NIST Technical Note 1457 

FY2003 Annual Report

Next Generation Fire Suppression 

Technology Program (NGP) 

Richard G. Gann 
NIST Technical Note 1457 

FY2003 Annual Report

Next Generation Fire Suppression 

Technology Program (NGP) 

Richard G. Gann 

Building and Fire Research Laboratory

January 2004 

U.S. Department of Commerce 

Donald L. Evans, Secretary 

Technology Administration

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology 

Arden L. Bement, Jr., Director
Certain commercial entities, equipment, or materials may be identified in this 

document in order to describe an experimental procedure or concept 

adequately. Such identification is not intended to imply recommendation or 

endorsement by the National Institute of Standards and Technology, nor is it 

intended to imply that the entities, materials, or equipment are necessarily the 

best available for the purpose. 

National Institute of Standards and Technology Technical Note 1457 

Natl. Inst. Stand. Technical Note 1457, 46 pages (January 2004) 

CODEN: NSPUE2

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON: 2004

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Mail: Stop SSOP, Washington, DC 20402-0001
FY2003 ANNUAL REPORT 

Next Generation Fire Suppression 

Technology Program (NGP) 

[PP-1059] 

January 2004

Richard G. Gann, Ph.D. 

Technical Program Manager 
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ABSTRACT 

The Department of Defense’s Next Generation Fire Suppression Technology Program (NGP) has 

completed its seventh year of research with a goal to develop and demonstrate technology for 

economically feasible, environmentally acceptable and user-safe processes, techniques, and 

fluids that meet the operational requirements currently satisfied by halon 1301 systems in 

aircraft. 

Research on new flame suppression chemistry and improved suppressant delivery has produced 

substantive results. 

The NGP is supported by the DoD Strategic Environmental Research and Development Program

(SERDP). 

Keywords: fire research, fire suppression, halon, aircraft 
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TABLE OF CONTENTS 

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

II. TECHNICAL PROGRESS ....................................................................................... 2 

A. NEW FLAME SUPPRESSION CHEMISTRY ....................................................... 2 

1. Minimum Release Temperature........................................................................ 2 

2. Vapor Loading and Suppression Effectiveness of Two-phase Fire 

Suppressants ........................................................................................................... 3 

3. Prediction of Cardiotoxicity................................................................................ 4 

4. New Candidate Suppressants........................................................................... 5 

B. IMPROVED SUPPRESSANT DELIVERY ............................................................ 8 

1. Solid Propellant Fire Extinguishers (SPFEs)..................................................... 8 

2. Dispersion of Suppressants at Low Temperature ........................................... 10 

3. Suppressant Dynamics in Engine Nacelles .................................................... 11 

4. Enhanced Powder Panels for Dry Bay Fire Protection.................................... 21 

C. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES .................................. 25 

III. INDEPENDENT PROGRAM ASSESSMENT..................................................... 26 

IV. WHAT LIES AHEAD?......................................................................................... 26 

APPENDIX A. NGP PROJECTS.................................................................................. 28 

APPENDIX B. REPORT OF THE INDEPENDENT REVIEW PANEL .......................... 31 
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I. INTRODUCTION 

Initiated in 1997, the Department of Defense’s Next Generation Fire Suppression Technology 

Program (NGP) has completed its seventh year of research with considerable accomplishment. 

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

the NGP goal is to “Develop and demonstrate technology for economically feasible, 

environmentally acceptable and user-safe processes, techniques, and fluids that meet the 

operational requirements currently satisfied by halon 1301 systems in aircraft.” 

Fires and explosions continue to be among the greatest threats to the safety of personnel and the 

survivability of military aircraft both in peacetime and during combat operations. Production of 

halon 1301 (CF3Br), long the fire suppressant of choice, ceased as of January 1, 1994 due to its 

high ozone depleting potential (ODP). By 1997 the DoD had identified the best available 

replacement for halon 1301 in aircraft, HFC-125 (C2H5F)1

, but it requires two to three times the 

mass and storage volume and contributes to global warming. The new Program was to identify 

fire suppression technologies with reduced compromises. 

While research to identify replacement suppressants for engine nacelle and dry bay fires has 

declined considerably over the past five years, the demand for new approaches is unabated. New 

aircraft are in various stages of design. No commercial or military aircraft have yet had their 

halon 1301 systems replaced, while new systems are being installed in the cargo bays of 

commercial jetliners. The international community is questioning the necessity of maintaining 

the large halon 1301 reserves and even considering the requirement of a total phaseout. 

The demands on the new technologies remain daunting. The requirements for environmental 

protection, fire suppression efficiency, materials compatibility, and personnel safety are severe 

constraints. 

The presentation of technical progress and new products and the genesis of ideas have been 

abetted by the Halon Options Technical Working Conferences, founded in 1991. In 2002, the 

NGP assumed responsibility for these workshops. The cumulative papers have been indexed and 

are available on CD and at www.bfrl.nist.gov/866/HOTWC. 

The systematic NGP search for new suppressant chemicals and technologies for assured, 

efficient delivery is continuing to produce new results. During the past year, an Independent 

Review Panel (IRP) was "Impressed by the thoughtful way the 2001 recommendations have been 

addressed and by the tightened focus of the program" and "confident that valuable design 

products will be delivered by this program." Their sole new recommendation will be

implemented in FY2004. 

The NGP participants have generated unparalleled contributions to the published literature in the 

field, all of which can be obtained via the NGP web site: www.bfrl.nist.gov/866/NGP. The 

following pages highlight the new knowledge gained from the NGP research and the progress 

made towards the NGP Goal. Recent publications are listed at the end of each research topic. A 

concluding section forecasts where the research will proceed from this time forward. Two 

appendices list the NGP projects to date and present the latest IRP report.

 

1 Technology Development Plan for Alternatives to Ozone-depleting Substances for Weapons Systems Use; Final 

Report (TDP), Office of the Deputy Undersecretary of Defense (Science and Technology)/Weapons Systems, 1998. 

1 
II. TECHNICAL PROGRESS 

A. NEW FLAME SUPPRESSION CHEMISTRY 

In prior years, the NGP had developed a new understanding of how efficient chemicals interact 

with flames and eventually suppress them. This is summarized as follows: 

Flame propagation results from the fast reactions of key species (H and O atoms, OH 

radicals) with vaporized fuel molecules. These species exist at concentrations far above 

those expected from thermal equilibrium at flame temperatures. Chemically active agents 

catalytically reduce the radical concentrations toward equilibrium levels. While this process 

slows the flame, it does not extinguish it. The suppressant also increases the heat capacity of 

the fuel/air mixture, reducing the flame temperature and thus the flame reaction rates below 

the level needed to sustain combustion. These two effects are synergistic. The need for both 

effects suggests that the lower limit for a suppression concentration may be at about 1 % by 

volume. 

With this knowledge the NGP had developed a list of criteria to guide the search: 

1. Fire suppression efficiency at least comparable to halon 1301 (about 3 % by volume) and 

certainly higher than the hydrofluorocarbons (HFCs). Based on prior experience, this 

focuses the search on compounds that contain at least one bromine, iodine or phosphorus 

atom, although other possible functionalities can arise. (See Section II.A.4.) 

2. Short atmospheric lifetime (current preference of the order of a month), to keep ozone 

depletion potential (ODP), global warming potential (GWP) and any future unidentified 

environmental contamination issues to a minimum. 

3. Boiling point sufficiently low that for gaseous agents, an extinguishing concentration can 

be achieved within a specified time following discharge. An approximate theoretical 

upper limit is near 30 °C if the minimum temperature in flight is -40 °C. 

4. Low toxicity relative to the concentration needed for suppression. 

1. Minimum Release Temperature 

With regard to criterion 3, an effort is underway to improve understanding of the actual aircraft 

temperatures at which halon 1301 has been deployed. Incorporating the chemical features that 

effect low atmospheric lifetime (criterion 2) generally results in molecules that are larger than 

halon 1301 and thus tends toward higher boiling points, Tb. As Tb rises, there are more 

compounds per, e.g., 10 °C band, so the domain of eligible chemicals increases significantly. 

Data from incidents of halon release from all three services have been gathered. They document 

the altitude at which each release occurred, and we are converting this to an approximate 

temperature. Consideration is also being given to aircraft operating in cold climates, where the 

limiting temperature for suppressant release during take-off may be close to the (low) ground 

temperature. Completion of this task is expected in winter 2003-2004. The results, combined 

with those from Section II.A.2 of this Report, will help refine the selection criterion for agent 

volatility, provide guidance to the dispersion optimization project presented in Section II.B, and 

assist platform managers in their selection of suppressant for their particular aircraft. 

2 
2. Vapor Loading and Suppression Effectiveness of Two-phase Fire 

Suppressants 

A rapidly released suppressant fluid disperses partially as droplets and partially as a gas. The 

high momentum droplets can fill a volume rapidly. For halon 1301, the droplets flash vaporize, 

completing the efficient dispersion of a gaseous suppressant. Thus all of the suppressant 

contributes to the effective concentration at the fire zone. 

For a chemical with a higher boiling point and/or a higher heat of vaporization, more of the fluid 

reaching the fire may still be in the liquid phase. Larger droplets may impact and stick to cold 

surfaces, may not flash vaporize en route to the flames, and also may pass through the flames 

without vaporizing fully. Thus, some (or even much) of the agent may not contribute to the 

effective concentration in the fire zone. To compensate for this, the mass of the fire suppression 

system may need to be increased significantly, either by carrying a larger mass of agent or by 

heating the storage and delivery hardware. 

Thus, given knowledge of the (low) ambient temperature, it is important to be able to estimate 

the true effective concentration of a potential halon alternative. This involves droplet 

evaporation time, flame zone residence time, and saturation vapor pressure. 

We are in the process of simulating the degree of vaporization of various aerosols in a simulated 

engine nacelle and developing criteria for the physical properties that lead to an acceptable 

suppression efficiency. The chosen computational code is the Fire Dynamics Simulator. The 

computational test environment is the simple engine nacelle ELEFANT developed under the 

NGP and described in previous NGP Annual Reports. The input conditions for the engine 

nacelle reflect an expected range of agent deployment conditions: 

• Incoming air temperatures from ambient (ca. 298 K) down to 233 K. 

• Nacelle interior temperatures from ambient (298 K at startup) to 373 K. 

• Input air flow velocity of 1 m/s. 

• Mean drop size of ca. 20 μm for the polydisperse mist drop distribution immediately after 

agent release. 

• Vapor fraction immediately following release of the pressurized agent (given by the 

Jacob number) between 0.2 and 0.7. The Jacob number relates a compound’s heat 

capacity to its heat of vaporization. Since a compound's heat of vaporization is generally 

tied to its boiling point (via Trouton’s rule), the Jacob Number computational range 

essentially determines the range of physical properties for the test liquids. 

We have completed computations for water droplets under ambient temperature conditions for 

incoming air and for all surfaces inside the nacelle either at ambient temperature or at 373 K. 

Assessment of the preliminary findings is underway and will likely result in tuning of the 

computational scheme. The remaining simulations covering the matrix of physical parameters 

dictated by the Jacob number will be completed within the next two months. Then we will 

perform calculations for actual compounds with properties that closely match those parameters 

determined to result in the most success. This will be combined with the results from our 

examination of chemical families, resulting in a list of compounds that are likely to lead to 

effective fire suppression at low operation temperatures. 

3 
3. Prediction of Cardiotoxicity

Sensitization to cardiac arrhythmia is recognized as the primary (but not only) toxic effect of the 

halogenated compounds that dominate the search for halon alternatives. The cost of the standard 

dog exposure test to determine a compound's LOAEL can reach $100 k for custom-synthesized 

chemicals. Hence, estimating the cardiac sensitization LOAEL for a single compound or the 

relative LOAEL values of a series of related compounds can have a major impact on whether an 

effective and safe alternative suppressant is identified. The NGP is monitoring and evaluating 

research into methods based on both physical properties and in vitro testing. 

Partition Coefficients. A wide range of chemically diverse compounds are known to induce 

cardiac arrhythmia. This situation has led to the hypothesis that the mechanism involved is not a 

chemical (reactivity based) toxicity but instead a generalized physical property effect that just 

happens to cause cardiac arrhythmia when sufficient chemical is absorbed into heart nerve and 

muscle cells membranes. The hypothesis suggests that if a chemical is preferentially soluble in a 

barely polar liquid such as octanol, and less soluble in a polar fluid such as water, it is less likely 

to be flushed from the tissue environment. Determination of the octanol-water partition 

coefficient, KOW, is rapid and requires only a few mg of the compound. 

Examining the quality of correlation between KOW values and LOAEL values requires a database 

for members of a given chemical family. While there are calculation and experimental methods 

to determine the former, there are far less data on the latter. One chemical family for which such 

data exist is that of volatile anesthesia gases where the need for quick induction, low toxicity, 

and quick recovery with few side effects has driven extensive research. Table 1 shows the 

results of measurements for several of these halon-like compounds. Halothane (CF3CBrClH) is 

prone to causing premature ventricular contractions (PVCs). The alternative anesthetics have 

progressively lower tendencies to induce PVCs and also progressively lower oil-water 

distribution ratios when compared to halothane. This correlation is worth further study and at 

least preliminary examination as a means of guiding the selection of halon replacement candidate 

compounds. 

In Vitro Cardiac Sensitization Screening Methods. We are monitoring the progress of a 

proposal (to another Federal agency) for the development of an in vitro method using human or 

animal cardiomyocytes with applicability to the testing of volatile compounds and generation of 

relative cardiotoxicty data. If successful, this screening method would improve the identification 

of suppressants with acceptably low cardiac sensitization properties. 

4 
Table 1. Anesthesia Compounds – Partitioning and Arrhythmia Properties2,3

Property Halothane Enflurane Isoflurane Desflurane Sevoflurane

Blood-gas Ratioa 2.5 1.9 1.4 0.42 0.6

Oil-water Ratiob 220 120 170 19 55

Arrhythmiac +++ + + ~ ~

MACd 0.74 % 1.68 % 1.15 % 6.3 % 2.0 %

a

 Ratio of the anesthesia agent concentration in the blood over the anesthesia agent concentration in the gas phase. 

High values indicate more effective transport of the chemical throughout the body and thus to cardiac tissue. 

b

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

c

 The symbols "+++," "+," and "~" reflect, in order, a decreasing tendency of the anesthetic to induce PVCs in

human patients during anesthesia. The last of these indicates only a slight tendency. 

d

 Minimum Alveolar (air) Concentration (MAC) for an anesthesia agent is a measure of the anesthetic potency of

the compound, i.e., the air concentration required to immobilize 50 % of patients such that they don't give a motor 

response to a pain stimulus. 

4. New Candidate Suppressants

The current phase of the examination of chemical families for potential CF3Br replacements is 

following the general guidance from the most recent assessment of the field.4

 The priorities are 

summarized in Table 2. The effort has led to the identification of promising directions likely to 

meet flame suppression needs and possibly toxicity and environmental goals. The compounds 

identified are being sourced and will have their cup burner flame suppression performance 

determined. The boiling points of some are predicted to be in the 0 °C to 10 oC range and as 

such represent some of the lowest boiling compounds yet tested. 

Last year, the NGP commissioned the synthesis of a series of eight phosphorus-containing 

compounds (PCCs). Of the seven that could be synthesized, four appeared to be stable. 

However, despite substantial fluorination, the lowest Tb was 42 °C. Thus, further examination of 

the PCCs awaits resolution of the boiling point criterion. 

Because of their high flame inhibition efficiency, metal-containing compounds continue to be of 

interest for possible use as suppression enhancers, e.g., in gas generators and powder panels. 

However, alkali metal compounds are corrosive to aluminum in moist environments and two 

iron-containing compounds have been found to be ineffective at fire suppression or too toxic for 

such use. To determine whether there is reason to pursue the metal-containing compounds 

further, The NGP is investigating:

 

2

 Hemmings, H. Jr., and Hopkins, P., Foundations of Anesthesia - Basic and Clinical Sciences, Chapters 24 and 41, 

Harcourt Publishers Ltd., 2000. 

3 www.virtual-anaesthesia-textbook.com/vat/volatile.htm. This is an excellent tutorial website with detailed

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

as well as further reference citations. 

4

 Tapscott, R.E., Sheinson, R.S., Babushok, V., Nyden, M.R., Gann, R.G., "Alternative Fire Suppressant Chemicals: 

A Research Review with Recommendations," NIST Technical Note 1443, National institute of Standards and

Technology, Gaithersburg MD, 2001. 

5 
• The features that lead to effective chemical action in quenching flame chemistry and 

• The features that can limit the concentration of the active species in the flame zone. 

Recognizing the importance of the binding energy of a suppressant to one of the free radicals that 

participate in the chain branching chemistry of flame propagation, we have conducted 

computation studies to elucidate the specific desirable values. The test bed was a stoichiometric 

methane-air mixture. Based on prior studies, the examples investigated were the binding of 

bromine and hydrogen atoms, sodium with hydroxyl radicals and iron with oxygen atoms. The 

binding energies were varied about the accepted values, and the resulting effect on the flame 

velocity was assessed. In all three cases, the largest reduction in flame velocity occurred at or 

very near the actual bond energy. It was concluded that the bond energy between a catalytic 

scavenger and a flame radical must be in the range of 300 kJ/mole to 400 kJ/mole. Work in the 

coming year will examine properties that can cap the effectiveness of flame suppressants. 

Table 2. Prioritized Potential Halon Replacement Families 

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- or tin-containing compounds X 

Iron-containing compounds X 

To keep boiling points low and fire suppression efficiency high, attention has been focused on 

fluorinated, generally bromine-containing compounds. The nitrile group (-CN) has been 

described as a "pseudohalogen," so compounds containing this functionality are being explored 

as well. In particular, members of the following families are in the process of being acquired for 

flame extinguishment testing: 

• Fluoronitiriles and bromofluoronitriles. The first fluoronitriles and bromofluoronitriles 

being acquired represent the expected lowest boiling compounds from these two groups 

and are readily available commercially. Trifluoroacetonitrile (CF3CN) has a Tb of -64 oC. 

6 
The flame extinguishment performance for this chemical and the full family is unknown, 

so this result could open an unanticipated direction for a new candidate. 

Bromodifluoroacetonitrile (CF2BrCN) is expected to have a suppression efficiency at 

least comparable to halon 1301. Its Tb is only 3 oC. The atmospheric lifetimes of the 

nitriles are expected to be limited by hydrolysis of the CN group and rainout. 

• Bromofluoropropene oxides. These compounds are expected to be stable under storage 

and will likely decompose readily in the flame front to liberate the chemical fire 

suppressing bromine atom. Their atmospheric lifetimes are expected to be short, but this 

needs to be confirmed. Cup burner values for the monobrominated compounds should be 

similar to halon 1301, with specific values possibly reflecting the location of the bromine 

in the molecule. Boiling points for the bromoperfluoropropene oxides (oxiranes) are 

estimated to be between 0 °C and 10 oC. They can be synthesized in a single step from 

existing bromofluoropropenes by a partial oxidation of the alkene bond. CF2(O)CFCF2Br 

(3-bromo-1,2-perfluoropropene oxide), CF2(O)CBrCF3 (2-bromo-1,2-perfluoropropene 

oxide), and CFBr(O)CFCF3 (-bromo-1,2-perfluoropropene oxide) are being sourced. 

• Bromofluoropropenes. The atmospheric lifetimes of these compounds should be low 

since the double bond is reactive in the troposphere. Log KOW values were calculated, 

using several available modeling methods, for the 35 possible penta-, tetra- and 

trifluorinated bromofluoropropenes. The values obtained from some of the methods 

varied considerably, indicating that that calculation method was sensitive to structural 

changes. Overall, the calculated log KOW values ranged from 1.4 to 2.5. Using the 

experimental KOW value of 1.84 for halon 1301 as a guide, a list of compounds whose 

low calculated values predicted a possibly equivalent or higher LOAEL was prepared and 

is shown in Table 3. Two other partially fluorinated compounds have demonstrated 

unacceptably low LOAEL values for cardiac sensitization, but the values for the 

compounds in Table 3 have not been measured. We are also seeking to obtain the three 

fully halogenated compounds with the lowest calculated KOW values: CFBr=CFCF3 

(1-bromoperfluoropropene, Tb = 27 oC), CF2=CBrCF3 (2-bromoperfluoropropene, 

Tb = 25 oC), and CF2=CFCF2Br (3-bromoperfluoropropene). 

• Bromofluoroethers. They are expected to have relatively low toxicity and good flame 

extinguishment properties but unless they prove sufficiently polar they will require some

degree of hydrogenation to minimize ODP impact. Two of the simplest brominated 

ethers are CBrH2-O-CF3 (Tb = 39 oC) and CBrF2-O-CF3, (Tb estimated between -30 °C 

and -8 °C). The tetrafluorinated C2 bromoethers CBrHF-O-CF3 (bromofluoromethyl 

trifluoromethyl ether) and CBrF2-O-CHF2 (bromodifluoromethyl difluoromethyl ether) 

are predicted to boil in the range 5 °C to 15 oC and are being sought for testing. CBrF2-

O-CF3, (bromodifluoromethyl trifluoromethyl ether) is also being sought. 

7 
Table 3. Low KOW Bromofluoropropenes

Compound Name Cis-, trans-isomerism

CF2=CFCF2Br 3-bromo-pentafluoropropene

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

CFBr=CFCF2H 1-bromo-1,2,3,3-tetrafluoropropene Y

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

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

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

CFH=CBrCF2H 2-bromo-1,3,3-trifluoropropene Y

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

CFH=CFCFBrH 3-bromo-1,2,3-trifluoropropene Y

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

CFH=CHCBrF2 3-bromo-1,3,3-trifluoropropene Y

CFBr=CFCFH2 1-bromo-1,2,3-trifluoropropene Y

CBrF=CHCHF2 1-bromo-1,3,3-trifluoropropene Y

CHBr=CFCHF2 1-bromo-2,3,3-trifluoropropene Y

 

Recent Publications: New Flame Suppression Chemistry

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

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

Institute, Albuquerque, NM, 2003. 

Williams, B.A., and Fleming, J.W., "Influence of Bond Energies on Catalytic Flame Inhibition: 

Implications for the Search for New Fire Suppressants," NRL/MR/6180--03-8728, Naval 

Research Laboratory, Washington DC, 2003. 

Mather, J.D., and Tapscott, R.E., "Tropodegradable and Other Environmentally Acceptable 

Flame Extinguishants," in Gann, R.G., Burgess, S.R., and Reneke, P.A., eds., Papers from 1991-

2003 Halon Options Technical Working Conferences (HOTWC), CD-ROM, NIST SP 984-1, 

National Institute of Standards and Technology, Gaithersburg, MD, 2003. 

B. IMPROVED SUPPRESSANT DELIVERY 

1. Solid Propellant Fire Extinguishers (SPFEs) 

Prior NGP research had developed new types of solid propellant fire extinguishers that have both 

reduced combustion temperatures and increased flame suppression efficiency, which in turn will 

enable freedom of selection of the momentum of the suppressant stream. These have now been 

examined further. 

The combination of propellants based on the advanced high nitrogen propellant BTATZ 

(C4H4N14) and incorporation of coolant species into the propellant composition reduces exhaust 

8 
temperatures by as much as 30 % vs. current baselines. The incorporation of potassium 

carbonate in the solid propellant composition decreases by up to a factor of three the mass of 

suppressant needed to extinguish mid-scale flames. Fire testing using hybrid fire extinguisher 

(HFE) configurations, in which the coolant or chemical additive is added downstream of the 

combusting propellant, showed that high-boiling agents can be delivered even at low 

temperatures, their low vapor pressures offset by the heating and pressurizing power of the solid 

propellant driven HFE. This has produced an additional ca. 30 % increase in mass efficiency 

(Figure 1). Hydrofluorocarbons and hydrofluoroethers were comparably effective on a mass 

basis. 

Figure 1. Side-by-Side Testing of Inert and Chemically Active (CA) SPFEs on 

Sub-scale (FTF) and Full-Scale Military Aircraft Platforms [blue bars: inert 

effluent, yellow bars: 1st generation chemically active systems; green bars: 2nd

generation chemically active systems] 

The SPFE technology examined under this NGP project is derived from fire protection products 

currently being installed on both the Navy F/A-18 E/F and V-22 aircraft. Our advanced fire 

suppression protection products incorporating improvements are currently being examined for 

further applications as expanded protection in the above platforms as well as on other aircraft 

platforms. 

The dry bays and engine nacelles in military aircraft platforms vary significantly in size, air flow, 

and clutter, as evidenced in Table 4: 

9 
Table 4. Representative Aircraft Test Platforms 

Platform Volume, L Clutter Airflow, kg/s 

V-22 loss of lube bay 280 Min < 1 

V-22 aft cove 200 High < 1 

F-22 landing gear bay (LGB) 700 Moderate < 1 

C-130 leading edge (WLE) 1530 Mod > 4 

V-22 mid-wing dry bay (MWDB) 4000 High > 4 

F/A-18 E/F engine bay 1200 Mod ≈ 2 

F-22 engine nacelle 2260 Mod ≈ 2 

Several of the above platforms were used to evaluate the effectiveness of SPFE technology. 

These test series typically included side-by-side testing of both inert and chemically active SPFE 

systems. While these test series differed in bay size, clutter, airflow, fuel flow rate and pre-burn 

conditions (and therefore fire threat), the resulting threshold successful propellant masses show a 

consistent benefit. 

These results show the validity both of the mid-scale test facility used to screen SFPE 

formulations and, more importantly, of the large improvements in efficiency from the NGPdeveloped SFPE technologies. The improved mass efficiency enables: 

• Greater flexibility in design, which can translate into a reduced number of different 

SPFE configurations on a given aircraft, resulting in lower per unit costs and also lower 

logistics costs; 

• Simplified existing fire protection system configuration by using a lesser number of 

different sizes of SPFEs; and 

• Opportunities to upgrade fire protection system performance without substantive 

changes to the platform. 

2. Dispersion of Suppressants at Low Temperature 

NGP experiments with CF3I (Tb = -22 °C) discharges into a simulated engine nacelle at -40 oC 

have shown that inefficient dispersion should be expected when discharging a suppressant fluid 

into a system whose temperature is well below the fluid boiling point. Much of the liquid 

deposited on the nacelle floor and evaporated over many seconds. Thus, basing the design mass 

of agent for an engine nacelle on room temperature test data could lead to significant 

underestimation of the mass needed for in-flight fire suppression. (See also Section II.A.2.) 

Current work is directed at generalizing these results to a broader range of fluid boiling points 

and to different temperature differentials. The first task in doing this is to identify high boiling 

point chemicals. For these tests, the chemicals need not be effective fire suppressants, but they 

should meet the following criteria: 

• Low toxicity, and thus no health hazard to the staff performing the experiments. 

• Reasonable cost, since the tests require kilogram quantities. 

10 
• Normal boiling point between about 5 °C and 35 °C. 

• Absorption of UV radiation, since the available measurement devices in the simulator are 

fiber-optic based UV spectrometers. 

The initial search resulted in several potential compounds with reasonable Tb and UV absorption: 

• ClO2 Tb = 11 °C 

• C2F5I Tb = 13 °C 

• NO2 Tb = 21 °C 

• CF2Br2 Tb = 24.6 °C 

• CH3I Tb = 42.7 °C 

The stability or toxicity of ClO2, NO2, and CH3I rendered them unacceptable for use in the 

laboratory environment. C2F5I costs about $2400/kg, and would only be used if no other 

compound meets the criteria. CF2Br2 (halon 1202) shows good promise. It is relatively 

inexpensive, ca. $200/kg, and readily absorbs UV with peak absorbance centered near 226 nm, 

well within the spectral response of the spectrometers. Although it is an ozone-depleting 

substance, arrangements have been made to obtain it from a stockpile, and discharge tests using 

CF2Br2 will be conducted using the NIST nacelle simulator at room temperature and 0 °C. The 

search continues for a second suitable chemical with a lower boiling point. 

3. Suppressant Dynamics in Engine Nacelles 

Droplet Flow Around Obstacles. We have completed a series of experiments to provide 

data regarding the behavior of suppressant droplets as they encounter a single well-defined 

obstruction in their path. These results become the basis for interpreting the interactions with 

complex clutter and for the treatment of aerosol suppressants in the modeling, both described 

later in Section II.B.3.

An air stream containing the sprayed agent flowed past a cylindrical object or a body-centered 

cube (BCC) object representing different degrees of clutter. The cylindrical object could be at 

ambient temperature or heated. The properties measured were: 

• The mass of fluid that struck an object and dripped into a collector pan. This fraction of 

the total would not have continued toward the fire zone. 

• The dispersion or entrainment for those droplets that didn't stick to the object, measured 

using three-dimensional particle imaging velocimetry (PIV). This was summarized in the 

FY2002 NGP Annual Report. 

• Changes in the droplet size distribution, measured using a Phase Doppler Interferometer 

(PDI). This involved substantial instrumentation development and is described below. 

The use of three fluids enabled obtaining results as a function of boiling point and the difference 

between the fluid temperature and the temperature of the obstacles. The fluids were: 

• Water Tb = 100 °C 

• CH3OC3F7 (HFE-7000) Tb = 34 °C 

• CH3OC4F9 (HFE-7100) Tb = 61 °C 

11 
Since the previous effects were seen to depend heavily on droplet size, the current work focused 

on spatial and temporal resolution of droplet size and velocity distributions in the upstream and 

downstream vicinity of the cylinder using a PDI. In particular, the PDI was used to provide 

further information on droplets rebounding off the upstream face of the cylinder, vaporization of 

droplets near the heated cylinder, droplet sizes that are entrained into the recirculation region 

behind the cylinder, and the effect of agent boiling point on droplet transport. The apparatus is 

shown photographically and schematically in Figure 2. 

The PDI creates an interference pattern (a region of alternating light and dark fringes) in the 

region where two laser beams intersect. This is called the probe volume or sample volume. The 

system used here uses the blue (wavelength = 488 nm) and green (wavelength = 514.5 nm) lines 

of an argon ion laser, separated by beam conditioning optics, and focused by the transmitting 

optics to intersect and form the probe volume. A droplet passing through the probe volume 

scatters light that exhibits an angular intensity distribution that is characteristic of the size, 

refractive index, and velocity of the droplet. For a droplet with known refractive index, the size 

and velocity can be determined by analyzing the scattered light. The PDI obtains information 

about the spray at a single point in space. It is also a single-particle instrument in that 

information is obtained for only one droplet at a time. This offers advantages over integrating 

techniques because the characteristics of a particular droplet (size, velocity, etc.) can be recorded 

and the data can be separated into classes (size classes, velocity classes) to further characterize 

the spray system. Analysis of a movie from a high-speed digital camera (1000 frames/s) 

provides information about the ensemble of droplets. The measurements were carried out at 

several radial (R, cross-stream) positions and over a range of axial (Z, streamwise) positions 

upstream and downstream of the cylinder. Measurements were carried out from approximately 

50 mm upstream of the cylinder to a downstream position of 100 mm. In the radial direction, 

measurements were carried out in increments of 5 mm from 0 to 20 mm in the upper hemisphere 

(i.e., in the positive radial direction).

The results show that: 

• As the droplets approach the upstream surface of the cylinder, there is a decrease in the 

streamwise velocity component and an increase in the cross-stream component. Thus, 

little of the water (< 5 %) impacted the surfaces and dripped into the collector. 

• The change in the PDI laser beam intensity showed that the concentration of droplets 

behind the cylinder was significantly reduced from the upstream value. The recirculation 

zone behind the obstacle was larger for larger droplets which require a longer distance to 

interact with the turbulent flow field and to reduce their higher momentum. 

• Many impinging droplets rebounded off of the surface and into the free stream. As 

expected, there was no evidence of secondary breakup of the droplets. 

• For the unheated cylinder, the Sauter mean diameter (D32) decreased in mean size on the 

downstream side of the cylinder (compared to the upstream side) (Figure 3a), increased in 

mean size with increasing radial distance from the central plane of the cylinder (Figure 

4a). This amplifies the prior finding that fine droplets were preferentially entrained into 

the recirculation region behind the cylinder while the larger droplets impacted the 

cylinder surface, accumulated and dripped off, and/or rebounded and dispersed radially 

outward into the free stream. 

• There is an increase in the droplet streamwise velocity over the cylinder for R = 15, and 

20 mm, which was also characteristic of the accelerated flow over the cylinder. 

12 
Figure 2. View and Schematic of the Experimental Arrangement with the Laser 

from the Phase Doppler Interferometry System

560 mm

760 mm

PDI transmitter

PDI receiver

Plexiglas chamber

Heated cylinder

Grid / atomizer /

honeycomb

θ

560 mm

760 mm

PDI transmitter

PDI receiver

Plexiglas chamber

Heated cylinder

Grid / atomizer /

honeycomb

560 mm

760 mm

PDI transmitter

PDI receiver

560 mm

760 mm

PDI transmitter

PDI receiver

Plexiglas chamber

Heated cylinder

Grid / atomizer /

honeycomb

θ

• The droplet Sauter mean diameter and both the streamwise and crossstream velocity 

components were consistently smaller for the heated cylinder as the droplets are 

transported past the cylinder surface (Figure 4a), although the changes are close to the 

uncertainty in the measurements. This indicates that droplet vaporization at the heated

surface does not result in the complete removal of the smaller size droplets from the 

13 
distribution, but rather decreases the size of all droplets. 

• Droplet size increases and velocity decreases with increasing agent boiling point (Figure 

5); the differences for the two HFEs are small but real. The HFE droplets with their 

lower boiling points vaporized even before reaching the obstacle surface. 

Figure 3. Variation of Droplet (A) Sauter Mean Diameter and (B) Mean Streamwise

Velocity with Streamwise Position at Different Cross-Stream Positions for the 

Unheated Cylinder. The heavy line on the abscissa represents the location of the 

cylinder

A B 

Figure 4. Variation of the Streamwise Velocity with Streamwise Position 

Upstream of the Unheated Cylinder at Z = –15 mm and Along the Centerline. 

A B

14 
Figure 5. Comparison of the Droplet (A) Mean Size and (B) Streamwise Velocity

for the Three Agents 

-120 -100 -80 -60 -40 -20 0 20 40 60

0

10

20

30

40

50

60

70

80

Flow

Direction

R = 20 mm

Diam

eter (

μm)

Streamwise Direction (mm)

 HFE7000

 HFE7100

 WATER

-120 -100 -80 -60 -40 -20 0 20 40 60

0

10

20

30

40

50

Flow

Direction

R = 20 mm

Stre

a

m

wise V

elo

city (m/s)

Streamwise Direction (mm)

 HFE7000

 HFE7100

 WATER

15 
Spray-clutter interactions. A detailed characterization of the three-dimensional velocity 

field and the distribution of agent drop sizes downstream of generic clutter have been completed. 

A three-dimensional phase Doppler anemometry system allows both droplet diameter and 

velocity components in all three directions to be acquired simultaneously. Measurements were 

performed within the Suppressant Spray Flow Facility (Figure 6) with the air/water nozzle set to 

ca. 0.3 L/s. 

Figure 6. Clutter Interaction with Fine Spray in Wind Tunnel 

Variable 

Clutter 

Modules

Air-water Mist 

Nozzle 

Data were acquired for three clutter spacings (0.25 D, 1 D, and 2 D) at two locations (2 D and 

5.5 D) downstream from the trailing edge of the clutter package for three airspeeds (1 m/s, 3 m/s, 

and 5 m/s). D, the clutter rod diameter, was 5 cm. The frequencies and length scales of 

turbulence upstream of the clutter were determined in order to validate the automatic data 

acquisition system and provide additional insight. Autocorrelation of the turbulent components 

derived the Prandtl mixing lengths and dimensional turbulence scales of generated eddies. 

Fourier spectral analyses on turbulent velocities from hot wire data and their peak frequencies 

determined additional modal length scales of the turbulent velocity field. These data are being 

organized and analyzed further for salient correlations to be used in the VULCAN modeling, and 

there is a coordinated team effort underway to evaluate the results from the spray-clutter 

16 
interaction measurements using this NAVAIR nozzle. 

Nacelle Simulator. The full-scale Fire and Flow Test Facility (Figure 7) is nearing

completion. Next summer, we will conduct pool fire tests in it to validate the computer models 

further and, since it has many viewing ports, we will conduct observations of anomalous test

conditions from the full-scale F/A-18 E/F ground test results. 

Figure 7. 2-D Full-Scale Nacelle Test Section

JP-8 Pool Fires 

Air Flow 

Optical Ports for 

 Laser 

Measurements 

Computer Modeling of Suppressant-Clutter Interaction. We have now demonstrated 

that VULCAN simulations are capable of reproducing observed behavior of a gas phase 

suppressant with a single clutter object. The behavior is shown in Figure 8. Case A1 compares 

well with the experimental measurements of flames stabilized behind an obstruction in a 

laboratory wind tunnel (Figure 9).5

We then investigated the effect of a second clutter element on the suppression of fires stabilized 

behind a primary clutter object. The second element was situated to affect the flow patterns but 

not directly stabilize the flame. Nonetheless, the aerodynamic drag on the secondary clutter can 

create high and low pressure regions on the leading and trailing sides of the clutter. For highpressure regions located adjacent to flame-stabilizing recirculation zones (Figure 9, Case A5), 

mixing of suppressant into the stabilization region is substantially enhanced, leading to reduced 

suppressant requirements. Conversely, if the low-pressure region is adjacent to the flamestabilizing recirculation zones (Figure 9, Case A3), mixing of suppressant into the stabilization 

region is inhibited, leading to slightly greater suppressant requirements. 

17 

 

5

 F. Takahashi, W. J. Schmoll, E. A. Strader, V. M. Belovich, “Suppression Behavior of Obstruction-Stabilized 

Pool Flames,” Combust. Sci. Tech. 163, 107-130 (2001). 
Figure 8. Fires Stabilized Behind a Backward-Facing Step in a Square Wind 

Tunnel. [The hot colors represent the flame, purple is the JP-8 pool, blue is the 

inlet and gray represents the structure, less the left wall and top surface that have 

been removed for visibility.] 

Case A1 

Case A3 

Case A5 

18 
Figure 9. Comparison of Calculated and Experimental5

 Suppression Times. The 

Correlation6

 is of the Experimental Values. 

Computer Modeling of Suppression in a Prototype F-18 E/F Engine Nacelle. 

Simulations are being conducted using the VULCAN code in preparation for full-scale fire 

suppression tests using a ground-based F-18 E/F engine nacelle simulator. The objective is to 

identify conditions for which suppression will and will not be successful in order to test the 

model’s capability to predict both outcomes correctly. 

Pool fires have been identified as among the most difficult fires to suppress. A four-nozzle 

design leads to good suppressant distribution (in the absence of a fire) over the expected range of 

operating conditions. Figure 10 demonstrates gross fire characteristics for two such pool fires 

located at the forward end of the nacelle. The fire is suppressed, as indicated by the volume of 

hot gases going to zero very soon after the suppressant begins to be injected at 20 s. 

In order to create conditions for which fires will not be suppressed, we have capped each of the 

nozzles in turn. Figure 11 indicates that capping nozzle 2 has the most dramatic effect, leaving a 

substantial fraction of the nacelle volume with insufficient suppressant to extinguish a fire. As 

shown in Figure 12, the lack of suppressant is most severe along the lower nacelle regions where 

pool fires would exist. Interestingly, Figure 11 also indicates that capping nozzle 3 has a 

minimal effect on the suppressant distribution. Suppressant dispensed from nozzle 3 tends to 

overlap in space with the suppressant dispensed from other nozzles. Thus, the outcome of an 

experiment with nozzle 3 capped will be instructive. 

19 

 

6 Hamins, A., Presser, C.;, and Melton, L., “Suppression of a Baffle-Stabilized Spray Flame by Halogenated 

Agents,” Proc. Combust. Inst. 26, 1413-1420 (1996).
Figure 10. Simulated Volume Fraction of the Nacelle for Which the Average 

Temperature Exceeds 700 K (Red Curves) and for Which the Suppressant Mass 

Fraction Exceeds 0.3 (Green Curves) during Fire Extinguishment for Two Flow

Conditions. Solid lines: air flow = 0.33 kg/s; dashed lines: 0.66 kg/s. 

Figure 11. Effect of Removing Distribution Nozzles

20 
Figure 12. Simulation of HFC-125 Mass Fraction Above and Below the Engine at 

the Completion of Suppressant Injection with Nozzle 2 Capped. Hot Colors 

Indicate Insufficient Suppressant. 

4. Enhanced Powder Panels for Dry Bay Fire Protection 

The NGP has completed its research into enhanced powder panels with both success and high 

visibility. These aircraft fire protection devices, attached to flammable fluid containers adjacent 

to dry bays, provide passive, lightweight, effective fire protection against ballistic impact. 

We first identified effectiveness issues with current commercial powder panels, developed 

enhanced concepts for improving powder panel performance, compared concepts through 

experimentation, and demonstrated performance improvements by the most promising concepts. 

Now, NGP researchers have optimized these concepts and verified their value through live fire 

testing. 

Panel Optimization. Aircraft production managers have expressed concerns over such 

factors as panel weight, thickness, and durability. Our new designs have resulted in a 60 % 

reduction of weight (to an areal density as low as 0.136 g/cm2

) and thickness (to as low as 1.65 

mm) over our prior designs. These are 30 % lighter and 40 % thinner than conventional 

commercial panels, yet they release as much as 21 times more powder mass or 42 times greater 

percentage of total powder. Much of this was due to an innovative overall panel design that 

maximizes its front face fracture relative to commercial powder panels. 

We also performed an assessment of the viability of these advanced panels. The original intent 

was to compare an enhanced powder panel protection system with a halon fire extinguishing 

system. However, a side-by-side comparison turned out to be difficult. Halon fire extinguishing 

systems are most often employed in areas such as engine nacelles, fuel tank ullage areas, and 

auxiliary power units, while powder panels have only been demonstrated in dry bay areas. When 

halon has been used in dry bay areas, it is typically for safety-related fires and activation of a 

powder panel by a ballistic threat is unlikely due to the location of the dry bay. Therefore, we 

compared the new devices to other active dry bay fire extinguishing systems and current 

21 
commercial powder panels. Two system weight comparisons were performed: 

• A conceptual forward-fit C-130 outboard wing leading edge dry bay fire protection 

system. The estimated enhanced powder panel system weight was 1.2 kg lighter than a 

theoretical SPGG system and about 4.0 kg lighter than a commercial powder panel 

system. 

• An existing V-22 outboard wing tip rib dry bay fire protection system. The enhanced 

powder panels were compared with SPGG systems and current commercial powder 

panels. The existing SPGG system for both V-22 outboard tip rib dry bays was estimated 

to be 369 g lighter than the enhanced powder panel system. The commercial powder 

panel system would be approximately 285 g heavier than the enhanced powder panel 

solution.

The results indicate that enhanced powder panels offer a justifiable option, in terms of system

weight, for previously unprotected dry bays or as an alternative to areas protected by other 

means. 

The culmination of the project was the conduct of live fire demonstration tests of the optimized 

enhanced powder panels. Testing involved a 0.45 m3

 dry bay and fuel tank containing at least 49 

liters of JP-8 fuel. Nine tests were conducted with 12.7 mm armor piercing incendiary 

projectiles fired at a velocity of approximately 757 m/s. Two tests were conducted to ensure 

fires could be ignited without fire protection, a test was conducted with a commercial powder 

panel, and six tests were conducted with enhanced powder panels. Figure 13A shows the 

commercial powder panel following a test that resulted in fire ignition, although the panel 

dislodged from the fuel tank during the impact event. Figures 13B and 13 C show two different 

enhanced powder panel designs. Four of the six enhanced powder panel tests resulted in 

prevention of fire ignition. One of the other two tests resulted in the extinguishment of a fire 

0.28 second after impact; however, it was most likely caused by the ignition of a pool of residual 

fluid from a previous fuel tank leak. The sixth test also resulted in fire ignition, but as in the 

commercial panel test, the panel dislodged from the fuel tank due to an ineffective adhesive. 

The tests demonstrated that enhanced powder panels as much as 26 % lighter and 29 % thinner 

than commercial powder panels could release at least four times more powder, and, in all but one 

test, resulted in at least three times more panel front face area removal. It was conclusive that

sufficient powder was released from each of the enhanced powder panels to significantly reduce 

the likelihood of a dry bay fire, even using Al2O3, an inefficient (but inert) fire extinguishing 

powder. It was estimated that the enhanced panels released 40 g to 70 g of powder, compared to 

less than 10 g released by the commercial panel. Powder dispersion was evident throughout the 

dry bay following enhanced powder panel tests and remained dispersed for at least five minutes 

or more in most tests as can be seen by observing the left side of the "dry bay" in Figure 13 D. 

We can thus conclude that the fire suppression performance of enhanced powder panels is: 

• Far greater than their predecessors, 

• Competitive with other non-halon alternatives, and 

• Predictable from non-live fire tests. 

22 
The developments initiated by this project have sparked other research and development interest, 

as well as interest from several aircraft programs examining fire protection alternatives. 

Evaluations have also been conducted recently for integrating powder panels into the AH-64 

Apache and the RAH-66 Comanche helicopters. There is potential in the Navy UH-1Y Huey 

and AH-1W Super Cobra legacy aircraft which are being upgraded to the AH-1Z Super Cobras 

and use powder panels for dry bay protection. The V-22 Osprey tiltrotor aircraft uses powder 

panels extensively. In addition, there is some interest for use in U.S. fixed wing aircraft that do 

not currently employ powder panels. 

Figure 13. Photographs Following Live Fire Demonstration Tests 

A. Commercial Powder Panel B. Enhanced Design 1 

C. Enhanced Design 2 D. Enhanced Design 2 

23 
Recent Publications: Improved Suppressant Delivery

(* indicates archival publications) 

Ghee, T. and Keyser, D. “Basic Aerodynamic Shapes in a Low-Speed, Highly Turbulent Flow 

Field,” AIAA 2003-3953, Am. Inst. Aero. Astro., Washington, DC, 2003. 

Presser, C., Widmann, J.F., and Papadopoulos, G., "PIV Measurements of Droplet Transport in a 

Homogeneous Turbulent Flow over a Cylinder," AIAA 2003-0846, Am. Inst. Aero. Astro., 

Washington, DC, 2003. 

Presser, C., Papadopoulos, G., and Widmann, J.F., "Droplet-Laden Homogeneous Turbulent 

Flow Past Unheated and Heated Cylinders," Proc. ASME/JSME Joint Fluids Engineering Conf. 

(FEDSM'03), FEDSM2003-45240, on CD, Am. Soc. Mech. Eng., New York, NY, 2003. 

DesJardin, P.E., Presser, C., Disimile, P.J., and Tucker, J.R.., "A Phenomenological Droplet 

Impact Model for Lagrangian Spray Transport." AIAA 2003-1322, Am. Inst. Aero. Astro., 

Washington, DC, 2003. 

Presser, C., Avedisian, C.T., and Johnson, B.S., "Phase Doppler Measurements of Liquid Agent 

Transport over a Heated Cylinder," in Gann, R.G., Burgess, S.R., and Reneke, P.A., eds., Papers 

from 1991-2003 Halon Options Technical Working Conferences (HOTWC), CD-ROM, NIST SP 

984-1, National Institute of Standards and Technology, Gaithersburg, MD, 2003. 

Disimile, P.J., Tucker, .R., Crosswell, B., and Davis, "The Transport of Water Sprays Past 

Generic Clutter Elements Found Within Engine Nacelles" in Gann, R.G., Burgess, S.R., and 

Reneke, P.A., eds., Papers from 1991-2003 Halon Options Technical Working Conferences 

(HOTWC), CD-ROM, NIST SP 984-1, National Institute of Standards and Technology, 

Gaithersburg, MD, 2003. 

J. C. Hewson, S. R. Tieszen, W. D. Sundberg, P. E. Desjardin, "CFD Modeling of Fire 

Suppression and Its Role in Optimizing Suppressant Distribution," in Gann, R.G., Burgess, S.R., 

and Reneke, P.A., eds., Papers from 1991-2003 Halon Options Technical Working Conferences 

(HOTWC), CD-ROM, NIST SP 984-1, National Institute of Standards and Technology, 

Gaithersburg, MD, 2003. 

Presser, C., Avedisian, C.T., and Johnson, B.S., "Phase Doppler Measurements of Liquid Fire 

Suppressants over a Heated Cylinder," AIAA 2004-0479, Am. Inst. Aero. Astro., Washington, 

DC, accepted for 2004. 

*Yang, J.C., Manzello, S.L., Nyden, M.R., Connaghan, M.D., “Cold Discharge of CF3I in a 

Simulated Aircraft Engine Nacelle,” Fire Safety Science – Proc. of the Seventh International 

Symposium, 715-728, (2003). 

Cyphers, D.C., Frederick, S.A., and Haas, J.P., “Demonstrating Enhanced Powder Panels,” in 

Gann, R.G., Burgess, S.R., and Reneke, P.A., eds., Papers from 1991-2003 Halon Options 

Technical Working Conferences (HOTWC), CD-ROM, NIST SP 984-1, National Institute of 

Standards and Technology, Gaithersburg, MD, 2003. 

Haas, J.P., Cyphers, D.C., and Frederick, S.A., “Enhanced Powder Panel Concepts,” Twenty 

Seventh Annual American Institute of Aeronautics and Astronautics Dayton-Cincinnati 

Aerospace Science Symposium, Dayton, OH, March 5, 2002. 

24 
Cyphers, D.C., “Enhanced Powder Panels - Applying New Ideas to an Old Fire Extinguishing 

Method,” Military Fire Protection Systems Edition, FS-World.com Magazine, accepted for 

publication. 

C. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES 

During the coming year, we will plan and begin conduct of a series of real-scale engine nacelle 

fire suppression tests. Their purpose will be to verify the fire suppression principles developed 

in the NGP by comparing the outcome of the tests with predictions based on NGP-developed 

technology and to identify any as-yet unexplained suppression phenomena. 

The first step in this process is to develop a set of "Lessons Learned" from each of the NGP 

projects. These include findings of both research and operational value. This compilation is 

nearly complete. The second step, to be completed this winter, will be to extract broader 

principles that underlie fire suppression science and practice. 

25 
III. INDEPENDENT PROGRAM ASSESSMENT 

The NGP Independent Review Panel (IRP) was again asked to assess progress to date and to 

recommend actions that could enhance the prospects for NGP research to result in viable and 

practical alternative fire suppression technologies with NGP resources remaining at or near 

currently projected levels. 

The IRP was impressed by the thoughtful way their 2001 recommendations have been addressed 

and by the tightened focus of the program. They further observed: 

1. They are confident that valuable design products will be delivered by this program. 

2. The new 2003 start to integrate and draw inferences from the results of the technically 

disparate studies is important and to be commended. A fully integrated effort to 

understand how each piece can be fitted into the whole will make the results much more 

valuable than the sum of the parts. 

3. The proposed new 2003 start to better understand the low-temperature fire history and 

requirements is also to be commended. Determining how the compartment lowtemperature operating limits, the ignition probability at low temperatures, and the fire 

histories at low temperatures combine to define the risk associated with low-temperature 

operation is also likely to open the design space and provide a wider range of options 

than would be achieved by simply using the worst-case combination of operating 

temperatures. 

The IRP had one new recommendation: Within the existing NGP budget and schedule 

constraints, evaluate the effects of discharges of CF3I in aircraft fire protection systems, as 

opposed to fuel tank inerting systems, on stratospheric ozone depletion and establish a 

methodology applicable for this purpose to other candidate agents containing bromine or iodine. 

The F-16 fuel tank inerting study using CF3I could easily be inappropriately interpreted to deny 

use of CF3I and similar chemicals in any application. 

IV. WHAT LIES AHEAD? 

As the NGP approaches the meeting of its goal, the research will be focusing on two technical 

components: 

• Evaluating the “world of chemistry” for new flame suppression chemicals that are 

operable in aircraft dry bays and engine nacelles. It is essential that as many candidates 

as possible are identified and screened as potential halon 1301 alternatives. It is equally 

important that chemical families with no potential be so designated, along with the 

reasons for the designation. Thus, for other applications or should suppressant 

requirements change for fire suppression in aircraft, future investigators will have the 

benefit of the current program findings. 

• Developing principles for optimizing suppressant storage and delivery. Both research 

and engineering experimentation have shown that there is much system effectiveness to 

be gained if the suppressant is deployed efficiently and much to be lost for a delivery 

design that is incompatible with the suppressant properties. 

26 
As these efforts near completion, a modest series of real-scale fire suppression tests will be

conducted with the purpose of demonstrating the validity of the above findings. 

The prognosis for successfully meeting the revised NGP goal is excellent, given the technical 

infrastructure and cadre of experts advanced by the NGP. The Department of Defense has 

already made use of NGP technology in testing, selecting, and designing suppression 

technologies for some Military Service aircraft. More such test series are being planned and 

presumably will become the norm for the remaining platforms. 

27 
APPENDIX A. NGP PROJECTS 

The system for the identifier codes for the projects was developed at the beginning of the NGP 

and follows the now outdated program structure in the original NGP Strategy Document, which 

is available at the NGP web site. For current use, the important information is located following 

the second slash (e.g., 3A/1/789). In this example, the project was funded in fiscal years 1997, 

1998, and 1999. 

A. SUPPRESSANT SCREENING TESTS 

3A/1/789. DISPERSED LIQUID AGENT FIRE SUPPRESSION SCREEN; Principal 

Investigator: Jiann C. Yang, NIST 

3A/2/890. TRANSIENT-APPLICATION-RECIRCULATING-POOL-FIRE AGENT 

EFFECTIVENESS SCREEN; Principal Investigator: William Grosshandler, 

NIST 

3B/1/89. TOXICOLOGICAL ASSESSMENT OF HUMAN HEALTH CONSEQUENCES 

ASSOCIATED WITH INHALATION OF HALON REPLACEMENT 

CHEMICALS; Principal Investigator: Darol Dodd, AFRL 

3B/2/8. AGENT COMPATIBILITY WITH PEOPLE, MATERIALS AND THE 

ENVIRONMENT; Principal Investigators: Marc Nyden, NIST, and Stephanie 

Skaggs, Universal Technical Services 

B. NEW FLAME SUPPRESSION CHEMISTRY

2A/1/7890, /2/890. MECHANISMS OF ULTRA-HIGH EFFICIENCY CHEMICAL 

SUPPRESSANTS; Principal Investigators: James Fleming, NRL, and Kevin 

McNesby, ARL 

4D/2/7. IDENTIFICATION AND PROOF TESTING OF NEW TOTAL FLOODING 

AGENTS; Principal Investigator: Robert E. Tapscott, NMERI; COR: Andrzej 

Miziolek, ARL 

 4B/1/8,4D/15/01. TROPODEGRADABLE BROMOCARBON EXTINGUISHANTS; 

Principal Investigator: J. Douglas Mather, NMERI; COR: Ronald Sheinson, 

NRL 

4B/2/8,4D/3/7. FLAME INHIBITION BY PHOSPHORUS-CONTAINING COMPOUNDS; 

Principal Investigator: Elizabeth M. Fisher, Cornell University; COR: Andrzej 

Miziolek, ARL 

4D/14/1. FLUOROALKYL PHOSPHOROUS COMPOUNDS; Principal Investigator: 

Douglas Mather, NMERI 

4C/1/890. SUPER-EFFECTIVE THERMAL SUPPRESSANTS; Principal Investigator: 

William Pitts, NIST 

4D/13/1. EFFECTIVE, NON-TOXIC METALLIC FIRE SUPPRESSANTS; Principal 

Investigator: Gregory Linteris, NIST 

28 
4B/3/8901. ENVIRONMENTAL IMPACT OF NEW CHEMICAL AGENTS FOR FIRE 

SUPPRESSION; Principal Investigators: Robert Huie and Marc Nyden, NIST; 

Andrzej Miziolek, ARL 

4B/4/0123. LOW TEMPERATURE PERFORMANCE OF HIGH BOILING POINT 

SUPPRESSANTS; Principal Investigator: Jiann Yang, NIST 

4B/5/0123. ALTERNATIVE SUPPRESSANT CHEMICALS; Principal Investigator: Richard 

Gann, NIST

4B/6/23 ENVIRONMENTALLY ACCEPTABLE SUPPRESSANTS; Principal 

Investigator: Douglas Mather, Chemical Development Systems; Scientific 

Officer: Richard Gann, NIST 

C. NEW AND IMPROVED AEROSOL SUPPRESSANTS

2B/1/78901. SUPPRESSION EFFECTIVENESS OF AEROSOLS AND PARTICLES; 

Principal Investigator: Ronald Sheinson, NRL 

2B/2/89. DROPLET INTERACTIONS WITH HOT SURFACES; Principal Investigator: 

Yudaya Sivathanu, En’Urga, Inc.; COR: William Grosshandler, NIST 

2B/3/89. TECHNICAL SUPPORT FOR THE STUDY OF DROPLET INTERACTIONS 

WITH HOT SURFACES; Principal Investigator: Jiann Yang, NIST 

4A/1/890. POWDER-MATRIX SYSTEMS; Principal Investigator: Gregory Linteris, NIST 

4D/1/7. ELECTRICALLY CHARGED WATER MISTS FOR EXTINGUISHING 

FIRES; Principal Investigator: Charles H. Berman, Titan Corp.; COR: Ronald 

Sheinson, NRL 

4D/4/7. DEVELOPMENT OF A SELF ATOMIZING FORM OF WATER; Principal 

Investigator: Richard K. Lyon, EER, Inc.; COR: William Grosshandler, NIST 

4D/7/8. DENDRITIC POLYMERS AS FIRE SUPPRESSANTS; Principal Investigator: 

Nora Beck Tan, ARL 

D. IMPROVED SUPPRESSANT DELIVERY 

2C/1/789. STABILIZATION OF FLAMES; Principal Investigator: Vincent Belovich, 

AFRL 

4D/6/8. DUAL AGENT APPROACH TO CREW COMPARTMENT EXPLOSION 

SUPPRESSION; Principal Investigator: Douglas Dierdorf, ARA Corp.; COR: 

Andrzej Miziolek, ARL 

4D/17/0. A METHOD FOR EXTINGUISHING ENGINE NACELLE FIRES BY USE OF 

INTUMESCENT COATINGS; Principal Investigator: Leonard Truett, Eglin AFB 

5A/1/012. PARAMETRIC INVESTIGATION OF DROPLET ATOMIZATION AND 

DISPERSION OF LIQUID FIRE SUPPRESSANTS; Principal Investigator: Cary 

Presser, NIST

29 
5D/1/9013. ADVANCED PROPELLANT/ADDITIVE DEVELOPMENT FOR GAS 

GENERATORS; Principal Investigators: Gary Holland, Aerojet, and Russell 

Reed, NAWC-WPNS; COR: Richard Gann, NIST 

5E/1/12. ENHANCED POWDER PANELS; Principal Investigator: Dan Cyphers, 

Skyward, Ltd.; COR: Martin Lentz, Eglin AFB 

6A/1/0123. FIRE SUPPRESSANT DYNAMICS IN CLUTTERED WEAPONS SYSTEM 

COMPARTMENTS; Principal Investigator: David Keyser, NAVAIR 

6B/1/89. SUPPRESSANT FLOW THROUGH PIPING; Principal Investigator: John Chen, 

Lehigh University; COR: William Grosshandler, NIST 

6C/1/1. MECHANISM OF UNWANTED ACCELERATED BURNING; Principal 

Investigator: Anthony Hamins, NIST 

E. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES 

1A/1/78. DEVELOPMENT OF MODEL FIRES FOR FIRE SUPPRESSION RESEARCH; 

Principal Investigator: Anthony Finnerty, ARL; Associate Investigators: James 

Tucker, AFRL and Juan Vitali, ARA; Ronald Sheinson, NRL 

1C/1/8901. RELATIVE BENEFIT ASSESSMENT OF FIRE PROTECTION SYSTEM 

CHANGES; Principal Investigator: Michael Bennett, Eglin AFB 

3C/1/789. LASER-BASED INSTRUMENTATION FOR REAL-TIME, IN-SITU 

MEASUREMENTS OF COMBUSTIBLE GASES, COMBUSTION BYPRODUCTS, AND SUPPRESSANT CONCENTRATIONS; Principal 

Investigator: Kevin McNesby, ARL 

3C/2/890. FAST RESPONSE SPECIES CHARACTERIZATION DURING FLAME 

SUPPRESSION; Principal Investigator: George Mulholland, NIST 

6E/1/3. VERIFICATION OF SUPPRESSION PRINCIPLES; Principal Investigator: 

Michael Bennett, Bennettech; COR: Martin Lentz, Eglin AFB 

F. FUEL TANK INERTION 

5C/1/9. ACTIVE SUPPRESSION FOR FUEL TANK EXPLOSIONS; Principal 

Investigator: Leonard Truett, Eglin AFB 

30 
APPENDIX B. REPORT OF THE INDEPENDENT REVIEW PANEL 

REPORT OF THE INDEPENDENT REVIEW PANEL 

ON THE

NEXT GENERATION FIRE SUPPRESSION TECHNOLOGY 

PROGRAM (NGP)

January 30, 2003 

Documenting the November 2002 Review

_________________________ 

Thor I. Eklund, Ph.D. 

Eklund Consulting Services 

_________________________ 

Phillip R. Westmoreland, Ph.D. 

Professor -Department of Chemical Engineering 

University of Massachusetts Amherst 

_________________________ 

Glenn Harper – Chair 

Technical Fellow 

Boeing - Phantom Works 

31 
The 2002 Independent Review Panel Report 

on the

Next Generation Fire Suppression Technology Program (NGP) 

Summary:

The 2002 Independent Review Panel (IRP) met November 13, 2002, coincident with the 2002 

Annual Research Meeting (ARM) of NGP participants. 

The IRP is impressed by the thoughtful way the 2001 recommendations have been addressed and 

by the tightened focus of the program. Several tasks have been completed, some are still in 

work and a few new tasks are about to be started. The following general observations are 

presented: 

Observations (No action recommended): 

1) We are confident that valuable design products will be delivered by this program. 

2) The decision not to be restrained by retrofit issues will open up the study space and is

likely to result better products for new aircraft designs. 

3) The proposed new 2003 start to integrate and draw inferences from the results of the 

disparate studies is important and to be commended. A fully integrated effort to 

understand how each piece can be fitted into the whole will make the results much more 

valuable than the sum of the parts. 

4) The proposed new 2003 start to better understand the low-temperature fire history and 

requirements is also to be commended. Determining how the compartment lowtemperature operating limits, the ignition probability at low temperatures, and the fire 

histories at low temperatures combine to define the risk associated with low-temperature 

operation is also likely to open the design space and provide a wider range of options 

than would be achieved by simply using the worst-case combination of operating 

temperatures. 

The IRP noted nothing that would change its conclusions and recommendations from the 2001 

IRP report; thus, the recommendations of that report still apply with the recognition that all the 

recommendations have been or are being thoughtfully addressed. 

There is one new general recommendation:

1) Within the existing NGP budget and schedule constraints, evaluate the effects of 

discharges of CF3I in aircraft fire protection systems, as opposed to fuel tank inerting 

systems, on stratospheric ozone depletion and establish a methodology applicable for this 

purpose to other candidate agents containing bromine or iodine. The F-16 fuel tank 

inerting study using CF3I, which is discussed in the following section, could easily be 

inappropriately interpreted to deny use of CF3I and similar chemicals in any application. 

It is important to insure that science, not the inappropriate application of some report’s 

conclusion, is used to allow or deny use of promising fire protection chemicals. 

32 
Background:

The Next Generation Fire Suppression Technology Program (NGP) is sponsored by the 

Department of Defense (DOD) Strategic Environmental Research and Development Program

(SERDP) and managed through the National Institute of Standards and Technology (NIST). The 

currently stated goal is to “develop and demonstrate technology for economically feasible, 

environmentally acceptable and user-safe processes, techniques, and technologies that meet the 

operational requirements currently satisfied by Halon 1301 in aircraft.” In December 2001, a 

SERDP-recommended Independent Review Panel (IRP) was convened by the NGP Program

Manager. Along with assessing the technical soundness of the NGP, the IRP was tasked with 

recommending actions that could enhance prospects for success in the program within 

anticipated funding levels and remaining timeframe. 

In evaluating the work done to that time and the individual projects underway, the IRP reached 

very favorable conclusions on the productivity, utility, and technical quality of research done 

within the NGP. The NGP research findings are particularly valuable to the extent that they are 

based on fundamental findings on physical and chemical mechanisms associated with fire 

suppression phenomena. As such, the findings should support generalization so that trends and 

behaviors could be used to optimize extinguishing system designs and to isolate primary factors 

associated with troublesome issues such as reignition after agent delivery. The IRP developed 

recommendations with a focus being on ensuring that the technical products of the NGP be 

transferable to and useful for future aircraft fire extinguishing applications. This report should 

be considered an extension of the IRP report issued February 2002 with the comments and 

recommendations of that report still applicable, recognizing that those recommendations have 

been, or are being, thoughtfully addressed. 

The NGP Program Manager invited the IRP to reconvene for an additional review coincident 

with the November 2002 Annual Research Meeting (ARM) of NGP participants. This afforded 

the IRP the opportunity to: 

1) Reevaluate its prior-year conclusions and recommendations, 

2) Ascertain the impact of the IRP recommendations on the present and planned NGP, 

3) Evaluate the present direction and scope of the NGP, and 

4) Revise previous or document new conclusions and recommendations in the context of

resource availability and technical influences emanating from outside the NGP. 

In this 2002 review, the IRP focus remains fixed on the goal of maximum utility for application 

in future aircraft fire-protection systems. 

External Developments:

In the worldwide efforts to find alternatives to the halons for aviation applications, the past year

has yielded continued incremental progress in the spectrum on fire protection installations, 

devices, and techniques. For the first time there are now available approved hand extinguishers 

that, though heavier, are equivalent to Halon 1211 bottles for civil aviation applications. Halon 

alternatives are also now available to protect the lavatories on commercial aircraft. The FAA has 

completed establishing Minimum Performance Standards (MPS) for halon alternatives for most

of the systems falling under its purview and is in the testing phase of MPS for engine nacelle 

certification requirements. It is recognized that promulgating an MPS provides the basis for 

33 
accepting a proposed Halon replacement but does not itself provide or identify specific 

alternative agents. Substantial new developments and demonstrations have been made using 

membrane technology for generating nitrogen-enriched air (NEA) not only for fuel tank inerting 

but also for potential in use for fire protection in aircraft unoccupied compartments. 

In rescue and firefighting, USAF testing has demonstrated an improved co-flowing potassium

bicarbonate and AFFF combination that offers a firefighting capability for large two-dimensional 

and three-dimensional fuel fires with effectiveness such that Halon 1211 would not be needed as 

a complementary firefighting agent. The general trend in successful halon replacement in the 

aviation arena has been application-specific. Rather than finding specific compounds that can be 

used in lieu of one or another of the halons, the trend has been to establish the level of protection 

needed in a specific application, then to develop an alternate “Agent” or new technology or 

approach to provide protection in that application. 

The May 2002 annual meeting of the Halon Options Technical Working Group (HOTWC) was 

for the first time was managed by the NGP, and future meetings will continue to be the 

responsibility of the NGP. Had it not been for the NGP support, this vital vehicle for Halon 

alternatives research would have ceased operations. The annual meeting has proven important 

for a host of different reasons, including the technical interchange of the NGP research 

community with the extinguishing system manufacturers and foreign researchers. The annual 

HOTWC meeting represents a valuable platform connection all the major communities involved 

in Halon Replacement. Continued NGP involvement in this activity is encouraged.

In terms of impact on the NGP and the use of CF3I, one of the most significant development was 

a report issued by an independent review panel assessing critical technical issues relating to 

implementation of CF3I as a replacement for Halon 1301 in F-16 wing tank inerting. This report 

was sponsored by the Director of Defense Research and Engineering (DDR&E) and is titled 

“Suitability of CF3I to Replace Halon 1301 as the Inerting Agent in Wing Fuel Tanks on the F16 Aircraft”. The report claims that CF3I’s stratospheric ozone depletion as compared to Halon 

1301 falls between one-eighth and one and two-thirds as damaging. While the subject F-16 wing 

tank inerting application is not one that is being addressed in the NGP effort, this new report has 

potentially far-reaching policy ramifications in terms of impact on acceptability of some h 

Halon replacements studied in the NGP. In as much as its limited resources allow, the IRP 

believes it important that the NGP formally assess the impact of the DDR&E conclusions on 

both past and future NGP work and document any resultant changes in conclusions, 

recommendations, and program direction. It would be unfortunate if the conclusions of this 

study were to be improperly applied to cancel research in an otherwise attractive technology. 

2002 ARM Highlights:

The ARM presentations covered twelve projects including two new starts for FY2003. Four of 

these project presentations stood out to the IRP – two (5E/1 and 6C/1) for strong progress 

evidenced since the preceding 2001 ARM and two (5D/1/901 and 5A/1/01) for their continued 

very strong multiyear progress and clear potential usefulness in replacing Halon 1301 for 

aviation applications. 

1) The powder panel research (5E/1) has apparently generated great interest in both the 

military aircraft vulnerability arena (specifically JTCG/AS) and the civilian aircraft

catastrophic failure prevention program (FAA). Both test programs evaluated the 

34 
Skyward research panels with extremely positive results. The subject applications 

(military aircraft dry bays and civil aircraft fuel lines exposed to projectiles from failed 

engines) have not traditionally been protected by Halon 1301 systems. However, the 

successful performance of the powder panels have provided a level of interest that may 

well result in a near-term deployed powder panel product in specific applications. 

Recommendation: This program’s success appears to be largely dependent on the 

innovative approach to design of the “front panel” which allows a much larger fraction of 

the powder to be released at impact. The new design for these panels needs to be 

carefully reviewed and tested to insure that the shock, vibration, acceleration (etc.)

environment of these panels will not cause the powder to “settle” and defeat the system. 

One of the reasons for selection of the older design was to address these issues. 

2) The project on Mechanisms of Unwanted Accelerated Burning (6C/1) successfully 

identified and analyzed salient tests from a variety of sources over the past year and was 

able to provide a credible rationale for the causes and deleterious effects of unwanted 

accelerated burning during discharge of extinguishing agents. The valuable research 

reported here indicates that attempting to optimize agent quantities to minimize system

weight could inadvertently expose the protected system to destructive pressure rise 

during the extinguishing process. 

The IRP believes these results have particular relevance to the extraction of design 

heuristics for suppression systems in order to avoid designs with marginal performance. 

3) Research on solid propellant fire extinguishers and hybrid fire extinguishers (4B/4/01)

continued to show excellent potential for various solid gas generator devices to replace 

Halon 1301 systems in aircraft powerplant applications. Effective fire extinguishing was 

shown by means of propellant-generated aerosol alone and by hybrid devices using 

propellant-generated aerosol in combination with water-based salt or higher-boiling 

fluorocarbon agents. Hybrid tests with CF3I were particularly promising and showed no 

adverse cold-temperature effects. 

Recommendation: The hybrid designs utilizing pyrotechnic charges to expel liquid or 

gaseous agents are also promising in that they appear to reduce the sensitivity of 

discharge pressure to “agent temperature” which can sometimes degrade performance at 

extreme temperatures. The potential negative impact of false discharge and material 

compatibility issues due to use of propellant-generated aerosols also need to be carefully 

considered. 

4) The experimental investigation of droplet atomization and dispersion (4B/4/01) appears 

to be on the threshold of gathering extremely important data on droplet dynamics in the 

vicinity of heated and unheated cylinders. In addition to water, the test liquids are slated 

to be HFE7000 and HFE7100. 

In addition to providing data sets for incorporation into the VULCAN fire code, the 

analysis of this data can be expected to provide valuable heuristics in terms of agent 

behavior in the vicinity of engine nacelle clutter. The heuristics also should also include 

information on design approaches to improve extinguishing performance. 

35 
The IRP has two additional comments: 

5) There are several tasks associated with assessment of alternate chemicals. This critical 

work potentially offers the best hope for an attractive long-term solution, and it should be 

continued. 

Recommendation: The IRP notes that the primary research organization conducting this 

effort is associated with a medical school. A larger role for the medical experts might 

expedite screening of candidate chemicals. 

6) In as much as its limited resources allow, the IRP believes it important that the NGP 

formally assess the impact of the DDR&E report (“Suitability of CF3I to Replace Halon 

1301 as the Inerting Agent in Wing Fuel Tanks on the F-16 Aircraft”) and its conclusions 

on both past and future NGP work, documenting any resultant changes in conclusions, 

recommendations, and program direction. It would be unfortunate if the conclusions of 

that study were to be improperly applied to cancel research in an otherwise attractive 

technology. 

Discussion:

Evidenced throughout the 2002 ARM were the conscientious pains taken both to recognize and 

comprehend the previous IRP recommendations and to respond appropriately through project 

redirection and NGP enhancement. The IRP membership had not anticipated such a thorough 

attempt to accommodate all recommendations. These recommendations represented concrete 

actions that the IRP considered would enhance prospects for products that could be applied 

practically for Halon 1301 replacement in aviation fire protection. The IRP emphasizes that the 

its overriding interest is in the technical soundness and practical viability of the end products of 

the NGP. Given real-world realities of resource availability and also the inherent limits to its 

own technical capabilities, the IRP did not expect such complete compliance with its 

recommendations. 

The NGP as presently constituted has funding directed mainly at new flame suppression 

chemicals and at improved suppressant storage and delivery. The IRP endorses this approach. 

In its preceding report, the IRP highlighted the apparent technical strength of the NGP program. 

The IRP anticipated that any near/mid-term successful replacements for Halon 1301 would likely 

come from higher-boiling compounds with CF3I being a particularly attractive candidate. The 

earlier review also highlighted possible discoveries of useful tropodegradable bromocarbons and 

phosphorus containing compounds. The propellant generators appeared promising provided 

certain practical issues could be adequately addressed. The environmental considerations were 

being addressed through project 4B/3/801. The consolidated IRP position was that it was 

extremely important to come to grips with the effects of temperature and boiling points and 

airflow on the behavior of extinguisher aerosols in the cluttered engine nacelle environment. 

The IRP would like to see project 4B/3/801 address the issues raised in the aforementioned 

DDR&E report head-on. The IRP would like the NGP to have a strong environmental basis to 

support the deployment of agents found in the program so that their use is not derailed by 

environmental arguments developed outside the program after the NGP research has been 

completed. 

36 
Recommendations:

The Independent Review Panel reaffirms and emphasizes the following recommendations from

the 2001 IRP report, recognizing that the present NGP is reflective of their incorporation. 

1) Establish a separate project on re-ignition, or elevate this issue within existing projects.

2) Expand delivery and dispersion research to include additional high-boiling-point 

compounds.

3) Request summation sheets on “Lessons Learned” from the principal investigators to serve 

as a starting point for future system design heuristics. 

4) Prepare a technical information package to expedite hand-off of the portable Differential 

Infrared Agent Concentration Sensor to organizations involved with aircraft extinguishing 

system certification and testing. 

5) Address directly the issue of gas-phase vapor loading from dispersed aerosols of higher 

boiling point extinguishing agents. 

6) Initiate an interim NGP report in the form of heuristic technical rules capable of being 

understood and utilized by extinguishing system design and test engineers. 

The Independent Review Panel adds one further recommendation. 

7) Evaluate the effects of CF3I installation discharges to protect engine and APU 

compartments on stratospheric ozone depletion and establish a methodology applicable for 

this purpose to other candidate agents containing bromine or iodine. 

37