NGP ADVANCES IN POWDER PANEL & PROPELLANT 

TECHNOLOGIES 

William Grosshandler 

National Institute of Standards and Technology, Gaithersburg, MD 20899-8660 USA 

Tel: (301) 975-2310; Fax (301) 975-4052 

wgrosshandler@nist.gov 

Daniel Cyphers 

Skyward, Ltd., Dayton, OH 45431 USA 

Tel: (937) 252-2710, x102; Fax (937) 252-3486 

dcyphers@skywardltd.com 

Gary Holland 

Aerojet, P.O. Box 97009, Redmond, WA 98073-9709 USA

 Tel: (425) 885-5000 

gfh@rocket.com 

INTRODUCTION 

Halon 1301 has a vapor pressure high enough to propel it from a storage bottle and through 

distribution piping rapidly enough to suppress even fast growing fires. Nitrogen gas is used to 

pressurize halon 1301 storage bottles to ensure that even at temperatures as low as -40 oC, when 

halon 1301 is a liquid, the pressure is sufficient for rapid discharge of the fire suppressing fluid. 

Hydrofluorocarbon alternatives to halon 1301 such as HFC 125 are discharged in a similar 

manner, but because around three times the amount of agent is required to ensure the fire is 

extinguished, the amount of nitrogen needed to pressurize the fluid is also increased, leading to a 

system that is considerably bulkier and heavier than the halon 1301 system. 

Two technologies were explored in the Next Generation Program (NGP) that avoid the need for 

a high pressure storage vessel to operate effectively. These technologies are (1) powder panels, 

and (2) solid propellant gas generators. Both of these technologies have the ability to discharge 

fire fighting agent in less than 100 ms, which makes them suitable for protecting dry bays 

(enclosed spaces adjacent to a fuel cell). The solid propellant gas generator can be adapted to 

aircraft engine nacelles, as well. 

Powder panels consist of powdered fire extinguishing agents sandwiched, unpressurized, 

between two rigid membranes that, as a unit, can be attached to or used in place of the skin of the 

aircraft confining a dry bay. The powder is released and dispersed into the dry bay when the 

panel is pierced by a projectile, forming an aerosol cloud sufficiently dense to prevent ignition or 

suppress a fire resulting from the rupture of the adjacent fuel tank. The system is entirely 

passive. 

The powder panel designs that existed prior to the NGP were inefficient. The research 

conducted as part of the NGP was aimed at enhancing the powder panel in three ways: (1) using 

1
more chemically active fire suppressant materials, (2) enhancing the dispersion of the powder, 

and (3) decreasing the system weight. 

Solid propellant gas generators (SPGGs) contain no fluids and are at atmospheric pressure prior 

to activation. The propellant within a chamber is activated by a spark and burns rapidly to 

produce large quantities of gases. These materials either can be dispersed directly into the 

volume being protected or through a manifold of piping similar to what is used for halon 1301. 

The focus of the NGP research was to better adapt SPGG technology for aircraft fire protection 

by finding ways (1) to reduce the temperature of the gases dispersed by the generator, (2) to 

reduce/control the exhaust momentum through control of the burning rate, and (3) to increase 

the suppression effectiveness of the products (including finely dispersed particulates) by 

changing the chemical reactants, their stoichiometry and morphology, by the geometry of the 

containment vessel, and by various additives thought to be adept at retarding ignition or at 

quenching the combustion process. In addition, a hybrid application was evaluated, with an 

SPPG used as a compact source of high pressure gas to vaporize and propel a liquid agent. 

ENHANCED POWDER PANELS [1]* †

In order to become a viable concept for combat fire protection in aircraft, two major technical 

problems for powder panels needed to be addressed. These two major problems, performance 

and practicality, are intertwined. Previous powder panel testing evaluated a number of different 

powder panel designs and materials and showed limited ranges of effectiveness. This project 

demonstrated the feasibility of completely re-designing a powder panel so that it could release a 

greater amount of powder. Additional work was required to optimize these panels for attaining 

potential design requirements. The problem was one of developing a powder panel that is 

competitive with other fire extinguishing technologies by releasing sufficient powder when 

penetrated by a ballistic projectile to prevent fire ignition, while remaining acceptable under 

tightly controlled aircraft environment requirements. 

EXPERIMENTAL PROGRAM 

An experimental test device (dry bay/fuel tank simulator) was designed and fabricated to enable 

a direct comparison of powder panel materials and designs, both existing and improved concepts. 

Through an impact dynamics study, various characteristics critical to the fire extinguishing 

effectiveness of powder panels were examined. The test device shown in Figure 1 allowed for 

the experimental screening of candidate powder panels by comparing these characteristics in a 

highly repeatable fashion. Among the characteristics examined were panel impact dynamics, 

including cracking and material removal, the amount of fire extinguishing powder released into 

the test article, the dispersion of this powder, and the time the powder remained suspended in the 

dry bay. The test device simulated a 0.057 m3 aircraft dry bay and a 0.028 m3 fuel tank, with a 

projectile entering the dry bay prior to the fuel tank (dry-to-wet shotline). The fuel tank was 

capable of holding fluid, and the dry bay was designed with Lexan windows to allow visual 

 

*

 The section on enhanced powder panels is based entirely on reference [1]. Portions of the text and figures have been used 

verbatim without further attribution. Consult the original document for details. 

†

 NIST policy is to use metric units and to provide statements of uncertainty for all original measurements; however, all data 

shown in this paper are from organizations outside of NIST, and may not comply with this policy. 

2
observation of each test. 

Replaceable 7075-T6 

aluminum panels of 2.0 

e dry bay. 

the tank, for evaluating 

released into the dry bay. The test device also 

allowed for the installation o

behind the dry bay wall wh

the test article. 

The test device was desig

dispersion information, so

der 

Figure 1 (right side) sh

methods used in the dry

located throughout the dr

slid over the rods to capt

each test. The plastic tubes were examined for signs of powde

collection cups were also located in the dry bay along the sh

concentration is most important during a ballistic projectile impact

before and after each test to determine the amount of powder releas

also individually weighed to assist in determining the mass of pow

The removed area of the front face (dry bay side) of the powder pane

aluminum foil panels. Also examined were 3.2 mm and 6.4 

m thicknesses of 5052 aluminum honeycomb, acting as the rib structure for various panels. A 

 

mm thickness were 

inserted to represent the 

fuel tank wall adjacent 

to th

In most of the tests, 

powder panels were 

secured directly in front 

of the fuel tank wall. 

scenario, without fluid in 

the amount of powder 

f powder panels directly 

ere the projectile entered 

ned to capture powder 

 a direct comparison 

panels could be made. 

ows the powder collection 

 bay. Witness rods were 

y bay. Plastic tubes were 

ure released powder during 

r after each test. Powder 

otline, where the powder 

. Each panel was weighed 

ed. Panel components were 

der loaded into each panel. 

l was also determined. 

A total of 32 powder panel tests were conducted using the light-gas gun at Wright-Patterson Air 

Force Base (WPAFB) during the first phase of this program. Among the materials tested were 

thin aluminum (0.41 mm thick) and 

This offered the worst-case

between candidate pow

Figure 1. Experimental Test Device and Powder Collection Methods 

Figure 2. Test Exampl

Powder Release a

e of Effective 

nd Dispersion 

m

Nomex‡ (aramid fiber paper) honeycomb core of 9.5 mm thickness was also tested. 

Thermoplastic and thermoset materials were the focus of most testing. For the front panel face 

(dry bay side), materials that exhibited brittle properties upon impact, but durability in handling, 

were of utmost interest. The goal was to find a front face material and powder panel design that 

resulted in significant front face material loss and powder release into the dry bay during a 

ballistic impact event. Front face materials evaluated included polycarbonate, polystyrene, 

polypropylene, and poly-methylmethacrylate. The use of intentional surface scoring of flat 

‡

 Certain trade names are used to properly describe materials or products used in this program. This does not imply that NIST 

endorses these materials or products nor that they are the best for the purpose stated. 

3
acrylic panels was also examined using a couple of different scoring patterns and different 

techniques for implementing the scoring lines. The intent was to determine if surface scoring 

could be used to enhance the fracture characteristics of the material. Figure 2 is a photograph 

showing the degree to which the powder was dispersed, with the fractured powder panel on the 

right (corresponding to the right side of Figure 1). 

Live fire tests of enhanced powder panels without reactive backing were conducted at the Naval 

Air Warfare Center (NAWC) in China Lake, CA, in a realistic size dry bay (0.45 m3), with an 

actual ballistic threat (12.7 mm armor piercing incendiary, or API), and about 50 L of JP-8. 

rojectiles were fired at a nominal velocity of 760 m/s at a 0° angle into the dry bay, impacting 

for 

ommercial powder panels. Greater powder dispersion throughout the dry bays was also evident 

ickness reduction, and 

P

an aluminum striker plate, which was separated from the powder panel/fuel tank by 

approximately 0.30 m. The projectiles functioned upon impact of the striker plate and then 

continued through the powder panel, penetrating the fuel tank and releasing JP-8 fuel. The 

powder panel was attached to this removable bulkhead panel with a 2-part epoxy adhesive. Tests 

were also conducted with commercial powder panels to provide a basis of comparison with the 

enhanced powder panel tests. An additional test was conducted at NAWC using a test article 

designed for the Federal Aviation Administration (FAA) to replicate a baggage area separated 

with a powder panel from an adjacent dry bay with fuel lines. Enhanced powder panels 

prevented ignition in all five tests they conducted (four in the first test article and one in an FAA 

test). Conversely, fires resulted in all four commercial powder panel tests in both test article. 

Figure 3 shows some images captured from high-speed video demonstrating the fire mitigation 

capability of enhanced powder panel designs. Powder discharge was estimated to be at least 90 

% of the pretest powder loading for the enhanced powder panels, compared to 5 % to 10 % 

c

for the enhanced powder panels. 

Following successful testing of enhanced powder panel concepts, optimization testing was 

conducted on the gun range at WPAFB, focusing on three areas: front face fracture and powder 

release; weight reduction, panel 

th Incendiary

Function

Fire

Ignition

Fire

Sustains

Incendiary

Function

Fire

Prevented

Dry Bay Engulfed

in Powder

practical production issues; and 

reliability improvement. 

Testing primarily involved the 

use of Al2O3, even though 

KHCO3 and other powders have 

been demonstrated to be more 

effective as fire extinguishing 

agents. Al2O3 is the only known 

powder panel agent to be 

incorporated into an aircraft due 

to its lack of reactivity with 

aircraft structure. Additionally, 

since Al2O3 has a much higher 

specific gravity than KHCO3

(3.95 compared to 0.88), it was 

Commercial

Powder Panels

Enhanced

Powder Panels

Figure 3. Enhanced Powder Panel Fire Mitigation Capability 

Demonstrated 

4
Table 1. Wing Leading Edge Dry Bay Total Fire Extinguishing System Weight Estimates 

thought to be worst-case and would help to determine success in weight reduction efforts. The 

Al2O3 tested was 5 μm in average size compared to an average of approximately 30 μm for the 

KHCO3. 

nhanced powder panels evaluated in final demonstrations ranged in weight from 141 g to 227 g, 

ith four of the six panels being lighter than the commercial powder panel evaluated (189 g). 

hicknesses ranged from 1.9 mm to 2.2 mm, while the commercial powder panel thickness was 

.7 mm. (Table 1 summarizes the result of a weight comparison for complete alternative fire 

xtinguishing schemes installed on a wing leading edge dry bay.) 

 four of five tests, the enhanced powder panels prevented fire ignition. The cause of the lone 

nsuccessful test resulting in a fire was attributed to an inadequate attachment adhesive on the 

ack of the enhanced powder panel. The test of a commercial powder panel resulted in a fire; 

owever, the attachment adhesive again failed to hold. Although the commercial panel test was 

ot conclusive, a further examination of the test results indicated a significant increase in vital 

ded powder in the commercial 

owder panel test. 

articular front face materials, thicknesses, rib designs, attachment methods to the ribs, 

Fire Extinguishing System Total System Weight 

Solid Propellant Gas Generator System Weight 21.4 kg 

Lighter Enhanced Powder Panel Design 1 

Weight - 1.60 kg/m2 (0.327 lb/ft2) 

22.2 kg 

Heavier Enhanced Powder Panel Design 2 

Weight - 2.05 kg/m2 (0.420 lb/ft2) 

27.8 kg 

Commercial Powder Panel Weight - 1.92 

kg/m2

 (0.394 lb/ft2) 

26.2 kg 

E

w

T

2

e

In

u

b

h

n

performance characteristics for the enhanced powder panels. In the FAA test, a fire starting from 

an existing pool of fuel was quickly extinguished (after only 0.28 s) by an enhanced powder 

panel. 

Despite being as much as 26 % lighter and 29 % thinner, the enhanced powder panel tests 

resulted in at least 34 % greater area opening and at least four times greater powder release. 

Powder was evident on surfaces throughout the dry bay following enhanced powder panel tests 

and was visibly suspended in the dry bay up to five minutes after some of the enhanced powder 

panel tests. No evidence was present of dispersed and/or suspen

p

FINDINGS AND CONCLUSIONS REGARDING POWDER PANELS 

A number of lessons were learned about effective powder panel design. Some, previously 

discovered, were reaffirmed. Among the key lessons learned were: 

• brittle or frangible front face materials outperform ductile or tough materials, 

• front face crack growth optimization can be designed into the powder panel through the use 

of p

5
and even surface scoring, 

tes, there are adhesives to attach the various elements of the panel that form 

xtremely tight bonds. The selection of a front face material and thickness can take into account 

cidental leakage has 

een a significant concern for aircraft designers considering powder panels and is the primary 

 perhaps other lighter weight 

and nly are other 

pow

requi

De e must be 

ach it 

ay be warranted to consider higher powder loading, which is the significant weight driver. For 

e dry bay; 

• better dispersion of powder to prevent ignition off-shotline; 

 

• a strong synergism exists between the rib structure and the front face design, and 

• the back face can be designed to aid in powder dispersion and/or to reduce fluid leakage. 

Another key finding in this program was that there are design features associated with enhanced 

powder panels that can make them very resistant to accidental leakage. With the use of plastics 

and certain composi

e

the likely harsh environment to which the powder panel will be exposed. Ac

b

reason that Al2O3 has been the only chemical fire extinguishing powder finding production 

usage. With this resistance to accidental leakage in certain designs,

 improved performance fire extinguishing agents can be considered. Not o

ders lighter in weight, but improved effectiveness of these powders may lead to reduced 

rements for powder loading. 

spite significant increases in powder release for enhanced powder panels, a balanc

ieved between weight/thickness and effectiveness. For protection against larger threats,

m

strict weight restrictions, testing may be required for the given powder panel to determine the 

type and size of the threat for which protection is afforded. Further examination of the more 

promising designs should be performed for potential qualification test requirements. These 

include operating temperature, humidity, chemical exposure, vibration, and impact resistance. 

Findings from this research revealed that realistic powder panel concepts could significantly 

enhance the fire extinguishing effectiveness of this vulnerability reduction method. Enhanced 

powder panel designs have the potential to afford the following benefits over current commercial 

powder panel designs: 

• greater front face area removal to allow more powder to escape; 

• greater powder release into th

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

• design flexibility of enhanced powder panels to target weight, durability and applicationspecific design goals; and 

• significantly improved fire extinguishing effectiveness over commercial powder panels at 

an equal or lighter weight and thickness. 

SOLID PROPELLANT GAS GENERATORS [2, 3]§

The SPGG program sponsored by the NGP was a collaborative effort between Aerojet (formerly 

Rocket Research Company) and the Naval Air Warfare Center - Weapons Division. The 

objectives of this program were to develop new highly efficient, environmentally acceptable, 

 §

 Th n references [2] and [3]. Large portions of the text from these 

d contain many details not included here. 

e section on solid propellant gas generators is based o

ocuments have been used verbatim without further attribution. The original reports

6
che rators; and to 

imp m 

was d following: 

8 

• Develop techniques for reducing the com ustion temperature of the propellant, such as 

tailoring the pr itives. 

• Develop techniques for cooling the combustion products to allay such problems as physical 

hanisms of solid propellant systems by determining 

nt. 

• those agents 

EX

Th

(a) in date mixtures of fuel, oxidizer, processing additives 

and

and 

supp

Bu

techn rains (pills) of approximately 12.7 mm diameter and 

2.7 mm thickness were prepared with a non-burning inhibitor (e.g., epoxy). The window bomb 

is a closed vessel, filled with an inert 

gas to a static pressure, and equipped 

pressure maxima. 

various agents under repeatable test 

conditions. (See Figure 4.) The SPGG 

discharge times were generally 

mically active fire suppressant capabilities based upon solid propellant gas gene

rove understanding of propellant and additive effectiveness in fire suppression. The progra

esigned to accomplish the 

• Establish baseline SPGG performance with a standard Aerojet propellant (22 % CH3N5, 3

% Sr(NO3)2, 40 % MgCO3). 

b

opellant formulations, and for incorporating chemical add

deformation or failure of distribution lines and threat to occupants. 

• Modify existing hybrid extinguisher technology using additional gaseous and liquid 

suppressants, assuring operability at low ambient operating temperatures. 

• Measure the exhaust temperature, burning rates, and suppression effectiveness of the new 

propellants with and without additives 

• Characterize the extinguishment mec

the relative contributions of oxygen displacement, cooling and flame strain effects upon the 

SPGG-driven suppression eve

• Correlate laboratory- and mid-scale results. 

Perform tests on real platforms defined by the weapon systems community on 

that performed best in mid-scale tests. 

PERIMENTAL PROGRAM 

e developmental propellants described here were made in 50 g to 1 kg batches, according to 

itial computational evaluation of candi

 coolants, followed by (b) small-scale processing of compositions down-selected from (a), 

then (c) scale-up of formulations down-selected from (b) in order to facilitate fire 

ression effectiveness testing. 

rn rate testing was performed by either a strand burner or a window bomb. In the strand burn 

ique, compression molded cylindrical g

1

with two optical windows. The 

pressure limit of this apparatus 

extended to 55 MPa, the higher end of 

nominal gas generator internal 

The mid-scale Fire Test Fixture (FTF) 

was used to test the effectiveness of 

maintained at ~150 ms to 200 ms. The 

F SPGG device used for most testing igure 4. Aerojet Fire Test Fixture (FTF) 

7
was mounted within the FTF, and could be re-used for additional testing. The relative efficiency 

of different suppressants was ranked based upon their threshold quantity, defined as the amount 

of agent needed to extinguish the fire at least two out of three times. Figure 5 presents video 

frames documenting the extinction of a fire in the FTF. A number of high nitrogen component 

formulations based on bis(5-aminotetrazolyl) tetrazine (C4H4N14, or BTATZ) have been 

evaluated for their suitability in agent generation devices as a function of the amount of coolant 

added. Gas temperatures were reduced in some cases by up to 20% when compared to the 

baseline formulation. Burning properties of three high nitrogen formulations based upon 

BTATZ are shown in Table 2 (rows 2, 3 and 4), compared to the baseline formulation (listed in 

the first row). The first column in the table provides the percentages of fuel, oxidizer, and 

Figure 5. Consecutive frames during SPGG suppression of a fire in the FTF 

coolants within the propellant mixture. The volume percentages of gases produced (assuming 

complete reaction) and the mass of condensed material formed are shown in the second column, 

followed by the calculated gas output per 100 gram of propellant in the third column. 

Thermodynamic calculations of the adiabatic temperature, Tc, at the chamber pressure, Pc, and of 

the exhaust temperature after undergoing expansion to the atmosphere, Tex, are included in the 

next columns. The last two columns are kinetic parameters determined from experiments: the 

propellant burning rate at 6.89 MPa (1000 psi), BR1000; and the pressure exponent, n, which is a 

measure of the sensitivity of the burning rate to the pressure in the combustion chamber. The 

findings of increased burn rate BTATZ compositions, while maintaining moderate gas 

temperatures, provides a means for further increases in agent cooling when these compositions 

are modified with endothermic chemical coolants. 

Chemical additives were incorporated into formulations wherein the chemically active agent was 

liberated upon combustion of the solid propellant, the exhaust consisting of inert gases plus 

entrained additives. These additives were blended directly into the propellant, or the additive 

was blended into a hybrid fluid. Several compositions were developed such that a common 

8
Table 2. Compositions and Burning Parameters of Chemically Active Developmental Propellants

Temperature, 

K Propellant Composition, 

wt % 

Exhaust species, 

vol % @ Tc

Gas 

output, 

mol/100 g Tc

Measured Measured 

Texh

BR1000, Pressure 

cm/s expon., n

Baseline: 5AT** 22,†† 

Sr(NO3)2 38, 

MgCO3 40 

N2 45, CO2 35, 

H2O 20 2 1450 1000 1.27 0.5 

BTATZ-2: 

BTATZ 86.0, 

KP 10.0, PBA 3.0 

C-black 0.5, Mica 0.5

N2 68, H2 23, 

CO 9 3.68 2290 1140 5.46 0.55 

BTATZ-3: 

BTATZ 86.0, 

KN 10.0, PBA 3.0, 

C-black 0.5, Mica 0.5

N2 69, H2 23, 

CO 8 3.72 2080 1090 4.57 0.57 

5AT/BTATZ-3: 

5AT 43.0, 

BTATZ 43.0, KP 10.0, 

PBA 3.0, C-black 0.5, 

Mica 0.5

N2 63, H2 28, 

CO 6, 

KCl (s) 5.3 g 

4.01 1960 970 3.85 

0.7 

(6.89-18.9 

MPa) 

CA-01: 5AT 17.2, 

Sr(NO3)2 30.0, 

MgCO3 30.0, KI 21.3, 

Graphite 0.5 

N2 47, CO2 31, 

H2O 22 

KI 21.3 g, 0.13 mol K 

1.47 1450 970 1.27 0.55 

CA-03: 5AT 20.0, 

Sr(NO3)2 34.7, 

MgCO3 36.4, K2CO3 8.9 

N2 47, CO2 31, H2O 22

K2CO3 9.0 g, 0.13 mol 

K

1.78 1450 1210 1.32 0.59 

CA-04: 5AT 19.7 

Sr(NO3)2 34.3, 

MgCO3 36.0, K2CO310. 

N2 47, CO2 32, H2O 22

K2CO3 10.0 g, 

0.15 mol K 

1.75 1440 1110 1.27 0.44 

CA-06: 5AT 22.1, 

Sr(NO3)2 24.8, 

MgCO3 39.5, 

KNO3 13.1, Graphite 0.5 

N2 47, CO2 31, H2O 22

K2CO3 9.0 g, 

0.13 mol K 

1.61 1440 1100 1.04 0.66 

CA-07: 5AT 22.1, 

Sr(NO3)2 22.9, 

MgCO3 40.0, KNO3 15.0 

N2 47, CO2 31, H2O 22

K2CO3 10.2 g, 

0.15 mol K 

1.78 1440 1090 1.62 0.52 

CA-08: 5AT 22.1, 

Sr(NO3)2 22.9, 

MgCO3 40.0, KNO3 30.0 

N2 47, CO2 31, H2O 22

K2CO3 20.5 g, 

0.3 mol K 

1.79 1470 990 .68 1.77 

CA-10: 5AT 81.0, 

KP 10.0, DBPE 5.0, PBA 

3.0, C-black 0.5, Mica 0.5 

N2 60, H2 28, CO 3, 

CH4 4, KCl(s) 2.0 g, 

KBr(s) 5.4g 

4.24 1630 870 0.25 1.0 

 H3N5. 

formulations or i

** 5AT is refers to 5-aminotetrazole, C

†† numbers represent mass percentages in n exhaust products 

9
composition family e

Figure 6. Threshold mass of inert propellant plus p ium otass compound for suppression in FTF 

volved having different percentages of additive. Burning properties of 

ompositions containing potassium are summarized in the last seven rows of 

aths to ant compositions were demonstrated in this program. 

pos ere used in conj n w he lly a addit or 

ven traps to the exhaust provided means for cooling, 

ical termination of the combustion process, hence increasing the overall 

 fire su

 in n pound BTATZ appeared to 

eans for reducing propellant com peratures. The preparation of 

the scale. T cre

pr ity of BTATZ formulations make them good candidates 

includi ith additional chemical coolants as well as 

re cor n

m exhaust temperatures by as much as 30 % vs. current 

m taining po m iodi carbonate as 

v nced effectiveness in the FTF as compared to 

mposit f 0 le additive into inert fire suppressants 

n fficiency. The otherwise sim rope compositions 

exam % to 70 % reduction (by mass) of agent loading for 

 carbonate appears to be a more effective 

ctiveness of potassium carbonate (vs. 

several of these c

Table 2. 

SUMMARY OF SOLID PROPELLANT GAS GENERATOR PROGRAM 

Several different p cooler propell

Cooler propellant com

adical sca

itions w unctio ith c mica ctive ives, 

combustion r

dilution and chem

gers. Adding radical

effectiveness of the ppressant. 

Propellant formulations corporati g the new high nitrogen com

provide increased m bustion tem

BTATZ progre sed to his in

attractive burn rate and 

s half kilog

essure sensitiv

ram ased production capability plus the

for fu u e wo t r rk, ng re-formulation w

suppression effectiveness testing in the FTF. Di

l

ct in poratio of coolant species into the 

prope lant composition ay reduce 

baselines. 

Testing of propellant co

additi

positions con tassiu de and potassium

chemically active 

al t co

es demonstrated enha

chemic ly iner n ration o

r

io s. Incorpo

on e

.1 mo

had a d amatic effect upo

ined during this testing

 suppressi

 indicated a 50

ilar p llant

suppression. On an equimolar basis, potassium

chemical additive than potassium iodide. The greater effe

10
potassium iodide) may be related to more facile vaporization of the carbonate-based species after 

melting, or to an antagonistic interaction between the halogen and alkali metal species in the 

flame region. 

Fire testing with chemically active compositions indicated that the CA-04 composition (20 % 

5AT, 34 % Sr(NO3)2, 36 % MgCO3, 10 % K2CO3) is the most effective. This composition 

incorporates potassium carbonate in its discharge, and is three times more effective per unit mass 

than the inert baseline propellant (22 % 5AT, 38 % Sr(NO3)2, 40 % MgCO3). Testing with 

compositions of lower active-agent loading resulted in less effective performance. This indicates 

that the additive loading in CA-04 is below (or at) the saturation level reported in sub-scale 

testing with numerous other chemically active suppressants. See Figure 6 for a comparison of 

the agent mass and the amount of potassium in several of these formulations at suppression 

thresholds. 

Testing of hybrid SPGGs with HFC-227ea and Novec-1230 indicated that high boiling point, 

low vapor pressure agents such as these could be delivered efficiently to the fire zone by heating 

and pressurizing the liquid with an SPGG. Both agents produced comparable results (on a mass 

basis) in fire suppression tests. Incorporation of CF3I into a hybrid SPGG proved convenient for 

m of t F3I. The water-based hybrids did not 

owev end ta acetate into the water 

pression effectiveness in the FTF. 

the suppression efficiency. Testing conducted with additives incorporated into the 

tive additives in 

est Facility to evaluate alternative SPGG fire suppression 

eness of SPGG fire extinguishers; and 

• determining the effectiveness of SPGG hybrid fire extinguishers using fluorocarbon and 

overcoming poor cold-te

perform any better than th

was shown to significantly

perature dispersion

e HFC-227 hybrid; h

 improve sup

he C

er, bl ing po ssium

On a mass basis, the inert hybrid and standard SPGG systems appear to provide similar 

suppression protection. Incorporation of chemically active species into the hybrid propellant 

improves 

hybrid fluid produced results similar to results with active agents added into the propellant. This 

indicates that active additives in the hybrid fluid may be just as effective as ac

the propellant. 

The Aerojet/NAWC program sponsored by the NGP has advanced solid propellant-based fire 

suppression technology in multiple directions. These include: 

• developing a methodology for screening candidate propellants; 

• developing a medium scale Fire T

technologies for a cluttered space such as a dry bay or small engine nacelle; 

• scaling up production of BTATZ to half kilogram quantities; 

• calculating exhaust temperature and composition of new, high nitrogen propellants; 

• measuring burning rate and pressure exponent for these new, high nitrogen propellants; 

exhaust temperature; 

• examining the effect of various halogen, alkali, and iron compounds on fire suppression 

effectiv

• tabulating the effect of different coolants on the effect of propellant burning rate and

aqueous fluids. 

Since initiation of this project in 1999, when inert SPGGs were installed in the first V-22 and 

F/A-18 dry bay fire protection systems, gas generator devices using advanced propellants and 

11
advanced additives have been demonstrated, developed and manufactured for three new 

platforms. Developments in improved, chemically active SPGGs are being implemented on the 

JSF F-35 dry bay fire protection system. Testing in 2005 validated the effectiveness of 

chemically active HFC-227ea hybrid devices in suppressing fires arising from ballistic events 

upon the US Army’s M1114 HMMWV. Figure 7 summarizes how the performance of SPGGs, 

as measured by suppression effectiveness, has improved over this period. 

rt," report number SKY-03-

01,

2. ellant/Additive 

De of the 

200 of 

Sta

3. "Advanced Propellant/Additive Development for Gas Generators," Report Number D03008, 

Ae

Figure 7. Relative effectiveness of various SPGG fire extinguishers: blue, inert effluent; 

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

systems. [SPFE (solid propellant fire extinguisher) is an alternative term for SPGG.]

REFERENCES 

1. Cyphers, D.C., "Enhanced Powder Panels: Final Technical Repo

 Skyward, Ltd, Dayton OH, December 2003. 

 Fallis, S., Reed, R., McCormick, J.L., and Holland, G.F., "Advanced Prop

velopment for Fire Suppressing Gas Generators: Development + Test," Proceedings

2 Halon Options Technical Working Conference, NIST SP 984, National Institute

ndards and Technology, Gaithersburg MD, 2002. 

rojet, Redmond, WA, March 2006. 

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