical 

extinguishment mechanism. The flame extinguishing results are comparable to HFCs. 

Table 7–47. Fluoroether Cup Burner Extinguishment Data. 

Compound Name Formula Tb (°C) 

Cup Burner Flame 

Extinguishment (Volume %) 

1-Methoxynonafluorobutane CF3CF2CF2CF2-O-CH3 60 6.1 

Hydrofluoropolyether HF2CO(CF2O)n(CF2CF2O)mCF2H 100 5.1 

Assessment Summary 

There was little reason to pursue hydrofluoroethers or perfluoroethers further. The fire suppression 

efficiencies were comparable to the HFCs, and the larger molecular weights led to higher boiling points. 

There was no indication that the ether linkage provided any significant contribution to rainout; the 

polarity is too small. Perfluorinated saturated ethers were expected to have atmospheric lifetimes similar 

to those of the perfluorinated alkanes, a property that generally made their use as halon replacements 

questionable. The atmospheric lifetimes for partially fluorinated ethers were much shorter. The low 

reactivity of the ether linkage causes ethers to be relatively biologically benign, though there are many 

exceptions; anesthesia is a problem in some cases. 

7.4.8 Bromofluoroethers 

Atmospheric Lifetime, ODP, and GWP 

The atmospheric lifetimes of bromofluoroethers are expected to be similar to those of the base 

fluoroether. The only bromofluoroether whose atmospheric lifetime has been studied is Roflurane, 

CH3-O-CF2CFBrH (Tb = 89 °C), a compound once employed as an anesthesia agent.262 The reported 

estimate of atmospheric lifetime was 14 days. 
692 Search for New Fire Suppressant Chemicals 

Toxicity Assessment Summary 

Toxicity data for the bromofluoroethers are scarce. However, Roflurane has been shown to have a very 

low toxicity.263 This is a hopeful sign that other members of the bromofluoroether family would be of 

acceptable toxicity. 

Volatility and Availability 

The boiling point screening criterion of 20 °C severely limited the number of bromofluoroethers 

considered. Bromofluoroethers with one or both of the alkyl groups having two or more carbons and with 

the bromine atom on a carbon atom not adjacent to the ether linkage typically have boiling points above 

60 oC. Thus attention focused on the halogenated dimethyl ethers and a limited number of methyl ethyl 

ethers. Having at least a one-to-one ratio of fluorine atoms to hydrogen atoms ensured non-flammability. 

With variation in site of bromination and fluorination, a large number of structural isomers are possible 

even with this very limited range of ethers. The number of compounds was reduced through a selection 

process which focused on the most symmetrically substituted compounds (lower expected boiling point) 

and those compounds expected to be the least polar based on calculated octanol water partition 

coefficients. This latter criterion was expected to help select the least toxic compounds (Chapter 6). 

Synthesis of the brominated dimethyl ethers was first presented by Adcock and co-workers in 1991.23 

Further clarification and elaboration from Prof. Adcock enabled the successful synthesis of 

bromodifluoromethyl difluoromethyl ether, CF2Br-O-CF2H.264 This information indicated that elemental 

bromine did not substitute in these ethers in good yields without decomposition, and that the more 

reactive interhalogen compound, bromine chloride, should be employed. In this method, equimolar 

amounts of chlorine and bromine formed bromine chloride during short pre-irradiation of the halogen 

mixture prior to introduction of the fluorinated ether. While a small excess of bromine suppressed 

virtually any chlorination, too large an excess of bromine significantly slowed the rate of reaction. 

Stepwise bromination of the dihydryl fluoroether, HCF2-O-CF2H was observed under these conditions. 

Additional synthetic information provided valuable guidance and enabled the successful synthesis of 

adequate amounts of CF2Br-O-CF2H for very limited extinguishment testing. That guidance included: 

• Employ a high pressure Hg lamp. The high pressure lamp gave a pressure broadened 

spectrum, unlike the older medium pressure or low pressure lamps, and therefore provided an 

increased rate of reaction. Medium and low pressure lamps did not work in this reaction. 

• Eliminate all O2 and H2O from the bromine and chlorine reactants and the bisdifluoromethyl 

ether. Remove all air (O2 and H2O) from all glassware and photolysis equipment. These 

were extremely important steps, and failure of the reaction resulted when they were not 

followed. 

• Adjust the Br2/Cl2 ratio such that Br2 is in very slight excess to Cl2. The amount of Br2

employed was approximately stoichiometric to the fluoroether being brominated. This 

method was reported to require only a couple of hours of photolysis. In the reaction, chlorine 

abstracted hydrogen and bromine, then added to form the product. When too high a 

Br2:halocarbon ratio was employed, the reaction slowed down due to light absorption. When 

too much chlorine was present, chlorination of the ether occurred instead of the desired 

bromination. 
NGP Surveys of Organic Compounds 693

The reaction is tricky, and several attempts were needed to optimize the synthetic conditions. With 

recycling of unreacted reactants, a high yield may well be achieved. 

Flame Extinguishment 

The contribution from the bromine atom was expected to dominate suppression of flame chemistry, with 

some thermal contributions to flame suppression from the more heavily fluorinated alkyl groups. 

Prior to the NGP, only two measurements of flame suppression by the higher boiling 

hydrobromofluoroethers (HBFEs) had been carried out. CH2=CBr(OCF3)CF2CF3, which is unsaturated, 

had a cup burner extinguishment concentration of 3.8 volume %.240 Roflurane, CH3-O-CF2CHBrF, was 

estimated to have a heptane cup burner volume fraction of 4.2 % and a short atmospheric lifetime.240 

Table 7–48 summarizes the NGP cup burner test data for five of the lowest molecular weight compounds 

in this family. All confirmed the flame extinguishment expectation. 

Table 7–48. Bromofluoroether Cup Burner Testing Summary. 

Compound Name, Formula Chemical Formula Tb (°C) 

Cup Burner 

Extinguishment 

(volume %) 

1-Bromo-1,2,2-trifluoroethyl trifluoromethyl ether CF3-O-CFBrCF2H 42 < c 4.5

2-Bromo-1,1,2-trifluoroethyl trifluoromethyl ether CF3-O-CHFCF2Br 37 < 4.5 

Bromomethyl trifluoromethyl ether CH2Br-O-CF3 39 3.2 

Bromodifluoromethyl difluoromethyl ether CF2Br-O-CF2Ha 20-24 (est.) 3.7 (2.4)b 

Bromomethyl difluoromethyl ether CH2Br-O-CF2H 70 3.6 

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 flame extinguishment performance of the sample of 65 volume % bromodifluoromethyl 

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

3.7 volume % extinguishment value was corrected for the actual 65 % purity of the sample, an 

extinguishment value of 2.4 volume % was obtained. It was unlikely that the major impurity in this 

sample (bisdifluoromethyl ether) contributed significantly to extinguishment at its effective low 

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

chlorinated analogues to the desired product. 

Substituting additional fluorine for a hydrogen on CH2Br-O-CF3 might yield a compound (probably a 

mixture of two structural isomers) with a boiling point in the vicinity of 20 oC to 30 °C. This might be 

worthwhile if the low temperature performance requirement were eased (Chapter 2). Bromofluoromethyl 

trifluoromethyl ether (CFHBr-O-CF3) was also of interest. However, the fluoroether starting material 

(CFH2-O-CF3) was not available. Other possible low boiling chemicals in this family are CF2Br-O-CH2F, 

CHFBr-O-CHF2, CF2Br-O-CF3, and CF2Br-O-CHF2. 
694 Search for New Fire Suppressant Chemicals 

Assessment Summary 

There is some potential for the bromofluoroethers as total flooding fire suppressants. While the lowest 

boiling points are not low enough for effective dispersion under the current operational requirement, there 

are some structural isomers with boiling points as low as 20 °C to 24 °C. There is reason to expect that

some of these compounds might have relatively low toxicity. Limited atmospheric lifetime estimates

suggest the possibility of acceptable performance. 

7.4.9 Bromofluorooxiranes 

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

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

Testing indicated that the non-brominated perfluoropropene oxide has a cup burner value of 

9.6 volume %.265 The toxicities of these compounds are unknown. Since they may be readily attached by

OH radicals, their atmospheric lifetimes may well be short, but this is unconfirmed. 

There are three possible bromine locations in the pentafluorinated propene oxide molecule. Further 

isomerism due to the formation of one or more optically isomeric carbons results in further isomeric 

complexity. This complexity yields a total of eight unique compounds, Figure 7–12. 

O

F

CF3

FBr 

O

Br

CF3

F2

O

F

CF2Br

F2

1-Bromopentafluorooxirane

(4 optical isomers possible) 

2-Bromopentafluorooxirane

(2 optical isomers possible) 

3-Bromopentafluorooxirane

(2 optical isomers possible) 

Figure 7–12. Structural and Optical Isomerism of Bromopentafluoropropene Oxide. 

Synthesis of 3-bromopentafluorooxirane has been reported.266 A brief survey of the literature also 

revealed that 30 % hydrogen peroxide in a basic medium had been used successfully in the epoxidation of 

fluorinated alkenes such as hexafluoropropene.267 These compounds might also potentially be

synthesized in a single step from existing bromofluoropropenes by a partial oxidation of the alkene bond. 

CF2(O)CBrCF3 (2-bromo-1,2-perfluoropropene oxide) was successfully sourced and its flame

extinguishment properties determined, as indicated in Table 7–49. Since the cup burner results was 

higher than generally expected of a brominated compound and since the boiling point was marginal, NGP 

investigation of the bromofluoropropene oxides was halted. 
NGP Surveys of Organic Compounds 695

Table 7–49. Bromofluoropropene Oxide Cup Burner Testing Summary. 

Compound Name Tb (°C) Cup Burner Extinguishment (volume %) 

2-Bromopentafluorooxirane 20 (est.) 4.9 

1-Bromopentafluorooxirane Unknown Sourced, not acquired 

3-Bromopentafluorooxirane Unknown Sourced, not acquired 

7.4.10 Bromofluoro / Fluorinated Aldehydes and Ketones 

Fluorinated Aldehydes and Ketones 

An analysis of the potential suitability of fluorinated aldehydes and ketones as halon replacements 

concluded that further study was warranted.39 This determination resulted in the “Highly Efficient 

Thermal Agents” research briefly described earlier in section 7.4.1 of this chapter.147

The suitability of fluoroketones was also demonstrated during the course of the NGP by 3M Corporation 

with their successful commercialization of the perfluoroketone, dodecafluoro-2-methylpentan-3-one, 

CF3CF2C(O)CF(CF3)2, FK-5-1-12. This compound has a cup burner heptane extinguishment of 

4.5 volume %,268 but a boiling point (49 oC) well above that required for efficient dispersion under inflight conditions. Its short atmospheric lifetime yields a lower GWP value than those of the HFCs. Other 

than the reported data for FK-5-1-12, fire suppression data are almost completely unknown for fluorinated 

carbonyl compounds. 

Bromofluoro Aldehydes and Ketones 

2-Bromo-2,2-difluoroethanal, CBrF2CHO, was the sole representative compound that had been studied. 

The cup burner value for this compound was reported to be 4.4 volume %, and the boiling point was 

about 40 oC.269 As all other examples of bromofluoro aldehydes would likely have higher boiling points, 

further consideration of this family was not pursued. 

7.4.11 Bromofluoro Alcohols 

Initial evaluations of bromofluoro alcohols were conducted by the Advanced Agent Working Group, 

which found that chemical instability of this family was problematic. NGP research identified no 

additional compounds worthy of study, as the boiling points of the brominated fluoroalcohols were higher 

than required for in-flight fire suppression (Table 7–50). 

It appeared that extinguishment might not be obtainable for alcohols in which the hydrogen content is 

significant. Thus, better flame extinguishment might be found for compounds such as CBrF2CF2OH and 

CBr2FCF2OH. While the alcohols have the advantage of being highly susceptible to “rain out” and would 

therefore have a lower atmospheric lifetime, they also have boiling points well above those required for 

aircraft applications and were not pursued further under the NGP. 
696 Search for New Fire Suppressant Chemicals 

Table 7–50. Bromofluoro Alcohol Boiling Points. 

Compound Formula Tb (°C) 

Cup Burner Flame 

Extinguishment Value 

(volume %) Reference 

CBrF2CH2OH 67 (2 kPa) did not always extinguish 270

CF3CHOHCH2Br 124 4.1 271

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 155-158 4.78 270 

CBr2FCH2OH 85 (2.7 kPa) 4.56, appeared flammable 270 

7.4.12 Iodinated Hydrocarbons 

Iodofluoroalkanes 

Nearly all the attention in this family has been directed at CF3I. CF3I has a boiling point that is uniquely 

low (Table 7–51), perhaps low enough for consideration for in-flight applications (although, see 

Chapter 8). In addition, the iodine atom imparts cup burner flame extinguishment effectiveness to these 

compounds that is comparable to the bromine atom in halon 1301. When released in the lower 

atmosphere, the fluorinated iodoalkanes all degrade by photolysis of the carbon–iodine bond and are 

expected to have short atmospheric lifetimes.19 These factors led to expectation that CF3I would be a near 

drop-in replacement for CF3Br, which has a cup burner value of 2.9 volume %. 

However, experiments revealed unsatisfactory low temperature distribution of CF3I (Chapter 8 and 

Reference 272) and raised concerns over its materials compatibility and chemical stability.273,274,275,276,277 

In addition, this compound’s LOAEL was measured to be 0.5 volume %,278,279 resulting in it being 

deemed unacceptable for use in normally occupied areas. 

There have been studies that indicate a reduced cardiac sensitization hazard from an inadvertent release of 

CF3I. An early report of experimental discharge modeling of the potential for CF3I exposure attempted to 

quantify the potential for aircraft service ground crew exposure to CF3I during inadvertent agent 

discharge in one of the engine nacelles during maintenance operations, or pre-take-off inspection.280 

Employing differential IR imaging and sampling of the CF3I plume, the study’s authors provided 

evidence of a CF3I plume at the LOAEL concentration and suggested a need for further investigation. 

Extensive efforts to model human inhalation exposure effects employed a physiologically-based 
NGP Surveys of Organic Compounds 697

pharmacokinetic (PBPK)281 approach, described in Chapter 6, that yielded a better understanding of the 

relationship between exposure concentration and the resulting blood levels following exposure to CF3I. 

Table 7–51. Iodoalkane Boiling Points. 

Chemical Formula Tb (°C) 

Cup Burner Flame 

Extinguishment Value265 

(volume %) 

CF3I -22.5 3.0 

CHF2I 21.6 

CH2FI 53.5 

CH3I 42.5 

C2F5I 12 2.1 

CHF2CF2I 39.4 

C3F7I 41.2 3.0 

C4F9I 2.8 

C6F13I 2.5 

C4F8I2 2.1 

One potential application of CF3I was for inerting aircraft fuel tanks, particularly in the F-16, against inflight fires and explosions. Considerable controversy arose over this use. As a result, at the request of the 

Under Secretary of Defense (Acquisition, Technology and Logistics), the Director of Defense Research 

and Engineering convened an Independent Review Panel (IRP) to assess the four critical technical issues 

and comment on how they might affect implementation of CF3I as a viable substitute for halon 1301 in 

the F-16 inerting application.282 This assessment of the suitability of CF3I as a replacement for halon 

1301 as an inerting agent in F-16 wing fuel tanks concluded, based on an analysis of materials 

compatibility, low temperature performance, human toxicology, and atmospheric chemistry, that: 

• CF3I is more chemically reactive than halon 1301. After further qualification testing, it may 

be possible to specify materials that could be used in service with CF3I. 

• CF3I is inadequate as a replacement for halon 1301 in the existing F-16 system due to its 

higher boiling point and resultant reduced delivery pressure at low temperatures. 

• CF3I is more toxic than halon 1301. It would be unwise to replace a chemical with a more 

toxic one. More rigorous toxicity testing of CF3I would provide a more quantitative estimate 

of its toxicity in realistic exposure scenarios.

• Ozone depletion from F-16 application of CF3I could be as small as 1⁄8 that of halon 1301 (at 

lower altitudes) or as large as 12⁄3 times as damaging as halon 1301 (at higher altitudes). In 

any case, CF3I use onboard an F-16 would be a Class I substance if significant amounts are 

released above 6,000 m (20,000 ft), and the U.S. Clean Air Act bans use of Class I 

substances. 

This last finding was based on (a) the historical altitudes at which halon 1301 was emitted to the 

atmosphere following deployment for inerting fuel tanks and (b) the ozone depleting effectiveness of 

CF3I. The latter is very sensitive to the altitude of release, since this compound degrades efficiently at 

low altitudes, but is even more effective than halon 1301 at destroying ozone should it reach the 

stratosphere following a high altitude release. For fuel tank inerting, the outcome of a detailed analysis 

was not favorable to the implementation of CF3I as a halon 1301 replacement. 
698 Search for New Fire Suppressant Chemicals 

Since the NGP was responsible for identifying potential candidates for replacing halon 1301 for fire 

suppression in aircraft engine nacelles, it was important to know whether the different release altitudes for 

this application might lead to different ozone depletion results. Wuebbles and co-workers at the 

University of Illinois used a two-dimensional atmospheric model (the 2004 version of the UIUC 2D 

Chemical Transport Model, CTM) to calculate the effect of CF3I on stratospheric ozone for this 

application. For comparison, they re-visited the use of this agent for fuel tank inerting.283,284 

The 2004 version of the CTM determined the atmospheric distribution of 89 chemically active 

atmospheric trace constituents with 70 photolytic reactions, 189 thermal reactions, and heterogeneous 

reactions. Reaction-rate constants and photochemical data in the model were primarily based on the 

recommendations compiled by the NASA Panel for Data Evaluation.285,286 The model domain extended 

from pole to pole and from the ground to 84 km in altitude. A grid box was 5 degrees of latitude and 

1.5 km in log-pressure altitude. 

The altitude profile of releases of halon 1301 for engine nacelle (and auxiliary power unit) fire 

suppression was from Bein’s compilation of historic data from the military Safety Centers (Chapter 2 and 

Reference 287). The data encompass over 6,000 incidents from 1980 through 2002. Table 7-51 shows 

the distribution as inserted into the CTM. 

Table 7–52. Compilation of Historic Firefighting Emissions of CF3Br. 

Flight Height (km) Model Layer Emission (kg) Percent of Total Emissions 

12 to 13.5 layer 9 8.7 0.57 

10.5 to 12 layer 8 13.3 0.87 

9 to 10.5 layer 7 77.9 5.07 

7.5 to 9 layer 6 22.4 1.46 

6 to 7.5 layer 5 142.3 9.26 

4.5 to 6 layer 4 45.0 2.93 

3 to 4.5 layer 3 61.5 4.00 

1.5 to 3 layer 2 115.6 7.52 

0 to 1.5 layer 1 1050.0 68.3 

Wuebbles and co-workers ran three cases for the latitudes at which the emissions occurred. For 0 °N to 

10 °N, the ODP value was 0.084; for 30 °N to 40 °N, the OPD value was 0.028; and for 55 °N to 65 °N, 

the ODP value was 0.036. All were well below the control value of 0.2 in the U.S. Clean Air Act, but 

near the cautionary value of 0.05 used by the U.S. Environmental Protection Agency (EPA). In general, 

since most of CF3I emissions in this estimate occurred at lower altitudes, they did not tend to deplete 

atmospheric ozone severely. Therefore, provided this CF3I emission profile continues to be representative 

of the actual release characteristics, CF3I released from aircraft for fighting engine nacelle fires should 

have a low impact on the ozone layer relative to that of CF3Br. 

In revisiting the effect of replacing CF3Br with CF3I for fuel tank inerting, Wuebbles and co-workers used 

an updated (2004) version of the CTM. They also used two different altitude distributions of suppressant 

release, thus performing a sensitivity analysis. The first distribution was that used in the original 

calculations described in Reference 282. The second was an alternative distribution from Van Horn et 

al.288 The two are shown graphically in Figure 7-13; the calculated ODP values are shown in Table 7–53. 
NGP Surveys of Organic Compounds 699

In the original estimate, the resulting ODPs were in the range of 0.07 to 0.25, mostly below the control 

value of 0.2 in the U.S. Clean Air Act, but above the EPA value of concern of 0.05. With respect to the 

Van Horn estimate, all the resulting ODPs were no more than 0.05. Given the fact that aircraft were

typically operated at mid-latitudes (the two southern cases calculated here) in the Northern Hemisphere,

CF3I emissions following the Van Horn estimate would not have a substantial impact on ozone. 

The model calculations show that the altitude where CF3I is released from aircraft is a dominant factor in 

its ozone depletion effects. However, using either distribution, the aircraft-released CF3I would have

much lower impact on the ozone layer than CF3Br. 

These computation estimates are subject to specific uncertainties. Iodine chemistry is not as well 

understood as that for chlorine and bromine. Heterogeneous reactions between reactive iodine and other

active atmospheric reactants on the surface of aerosols could accelerate the ozone destruction rate of 

iodine catalytic cycles, which could result in much larger ODP values for CF3I. Extensive studies using a 

three-dimensional global transport model of the troposphere and stratosphere would enhance confidence 

in the results from this two-dimensional model. 

Figure 7-13. Vertical 

Profiles of CF3I Emissions 

for Fuel Tank Inerting in 

Military Aircraft. 

Percent unit is massweighted. 

Table 7–53. Estimated Ozone Depletion Effects of CF3I for Two Emission Profiles. 

ODP 

Latitude Range Reference 282 (Rupnik et al.) Reference 288 (Van Horn et al.) 

0 °N to 10 °N 0.254 0.050

30 °N to 40 °N 0.084 0.019

55°N to 65 °N 0.071 0.025

In summary, technical issues with CF3I remain, as far as aircraft use is concerned. While the ODP

contribution is much lower than that of halon 1301, it is still close to being a Class 1 substance, depending 
700 Search for New Fire Suppressant Chemicals 

on the specific altitudes at which it is deployed. The industrial hygiene issues from maintenance 

discharge persist. Dispersion is questionable in cases of low temperature nacelle and dry bay use. 

Iodofluoroalkenes 

A prior estimate of the suitability of iodinated alkenes to perform as halon replacements concluded that 

further study was warranted.39 No extinguishment studies have been carried out on any iodoalkene, and 

the effect of the double bond on extinguishment is unknown. As with bromofluoroalkenes, it is possible 

that some highly halogenated, lower molecular weight iodoalkenes may be flammable.289 Examples of 

some of the simplest iodofluoro ethenes are CF2=CFI, CFH=CHI, CF2=CHI, CH2=CFI, and CFH=CFI, 

A review of physical property data indicated that boiling points would likely be much higher than 

acceptable. For example, CF2=CFI, expected to be one of the most volatile compounds in this family, has 

a Tb of 30 °C.192 The values for partially hydrogenated iodofluoroethenes would be higher. There was a 

lack of sources for these compounds, along with expectation of chemical instability. These ended 

consideration of these compounds. 

Iodine-containing Ethers 

Prior analysis of the suitability of iodinated ethers as potential halon replacements concluded that limited 

further study was warranted.39 There were no published data regarding the fire suppression effectiveness 

of these iodinated derivatives. However, as with brominated compounds, the cup burner values should 

reflect the presence of the iodine atom and should in the vicinity of 3 volume %. 

The lightest iodine-containing ether, iodomethyl methyl ether (iodomethoxymethane) has a relatively high 

boiling point of 122 °C at 101 kPa.290 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, all 

these compounds will have volatilities that are unsuitable for total flood application. This undesirable 

attribute of these compounds resulted in a decision to direct efforts to more promising areas. 

7.5 CHEMICAL FAMILY OPTIONS AND REPLACEMENT ISSUES 

7.5.1 Suppressant Criteria and Selection Constraints 

In this part of the NGP, researchers built on prior work, assessed the state of knowledge, and greatly 

extended understanding of fire suppression as well as the potential of both inorganic and organic 

compounds to serve as halon replacements for suppressing in-flight fires in aircraft. Using the screening 

criteria discussed in Chapter 6 and listed earlier in this chapter, NGP research appraised a near-universal 

range of chemistries, focusing on those most likely to provide acceptable replacements. Operationally, 

these criteria were:

• Cup burner flame extinguishment level measured or estimated to be below 5 volume %. This 

was to obtain fire suppression and reignition quenching efficiency comparable to halon 1301 

and higher than the HFCs. To better this 5 volume % limit, a compound must catalytically 

suppress combustion or have a high heat capacity. 
Chemical Family Optionss and Replacement Issues 701

• Boiling points below about 20 °C. For fluids with slightly higher boiling points, similar 

fluids were considered to see if there might be a lower boiling member of the chemical 

family. As discussed in Chapter 8, highly effective dispersion at the lowest in-flight 

temperatures would require boiling points below -40 °C. However, analysis of the altitudes 

of historical CF3Br discharges (Chapter 2) indicated that significantly higher boiling points 

might well be tolerated. Dispensing the agent as a fine mist might also allow for the use of 

higher boiling fluids, although establishing a sufficiently high dispensing rate is likely to 

require more extensive and weighty distribution hardware. 

• Inclusion of a chemical feature that rendered the chemical tropodegradable, i.e., likely to have 

a atmospheric lifetime on the order of a month or less. 

• Absence of any toxicological data showing that serious effects on people could occur at a 

concentration lower than that needed to effect flame extinguishment. 

During the nearly two decades of searching for halon alternatives since the signing of the Montreal 

protocol, there has been a major evolution of the most limiting performance criterion. Initially, there was 

concern that compounds with halon-like fire suppression efficiency and low ozone depletion contribution 

would be difficult to find. Later, toxicity became prominent, as several potential alternatives to ozone 

depleting chemicals performed poorly in cardiotoxicity testing (Chapter 6). For suppressing in-flight fires 

in aircraft, identifying chemicals that would disperse readily emerged as a principal limiting factor. 

The premium on compounds with effective dispersion at low temperatures frequently led to conflict with 

the other screening criteria. Chemicals with a high heat capacity generally were of high molecular weight 

and high boiling point. Chemicals with a feature that led to tropospheric reactivity were often polar or 

were composed of a large number of atoms, both of which typically led to higher boiling points. 

Finally, many of the compounds that appeared promising in theory were not available commercially. For 

some of these, the NGP was able to identify a laboratory that was willing to try to synthesize enough 

chemical for screening tests. This was not always successful. For still other compounds, the NGP was 

unable to find any source. 

7.5.2 General Conclusions 

During the formulation of the NGP and continuing through the research stages, the expectation of 

identifying a true drop-in replacement for halon 1301 for the suppression of in-flight fires in aircraft was 

quite low. After appraising thousands of compounds, the NGP was indeed unable to identify such a 

chemical. The requirement that all the properties of the replacement chemical be so similar to those of 

halon 1301 as to ensure compatibility with existing weapons platforms was too stringent. 

The more realistic objective was to identify chemicals that had promise to perform significantly better 

than HFC-125. Even that proved difficult: 

• No strictly thermally active compounds had a boiling point below -40 °C and a fire 

suppression efficiency superior to that of HFC-125. As will be seen in Chapter 8, a much 

higher mass of a higher boiling compound would be needed to compensate for condensation 

losses on cold surfaces. Even if the temperature requirement were relaxed, as discussed in 

Chapter 2, there were no strictly thermally active compounds that were deemed worthy of 

further consideration. 
702 Search for New Fire Suppressant Chemicals 

• Only one compound, CF3CN, with a boiling point of -67 °C, met the strictest volatility 

criterion. However, it required about 9 volume % to suppress a cup burner flame, about the 

same as HFC-125. 

• A few iodoalkanes had boiling points near 0 °C and extinguished cup burner flames at about 

3 volume %. However, it was expected they would be no less toxic than CF3I. 

• There were two other compounds with boiling points near or below 0 °C. Attempts were 

unsuccessful to synthesize N(CF3)3 (Tb = -10 °C). CF2BrCN (Tb = 3 °C) extinguished cup 

burner flames at less than 4 volume %. 

• There were some bromoalkenes with cup burner values about 3 volume % to 4 volume % and 

with boiling points of 25 °C or slightly above. These temperatures are not likely to lead to 

effective dispersion at cold temperatures, and two similar compounds had performed poorly 

in cardiotoxicity testing. 

Were the low temperature requirement to be relaxed modestly, N(CF3)3 and CF2BrCN would have 

sufficient volatility. However, for the former, a synthesis path is needed, along with an assessment of 

whether the nitrogen oxides formed following decomposition pose an ozone threat comparable to halon 

1301. For the latter, toxicity and atmospheric lifetime data are lacking. Some bromofluoroalkenes would 

be eligible if the low temperature requirement were relaxed substantially and toxicity data were 

developed. 

The development of hybrid solid propellant fire extinguishers (Chapter 9) presents an alternative means of 

dispensing a chemically active fire suppressant. In these devices, the compound is either mixed in with 

the solid propellant or is added to the high temperature exhaust from the unit. In either mode, the boiling 

point and toxicity are unimportant. What matters is that the additive be chemically effective at flame 

suppression, that the chemical species that effects the suppression be present in the exhaust flow, and that 

the mass of the additive be minimized. The NGP has affirmed or established that effective chemical 

activity is characteristic of compounds containing P, Br, I, Na, or K atoms. Low mass compounds of 

some of these atoms have significantly increased the effectiveness of SPFEs (Chapter 9). 

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