NIST Technical Note 1451 

FY2002 Annual Report 

Next Generation Fire Suppression Technology 

Program (NGP) 

Richard G. Gann 
FY2002 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

January 2003 

U.S. Department of Commerce 

Donald L. Evans, Secretary 

Technology Administration

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology 

Dr. Arden L. Bement, Jr., Director

NIST Technical Note 1451 
National Institute of Standards U.S. Government Printing Office For sale by the 

and Technology Washington: 2002 Superintendent of Documents 

Technical Note 1451 U.S. Government Printing Office 

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

Tech. Note 1451 

54 pages (January 2003)

CODEN: NTNOEF 
FY2002 ANNUAL REPORT 

Next Generation Fire Suppression 

Technology Program (NGP) 

[PP-1059] 

Richard G. Gann, Ph.D. 

Technical Program Manager 

January, 2003
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ABSTRACT 

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

completed its sixth 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 complete 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...................................................................................................... 3 

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

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

1. Low Boiling Point Compounds .......................................................................... 2 

2. Prediction of Cardiotoxicity................................................................................ 3 

3. Fluoroalkyl Phosphorus Compounds ................................................................ 5 

4. Agent Stability During Long-term Storage......................................................... 7 

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

1. Solid Propellant Fire Extinguishers ................................................................... 8 

2. Dispersion of Suppressants at Low Temperature ........................................... 14 

3. Suppressant Dynamics in Engine Nacelles .................................................... 16 

4. Enhanced Powder Panels for Dry Bay Fire Protection.................................... 24 

5. Mechanisms of Unwanted Accelerated Burning.............................................. 27 

6. Enhancing Engine Nacelle Extinguishment with Intumescent Coatings.......... 29 

C. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES .................................. 31 

1. Benefit Assessment of Fire Protection System Changes................................ 31 

2. Suppressant Concentration Measurement for Real-scale Fire Tests.............. 32 

III. INDEPENDENT PROGRAM ASSESSMENT..................................................... 33 

IV. WHAT LIES AHEAD?......................................................................................... 33 

APPENDIX A. NGP PROJECTS.................................................................................. 35 

APPENDIX B. REPORT OF THE INDEPENDENT REVIEW PANEL .......................... 39 

APPENDIX C. RESPONSE TO RECOMMENDATIONS OF THE 2001 NGP 

INDEPENDENT REVIEW PANEL (IRP) ....................................................................... 49 
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I. INTRODUCTION 

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

Program (NGP) has completed its sixth 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, had 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. 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. 

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 found the NGP program to be “technically strong and targeted realistically” and 

“resulting in research output in quality and quantity far above what is considered typical for the 

resources available and applied,” with “much of the research output having high potential for 

near term use in design of fire protection systems for aircraft.” They made a number of 

suggestions for tuning the Program, all of which will be implemented by FY2003. 

The NGP participants continue to generate unparalleled contributions to the published literature, 

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. The uncertainties in the reported data are discussed in the individual 

research reports. 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. 
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 and given the availability of HFC-125, 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). 

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. 

 

The NGP has systematically examined (and continues to examine) many of the most promising 

chemical families. While this search has produced additional knowledge of what makes a good 

suppressant, we have to date not identified a likely successor to halon 1301 for in-flight aircraft 

fires. 

1. Low Boiling Point Compounds 

The third criterion is the subject of NGP activity. There is some uncertainty as to the typical low 

ambient temperature experienced during in-flight fire suppression; -40 °C has been used thus far. 

A project has been commissioned for FY2003 to examine reports of the in-flight deployment of 

halon 1301, with an eye toward identifying a realistic value. In an additional effort to identify 

compounds with low boiling points, a search of the chemical literature is underway for all 

compounds with boiling points under 35 °C that contain bromine, iodine and/or phosphorus. 

2 
2. Prediction of Cardiotoxicity

There is also research activity on the toxicity criterion. Many of the most promising alternative 

chemicals are in the category of tropodegradable bromocarbons. As the name implies, these are 

compounds that contain a bromine atom for efficient fire suppression (criterion 1) and a chemical 

feature that enables the molecule to meet criterion 2. One of the most appealing bromoethers 

(CF3CBr=CH2) did well in all screens, but its LOAEL (lowest observed acute exposure level) 

for cardiac arrhythmia in laboratory dogs was found to be 1 % (volume), a concentration well 

below the extinguishing level of about 3 %. [For reference, halon 1301 has a LOAEL value of 

7.5 % by volume.] These tests are expensive (at least $70 k) and require significant mass of a 

test chemical that may not be in commercial production. Thus, we have reprogrammed resources 

to improve our ability to estimate the cardiotoxicity of halogenated compounds from their 

chemical composition and structure. 

Unfortunately, there are no recognized quantitative structure-activity relationships (QSARs) for 

estimating LOAEL values for members of the chemical families that comprise tropodegradable 

bromocarbons. A re-examination of the field has led to a focus on two approaches: partition 

coefficients and in vitro toxicity tests. 

Partition Coefficients. A wide range of compounds, including halogenated and 

unhalogenated alkanes, alkenes, and ethers are known to induce cardiac arrhythmia. The 

mechanism is not known. A hypothesis is that the effect results not from chemical (reactivity 

based) toxicity, but from the absorption into or adsorption onto heart nerve and muscle cells and 

cell membranes. The pharmaceutical industry and environmental scientist use octanol-water 

partition coefficient in QSAR analysis for rational drug design (absorption, bioavailability, 

hydrophobic drug-receptor interactions, metabolism and toxicity) and estimating the 

environmental fate of chemicals. The property being assessed is molecular hydrophobicity, the 

disaffinity for the polar environment of water in favor of the far less polar octanol. 

Partition coefficients are determined experimentally using reverse phase chromatographic 

methods. The measured property is the equilibrium constant for the concentrations of the 

chemical in the two liquids, KOW. Compounds of known KOW are used to determine 

relationships between measured chromatographic retention times and partition coefficients. For 

an unknown compound, a determination then requires only a few mg sample. 

Values of KOW may also be calculated from the contributions of molecular fragment-based terms 

plus correction factors. The algorithms can give different results, so some experience is needed 

to select or develop an appropriate version for the particular chemicals under consideration. 

Two of the most commonly used algorithms are from Molinspiration Cheminformatics 

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

An indication of the disparity as well as trends in the predicted values for the two calculation 

methods can be seen in Table 1. 

3 
Table 1. Comparison of Calculated and Measured Values of Log KOW of Selected 

Halocarbons 

Compound 

Log KOW * 

(calculated) 

Log KOW ** 

(calculated) 

Log KOW

(measured) 

LOAEL 

(vol. %)

CF3Br (halon 1301) 1.833 1.591 1.86 7.4 

CHBrF2 1.849 0.98 NA 3.9 

CH2=CBrCF3 2.141 2.49 NA 1.0 

CF2ClBr (halon 1211) 2.175 1.905 2.1 1.0 

CF3I 2.219 2.007 NA 0.4 

C3HF7 2.349 10.5 

* Molinspiration Cheminformatics algorithm

** Syracuse Research Corporation algorithm

It is probable that the use of calculated partition coefficient values to develop predictions of 

trends in LOAEL performance may work best when only applied to narrowly defined groups of 

compounds (for instance bromofluoro-alkenes) and even then only used as a tentative predictor 

of LOAEL value. This limitation is shown when comparing the last two lines of Table 1. The 

calculated Log KOW value for C3HF7 suggests a LOAEL lower than that any of the other 

compounds, which is clearly not the case. 

For calculated and/or experimental partition coefficients to be employed to select fire 

suppressant compounds for further evaluation, greater assurance in the relationship to cardiac 

sensitization LOAEL values is needed. The next step in our examination of this approach will be

to expand the above table to include the experimental determination of KOW values for the 

halons, HFCs, current candidate compounds and alternate fire suppressants. Medical anesthetics, 

which are chemically related to the above fire suppressants, will also be examined. Preference 

will be given to those compounds for which LOAEL values for cardiac sensitization have been 

determined. Additional work will further evaluate the merits of the various types of partition 

coefficients (water/octanol, water/membrane, etc.). Success will enable intelligent selection of 

compounds for synthesis in the quantities needed for further study. 

In Vitro Screening Methods. While no in vitro method exists for evaluating the cardiac 

sensitization properties of compounds there is strong interest in this area by pharmaceutical 

companies. One example is development of micro-scale in vitro testing systems based on human 

or animal cardiomyocytes. These systems are expected to outperform generic cell systems when 

cardiac cells are the target of the tested chemical. The results should also be directly relatable to 

the abnormal clinical ECG patterns that define drug-induced arrhythmia. The NGP is evaluating 

its possible role in this field. 

 

4 
3. Fluoroalkyl Phosphorus Compounds 

Work is continuing in our effort to assess whether there are members of this family with 

estimated acceptably low toxicity, ODP, and GWP that could be used as replacements for halon 

1301. Of the eight compounds initially targeted for synthesis (Table 2), about 7 g of seven of 

them were ultimately delivered for testing. Some general observations are: 

• Fluorine substitution does yield compounds of lower boiling point, as expected. 

• Several compounds exhibited instability on exposure to air and may either be hydrolyzing 

due to reaction with the ambient humidity and/or reacting with oxygen. A compound is 

listed as not air reactive if no heating of the glass vial container occurred on opening, and 

no flame or white fumes were observed on exposure of the compound to air. 

For measuring the extinguishment concentration of these high boiling chemicals, the cup burner 

(Figure 2) was modified to pre-heat the incoming air, to nebulize the chemicals and to dilute the 

chemical before it entered the flame zone. This prevented condensation of test compounds on 

the cup-burners inner glass surfaces. The apparatus can now address compounds with boiling 

points from at least –57 °C (halon 1301) to 130 °C. Extinguishment data for these compounds 

are listed along with boiling point information and air reactivity observations in Table 2. The 

extinguishment data are upper limits due to the small quantity of chemical available. 

Table 2. Fluoroalkyl Phosphorus Compound Cup Burner Results 

ID Compound

Boiling Point 

(°C) 

Extinguishment 

(vol. %) Air Reactivity, Ignition

1 O=P(CF3)3 32 No extinguishment

@ 5 % 

Not air reactive 

- no ignition 

2 P(OCH3)(CF3)2 55 Spontaneously

ignites in air – Not 

tested 

Ignites spontaneously 

3 P(OCH2CF3)3 131 3.1 % Not air reactive 

- no ignition 

4 O=P(OCH3)(CF3)2 42 4.6 % Some reactivity 

- no ignition 

5 P(OCH2CF3)2CF3 112 3.0 % Some reactivity 

- no ignition 

6 P(OCH2CF3)(CF3)2 ~90 1.8 % Very reactive, no 

spontaneous ignition 

7 O=P(OCH2CF3)(CF3)2 >130 No extinguishment

@5 % 

Not air reactive 

- no ignition 

8 O=P(OCF3)3 32 Not tested Not yet synthesized 

5 
Phosphonates (P+5 oxidation state, compounds 1, 4, 7). The limited data suggest that 

phosphonates may need sufficient hydrogen atoms in their structures to break down in the flame 

zone and become chemically active flame suppressants. Only compound 4 approaches the 

needed boiling point range. If the trade-off is between high fluorination to reduce the boiling 

point and moderate hydrogenation for efficient fire suppression, there may not be much further 

promise in this family of compounds. 

Phosphines (P+3 oxidation state, compounds 2, 3, 5, 6). None of these compounds has a 

sufficiently low boiling point to be of practical value for aircraft application, and high volatility 

(high fluorination) compounds tend toward spontaneous flammability. Thus, this family shows 

little promise. For other uses, identification of the decomposition products of compound 6 might 

point the way to dramatically better phosphorus-based extinguishants.

Figure 1. Cup Burner with Nebulizer 

6 
4. Agent Stability During Long-term Storage 

Under the Technology Development Plan1

 an assessment was performed as to the potential for 

degradation of a number of candidate suppressants during four-year exposure to metal storage 

bottle materials. For all compounds there were some metals for which the exposures at 

temperatures up to 150 °C and 4.13 MPa showed no ill effects. CF3I manifested the most serious 

interactions; those samples, stored for an additional five years at ca. 23 °C, have now been reexamined under the NGP. 

 

Metal coupons made from one of four test metals (C4130 alloy steel, Ti-15-3-3-3 titanium alloy, 

Nitronic 40 stainless steel, and Inconel 625 nickel alloy) had been inserted into 

polytetrafluoroethylene-lined stainless steel cylinders. The coupons had roughly the same surface 

area as the inside of the cylinders to simulate the agent contact area if the cylinder had been 

made of that metal. Some cylinders were left without metal coupons as a control. In addition to 

the test metals, half of the cylinders received metal coupons made of copper (type CDA 110), 

since copper reacts with iodine to form the nearly insoluble cuprous iodide. While some 

cylinders contained only dry materials, some cylinders received 100 μL of distilled water. The 

cylinders were then filled with a mixture of CF3I vapor and nitrogen to a pressure of 4.13 MPa as 

measured at 23  ̊C. During the initial testing period, from 1993 to 1997, each cylinder was stored 

at its assigned temperature of either 100  ̊C, 150  ̊C, or ambient temperature (approximately 

23  ̊C). Fourier transform infrared (FTIR) spectroscopy was used to analyze the cylinder 

contents at various times during the storage. The spectra were analyzed for the magnitude of the 

CF3I peak and examined for new peaks that would also indicate degradation of the agent. 

No significant changes were found in the CF3I concentration and no new peaks were found, 

indicating stability during the five-year period at ambient temperature. [Note that the 

combination of copper and Nitronic 40 had already resulted in a complete breakdown of CF3I 

during storage at 150  ̊C.] 

Recent Publications: New Flame Suppression Chemistry

 

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

Compound Selection and Testing Issues,” Proceedings of the 2002 Halon Options Technical 

Working Conference, NIST Special Publication 984 (CD), National Institute of Standards and 

Technology, Gaithersburg, MD, 2002. 

Tapscott, R.E., Shreeve, J.M. and Mather, J.D., “Fluoroalkyl Phosphorus Fire Extinguishing 

Agents,” Proceedings of the 2002 Halon Options Technical Working Conference, NIST Special 

Publication 984 (CD), National Institute of Standards and Technology, Gaithersburg, MD, 2002. 

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

Selection and Testing Issues,” Proceedings of the 2002 Halon Options Technical Working 

Conference, NIST Special Publication 984 (CD), National Institute of Standards and 

Technology, Gaithersburg, MD, 2002. 

7 
Tapscott, R.E., Shreeve, J.M. and Mather, J.D., “Fluoroalkyl Phosphorus Fire Extinguishing 

Agents,” Proceedings of the 2002 Halon Options Technical Working Conference, NIST Special 

Publication 984 (CD), National Institute of Standards and Technology, Gaithersburg, MD, 2002. 

B. 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. There are two different 

design categories (Figure 2): 

• 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. 

Propellant/Additive Development. Direct incorporation of coolant compounds into the 

propellant composition was shown to be an effective means for reducing exhaust temperatures. 

However, while the effect of coolant level upon ballistic performance is consistent within a given 

family of compositions, this trend is not consistent for different propellant families. These 

findings suggest that the benefits of decreased exhaust temperatures are often offset by a 

decrease in the burn rate of the propellant, which in turn relates to a decrease in the rate of 

suppressant delivery. 

Figure 2. Solid Propellant Fire Extinguishers 

SPGG HFE

8 
Figure 3. Relationship Between Propellant Burn Rate and Exhaust Temperature

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

0.0003 0.0004 0.0005 0.0006 0.0007 0.0008

ln(BR1000,) (in/s)

1/T

c

, (°K-1)

Propellant formulations incorporating the new high nitrogen compound BTATZ (C4H4N14) 

(Table 3) appear to provide increased means for reducing propellant combustion temperatures 

while maintaining agent delivery rates at levels sufficient for rapid flame extinction. Preliminary 

ballistic testing (Figure 4) indicates that burn rates may be maintained within workable 

constraints at the same time that exhaust temperatures are reduced as much as 30 % below 

current baseline levels. 

The preparation of BTATZ has progressed to the kg scale, with a purity of 97 % to 99 %. Scaleup work on propellant batches approaching the 10 L scale has proven successful. Further safety 

data on BTATZ shows acceptable friction and impact sensitivity but some sensitivity to 

electrostatic initiation. When formulated into a molding powder with poly(ethylacrylate), 

electrostatic sensitivity is still a concern, even when 0.5 % carbon black is added. However, 

when pressed into pellets or deposited as a thin layer the material meets the criteria set for 

routine handling of energetics. 

Chemical additives (or their precursor) were blended directly into the propellant for SPGG (or 

HFE) delivery, or the additive (or precursor) was blended directly into the hybrid fluid for HFE 

delivery. Several compositions were developed such that a common composition “family” 

evolved having different levels of additive. 

9 
Table 3. Propellant Physical Properties 

Descriptors Major Constituents(a) Tc

(K) 

Gas 

(mol/100g)

Theoretical Density 

(g/cc)

BR1000

(in/s)

BTATZ KP BTATZ-5AT KP 1961 4.12 1.72 1.31

BTSN-00 BTATZ Sr(NO3)2 2774 2.27 2.38 1.09

BTSN-10 BTATZ Sr(NO3)2 2562 2.12 2.43 TBD

BTSN-20 BTATZ Sr(NO3)2 2258 2.00 2.49 0.75(b)

BTSN-30 BTATZ Sr(NO3)2 1890 1.89 2.55 TBD

BTSN-40 BTATZ Sr(NO3)2 1503 1.79 2.61 0.35(c)

BTSN-50 BTATZ Sr(NO3)2 1444 1.54 2.67 0.15

Aerojet-04 5AT Sr(NO3)2

MgCO3 K2CO3

1445 1.61 2.54 0.56

Aerojet-05 5AT Sr(NO3)2

MgCO3 K2CO3

1444 1.81 2.54 0.55

Aerojet-06 5AT Sr(NO3)2

MgCO3 KNO3

1445 1.78 2.36 0.41

(a) The balance remaining in each formulation is made up of coolant, binder, opacifier and process aid.

(b) Reported burn rate corresponds to 17% coolant composition.

(c) Reported burn rate corresponds to 34% coolant composition.

Figure 4: Plot of Adiabatic Agent Temperature and Burn Rate vs. Coolant Level

10 
Fire Suppression Testing. The mid-scale Fire Test Fixture (FTF) developed by Aerojet was 

used to test the effectiveness of various agents. The fuel was JP-8, the air flow was 450 g/s, and 

the equivalence ratio was 0.5, resulting in a flame temperature of ca. 1000 K and ca. 700 kW

intensity. The residence time through the fire zone of the fixture was calculated to be 1.2 s and 

the discharge time of the SPGG and HFE units was ca. 100-200 ms. Typical flame 

extinguishment times were shorter, generally ca. 100 ms (Figure 5). The results of testing are 

summarized in Table 4. 

The presence of chemically active additives greatly enhances the fire suppression efficiency of

both SPGG and HFE devices (Figure 6). AEROJET-04 was the most effective solid propellant 

composition tested. This composition incorporates potassium carbonate in its discharge, and is 

ca. 3x more effective per unit mass than the inert baseline FS01-40. Testing with compositions

of lower loading levels of active agent resulted in less effective performance. This indicates that 

the additive loading in AEROJET-04 is at or below the saturation level reported in sub-scale 

testing with numerous other chemically active suppressants. Variation in propellant ballistics 

was examined at several different temperatures and was shown to be on the order of 13 % from

25 °C to 75 °C. 

Figure 5. Fire Out Sequence (Aerojet-04/HFC-227 HFE) 

Fire testing using hybrid fire extinguisher (HFE) configurations showed that “cold soaked” CF3I 

hybrids and other high-boiling agents perform well at low temperatures, their low vapor 

pressures offset by the heating and pressurizing power of the solid propellant driven HFE. FS01-

40/Novec-1230 HFEs were as effective as FS01-40/HFC-227 HFEs on a mass basis. Hence other 

factors (e.g., atmospheric lifetime) may provide the discrimination between their use. 

11 
HFE testing with aqueous agents provided additional insight into necessary levels of active agent 

required to effect suppression. Tests using an inert propellant configuration with pure water were 

found to require higher agent loads than the same propellant plus HFC-227. Testing with FS01-

40/water/potassium acetate HFEs showed a 36 % reduction in the mass needed for flame 

extinguishment. 

This NGP solid propellant technology forms the basis for fire protection products currently 

installed on both the Navy F/A-18 E/F and V-22 aircraft. Advanced fire protection products 

incorporating improvements supported by this NGP project are currently being examined by 

each branch of the U.S. military as well as other government organizations. 

Figure 6. Performance Summary of Fire Testing

12 
Table 4. Suppression Effectiveness Summary

Agent Active 

Additive 

Gas

Fractiona

MW 

(g/mol) 

Mole Active/ 

100 g Discharge 

GG Load 

(g) 

Discharge 

Mass (g) 

Mole Active 

Discharged 

Average 

m-dot (g/s) 

SPGG RESULTS

FS01-40 - 50 % 30 0 347 173.5 0 868

A-02 KI 50 % 30 0.26 (K) 157 78.5 0.199 393 

A-04 K2CO3 50 % 30 0.29 (K) 105 52.5 0.152 263 

A-05 K2CO3 50 % 30 0.15 (K) 157 78.5 0.110 393 

A-06b K2CO3 50 % 30 0.29 (K) 105 52.5 0.152 263 

HFE RESULTS 

FS01-40/ 

HFC-227 - 95 % 170 0 358 340.1 0 1701

A-02/

HFC-227 KI 95 % 170 0.019 (K) 228 216.6 0.040 1083 

A-04/

HFC-227 K2CO3 95 % 170 0.021 (K) 228 216.6 0.046 1083 

FS01-40/ 

HFC-227 

KHCO3

KHCO3 95 % 170 0.021 (K) 265 252 0.052 1260 

FS01-40/ 

HFC-227 

NaHCO3

NaHCO3 95 % 170 0.021 (Na) 228 216.6 0.039 1083 

FS01-40/ 

CF3I CF3I 95 % 196 0.46 (I) 98 93 0.43 450 

A-02/

Waterc KI 95 % 18 0.019 (K) >358 - - - 

A-04/

Waterc K2CO3 95 % 18 0.021 (K) >358 - - - 

FS01-40/ 

Water 

KOAc 

KOAc 95 % 30 0.46 (K) 228 216.6 0.96 1083 

FS01-40/ 

HFE-7100c - 95 % 250 0 >358 - - -

FS01-40/ 

Novec 1230 - 95 % 316 0 358 340.1 0 1701

a

 Assuming all of the Hybrid fluid is vaporized. 

b

 KNO3 as additive in propellant blend rather than K2CO3. Upon combustion K2CO3 is produced. 

c

 Fire was not able to be extinguished using same amount of agent as FS01-40/HFC-227 HFE.

13 
2. Dispersion of Suppressants at Low Temperature 

Based on prior TDP and NGP work, there is reason to believe that fluid suppressants with 

boiling points considerably higher than that of halon 1301 (-58 °C) might not disperse efficiently 

throughout the volume of a cold nacelle or dry bay (ca. -40 °C; see above). Experiments using 

fluids with differing boiling points are continuing to explore the temperature regime where 

difficulty might be encountered. 

The initial experiments involved examination of CF3I (boiling point of -22 °C) discharges in a 

simulated engine nacelle (Figure 7) under different thermal conditions: a low temperature of -40 

oC and an ambient temperature of 22 oC. The measurements were made using two UV/VIS 

fiber-optic spectrometers. The initial time (t = 0) in Figure 8 corresponds to the initiation of the 

agent release. The data indicate two findings: 

• Inefficient dispersion should be expected when discharging a suppressant fluid into a 

system whose temperature is well below the fluid boiling point. In the low temperature

release shown here, much of the liquid deposited on the nacelle floor and evaporated over 

many seconds. 

• 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. 

Similar examination of compounds with other boiling points will complete this effort in the 

coming year. 

14 
Figure 7. Schematic of the Simulated Engine Nacelle Test Facility

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

Figure 8. Concentration Profiles of CF3I in the Engine Nacelle Simulator

0

5

10

15

20

0 5 10 15 20 25 30

Room temperature release, forward port

Room air / Cold agent release, forward port

Cold temperature release, forward port

Volume Fraction (%)

Time (s)

0

5

10

15

20

0 5 10 15 20 25 30

Room temperature release, aft port

Room air / Cold agent release, aft port

Cold temperarure release, aft port

Volume Fraction (%)

Time (s)

15 
3. Suppressant Dynamics in Engine Nacelles 

Guidance on preferred locations for and styling of suppressant discharge can best be developed 

from validated computer modeling of the process. 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. 

Droplet Flow Around Obstacles. Existing apparatus was re-oriented horizontally to enable 

collection of liquid agent that drips off of the obstacle and to prevent liquid droplets downstream

of the obstacle from falling back upstream into the oncoming stream (Figure 9). The agent used 

in this phase of the study was water. The flow field, seeded with fine water droplets (ca. 1 μm 

diameter) to enable characterization using a three-dimensional particle image velocimetry (PIV) 

system, was also recorded with a digital movie camera. Measurements were carried out with 

two obstacles: 

• an aluminum cylinder of 32 mm diameter (larger than the turbulence length scale) and 

305 mm length (Figure 10), with measurements made at both 296 K and 423 K, and 

• a body-centered cube (BCC) arrangement of wooden spheres and connecting posts 

(Figure 11), whose flow blockage fraction was about 0.64. 

Figure 9. Apparatus Schematic for Droplet-laden Turbulent Flow Field 

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

atomizer

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

atomizer

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

atomizer

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

atomizer

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

atomizer

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

air

liquid

agent

honeycomb

distributor grid

spray

heated obstacle

plexiglas chamber

collector

collector (pan)

exhaust

seeding

agent

atomizer

16 
Figure 10. Heatable Cylinder. a: Schematic; b: Photograph 

cont

aluminum rod heater

thermocouples

roller

data acquisition

305 mm

13 mm 32 mm

aluminum rod heater

thermocouples

roller

data acquisition

305 mm

13 mm 32 mm

aluminum rod heater

thermocouples

roller

data acquisition

305 mm

13 mm 32 mm

aluminum rod heater

thermocouples

roller

data acquisition

305 mm

32 mm

aluminum rod heater

thermocouples

roller

data acquisition

305 mm

13 mm 32 mm

a

b 

heater wires 

controller

thermocouple for set 

point temperature 

17 
Figure 11. Schematic of Body-centered Cube Obstacle 

streamwise flow

direction

streamwise flow

direction

2828 mm 

24 m4 mmm

Photographs of the observed droplet transport are shown in Figure 12. The three components of 

droplet velocity for the flow over the unheated cylinder are presented in Figure 13. Comparison 

of the two cases with spray to the seed-only case indicates that the recirculation zone is larger for 

the spray cases. Larger size droplets require a longer distance to interact with the turbulent flow 

field, to reduce their higher momentum, and to be entrained into the recirculation zone, if at all. 

Dispersion of droplets/particles around the obstacle is dependent on its size. Fine droplets were 

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. [The droplet size in the region around the cylinder will be measured in the 

next phase of the work using phase Doppler interferometry.] Even with nearly two thirds of the 

flow path blocked by the BCC, only about 5 % of the (large droplet) inlet water flow impacted 

the surfaces and dripped into the collector. An even lower fraction was observed for the 

cylinder. Nonetheless, significant spray cooling of the surface was observed for the heated 

cylinder. 

The research is continuing with sprays of two additional fluids: HFE-7000 (boiling point of 307 

K) and HFE-7100 (boiling point of 334 K). Phase Doppler interferometry will be used to obtain 

spatial profiles of the droplet size and velocity distributions, and number density, and allow 

comparison of the different liquid physical properties to droplet transport processes. 

18 
Figure 12. Photographs of Flow Fields Around Unheated Obstacles. a: 

Seed/Droplet-laden, Unheated Cylinder; b: Droplet-laden, Unheated Cylinder; c: 

Seed/Droplet-laden, Body-centered Cube. Flow is from Right to Left. 

c 

b

a

19 
Figure 13. Variation of Mean Streamwise and Cross-stream Velocities with 

Downstream Distance for the Unheated Cylinder (Black Circles). The black 

contours represent traces of the in-plane velocity vectors. 

20 
Spray-Clutter Interactions. For the next step in complexity, we modified a low-speed flow 

visualization tunnel to investigate liquid fire suppressant spray dynamics in the presence of 

generic clutter (Figure 14). This included the fabrication of an additional flow section and 

installation of interchangeable turbulence-generation grids, a newly developed suppressant spray 

nozzle, and an adjustable array of three banks of cylindrical clutter elements. The new 1.23 m (4 

ft.) section, mounted upstream of the existing 2.44 m (8 ft.) long test section, has two transparent 

surfaces, top and side, which enable optical measurement access to the spray and clutter 

elements. A top speed approaching 12 m/s (39.4 ft/s) has been achieved. New software will 

provide data on the energy spectrum, power spectral density, and signal autocorrelation. 

Figure 14: Suppressant Spray Flow Facility

ocumentation of the dual-fluid spray nozzle has been completed using a three-dimensional 

tion

acelle Simulator. Figure 15 shows the full-scale F/A-18 E/F Nacelle Ground Test Fire 

e air

n 

ere

lified 

will be given to an improved model.

D

particle dynamics anemometer (PDA). The dependency of data accuracy on optical configura

is not well documented, so the current measurements represent the state of the art. Flow 

visualization of the patterns in and around the clutter elements were then obtained. 

N

Simulator that will be the eventual test bed for the predictions of suppressant dispersion. Th

inlet source is seen in the lower left corner, with the air flowing into the bottom of the nacelle. 

There are two vents in the top and four exit holes in the front face. The various internal ventilatio

paths have been sized to provide the flow distributions predicted in an airflow analysis conducted by

Northrop-Grumman. Therefore this simulator is designed for testing at one flight condition: the 

aircraft traveling at 0.55 M at sea level. Given this restriction, three flows were selected to 

correspond to high speed, high altitude cruise; loiter; and precision approach. These flows w

derived from flight tests of the F/A-18 C/D, from which data for the E/F aircraft were scaled. 

Input/output air flow measurements were completed for each of these (without a fire). A simp

model was developed to estimate the overall flow and average pressures for any desired future test 

conditions. It is difficult to predict the pressure distribution inside the nacelle, and consideration 

21 
Figure 15. F/A-18 E/F Nacelle Ground Test Fire Simulator, Port Side 

ind Tunnel Data. NGP staff have compiled a large amount of data needed as input to the 

odeling of the Simulator: 

 

o cribing

e interaction of sprays with objects in the flow has been formulated for use with the VULCAN 

,

s

s

t

W

m

• Wind tunnel turbulence data to characterize the tunnel for the clutter models and 

• Coefficient of drag by momentum balance for all the three-dimensional clutter. 

C

th

mputer Modeling and Simulation. A preliminary phenomenological model des

spray model. The fate of particles impacting a surface is known to depend on the impact energy

and the impact model accounts empirically for energy lost in the impact, providing a post-impact 

kinetic energy for particles that bounce off or shatter on the surface. The model has been 

evaluated using HFE-7100 as the fluid (Figure 16). Initial particle velocities are slow, and 

droplet bouncing is the prevalent behavior. Because the inlet flow is turbulent, the particle

deviate from the centerline, and post-bounce particles exhibit a range of transverse velocitie

including negative rebound. Because the mean flow is upward, drag causes the particles to 

accelerate. However, the rebound results in most particles exiting the sides of the domain, and

the number of particles convected through the wake is observed to be small. Results differen

from those in Figure 16 are found in simulations for different initial droplet velocity and size 

distributions. Results range from droplets sticking to the cylinder to droplets shattering upon 

impact into smaller droplets. 

22 
Figure 16. Particle locations and velocities during the impingement of a 1 mm 

HFE-7100 droplet stream on a cylinder. [Actual number of droplets simulated is 

orders of magnitude greater than shown, and particle sizes are exaggerated for 

visibility.]

A numerical study of flow past a rib protruding from a wall was conducted to analyze the 

effectiveness of the subgrid clutter model. Results are used to evaluate clutter-induced changes 

in turbulent energy and its dissipation rate. Simulations were conducted with a pool fire near the 

end of the recirculation zone that exists behind the rib. Figure 17 shows temperature contours 

for the pool fire both with and without the rib. Results indicate that the fire is convected 

upstream through the recirculation zone and that the fire zone behind the rib is significantly 

wider than the pool itself because of the secondary flow generated by the pool fire. The existing 

VULCAN suppression model was used to simulate the suppression of this flame. Some changes 

were made in the VULCAN suppression model because the original version was too 

conservative and predicted suppressant requirements well in excess of requirements observed 

experimentally. This work has also identified necessary extensions to the clutter model to 

account for the flame stabilization effect. This work will continue to take advantage of empirical 

correlations for transport of suppressant into recirculation regions behind steps developed as part 

of earlier NIST (Gann, 1995) and NGP efforts (Takahashi et al, 1998). 

23 
Figure 17. Temperature Contours for a Pool Fire with (right) and without (left) a 

Small Rib (1/16 of the Wind Tunnel Height). The Rib Acts to Create Recirculation 

Zones that Stabilize the Flame and Draw it Upstream. 

 

Pool fire 

generates 

4. Enhanced Powder Panels for Dry Bay Fire Protection 

Powder panels have been applied to the lining of aircraft dry bays to provide passive, 

lightweight, effective fire protection against ballistic impact. Projectile penetration of the dry 

bay and adjacent fuel tank releases agent from the powder panel into the fire zone to inert the 

space before the adjoining fuel spills into the space and is ignited by incendiaries. An NGP 

survey indicates that U.S. fixed wing aircraft do not employ powder panels, but there is growing 

interest. Their use in rotary wing aircraft is established. Currently, the Navy UH-1Y Huey and 

AH-1W Super Cobra aircraft operate with powder panels. AH-1W and UH-1N legacy aircraft 

are being upgraded to the AH-1Z Super Cobras, which uses powder panels for dry bay 

protection. The V-22 Osprey tiltrotor aircraft uses powder panels extensively. Evaluations have 

also been conducted recently for integrating powder panels into the AH-64 Apache and the 

RAH-66 Comanche helicopters. 

NGP success with enhanced powder panel designs has sparked interest by several aircraft 

programs. As a result, NGP researchers have entered into proprietary rights agreements with 

Bell Helicopter Textron, Inc./The Boeing Company and Sikorsky Aircraft Corporation/The 

Boeing Company to discuss the possibility of integrating enhanced powder panels into aircraft

such as the V-22 and RAH-66. These agreements allow for the free exchange of design details 

and production or qualification requirements that may be levied on newly developed panels. In 

addition, discussions have been held recently with F-35 Joint Strike Fighter engineers to apprise 

them of recent enhanced powder panel developments for dry bay fire protection. 

24 
In addition, under sponsorship of the DoD Joint Technical Coordinating Group on Aircraft 

Survivability (JTCG/AS), NGP researchers participated in live fire proof-of-concept testing in 

early FY2002. The tests examined the concept of reactive powder panels that add an energetic 

backing to any powder panel design to enhance powder delivery effectiveness. Four tests of 

enhanced powder panels without reactive backing were conducted, demonstrating their 

capability to prevent dry bay fires in tests involving JP-8 fuel and 12.7mm Armor Piercing 

Incendiary Projectiles. Figure 18 compares the amount of fire extinguishing powder released 

from an enhanced powder panel with a commercially available powder panel. Figure 19 shows 

some images captured from high-speed video demonstrating the fire mitigation capability of 

enhanced powder panel designs. 

Figure 18. Comparison Of Commercial And Enhanced Powder Panel Agent 

Release In JTCG/AS Dry Bay Fire Extinguishing Testing 

Commercial Powder Panel

~5-10% Powder Release

Enhanced Powder Panel

~90% Powder Release

Additional examination of NGP enhanced powder panel designs was conducted by the Federal 

Aviation Administration (FAA). They were interested in the feasibility of using powder panels 

to prevent commercial aircraft fuselage fires caused by the impact of an uncontained engine rotor 

blade with flammable fluid lines. Figure 20 shows that impact of the enhanced powder panel by 

a rotor blade resulted in release of all the fire extinguishing agent, as it prevented a fire ignition. 

Baseline testing showed that unprotected fuselage areas did indeed result in sustained fires. 

25 
Figure 19. Enhanced Powder Panel Fire Mitigation Capability Demonstrated 

Fire

Prevented

Dry Bay Engulfed

in Powder

Enhanced

Powder Panels

Incendiary

Function

Fire

Ignition

Fire

Sustains

Incendiary

Function

Commercial

Powder Panels

Figure 20. Post-test Remains of Enhanced Powder Panel Showing All Powder 

Released (Fire Prevented) 

In both the JTCG/AS and FAA test programs, the NGP enhanced powder panels showed a vast 

improvement over current powder panel designs. Fire ignition was prevented in all five tests 

involving enhanced powder panels. These tests will be documented in the NGP Enhanced 

Powder Panel Final Report. 

26 
Meanwhile, the NGP continues experiments to examine means for effecting: 

• Greater powder release into dry bay 

• Better dispersion of powder to prevent ignition off-shotline 

• Longer powder suspension to prevent fire ignition for longer period of time

• Design flexibility of enhanced powder panels which can be utilized to target weight, 

durability, and application-specific design goals 

Optimization test variables include panel materials and thicknesses, fire extinguishing powder 

loading (density of powder inserted into a given panel size), rib designs, and the assembly 

process. The project will conclude with live fire demonstration tests of the optimized powder 

panels at the Air Force 46th Test Wing Aerospace Vehicle Survivability Facility, WrightPatterson Air Force Base. 

5. Mechanisms of Unwanted Accelerated Burning 

In real-scale fire suppression tests, the operators have observed flare-ups of the fire and pressure 

surges as the agent is applied. If experienced during flight, this could have a negative effect on 

aircraft survivability. 

The cause of this phenomenon appears to be enhanced combustion of vaporizing liquid fuel that 

mixes with air more efficiently in the turbulence accompanying suppressant delivery. To 

understand this process, NGP staff analyzed three sets of fire suppression tests, one in an aircraft 

dry bay and two in large compartments. The three cases varied in the timescale of the 

suppression events and the geometric configuration of the experiments, yet in all cases a volatile 

liquid was the fuel. When wood was substituted for the liquid fuel in one of these series, the 

large pressure fluctuations were not observed. 

In the first series of enclosure fires2

 significant fire flare-up and pressure increases were observed 

for HFC agents, water mist, and hybrid agents involving HFC/powder mixtures. All the 

deflagrations observed were in the presence of a hot (~550 oC) ignition source. The 

investigators suggested that these unwanted burning effects occurred when there was insufficient 

suppressant to assure quenching and prevention of re-ignition. In this sense, unwanted 

accelerated burning effects are already embedded in the resulting design equations.

The second case study examined suppression of moderate-sized (~400 kW) heptane pool fires in 

an enclosure.3

 Figure 21 shows that calculations using the NIST Fire Dynamics Simulator (FDS) 

show pressure fluctuations similar to the experimental observations. Figure 22 is a snapshot of 

the simulation showing the fire and temperature-colored velocity field just as an inert 

suppressant was released from the ceiling of the room. 

27 
Figure 21. Comparison of the Room Pressure Measured Experimentally (Left) and 

That Calculated Using FDS (Right) 

-20

-10

0

10

20

30

40

50

-20 0 20 40 60 80 100

Time After Agent Discharge (s)

Room Pressure (mm H2O)

-20

0

20

40

60

80

-20 0 20 40 60 80 100

Room Pressure (mmH 2O)

Time after Agent Discharge (sec)

(a) Agent: IG-55

Fire source: n-heptane

0.3m 2 (420 kW) 

Door closed.

Figure 22. FDS Calculation Showing the Fire and Temperature-Colored Velocity

Field of the Suppression of a Heptane Pool-Fire in an Enclosure 

The third case was the unanticipated over-pressurization that destroyed a C-130 Wing Leading 

Edge Dry Bay Test Facility during real-scale fire suppression testing. Six tests previous to the 

catastrophic event using N2-pressurized HFC-125 had led to routine suppression results. The 

seventh test was designed to test the impact of the N2 used for pressurization on the fire. The N2

concentration was 0.4% of the cup burner value, an amount that would have little impact on the 

stability of the fire and certainly would not extinguish the fire. The fire scenario was extremely 

complex due to the presence of a ballistic round, accompanying shock waves, fuel splashing 

28 
(two-phase flow), multiple ignition sources (hot shrapnel), etc. To better understand the 

conditions in the dry bay during fire suppression, an analytic approach was taken to simulate the 

pressure in the enclosure. Two salient results emerged: 

• Only a small difference in the sensible enthalpy release could have caused failure of the 

fixture and 

• The pressure rise is larger for smaller vent sizes (small diameter projectiles). 

The most important overall finding from analysis of these three cases is that the over-pressure 

risk is low unless insufficient amounts of suppressant are applied to a fire. The viability of 

design equations derived from full-scale tests hinges on the assumption that the tests are 

representative of the range of actual fire conditions. The fire conditions in full-scale suppression 

tests should be carefully designed to be worst-case, or else extreme or unanticipated unwanted 

burning effects may occur in actual applications. 

6. Enhancing Engine Nacelle Extinguishment with Intumescent Coatings 

Quenching a fire in an engine nacelle requires maintaining a sufficient concentration of agent in 

the flame zone for a sufficient time interval. This must be accomplished while a forced air flow 

through the nacelle (to prevent the accumulation of any flammable vapors, and possibly also 

provide some machinery cooling) serves to sweep the suppressant out the exhaust. 

The NGP had pioneered the novel approach of using strategic placement of an intumescent 

material to reduce the cross sectional area of the nacelle in the event of a fire. This “instant 

firewall” allows achieving the needed residence time with a smaller amount of suppressant. 

 

Now, a project funded by the Joint Technical Coordinating Group on Aircraft Survivability 

(JTCG/AS) will demonstrate and optimize the use of these intumescent materials, and identify

and evaluate the potential for use on unmanned aerial vehicles, rotorcraft, and other customers 

needing low-cost protection. 

The first phase of the project is already underway, evaluating the expansion ratios and response 

times of candidate intumescent materials and designs in a mini-nacelle fire test fixture. 

Successful candidates will then be tested in a full-size mock-up of an X-45 UCAV engine 

nacelle supplied by Boeing Aerospace, the manufacturer of the X-45 UCAV. 

Recent Publications: Improved Suppressant Delivery

(* indicates archival publications) 

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

Simulated Aircraft Engine Nacelle,” Proceedings of the 2002 Halon Options Technical Working

Conference, NIST Special Publication 984 (CD), National Institute of Standards and 

Technology, Gaithersburg, MD, 2002. 

29 
*Yang, J.C., Manzello, S.L., Nyden, M.R., Connaghan, M.D., “Cold Discharge of CF3I in a

Simulated Aircraft Engine Nacelle,” Proc. Seventh International Symposium on Fire Safety

Science, Worcester, MA, June 16-21, 2002. 

Dolinar, J., Hudgins, D., and Keyser, D.R.,” F/A-18 E/F Nacelle Simulator Input/Output 

Boundary Condition Flows,” Report NAWCADPAX/SUM-2002/171, 2002. 

Black, A.R. et al, "Numerical Predictions and Experimental Results of Air Flow in A Smooth 

Quarter-Scale Nacelle," Sandia National Lab Report SAND2002-1319, 2002. 

DesJardin, P.E., et al., “On the Development of a Subgrid Model for Clutter,” AIAA2002-0984, 

40th AIAA Aerospace Sciences Meeting and Exhibit, Reno, NV, 2002. 

Black, A.R. et alia: "Numerical Predictions and Experimental Results of Air Flow in A Smooth 

Quarter-Scale Nacelle", AIAA2002-0856, 40th AIAA Aerospace Sciences Meeting and Exhibit,

Reno, NV, 2002 

Presser, C., Widmann, J.F., DesJardin, P.E., and Gritzo, L.A., “Homogeneous Turbulent Flow 

over a Cylinder: Measurement and Numerical Prediction,” AIAA 2002-0905, Am. Inst. Aero. 

Astro., Washington, DC, 2002. 

Presser, C., Widmann, J.F., and Papadopoulos, G., "Liquid Agent Transport Around Solid 

Obstacles," Proceedings of the 2002 Halon Options Technical Working Conference, NIST 

Special Publication 984 (CD), National Institute of Standards and Technology, Gaithersburg, 

MD, 2002. 

DesJardin, P.E., Presser, C., Disimile, P.J., and Tucker, J.R.., "A Droplet Impact Model for 

Agent Transport in Engine Nacelles," Proceedings of the 2002 Halon Options Technical 

Working Conference, NIST Special Publication 984 (CD), National Institute of Standards and

Technology, Gaithersburg, MD, 2002. 

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

Homogeneous Turbulent Flow over a Cylinder," 41st AIAA Aerospace Sciences Meeting & 

Exhibit, Reno, NV, accepted, 2003. 

Presser, C., Papadopoulos, G., and Widmann, J.F., "Droplet_laden Homogeneous Turbulent 

Flow past Heated and Unheated Cylinders," 4th ASME/JSME Joint Fluids Engineering Conf., 

Honolulu, Hawaii, accepted, 2003. 

Cyphers, D. C., Frederick, S. A., and Haas, J. P., "Enhanced Powder Panels," Proceedings of the 

2002 Halon Options Technical Working Conference, NIST Special Publication 984 (CD), 

National Institute of Standards and Technology, Gaithersburg, MD, 2002. 

30 
C. VIABILITY OF NEW SUPPRESSANT TECHNOLOGIES 

1. Benefit Assessment of Fire Protection System Changes 

Both objective cost factors and subjective value factors must be considered when making a 

decision on whether and how to retrofit a fire suppression system. Accordingly, the NGP has 

developed a methodology (Figure 23) to quantify a fire suppression technology by its total, life 

cycle cost and to enable superimposing on this a subjective value system. The purpose is to 

provide a means of identifying a halon alternative agent/system option that provides the best 

cost-of-ownership value to specific aircraft customers over the operating lifetime of their 

platform. 

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 developed 

examples: 

• compare an existing halon 1301 system and a system of equivalent and altered 

performance using an off-the-shelf-alternative, HFC-125; 

• include both legacy platforms (for decision makers who must consider retrofit costs for 

existing platforms) and future platforms (for decision makers currently designing new 

platforms); and 

• apply to engine nacelle applications for representative and rotary wing aircraft in 

addition to the cargo and fighter aircraft present in last year’s Annual Report. 

In all cases, the benefit of having either fire protection 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. 

Using the rotary wing aircraft fire suppression system cost and cost savings information, the 

following conclusions were reached: 

• Even if the rotary-wing aircraft fire suppression system only saved eight percent of the

aircraft assets it was designed to protect, the benefit (assets saved) would still be greater than 

the cost of the fire suppression system. 

• Using a conservative value of 60 percent fire suppression system effectiveness, a system cost 

of up to $307K per aircraft could be justified. Note that the current as well as forecast fire 

suppression system costs per aircraft are an order of magnitude less than this value. This 

value is a breakpoint between system cost and benefit. 

 

The U.S. Army is now using this methodology, in concert with the baseline cases for halon 1301 

and HFC-125, as part of their evaluation of three additional fire suppression alternatives (CF3I, 

Novec 1230, and gas generators) for the Comanche rotorcraft. This same model will be used by 

the Army Chinook, Apache and Blackhawk rotorcraft Programs for their retrofit selection 

criteria. 

31 
Figure 23. Life-Cycle Cost Estimating Process 

Life-Cycle

Cost Estimating

Process

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

2. Suppressant Concentration Measurement for Real-scale Fire Tests 

A user’s guide to the Differential Infrared Rapid Agent Concentration Sensor (DIRRACS-2) is in

final preparation. It contains a description of the device, its potential for use in both fire tests and 

system certification, detailed operating procedures, components list, etc. Before release the 

Guide will be evaluated by an inexperienced user to promote its utility by the engineering 

community. 

Recent Publications: Viability of New Suppressant Technologies 

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

the 2002 Halon Options Technical Working Conference, NIST Special Publication 984 (CD), 

National Institute of Standards and Technology, Gaithersburg, MD, 2002. 

32 
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 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. 

They then offered 19 specific recommendations, all of which have been incorporated into the 

NGP. 

The final report of the IRP is attached as Appendix B and the implementation response by the 

NGP is attached as Appendix C. 

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 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. 

33 
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 Conference 

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. 

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 

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. 

2

 Maranghides, A., and Sheinson, R.S., “Deflagration Induced During Total Flooding Halon 

Replacement Suppression,” Fire Safety Science-Proceedings of the Sixth International 

Symposium, IAFSS, p.1199, 2000. 

3

 Kashiwagi, H., Oshikawa, S., Yui, J., Fujii, M., Kitano, J., Shiga, A., and Saso, Y., “Effect of 

Fire Size on Suppression Characteristics of Halon Replacement Total-Flooding Systems,” 

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

272-281, 2001, and companion report, “Report of the Research Committee for Establishment of 

Safety Standards on Halon Replacement Agents,” Fire and Disaster Management Agency and 

the Japanese Fire Equipment Inspection Institute, 2000.

34 
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; 

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/15/01. TROPODEGRADABLE BROMOCARBON EXTINGUISHANTS 

Principal Investigator: J. Douglas Mather, NMERI 

COR: Ronald Sheinson, NRL 

35
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/5/012. ALTERNATIVE SUPPRESSANT CHEMICALS 

Principal Investigator: Richard Gann, NIST 

4B/6/2 ENVIRONMENTALLY ACCEPTABLE SUPPRESSANTS 

 Principal Investigator: Douglas Mather, NMERI 

 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

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 

36
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 

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

GENERATORS 

Principal Investigators: Gary Holland, General Dynamics; Russell 

Reed, NAWC-WPNS 

COR: Richard Gann, NIST 

5E/1/12. ENHANCED POWDER PANELS 

Principal Investigator: Dan Cypher, Skyward, Inc. 

COR: Martin Lentz, Eglin AFB 

6A/1/012. FIRE SUPPRESSANT DYNAMICS IN CLUTTERED WEAPONS 

SYSTEM COMPARTMENTS 

 Principal Investigator: David Keyser, NAVAIR 

37
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

F. FUEL TANK INERTION 

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

Principal Investigator: Leonard Truett, Eglin AFB 

 

38
APPENDIX B. REPORT OF THE INDEPENDENT REVIEW PANEL

REPORT OF THE 2001 INDEPENDENT REVIEW PANEL 

ON THE

NEXT GENERATION FIRE SUPPRESSION TECHNOLOGY 

PROGRAM (NGP)

February, 2002 

_________________________ 

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 

39
REPORT OF THE 2001 INDEPENDENT REVIEW PANEL (IRP) 

ON THE 

NEXT GENERATION FIRE SUPPRESSION TECHNOLOGY PROGRAM (NGP)

This report summarizes the general comments and recommendations of the IRP. For comments 

and recommendations for individual NGP projects, see the attached Appendix A. 

INTRODUCTION 

The Department of Defense (DoD) Strategic Environmental Research and Development Program

(SERDP) has been supporting a multi-year interagency effort to develop new fire-suppression 

chemicals, techniques, and systems to replace halon fire extinguishing agents in DoD weapon 

systems. The SERDP initiative, the Next Generation Fire Suppression Technology Program

(NGP), targets the halons because of their recognized high ozone depletion potential and the 

resultant adverse influence on stratospheric ozone. 

An Independent Review Panel (IRP) was commissioned by the NGP Technical Program

Manager at the suggestion of SERDP to assess progress to date in the NGP program and to 

recommend changes to the program or 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 convened coincident with the 

NGP annual review meeting on December 18-19, 2001. The IRP encompassed an array of 

expertise and experience from university, government, and industry environments. 

This report summarizes the findings of the IRP. This NGP program evaluation was based on the 

present research status as seen as a snapshot through the annual review meeting in the context of 

the history of the research, the SERDP goals, and the collective expertise imbedded in the IRP. 

BACKGROUND 

Research to find alternative technologies to replace halon fire extinguishing agents has been but 

one of many efforts over the past 15 years to reduce or eliminate emissions of substances with 

high ozone depletion potential. However, the specific requirements associated with fireextinguishing agents for military weapons systems have proven refractory in many applications. 

These applications are characterized by the unusual convergence of three issues: 

1) Threat of immediate loss of life due to proximity of fire to personnel and flight critical 

systems; 

2) High-energy environment associated with substantive quantities of fuel and flammable 

fluids, weapon explosives and propellants, and kinetic energy levels of the weapons 

platform along with threats and targets; and 

3) Severe retrofit constraints due to weight and space limitations on legacy systems 

(especially true of airborne systems). 

40
In addition to these major considerations, there are issues of replacement agent toxicity and 

corrosivity, material compatibility, cost, and agent effectiveness throughout the operating 

environment. With alternate technologies such as solid gas generators and powder panels, the 

same or similar issues need to be considered. 

The original NGP goal was to “develop and demonstrate, by 2004, retrofitable, economically 

feasible, environmentally acceptable and user-friendly process, techniques, and technologies that 

meet the operational requirements currently satisfied by halon 1301 systems in aircraft, ships, 

land combat vehicles, and critical mission support facilities.” This program was originally 

expected to be an 8-year program with funding peaking at about $7 million per annum. In 

actuality, the funding is presently running at about $1 million per year with a slightly protracted 

time duration. This reduction has forced considerable contraction in the goals that would be 

realistically attainable. The present program focus is now almost exclusively on solutions for 

aircraft fire protection, especially for engine nacelles. 

In both U.S. military and commercial aircraft, the dominant type of engine nacelle fire protection 

system involves the high rate discharge of halon 1301. While there have been a limited number 

of system designs with other agents like CB, halon 1211, halon 1011, and halon 2402 in certain 

aircraft, halon 1301 by far comprises the dominant portion of the airborne inventory for nacelle 

applications. “High rate discharge” is aerospace terminology referring to the design 

requirements, which specify that upon discharge, the extinguishing gas sensors throughout the 

nacelle must simultaneously indicate a 6 % halon 1301 concentration for a one-half second 

interval. Historically, the high rate systems replaced less efficient systems involving longer 

duration but lower rate agent discharge into an engine compartment. For the last half century, 

halon 1301 has filled the aircraft engine nacelle niche because of its properties of low toxicity, 

high effectiveness, cleanliness, and high volatility for low temperature operations. To date, no 

“drop-in” replacements have been deployed on an equivalent weight or volume basis. While 

there has been successful testing and deployment of the F/A-18E/F, V-22 and F-22 with HFC125, modest weight penalties and changes to the distribution systems, compared to halon 1301, 

have been accepted. Some helicopters are also considering HFC-125; however, some of these 

replacements involve substituting a two-shot halon 1301 system with a single shot HFC-125 

system to accommodate the larger quantities of HFC-125 needed to reliably extinguish an engine 

nacelle fire.

Because aviation has been exempted from the environmental ban on usage of halon 1301 so long 

as the agent obtained from the bank of existing stockpiles, there has been a tendency in some

quarters to dismiss the earlier urgency attendant on halon replacement research. The present 

quasi-equilibrium with regard to use of the halon bank is susceptible to rapid upset from any 

number of circumstances. An example is the present controversy on whether CF3I should be 

immediately substituted for halon 1301 in F-16 wing tank inerting applications. (The F-16 now 

discharges halon 1301 on each combat sortie to protect the fuel tanks from fire or explosions 

produced by ballistic damage.) In starts and stops, the justifications for continued use of halon 

1301 in aerospace applications appear to be becoming more arguable, and the U.S. 

Environmental Protection Agency support of the exemption is contingent on credible efforts to 

find alternative technologies or chemicals. 

41
DISCUSSION 

The present revised NGP 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.” This goal is 

considerably scaled back from the initial NGP goal quoted in the background section of this 

report. 

The IRP observed that not only are the applications reduced from ships, aircraft, ground vehicles, 

and ground installations to halon 1301 systems in aircraft but also the comprehensiveness of the 

approach to nacelle installations has been affected by the budget constraints. The IRP observed 

that toxicity testing has been all but eliminated, that large-scale demonstrations have been 

minimized, and that the synthesis and screening of new chemicals is at a barely sustainable level. 

The IRP believes that the remaining core of research, if brought to conclusion, can provide a 

product that will enable successful substitutions for halon 1301 in aircraft nacelle applications. 

This belief assumes the research findings will be translated into useable heuristics for design and 

test personnel in government installations and in the aerospace industry. The IRP cautions that 

the research efforts omitted or dropped comprise an “IOU” that is likely to become due in the 

future. Halon 1301 substitutes that are effective in firefighting but less desirable from

standpoints of toxicity and material compatibility may result in future costs associated with 

special handling requirements, revised maintenance procedures, and modified engine system

component specifications. Reduction of full-scale demonstration testing 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. 

During the annual research meeting, the IRP was briefed by the principal investigator of each 

active NGP project and had adequate time and opportunity to ask any pertinent questions. The 

IRP's specific comments and recommendations on each project are documented in the Appendix 

to this report. 

The NGP projects included those seeking and evaluating new agents including tropodegradable 

bromocarbons and phosphorus-containing compounds. Also presented were experimental and 

modeling research on metallic fire suppressants (both transition metal and alkali metals) in 

aerosol and powder form, research on powder panels and on solid propellant gas generators, and 

life-cycle system cost comparisons between various alternate agents and halon 1301 in given 

aircraft model fleets. Finally, a series of projects were briefed that dealt with modeling and 

experimental investigations of atomization and dispersion of aerosols in nacelle type, clutterfilled, ventilated enclosures. These projects were especially relevant to the behavior of higher 

boiling point replacement agents in cold environments. 

It is hard to imagine any viable halon 1301 replacement with lower molecular weight or 

equivalent volatility. Consequently, the issues of dispersion and evaporation of higher boiling 

point liquids gets elevated in importance. Major associated issues are: vapor pressure as a 

42
function of temperature, droplet evaporation times, droplet penetration and residence in fire 

zones, droplet impingement on surfaces, and localized liquid accumulation. These factors all 

come into play in development of heuristics for system design. 

CONCLUSIONS 

The NGP is an excellent example of a government-managed research program. Information 

developed here is likely to be used for decades. This type of research should be managed by the 

government with a large government laboratory role and should not be left to private industry 

alone, although private industry can play an important role. Some of the projects under this 

program may appear to be interesting but not necessarily critical research, but that is not the case. 

This program needs this fundamental science to solve an important real-world problem, and this 

scientific work is being done nowhere else. This program is a well balanced blend of basic 

scientific study and hard headed application. Managers and participants have made excellent 

progress with limited funds, and should be recognized for their efforts. 

The Independent Review Panel unanimously reached the following general conclusions: 

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

and targeted realistically. 

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

quantity exceeding what is considered typical by the review panel for the resources 

available and applied. 

3) Much of the research output has high potential for near-term use in design of fire 

protection systems for aircraft. 

4) With relatively modest adjustments, the review panel concludes that the utility of the 

NGP research findings can be further enhanced. 

The review panel is optimistic that the NGP research is elucidating important mechanisms and 

principles involved in fire suppression. The present NGP emphasis can be considered as focused 

on evaluation of chemical candidates and research on agent delivery. The review panel has used 

these conclusions as the basis from which to derive recommendations that would facilitate 

eventual use of the NGP research findings in practical aerospace applications. 

GENERAL RECOMMENDATIONS 

The Independent Review Panel presents three major recommendations: 

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

engine nacelle fire extinguishing systems, relight of fire after agent delivery has been a 

continuing design, test, and evaluation problem. Experience has shown that even the 

delivery of air through an agent distribution system can sometimes blow out the fire but 

rapid re-ignition is likely to follow. 

43
2) Expand delivery and dispersion research to include additional high boiling point 

compounds in the individual research projects. These compounds could include both 

phosphorus-containing chemicals and tropodegradable bromocarbons. 

3) Request summation sheets on “Lessons Learned” from the principal investigators to serve 

as a starting point for future system design heuristics. These summation sheets should 

cover the best understanding of the knowledge gained and how it might apply to both 

future research efforts and design of fire protection systems. Both positive and negative 

results should be reported. 

The review panel presents three secondary recommendations: 

1) 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. If possible, make this system available to at least one of the largescale engine nacelle test programs planned for 2002. (FAA engine nacelle testing at the 

FAA Technical Center {Doug Ingerson}, and the Army engine nacelle testing at AFRL 

{Jim Tucker}.) 

2) Address directly the issue of gas-phase vapor loading from dispersed aerosols of higher 

boiling point extinguishing agents. At issue are droplet evaporation times, residence 

times, and saturation vapor pressures. Also at issue is whether fine droplets behave as a 

vapor in flame suppression. This is particularly important to evaluators because it is 

frequently cited by advocates of high boiling point fluids in response to expressed 

concerns about low-temperature performance. 

3) Initiate an interim NGP report 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. It is recommended the NGP final report should be designed to 

serve as an interface that could convey the research findings to the user community in 

practical form. Insure that both positive and negative information is included. 

44
REPORT OF THE 2001 INDEPENDENT REVIEW PANEL 

ON THE 

NEXT GENERATION FIRE SUPPRESSION TECHNOLOGY PROGRAM (NGP) 

APPENDIX 

This appendix summarizes the comments and recommendations of the IRP for each individual 

NPG project. For general comments, see the body of the report 

4B/5/01 Assessment of Search for Alternative Chemicals 

This work is a central part of the program. Although no cure-all has been identified, some

potential candidates have been and the search should continue. For the long term, this may well 

be the most valuable or one of the most valuable elements of the NPG program. If any true dropin halon replacement “agent” is ever found it is likely to come from this or related programs. 

The attributes sought and evaluated make sense. The broadness of the search is well justified. It 

is not clear how the list is winnowed. 

4D/14/1 Fluoroalkyl Phosphorous Compounds 

It is essential that this work be completed. Most of the potential candidates appear to have 

relatively high boiling points. If funding allows, related compounds with lower boiling point 

materials should be considered. 

4D/15/01 Tropodegradable Bromocarbon Extinguishants 

It is essential that this work be completed Drawing on the medical database is a valuable 

innovation. The “tropodegradable” concept is a very attractive method of gaining the benefits of 

Br and related compounds without the ODS penalties. The expense of some compounds needs to 

be reconsidered. Although the cost of some of the compounds may stress the R&D budget, 

researchers should be aware that aircraft programs frequently pay premiums in excess of $1,000 

/ pound / aircraft to acquire lighter-weight technologies. 

4B/3/801 Environmental Impact of New Chemical Agents for Fire Suppression 

This project is developing basic information and procedures that support and are essential for 

many of the other projects. It provides a rational basis for avoiding research on alternate 

suppressants that in the end would have to be rejected on environmental grounds. The project is 

exemplary in that the modeling is done in a manner consistent with experimental findings. 

45
4D/13/1 Effective, Non-Toxic Metallic Fire Suppressants 

This work appeared extremely thorough, even though the results are discouraging in light of high 

initial expectations. The IRP recommends enough additional research in this area be done to 

provide a more complete explanation on why the limiting behaviors exist. The IRP believes 

further work should be done with light scattering on additional metallic compounds to see if the 

condensation phenomena observed with iron compounds are generic to other transition metals. 

The IRP further suggests thermophoretic sampling and chemical analysis of the aerosols. 

2B/1/78901 Suppression Effectiveness of Aerosols and Particles 

The IRP viewed this project as having an excellent mix of modeling and experiment. The IRP 

believes this work should be expanded to include some of the higher boiling point replacement 

agents from the other projects as well as solutions of alkali metal compounds in some of the 

higher boiling point liquids. It may be possible to substitute one or more of the high boiling 

point liquids for water in the water mist work, gain the benefits of water mist and some chemical 

activity, yet avoid the problems with water. Some simple corrosion screening analysis or simple 

corrosion screening test for the dry powder aerosols, similar to the environmental screening of 

4B/3/8901, should be considered. 

1C/1/8901 Relative Benefit Assessment of Fire Protection System Changes 

The IRP believes the information developed in this project is essential to implementing alternate 

compounds and technologies into the military aircraft fleet. The IRP believes that rather than 

expanding the project into UAV’s, it is more important to continue cost comparisons for a 

targeted model with a view to getting estimates for an optimized halon 1301 system, a CF3I 

system, and a gas generator system. Note that at least some of the UAV programs are based on 

providing no fire protection systems. 

5E/1/1 Enhanced Powder Panels 

The IRP found the powder panel project an interesting approach to a passive system for dry bay 

protection. Because of the complexity of dry bay ignition phenomena under live fire conditions 

and the many variables involved, the IRP does not consider it feasible to demonstrate a 

developed form of this technology within the time frame remaining for the NGP program. The 

program would have been stronger if past history of an older version of this technology were 

better integrated. Although the passive discharge principle on which this project is based is 

attractive, it is potentially vulnerable to undetected passive failure, hidden corrosion/damage of 

basic structure, and performance variation based on the impact area, the energy of the ballistic 

round, etc. The IRP recommends against renewing this program after the current contract phase 

ends. 

46
6C/1/1 Mechanism of Unwanted Accelerated Burning 

The IRP believes the burning acceleration observed during the application of suppressants can be

of pertinent interest in relation to the mechanisms by which the suppressants act on combustion. 

To date, the phenomena seem to be evidenced more in the suppression of pool fires than in 

nacelle type installations. Nevertheless, this evidence of burning enhancement by physical 

mixing from the suppressant's addition will be of use in planning future experiments on 

suppressant effectiveness. This study has the potential for significantly increasing the 

effectiveness of fire suppression systems. 

The feasibility of verifying the current hypotheses using one or more of the scheduled 2002 

engine nacelle tests (the FAA engine nacelle testing at the FAA Technical Center {Doug 

Ingerson} and the Army engine nacelle testing at AFRL {Jim Tucker}) should be considered.

5D/1/901 Advanced Propellant/Additive Development for Gas Generators 

The IRP view is that past experience with test and evaluation of gas generators as candidates for 

engine nacelle applications has been poor due to high temperatures of the generator products, the 

difficulties in cleaning the residue, and the costs associated with periodic (life-limited)

replacement of the pyrotechnics. Relight has also been a dominant issue in all past nacelle tests. 

The IRP believes the new propellant formulations show clear performance benefits over the 

older formulations, and that the hybrid devices involved in this project demonstrate clear 

possibilities to overcome the past problems with gas generators. 

The IRP recommends: 

a) Further work on the hybrid devices with effort devoted to flame suppression mechanisms

and relight susceptibility. 

b) Emphasis on design concepts to minimize the periodic replacement costs of the 

pyrotechnic elements. 

c) Verification testing to show that “Cooled Soaked” CF3I hybrids (or other high-boiling 

"agents") will perform well at low temperatures.

d) Generation of chamber pressure and burning time variation with temperature for the all 

the propellants being considered. In older propellants, peak chamber pressure variations 

of 4 to 1 over a 135 °F temperature range were reported. 

4B/4/01 Performance Data on Cold Temperature Dispersion of CF3I and on 

Materials Compatibility with CF3I

The IRP considers this work invaluable and recommends that the work be augmented to include 

additional high boiling point candidates from the other projects. The IRP would like to see 

useful heuristics from this project relating agent volatility and drop size distribution to vapor 

phase loading during droplet dispersion. One should consider re-naming this project “Low 

47
Temperature Performance of High Boiling Point Agents” to re-focus the attention of both the 

researchers and the audience interested in more general results. 

The IRP briefing contained no reference to the material compatibility work. The status of the 

material compatibility tasks needs to be clarified. 

6A/1/0 Fire Suppressant Dynamics in the Fire Compartment 

The presented work appears to be a valuable attempt to develop computer sub models that could 

accurately represent small-scale clutter and spray phenomena for use in a larger grid scale 

physics-based computer code. However, the IRP believes the project should be restructured and 

focused to also use the computer capability to develop heuristics that can be applied in practice 

rather than use the project exclusively as a vehicle for developing the computer code as the end 

product. Researchers are encouraged to keep in mind the multiple potential applications for the 

results of this project: 

a) Better scientific understanding of the phenomena (Research) 

b) Guidance for vent and distribution configurations in future tests. (Test) 

c) Potential for future design using a simplified model. (Product Design) 

5A/1/01 Parametric Investigation of Droplet Atomization and Dispersion of Liquid 

Fire Suppressants 

The IRP believes the experimental work is valuable for characterizing droplet behavior in flow 

through a clutter-filled environment. 

IRP recommends: 

a) The addition of at least one additional liquid test candidate to the project with a lower

boiling point than the present two test liquids. 

b) Insure that the size of the droplets tested covers the range of sizes expected in normal 

discharge. 

c) If warranted, recommend modifications to the distribution system, based on the results of 

this study. 

Note: Determining realistic droplet size may become a difficult problem considering the 

variation in “Agent” characteristics, bottle pressure variations as a function of temperature, and 

discharge nozzle variations. If performance is found to be highly dependent on size, and if size 

is found to be highly variable, then this program has discovered a valuable truth, but the 

implications could be serious. 

48
APPENDIX C. RESPONSE TO RECOMMENDATIONS OF THE 2001 NGP INDEPENDENT REVIEW 

#

Recom

men

dation

Response

1 General, 1 Establish a separate project on re-ignition or elevate this issue 

within existing projects. In en

gine nacelle fire extinguishin

g

syste

ms, relight of fire after agent delivery has been a 

continui

n

g design, test, a

nd e

valuation 

problem. Experience has

shown that even the delivery of air through an agent distri

b

ution

syste

m can sometimes blow out the fire but rapid re-i

g

nition is 

likely to follow. 

A 

project in this area will be funded in 

2 General, 2 Expan

d delivery and dispersion researc

h to i

nclude a

dditional

high

boiling

point co

mpounds in the individ

ual research

projects. These co

mpounds co

uld incl

u

de both phosphoruscontaining c

hemicals and tropodegradable bromocarbons. 

Technically, the issue is whether deliveffectiveness fall off as boiling point iboiling co

mpounds have been ad

ded t

FY2002 and will be considered in 6A/

3 General, 3 

Request sum

mation s

heets on “Lessons Learned” from t

he 

pri

ncipal i

nvestigators to serve as a startin

g point for future

system design heuristics. T

hese sum

mation sheets s

hould cover 

the best understan

ding of the knowledge gained and how it 

might appl

y to both future research efforts a

n

d desi

g

n of fire

protection syste

ms. Both positive and negative results should

be

reporte

d. 

Using FY2003 funds, members of the output of prior projects and e

xtract Le

The Princi

pal In

vestigators of current 

do t

he same for t

heir o

ngoing work. T

Manager will then fashion a living rep

4 Secondary 1 Pre

pare a technical information pac

kage to expedite han

d-off of

the portable Differential Infrared Agent Concentration Sensor togovernment agencies, a

nalyzer vendors, a

nd aerospace 

man

ufacturers involved with aircraft exting

uishing system

certification a

nd testing to replace the tra

ditional a

nalyzer used 

for airborne applications. If 

possible, make t

his system

available to at least one of the large-scale engine nacelle testprograms planned for 2002. 

Funds were reprogram

med i

n FY200

The prototype syste

m will be made av

the large-scale engine nacelle test prog2003, if “trai

ning” staff is available. 

5 Secondary, 2 Address directly t

he issue of gas-p

hase vapor loadi

n

g from

dispersed aerosols of hi

g

her boiling point extinguishi

n

g age

nts. 

At issue are dro

plet evaporation times, residence times, and 

saturation vapor press

ures. Also at issue is w

hether fine 

droplets behave as a vapor i

n flame suppression. This is

particularly important to e

valuators because it is frequently cited 

b

y advocates of high boiling point fl

uids in response to

expressed concerns about low-temperature performance. 

This will 

be done using FY2003 fun

ds

49
# Recommendation Response

6 Secondary, 3 Initiate an interim NGP report 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. It is recommended the NGP final report should bedesigned to serve as an interface that could convey the research findings to the user community in practical form. Insure that both positive and negative information is included.

See response to General RecommendaThe NGP Final Report will have a secProgram output. 

7 4B/5/012

Assessment of Search for Alternate Chemicals 

The search should continue. It is not clear how the list is winnowed. 

The project is projected to continue unfamilies have been considered. The alist of families and of chemicals withiNIST Technical Note 1443. 

8 4D/14/1

FluoroalkylPhosphorus Compounds 

If funding allows, compounds with lower boiling point materials should be considered. 

We are already looking for low boilinFY2002 funds. If the precepts for ideto be valid and if lower boiling compothe project will be extended. 

9 4D/15/01

Tropodegradable BromocarbonExtinguishants 

The expense of some compounds needs to be reconsidered.Although the cost of some of the compounds may stress the R&D budget, researchers should be aware that aircraft programs frequently pay premiums in excess of $1,000 / pound / aircraftto acquire lighter-weight technologies. 

Cost is not an issue in looking at posseventual price reduction from commerimpossible to predict. At times, howedifficulty finding someone to synthesicompounds. 

10 4B/3/801

EnvironmentalImpact of New Chemical Agents for Fire Suppression 

Continue. At present, this work has produced gu

volatile halogenated compounds. Ratfamilies systematically and sequentialapplied as needed to compounds for watmospheric and ground effects are in 

11 4D/13/1 Effective, 

Non-Toxic Metallic Fire Suppressants 

The IRP recommends enough additional research in this area bedone to provide a more complete explanation on why thelimiting behaviors exist. The IRP believes further work should be done with light scattering on additional metallic compounds to see if the condensation phenomena observed with iron compounds are generic to other transition metals. The IRP further suggests thermophoretic sampling and chemical analysis of the aerosols. 

The recent experimental work supporthypothesis for the confounding behavwill consider a thermodynamic search which particle formation is unfavorabtemperatures. Positive findings would limited search for the presence of partundergoing suppression. 

50
# Recommendation Response

12 2B/1/78901

SuppressionEffectiveness of Aerosols andParticles 

This work should be expanded to include some of the higherboiling point replacement agents from the other projects as well as solutions of alkali metal compounds in some of the higher boiling point liquids. It may be possible to substitute one or more of the high boiling point liquids for water in the water mist work, gain the benefits of water mist and some chemicalactivity, yet avoid the problems with water. Some simplecorrosion screening analysis or simple corrosion screening test for the dry powder aerosols, similar to the environmental screening of 4B/3/8901, should be considered. 

This project has already indicated that need long residence times for the heat contribute to the flame suppression ef4B/4 & 5A/1 and modeling in 6A/1 wpursuing higher boiling compounds. that alkali metal compounds and their threat to aluminum surfaces.]

13 1C/1/8901 Relative 

Benefit Assessment of Fire Protection System Changes 

The IRP believes that rather than expanding the project intoUAV’s, it is more important to continue cost comparisons for a targeted model with a view to getting estimates for an optimizedhalon 1301 system, a CF3I system, and a gas generator system. 

The purpose of the project is to establestimating the life cycle costs of both platforms. That has been completed, the use of the method. The applicatiomore readily performed by the platforbetter access to the pertinent input dat

14 5E/1/1 Enhanced 

Powder Panels

Because of the complexity of dry bay ignition phenomena under live fire conditions and the many variables involved, the IRP does not consider it feasible to demonstrate a developed form of this technology within the time frame remaining for the NGP program. The program would have been stronger if past historyof an older version of this technology were better integrated. The IRP recommends against renewing this program after the current contract phase ends. 

The current two-year project is directeapproaches to this old concept. When the results will be transferred to platfocommercial product manufacturers, winterest in the preliminary findings. 

15 6C/1/1 Mechanism

of UnwantedAccelerated Burning 

To date, the phenomena seem to be evidenced more in the suppression of pool fires than in nacelle type installations. The feasibility of verifying the current hypotheses using one or more of the scheduled 2002 engine nacelle tests (FAA, AFRL) should be considered. 

The current project is aimed at determobserved phenomenon poses a safety prepared to extend this project (probabhypotheses indicated that the risk of aunder aircraft suppression conditions. 

51
# Recommendation Response

16 5D/1/901

AdvancedPropellant/Additive Development forGas Generators

1. Further work on the hybrid devices with effort devoted toflame suppression mechanisms and relight susceptibility. 2. Emphasis on design concepts to minimize the periodic replacement costs of the pyrotechnic elements. 3. Verification testing to show that “Cooled Soaked” CF3I 

hybrids (or other high-boiling "agents") will perform well at low temperatures. 4. Generation of chamber pressure and burning time variationwith temperature for the all the propellants being considered. In older propellants, peak chamber pressure variations of 4 to 1over a 135 °F temperature range were reported. 

1. Additional work on cooler, more eslower burn rates will be supported wAlternative engineering concepts may relight and increase assured durability2. This is at the perimeter of the scopbe a market-driven stimulus for manuwill be passed on to the Principal Inve3. Low temperature effects are not exbut tests of devices with reduced effluappropriate. 4. These measurements are being mad

17 4B/4/01

Performance Data on Cold TemperatureDispersion of CF3I 

and on Materials Compatibility withCF3I 

The work should be augmented to include additional highboiling point candidates from the other projects. The IRP would like to see useful heuristics from this project relating agent volatility and drop size distribution to vapor phase loadingduring droplet dispersion. One should consider re-naming this project “Low Temperature Performance of High Boiling Point Agents.”The status of the material compatibility tasks needs to beclarified. 

This name change has been made. Hiare in the plan for FY2002. The heuriunder General Recommendation 3.The materials compatibility work was report is in review. 

18 6A/1/0 Fire 

SuppressantDynamics in the Fire Compartment 

The project should be restructured and focused to use thecomputer capability to develop heuristics that can be applied in practice rather than use the project exclusively as a vehicle for developing the computer code as the end product. Researchersare encouraged to keep in mind the multiple potential applications for the results of this project: a) Better scientific understanding of the phenomena (Research) b) Guidance for vent and distribution configurations in futuretests (Test) c) Potential for future design using a simplified model (Product Design) 

The project includes developing practdispersion hardware. The developmenwill be considered as soon as the capacode is assessed. 

52
# Recommendation Response

19 5A/1/01 Parametric

Investigation of Droplet Atomization and Dispersion ofLiquid FireSuppressants 

1. Add at least one additional liquid test candidate to the project with a lower boiling point than the present two test liquids. 2. Insure that the size of the droplets tested covers the range of sizes expected in normal discharge. 3. If warranted, recommend modifications to the distribution system, based on the results of this study. 

Note: Determining realistic droplet size may become a difficult 

problem considering the variation in “Agent” characteristics, bottle pressure variations as a function of temperature, and discharge nozzle variations. If performance is found to behighly dependent on size, and if size is found to be highly variable, then this program has discovered a valuable truth, butthe implications could be serious. 

1. The intent is to provide data 

properties indicate they will t

2. Small masses of low boiling 

before impacting surfaces or can be treated as gases. 

3. These results feed into 6A, w

guidance for distribution syst

53