FY2001 Annual Report

Next Generation Fire Suppression Technology 

Program (NGP)

Richard G. Gann

NIST Technical Note 1445
NIST Technical Note 1445

FY2001 Annual Report

Next Generation Fire Suppression 

Technology Program (NGP)

Richard G. Gann

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8664

March 2002

U.S. Department of Commerce

Donald L. Evans, Secretary

National Institute of Standards and Technology

Dr. Arden Biment, Director
National Institute of Standards U.S. Government Printing Office For sale by the

and Technology Washington: 2002 Superintendent of Documents

Technical Note 1445 U.S. Government Printing Office

Natl. Inst. Stand. Technol. Washington, DC 20402-9325

Tech. Note 1445

40 pages (March 2002)

CODEN: NTNOEF
FY2001 ANNUAL REPORT

Next Generation Fire Suppression 

Technology Program (NGP)

[PP-1059]

Richard G. Gann, Ph.D.

Technical Program Manager

March 11, 2002
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ABSTRACT

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

completed its fifth 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 to comple te a suite of suppressant screening tests has been completed. 

Research on new flame suppression chemistry, new and improved aerosol suppressants, 

improved suppressant delivery, and viability of new suppressant technologies 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

B. NEW AND IMPROVED AEROSOL SUPPRESSANTS ...................10

C. IMPROVED SUPPRESSANT DELIVERY .........................................11

D. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES...............23

III. INDEPENDENT PERFORMANCE ASSESSMENT .....................................26

IV. WHAT’S COMING NEXT?................................................................................27

APPENDIX: NGP PROJECTS ....................................................................................29
1

INTRODUCTION

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

completed its fifth year of research. Initiated in 1997, 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.”

The principal support for the NGP is from the DoD Strategic Environmental Research and 

Development Program (SERDP), with cost sharing from some of the participating laboratories.

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

survivability of military aircraft, ships, and land vehicles in peacetime and during combat 

operations. Production of halon 1301 (CF3Br), long the fire suppressant of choice, had ceased as 

of January 1, 1994 due to its high ozone depleting potential (ODP). By 1997 the DoD had 

identified the best available replacements for halon 1301, but each had unresolved operational 

features that compromised its implementation. 1 The new Program was to identify fire 

suppression technologies with reduced compromises. 

Over the past five years, research to identify replacement fire suppressants has declined 

considerably, within the NGP, domestically and internationally, despite the continuing need. To 

date no commercial or military aircraft have had their halon 1301 systems replaced, while new 

systems are being installed in the cargo bays of commercial jetliners. Since new halon 1301 is 

unavailable, these systems are being filled with recovered chemical or existing reserves. 

Meanwhile the concentration of bromine in the stratosphere is predicted to peak within the next 

few years, signaling the beginning of a rise in the earth’s protective ozone layer. The 

international community is continuing to cast an eye on the necessity of maintaining the larger 

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

Thus, the demands on research to identify new approaches to aircraft fire suppression are 

unabated, nor have the demands on the new technologies lessened. These need to be of low 

mass and volume and compatible with the host aircraft design. New chemicals must have high 

suppression efficiency and perform well in evaluations of ODP, global warming potential, 

atmospheric lifetime, reignition quenching, residue level, electrical conductivity, corrosivity to 

metals, polymeric materials compatibility, long-term storage stability, toxicity of the chemical 

and its combustion and decomposition products, speed of dispersion, and occupational safety.

As the NGP enters its sixth year of research, the participants have generated unparalleled 

contributions to the published literature, all of which can be obtained via the NGP web site, 

which has moved to www.bfrl.nist.gov/866/NGP. The systematic search for new suppressant 

chemicals and technologies for assured, efficient delivery is continuing to produce new results. 

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. 

An appendix lists the NGP projects to date.
2

I. TECHNICAL PROGRESS

A. NEW FLAME SUPPRESSION CHEMISTRY

From the time when it was realized that environmentally friendly alternatives to halon 1301 

would be needed until the initiation of the NGP, nearly all research on alternative fire 

suppressants was focused on saturated halocarbons, a subset of the possible halons (halogenated 

hydrocarbons). In large part, this was because the other ozone depleting chemicals (e.g., 

refrigerants, degreasers) constituted far larger markets, and it was assumed that the search for 

alternatives to those chemicals would lead to usable fire suppressants. In the research 

documented in the 1998 final report of the Department of Defense’s Technology Development 

Plan for Alternatives to Ozone Depleting Substances for Weapons Systems Use1, all the fluids 

investigated as fire suppressants were halons.

There had been more far-reaching work in the search for a replacement for halon 1211, a 

streaming agent, as well as a survey of non-conventional alternatives to halon 1301. As a result, 

in the earlier years of the NGP, investigators were in a position to look at some families of 

chemically diverse compounds. We sought to identify chemicals that met a list of criteria that 

has evolved to the following:

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

certainly higher than the hydrofluorocarbons (HFCs).

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

depletion, global warming and any future unidentified environmental contamination 

issues to a minimum.

· Low toxicity relative to the concentration needed for suppression.

· 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 80 °C, but slow evaporation or poor dispersion will reduce this significantly 

for some chemicals.

The families examined each produced additional knowledge of what makes a good suppressant, a 

list of most suitable members of that family, and criteria for future searches. 

· Physically-active suppressants. The most effective compounds identified were already 

known: lactic acid and CH3OC4F9. The latter has a cup burner suppression molar 

concentration of 5.5 % when introduced as a gas. This compound is four times more 

effective when introduced as a liquid aerosol, emphasizing the contribution of the heat of 

vaporization of the suppressant when the aerosol reaches the flame zone.

· Main group compounds (e.g., based on Si, S, B chemistry). There were no compounds 

identified within these families that were especially attractive relative to HFC-125 

(C2HF5) or HFC-227ea (CF3CHCF3), both of which are in current production.

· Tropodegradable bromocarbons. The initial look was at brominated alkenes, and was 

performed in conjunction with the Advanced Agent Working Group. Four compounds 

were shown to have fire suppression efficiency comparable to halon 1301, boiling points 

of 34 oC to 56 oC, atmospheric lifetimes of the order of days, and low acute inhalation 
3

toxicity. However, the one compound tested for cardiotoxicity produced effects on the 

test animals at a molar concentration of about 1 %. This showed that our ability to 

anticipate this use-limiting effect needed refinement.

· Metal-containing compounds (Fe, Mn, Sn). Some iron, manganese, and tin compounds 

showed very high flame inhibition effectiveness on premixed flames and highly strained 

diffusion flames (Figure 1), but were unimpressive on cup burner flames. We are in the 

process of identifying why this difference occurs and which set of laboratory test 

conditions are appropriate for capturing the suppression efficiency of these compounds 

under aircraft fire conditions. These compounds are all very high boiling liquids or 

solids, and thus would most likely be used in conjunction with solid propellant gas 

generators (SPGGs).

Figure 1. Mole fraction of CO2 required for methane-air cup burner flame 

extinction as a function of catalytic inhibitor mole fraction, CF3Br, Br2 , 

Fe(CO)5, (Sn(CH3)4, MMT [(CH3C5H4Mn(CO)3], or a blend of the last three 

(insert shows data with expanded x- and y-axes). The termination of the 

curves at high CO2 mole fraction indicates the limit of suppression 

effectiveness.

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0 5000 10000 15000 20000 25000

Catalytic Inhibitor Volume Fraction (mL/L)

CO2 Mole Fraction Required for Extinction

CF3Br

Sn(CH3)4

Br2

0.12

0.13

0.14

0.15

0.16

0 500 1000

Sn(CH3)4

CF 3Br

Br 2

MMT

Fe(CO)

5

MMT(200) + Fe(CO) 5 (420)+ Sn(CH3)4 (3100)
4

· Phosphorus-containing compounds. NGP research established that the phosphorus atom 

imparts good flame suppression efficiency to a compound and that the binding state of 

the phosphorus is unimportant. There are very few low boiling phosphorus-containing 

compounds, so these would need to be dispersed as aerosols or be used with SPGGs.

During FY2000 and FY2001, the NGP used this updated knowledge to conduct a comprehensive 

review of the world of chemicals to identify those chemical families still ripe for examination in 

the NGP. For each type of chemical functionality, assessments were made of the extent of prior 

fire suppression studies and the potential for success in any (further) study. Expected flame 

suppression efficiency, atmospheric persistence, boiling point, and toxicity were again the main 

screening criteria.

The following families were identified as the most promising:

· N compounds: amines nitriles

· P Compounds: acids esters nitriles halides

· S Compounds: sulfides mercaptans sulfoxides

· Metal Compounds: manganese tin

· Halogenated Organics: alkenes (I) fluoroethers (Br, I)

Those families in italics are the highest priorities for examination. It was expected that 

substantial fluorination would be needed to obtain the desired low boiling points. In an 

additional effort to identify compounds with low boiling points, a search of Chemical Abstracts

was instituted for all compounds with boiling points under 25 °C that contain bromine, iodine 

and/or phosphorus. The results will be available soon.

Study of the fluoroalkyl-phosphorus compounds is currently underway, with eight selected for 

synthesis and testing. To minimize inhalation toxicity, these have no halogen-to-phosphorus 

bonds. The compounds are: 

O=P(CF3)3 O=P(OCH3)(CF3)2 P(OCH3)(CF3)2

O=P(OCF3)3 O=P(OCH2CF3)(CF3)2 P(OCH2CF3)(CF3)2

P(OCH2CF3)3 P(OCH2CF3)2CF3

These represent some of the lowest boiling points for phosphorus-containing compounds, with 

the first having the highest volatility of any non-flammable chemical in the family, 32 oC. The 

cup burner extinguishment concentration for P(OCH2CF3)3 was found to be 1.9 % by volume. 

We are also continuing our examination of the tropodegradable halocarbons, now concentrating 

on the brominated ethers. Some of these are used as surgical anesthetics, but thus have high 

boiling points for ease of handling and administration. Therefore, the candidate ethers will need 

to be synthesized. Cup burner extinguishment values for two ethers, CH2BrO(CF3)3 and 

CH2BrOCF2H, are close to that for halon 1301 and the atmospheric lifetimes should be very 

short. The boiling points are 40 °C and 70 °C, respectively.
5

However, before extensive resources are expended in synthesizing new bromocarbons, it is first 

necessary to find out if we can improve our ability to estimate the cardiotoxicity of such 

compounds. These estimates are based on quantitative structure-activity relationships (QSARs). 

We will summarize the compound attributes and physical properties that could be used in QSAR 

predictions of cardiac sensitization; review anesthesiology research to identify and collate 

relevant test data, QSAR methods and any attributes that might be employed in evaluating the 

cardiac sensitization properties or establishing a relative ranking of the cardiac sensitization 

properties of a series of brominated fluorocarbons; and search for possible in vitro methods 

applicable to the low cost assessment of the cardiac sensitization potential of a candidate halon 

replacement chemical or a series of such chemicals. 

Another factor affecting the use of brominated compounds is their atmospheric lifetimes. Since 

bromine atoms are potent depleters of stratospheric ozone, brominated species must not rise to 

those altitudes. A sure way to prevent this transport is for the compound to be degraded in the 

lower atmosphere. The NGP has completed a methodology for estimating the reactivity of 

halocarbons with atmospheric OH, the major tropospheric elimination pathway. Beginning with 

compounds for which the reaction rates are known, the method developed relationships for 

extending to related compounds, such as those with increased fluorination. The tropospheric 

lifetime together with the stratospheric lifetime lead to the impact of the particular compound on 

the ozone layer. We have developed a method to estimate the latter using the integrated 

molecular absorption over the 200 nm to 210 nm band in the ultraviolet. With this new array of 

techniques, we have now estimated ozone depletion potentials for a variety of halogenated 

alkanes, alkenes, and ethers (Tables 1 and 2).
6

Table 1. Arrhenius Parameters for Reactions with OH, Estimated Atmospheric 

Lifetimes, and Ozone Depletion Potential (ODP) values.

Molecule k(298)¥1012  A¥1012 E/R Lifetime* ODP*

 cm3molecule-1s

-1

 cm3molecule-1s

-1

 K days

CF3Br - - - 65. (years) 13.

CF2=CFBr 7.62 2.02 -396 1.4 0.0015

CF2=CHBr 4.53 1.30 -370 2.4 0.0028

CH2=CBr-CF3 3.94 1.36 -317 2.8 0.0049

CH2=CBr-CF2-CF3 3.39 0.98 -369 3.2 0.0049

CH2=CH-CF2-CF2Br 1.68 0.85 -201 7.0 0.0045

CH2Br-CH2-CH3 1.01 3.04 329 14. 0.015

CH3-CHBr-CH3 0.76 1.90 275 19. 0.018

CHF2-O-CHF2 0.0025 0.63 1646 24. (years)

CF3-CH2-O-CH2-CF3 0.16 2.32 790 0.28 (years)

CH3-O-CF2-CH2Br 0.065 1.5 930 0.76 (years) 0.21

CF2=CF2 9.98 3.39 -323 1.1

CF2=CF-CF3 2.20 0.54 -413 5.3

CF3-CF=CF-CF3 0.51 0.33 -126 25.

(CF3)2-CF=CF-C2F5 0.073 0.085 46 182.

* Lifetimes are due to reactions with tropospheric OH only. Atmospheric lifetimes and ODP 

values were estimated in the manner typically used for long-lived compounds. Such estimation 

assumes a uniform tropospheric distribution that is not necessarily correct for short-lived 

compounds.
7

Table 2. Calculated Arrhenius Parameters for Reactions with OH, Estimated 

Atmospheric Lifetimes, and ODP values.*

Molecule k(298)¥1014 A ́1012 E/R Lifetime** ODP**

 cm3molecule-1s

-1

 cm3molecule-1s

-1

 K, years

CF3Br - - - 65. 13.

CH3Br 2.4 5.4 1610 2.5 1.2

 2.9 4.0 1470 2.0 0.99

CHF2Br 1.0 1.5 1505 6.0 1.6

 1.0 1.1 1400 5.6 1.5

CH2FBr 3.0 3.8 1440 1.9 0.59

CH2ClBr 9.2 2.2 945 0.52 0.23

11.4 3.04 978 0.43 0.19

CHFClBr 6.8 1.5 920 0.70 0.27

CH2Br2 8.9 2.5 995 0.55 0.43

12.0 2.4 900 0.41 0.32

CHFBr2 10.0 1.6 825 0.46 0.30

CHCl2Br 26.4 0.8 330 0.15 0.047

12.0

CHClBr2 34.6 0.8 250 0.11 0.08

*

 Parameters obtained from the available experimental measurements are shown in italics.

** Lifetimes are due to reactions with tropospheric OH only. Atmospheric lifetimes and ODP 

values were estimated in the manner typically used for long-lived compounds. Such estimation 

assumes a uniform tropospheric distribution that is not necessarily correct for short-lived 

compounds.
8

As noted in the FY2000 NGP Annual Report2, we had discovered that while metalcontaining compounds could be effective flame inhibitors, they might not be effective in any 

form in quenching practical flames. This made it imperative to determine the reasons for the 

unexpected low effectiveness in cup burner flames. Now, a clear picture has emerged 

concerning the potential and limitations of metallic agents as fire suppressants in unoccupied 

areas. 

· Computer modeling of inhibited flames showed that the metal must have 

intermediate species with thermodynamic properties such that the stable dihydroxide intermediate can be formed, and the equilibrium concentration of this 

species must be large so that it can remove H atoms from the flame chemistry.

· The first measurements of particle formation in cup burner flames inhibited by the 

metallic agent Fe(CO)5 (Figure 2) showed that particle formation acts as a sink for 

the active metal species, preventing them from reaching the flame zone in which 

they are required to suppress the flame. Thus, condensation of one or more of the 

metal-containing species must not occur. Analysis of previously published results 

for the antimony- halogen system showed a strong loss of effectiveness above a 

certain mole fraction, also likely caused by particle formation from antimony oxide. 

This phenomenon even occurs for the alkali metal compounds (which are highly 

effective on practical flames) where condensation to either liquid hydroxide or a salt 

(e.g., NaCl) can detract from their efficiency. 

Figure 2. Scattering cross section as a function of radial position in flame and 

height above cup-burner rim, with 200 :L/L of Fe(CO)5 added to the air stream, and 

a CO2 volume fraction of 8 %. Dotted lines show flame location from a digitized 

video image of the uninhibited flame. -20 -18 -15 -13 -11-8-6-3-1

1469

11131618

0

3

6

9

12

15

18

Z (cm)

-20 -15 -10 -5 0 5 10 15

Radial Position (cm)

0.0

5.0

10.0

15.0

20.0
9

Recent Publications: New Flame Suppression Chemistry

(* indicates archival publications.)

*Rumminger, M.D. and Linteris, G. T., “Particle Formation in Counterflow Diffusion Flames 

Inhibited by Iron Pentacarbonyl,” Combustion and Flame,128, 145-164 (2002).

*Linteris, G. T., Knyazev, V., and Babushok, V., “Inhibition of Premixed Methane Flames by 

Manganese and Tin Compounds,” Combustion and Flame, accepted for publication (2001).

Linteris, G.T. “Suppression of Cup-Burner Diffusion Flames by Super-Effective Chemical 

Inhibitors and Inert Compounds,” Proceedings of the 2001 Halon Options Technical Working 

Conference, Albuquerque, pp.187-196, Albuquerque, 2001.

Linteris, G. T., Knyazev, V., and Babushok, V., “Premixed Flame Inhibition by Manganese and 

Tin Compounds,” Proceedings of the 2001 Halon Options Technical Working Conference,

Albuquerque, pp. 72-82, Albuquerque, 2001.

Chelliah, H.K., Lazzarini, A.K., Wanigarathne, P.A., and Linteris, G. T., “A Comparison of Fire 

Suppression Effectiveness of Sodium Bicarbonate Particles and Fine-Water Droplets in NonPremixed and Premixed Flames,” Proceedings of the 2001 Halon Options Technical Working 

Conference, Albuquerque, pp. 389-394, Albuquerque, 2001.

*Linteris, G.T., Rumminger, M.D., Babushok, V.I., and Tsang, W., “Flame Inhibition by 

Ferrocene, and by Blends of Inert and Catalytic Agents,” Proceedings of the Combustion 

Institute 28, 2965-2972 (2000).

*Lazzarini, A.M., Krauss, R.H., Chelliah, H.K., and Linteris, G.T, “Extinction Conditions of 

Non-premixed Flames with Fine Droplets of Water and Water-NaOH Solutions, Proceedings of 

the Combustion Institute 28, 2939-2945 (2000).

Pitts, W.M., Bryant, R.A., and Yang, J.C., “Thermal Agent Extinguishment of Two Types of 

Diffusion Flames,” Proceedings of the Second Joint Meeting of the United States Sections: The 

Combustion Institute, March 26-28, 2001.

Pitts, W.M., “Detailed Chemical-Kinetic Modeling of Thermal-Agent Diluted Methane and 

Propane Flames Near Extinguishment,” Proceedings of the 2001 Technical Meeting of the 

Eastern Section of the Combustion Institute, Hilton Head, SC, 2001.

Pitts, W.M., Yang, J.C., and Bryant, R.A., “Fuel Effects on the Extinguishment of Laminar 

Diffusion Flames by Thermal Agents,” Proceedings of the 2001 Halon Options Technical 

Working Conference, Albuquerque, pp. 241-252, Albuquerque, 2001.

Mather, J.D., and Tapscott, R.E., “Tropodegradable Bromocarbon Extinguishants – II. Research 

Update,” Proceedings of the 2001 Halon Options Technical Working Conference, Albuquerque, 

pp.197-203, Albuquerque, 2001.

*Louis, F., Gonzalez, C., Huie, R. E., and Kurylo, M. J., “An Ab Initio Study of the Kinetics of 

the Reactions of Halomethanes with the Hydroxyl Radical. Part 3. Reactivity Trends and 

Kinetics Parameter Predictions for the Potential Halon Replacements CH2FBr, CHFBr2, 

CHFClBr, CHCl2Br, and CHClBr2,” J. Phys. Chem. A, 105, 1599-1604 (2001).
10

B. NEW AND IMPROVED AEROSOL SUPPRESSANTS

FY2001 brought to a close the NGP investigation of the properties of droplets that enhance their 

flame suppression efficiency. Collaborative research with NASA-funded collaborators led to a 

validated model for the inhibitory effects of small drops (< 5 mm) and water vapor on premixed 

flames (Figures 3 and 4). The multi-phase flame model includes elementary combustion 

chemistry and multicomponent molecular transport. The model also predicts a small-drop 

limiting behavior for premixed flames similar to that previously observed for non-premixed 

counterflow flames consistent with other NGP modeling predictions.

.

Figure 3. Schematic for the experimental 

determination of the effect of aerosols on 

the burning velocity of atmospheric 

pressure premixed methane/air flames. 

Flame cone heights are typically 0.3 to 1.5 

times the diameter of the burner exit. 

Burning velocities are determined by the 

total area method [1]. 

Figure 4. Premixed methane-air 

burning velocity as a function of 

agent mass fraction, normalized by 

the uninhibited burning velocity.

0.35 :m water mist in dry flame (gray 

diamond), 0.35 :m water mist in 

humidified (1.5 % mass fraction water 

vapor) flame (gray circle), water vapor 

(open circle). Modeling results for 

humidified flames inhibited with mists 

(solid lines), and modeling results for 

humidified flames (dashed line).

fuel/air and aerosol
11

Recent Publications: New and Improved Aerosol Suppressants

(* indicates archival publications)

*Zegers, E.J.P., Williams, B.A., Sheinson, R.S., and Fleming, J.W., “Dynamics and Suppression 

Effectiveness of Monodisperse Water Droplets in Non-Premixed Counterflow Flames,” 

Proceedings of the Combustion Institute 28, 2931-2938 (2000). 

Zegers, E.J.P., Fuss, P., Fleming, J.W., Williams, B.A., Maranghides, A., and Sheinson, R.S., 

“Better Use of Water for Fire Suppression,” NRL Review, Naval Research Laboratory, 

Washington DC, pp.102-104, 2001.

C. IMPROVED SUPPRESSANT DELIVERY

1. Solid propellant Fire Extinguishers

NGP research is developing new types of solid propellant gas generators (SPGGs) 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. The approaches 

include modification of the solid propellant, inclusion of additives in the propellant formulations, 

and entrainment of a chemically active additive into the gas stream.

NGP research had co-developed a new high nitrogen propellant compound, BTATZ (C4H4N14), 

and prototype formulations incorporating it have reduced discharge temperatures by 20 %. This 

year, process improvements in the preparation of BTATZ have progressed to the 0.5 kg scale, 

enabling more extensive use in testing, including re-formulation with additional coolants.

There are two approaches to cooler, more efficient solid propellant fire extinguishers (Figure 5): 

· Solid propellant Gas Generators (SPGGs), in which the coolant or chemical additive is 

incorporated directly into the solid propellant composition, and 

· Hybrid Fire Extinguishers (HFEs), in which the coolant or chemical additive comprises 

an auxiliary “hybrid” fluid that is discharged with the propellant effluent.

Following last year’s demonstration that some chemical additives enhanced the efficiency of an 

otherwise inert gas generator, additional experiments were performed to quantify the benefit. 

Additives were added to either the propellant (SPGG) or the fluid (HFE). Several solid 

propellant and hybrid configurations were evaluated for fire suppression effectiveness using a 

mid-scale Fire Test Fixture (FTF), developed to simulate typical military aircraft fire scenarios. 

The structure was approximately 0.7 m3 (24 ft3) in volume, with a JP-8 flame in a forced air 

stream yielding a fire intensity of about 1 MW. SPGG and HFE fire suppression devices were 

used to deliver both inert and active agents into the fire. The gas generator device was mounted 

upstream of the fire, on an arm in the middle of the airflow, but shielded from the fire zone by a 

baffle. All SPGG and HFE discharge times were maintained at a200 ms for ease of comparison.
12

Figure 5. Solid Propellant Fire Extinguishers

SPGG HFE

The test results are summarized in Figure 6. The values are based on multiple tests and represent 

the threshold amount of agent needed to extinguish the fire. The threshold is defined as the 

amount of agent needed to extinguish the fire at least two out of three times. Typically three 

tests were conducted at the threshold amount and three additional tests were conducted at an 

agent load greater than the threshold amount. 

There is clearly an efficiency improvement with any of the blends of inert gases with chemically 

active additives in both systems. On an equimolar basis, potassium carbonate appears to be a 

more effective chemical additive than potassium iodide. This may be related to more facile 

vaporization of the carbonate-based species after melting or to an antagonistic interaction

between the halogen and alkali metal species in the flame region. On a mass basis, the inert HFE 

and SPGG systems appear to provide similar suppression protection. Testing conducted with 

additives incorporated into the hybrid fluid of the HFE system produced results similar to results 

with active agents added into the propellant. 

Testing conducted with the HF scavengers KHCO3 and NaHCO3 added into the hybrid fluid of 

the HFE system produced results similar (based on moles of K/Na) to results with active agents 

(KI, K2CO3) added into the propellant. Active hybrid systems were also tested using potassium 

acetate (KOAc)/water blends, and using trifluoromethyl iodide (CF3I). The water-based system 

delivers performance comparable to HFC-227/active-agent blends, and avoids the formation of 

toxic and corrosive HF. The CF3I system was the most effective HFE system tested, but was 

observed to produce significant quantities of I2 vapor during suppression testing.
13

Figure 6. Summary of SPGG and HFE Fire Effectiveness Testing

0.57 mol I

0.039 mol Na 0.96 mol K

0.052 mol K

0.046 mol K

0.04 mol K

(0.04 mol I)

0.15 mol K

0.2 mol K

(0.2 mol I)

0

50

100

150

200

250

300

350

400

Total Initial Mass (g)

Mass of Active Agent

Mass of Inert Agent

FS01-40 GD-02

(KI)

GD-04

(K2CO3)

FS01-40/

HFC-227

GD-02/

HFC-227

GD-04/

HFC-227

FS01-40/

HFC-227/

KHCO3

FS01-40/

HFC-227/

NaHCO3

FS01-40/

Water/

KC2H3O2

SPGG Testing HFE Testing

FS01-40/

CF3I

2. Dispersion of Suppressants at Low Temperature

In a space where the fire could be anywhere, efficient dispersal of a suppressant throughout the 

volume is essential. Halon 1301, with a boiling point of -58 °C, flash vaporizes and distributes 

well, even at the lowest temperatures (ca. -40 °C) it experiences in in-flight aircraft. Earlier 

research had indicated that fluids with higher boiling points might not disperse well. For 

instance, while CF3I has a flame suppression efficiency and heat of vaporization similar to halon 

1301, it has a higher boiling point of -22 °C. Similar concerns arose over many of the novel 

compounds being examined under the NGP. This could lead to a reduction in the upper boiling 

point limit for screening chemicals for further consideration.

The initial experiments involved examination of CF3I discharges in a simulated engine nacelle 

(Figure 7) under different thermal conditions (Table 3). Two outer circular ribs and one 

horizontal rib in the cylindrical flow space induce turbulence, mimicking the flow a real engine 

nacelle. 
14

Figure 7. Schematic of the modified test facility

Table 3. Experimental matrix for cold temperature agent dispersion

Nominal initial conditions

of vessel

Nominal conditions of vessel 

before discharge

Nominal conditions in the 

simulator

22 oC and 4.12 MPa –40 oC at prevailing P

§

–40 oC §

22 oC and 4.12 MPa 22 oC and 4.12 MPa 22 oC (baseline)

22 oC and 4.12 MPa 22 oC and 4.12 MPa –40 oC§

§ Tests were performed in an environmental test chamber.

The agent bottle was charged with a1 kg of CF3I and then pressurized with nitrogen to the 

desired pressure (4.21 MPa) at room temperature. The airflow through the simulator was 

maintained at 1.5 kg/s ± 0.1 kg/s (mean ± standard deviation).

As shown in Figure 8, during the cruc ial initial 10 s, for this temperature differential of about -20 

oC (ambient temperature minus fluid boiling point), the concentration of suppressant is well 

below the concentration when the temperature differential is 44 oC. Liquid CF3I droplets were 

present for only a short period of time (< 2 s) immediately following the discharge. Rather, a 

significant amount of the fluid pooled at the bottom of the chamber upon release, then 

evaporated slowly over many seconds. Heating the storage container to room temperature shows 

improvement but does not correct the problem.

To exhaust

Video camera

Baffle

Air from blower

Observation window

2 m

60 cm

Pitot tube

15 cm

Agent bottle

Fiber-optic probes (UV spectrometer)

Agent release location

Simulated

engine core

1

2

3 4

Horizontal rib
15

Figure 8. Concentration profiles of CF3I at the forward measurement location 

under three test conditions

0

5

1 0

1 5

2 0

0 5 1 0 1 5 2 0 2 5 3 0

Room temperature release, forward port

Heated agent / cold air release, forward port

Cold temperature release, forward port

Volume fraction (%)

Time (s)

3. Suppressant Dynamics in Engine Nacelles

Understanding of the dispersion of a suppressant to random fire locations in the variety of engine 

nacelle geometries under diverse flight conditions can best be developed by either an extensive 

set of full-scale fire suppression tests or from validated computer modeling of the process. The 

NGP is following the latter approach in order to provide guidance on preferred location(s) and 

styling of suppressant discharge. The computational fluid dynamic (CFD) model will include 

gaseous and aerosol suppressant flow, a fire, and fire extinguishment in cluttered environments. 

Several flow facilities are being used concurrently to provide both input and validation data in a 

timely manner.

The model for air flow through a smooth nacelle was completed last year. Sensitivity studies 

have now been performed to assess the effect of grid resolution, turbulence models, and wall 

functions on the predictions. The results were not sensitive to mesh size except near the walls 

from lack of resolution. Examination of two turbulence approaches showed that an assumption 

of zero cross-stream turbulent velocities produced results in better agreement than did an 

assumption of isotropic turbulent flow. This conclusion also agrees with experimental 

observations. Finally, calculations with two different wall functions showed no impact on the 

solution for this application.
16

The next step is to add the effects of nacelle clutter to the calculations. This requires data (drag 

and turbulence intensity) on the change in flow behavior as the droplet-laden stream moves 

around obstacles. For these experiments, three obstacle tubes (diameters of 3 mm, 13 mm, and 

32 mm) were chosen to span the ranges of clutter sizes: smaller, on the same order, and larger 

than the integral length scales of turbulence. Each, in turn, was placed in a straightened air flow 

in an existing spray facility (described in the FY2000 NGP Annual Report2). The flow field 

upstream and downstream of the obstruction was characterized using three-dimensional particle 

image velocimetry (PIV) with a spatial resolution of approximately 600 μm. The 3-D stereo PIV 

system differed from traditional PIV systems in that two CCD cameras were used and three 

velocity components were measured. The flow mean velocity of 4.5 m/s, corresponding to a 

Reynolds number of 3700, was representative of air speeds through aircraft engine nacelles. 

The downstream flow field was relatively uniform as shown in Figure 9 except for some local 

jetting within 25 mm downstream of the flow straightener. The cylindrical obstacles were placed 

100 mm downstream where these jets had dissipated. 

A preliminary version of this case of a single cylinder in a cross flow was integrated into the 

VULCAN fire physics code, along with a more sophisticated turbulence model. Comparison of 

the CFD predictions to the PIV measurements indicate that qualitatively the location and size of 

the recirculation zone for the largest cylinder case was well captured. The numerical results 

overpredicted the streamwise mean velocity by 20 % and underpredicted the RMS fluctuations in 

the streamwise velocity by 15 %. These differences indicate that the numerical predictions 

underestimate the extent of turbulent mixing behind the cylinder, and may be attributed to the 

use of the k-, model that is known to perform poorly in highly recirculating flows.

The next experiments will inject liquid fire suppressant agents (water, boiling point 373 K, and 

HFE-7100, boiling point 334 K) and study the change in droplet transport as the spray interacts 

with different obstacles. These agents were chosen because of the effectiveness of high boiling 

point liquids to extract heat from a flame zone. Measurements will be made of the impingement 

and breakup of droplets on the 32 mm cylinder considered earlier. This cylinder will also be 

heated to study the effects of a heated surface on droplet vaporization and transport as a droplet 

approaches the heated surface. 

The third component is the evolution of a fire suppression capability for VULCAN. Prototype 

simulations of the 2-D nacelle fixture have been run for two agents (N2 and HFC-125) with and 

without a typical rib located downstream of the inlet. The flow and size of the rib and nacelle 

were chosen to be representative of the flow and geometry in an actual nacelle. Fire 

extinguishment occurs between 40 % and 60 % N2 by volume without a rib. Cold flow cases 

with the rib geometry reveal a sharp increase in turbulent kinetic energy over the top of the step 

resulting in high values of turbulence intensity (75 % or greater) as indicated in Figure 10.
17

Figure 9. Variation of mean streamwise and cross-stream velocities with 

downstream distance. (The black circles are the ends of the obstruction 

cylinders.)
18

Figure 10. Contour plots of turbulent kinetic energy and velocity field around rib 

at the centerline of the domain

This detailed information will be used to parameterize the clutter model for regions around the 

ribs near the nacelle wall. Scenarios using N2 and HFC-125 agents are being explored to 

determine the extra suppressant required for a fire stabilized on the downstream side of a rib. 

The results from these simulations will help provide guidance for the experimental test series of 

a full-scale nacelle simulator to be conducted in FY2003.

4. Powder Panels for Dry Bay Fire Protection

The NGP is examining new concepts for an old alternative to the discharge of pressurized fluids 

or dry chemical fire extinguishing agents. Powder panels lining a dry bay can provide passive, 

lightweight, effective fire protection against ballistic impact by releasing powder into the fire 

zone to inert the space before the adjoining fuel spills into the space and is ignited by 

incendiaries. Previous powder panel testing has shown that only about one gram of a typical fire 

extinguishing powder could prevent a pool fire from igniting for over one minute. In U.S. 

aircraft, the widest use of powder panels has been in helicopters. Currently, the AH-1W Super 
19

Cobra uses powder panels, as does the V-22 Osprey tiltrotor aircraft, with evaluations underway 

for the AH-1Z and the RAH-66 Comanche helicopters. 

The design and acceptability criteria for these devices are different from conventional fluid 

suppressant systems. Powder panels add weight based upon the surface area of the fuel wall/fire 

zone interface, as opposed to the volume of the fire zone, so the relative benefit of the panels is 

dependent upon the configuration of the particular bay. False discharges do not occur, but

cleanup following a fire or inadvertent damage remains a concern. 

Today’s panels are in essence the same designs that have existed for decades. NGP staff have 

compiled a list of powder panel materials and designs previously evaluated and those that have 

been integrated into aircraft designs. The survey also includes powder panel test programs 

extending back to the 1970s.

An experimental dry bay/fuel tank simulator (Figure 11) was fabricated to enable comparison of 

powder panel materials and designs. The characteristics examined were panel fracture and 

material removal, the amount of fire extinguishing powder released into the test article, the 

dispersion of this powder, and the time the powder remains suspended in the dry bay. 

Figure 11. Experimental Test Device and Powder Collection Methods

Fuel Tank

(1 ft3)

Dry Bay

(2 ft3)

Powder

Panel

Shotline

Shotline

Powder

Collection Cups

Witness Rods Powder Panel

Witness rods were located throughout the dry bay to capture qualitative powder dispersion 

characteristics. Powder collection cups were also located in the dry bay along the shotline, 

where the powder concentration is most important during a ballistic projectile impact. In 

addition, each panel was weighed before and after each test to determine the amount of powder 

released. The removed area of the front face (dry bay side) of the powder panels was also 

determined. Digital video was captured for each test to assist in determining the length of time 

powder was suspended in the dry bay. 

In each test, a light-gas gun was used to launch a 0.50 caliber hard steel ball projectile at a 

velocity of at least 670 m/s (2,200 ft/s). The initial tests did not involve fluid in the fuel tank nor 

Powder Collection Cups
20

air flow to simplify the screening process. The powder was KHCO3 (Purple K). The tested 

panel features included the following: 

· For the front panel face (dry bay side), materials that exhibit brittle properties upon 

impact, but durability in handling, were of utmost interest. Thermoplastic materials 

evaluated included a polycarbonate, a polystyrene, a polypropylene, and an acrylic. 

Intentional surface scoring of acrylic panels was examined to determine if fracture 

characteristics could be enhanced. Thermoset polymers evaluated included two polyester 

resins, a thin epoxy primer, and an epoxy resin. 

· Thermoplastic materials were examined for the back panel to determine if the fracture 

characteristics of the back panel influenced the front panel in any way.

· A number of materials and designs were examined for the powder panel internal rib 

structure. Panel designs included such diverse features as integral front and back walls 

and internal channels and honeycomb material. Several rib designs were conceived to 

enhance powder release and yet prevent the settling of powder. Attempts were made to 

minimize the number of these ribs, maximize the spacing, and minimize the overall panel 

thickness.

Table 4 lists some of the more effective (upper section) and ineffective (lower section) designs.

Table 4. Comparison of Effective and Ineffective Powder Panel Designs

Test 

No.

Material Description Thickness 

(mm)

Panel 

Weight 

(g)

Powder 

Loss 

(g)

Powder 

Loss

(%)

Front Face 

Area 

Removed 

(cm2)

8 0.08" clear acrylic faces, 0.375" acrylic tube ribs 13.5 1402 48 5.6 31.6

9 0.07" cracked Ice acrylic front, 0.06" white styrene 

back, two white styrene ribs (0.12" thick) at 4" and 8"

6.9 769 23 5.0 17.7

12 0.08” (2" x 2" scored) clear acrylic, 0.08" clear acrylic 

back, 0.125" polycarbonate honeycomb rib

7.6 579 9 4.6 22.6

21 0.07" acrylic prismatic front, 0.06" white styrene 

back, two white styrene ribs (0.12" thick) at 4" an 8"

7.8 552 30 12.8 20.3

23 0.07" styrene prismatic front, 0.06" white styrene 

back, two white styrene ribs (0.12" thick) at 4" and 8"

6.5 517 28.4 12.8 25.6

27 0.098" polyester resin front, 0.06" white styrene back, 

two white styrene ribs (0.12" thick) at 4" and 8"

7.1 620 8.2 4.0 25.4

28 0.098" polyester resin front, 0.06" white styrene back, 

two white styrene ribs (0.12" thick) at 4" and 8"

7.4 876 83.3 18.7 80.6

1 0.016" Al front, polyethylene corrugated rib, 0.01" Al 

foil back

6.0 630 0.6 0.17 1.3

2 0.01" Al foil front, polyethylene corrugated rib, 0.016" 

Al back

5.9 594 0.04 0.01 1.3

13 0.06" white styrene faces, 0.375" aramid rib 13.5 1128 1.5 0.2 1.3

14 0.07" cracked ice acrylic front, 0.08" clear acrylic 

back, 0.25" Al honeycomb rib

10.5 832 1 0.23 1.3

15 0.06" white styrene faces, 0.25" Al honeycomb rib 10.2 764 1 0.25 1.3

16 0.08" clear acrylic faces, 0.25" Al honeycomb rib 10.8 942 3 0.65 1.6

18 0.08” (2" x 2" scored) clear acrylic front, 0.08" clear 

acrylic back, 0.125" Al honeycomb rib

7.2 638 2 0.82 9.5
21

The outcome of these non-fire screening tests was gratifying.

· The best of the new powder panel designs examined in this project offer the potential to 

be competitive with halon 1301 in a wider variety of dry bay designs. In one of these 

cases (epoxy primer front face), nearly 50 % of the front face area was removed, almost 

60 % of the powder was released, and the powder remained suspended throughout the dry 

bay for over four minutes. This compares with testing of other powder panel designs 

integrated into operational aircraft, where the powder dispersed only along the shotline, 

dissipated in tenths of a second, and the amount of dispersed powder was limited to the 

region of projectile penetration. Figures 12 and 13 show major performance benefits 

achievable with the enhanced design concepts in Table 4. 

Figure 12. Effect on Suppressant Delivery of Standard Design Features and 

Enhanced Designs Showing 5x to 10x Greater Powder Release in the Latter

Powder Release

0

5

10

15

20

% of Powder Release

More Standard Design Elements

Promising Enhanced Designs

8

9 12

21

23

27

28

1 2 13 14 15 16 18
22

Figure 13. Effect on Powder Panel Fracture Area of Standard Design Features 

and Enhanced Designs, Showing 15x to 20x More Front Face Area Removed in 

the Latter

0

10

20

30

40

50

60

70

80

90

7 Powder Panels from Both Categories

Front Face Area Removed (sq. cm.)

More Standard Design Elements

Promising Enhanced Designs

8

9

12 21

23

28

27

1 2 13 14 15 16

18

· As expected, the front face material properties were of utmost importance. More brittle 

materials outperformed more ductile materials. Crack growth optimization techniques 

enhanced performance. 

· A strong synergism was found between the rib structure and the front face. Increasing 

the bond area between the face and ribs inhibited powder dispersion. Tradeoffs will be 

necessary between rib spacing and powder loading, as sufficient powder must be 

available at all potential impact sites. 

· Three-piece powder panel designs outperformed easy-to-assemble double-wall extrusion 

designs, as built-in rib channels inhibited cracking. 

· Channel designs allowed more powder to be released from the impact location than more 

segmented or cellular designs.

· Variation in the powder panel back face had less effect. In fact, limiting back face 

fracture might mitigate the chance of a dry bay fire by reducing fuel leakage and 

confining it to an area along which most of the powder is released.
23

Recent Publications: Improved Suppressant Delivery

Presser, C., Widmann, J.F., DesJardin, P.E., and Gritzo, L.A., “Measurement and Numerical 

Prediction of Homogeneous Turbulent Flow over a Cylinder: A Baseline for Droplet-laden Flow 

Studies,” AIAA 2002-0905, Am. Inst. Aero. Astro., Washington DC, 2002.

Fallis, S., Reed, R., McCormick, J.L., Wilson, K.A., and Holland, G.F., “Advanced 

Propellant/Additive Development for SPGG Fire Suppression Systems: Hybrid Systems,” 

Proceedings of the 2001 Halon Options Technical Working Conference, Albuquerque, pp.364-

372, Albuquerque, 2001.

Presser, C., Widmann, J.F., DesJardin, P.E., and Gritzo, L.A., "Measurements and Numerical 

Predictions of Liquid Agent Dispersal Around Solid Obstacles," Proceedings of the 2001 Halon 

Options Technical Working Conference, Albuquerque, pp.122-130, Albuquerque, 2001.

Yang, J.C., Nyden, M.R., and Manzello, S.L., “Cold Discharge of CF3I in a Simulated Aircraft 

Engine Nacelle,” Proceedings of the 2001 Halon Options Technical Working Conference,

Albuquerque, pp.64-71, Albuquerque, 2001.

D. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES

Benefit Assessment of Fire Protection System Changes

There are a large number of contributing factors that must be considered when deciding which 

fire suppression system to select for a new platform or whether to retrofit the fire suppression 

system on a legacy platform. These include both objective cost factors and subjective value 

factors. Accordingly, the NGP has developed a methodology to quantify a fire suppression 

technology by its total, life cycle cost and to enable superimposing on this a subjective value 

system. The methodology determines the net cost of the fire suppression system: the cost of the 

system (which is a function of system size/weight) minus the cost savings provided by the 

system (which are a function of extinguishant effectiveness and result in aircraft saved). The 

process shown in Figure 14 was used to determine the fire suppression system costs. The 

following paragraphs detail this process.

The example used in developing the methodology is a comparison of an existing halon 1301 

system and a system of equivalent and altered performance to halon 1301 using an off-the-shelfalternative, HFC-125. This methodology was developed to be applicable to both legacy

platforms (for decision makers who must consider retrofit costs for existing platforms) and future 

platforms (for decision makers currently designing new platforms). 

Significant uncertainties arise because of the need to use engineering estimates where data were 

not available, because of limited historical information over the life of the legacy aircraft, and 

because of the non-existence (in some cases) of a fielded HFC-125 system. Thus the following 

figures are indicative, all in FY2000 dollars, rather than definitive.
24

Figure 14. Life-Cycle Cost Estimating Process

Cost Analysis of Fire Suppression Systems for Cargo Aircraft. The total cost of ownership of 

the halon 1301 systems in the current fleet of an individual legacy aircraft platform (assuming a 

life cycle of FY00-22 and a platform total of 121 aircraft) is estimated to be $25 M and for a 

legacy HFC-125 system ranges from $35 M to $41 M. These are approximately two tenths of 

one percent of the total (life cycle) cost of the aircraft. Based on an estimated fire cost per flight 

hour, the total estimated number of flight hours over the life of the legacy cargo aircraft, and a 

traditional success rate of halon 1301 suppression systems in military aircraft of 60 % to 80 %, it 

is estimated that the legacy cargo aircraft halon 1301 systems would save the Air Force between 

$122 M and $163 M in avoided fire losses. 

The total cost of ownership of the halon 1301 systems (equivalent to that in the current fleet, 

above) in a fleet of a future individual cargo aircraft platform (assuming a life cycle of FY00-31 

and a platform total of 121 aircraft) is estimated to be $36 M. For an HFC-125 system of 

comparable effectiveness, the cost ranges from $35 M to $44 M. These are about 0.2 % of the 

total (life cycle) cost of the aircraft. Based on an estimated fire cost per flight hour, the total 

estimated number of flight hours over the life of the future cargo aircraft, and a traditional 

success rate of halon 1301 suppression systems in military aircraft of 60 % to 80 %, it is 

estimated that the future cargo aircraft halon 1301 systems would save the Air Force between 

$136 M and $181 M in avoided fire losses. 

Life-Cycle

Cost Estimating

Process

•MNS

•Functional Experts

•Analysis of Alternatives

•Preferred Solution

 

• Technical Specialists

• Program Analysts

• Cost Analysts

• LCCE Schedule

• Finalize cost

proposal

• List proposed

deliverables

• Functional Description

• Mission Requirements

• Development Scenario

• Technical Characteristics

• Program Characteristics

• Tech Baseline

• System Description

• Integration

• Schedule

• Acquisition Strategy

• Test Plan

• MIL-STD-881B

• OSD CAIG O&S Hdbk

• Time Phasing

• Inflation

• Budget Profiles

• Logistics

• WBS/CES

• Similar Systems

• Technology Projections

• Cost/Technical Data Sources

• Contractor Internal Data

• Comparative Analysis

• Cost Estimating

 Relationships

• Parametrics

• Analogous Techniques

• Engineering Methods

• Ops & Support Estimate

• Estimating Uncertainties

• Technical Risk

• Schedule Risk

• Program Risk

• Sensitivity Analysis 

• Ground Rules

• Methodology

• Data Sources

• Updates

Customer

Interface

Customer

Interface

Customer

Interface

Team Selection

and

Planning

System

Characterization

Ground Rules

&

Assumptions

Data Collection

& Methodology

Selection

Application of

Estimating

Techniques

Uncertainty

and

Risk Evaluation

Cost Estimate

Documentation

& Delivery
25

Therefore, it appears that the benefit of having either fire suppression system substantially 

outweighs its cost, and the difference in total cost of the two systems is modest compared to the 

total cost of owning and operating the aircraft. 

Cost Analysis of Fire Suppression Systems for Fighter Aircraft. The total cost of ownership of 

the halon 1301 systems in the current fleet of an individual legacy aircraft platform (assuming a 

life cycle of FY00-28 and a platform total of 549 aircraft) is estimated to be $11.2 M and for a 

legacy HFC-125 system ranges from $15.6 M to $17.8 M. These are approximately 0.05 % of 

the total (life cycle) cost of the aircraft. Based on an estimated fire cost per flight hour, the total 

estimated number of flight hours over the life of the legacy fighter aircraft, and a traditional 

success rate of halon 1301 suppression systems in military aircraft of 60 % to 80 %, it is 

estimated that the legacy fighter aircraft halon 1301 systems would save the Navy between 

$154.7 M and $206.3 M in avoided fire losses. 

The total cost of ownership of the halon 1301 systems in a proposed fleet of a future individual 

fighter aircraft platform (assuming a life cycle of FY00-32 and a fleet of 549 aircraft) is 

estimated to be $14.4 M. For an HFC-125 system of comparable effectiveness, the cost ranges 

from $15.8 M to $18.0 M. These are approximately 0.05 % five of the total (life cycle) cost of 

the aircraft. Based on an estimated fire cost per flight hour, the total estimated number of flight 

hours over the life of the future fighter aircraft, and a traditional success rate of halon 1301 

suppression systems in military aircraft of 60 % to 80 %, it is estimated that the future fighter 

aircraft halon 1301 systems would save the Navy between $156.5 M and $208.7 M in avoided 

fire losses. 

Similar cost analyses are underway for engine nacelle protection in rotary wing aircraft and for 

dry bay applications for typical fighter, rotary-wing, and unmanned aircraft. 

Changes in Cost Analysis for Altered Fire Suppression Performance. The objective of this 

project included consideration of fire suppression systems with performance different from a 

halon 1301 system. Using the above methodology, modifications were made to the performance 

of the cargo and fighter fire suppression systems by utilizing data from the Factor of Safety 

(FOS) study performed during Phase III of the Halon Replacement Program for Aviation. These 

suppression system weights and corresponding effectiveness were correlated to the cargo and 

fighter aircraft platforms. For cargo aircraft, the net cost change per single percent change in 

extinguishing effectiveness (i.e., 91 % successful vs. 90 % in the field) of the fire system was 

approximately -$2.0 M. For fighter aircraft, the net cost change per single percent change in 

system effectiveness was approximately -$2.5 M. These estimates showed that additional 

investment in optimizing fire suppression system performance pays off in assets (costs) saved. 

Recent Publication: Viability of New Suppression Technologies

Bennett, J.M. and Kolleck, M.L., “Cost Analysis of Fire Suppression Systems,” Proceedings of 

the 2001 Halon Options Technical Working Conference, pp. 160-170, Albuquerque, 2001.
26

III. INDEPENDENT PROGRAM ASSESSMENT

At the suggestion of SERDP management, the NGP Technical Program Manager commissioned 

an Independent Review Panel (IRP) to assess progress to date and to recommend actions that 

could enhance the prospects for the NGP program to result in viable and practical alternative fire 

suppression technologies with NGP resources remaining at or near currently projected levels. 

The IRP examined an array of technical and strategic documents before convening coincident 

with the 2001 NGP Annual Review Meeting in December 2001. The three-member IRP 

encompassed an array of expertise and experience from university, government, and industry 

environments. They have delivered a preliminary report, with the final version expected shortly.

The IRP draft conclusions are that:

· The NGP program as presently structured and as modified to date is technically strong 

and targeted realistically.

· The NGP program as presently structured is resulting in research output in quality and 

quantity far above what is considered typical by the review panel for the resources 

available and applied.

· Much of the research output has high potential for near term use in design of fire 

protection systems for aircraft.

· With relatively modest adjustments, the utility of the NGP research findings can be 

further enhanced.

The Panel also warned that some of the NGP reductions necessitated by reduced resources (e.g., 

in large scale testing, synthesis and screening of new chemicals, toxicity testing) “comprise an 

IOU that is certain to become due in the future” and will lead to more costly weapon system 

platform development and test programs to obtain the actual fire extinguisher system 

performance that the research program demonstrates as attainable.

Along with specific comments on each of the ongoing projects, the Panel made three priority 

recommendations:

· Establish a separate project on engine nacelle fire reignition or elevate this issue within 

existing projects. This has been a continuing design problem. 

· Expand delivery and dispersion research to include additional high boiling point 

compounds in the individual research projects. 

· Request summation sheets on lessons learned from the principal investigators to serve as 

a starting point for future system design heuristics.

They also made three further recommendations:

· Prepare a technical information package to expedite hand-off of the portable Differential 

Infrared Agent Concentration Sensor to government agencies, analyzer vendors, and 

aerospace manufacturers involved with aircraft extinguishing system certification and 

testing. There is a dire need for a system to replace the traditional analyzer used for 

airborne applications.
27

· Address directly the issue of gas phase vapor loading from dispersed aerosols of higher 

boiling point extinguishing agents. 

· Initiate the NGP final report preparation as early as FY2002 in the form of a compendium 

of heuristic technical rules capable of being understood and utilized by extinguishing 

system design and test engineers.

The perceptions inherent in these recommendation validate the value of convening the IRP. The 

recommendations themselves will be implemented as soon as possible.

IV. WHAT LIES AHEAD? 

From this point forward, NGP 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. 

As these results 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. Ideally such a 

project would be carried out well before the conclusion of a program, with the outcome of the 

tests indicating the optimal use of the remaining resources. As warranted and feasible, such 

follow-on tasks will be proposed.

Over the past five years, the NGP has solicited proposals for “outside the box” approaches to fire 

suppression. Some of these novel ideas have proven successful at broadening the thinking of the 

fire suppression community. A modest resumption of these solicitations is possible beginning in 

FY2003.

Much of the innovation in NGP projects has resulted from interactions among a large set of 

investigators in diverse but related aspects of fire suppression. The number of concurrent 

projects, which peaked at 23, has decreased to 12 in FY2001 and to 5 in FY2002. Maintaining 

an active presence in broader meetings is thus an essential factor in NGP success. The NGP has 

recently enabled the continuation of the annual Halon Options Technical Working Confe rence 

and will work to keep this as a principal forum for communication and collaboration. The NGP 

will seek to enhance the participation in its autumn Annual Research Meeting, inviting past 

investigators and other experts. It is hoped that these two meetings will continue to broaden the 

perspective and stimulate the innovation of the NGP investigators.
28

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 will then 

need to set in place the engineering programs to develop the new technologies for 

implementation in its fleet of aircraft.

References (available from the NGP web site)

1

Technology Development Plan for Alternatives to Ozone-depleting Substances for Weapons 

Systems Use; Final Report, Office of the Deputy Undersecretary of Defense (Science and 

Technology)/Weapons Systems, 1998.

2

 Gann, R.G., FY2000 Annual Report: Next Generation Fire Suppression Technology Program 

(NGP), Technical Note 1437, National Institute of Standards and Technology, Gaithersburg 

MD, 48 pages (2001).
29

APPENDIX I. 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; 

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; 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/15/0. TROPODEGRADABLE BROMOCARBON EXTINGUISHANTS

Principal Investigator: J. Douglas Mather, NMERI

COR: Ronald Sheinson, NRL
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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

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

FIRE SUPPRESSION

Principal Investigators: Robert Huie and Marc Nyden, NIST; 

Andrzej Miziolek, ARL

4B/4/01. PERFORMANCE DATA ON COLD TEMPERATURE DISPERSION 

OF CF3I AND ON MATERIALS COMPATIBILITY WITH CF3I

Principal Investigator: Jiann Yang, NIST

4B/5/01. ASSESSMENT OF COMPLETENESS OF SEARCH FOR 

ALTERNATIVE SUPPRESSANT CHEMICALS

Principal Investigator: 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

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 Investigators: Gregory Linteris, NIST
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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/1/01. PARAMETRIC INVESTIGATION OF DROPLET ATOMIZATION 

AND DISPERSION OF LIQUID FIRE SUPPRESSANTS

Principal Investigator: Cary Presser, NIST

5D/1/901. ADVANCED PROPELLANT/ADDITIVE DEVELOPMENT FOR GAS 

GENERATORS 

Principal Investigators: Gary Holland, General Dynamics; Russell 

Reed, NAWC-WPNS

COR: Lawrence Ash, NAVAIR

5E/1/1. ENHANCED POWDER PANELS

Principal Investigator: Dan Cypher, Skyward, Inc.

COR: Martin Lentz, Eglin AFB

6A/1/01. FIRE SUPPRESSANT DYNAMICS IN CLUTTERED WEAPONS 

SYSTEM COMPARTMENTS

Principal Investigator: David Keyser, NAVAIR
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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: William Pitts, 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

F. FUEL TANK INERTION

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

Principal Investigator: Leonard Truett, Eglin AFB