Chapter 9: POWDER PANEL AND 

PROPELLANT DISCHARGE 

TECHNOLOGIES

William L. Grosshandler 

National Institute of Standards and 

Technology

TABLE OF CONTENTS

9.1 Introduction......................................................................................................................925 

9.2 Enhanced Powder Panels.................................................................................................927 

9.2.1 NGP Objectives.....................................................................................................927 

9.2.2 Background on Powder Panel Technology ...........................................................928 

9.2.3 Operating Principle................................................................................................929 

9.2.4 Technical Issues ....................................................................................................931 

9.2.5 Survey of Powder Panel Applications...................................................................932 

9.2.6 Powder Dispersion Screening Experiments..........................................................935 

9.2.7 Live-fire Proof-of-concept Demonstrations..........................................................945 

9.2.8 Optimization Program...........................................................................................949 

9.2.9 Live-fire Demonstration Testing of Optimized Enhanced Powder Panels ...........955 

9.2.10 Mass-trade Comparison Analysis..........................................................................968 

9.2.11 Summary of Powder Panel Research Program......................................................972 

9.3 Solid Propellant Gas Generators,,.....................................................................................974 

9.3.1 Brief History..........................................................................................................974 

9.3.2 Operating Principles..............................................................................................975 

9.3.3 Experimental Techniques......................................................................................976 

9.3.4 Results: General Behavior of Propellants ............................................................988 

9.3.5 Results: Cooled Propellant Formulations.............................................................992 

9.3.6 Results: Chemically Active Fire Suppressants...................................................1001 

9.3.7 Results: Hybrid Fire Extinguishers ....................................................................1011 

9.3.8 Summary of Solid Propellant Gas Generator Research ......................................1018 

9.4 References......................................................................................................................1021 

9.1 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 °C, where the halon 1301 vapor pressure

has dropped considerably, the total 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, a larger
926 Powder Panel and Propellant Discharge Technologies 

pressure vessel is needed, and the total system is considerably bulkier and heavier than the halon 1301 

system. 

Two technologies were explored in the Next Generation Fire Suppression Technology Program (NGP) 

that avoid the need for, and the attendant bulk and safety issues of, 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 aircraft 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: 

• using more chemically active fire suppressant materials, 

• enhancing the dispersion of the powder, and 

• decreasing the system mass. 

Solid propellant gas generators (SPGGs, alternatively referred to as SPFEs, solid propellant fire 

extinguishers, for the current application) contain no fluids and are at atmospheric pressure prior to 

activation. The propellant within a chamber is activated by an initiator 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. Prior to the advent of the NGP, the 

primary application for SPGGs was for automotive airbags and aircraft inflatable escape slides. As first 

mentioned in Chapter 2 of this book, the gas mixture is very hot upon exit from the SPGG but cools 

rapidly as it expands within the compartment into which it is discharged. During testing on the F-22 

program, distribution lines from the generators to the nacelle would become white hot during discharge 

and for a brief period thereafter. In testing performed by the U.S. Navy using a “single grain” inert gas 

generator, the same effect of heating of the distribution line during discharge was also noted. Placing 

inert gas generators within a nacelle and thus eliminating the need for distribution lines previously had 

been considered impractical due the potential degrading affect of the nacelle operating temperature 

environment on the life of the solid propellant. Inconel distribution lines were demonstrated to not melt, 

but would still become white hot. 

The focus of the NGP research was to develop upgraded SPGG technology for aircraft fire protection by 

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

suppression effectiveness of the products (including finely dispersed particulates). The latter involved 

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

vessel, and incorporating various additives thought to be adept at retarding ignition or at quenching the 

combustion process. In addition, the concept of a hybrid fire extinguisher (HFE) was studied, with a 
Enhanced Powder Panels 927

SPGG used as a compact source of high pressure gas to propel a liquid hydrofluorocarbon or aqueous 

mixture. 

9.2 ENHANCED POWDER PANELS 

9.2.1 NGP Objectives 

The combat environment for military aircraft or even a terrorist environment for civilian aircraft poses a 

significant fire hazard when a ballistic threat is introduced. These threats are designed to act as ignition 

sources upon penetration of onboard flammable fluid containers. As previous combat experience and 

vulnerability analyses have shown, fire is the most significant vulnerability faced by an aircraft subjected 

to ballistic threat impact. 

One area of focus for the NGP has been improved storage and delivery of fire extinguishing agents. One 

such technology, the powder panel, passively stores and then delivers agent upon the impact of a ballistic 

projectile. Powder panels have most often been applied to the lining of aircraft dry bays to provide 

passive, light mass, 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 or 

as the adjoining fuel spills into the space and is ignited by incendiaries. The recognition of ballistic 

threat-induced fires as a major contributor to aircraft vulnerability and a need to avoid active halon fire 

extinguishing systems has led to a renewed interest in powder panels as a fire protection device. 

Despite the potential for powder panels, commercial units are of roughly the same design that has existed 

for decades, and their limited range of effectiveness has prevented further implementation in production 

aircraft. In 2001, the NGP embarked on an effort to use current technology and new ideas to examine the 

feasibility of enhanced powder panel designs and demonstrate proofs-of-concept. This section details a 

two-phase effort to accomplish this work.1,2,3,i 

The objective of the NGP research was to identify concepts for powder panel enhancement (relative to 

current capability and to halon 1301) and demonstrate their performance. The basis for this advanced 

protection consisted of characterization of current powder panel technology and assessment of recently 

developed improvements in powder panel materials and construction. The expected outcome of this work 

was enhanced powder panel concepts that are competitive with halon 1301 in critical parameters such as 

mass, volume occupied, and fire extinguishing capability, and, thus, are candidates for use in its place. 

NGP research into enhanced powder panels was performed by Cyphers and co-workers at Skyward, Ltd. 

The Aerospace Survivability and Safety Flight (46 OG/OGM/OL-AC) was the managing laboratory. In 

Phase I of the work, background information was gathered on the state of current powder panels, initial 

concepts for enhanced powder panels were examined, and the feasibility of improved powder panel 

features was demonstrated. In Phase II, the examination was widened to study whether enhanced powder 

panels could become practical, while maintaining improved performance. Optimized powder panels were 

examined for their potential to meet production requirements and their benefits were examined against 

other fire protection alternatives. The program concluded with live fire demonstration tests of the 

optimized powder panels. 

 

i

 Large portions of the text of Section 9.2, as well as all the figures, have been used from Reference 1 without further attribution. 

The reader should consult the original document for additional details. 
928 Powder Panel and Propellant Discharge Technologies 

9.2.2 Background on Powder Panel Technology

Powder panels are passive fire protection devices for discharging dry chemical agents to prevent or 

extinguish combat-induced fires in military vehicles. They consist of two walls, an internal rib or core

structure, and a fire extinguishing agent, typically a dry chemical powder, that fills the interior space. 

Historically, commercial powder panels have consisted of thin walls of aluminum foil or composite 

sheets, with an aluminum or Nomex honeycomb core. Typical thicknesses for commercial powder panels 

have been reduced to just over 2.5 mm. Powder panels are typically arranged along the walls of a void

area in a military vehicle (called a dry bay in an aircraft) adjacent to or on the walls of a flammable fluid

container (fuel tank, fuel line, hydraulic fluid reservoir, etc.). Figure 9–1 depicts the typical arrangements 

of powder panels. They are typically attached directly to the wall of the flammable fluid container by an

epoxy adhesive. Testing has shown this arrangement to be more effective than mounting on the walls of 

the dry bay separated from the fluid container.4

 Upon penetration by a ballistic projectile, powder panels

release powder into the fire zone before or as the adjoining fuel spills into the space and is ignited by

incendiaries or other ignition sources. 

Figure 9–1. Typical Powder Panel Arrangements. 

The design and accep ventional active fluid 

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

ballistic threat-induced fires in aircraft, as 

discussed previously. Powder panels around aircraft fuel tanks were first developed and used by the 

 devices, powder panels

have seen limited use in aircraft for several reasons. False discharges do not occur with these passive fire

protection devices, but cleanup following a fire or inadvertent damage has been a concern. This concern, 

Fuel Tank Dry Bay Fuel Tank Dry Bay

Projectile Shotline Projectile Shotline

Powder Panel

Powder Panel

tability criteria for these devices are different from con

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

the configuration of the particular bay. Typical areal densities (mass/surface area) for commercial 

powder panels are on the order of 1.95 kg/m2

 to 2.44 kg/m2. 

Powder panels are not a new concept for extinguishing

Royal Aircraft Establishment in England. Some U.S. military helicopters (e.g., the AH-1W/Z and the

UH-1N/Y) and the V-22 aircraft have implemented powder panels in their vulnerability reduction 

designs. Powder panels have also been widely examined for military combat land vehicles, such as tanks 

and armored personnel carriers, but have been applied in limited circumstances. 

Nonetheless, despite testing which has demonstrated the effectiveness of these
Enhanced Powder Panels 929

primarily in aircraft, stems from the possibility of corrosion by the contact of chemical powders with 

vehicle structure. As a result, current powder panels often use an inert fire extinguishing powder, such as 

aluminum oxide (Al2O3), to prevent reaction with the metal. In military ground vehicles, wide application 

of powder panels has been limited due to the potential ill, albeit limited, effects on crew members or 

obscuration of the crew compartment upon activation. Although non-toxic agents can be used, during the 

period of time the powder particles are suspended in crew areas, the crew may have difficulty breathing 

and operational effectiveness may be limited. Several other reasons cited for their limited use overall 

include concerns over durability, potential adverse effects on electromechanical components and optics, 

their ability to protect highly cluttered areas, airflow influences, and a lack of protection from accidental 

fires. 

Although powder panels have been examined for years, current commercial powder panel designs are in 

essence very similar to those that have existed for decades. However, a number of factors have renewed 

interest in powder panel technology. First, the banned production of halon 1301 has created a demand for 

ique. Powder panel technologies are viable alternatives for some of these 

applications. They don’t require detectors, plumbing, wiring or bottles, and they are false-discharge 

 New powder panel concepts with enhanced characteristics have 

been proposed recently. These include frangible materials to optimize dispersion, single-piece 

Powder panels work through the release of fire extinguishing powder into the mixing zone of a flammable 

entially inert the zone and prevent a fire from igniting. To assist in the 

discussion of powder panels and their effectiveness, it is helpful to discuss fire ignition as it relates to an 

s not ensure fluid ignition or the initiation of a 

sustained fire. Fire initiation by a ballistic threat is a complex phenomenon involving a process that 

new techniques to fill its role. Also, new materials, powders, and construction techniques have been 

developed, which may allow for improved powder panel performance, in terms of both system mass and 

fire extinguishing capability. 

Systems that have used halon 1301 for ballistic threat-induced fire protection in fire zones eventually may 

require some substitute techn

resistant. Current designs have limitations, particularly limited powder dispersion ability, and problems 

providing protection against relatively small caliber threats. As a result, most don’t compare favorably 

against halon 1301 in trade-off studies. 

Improved powder panels could expand use of this fire protection technology for additional vulnerable fire 

zones on our critical weapons systems. 

construction technology, modular designs, pre-dosed sections, lighter mass materials, and lower cost 

materials. These enhanced powder panels could be used in applications as halon 1301 or other fire 

extinguishing system replacements, or they could replace existing powder panels with superior 

technology. 

9.2.3 Operating Principle 

fluid and an ignition source to ess

onboard aircraft fire due to ballistic projectile penetration. 

For any fire to initiate, the interaction of a flammable fluid, oxidant, and ignition source is required.5

 

However, the simple mixing of these three ingredients doe

sequentially brings together the three ingredients at the right time, in sufficient and properly proportional 

quantities, and with the needed intensity. The process begins when the ballistic threat penetrates the 

vehicle, generates an ignition source, and traverses the vehicle penetrating the fluid container, thereby 
930 Powder Panel and Propellant Discharge Technologies 

releasing fluid into the open volume of the vehicle. This open volume is referred to as a dry bay in 

aircraft. While each threat type is inherently different, the result is the same, i.e., deposition of thermal 

energy into a volume of air in front of the impact hole and the raising of the temperature of this volume. 

If the threat impacts a flammable fluid container within the vehicle and releases fluid, the fluid will be 

injected into the dry bay some distance by the threat/container impact and the container pressure. As the 

fluid is injected into the dry bay, it atomizes (i.e., breaks up into droplets). As the droplets penetrate into 

the heated air, they begin to vaporize, and the fluid vapor mixes with the surrounding air and produces a 

flammable fluid/air mixture. As the fluid/air mixture is heated, a chemical reaction will commence. 

As the reaction proceeds, heat is lost to the surrounding air by conduction. If the rate of heat produced by 

the reaction exceeds the rate of heat lost, the chemical reaction will accelerate until all the oxygen (for 

fuel rich conditions) within this volume is consumed; a flash is seen more or less simultaneously 

otential to reduce the probability of a fire ignition. The powder must render the fuel/air mixture 

nonflammable so the chemical reaction does not continue. The powder can do this in two ways. 

tain fire extinguishing powders that contain alkali metals, such as sodium 

and potassium. Potassium salts have been shown to be more effective than sodium salts, and iodide 

fective at reducing the chance of ignition than 

fewer, larger particles. A large total surface area of the powder is important in both heat absorption 

ize), and by maximizing the amount of powder released into the 

mixing zone consisting of the flammable fluid and the ignition source. The objective of the enhanced 

throughout this volume as ignition occurs. If the rate of heat lost exceeds the rate of heat produced, then 

the temperature of the volume will begin to decrease, and the rate of reaction will decline as well. 

Eventually the reaction will cease and ignition will not occur. As such, ignition is simply a reaction that 

proceeds to consume the available flammable fluid/air mixture contained within the volume encompassed 

by the ignition source, resulting in a flame visible within this volume. If, after ignition occurs, sufficient 

oxygen and flammable fluid are available, a sustained fire may result that could lead to a loss of the 

aircraft. 

Fire extinguishing powder introduced into this volume immediately upon impact by the ballistic projectile 

has the p

According to Finnerty et al.6

 (and further citations in Reference 6), it is widely believed that fire 

extinguishing powders can function as both energy-absorbing materials and as solid surfaces on which 

free radicals can be destroyed. Heat may be absorbed by the heat capacity of the solid, the heat of fusion 

at the melting point, the heat capacity of the liquid, heat of dissociation from breaking of chemical bonds, 

and heat of vaporization. These all contribute to the total energy absorbing capability (endothermicity) of 

the fire extinguishing powder.7

From a chemical aspect, it has been found that there is a catalytic path for the destruction of free radicals, 

especially O, OH and H, by cer

8,9

anions are more effective than chloride anions. Any powder that has a chemical fire extinguishing 

capability will also have the heat-absorbing capability.10 

Testing has shown that, for a fixed total mass of powder, smaller and more numerous powder particles, 

through the increased surface area available, are more ef

7,11

and chemical interference mechanisms. The former is why even an inert material like aluminum oxide can 

be effective if it is sufficiently finely divided. Conversely, large particles may actually pass through the 

flame zone before they can reach flame temperature, further reducing their ability to absorb as much heat 

as an equivalent mass of finer particles. 

The effectiveness of the powder panel can, therefore, be enhanced through the proper use of a fire 

extinguishing powder (type and particle s
Enhanced Powder Panels 931

powder panels is to appropriately select a powder and maximize the mass of powder released into the 

mixing zone. 

9.2.4 Technical Issues 

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

dressed. These attributes, performance and practicality, are intertwined. 

Previous testing evaluated a number of different powder panel designs and materials and showed limited 

ycomb provides several benefits to powder panels. First, it adds structural 

integrity to the panel, much as honeycomb has proven valuable for structural design in aircraft 

y of these efforts have focused on durability in the aircraft 

environment. However, performance, as quantified through surface area removal or fracturing, has been 

ification 

requirements levied on fire protection methods, such as powder panels, might show these designs to be 

powder panels needed to be ad

ranges of effectiveness. 

One consistent factor in many of these designs was the use of a honeycomb structural material as the rib 

or core material. Hone

construction. Honeycomb also allows for even distribution of the fire extinguishing powder throughout 

the panel, minimizing concerns over powder settling. It also can be constructed of very light mass 

materials such as Nomex or aramid fibers. The limiting factor for honeycomb has been its performance. 

Only cells in the direct path of projectile penetration, and perhaps those just around the penetration area, 

are torn and allow powder to escape. 

Different faces for the powder panel have been tested, focusing on materials such as aluminum foil and 

several different composites. Man

limited. This is true despite techniques to enhance opening of the powder panel walls, such as weak or 

selective bonding of the panels to the core, particularly for the front or open face to the fire zone. Very 

thin sheets or films have also been tried to promote surface removal and allow powder to escape. 

Consequently, the NGP needed to demonstrate the feasibility of completely re-designing a powder panel 

so that it could release a more effective amount of powder. However, production and qual

impractical for aircraft applications. Therefore, additional work was required to optimize these panels for 

attaining potential design requirements. For example, with aircraft mass restrictions being very 

demanding, powder panel mass needs to be minimized before it can even be considered competitive as a 

fire protection solution for a particular aircraft application. This goal involves proper material selection 

and powder panel thickness determinations. Another key aircraft requirement is durability in the 

aircraft’s harsh operating environment. This includes an ability to survive under extreme (both hot and 

cold) temperature, vibration, g-loading, and exposure to a variety of chemicals (jet fuel, hydraulic fluid, 

etc.). These environmental restrictions further reduce the set of materials and design concepts that can be 

used. Other production requirements may be related to such items as toxicity, maintainability and 

reliability. Thus, the problem becomes 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 still remaining acceptable under tightly controlled aircraft environment 

requirements. 
932 Powder Panel and Propellant Discharge Technologies 

9.2.5 Survey of Powder Panel Applications 

Cyphers and co-workers began with a survey of powder panel applications in operational U.S. aircraft and 

investigations of previous powder panel testing. The purpose of the survey was to identify powder panel 

materials and designs that have been previously evaluated and those that have actually been integrated 

into aircraft designs. The survey included the collection of all available data; however, it focused on 

more recent test programs and on testing related to U.S. aircraft applications. Using this information as a 

baseline, it was then possible to explore potential improvements in powder panel designs. 

Powder panels around aircraft fuel tanks were first developed and used by the Royal Aircraft 

Establishment in England.12 They have also been examined widely for military combat land vehicles, 

such as tanks and armored personnel carriers.13,14,15,16 An example of the integration of powder panels 

into a U.S. aircraft design is the use of these fire extinguishing devices in the V-22 Osprey. The widest 

use of powder panels has been in helicopters, for which a number of test programs have been conducted 

to evaluate powder panel applications. A significant effort was conducted, for example, to evaluate both 

parasitic (attached to existing structure) and structural (panels themselves function as structure) powder 

panels in Army AH-1S Cobra helicopters.12,17,18,19 Although powder panels were never integrated into the 

AH-1S, they did find their way into the Navy UH-1N Huey and AH-1W Super Cobra.20 These legacy 

aircraft are being upgraded to UH-1Y and AH-1Z configurations, both of which also will use powder 

panels for dry bay protection. Testing was conducted at Boeing to evaluate powder panel applications in 

the AH-64 Apache. This evaluation examined the use of powder panels along various fuel tank walls. 

Powder panels have also been evaluated recently for the RAH-66 Comanche helicopter. 

The powder panel application survey indicated that no U.S. fixed wing aircraft currently employ powder 

panels. A number of reasons have been offered for this: 

• Powder panels do not assist with accidental fires. 

• Low-tech approaches are difficult to sell. 

• There are concerns over accidental leakage that could lead to corrosion, durability, volumefilling capability with clutter involved, and detrimental airflow influences. 

There have been powder panel test programs relating to U.S. applications extending back to at least the 

late 1970s.16 Many of the test programs included evaluations of the fire extinguishing effectiveness of 

various powder panel designs and various dry powders contained within the panels.3,21,22 Standard 

designs included the use of thin aluminum foil, Nomex, or composite panels sandwiching an aluminum or 

Nomex honeycomb core, which contained the fire extinguishing powder. Typical powders included 

aluminum oxide (Al2O3), Purple K (KHCO3), and Monnex (KC2N2H3O3). Al2O3 has been extensively 

used in powder panel testing and is the only powder identified in U.S. aircraft applications, primarily due 

to its low corrosiveness compared to the other powders.5,13 A summary of some previously tested powder 

panel materials is included in Table 9–1. 

The literature review revealed some unique powder panel designs and configurations evaluated in 

previous testing,23,24 but also more common powder panel materials and designs. Very thin aluminum or 

aluminum foil and composite materials have most often been evaluated for the front face or the face 

toward an open dry bay. Similar materials have been evaluated for the back face or the face attached to or 

directly adjacent to the flammable fluid container. As Table 9–1 indicates and the literature search 

showed, the most commonly evaluated rib structural design by far has been honeycomb. The honeycomb 
Enhanced Powder Panels 933

has been composed of various materials, but it has most often been evaluated on its ability for even 

distribution of powder and for its structural rigidity. 

Table 9–1. Examples of Previously Tested Powder Panel Materials. 

Front Face Rib Structure Back Face 

Panel 

Thickness 

(mm) Powder 

0.025 mm 8111-0 

aluminum (Al) alloy foil 

0.10 mm Al 

0.51 mm 2024-T3 Al 

0.025 mm stainless steel 

5.1 mm titanium 

2-ply graphite-epoxy tape 

3-ply (0/90/0) graphite 

epoxy 

2-ply Kevlar-epoxy cloth 

polyethylene 

Pro-Seal coated ballistic 

nylon bags 

2024-T2 Al 

honeycomb 

fiberglass 

honeycomb 

Al foil bags 

Nomex 

honeycomb 

0.025 mm 8111-0 alloy Al foil 

0.33 mm Al 

0.51 mm 2024-T3 Al 

4.06 mm 2024-T3 Al 

2-ply fiberglass/ epoxy 

2-ply graphite/ epoxy tape 

3-ply (0/90/0) graphite/epoxy 

2-ply Kevlar/epoxy cloth 

polyethylene 

Pro-Seal coated nylon 

1.3 

1.8 

2.3 

2.5 

3.0 

3.0 

6.4 

9.5 

12.7 

25.4 

Monnex 

KDKI 

Al2O3

Al2O3+10 % KI 

Al2O3 with 1 % 

silicon oxide 

Purple K 

potassium 

bicarbonate 

10 % acetate in 

water 

In addition to examining military-specific powder panel testing, an examination of recent powder panel 

work for non-ballistic applications was performed. Data were obtained for powder panel evaluations 

using a much wider variety of materials with potential for greater fire extinguishing effectiveness. 

Drawing upon data from the powder panel survey, a baseline set of materials and designs was established 

for examination in the first phase of this project. 

The second phase of the NGP research involved an expanded survey and investigation that included the 

identification of aircraft using active halon systems for fire protection, particularly in areas where powder 

panels could be used. This research was to be used for later comparisons of potential powder panel fire 

protection systems with current halon systems. The expanded survey also included the identification of 

design issues for integrating enhanced powder panels into production aircraft and the identification of any 

necessary qualification testing required before implementation. 

The examination of aircraft fire protection systems in the expanded survey revealed that halon systems 

are infrequently used in dry bay areas.25 Conversely, powder panels have been demonstrated to be 

effective almost exclusively in these areas. Active halon fire extinguishing systems are prevalent in 

engine nacelles or auxiliary power unit compartments for fire protection (e.g., in the A-10, B-2, C-12, 

C-130, F-14, F-22, P-3 and many other aircraft) or for inerting in fuel tank ullage areas to protect against 

ullage explosion (e.g., in the A-6, F-16, and F-117). Powder panels have typically been evaluated in 

aircraft dry bay areas and have only been integrated into production aircraft in these areas (e.g., in the 

V-22 and AH-1W). Therefore, as a part of the cost-benefit or return-on-investment analysis presented 

later, a direct comparison of an existing halon fire extinguishing system with an enhanced powder panel 

system proved to be difficult. 

There are only a few potential examples of halon fire protection systems that could provide direct 

comparisons for a dry bay area. Most of these examples, however, do not offer likely replacement 

possibilities and are not applicable across a wide range of aircraft. For example, the C-5 aircraft has a 

center wing leading edge dry bay which is protected by a halon fire extinguishing system. However, this 
934 Powder Panel and Propellant Discharge Technologies 

system was incorporated to protect against overheat or safety-related fires from hydraulic components, 

not ballistic impact. It is located above the fuselage and would be difficult to hit in most reasonable 

combat scenarios. Replacement with a passive powder panel fire protection system may not prove 

practical in this case. As in this example, some of the current halon systems are focused on protecting 

flammable fluid lines or electronics, which has not been a focus for integrated powder panels thus far. 

The C-5 has two other dry bay-type areas with halon protection, focusing on electronics protection, not 

flammable fluid container protection. The B-1 also has an overwing fairing protection system, meant for 

protection of a hydraulic line and fuel line. It is not an ideal area for comparison with powder panels, 

either, for the same reasons discussed for the C-5 aircraft. Data were gathered during this survey for other 

aircraft areas that provide a more practical application for enhanced powder panels. 

Discussions were held with various aircraft manufacturers to examine production design requirements or 

issues, and to provide data to them, which could allow for the consideration of enhanced powder panels in 

design trade studies. The manufacturers included Bell Helicopter-Textron, Inc., The Boeing Company, 

Sikorsky Aircraft Corporation, and Lockheed Martin Corporation. The specific aircraft discussed were 

the V-22, RAH-66, and F-35. 

Specific production aircraft requirements were considered proprietary in most cases, but general design 

requirements were not and are notable. Among the key design criteria often mentioned in the discussions 

were powder panel thickness, areal density (mass per unit area), and temperature environment. As with 

any other aircraft component, particularly a forward-fit component, size and mass are big factors. The 

powder panel must not interfere with existing equipment and cannot create a significant mass penalty. 

Since design values associated with specific military aircraft are part of the technical specifications for the 

respective aircraft, these values will not be discussed herein. 

However, these values along with current commercial powder panel thicknesses and mass were used as 

design goals for the Phase II optimization effort. Commercial powder panels used for testing had 

thicknesses greater than 2.54 mm. The core was composed of a honeycomb design and the face sheets 

were constructed of a composite material. These panels had areal densities of around 2 kg/m2

. In 

repeated conversations with aircraft manufacturers, the temperature range most often quoted as a potential 

extreme requirement for powder panels was from -40 °C to 104 °C. In many aircraft areas, continuous 

service temperature would not reach these extremes, but for purposes of the optimization design effort, 

these temperatures were considered important. 

The aircraft prime contractors were also asked if enhanced powder panels would have to undergo any 

qualification tests such as thermal cycling, impact resistance, vibration or other durability testing, 

chemical resistance examinations, and moisture absorption evaluations, for example. Based upon their 

responses, data suggest that commercially available powder panels may have used individual material 

data to support such qualification, but the assembled powder panels did not appear to be subjected to 

many of these tests for production qualification. This is not to imply that future powder panel 

applications may be relieved of such requirements. Some limited production design criteria were 

considered for the fully assembled enhanced powder panel, such as panel thickness, areal density, and 

temperature environment, as mentioned above. However, resources in this program did not permit a full 

examination of many of these other potential production requirements. 
Enhanced Powder Panels 935

9.2.6 Powder Dispersion Screening Experiments 

Experimental Setup 

Phase I experimental testing was conducted at the Air Force 46th Test Wing Aerospace Survivability and 

Safety Flight’s Aerospace Vehicle Survivability Facility (AVSF) at Wright-Patterson Air Force Base 

(WPAFB), Ohio. 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 9–2 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.

Figure 9–2. Experimental Test Device and Powder Collection Methods. 

The test de a dry-towet shotline. The fuel tank is capable of holding fluid, and the dry bay has Lexan windows to allow for 

n 

candidate powder panels could be made. Figure 9–2 (right side) shows the powder collection methods 

Fuel Tank

(1 ft3)

Dry Bay

(2 ft3)

Powder

Panel

Shotline

Shotline

Powder

Collection Cups

Witness Rods Powder Panel

vice simulates a 0.057 m3

 (2 ft3) aircraft dry bay and a 0.028 (1 ft3) m3 fuel tank, with

visual observation of each test. Testing in Phase I did not involve fluid in the tank or airflow, to simplify

the screening process. Replaceable 7075-T6 aluminum panels of 2.03 mm thickness were inserted to 

represent the fuel tank wall adjacent to the dry bay. In most of the tests, powder panels were secured

directly in front of the fuel tank wall. This offered the worst-case scenario, without fluid in the tank, for 

evaluating the amount of powder released into the dry bay. The test device also allowed for the 

installation of powder panels directly behind the dry bay wall where the projectile enters the test article. 

The test device was designed to capture powder dispersion information so a direct comparison betwee

used in the dry bay. Witness rods are located throughout the dry bay. Plastic tubes are slid over the rods 

to capture released powder during each test. The rods are placed in a pattern to ensure that the powder 

dispersion characteristics throughout the dry bay are understood. The plastic tubes are qualitatively 

examined for signs of powder after each test. Powder collection cups are also located in the dry bay.
936 Powder Panel and Propellant Discharge Technologies 

These cups are located along the shotline, where the powder concentration is most important during a 

ballistic projectile impact. The path of the projectile incendiary or impact flash is the location where the 

mixture of flammable fluid and ignition source is most likely to result in fire initiation. The collection

cups were examined and weighed after each test to determine the amount of powder collected. In 

addition to these collection methods, each panel was weighed before and after each test to determine the

amount of powder released. Panel components were also individually weighed to assist in determining 

the mass of powder loaded into each panel. The removed area of the front face (dry bay side) of the

powder panel was also determined. This area was typically a direct correlation with the amount of 

powder released into the dry bay and provided another measure to compare the panels. The back face

(fuel tank side) removed area of the powder panel was also determined for comparison with the front face

and to examine the influence of one upon the other. Digital video was captured for each test to assist in

determining characteristics related to powder suspension and dispersion. 

Figure 9–3 shows the light-gas gun (compressed helium-filled bottle rated at 20.68 MPa) used to launch 

0.50 caliber hard steel ball projectiles at velocities of approximately 671 m/s. The kinetic energy of these 

igure 9–3. AVSF Range A Light-gas 

Gun. 

fire extinguishing agent. The powder selected was 

Purple K (KHCO3) due to its non-toxic nature, visibility for post-test inspection, and fire extinguishing 

ng the first phase of this program. These tests 

included components similar to those examined in previously tested powder panel programs to provide

projectiles was roughly equivalent to a threat greater than a 7.62 mm armor piercing incendiary (API), but

just less than a 12.7 mm API projectile. 

F

Testing during Phase I involved only one dry chemical 

effectiveness. Corrosion from long-term exposure was not a concern in these tests. 

Results of Powder Dispersion Screening Tests 

A total of 32 powder panel tests were conducted duri

some baseline data. Among the materials tested were thin aluminum (0.41 mm thick) and aluminum foil 

panels. Also examined were 3.2 mm and 6.4 mm thicknesses of 5052 aluminum honeycomb, acting as 

the rib structure for various panels. A Nomex (aramid fiber paper) honeycomb core of 9.5 mm thickness 

was also tested. Table 9–2 is a compilation of all systems examined. 
Enhanced Powder Panels 937

Table 9–2. Phase I Powder Panel Configurations Tested. 

Test 

No. Material Description 

Total 

Thickness 

(mm) 

Pretest 

Mass (g) 

1 0.41 mm Al front, 5.3 mm corrugated polyallomer, 0.25 mm Al back 6.0 630 

2 0.25 mm Al front, 5.2 mm corrugated polyallomer, 0.41 mm Al back 5.9 594 

3 Double wall polypropylene 4.5 427 

4 Double wall polycarbonate 6.6 561 

5 Double wall polycarbonate, scored 6.6 704 

6 1.52 mm ABS faces, 9.5 mm acrylic eggcrate rib 12.4 963 

7 1.8 mm (peak) acrylic prismatic faces, 9.5 mm acrylic eggcrate rib 12.9 1038 

8 2.0 mm clear acrylic faces, 9.5 mm acrylic tube ribs 13.5 1402 

9 1.8 mm textured acrylic front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 

102 mm and 203 mm 

6.9 769 

10 1.8 mm acrylic prismatic front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 

102 mm and 203 mm 

7.2 830 

11 102 mm x 102 mm scored clear 1.5 mm acrylic front, 2.0 mm clear acrylic back, 3.2

mm polycarbonate honeycomb rib 

6.9 574 

12 51 mm x 51 mm scored clear acrylic, 2.0 mm clear acrylic back, 3.2 mm 7.6 579 

polycarbonate honeycomb rib 

13 1.5 mm ABS faces, 9.5 mm Nomex rib (PN2-1/8-6.0) 13.5 1128 

14 1.8 mm textured acrylic front, 2.0 mm clear acrylic back, 6.4 mm Al honey

(PAMG-XR1-8.1-1/8-002-5052) 

comb rib 10.5 832 

15 1.5 mm ABS faces, 6.4 mm Al honeycomb rib (PAMG-XR1-8.1-1/8-00205052) 10.2 764 

16 2.0 mm clear acrylic faces, 6.4 mm Al honeycomb rib (PAMG-XR1-8.1-1/8-002-

5052) 

10.8 942 

17 1.5 mm ABS faces, 9.5 mm hollow acrylic tube ribs 13.3 1268 

18 51 mm x 51 mm scored 2.03 mm clear acrylic front, 2.0 mm clear acrylic back, 3.2

mm Al honeycomb rib 

7.2 638 

19 0.08 mm epoxy primer sheet front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) 

at 102 mm and 203 mm 

5.6 441 

20 1.8 mm acrylic prismatic front, 1.5 mm ABS back, 1.6 mm Al corrugation 5.6 434 

21 1.8 mm acrylic prismatic front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 

102 mm and 203 mm 

7.8 552 

22 1.8 mm styrene prismatic front, 1.5 mm ABS back, 1.6 mm Al corrugation 5.4 328 

23 1.8 mm styrene prismatic front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 

102 mm and 203 mm 

6.5 517 

24 1.5 mm fiberglass polyester resin front, 1.5 mm ABS back, two ABS ribs (3.0 mm 

thick) at 102 mm and 203 mm 

6.3 722 

25 1.5 mm polyester resin front, 1.52 mm ABS back, two ABS ribs (3.0 mm thick) at 

102 mm and 203 mm 

6.5 746 

26 Double wall polypropylene, scored, panel - on dry bay wall 4.3 402 

27 2.5 mm polyester resin front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 102 

mm and 203 mm 

7.1 620 

28 2.5 mm polyester resin front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 102 

mm and 203 mm 

7.4 876 

29 2.5 mm epoxy resin front, 1.5mm ABS back, two ABS ribs (3.0 mm thick) at 102 mm 

and 203 mm 

7.1 791 

30 1.3 mm clear acrylic front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 102 

mm and 203 mm 

6.7 597 

31 1.3 mm clear acrylic front, 1.5 mm ABS back, two ABS ribs (3.0 mm thick) at 102 

mm and 203 mm, dry bay clutter 

6.2 596 
938 Powder Panel and Propellant Discharge Technologies 

The majority of tests featured unique materials and designs not evaluated in previous powder panel 

ballistic testing. The goal was to find a front face material and powder panel design that results in 

significant front face material loss and powder release into the dry bay during a ballistic impact event. 

T o he front el face ( ay 

ide), materials that exhibited brittle properties upon impact, but durability in handling, were of utmost 

y in an actual production 

ycarbonate and polypropylene. They were filled with powder in their production form, 

its flexure, thereby working against crack propagation. 

the solid strips was minimized since powder would not be present in these locations during a projectile 

herm plastic and thermoset materials were the focus of most testing. For t pan dry b

s

interest. Front face materials evaluated included a polycarbonate (Lexan), polystyrene, polypropylene, 

and polymethylmethacrylate (acrylic, Plexiglas). These materials are cost-effective and easily obtainable 

in off-the-shelf forms. For example, off-the-shelf acrylic and polystyrene overhead fluorescent lighting 

panels in a variety of faceted designs were tested. These designs may enhance or degrade their brittle 

nature. The use of intentional surface scoring of flat 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. 

Thermoset polymers were also evaluated for the front face. Tested materials included two polyester 

resins, an epoxy resin, and a thin epoxy primer. The thin epoxy primer tested was only 0.076 mm 

(0.003 in.) thick. It is available commercially as a spray and requires a careful procedure for forming it 

and bonding it to the rib structure. The other thermoset materials are readily available in commercial 

form, requiring the mixing of a two-part liquid resin. 

Plastics were also tested for the back face (fuel tank wall side) and in various configurations for the 

internal rib structure of the panel. The impetus for experimenting with the back panel was to determine if 

the fracture characteristics of the back panel influence the front panel in any way. For the dry bay/fuel 

tank configuration examined, there was a desire to inhibit the back panel hole size to reduce flammable 

fluid leakage, which could assist in reducing fire ignition probabilit

configuration. 

Finally, a number of materials and designs were examined for the powder panel internal rib structure. 

The rib structure adds rigidity and strength to the panel, prevents settling of the powder, and must allow 

for easy release of as much powder as possible. Some of the panels examined in Phase I were single 

piece extruded materials that had front and back walls and internal channels. These panel designs were 

composed of pol

and the ends were sealed for testing. 

As mentioned, honeycomb materials were also examined. One honeycomb material evaluated was 

3.2 mm thick, composed of polycarbonate material, and featured a circular cell structure. The honeycomb 

materials maximized the amount of bonding area to the front panel, which typically inhibited front face 

cracking. Bonding areas could be reduced to allow for more cracking of the front face, however, the 

support of the honeycomb structure inhib

Several other rib designs were conceived to enhance powder release and yet prevent the settling of 

powder that might reduce its effectiveness to impacts in certain areas. One design included sections of 

hollow acrylic tubing aligned horizontally and spaced at vertical distances of one inch or less. Both the 

tubes and the spaces between the tubes were filled with powder to ensure total coverage to threat impact. 

This rib design provided significant panel stiffness due to the amount of bonding surface area and seemed

to provide leverage for sections of the front face to flex and break out. Another design concept was to use 

strips of solid plastic oriented horizontally in a fashion similar to the tubes. In these trials, the width of 
Enhanced Powder Panels 939

impact. Tests were conducted with the number of these ribs minimized, the spacing maximized, and the 

overall panel thickness minimized. These panels were relatively stiff due to the strength of the panel 

face-to-rib bonds, but allowed for significant flexing of the front face due to the rib spacing. This rib 

arrangement required several tradeoffs. Ribs that formed channels too far apart allowed powder settling 

or bulging of the face sheets, but allowed for flexure of the front face during impact, which optimized 

cracking. Rib channels that were too close together prevented powder settling, but were more prone to 

function like honeycomb and provide too much support to the front face, reducing the likelihood of 

significant cracking. In these rib arrangements, powder along the length of the panel could be released 

from all open channels, which afforded greater performance than a honeycomb design. In a honeycomb 

design, only the cells penetrated or torn around the perimeter of the impact will release powder, unless 

significant cracking or area is removed from the front face. 

A corrugated aluminum foil with 1.6 mm peak-to-peak height was also examined in some tests. The 

metal did not show a propensity to break up in these tests, so the front face would need to break up and 

separate for the panel to be effective. Some of the benefits of this design are similar to the channel 

design; however, the combination of metal and plastic in these trials may have some operational 

environment drawbacks, such as significantly different coefficients of thermal expansion. This design, 

the acrylic tube design, and variations of the horizontal plastic strip design allowed for filling of the 

gns in Experimental Testing. 

powder panel after the panel was nearly assembled. Only the one edge had to be sealed after filling. This 

design variation could offer some improvement for assembly. 

Phase I testing was able to identify novel powder panel designs with enhanced performance over more 

standard design concepts. Table 9–3 lists some of the more novel and effective designs, while Table 9–4 

lists some designs that feature more baseline design concepts and less effective performance. 

Table 9–3. More Effective Powder Panel Desi

Test 

No. Material Description 

Thickness 

(mm) 

Panel 

Mass (g)

Powder 

Release 

(g) 

% Powder 

Released 

Front Face 

Area 

Removed 

(cm2) 

8 2.03 mm clear acrylic faces, 9.53 mm acrylic 13.5 1402 48 6 

tube ri

32 

bs 

9 1.7

ABS back, two ABS ribs (3.05 mm thick) 

8 mm cracked ice acrylic front, 1.52 mm 6.9 769 23 5 18 

12 2.03 mm (50.8 mm x 50.8 mm scored) clear 

acrylic, 2.0 , 3.18 mm 

polycarbon

3 mm clear acrylic back

ate honeycomb rib 

7.6 579 9 5 23 

21 1.78 mm acrylic prismatic front, 1.52 mm 

ABS back, two ABS ribs (3.05 mm thick) 

7.8 552 30 13 20 

23 1.78 mm styrene prismatic front, 1.52 mm 

ABS back, two ABS ribs (3.05 mm thick) 

6.5 517 28 13 26 

27 2.49 mm polyester resin front, 1.52 mm ABS 

back, two ABS ribs (3.05 mm thick) 

7.1 620 8 4 25 

28 2.49 mm polyester resin front, 1.52 mm AB

back, two ABS ribs (3.05 mm thick) 

S 7.4 876 83 18 81 
940 Powder Panel and Propellant Discharge Technologies 

Table 9–4. Less Effective Powder Panel Designs in Experimental Testing. 

Test 

No. Material Description 

Thickness 

(mm) 

Panel 

Mass (g)

Powder 

Release 

(g) 

% Powder 

Released 

Front Face 

Area 

Removed 

(cm2) 

1 0.41 mm Al front, 5.3 mm polyethylene 

cor

6.0 630 0.6 0.2 1 

rugated rib, 0.25 mm Al foil back 

2 0.25 mm Al foil front, 5.2 mm polyethylene 

corrugated rib, 0.41 mm Al back 

5.9 594 0.04 0.01 1 

13 1.5 mm ABS faces, 9.5 mm aramid rib 13.5 1128 1.5 0.2 1 

14 1.8 mm textured acrylic front, 2.0 mm clear 

acrylic back, 6.4 mm Al honeycomb rib 

10.5 832 1 0.2 1 

15 1.5 mm ABS faces, 6.4 mm Al honeycomb 

rib 

10.2 764 1 0.2 1 

16 2.0 mm clear acrylic faces, 6.4 mm Al 

honeycomb rib 

10.8 942 3 0.6 2 

18 2.0 mm (5.1 cm x 5.1 cm scored) clear acrylic 

front, 2.0 mm clear acrylic back, 3.2 mm Al 

honeycomb rib 

7.2 638 2 0.8 10 

T t er panel, h wer about 2 mm square. Total powderfilled s tested in the first year of testing ranged from 428 g to 1,400 g. Most of the mass 

d r e ls, w he ma of the powder contributing 

signif l volume. By contrast, commercial panels obtained during 

e N tween 175 g and 189 g for a similar size. Obviously, this was one design feature 

nel may have been virtually the same size as the projectile 

 the entire dry bay and remained for a matter of minutes. Many tests 

he ables indicate the mass of each powd

mass for panel

whic e all 30

iffe ence is due to varying thicknesses of th

icantly because of increased panel interna

GP weighed be

pane ith t ss 

th

requiring optimization in Phase II testing. 

Some measures of effectiveness are also noted in Table 9–3 and Table 9–4, including powder release or 

loss as a result of the ballistic test, percentage of the powder released, and the front face area removed. 

The estimate of the powder release is determined by comparing the panel mass before and after each test 

and weighing/estimating panel material lost. In cases where the panel was not effective at dispersing the 

powder, the hole on both faces of the pa

(12.7 mm diameter). In other cases, a significant amount of the front face material may have been lost 

(Figure 9–4). Obviously, in these cases, a significant amount of powder was also released from the panel. 

The amount of powder released during testing varied from a fraction of a gram in some of the more 

standard designs to over 100 g. 

A review of the Phase I test data indicated a wide disparity in the reaction of the panels. In some tests, the 

powder release was negligible, i.e., no powder was detected on the witness rods and no powder deposited 

in the cups. In these ineffective powder panel tests, more powder is actually observed exiting the back of 

the panel, along with the projectile, versus entering the dry bay. In other tests (Figure 9–5), the cloud of 

powder in the dry bay engulfed

resulted in some minute residue in the cups that was more likely spall from the powder panel front face 

and/or ribs, rather than the powder. In tests of effective powder panel concepts, powder was observed on 

all the witness rods and measurable powder mass was observed in all six cups. The amount of powder 

deposited in the collection cups varied during testing from no trace to over seven grams by mass. 
Enhanced Powder Panels 941

Figure 9–4. Test 

xample of

Significant Panel 

racture and

Material Loss. 

Typically, 0.05 g or less was captured in any single cup, with the highest concentration of the powder 

being closest to the powder panel, as expected. Twenty different witness rods were placed throughout the

dry bay and visible powder was noticed in more effective tests on all of the witness rods. To further

verify the dispersion of the powder for effective designs, several panels were tested with dry bay clutter 

and powder was still observed on all witness rods, even those in isolated areas. 

ffective

owder Release and 

ispersion.

E

F

Figure 9–5. Test

Example of E

P

D
942 Powder Panel and Propellant Discharge Technologies 

Front Face Removal

60

70

80

90

0

10

20

30

40

50

7 Powder Panels from Both Categories

Front Face Area Removed (sq. cm.)

More Standard Design Elements

Promising Enhanced Designs

28

minutes in one test compared to one second or less). Finally, the design and fabrication effort revealed 

enhanced powder panels afforded greater design flexibility, which can be utilized to target mass, 

durability, and other application-specific design goals. These findings revealed that new powder panel 

concepts could significantly enhance the fire extinguishing effectiveness of this vulnerability reduction

method, thereby demonstrating the feasibility of enhanced powder panels. 

Figure 9–6. Effect on 

Powder Panel Fracture 

Area of Standard 

Design Features and

Enhanced Des 8

9

12 21

23 27

1 2 13 14 15 16

18

The el designs examined in this research offer the potential to be 

competitive with halon 1301 in a wider variety of dry bay designs. In one of these cases (epoxy primer

ont face), nearly 50 % of the front face area was removed, almost 60 % of the powder was released, and 

the powder remained suspended throughout the dry bay for over four minutes. This occurred despite the

ct that this was one of the thinnest panels tested. This compares with testing of other powder panel 

e powder disperses only along the shotline, dissipates 

tenths of a second, and the amount of dispersed powder was limited to the region of projectile 

enetration (approximate powder release of a few percent).26

t n standard powder panels (as much as four 

igns.

most promising of the new powder pan

fr

fa

designs integrated into operational aircraft, where th

in

p

Figure 9–6 and Figure 9–7 show major performance benefits achievable with some of the enhanced

design concepts listed in Table 9–3 (by test number) over more standard powder panel designs

(Table 9–4). Results indicated the powder panel front face area removed could be increased by 15 to 

20 times over more standard designs (Figure 9–6). Testing also revealed the amount of powder released

into a dry bay could be increased 5 to 10 times with an enhanced powder panel design (Figure 9–7). 

Testing also indicated that powder dispersion could be enhanced, even with dry bay clutter, ensuring the 

prevention of fire ignition over a wider area (Figure 9-8). In this figure, the number of witness rods with 

detectable powder residue is indicated for each test. Effective designs resulted in powder being 

suspended in the dry bay for much longer periods of time ha
Enhanced Powder Panels 943

Figure 9–7. Effect on 

Powder Delivery of 

Standard Design 

Features and 

nhanced Designs.

igure 9–8. Effect on

Powder Dispersion of 

tandard Design

Features and 

nhanced Designs.

i tmost 

importance. More brittle materials outperformed ductile materials (that res ing

more powder into the dry bay. The projectile seemed to melt its way nd

Powder Release

E

F

S

E

al properties are of u

ist fracturing) by releas

through polycarbonate a

0

5

10

15

20

7 Powder Panels from Both Categories

% of Powder Release

More Standard Design Elements

Promising Enhanced Designs

8

9 12

21

23

27

28

1 2 13 14 15 16 18

Witness Rods

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

1234567

7 Powder Panels from Both Categories

No. of Witness Rods with Visible Powder (out of 20)

More Standard Design Elements

Promising Enhanced Designs

8 9 12 21 23 27 28

1

2

13

14

15

16

18

Experimental observations indicate, as predicted, that the front face mater
944 Powder Panel and Propellant Discharge Technologies 

polypropylene materials, and even some polystyrene materials, resulting in little or no powder released 

into the dry bay. Acrylic front face panels and faceted acrylic and styrene materials reacted in a much 

ore brittle nature, resulting in lost material or cracking that more effectively released powder into the 

dry bay. One acrylic panel with a prismatic square pattern actually did not perform very well. It appears 

at the pattern on the panel inhibited crack growth. Mixed results were found during testing of scored 

lic panels. Some cracking seemed to follow scoring lines in the vicinity of the impact that may have 

ontributed to more material loss. However, comparisons between 5.1 cm and 10.2 cm scoring patterns 

showed that cracks emanating from the hole area, created directly by the projectile impact, were actually 

area without allowing critical flexure of the front face. Design concepts using channels or horizontal ribs 

age sustained by the 

back face was a hole just larger than the diameter of the 12.7 mm diameter ball projectile. 

m

th

acry

c

prevented from growing longer, i.e., scoring lines acted as crack stoppers. With appropriate scoring 

designs, though, it appears crack growth optimization techniques could be used to enhance performance. 

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

area between the front face and ribs inhibited powder dispersion for the designs tested. Results indicated 

that standard honeycomb ribs resisted greater front face cracking because of the increased number of 

bond sites. Experiments on bonding honeycomb materials to the front face in a reduced number of 

selected areas, such as the panel perimeter, proved effective for polycarbonate honeycomb, but not 

necessarily for the aluminum honeycomb. It was reasonable to conclude from the testing, weaker and 

fewer bonding sites would allow both designs to function more effectively, as previous work has shown. 

Multiple explanations were plausible for the more effective polycarbonate tests. It is probable there was a 

contribution from the more brittle properties of the polycarbonate, which did fracture in some locations, 

and the design of the aluminum honeycomb likely distributed the impact energy over a greater surface

proved to be associated with the most effective powder panels, particularly when a more frangible front 

face was used. Channel designs allowed more powder to be released from the impact location than more 

segmented or cellular designs. Tradeoffs would be necessary for these designs between rib spacing and 

powder loading, as sufficient powder must be available at all potential impact sites, but more powder 

translates to greater mass. Testing indicated three-piece powder panel designs outperformed easy-toassemble double-wall extrusion designs, as built-in rib channels inhibited cracking. 

Variation in the powder panel back face had much less effect on powder panel performance than the front 

face or rib design. A number of tests involved less brittle ABS material for the back face, since it is 

postulated that a smaller hole in the back face may actually mitigate the chance of a dry bay fire by 

reducing fuel leakage and confining it to an area along which most of the powder is released. This would 

provide a second means to increase powder panel effectiveness. The first being the use of a more brittle 

front face to maximize fire extinguishing powder release, while the flammable fluid leakage is minimized. 

Experimental testing did reveal that the front face of the powder panel can be designed to fracture and 

release large amounts of powder, while minimizing the damage to the panel back face. Phase I testing did 

not involve a fluid-filled tank, thereby eliminating hydrodynamic ram pressures on the fuel tank wall and 

reducing the chance of damage to the back face. In the tests involving ABS, the dam
Enhanced Powder Panels 945

9.2.7 Live-fire Proof-of-concept Demonstrations 

China Lake Testing Facilities 

Following Phase I experimental testing, Skyward, Ltd. was afforded the opportunity to participate in 

several live fire demonstration tests of enhanced powder panels. These proof-of-concept tests were 

 bays and involving the potential ignition of a 

fuel fire. These tests provided Skyward with an opportunity to select some of the more effective 

res identified in Phase I, perform some quick optimization, add some 

y evaluated, and perform live fire testing, all in advance of the 

rgetic backing with any powder panel design to enhance powder delivery 

nducted at the Naval Air Warfare Center-Weapons Division Weapons 

ke, California. Four tests of enhanced powder panels without 

or blade with 

 9-10 shows a schematic of the test article. A simulated rotor blade was 

into the luggage compartment and an ignitor initiated a fire in the 

conducted in two different test series simulating aircraft dry

enhanced powder panel design featu

unique design features not previousl

initiation of Phase II. The promising results of these demonstration tests provided a leap forward for the 

initiation of Phase II. 

JTCG/AS Demonstration Testing 

The ability of enhanced powder panels to prevent fire ignition was first demonstrated in a Joint Technical 

Coordinating Group on Aircraft Survivability (JTCG/AS), since renamed Joint Aircraft Survivability 

Program Office (JASPO), test program examining reactive powder panel concepts, which is a method of 

using a reactive ene

effectiveness.27 These tests were co

Survivability Laboratory in China La

reactive backing were conducted. These tests involved the firing of 12.7 mm API projectiles into a dry 

bay/fuel tank simulator containing JP-8 fuel. Projectiles were fired at approximately 757 m/s at a 

0° angle into the dry bay, impacting an aluminum striker plate, which was separated from the powder 

panel/fuel tank by approximately 0.30 m. The projectiles then continued through the powder panel, 

penetrating the fuel tank and releasing JP-8 fuel. A 0.46 m wide x 0.61 m high x 1.22 m long dry bay 

(right side of Figure 9–9) was connected to a 1.22 m x 1.22 m x 1.22 m fuel tank (left side of Figure 9–9). 

A 3.18 mm thick 2024-T3 simulated fuel tank bulkhead was positioned on the front or initial impact side 

of the fuel tank. The powder panel was attached to this removable bulkhead panel with a 2-part epoxy 

adhesive. Tests were also conducted with commercial powder panels in this test series to provide a basis 

of comparison with the enhanced powder panel tests, as well as to tests with no protection. 

FAA Demonstration Testing 

A second demonstration test series of an enhanced powder panel was conducted in a Federal Aviation 

Administration (FAA) program.28 This test series was also conducted at China Lake, just after the 

JTCG/AS series. This test examined the feasibility of powder panels in preventing fuselage fires in 

commercial aircraft caused by the release and impact of an uncontained engine rot

flammable fluid lines. Figure

fired through the lower bay and 

presence of leaking fuel as the rotor blade penetrated the lower bay. An enhanced powder panel 

successfully prevented a fire from igniting in one of the tests. A second test was invalidated due to 

problems with the timing sequence, but unrelated to the powder panel. Two commercial powder panel 

tests were also conducted during this test series to evaluate their effectiveness and allow comparison of 

the results with those of the enhanced powder panel test. 
946 Powder Panel and Propellant Discharge Technologies 

Figure 9–10. Schematic of the FAA Test Article. 

Figure 9–9. JTCG/AS Test Article. 

Fuel Tank Dry Bay 

Cabin Area

Lower Bay Containing

Flammable Fluid Lines Luggage Compartment
Enhanced Powder Panels 947

Live Fire Test Results 

Following the experimental testing of Phase I, the opportunity for demonstrating enhanced powder panels 

at the Navy’s Weapons Survivability Laboratory. Lessons learned from the NGP Phase I 

ental testing were used to design and fabricate some new, slightly more optimized powder panels. 

These panels again incorporated thermoplastic materials. However, thinner panels and reduced powder 

loading resulted in reduced mass, and new panel designs were utilized. Masses were decreased o

average 100 g to 200 g from those designs evaluated in experimental testing for 30.2 cm x 30.2 cm 

panels. The mass of the panels tested at China Lake varied from 320 g to 422 g, and the thicknesses 

ranged from 2.4 mm to 3.3 mm. In both the JTCG/AS and FAA test programs, the enhanced powder 

panels showed solid improvement over current powder panel designs. Fire ignition was prevented in all 

five valid tests involving enhanced powder panels (four JTCG/AS tests and one FAA test). Conversely

fires resulted in all four valid commercial powder panel tests (two JTCG/AS and two FAA tests). 

The powder releases from both the commercial and enhanced panel designs in the China Lake tests wer

uch as ten times those experienced in the light gun tests conducted at WPAFB due to a num

arose 

experim

n

,

e

as m ber of 

ignificant differences in the two facilities and test protocols: the energy of the projectile used at China 

ake was about 17% larger; the striker plate at China Lake caused the projectile to spall and yaw; and, 

most significantly, fuel w ures from the hydraulic

ram effect, distorting the wall and imparting additional forces on the panel. 

Figure 9–11 shows some images captured from high-speed video in JTCG/AS testing demonstrating the

Capability. 

s

L

as present in the China Lake tests that applied extra press

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 % for 

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

enhanced powder panels. Figure 9–12 compares the amount of fire extinguishing powder released from

an enhanced powder panel with a commercially available powder panel in the JTCG/AS tests. 

Incendiary

Function

Fire

Ignition

Fire

Sustains

Commercial

Powder Panels

E

P

Figure 9–11. 

Enhanced 

Powder Panel 

Fire Mitigation 

Incendiary

Function

Fire

Prevented

Dry Bay Engulfed

in Powder

nhanced

owder Panels
948 Powder Panel and Propellant Discharge Technologies 

Figure 9–13 shows that impact of the enhanced powder panel by a rotor blade in the FAA test resulted in

release of all the fire extinguishing agent, as it prevented fire ignition. Baseline testing showed that

unprotected fuselage areas did indeed result in sustained fires. 

n of 

ommercial

owder Panel 

Agent Release 

JTCG/AS

Dry Bay Fire

l Released During FAA Test in 

Figure 9–12.

Compariso

C

and Enhanced 

P

in

Extinguishing 

Testing. 

Commerci

~5-10% Powde

al Powder Panel

r Release

Enhanced Powder Panel

~90% Powder Release

Figure 9–13. Entire Contents of Enhanced Powder Pane

Which the Fire Was Prevented. 
Enhanced Powder Panels 949

9.2.8 Optimization Program 

Optimization Testing Methodology

In Phase II, Skyward continued their impact dynamics research, with a focus on optimizing the enhanced

powder panels, parametrically examining design variations, and then demonstrating the optimized panels.

Panel materials, thickness, and construction techniques were optimized to reduce the panel mass and 

thickness, while maintaining effective powder release and dispersion. 

Testing was conducted in the same simulated dry bay experimental device used for concept evaluations in

Phase I, and with the same light gas gun launching 12.7 mm diameter ball projectiles. Optimization test

variables included panel materials and thicknesses, fire extinguishing powder loading (mass of powder

inserted into a given panel size), rib designs, and the assembly process. Optimization testing focused on 

three primary areas of investigation: 

• effectiveness optimization (maximize front face fracture and powder release); 

• reliability improvement veness, increase durability, 

tal leakage).

Maximizing powder release into the dry bay continued to be the defining goal, but other requirements 

that the enhanced powder panels were as practical and reliable

 was minimized, and other potential production 

) over Purple K (KHCO3) or other 

powders, even though these other powders have been demonstrated to be more effective as fire

ce Al2O3 has a much higher specific gravity than KHCO3 (3.95 

compare t ccess in mass

reductio an average of

approxi t

Certain n

Phase II. T

ront and back faces. The rib design was examined in detail

because it directly affects the potential fire extinguishing powder loading, which can be the primary mass 

• practicality enhancement (reduce mass, decrease panel thickness, address production issues); 

and 

(quantify reliability of measures of effecti

and reduce risk of acciden

were levied on the design effort to ensure

as possible. Mass was reduced, panel thickness

requirements were considered. An areal density (mass per unit area) target was provided by one of the 

vehicle manufacturers for the design effort. 

Phase II testing primarily involved the use of aluminum oxide (Al2O3

extinguishing agents. At least two of the aircraft manufacturers in the powder panel survey expressed

doubt that any potentially corrosive chemical powder would be acceptable by their aircraft, so there was a 

conscious effort made to demonstrate the effectiveness of Al2O3 during the optimization testing. Al2O3 is 

the only known powder panel agent to be incorporated into an aircraft due to its lack of reactivity with

aircraft structure. Additionally, sin

d o 0.88), it was thought to be worst-case and would help with determining su

n efforts. The Al2O3 tested was 5 μm in average particle diameter, compared to

ma ely 30 μm for the KHCO3, which may also mean the former could pack more tightly. 

fro t face materials evaluated in Phase I testing proved to be effective and remained a focus in 

hese materials included thermoplastics with brittle material properties and some thermoset 

resins. Other unique materials were also examined that more appropriately targeted optimization 

requirements. Efforts were made to minimize front face and overall thickness and yet maintain sufficient 

strength to avoid accidental fracture. Lower density materials were compared to more dense materials. 

Various new and unique designs were examined for the rib structure in Phase II, including the thickness 

of the ribs and attachment methods to the f
950 Powder Panel and Propellant Discharge Technologies 

driver in the overall design. Various rib materials were examined for influence on powder panel 

performance, including some materials evaluated in the more effective Phase I designs. 

Phase II testing also included examinations of back face materials and thicknesses and their influence on 

powder panel effectiveness. Materials examined in Phase I were once again tested along with some 

materials not previously evaluated. Testing included designs where the front and rear faces and the rib 

materials were the same and others where dissimilar materials were used. 

Bonding techniques were also examined, with an emphasis on ensuring a robust overall design that 

reduced the risk of accidental leakage. In addition, rib-to-face bonding was examined for its influence on 

the performance of the powder panel. This influence was noted in Phase I testing and further examined in 

ts 

the panels tested and includes pretest panel masses and areal densities, along with the mass of powder 

Phase II. Bonding materials were examined, as well as bonding patterns or techniques. 

Parametric/Optimization Experimental Results 

A total of 25 tests were conducted in Phase II optimization tests in Range A at the AVSF. Table 9–5 lis

released, the percentage of powder released, and the estimated front face area removed. The panels are 

listed in descending order by the mass of powder released in each test. 

Table 9–5. Phase II Optimization Tests. 

Test 

No. Material Description 

Total 

Thickness 

(mm) 

Pretest 

Mass (g)

Areal 

Density 

(kg/m2) 

Powder 

Release 

(g) 

% Powder 

Released 

Face Area 

Removed 

(cm2) 

5 0.64 mm polystyrene front 

1.3 mm polycarbonate ribs 

0.51 mm polycarbonate back 

2.4 295 3.24 5.2 3.2 11 

22 0.76 mm acrylic front 2.3 215 2.37 4.

0.76 mm polycarbonate ribs 

0.76 mm polycarbonate back 

0 8.4 6 

24 0.51 mm composite front 

0.76 mm polycarbonate ribs 

0.38 mm polycarbonate back 

1.6 141 1.55 3.0 6.3 1 

8 0.76 mm acrylic front 

0.76 mm polycarbonate back 

3.0 348 3.82 3.0 1.8 12 

1.3 mm polycarbonate ribs 

18 0.64 mm polystyrene front 

0.76 mm polycarbonate ribs 

0.51 mm polycarbonate back 

1.9 332 3.65 2.5 1.2 2 

14 0.64 mm polystyrene front 2.7 368 4.05 

1.3 mm polycarbonate ribs 

0.76 mm polycarbonate

2.2 1.9 10 

 back 

2 0.64 mm polystyrene front 

0.76 mm polyc onate ribs 

0.51

252 1.8 

arb

 mm polycarbonate back

2.4 2.77 2.2 5 

10 0.76 mm acrylic front 

1.3 mm polycarbonate ribs 

0.76 mm polycarbonate back 

2.8 453 4.98 2.1 0.7 1 
Enhanced Powder Panels 951

Test 

No. Material Description 

Total 

Thickness 

(mm) 

Pretest 

Mass (g)

Areal 

Density 

(kg/m2) 

Powder 

Release 

(g) 

% Powder 

Released 

Face Area 

Removed 

(cm2) 

4 0.64 mm polystyrene front 

1.3 mm polycarbonate ribs 

0.51 mm polycarbonate back 

2.4 330 3.63 1.7 0.8 24 

23 0.51 mm composite front 

0.76 mm polycarbonate ribs 

0.38 mm polycarbonate back 

1.6 140 1.54 1.6 2.8 2 

17 0.64 mm polystyrene front 

0.76 mm polycarbonate ribs

0.51 mm polycarbonate back 

1.9 330 3.63 1.5 0.8 2 

6 0.64 mm polystyrene front 

0.76 mm ABS ribs 

0.76 mm ABS back 

2.2 201 2.21 1.4 1.5 10 

11 0.64 mm polystyrene front 

1.3 mm polycarbonate ribs 

0.76 mm polycarbonate back 

2.7 404 4.44 1.0 0.7 7 

13 0.64 mm polystyrene front 

1.3 mm polycarbonate ribs 

0.76 mm polycarbonate back 

2.7 410 4.51 0.8 0.5 3 

16 0.64 mm polystyrene front 

0.76 mm polycarbonate ribs

0.51 mm polycarbonate back 

1.9 306 3.37 0.8 0.4 2 

7 0.64 mm polystyrene front 

0.76 mm ABS ribs 

0.76 mm ABS back 

2.2 194 2.13 0.8 0.9 6 

21 0.64 mm polystyrene front

0.76 mm polycarbonate ribs 

0.76 mm polycarbonate back 

2.2 192 2.10 0.6 1.2 1 

9# 0.08 mm glass epoxy front 

0.1” Nomex honeycomb ribs 

0.08 mm glass epoxy back 

2.7 175 1.92 0.3 0.2 1 

1 

ycomb 

5# 0.08 mm glass epoxy front 

2.5 cm Nomex hone

ribs 

0.08 mm glass epoxy back 

2.7 175 1.92 0.2 0.2 0.5 

19 

k 

1.0 mm polycarbonate front 2.5 270 2.96 0.1 0.3 0.7 

0.76 mm polycarbonate ribs 

0.76 mm polycarbonate bac

20* 

k 

1.0 mm polycarbonate front 2.5 261 2.87 N/A N/A 0.7 

0.76 mm polycarbonate ribs 

0.76 mm polycarbonate bac

25* 

k 

0.51 mm composite front 1.6 124 1.36 N/A N/A 19 

0.76 mm polycarbonate ribs 

0.38 mm polycarbonate bac

# Existing . 

*Tests co el tank; not able to accurately determine powder release. 

 powder panel designs

nducted with water in fu
952 Powder Panel and Propellant Discharge Technologies 

A summary of the designs is also provided in Table 9–5, listing the front and back face materials and the 

material thickness. Effective front face materials tested in Phase I were evaluated, including a textured 

polystyrene. Some other materials were also examined, including other thermoplastics and some 

compos d in Phase I. Materials used for the back face concentrated on 

polycarb ffective in Phase I, although some tests were conducted with ABS, a 

m du also s the aterials tested and the thicknesses of the internal 

section ib designs and manufacturing processes were examined in the 

optimiza s most often mirrored the back face material. 

Optimiz ificant decreases in mass were possible from Phase I test panels, while 

maintain lease. Panel masses were reduced as much as 57 % from the lightest 

p te th an ease i der e. Fi 9–14 ares the lightest 

Ph e II se I panel and a c rcial powder panel. Two of the lightest pretest 

filled pa 140 g. By comparison, commercial powder panels tested in Phase II 

w ed erefo he enh d pow anels were reduced as much as 29 % 

below t . Enhanced powder panel thicknesses ranged between 1.6 mm and 

3.0 mm . This was a reduction of more than 60 % from the thinnest panel 

t in panels uated ase II 2.7 mm in thickness. The enhanced 

powder ced about 39 % in thickness below the commercial powder panel. 

Powder release is an important factor in the testing because the greater the amount of powder dispersed in 

the dry bay, particularly along the shotline, the lower the chance of an ignited fire. The amount of powder 

released in Phase II testing ranged from as low as 0.1 g to as much as 5.2 g. This powder release or loss 

is not as much as the most effective panels in Phase I testing, but the panel thickness and available 

powder has been significantly reduced to meet likely design goals. Powder release for the commercial 

ite materials not evaluate

onate, which proved to be e

ore ctile material. Table 9–5 show rib m

of the panel. Different r

tion testing. Rib material

ation testing indicated sign

ing improved powder re

anel

as

sted in the first phase, wi incr n pow

omme

releas gure comp

 panel with the lightest Pha

nel masses were 124 g and 

eigh approximately 175 g. Th re, t ance der p

he commercial panel mass

 in optimization evaluations

ested Phase I. Commercial eval in Ph were

panels were, therefore, redu

Figure 9–14. Enhanced Powder Panel 

Mass Reduction. 

Figure 9–15 compares the thinnest panels tested in Phase I and Phase II with the commercial powder 

panels. Reductions in thickness reduce the amount of powder in the panel, which is the significant mass 

consideration. However, a thicker panel along the shotline also reduces the potential powder release, 

which obviously affects powder panel effectiveness. Therefore, there is a balance necessary between 

panel thickness, which affects panel mass, and the effectiveness of the panel, as measured by powder 

release or loss. Front and back face materials and the rib structure design were other variables examined 

to increase performance without increasing mass. 

Filled Powder Panel Weight

0.00

50.00

100.00

150.00

200.00

250.00

300.00

350.00

Phase I Lightest Phase II Lightest Commercial Powder

Weight (g)

Enhanced Powder Enhanced Powder Panel

Panel Panel

Mass (g) 

Filled Powder Panel Mass
Enhanced Powder Panels 953

powder panel tests was 0.2 g and 0.3 g. Figure 9–

powder panel (no water in the tank) with the best perform

the amount of powder released from the enhanced powd

16 compares the best performing Phase II enhanced

ing commercial powder panel. These data show

r panels was as much as 21 times greater than 

the commercial powder panels. 

he percentage of powder released (powder released or lost divided by pretest total powder loading 

ultiplied by 100) has also been used as a measure of powder release effectiveness. The enhanced panel

esign attempts to maximize the release of the available powder in the panel. Optimized panels tested

0.3 % to 8 % of the total powder released. The commercial panels released approximately 

.2 % of the total powder contained. 

 with a ranking of the panels by total powder released, since there was

some considerable variance in overall pretest panel mass. 

Tests 9 and 15 in Table 9–5 were conducted on the commercially available powder panels. As mentioned 

reviously, these panels are composed of a honeycomb core and two thin composite face sheets. The 

commercial powder panels were among the lighter panels tested (empty mass and with powder), but also

leased nearly the least amount of powder and the smallest percentage of powder. Except for one test

e

Figure 9–15. Enhanced Powder Panel 

Thickness Reduction. 

Powder Panel Thickness

0.00

1.00

2.00

3.00

4.00

5.00

Phase I Thinnest Phase II Thinnest Commercial Powder

Thickness (

m

m)

Enhanced Powder

Panel

Enhanced Powder

Panel

Panel

T

m

d

ranged from

0

Figure 9–16. Comparison of Enhanced 

and Commercial Panel Powder 

Released. 

Figure 9–17 compares the best performing Phase II enhanced panel (no water in the tank) with the best

performing commercial panel. These data show the enhanced panels could increase the percentage of

total powder released by as much as 42 times. A ranking of the panels using percentage of powder 

released does not track directly

Estimated Powder Release

2

3

4

5

6

er Release (g) 0

1

Phase II Panel - Greatest Powder

Release

Commercial Powder Panel

P ow d

p

re
954 Powder Panel and Propellant Discharge Technologies 

examining a ductile front face, the powder release and percentage of powder released for the commercial

panels is less than half the next enhanced powder panel. As discovered in previous testing with Nomex

oneycomb cores, powder is released from those cells directly penetrated by the projectile and those torn

on the perimeter of the penetration either by the penetrating projectile or hydrodynamic ram forces acting 

n the fuel tank panel. However, the damage area is relatively well contained and powder is not able to

escape from the rest of the panel. Enhanced powder panels offer the potential for a much greater

carbonate throughout the design, including the 

front face. In this test, the entrance hole in the front face and exit hole in the rear face essentially selfm2

 being removed. 

h

o

percentage of the panel’s contents to be released. It was anticipated at this point in the program that the 

effects of hydrodynamic ram on the powder panel will only increase the amount of improvement an

enhanced powder panel can offer. Further testing would verify this assertion. 

Figure 9–17. Comparison of Enhanced 

and Commercial Panel Percent Powder 

Released. 

The outlier enhanced powder panel (Test 19) utilized poly

sealed together and prevented virtually any powder from escaping, except through the penetration area 

alone. This design was also examined in Test 20 with water in the fuel tank and yielded the same

damage. The front face area removed for these tests was approximately 0.7 cm2

, the least effective

performance by an enhanced powder panel. By contrast, Test 4 resulted in almost 25 cm2

 of the front 

face removed and Test 25, with water, resulted in over 19 c

Figure 9–18 compares the enhanced powder panel experiencing the greatest front face area removal (no 

water in the tank) with the better performing commercial powder panel (1.1 cm2

). An improvement of 

over 22 times is shown with this enhanced powder panel. 

Figure 9–18. Comparison of Enhanced 

and Commercial Panel Front Face Area 

Removal. 

Estimated % Powder Released

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

9.00

Phase II Panel - Greatest %

Released

Commercial Powder Panel

% Powder Released

Estimated Front Face Area Removal

5

10

15

20

25

30

ont Face Area Removed (sq c

m)

0

Phase II Panel - Greatest Area

Removed

Commercial Pow der Panel

Fr
Enhanced Powder Panels 955

For Tests 20 and 25, conducted with water in the fuel

powder release or loss was not practical. The powder

These two tests, however, demonstrated that hydrodynam

fracture for a more brittle front face, leading to greater powder release, but woul

 tank, a post-test mass of the panel to determine 

 in both panels absorbed water as a result of the test.

ic ram would significantly enhance front face

e 

for a ductile front face. Front face area removal was inc s

12 times (comparing Test 24 to Test 25) due to the ad

associated with hydrodynamic ram. This result demonstr ases were the powder panel will be

attached to a flammable fluid container, and hydrody ic ram is expected when the container is 

punctured, the powder panel can be designed to take advantage of the expected hydrodynamic ram event. 

In summary, the Phase II data showed that an enhanced powder panel (Test 24) can be 19 % lighter and 

g enhanced powder panel designs could prevent 

r panels in vital design criteria such as mass and

s results shown in the small experimental

test article could be extrapolated to a larger, more realistic test article. They also examined attachment 

techniques for the panels, the effectiveness of Al2O3 (historically the preferred dry chemical powder in 

aircraft applications), and the effect of certain variables o

Wright-Patterson AFB Facility

Phase II live fire demonstration testing was conducted by the Air Force 46th Test Wing Aerospace

Survivability and Safety Flight. The tests were conducted in outdoor Range 2 at their Aerospace Vehicle 

Survivability Facility, Wright-Patterson Air Force Base (WPAFB), Ohio (Figure 9–19). 

Baseline testing was conducted to ensure that fire could

One test was conducted with a standard commercial po

d not likely assist fractur

reased for the same panel design by as much a

ditional forces and fuel tank panel deformation

ated that in c

nam

39 % thinner than a commercial powder panel, yet release over 10 times more powder mass, 30 times

greater the percentage of powder originally contained in the panel, and sustain at least 32 % greater front

face area removal. The data also showed that the effects of hydrodynamic ram would further increase the 

performance of an enhanced powder panel. 

9.2.9 Live-fire Demonstration Testing of Optimized Enhanced Powder Panels

Testing Objective 

At the end of Phase II, a series of live fire demonstration tests was conducted of the optimized designs. 

These tests were to demonstrate (a) that the most promisin

fire ignition and be competitive with commercial powde

thickness; and (b) that powder dispersion and fracture mechanic

n enhanced powder panel effectiveness. 

be ignited when a powder panel was not present. 

wder panel to evaluate its effectiveness for the 

same test variables. Finally, six enhanced powder panel tests were conducted. Figure 9–20 shows the test 

article setup. 
956 Powder Panel and Propellant Discharge Technologies 

Figure 9–19. Range 2 at the WPAFB Aerospace Vehicle Survivability Facility. 

Figure 9–20. Test Article. 

Instrumentation 

Threat Velocity Measurement Equipment - The projectile velocity at impact was calculated for each test 

by measuring the elapsed time required to travel from the gun barrel muzzle to the striker plate. A gun 

break wire was installed in a small hole drilled in the side of the barrel near the exit end. The wire was 

Fuel Tank Dry Bay 

Striker Plate 

Powder Panel 

RANGE 2
Enhanced Powder Panels 957

severed act point

d be 

be 

Therm

as the projectile exited the muzzle. A break-paper grid was located at the intended imp

on the striker plate, and was broken when the projectile impacted the target. With the break wire and

break paper time increments determined and the standoff distance known, the impact velocity coul

calculated. If the paper grid and strain gage failed before impact, the projectile velocity could still 

estimated using the gun break signal and the pressure transducer signal recorded on the Nicolet data 

acquisition system. 

ocouples - Temperature-time histories were collected to obtain a temperature profile for the dry

article. Thermocouples were located within the dry bay. All thermocouples operated in the -18°C to 

 °C range with a 1 kHz sampling rate. One thermocouple was located on the back side of the striker 

plate below the target location and the other near the fuel tank wall above the powder panel. 

Optical Records

 bay 

test 

1330

 - A high-speed video camera (approximately 500 frames/s) was mounted beside the test

article to record the view looking through a Lexan panel on the side of the test device. Skyward provi

a digital video camera (approximately 30 frames/s) that also recorded the event through the Lexan panel. 

Both cameras were aimed toward the powder panel, but covered as much of the dry bay as possible. A 

standard video camera (30 frames/s) was positioned more distant to focus on the overall test article and 

capture the entire event. 

Test Article and Procedures 

Nine ballistic tests were conducted, including unprotected and powder panel-protected configurations of

y bay/fuel tank simulator. The test article and test setup were similar to the enhanced powder panel 

ded 

the dr

onstration tests conducted at the Weapons Survivability Laboratory at China Lake, California. A 

simula al test

device. The dry bay measured 0.61 m wide x 0.61 m high x 1.22 m long. The fuel tank attached to one 

end of the dry bay measured 0.36 m wide x 1.22 m high x 0.61 m long. The powder panels were 

connected to a simulated fuel mposed of 1.8 mm thick 2024-T3 for most tests. A striker plate 

was lo 0 m in front of the powder panel/fuel tank wall to ensure projectile functioning. Lexan 

panels in the test article allowed test results to be observed directly. 

Figure 9–21. 

Schematic of Test 

Article. (Top and Lexan 

Side Removed for 

dem

ted dry bay/fuel tank test article (Figure 9–21) was used of a larger size than the experiment

tank wall co

cated 0.3

Clarity) 

Existing Dry Bay Box

Aluminum Panel

Shotline

Frame for Fuel Tank Attachment

Striker plate

Fuel Tank

Powder Panel
958 Powder Panel and Propellant Discharge Technologies 

The test article was placed near the east wall of AVSF Range 2, with the fuel tank on the east side. The

gun was positioned to the west of the test article, and fired from the west toward the east wall of the 

range. This configuration ensured projectiles did not leave the range enclosure. Figure 9–22 shows the

relative position of the test article and gun setup. 

A single threat type was used for each of the enhanced powder panel tests. The 12.7 mm API Type B-32

projectile was fired through the center of the test article at a velocity of approximately 760 m/s. A 

e

proper location, the fuel tank was filled, and the appropriate impact location on the striker plate was 

targeted. The principal safety issue with this testing was the safe containment . The

principal method of stopping the threat was through a catch plate located on the back wall of the fuel tank

test article. The east wall of Range 2 was behind the test article if the projectile were to escape. An

external catch plate was positioned on this wall as well. 

The powders that were used for testing were non-toxic; however, because the dry powder is a finely 

divided solid material, it can become suspended in the air causing a mild discomfort similar to that 

physical description of the projectile is provided in Figure 9–23. The projectiles were fired from Mann 

barrels at close range to minimize targeting error, and the projectile powder mass was modified, as 

necessary, to achieve the desired impact velocity.

Figure 9–22. Test Article 

Setup in Range 2. 

The setup was reviewed prior to each test to ensure that the appropriate powd r panel was installed in the 

of the ballistic threat
Enhanced Powder Panels 959

experienced in any dust-laden atmosphere. To minimize the exposure to the dust, all participants used

dust masks during test clean-up. 

Figure 9–23. 12.7 mm API 

T pe B-32 Projectile 

Description. 

 panels were evaluated in live fire 

o any of the same elements 

involved in proof-of-concept testing after Phase I. However, in these tests, the thinner and lower mass 

Phase II optimized panels were evaluated. A total of nine tests were conducted, as summarized in

Table 9–6. The test was set up to ensure a threat function for each powder panel test. A successful

powder panel test was considered to be one where no fire ignition occurred, assuming both fuel leakage 

and functioning of the ballistic threat. Estimates of the front face area emoved and the percentage of 

powder released were made. Due to the presence of JP-8 fuel, it was not possible to weigh the precise

mount of powder released or lost, so an estimate of the percentage of the original powder released was 

made. This was a rough estimate based upon a post-test examination of the panel and area calculations.

ed Design 1, in Table 9–6, was lighter with

potentially better thermal resistance capability. Enhanced Design 2 was heavier, with features to make it

6.4 cm

1.3 cm 

6.4 cm 

12.7 mm

5.2 cm

5.2 cm 

1.1 cm 

~ 860 m/s

29 g 

48 g 

1 g 

Mass 

Mass 

Mass 

y

Live Fire Demonstration Test Results of Optimized Enhanced Powder Panels 

Some of the more practical, yet effective enhanced powder

demonstration tests conducted at the end of Phase II. This testing inv lved m

r

a

It was impossible to determine the influence of leaking fuel on remaining powder in the panel

immediately after the test, but the estimates do correlate well with powder dispersion evidence and fire 

ignition results. 

Two different enhanced powder panel designs were evaluated in the demonstration tests, with the primary 

differences involving material composition. Enhanc
960 Powder Panel and Propellant Discharge Technologies 

more durable. Test EPP-08 varied in design somewhat from the Enhanced Design 1, utilizing a selfsealing back face material, but was essentially the same in other respects. 

Table 9–6. Phase II Enhanced Powder Panel Live Fire Demonstration Tests. 

Powder 

Panel 

Panel 

Mass 

(g) 

Panel 

Thickness 

(mm) Powder 

Threat 

Function? 

Fire 

Ignition? 

Front Face 

Area 

Removed 

(cm2) 

Estimated 

% 

Powder 

Released

EPP-01 No Panel -

Baseline 

N/A N/A N/A Yes No N/A N/A 

EPP-02 No Panel -

Baseline 

N/A N/A N/A Yes Yes N/A N/A 

EPP-03 Commercial 189.0 2.69 Al2O3 Yes Yes* 50 8 

EPP-04 Enhanced

Design 1 

145.4 1.90 Al2O3 Yes No 156 70 

EPP-05 Enhanced

Design 1 

140.8 1.90 Al2O3 Yes Yes* 146 83

EPP-06 Enhanced

Design 2 

186.5 1.90 Al2O3 Yes No 309 88 

EPP-07 Enhanced

De

1.90 KHCO3 Yes es, but 

wder

tinguis

ed fire 

227.0 Y 329 83 

sign 2 po

ex

h

EPP-08 Enhanced

De

157.1 2.13 Al2O3 Yes No 54 61 

sign 1 

EPP-09 Enhanced

De

226.3 2.16 KHCO3 Yes No 252 62 

sign 2 

* Panel dislodged from fuel tank wall during test 

Two baseline tests were conducted at the beginning of the test program. The purpose of these tests was to

ensure threat functioning and the ignition of a fire in an unprotected or inadequately protected dry bay.

For these conditions, a successful powder panel would prevent fire ignition, despite the functioning threat,

, the fuel tank 

panel was a 2.0 mm thick 7075-T6 plate. This was the same material and thickness used as the simulated

not ignited in this first test (and the potential for fire was essential for the powder panel

evaluations), modifications were made to the test article and setup to better ensure fire ignition. For the 

second baseline test, the fuel tank material was changed to 1.8 mm thick 2024-T3 and a structural frame 

and an unsuccessful powder panel would not prevent fire ignition. In the first baseline test

fuel tank panel in all Range A experimental tests. In EPP-01 a fire was not ignited, as a large deluge of 

fuel was seen engulfing the dry bay almost immediately, creating an extremely fuel rich environment.

The threat did function, but the fuel tank panel resisted the significant hydrodynamic ram pressures and

peeled away from the fasteners attaching it to the fuel tank. The fuel tank panel deformed significantly 

before its edges at the fastener locations tore through, but the impact hole was not significantly larger than

the threat size. The toughness of this material was also evident in the Range A tests, where hydrodynamic 

ram was most often not a variable and worst-case conditions were desired. In these demonstration tests, it 

was desired to allow hydrodynamic ram damage to occur. Without hydrodynamic ram forces and 

minimized fuel spurting, it is possible an inaccurate judgment could be made regarding powder panel

effectiveness. In this first baseline test, the panel resisted hydrodynamic ram forces such that the weakest 

failure point was the fuel tank panel attachment mechanism.

Since a fire was
Enhanced Powder Panels 961

was used to hold the fuel tank panel to the fuel tank without interfering with the powder panel positioned 

between its boundaries. In addition, the planned projectile velocity was lowered to 762 m/s to mirror 

proof-of-concept testing after Phase I and to reduce energy somewhat. The fuel level was lowered from 

completely full (about 64 l) to about three-fourths full (49 1) to permit pressure relief in an ullage area 

and reduce the amount of fuel that might immediately spill out into the ignition zone and create another 

over-rich condition. These modifications proved worthwhile, as EPP-02 did result in a fire. The fire was 

visible ide an 

adequate burn time for an evaluation of the powder panels, but an alteration a

envisioned to be necessary

The third te involved a commercial powde

functioned as planned, ho a f s ign The fire only lasted a short duration, as the fire 

a to king en. g jet o e actu entrance hole at the front 

of the dry b fire lasted over 1 s, but thick black smoke from the combustion filled the dry bay and 

lasted for m a d. T mperatur the d y climbed about 49 °C. The conclusion 

w he not sful ibitin gnitio preventi sustain re, rather a selfextinguishi curred due to a lack of oxygen. Closer inspection of the dry bay and the high-speed 

video revealed the comme owd el di main red to l tank el with the twopart epoxy e panel was dislodged after the threat flash and started coming loose as the fire was 

i lo ost the as it ff. The powder release was not sufficient to allow 

p o pend the d ; however, its effectiveness could remain in question since it 

d here properly. B arki vide only h, bu nited were present in 

the dry bay. y bay following th ough the panel did break 

up better than in non-fluid tests in Range. The damage area was appr y 10.2 cm high x 6.4 cm 

w is from pect f the at the t face a emoved s approx tely 

50 cm2

 and of the powder was released. 

n to be available to the combustion process. 

However, since more enhanced powder panel tests were to be conducted, it was desired to conduct at least 

for about 4 s, but appeared to be self-extinguishing near that time. This would prov

to the test rticle was 

. 

st (EPP-03) r panel, as Table 9-6 indicates. The threat 

wever ire wa ited. 

ppeared be and see

ay. The 

 oxyg A lon f flam ally shot out of the

any minutes fterwar he te e in ry ba

as that t panel was

ng fire oc

 succes in inh g fire i n or ng a ed fi

rcial p er pan d not re adhe the fue pan

used. Th

gnited be w and alm

remain su

behind panel flew o

owder t

id not ad

s

 No powder residue was found in the dr

ed in 

lack m

ry bay

ngs e nt of not a flas t of an ig

e test, alth

oximatel

 fire,

ide. It estimated 

 about 8 %

 an ins ion o panel th fron rea r wa ima

Figure 9–24. Post-Test Damage 

Image of EPP-03 Commercial 

Powder Panel. 

The fourth test (EPP-04) involved an enhanced powder panel. For this test, modifications to the test 

article were considered to allow more venting or fresh oxyge
962 Powder Panel and Propellant Discharge Technologies 

one with the exact same conditions as the commercial powder panel for a direct comparison. In this test,

the threat functioned as expected, with the high-speed video indicating a flash duration of approximately

0.008 seconds or more, which was comparable to the previous two tests. However in this test, as soon as 

the flash dissipated, the dry bay was engulfed in fire extinguishing powder, and no fire ignition occurred. 

The temperature in the dry bay around the flash climbed only about 10 °C. A review of the video

confirmed that no combustion occurred after the threat function. Powder was visible on the walls of the 

dry bay, with powder on the Lexan window all the way to the end of the 1.2 m long dry bay. A 

significant amount of powder also covered the striker panel on the surface facing the powder panel. 

Powder was also visible in the dry bay for a number of minutes after the test. The panel was adhered with

a two-part, fast curing epoxy, which was the same adhesive used in the commercial panel test. However,

in this case the panel held fairly well, although some loss of adhesion occurred. Figure 9–25 shows a 

post-test image of the powder panel, demonstrating the front face fracture. The damage area was

approximately 14 cm high x 18 cm wide. It is estimated from an inspection of the panel that the front 

llow for more fresh air to vent into the

fire zone. A 7.62 cm diameter hole was drilled into the aluminum side wall of the dry bay. It was 

centered along the length of the dry bay, 0.61 m from the fuel tank 3 cm from the 

top of the dry bay. In this test, a double-sided adhesive tape was used to adhere the powder panel, versus 

a two-part epoxy. The threat functioned in the test, as planned,

ignited about 0.02 seconds after the flash dissipated. The fire las ture

climbed about 194 °C in the dry bay near the fuel tank. In the rea ed video, the powder 

panel was visible being dislodged from the fuel tank and slammi g into the side Lexan panel. The fire 

started behind the powder panel in the corner opposite the direction the powder panel flew off. Powder 

was visible in the video emanating from the panel into the Lexan and down onto the floor. As the panel

lay against the Lexan, continued powder leakage was visible onto the floor, and it suspended in the 

vicinity of the dry bay. It is unclear if the continued release of powder was responsible for the fire 

extinguishing later or if the fire self-extinguished. Inspection of the test article did indicate some black

residue around the new dry bay opening, so the extra vent did pr vide an oxygen source to the fire. In

this test, the powder panel design was exactly the same as in EPP-04. In addition, the powder panel broke 

face area removed was approximately 156 cm2

 and about 70 % of the powder was released. 

Figure 9–25. Post-Test Damage 

Image of EPP-04 Enhanced 

Powder Panel. 

In preparation for EPP-05, the dry bay test article was modified to a

wall and down about 13.

and the high-speed video showed a fire

ted several seconds and the tempera

l-time and high-spe

n

o
Enhanced Powder Panels 963

up at least as effectively as in EPP-04, so it was surmised that if the panel had not dislodged from the fuel 

tank wall, it would likely have prevented a fire. However, further tests were required to determine if the

additional oxygen available would hinder the effectiveness of the enhanced powder panels. The post-test

damaged powder panel is shown in Figure 9–26. The front face damage area was approximately 18 cm 

high x 15 cm wide. The front face area removed was approximately 145 cm2

. About 83 % of the powder 

was released, but as described, much of this may have exited the panel as it flew into the Lexan side panel 

and then rested against it. 

Figure 9–26. Post-Test Damage 

Image of EPP-05 Enhanced 

Powder Panel. 

p

face material. It also marked the first test using MIL-S-8802 aircraft sealant, rather than a faster curing

epoxy sealant, as the adhesive to attach the powder panel to the fuel tank wall. All tests conducted after 

EPP-05 used this adhesive. This powder panel and all the panels utilizing this sealant remained well 

adhered to the fuel tank during testing. In this test, the flash was visible in the high-speed video, and then

powder was seen once again engulfing the dry bay with no fire ignition occurring. The temperature in the 

dry bay climbed no more than about 14 °C near the flash. Powder seemed to distribute well and quickly. 

Powder was still lingering in the dry bay nearly fifteen minutes fter the test, when the side panel was 

removed (Figure 9–27). Upon inspection of the fuel tank, powder was visible along the length of the 

Test EPP-06 involved a different enhanced powder panel design, rimarily involving a change to the front

a

Lexan window and across the surface of the striker plate facing the powder panel (Figure 9–28). 

Some large pieces of the powder panel front surface were actually stuck to the striker plate along with the

powder. Powder was also detected on the aluminum side panel nearly the length of the dry bay. Powder 

was also visible on the structural framework of the dry bay. In all of the powder panel tests, sufficient 

fuel leaked into the dry bay to make visible powder on the surface of the fuel very difficult to distinguish. 

As shown in Figure 9–29, the powder panel was fractured in EPP-06 similar to the previous enhanced 

powder panel tests. The front face damage area extended nearly to the edges of the panel, measuring 

approximately 30 cm high by 27 cm wide. The front face area removed was approximately 309 cm2

 and 

about 88 % of the powder was released. 
964 Powder Panel and Propellant Discharge Technologies 

Figure 9–27. Powder 

Suspension in the Dry Bay Well 

After the Test. 

powder, rather than Al O , to examine any

difference in powder release or powder dispersion and suspensio

was the same as in EPP-06. In this test, however, powder loadin ighed

approximately 22 % more. In this test, the threat functioned as pla of less than 0.016 s. 

Figure 9–28. Powder Dispersion 

d. The 

In Test EPP-07, KHCO3 was used as the fire extinguishing 2 3

n within the dry bay. The panel design

g was increased and the panel we

nned for a duration

on Striker Plate and Side Lexan 

Panel. 

After the flash dissipated, the powder was seen in the video beginning to engulf the dry bay. However, a 

fire was ignited in the lower corner of the dry bay near the fuel tank panel and Lexan panel. It lasted only 

about 0.28 s as the powder was seen reaching this area about the time it was extinguishe

temperature in the dry bay climbed no more than 17 °C near the fuel tank. A small leak was evident from

the fuel tank in pretest preparations and it occurred in this corner. It is plausible that some fuel remained

in this corner of the dry bay after the leak was fixed. This likely allowed for an ignition of fuel already 

present in the dry bay, before fuel from the threat penetration hole fully began to spray into the dry bay.

Based upon the evidence provided, this powder panel was considered successful, despite the brief ignition

of a fire, because the powder was considered responsible for extinguishing the fire. Upon inspection of 

the test article, powder was evident on the Lexan panel and aluminum side panel similar to the previous 
Enhanced Powder Panels 965

test. Powder was also evident on the dry bay structural frame

expected, the KHCO3 was somewhat easier to distinguish than th

fracture was similar to EPP-06, as shown in Figure 9–30. The fro

edges of the panel again, measuring approximately 30 cm high face area

removed was approximately 329 cm2

 and about 83 % of the powder was released. 

6 Enhanced 

Powder Panel. 

a self-sealing material for the back face

ignited. The cloud of powder quickly m

climbed no more than 13 °C. 

aluminum side panel. It was also found

wall and back wall. The front face are removal was somewhat reduced from previous panels using the

same front face, but cracking was extensive, allowing large flaps of material to easily release powder 

( d about 29 cm high x 24 cm wide. The front face area removed

w % of the powder was released. The hole in the back face of the

powder panel was approximatel x 1.3 cm, resulting in an area removal about 66 % less than any 

of the other enhanced powder panel tests. It is, therefore, likely that less fuel was immediately available

for fire ignition than in tests without a self-sealing back face. It is believed the thickness of the back face 

could be increased for such a design to mprove self-sealing capability, while still maintaining an overall 

mass and thickness comparable to commercial powder panels. A test to verify this assertion was not

possible during this test program. 

work, top panel, and striker plate. As 

e Al2O3. The powder panel front face 

nt face damage area extended nearly to 

x 27 cm wide. The front

Figure 9–29. Post-Test Damage 

Image of EPP-0

Test EPP-08 utilized Al2O3 and used the same front face material evaluated in Tests EPP-04 and EPP-05. 

This panel had a slightly larger total thickness (2.1 mm) than these previously tested enhanced powder

panels, but still weighed less than the commercial powder panel tested. This test also involved the use of 

. In this test, the threat functioned as planned and no fire was 

oved throughout the dry bay. The temperature in the dry bay

 Powder was evident along the length of the Lexan panel and the other 

 on the striker plate facing the powder panel and the dry bay top

a

Figure 9–31). The damage area extende

as approximately 54 cm2

 and about 61

y 1.3 cm

i

The final Phase II live fire demonstration test (EPP-09) again involved KHCO3. The same design used in 

Tests EPP-06 and EPP-07 was used, except the panel internal width was wider, and, therefore the overall 

panel was wider (2.16 mm). Despite the increased thickness, powder loading was such that it was very 

close in mass to EPP-07, which also examined KHCO3. A large flash was evident in this test upon review 

of the high-speed video. However, no fire was ignited. The temperature in the dry bay near the flash

climbed on average around 20 °C. A large cloud of powder enveloped the dry bay and powder was 
966 Powder Panel and Propellant Discharge Technologies 

visible striking the Lexan wall. Both side walls had visible powder deposits, as well as the top panel 

beyond the striker plate, and the striker plate itself. When the side wall was removed more than five 

minutes after the test, a large cloud of powder was still evident in the dry bay (Figure 9–32). 

Figure 9–30. Post-Test Damage 

Image of EPP-07 Enhanced 

Powder Panel. 

sidered unsuccessful, and it was likely due to the lack of adherence of 

the panel to the fuel tank. This problem was associated with the selection of adhesive for attaching the 

Figure 9–31. Post-Test Damage 

Image of EPP-08 Enhanced 

Powder Panel. 

The damage to the enhanced powder panel front face was significant, as shown in Figure 9–33. The 

damage area extended about 30 cm high x 26 cm wide. The front face area removed was approximately 

252 cm2

 and about 62 % of the powder was released. 

The results of the Phase II live fire demonstration tests were very promising. Out of six enhanced powder 

panel tests, only one test was con

panel to the fuel tank, not the panel design itself. The same panel design was able to prevent fire ignition 

in two other tests. The commercial powder panel was unsuccessful in preventing fire ignition, but it too 
Enhanced Powder Panels 967

failed to adhere to the fuel tank panel. Demonstration testing after Phase I at China Lake, with many of 

the same test conditions including the ballistic threat, showed these panels were not effective under these 

conditions. In these NGP demonstration tests, the enhanced powder panels released at least 87 % more 

powder than the commercial powder panel. Except for one enhanced powder panel, which still released

significantly more powder, the size of the front face area removed was at least 34 % better for the 

enhanced powder panels compared to the commercial powder panel. 

Figure 9–32. Powder Evident in 

oved)

Figure 9–33. Post-Test Damage

Image of EPP-09 Enhanced 

Thinner enhanced powder panels appeared to release 

they also likely contained less powder, so the total powder release may have been fairly close to the

back face hole, also likely contributed to the panel 

effectiveness by reducing immediate fuel leakage. 

Dry Bay More Than 5 min after 

EPP-09 Test. (Side Wall Rem

Powder Panel. 

more of the total panel’s powder content. However,

thicker panels. The powder panel utilizing a self-sealing back face (EPP-08) did appear to sustain less 

front face break-up than other enhanced powder panels. This could have been a result of this design 

variation. However, the reduction in the size of the
968 Powder Panel and Propellant Discharge Technologies 

Both tests with KHCO3 resulted in successes, although Test EPP-07 did show evidence of a very brief fire 

ignition. It appeared the powder release did, however, result in the fire being extinguished. KHCO3 was 

expected to be at least as effective as Al2O3, however, the grain size of the KHCO3 was on average around

30 μm compared to the 5 μm Al2O3. As previous testing has shown, a smaller grain size has proven to be 

more effective in fire extinguishing. It is inconclusive, however, in these few tests, whether or not grain

size was even a factor. 

It was conclusive that sufficient powder was released from each of the enhanced powder panels to

significantly reduce the likelihood of a dry bay fire, regardless of the powder type. It was estimated that 

at least 40 g of powder was released in most of the enhanced powder panel tests, with as much as 70 g 

from the heavier panels. By contrast, it was estimated the commercial powder panel likely released less

than 10 g of powder. 

y for many aircraft. However, the cost, 

 justified the installation of halon 

io s

generator systems, void space foam fillers, or even commercial p in

some cases, but many dry bay areas still go unprotected. It is po

could offer a justifiable option for previously unprotected dry bay

areas protected by other means. 

Cyphers and co-workers performed a comparison of an enhance stem with a 

halon fire extinguishing system to demonstrate its potential as a halon alternative. The powder panel 

survey had revealed that it was very difficult to find a practical example for which to perform a direct

comparison. In addition, obtaining design information for certain areas that might provide a comparison

was very difficult within the resources of this program. To further complicate this task, when information

was obtained on a potential aircraft are

was often considered proprietary an

generating some estimates for integrati

When possible, active system informati was estimated for possible integration into the same areas. It

turned out that the most practical comparisons were with current powder panels and other currentlyfie such as solid propellant gas generators (SPGGs) that generate a 

mixture ater vapor.

Comparisons with halon fire extinguishing systems in engine nacelles or APU compartments were 

considered, but rejected because significant additional work would be necessary to demonstrate that

powder panels would even work in suc an area, where airflow and hot surface ignition are concerns.

Additionally, in these areas where accidental fires are of an equal or greater concern than ballistic threatinduced fires, powder panel protection is not currently a consideration due to the passive nature of powder 

panels. This eliminated some potential comparisons on the C-5 and B-1 aircraft, for example. 

One forward-fit example explored was the C-130 Hercules aircraft. The C-130 outer wing leading edge is

not currently protected by a fire extinguishing system. The wing is divided into two segments, the center 

9.2.10 Mass-trade Comparison Analysis 

Combat-related aircraft dry bay fires are a known vulnerabilit

mass, maintenance, and/or performance parameters have infrequently

fire extinguishing systems for these areas. Other fire protect n methods such as solid propellant ga

owder panels have been implemented

ssible that a more effective powder panel 

 areas or a well-supported alternative to

d powder panel protection sy

a or an alternative system used in trade studies, the information 

d was not releasable. Therefore, an emphasis was placed on

ng powder panels into forward-fit or currently unprotected areas.

on

lded active fire extinguishing systems,

of nitrogen, carbon dioxide and w

h

wing section (CWS) and the outer wing section (OWS). Since the outer wing fuel tanks are vulnerable to
Enhanced Powder Panels 969

enemy fire, but currently have no fire protection, and because data were available (including wing 

geometry) for an estimated active fire extinguishing system, it was practical to use this example. 

A preliminary analysis was conducted for the OWS leading edge dry bays circa 1996 to estimate the mass 

of an SPGG fire extinguishing system using then off-the-shelf components. The masses were estimated 

for the wing leading edge dry bays between engines #1 and #2 and between #3 and #4 (referred to as 

inboard leading edge dry bay) and outboard of the #1 and #4 engines (referred to as outboard leading edge 

dry bay). This analysis also included estimates for the engine area dry bays, but for purposes of this 

study, the comparison is limited to the leading edge dry bays. It was estimated one inboard leading edge 

dry bay would require about 1,070 g of agent and an outboard leading edge dry bay would require about 

1,190 g. To provide this agent to each dry bay would require three 420 g unit generators each. The mass 

for each unit is about 1,300 g, for a total generator mass on one wing of 7,810 g. One controller would 

weigh about 1,920 g, which would be capable of controlling all the SPGGs in both wings. It is estimated 

both the inboard leading edge and the outboard leading edge would each require three optical sensors. 

Each sensor weighs approximately 177 g, for a total mass on one wing of 1,060 g. For purposes of this 

study, the cables and braces or mounting hardware required was arbitrarily assumed to weigh about 10 % 

of the SPGG and sensor mass for each dry bay. This mass could be more significant, depending upon 

where the controller is located, but should provide a slightly better estimate than ignoring this mass. 

Feasibility and demonstration testing of SPGGs was conducted in the C-130 Vulnerability Reduction 

Program, as part of C-130J Live Fire Test & Evaluation, and determined that the mass of agent in the 

1996 preliminary analysis was likely overestimated.29 However, the estimates provided are the best 

available since a fully optimized system has not been examined. Table 9–7 provides mass estimates for 

each of the SPGG system components for the C-130 outer wing’s leading edge dry bays. 

Table 9–7 also provides estimates for enhanced powder panel fire protection systems. Estimates are 

shown for both a lower mass version (areal density of 1.60 kg/m2

) and a heavier version (2.05 kg/m2), 

both of which have been demonstrated to be effective in this program. Areal densities for the commercial 

powder panels tested in this program ranged from 1.92 kg/m2 to 2.08 kg/m2

. An estimate using the lower 

mass 175 g commercial powder panel is shown. An estimate is also provided for the mass of adhesive to 

attach either enhanced or commercial powder panels. Finally, Table 9–7 shows estimated areas and 

volumes for the OWS wing leading edge dry bays. The SPGG agent requirements are estimated based 

upon volume, and the powder panel requirements are based upon wetted front spar area. 

Table 9–8 summarizes total mass estimates for each wing leading edge fire extinguishing system for an 

entire C-130 aircraft (both wings). The data show that enhanced powder panels can be very competitive 

with SPGGs in terms of mass for such a system. For this example, the1.60 kg/m2

 enhanced powder panel 

system would weigh about 0.8 kg more than the SPGG system for the entire aircraft. The lighter mass 

enhanced powder panel would obviously be a design objective, since for this application it could be as 

much as 5.6 kg lighter than its higher areal density counterpart. Future work will determine if further 

optimization is possible. The lighter commercial powder panel evaluated in this program was just under 

the mass of the heavier enhanced powder panel by 1.6 kg. The powder panel mass was calculated, as if 

they were applied across the entire surface area of the leading edge spar. With external stiffeners located 

across the surface of the spar, it is likely modular powder panel sections would be inserted between 

stiffeners. This would further reduce powder panel mass. Also, the mass of protective foam and tape 

typically used in the vicinity of SPGG discharge areas was not estimated, so the SPGG system mass 

would likely be higher. For a full analysis of this example, other issues such as cost and complexity 
970 Powder Panel and Propellant Discharge Technologies 

would also need to be examined. Obviously, the powder panel systems should be relatively simple to 

apply and maintenance free once applied. The complexity of integrating an active fire extinguishing 

system would be more complicated and involve some power requirements, safety concerns, and perhaps 

integration issues with other systems. 

Table 9–7. C-130 Wing Leading Edge Dry Bay Fire Extinguishing System Component 

Mass Estimates. 

Description 

Inboard 

Leading Edge 

Outboard 

Leading Edge 

Volume 1.52 m3 1.68 m3

Area 2.73 m2 3.43 m2

SPGG Propellant Required 1,070 g 1,190 g 

Number of SPGGs (420 g Units) 3 3 

SPGG Mass (3) 3,910 g 3,910 g 

Number of Optical Sensors 3 3 

Optical Sensor Mass (3) 530 g 530 g 

SPGG Controller Mass 1,920 - 

Wiring, Brackets and Mounting Hardware (Estimate 10 % of 

SPGG/Sensor Mass) 

444g 444g 

Light Enhanced Powder Panel Mass - 1.60 kg/m2 4,370 5,490 

Heavier Enhanced Powder Panel Mass - 2.05 kg/m2 5,600 7,030g 

Commercial Powder Panel Mass - 1.92 kg/m2 5,240g 6,590 

Adhesive Mass for Powder Panels (Estimate 10 % of Heaviest Panel 560 g 700 g 

Mass) 

Table 9–8. C-130 Wing Leading Edge Dry Bay Total Fire Extinguishing System Mass 

Estimates. 

Fire Extinguishing System Total System Mass 

Solid Propellant Gas Generator System Mass 21.4 kg 

Lighter Enhanced Powder Panel Design 1 Mass - 1.60 kg/m2 (0.327 lb/ft2) 22.2 kg 

Heavier Enhanced Powder Panel Design 2 Mass - 2.05 kg/m2 (0.420 lb/ft2) 27.8 kg 

Commercial Powder Panel Mass - 1.92 kg/m2 (0.394 lb/ft2) 26.2 kg 

Data were available for a second comparison of enhanced powder panels, in this case with a current gas 

generator system on the V-22 aircraft. The outboard tip rib dry bay on this aircraft has a volume of 

3

ring would 

approximately 0.260 m . No airflow passes through this dry bay. Other relevant design details are part of 

the aircraft technical specifications and will not be described in detail. The active fire suppression system 

in this area consists of a 626 g inert SPGG, including 189 g of agent, and a 284 g sensor/detector. Testing 

was conducted on a larger inboard tip rib dry bay and this system was sized according to successful 

configurations in that area. The dry bay is monitored by a control box that currently monitors other areas 

of the aircraft, so no new mass was added for this equipment. Wiring and mounting hardware was added 

to the mass estimate, since this equipment is necessary specifically for this dry bay. The wi

have to run to the control box in a central location. In the previous example, approximately 444 g was 

added for wiring and accessories. For this single generator and sensor, the mass for this estimate was 

reduced to 33 % of this estimate or 148 g for one wing, which is likely a favorable estimate. The total 

mass estimate for one wing would, therefore, be approximately 1060 g. For comparison, masses for both 
Enhanced Powder Panels 971

enhanced powder panel designs discussed previously were estimated for this dry bay. The lighter mass 

powder panel, with an areal density of 1.60 kg/m2

, would weigh about 710 g per wing. Incorporation of 

the heavier enhanced powder panel, with an area density of 2.05 kg/m2

, would weigh about 910 g. The 

commercial powder panel by contrast, with an areal density of 1.92 kg/m2

, would weigh approximately 

860 g. Table 9–9 summarizes these mass estimates. 

Table 9–9. V-22 Outboard Tip Rib Dry Bay Fire Extinguishing System Component Mass 

Estimates. 

Description Outboard Tip Rib Dry Bay 

Solid Propellant Gas Generator Mass(1) 630 g 

Sensor/Detector Mass (1) 280 g 

Wiring, Brackets and Mounting Hardware Mass (Estimate 33 % of Previous 

Example with 3 SPGGs) 

150 g 

Lighter Enhanced Powder Panel Design 1 Mass - 1.60 kg/m2 710 g 

Heavier Enhanced Powder Panel Design 2 Mass - 2.05 kg/m2 910 

Commercial Powder Panel Mass - 1.92 kg/m2 860 g 

Adhesive Mass for Powder Panels (Estimate 10 % of Heaviest Panel 

Mass) 

90 g 

Table 9–10 tabulates the total mass for the aircraft (both wings) for each of the fire protection systems. 

These data show the lightest enhanced powder panel weighs about 500 g less than the inert SPGG system. 

Even the heavier enhanced powder panel design would be very comparable, weighing about 100 g less 

than the inert SPGG system. The commercial powder panel system would weigh about 280 g more than 

the enhanced powder panel design, but still less than the SPGG system. Obviously, one major difference 

in this example was the existence of a controller on the aircraft for the active system, which did not add 

ply demonstrate 

that enhanced powder panels, which have been demonstrated in live fire tests to be effective, have also 

mass, but the overall active system still weighed a little more. Although the differences in mass for both 

comparisons are quite small, it is well known that aircraft mass increases carry large price tags. A 

judgment would need to be made based upon system cost and the savings in complexity, whether or not 

the mass differences (savings or cost) for the enhanced powder panel system would be worthwhile. 

Further optimization of these enhanced powder panel designs in subsequent programs may further reduce 

the mass differences between this passive fire extinguishing system and this active fire extinguishing 

system. Many other comparisons are possible between the enhanced powder panels and other fire 

protection methods. However, the purpose of the examples provided above was to sim

been optimized to levels that make consideration of this vulnerability reduction technique valuable. 

Table 9–10. V-22 Outboard Tip Rib Dry Bay Total Fire Extinguishing System Mass 

Estimates. 

Fire Extinguishing System Total System Mass 

Solid Propellant Gas Generator System 2,120 g 

Lighter Enhanced Powder Panel Design 1 Mass - 1.60 kg/m2 1,610 g 

Heavier Enhanced Powder Panel Design 2 Mass - 2.05 kg/m2 2,010 g 

Commercial Powder Panel Mass - 1.92 kg/m2 1,900 g 
972 Powder Panel and Propellant Discharge Technologies 

9.2.11 Summary of Powder Panel Research Program 

This NGP research has led to major gains in efficiency and effectiveness of powder panels, and has 

reached the point where there are alternatives to halon-like compressed systems suitable for controlling 

fires in aircraft dry bays. Although additional work is necessary to address manufacturing issues and 

en l 

technology is a viable option for future fire protection of aircraft dry bays. 

Findings from this research revealed that realistic powder panel co ific he 

fire extinguishing effectiveness of this vulnerability reduction method. Enhan ed powder signs 

can afford the following benefits over current commercial powder panel designs: 

moval to allow more powder to esca

r powder release into the dry bay, 

 of powder to prevent ignition off-shotline, 

er suspension to prevent fire ignition for longer p of time, 

 application-sp design goals

uishing effectiveness ov mercial po panels, 

d thickness. 

O his pr hese goals w lower 

en ent com l powder panels or below 

n emonstrate greater performance in live fire testing. Enhanced powder panels evaluated in final 

onstrations ranged in mass from 140 g to 230 g, with four of the six panels being lighter than the 

com he 

commercial powder panel thickness was 2.7 m

L realistic size for an aircraft (0.45 m3

), with an actual ballistic 

th n of fire ignition ut of six 

te s quickly extingu fter only 

0 a lone unsuccessful test result fire was 

ttributed to an inadequate attachment adhesive on the back of the enhanced powder panel. The test of a 

sure enhanced powder panels meet the requirements of individual aircraft programs, powder pane

ncepts can sign antly enhance t

c panel de

• greater front face area re pe, 

• greate

• better dispersion

• longer powd eriods

• design flexibility to target mass, durability, and ecific , and 

• significantly improved fire exting er com wder 

achieved at an equal or lighter mass an

ptimization goals were achieved for enhanced powder panels in t

hanced powder panel mass and thickness to the levels of curr

d to d

oject. T ere to

mercia

a

dem

mercial powder panel evaluated (190 g). Thicknesses ranged from 1.9 mm to 2.2 mm, while t

m. 

ive fire testing conducted in a dry bay of 

reat (12.7 mm API), and about 50 l of JP-8, resulted in the preventio in four o

sts. In a fifth test, a fire starting from an existing pool of fuel wa ished (a

.28 s) by an enhanced powder panel. The cause of ing in a

a

commercial powder panel resulted in a fire; however, the attachment adhesive again failed to hold. 

Although the commercial panel test was not conclusive, a further examination of the test results indicated 

a significant increase in vital performance characteristics for the enhanced powder panels. Despite being 

as much as 26 % lighter and 29 % thinner, the enhanced powder panel tests resulted in at least 34 % 

greater front face area removal 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 suspended powder in the commercial powder panel test. 

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. 
Enhanced Powder Panels 973

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

of particular front face materials, thicknesses, rib designs, attachment methods to the ribs, and 

even surface scoring. 

• A strong synergism exists between the rib structure and the front face design. 

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

Another key finding in this program is that t n features associated with enhanced powder 

panels that can make them ve to accidental leakage. With th in 

c ach the various elements of the panel that form extremely tight 

b a front face material and thickness can take into account the likely harsh 

e l leakage has a significant 

concern for aircraft designers considering powder panels and is the primary reason that Al2O3 has been 

th uction usage. With this resi

le mproved performance fire extinguishing agents 

c ders lighter in mass, but improved effectiveness of these 

p

o fully take advantage of the potential benefits from enhanced powder panels, further examination of the 

als or 

othe

The potential of enhanc r increasing effectiveness wi

m ated renewed interest by several aircraft pro Among the 

p ment are the F-35 Joint Strike Fighter, CH-53E 

S Osprey. Successful live-fire tests have been 

c ra. 

here are desig

ry resistant e use of plastics and certa

omposites, there are adhesives to att

onds. The selection of

nvironment to which the powder panel will be exposed. Accidenta been 

e only chemical fire extinguishing powder finding prod stance to accidental

akage in certain designs, perhaps other lighter mass and i

an be considered. Not only are other pow

owders may lead to reduced requirements for powder loading. 

T

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

include, but are not limited to, operating temperature, chemical exposure, vibration, impact resistance, 

and moisture absorption. These issues were considered in the selection of materials for Phase II 

optimization testing, but qualification testing for these parameters was not conducted. 

Despite significant increases in powder release for enhanced powder panels, a balance must be achieved 

between mass/thickness and effectiveness. For protection against larger threats, it may be warranted to 

consider higher powder loading, which is the significant mass driver. For strict mass restrictions, testing 

may be required for the given powder panel to determine the type and size of the threat for which 

protection is afforded. 

As the previous section detailed, enhanced powder panels have been developed with increased 

effectiveness over current powder panel designs at equivalent or better mass and size. These enhanced 

powder panel designs can now be examined for various applications, particularly in military aircraft, as a 

trade-off with other fire extinguishing systems. Additional work will be required with the examination of 

production design requirements, which may cause some adjustments in the selection of materi

sizing, but the design principles should be in place. Some manufacturing concepts were developed and 

rs conceived as a result of this work, which will need to be optimized for production application. 

ed powder panel designs fo thout negatively impacting 

ass and other concerns has gener grams. 

rograms inquiring about enhanced powder panel develop

uper Sea Stallion, RAH-66 Comanche, and the V-22 

onducted on a production AH-1Z Super Cob
974 Powder Panel and Propellant Discharge Technologies 

9.3 SOLID PROPELLANT GAS GENERATORS30,31,ii

fires, they do this quickly 

attribute (high exhaust 

temperature) 

Prior to e program to identify alternatives to halon 1301 for 

aircraft arily for automobile airbags and 

for infla l 1990s, development of the F/A18 E/F zard of fires due 

to equip n ity Lab 

of the Naval 

could be

military airc

g., coolant beds) to allay such 

problems as physical deformation or failure of distribution lines and threat to occupants. 

 

9.3.1 Brief History 

Solid propellant gas generators (SPGGs) are devices designed to produce gases of a desired composition 

(e.g., nitrogen, water vapor, and carbon dioxide) from condensed reactants similar to those used in solid 

rocket motors. SPGGs are compact, they can generate gases that are inert in 

(fractions of a second) and on demand, and they produce gas temperatures that are very hot (greater than 

1200 oC). The first three attributes (compactness, inert gases, and release on demand) are what make 

SPGGs attractive for fire suppression applications in aircraft; the fourth 

is a limitation. 

 th advent of the NGP and its predecessor

fire suppression applications, gas generators had been used prim

tab e slides for emergency evacuation of airplanes. In the early

and V-22 aircraft demanded a non-halon fire protection system to mitigate the ha

me t failures, accidents and enemy attack. Testing performed at the Weapons Survivabil

Air Warfare Center-Weapons Division (NAWCWD)-China Lake demonstrated that SPGGs 

 integrated into a system that provided an effective alternative to halon 1301 for fire protection in 

raft dry bays.32,33,34,35 

Between 1993 and 1996, the Naval Air Systems Command (NAVAIR) sponsored live fire testing of 

SPGG systems develop by the Rocket Research Company (now Aerojet Redmond). The tests 

demonstrated the effectiveness of SPGGs in suppression of various fires in the F/A-18 E/F dry bays and 

the V-22 wing dry bays. Since the original F/A-18 E/F and V-22 programs, new propellants have been 

developed that implement some degree of chemical activity into the formulation.36,37,38,39 

The SPGG program sponsored by the NGP was a collaborative effort between a group at Aerojet (that 

had been with its predecessor companies) and the Naval Air Warfare Center-Weapons Division. The 

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

active fire suppressant capabilities based upon solid propellant gas generators; and to improve 

understanding of propellant and additive effectiveness in fire suppression. The program was designed to 

accomplish the following: 

1. Establish baseline SPGG performance with Aerojet propellant designated FS-0140 (EPA 

SNAP-approved for use in normally occupied spaces). 

2. Develop techniques for reducing the combustion temperature of the propellant, such as 

tailoring the propellant formulations, and for incorporating chemical additives (radical traps 

and re-light inhibitors). 

3. Develop techniques for cooling the combustion products (e.

 ased on References 30 and 31. Large portions of the text from these documents, along with the fig ii Section 9.3 is b ures shown 

here (except as noted), have been used without further attribution. 
Solid Propellant Gas Generators 975

4. Characterize the extinguishment mechanisms of solid propellant systems by examining the 

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

SPGG-driven suppression event. 

us and liquid 

related to the discharge coefficient Cd of 

 P = P (agent) + P (9-2) 

For solid propellants, P is directly related to the product of the burning surface area A and the rate at 

f 1 

to 2 result in extremely unstable combustion, with the relevant chemistry dominated by gas phase 

heat. For typical solid propellant reactions, exhaust 

temperatures are in the range of 1700 °C to 2200 °C. 

Propellants used in SPGG fire extinguishers are designed to produce an inert gas blend of carbon dioxide, 

nitrogen and water vapor and to yield cooler exhaust temperatures. The Aerojet propellant FS-0140 used 

5. Modify existing hybrid extinguisher technology using additional gaseo

suppressants, assuring operability at low ambient operating temperatures. 

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

propellants with and without additives. 

7. Correlate laboratory- and mid-scale results. 

8. Perform tests on real platforms defined by the weapon systems community (through 

JTCG/AS) on those agents that performed best in mid-scale tests. 

9.3.2 Operating Principles 

Conceptually, both SPGGs and pressure-bottle (blow-down) systems deliver agent according to the same 

analytical expression, whereby the rate of agent delivery m'd is 

the agent, the throat area At and the pressure inside the delivery device Pc, i.e. 

 m'd = Cd x At x Pc . (9-1) 

In a blow-down system, the initial bottle pressure is given by the sum of agent vapor pressure Pvap plus 

that of a pressuring gas (typically nitrogen) Ppressurant:

c vap pressurant

Here, Pc is at its maximum in the pre-discharge condition, and both Pc and m'd decrease rapidly upon 

initiation of the discharge process. Where the SPGG differs from the blow-down bottle is its ability to 

store agent at zero internal pressure, and then to generate high pressures internally by the combustion of 

the solid propellant to form a blend of inert gases. 

c surface

which gas is generated from the propellant, referred to as the burn rate (BR, in units of cm/s), raised to a 

power. The logarithm of BR typically increases linearly with log(Pc) with slope determined by the 

pressure exponent, n: 

log BR = n log (Pc /Asurface ) + constant (9-3) 

A pressure exponent less than one assures that high combustion-induced internal pressures can be 

maintained, translating into sustained high rates of agent discharge. Pressure exponents in the range o

reactions. 

Solid propellants are typically comprised of an intimate mixture of finely ground solid fuels and 

oxidizers, often blended together with a polymeric binder. The component fuel and oxidizer combine to 

create exhaust gases, with the generation of 
976 Powder Panel and Propellant Discharge Technologies 

as the baseline for the current study has CH3N5 as its fuel and Sr(NO3

to absorb heat and reduce the exhaust temperature. The exha

)2 as its oxidizer, with MgCO3 added 

ust product gases from FS-0140 consist of 

about 45 % N , 35 % CO , and 20 % H2O by volume. The strontium and magnesium form solid oxides in 

er temperatures are around 1200 °C, and are reduced to about 775 °C in the 

brid arrangement (a so-called Hybrid Fire Extinguisher), with the propellant 

echniques 

llets. Larger 

Comput

the NAWC by the JANNAF Thermodynamic 

Databas

equilibrium

equilibrium

Computation

• enthalpy of individual ingredients 

• density and mass fraction of individual ingredients in the mixture 

2 2

the process. Peak chamb

exhaust stream. 

Exhaust temperatures can be reduced further by mixing the fuel and oxidizer in off-stoichiometric 

proportions, by selecting less exothermic fuel/oxidizer combinations, or by adding materials that absorb 

heat through dilution, phase change, or endothermic decomposition. Propellant additives are also used to 

increase the radical scavenging propensity of the exhaust products, which, in turn, improve the efficiency 

by which the fire is suppressed. The temperature and chemical activity of an SPGG fire extinguisher can 

also be tailored through a hy

exhaust used to pressurize, disperse, and vaporize a liquid agent such as a hydrofluorocarbon or an 

aqueous solution. 

While the mechanisms described above for controlling the exhaust temperatures and chemical activity of 

the effluent are easy to state on a theoretical basis, the effect of changing the propellant mixture is far 

from being predictable. This means that many combinations of propellants, additives, pressures and 

geometries need to be explored experimentally over a range of scales. 

9.3.3 Experimental T

Propellant Screening Tests 

The developmental propellants described here were made up in batches less than 1 kg. In a typical 

process, individual ingredients were pulverized and then wet-mixed in an inert fluorocarbon medium with 

a polymeric binder. The solid was then collected, dried and compression molded into pe

batches of propellant were manufactured and pressed on an automated rotary press. 

Propellant development for the Aerojet-NAWS China Lake effort generally took place according to (a) 

initial computational evaluation of candidate mixtures of fuel, oxidizer, processing additives and coolants, 

followed by (b) small-scale processing of compositions down-selected from (a), and then (c) scale-up of 

formulations down-selected from (b) in order to facilitate fire suppression effectiveness testing. 

ational evaluation consisted of thermodynamic analysis of the solid propellant compositions using 

 Propellant Evaluation Program (PEP)40 augmented

e. PEP models the combustion process in a gas generator in two steps, the first determining 

 of the input mixture at a fixed combustion pressure, and the second calculating the 

 condition of that combustion chamber mixture upon expansion to atmospheric pressure. 

al inputs consisted of: 

• chemical composition of individual ingredients 

• equilibrium chamber pressure (generally 6.9 MPa) 
Solid Propellant Gas Generators 977

• equilibrium exhaust pressure (generally 101 kPa) 

The outputs were: 

• ium at combustion 

Preparations propellant mixture, with initial preparation of small 

(1 g to g to verify adequate safety properties (standard 

propella t

mixtures we

er the NGP were prepared by either dry or wet techniques. In a 

edients were weighed, combined with ceramic grinding media in a 

n medium, 

 blends typically included analysis according to a 

window bomb. In the strand burner 

mb, pressurized to a predetermined level (usually 6.9 MPa and 17.2 MPa). The 

uncoated face of the grain was ignited using an electric match and the time was measured from ignition to 

e end of the linear burn event

ly is shown in the center, with the window for viewing and filming near the bottom. Single 

burn rate samples (e.g., single extruded grains) were ignited by a hot wire (seen on the left of Figure 9-34) 

nalyzed to determine burn distance, burn time and 

hence burn rate. The pressure limit of this apparatus extends to 55 MPa, the higher end of nominal gas 

• chemical constituents (and their respective fraction) at specified equilibrium conditions 

bulk adiabatic temperatures of combustion products formed at equilibr

chamber pressure (6.9 MPa) and exhaust pressure (101 kPa) 

followed standard practices for any new 

 5 ) batches of propellant by hand grinding,

nt esting includes sensitivity to impact, friction, and electrostatic discharge, ESD). Suitable 

re then scaled up to batches of 50 g to 1 kg for further evaluation. 

New propellant formulations tested und

typical dry process, individual ingr

mechanical ball mill for dry-blending, and then dry-pressed into tablets for burn rate testing. Individual 

components were normally pre-ground to specific particle sizes and then added to the mixture for 

blending to a uniform composition, and then pressed on an automated rotary press. In a typical wet 

process, ingredients were weighed, pulverized and then wet-mixed in an inert fluorocarbo

where polymeric binder was deposited upon the powder and the mixture precipitated. The solid was then 

collected, dried and compression molded into pellets. 

Preliminary characterization of the different propellant

burn rate test. Burn rate testing, when taken together with the gas output from PEP thermochemical 

calculations, provides a measure of the rate of gas/agent evolution from different solid propellant 

compositions. Most propellant burn rates were evaluated over a range of pressures between 3.4 MPa and 

21 MPa. 

Burn rate testing was performed by either a strand burner or a 

technique, compression molded cylindrical grains (pills) of approximately 12.7 mm diameter and 

12.7 mm thickness were prepared with a non-burning inhibitor (e.g., epoxy). The inhibitor was coated 

onto the outside circumference of the cylinder, as well as on one circular face. The inhibited grains were 

placed in a closed bo

th . The burn distance/burn time yielded the burn rate. 

Initial testing at China Lake was performed in a high pressure window bomb (Figure 9–34). This is a 

closed vessel, filled with an inert gas to a static pressure, and equipped with two optical windows. The 

full assemb

and the rate at which the burning front advanced through the sample was recorded on film. For evaluating 

burn rate temperature sensitivity, a variable temperature stage was used, with a flow of liquid and gaseous 

nitrogen through the holes in the copper block surrounding the sample (right side of Figure 9–34) used to 

control temperature. This film was calibrated and a

generator internal pressure maximum. More promising candidates were scaled up to larger batches, and 

the most promising up to several kilograms in size. 
978 Powder Panel and Propellant Discharge Technologies 

Figure 9–34. NAWS-China Lake Propellant Burn Rate Apparatus. 

Fire Test Fixture 

The mid-scale Fire Test Fixture (FTF) developed by Aerojet was used to test the effectiveness of various 

• Main test chamber 

agents under repeatable test conditions. The FTF fixture (shown in Figure 9–35 and Figure 9–36) is 

1.87 m long x 0.61 m wide x 0.61 m high and is located in a concrete reinforced test cell with the floor 

coated with fuel-resistant, non-absorbing material. A schematic of the FTF test facility is shown in 

Figure 9–37. It consists of several major subsystems including: 

• Air supply system 

• Fuel supply system 

• Ignition system 

• Suppressant discharge system 

• CO2 emergency extinguishing system 

• Control and data acquisition system
Solid Propellant Gas Generators 979

Figure 9–35. Aerojet Fire Test Fixture (FTF). 

Figure 9–36. Photograph of Fire Test Fixture. 

1.87 m 

0.61 m 

0.61 m 
Powder Panel and Propellant Discharge Technologies Powder Panel and Propellant Discharge Technologies 980

Figure 9–37. FTF Test Facility Schematic.

FM1

Flow Meter

0.01 to 0.15 gpm

Fire test

fixture

Baffle Assy.

Air Inlet

1/4" Flex line

detonation loop

Piezo Igniter

Fuel supply located inchamber in locations attached sketch (nozzassemblies are hiddedirect air flow by baffl

SprayNozzle

CO2 Supply

CO2 Supply

CO2 Supply

Remote CO2 Closet

CO2 Supply

Remote Fuel Closet

Fuel Supply

RegulatedGN2Supply

SOV1

SOV2

RV1

SOV4

Sight Glass

FD1

SOV3

SOV5

EV1

SG1

SG2 R1

EV2

Propane

Supply

SOV6

Vacuum Pump

VV1

VV2

F1

Outlet Filter

(EV3-EV9)

980
Solid Propellant Gas Generators 981

Various instruments were installed in the solid propellant fire extinguisher and FTF to monitor and

control test variables, and to make sure they were in the similar ranges from test to test. These 

instruments included a pressure transducer in the hybrid fire extinguisher cham thermocouples, 

pressure transducers, and flow meters in the FTF. The instrumentation layout is p 8. 

Figure 9–38. Fire Test Fixture Oper

JP-8 was used as the fuel i

produced a nominal heat release rate of 1000 kW. The air mass flow was

n all of the tests conducted in the FTF. The fuel mass flow was 20.3 g/s,

ational Configurations. 

 which

385 g/s, producing a global 

ber, and

resented in Figure 9–3
982 Powder Panel and Propellant Discharge Technologies 

equivalence ratio of 0.80, if one assumes the stoichiometric air-to-fuel mass ratio for JP-8 is 15.18. 

Table 9–11 provides a summary of the operating conditions for the FTF and Table 9–12 compares these 

to the operating conditions of other fire test fixtures used in the NGP. 

Table 9–11. Fire Test Fixture Operating Conditions. 

Parameter Value 

Flow Conditions Air JP-8

Mass flow, m', g/s 385 20.3 

Volumetric Flow, L/s 316 25 

Linear Flow in pipe, cm/s 670 - 

Stoichiometry 

Air-fuel Ratio (m'air/m'fuel) 19 

Equivalence Ratio 0.8 

Flame Zone Conditions 

Flame Temperature, K 1200 

Heat release rate, kW 1000 

Length, cm 180 

Cross-Sectional Area, cm2 3700

Volume, L 670 

Residence time, s 0.27 

Agent Injection Interval, ms Up to 8000

Table 9–12. Comparison of Aerojet FTF to Other Fire Test Fixtures. 

Fixture 6

Characteristic

Turbulent Spray 

Burner 41

Turbulent 

Spray 

Burner42

Baffle 

Stabilized 

Pool Fire43

Baffle 

Stabilized 

Pool Fire44 FTF 

Length (cm) 5.5 7.5 190 190 180 

Cross-Sectional Area (cm2) 13.0 19.6 84.6 84.6 3716

Volume (L) 0.09 0.15 16.1 16.1 670 

Air Mass Flow (g/s) 21.8 33.0 539 539 385 

Residence Time (ms) 5 5 112 35 270 

Fuel JP-8 JP-8 Propane Propane JP-8

Fuel Mass Flow (g/s) 0.28 0.34 0.15 0.15 20.3 

Equivalence Ratio 0.19 0.16 0.01 0.005 0.80 

Fire Heat Release Rate 

(kW) 13 15.8 7 7 943 

The nominal inlet air velocity in the FTF was 6.7 m/s, which, assuming a well-stirred model, leads to a 

characteristic residence time under cold conditions of about 1.3 s. The residence times when hot or along 

streamlines that pass by the baffles would be significantly shorter. 

Once the desired SPGG device was mounted, the JP-8 spray was initiated and ignited with a propane pilot 

flame, and the air flow was set to the standard condition. Experience showed that a steady fire could be

attained in about 4 s to 5 s. At that time the SPGG was fired, and the agent was discharged.
Solid Propellant Gas Generators 983

Depending upon the design, the gas generator device either was located within the FTF in the forward

chamber (on a metal bar in the middle of the air flow, shielded from and upstream of the fire), or mounted

outside of the FTF adjacent to the air inlet. Figure 9–38 illustrates the gas generator device placement

within and outside of the FTF. 

Tests were perform the FTF. In

determined. 

ng this unit

resulted in en for delivery to 

the fire. e 9–40, was 

mounted in t e strain and

mi difference

am

approxima of the agents to 

enhance the n tube. The

distribution tube was to 

am ount of agent

d the initial

agent quantit

ed using two distinctly different configurations of suppressors mounted to

the first configuration, the relative performance of several chemically active additives was 

This testing utilized a slow discharge (5 s to 8 s) gas generator located outside the FTF; igniti

trainment of candidate chemically-active agents into a SPGG exhaust stream 

 A neutral-burning solid-propellant gas generator, shown in Figure 9–39 and Figur

he external location; the slow discharge was used in an attempt to minimize flam

xing effects anticipated in rapid discharge tests, thereby emphasizing the performance

ong the various candidates. The discharge of the SPGG for these initial tests had a duration of 

tely 5 s. Fine-grid metallic meshes and porous plates were used downstream

mixing between the SPGG exhaust and agents prior to entering a distributio

split into two lines, one entered the test fixture, and the other discharged directly

bient. (See Figure 9–38.) By varying the flow ratio between these two lines, the am

entering the fire zone could be controlled. In the tests, the split ratio was fixed to be 50 %, an

y in the SPGG was varied. 

Figure 9–39. Aerojet Slow Discharge Solid Propellant Gas Generator Test Unit. 
Powder Panel and Propellant Discharge Technologies 

Figure 9 . w Discharge Solid Propellant Gas Generator Test Unit. –40 Cutaway of Aerojet Slo

0.05 mm CRES Dia. 3.18 mm 

Orifice assyfrom 0 to 3.1

. Dia

8

meter 

 mm

984
Solid Propellant Gas Generators 985

hin the FTF and could be disassembled after a test, refurbished between

runs, loaded with weighed quantities of test propellant, readily reassembled, and re-used for additional

Figure 9–41. Aerojet Reusable Rapid Discharge Solid Propellant Fire Extinguisher Unit. 

testing. For the hybrid extinguisher, the hybrid fluid typically surrounds the SPGG, resulting in a bottle

within a bottle configuration, as shown in Figure 9–42.

45

The relative efficiency of different suppressants was ranked based upon their threshold quantity. The

threshold was defined as the amount of agent needed to extinguish the fire at least two out of three times. 

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

an agent load greater than the threshold amount. In the first (external SPGG) configuration, a “bleed” line 

with an orifice to ambient was used to adjust the percentage of agent delivered to the fire; the orifice in 

this line is gradually closed until testing yields a fire-out time of ≈ 5 s. In the second (internal 

SPGG/hybrid extinguisher) configuration, total agent loads were adjusted up (or down) until threshold 

levels were achieved. In Figure 9–43 are consecutive frames of a successful suppression event in the

FTF.

The second test configuration used the fire extinguisher mounted within the FTF in a chamber upstream

of the fire. For this testing, the SPGG discharge times were generally maintained between 150 ms and 

200 ms for ease of comparison with the original data. The SPGG used for this testing, shown in

Figure 9–41, was mounted wit

Figure 9–42. Arrangement 

of a Typical Hybrid Fire

Extinguisher.
986 Powder Panel and Propellant Discharge Technologies 

Figure 9–43. Consecutive Frames during SPGG Suppression of a Fire in the FTF

Full-scale Demonstration Tests at China Lake 

Although not included in the NGP-funded program, it is relevant to briefly describe the live-fire testing 

conducted by Aerojet for NAVAIR to demonstrate SPGG fire suppression technology on full-scale 

aircraft dry bays. The tests were conducted at China Lake on mid-wing sections and landing

sponsons. 

Figure 9–44 shows an SPGG fire extinguisher with 210 g of chemically active propellant mounted in the 

landing gear sponson test article. JP-8 filled the fuel line. The main landing gear door was either open or

closed, and the external airflow was run up to about 120 m/s. The gun was then loaded, and fired.

projectile impacted the striker plate and fuel line, resulting in a fuel spray that immediately ignited. The

SPGG extinguishers were initiated either automatically or following a set delay period after initial im .

The intent of the mid-wing testing was to evaluate the potential for a common size gas generator for the 

entire aircraft. Testing evaluated the extinguishment performance of a common sized generator 

extinguisher at the most challenging fire location of the aircraft (the high airflow mid-wing compartm .

The chemical gas generators were installed at various positions, with a typical installation shown in

Figure 9–45. 

.

 gear 

The

pact

ent)
Solid Propellant Gas Generators 987

Figure 9–44. SPGG Installed in Sponson Test Article for Live-fire Demonstration.46 

(Photograph reprinted with permission of the Naval Air Systems Command.)

t Article for Live-fire Demonstration.47 

nd.)

Figure 9–45. SPGGs Installed in Mid-wing Tes

(Photograph reprinted with permission of the Naval Air Systems Comma
988 Powder Pan der Panel and Pro and Propellant Dischar nt Discharge Technologies 

.3.4 Results: General Behavior of Propellants 

General 

This research explored several complementary approaches directed toward identifying more effective

solid propellant-based fire extinguishers. All of these approaches utilized a solid propellant gas generator 

to deliver the suppression agent to the fire, including: 

• development and characterization of new, cooler solid propellant compositions 

• development and characterization of new chemically active solid propellant compositions, 

and 

• development and characterization of new hybrid fire extinguishers.

The benchmark by which all these improvements were measured was the first solid propellant

composition manufactured by Aerojet and used on the F/A-18 E/F Dry Bay Fire Extinguisher and the 

V-22 Wing Fire Protection System. This propellant is referred to as FS01-40. 

The thermodynamics, burn rate, and fire suppression effectiveness were studied using the techniques and

apparatus described in the previous section, and the results of these studies are reported in this section for 

each of the three above approaches. The exhaust temperature and momentum, and the temperature of the 

propellant during discharge, are also important parameters that were examined. 

SPGG Temperatures and Discharge Pressures 

SPGG exhaust temperatures for different propellant compositions were measured at several points along 

the exit streamline. These measurements indicated gas temperatures varied widely with distance from the

gas generator exit, with values near 600 °C directly outside the generator to below 200 °C at points 

~ 30 cm from the gas generator. Temperature measurement of SPGG exhaust is complicated by the need 

for rapid (ms) response in the face of high velocity, high temperature gases. Fine wire thermocouples, 

while giving good response times, eroded/broke during testing near the gas generator exit; hence, no

temperature data for this region are reported. 

In a series of hybrid SPGG tests with propellant-to-liquid suppressant mass ratios ranging from about

1:10 to 1:5, exhaust temperatures were much lower than for the SPGG alone, dropping to values between 

50 °C and 65 °C. The tests were conducted as “vise shots,” where a hybrid SPGG is mounted in a benchtop vise and held there for functioning (Figure 9–46). 

Figure 9–46. Typical Setup of 

Preliminary Vise Shot for Hybrid 

Extinguisher. 

9

30 cm
Solid Propellant Gas Generators 989

The hybrid configuration used a fixed mass (18 g) of inert solid propellant and different quantities of the 

HFE-1230 hybrid fluid. The quantity of hybrid fluid varied from 176 g (the standard 1:10 

propellant:hybrid mass ratio) to 103 g (a 1:5 ratio). 

For each of the tests, the following performance characteristics were recorded: chamber pressure (Pc) and 

temperature of gas downstream of the discharge orifices (Tgas). Type-K thermocouples were mounted on a

screen ≈ 30 cm from the gas outlet (location was aligned with one set of gas outlet orifices) and data were 

collected at 100 Hz. 

Temperatures recorded for the standard 1:10 propellant:hybrid mass ratio were reduced significantly as

compared to all-SPGG configurations (55 °C to 60 °C vs. ≈ 200 °C, respectively). The recorded

performance characteristics reveal that as the quantity of hybrid fluid is reduced (from 176 g to 103 g), 

the measured internal suppressor pressures are reduced proportionally (17.2 MPa to 9.9 MPa).

Temperatures of the mixed air-suppressant exhaust blend, however, vary only slightly, with the reduced

quantity of hybrid fluid yielding temperatures of ≈ 65 °C as compared to 57 °C for the 1:10 mass ratio. 

Discharge rates were varied across a range to determine if this parameter played a role in suppression 

effectiveness. The rate of mass discharged from a gas generator is related to the internal pressure, which

increases y using a 

mmon propellant but varying the relative surface areas available for burning by making use of different 

izes of tablets, while keeping the burning rate constant. 

The three tablet sizes considered were small (9.5 mm diameter x 2.4 mm thick); standard or medium

mm diameter x 12.7 mm thick). For the standard 

e device discharged the agent in about

n burn (yellow trace, Figure 9–47), and peak pressures reached only 5.5 MPa. In some cases 

the pressures were too low to rupture the burst disks, and when the disks did rupture, burn times stretched

Even with the variations in peak pressures, all the SPGGs evaluated in Figure 9-46 were able to

rmance times (as seen in the pressurization curve above), the heat output is expected to be

unchanged with tablet size, which is approximately the case for the blue and yellow traces in Figure 9–48. 

The significantly different surface temperatures shown in the pink trace appear to be the result of 

differences in measurement location and thermocouple attachment quality.

with the exposed area of the propellant. Different discharge rates were prepared b

co

s

(12.7 mm diameter x 6.4 mm thick); and large (12.7 

sized tablet (CA-04), internal pressures reached 12.4 MPa, and th

0.2 s. For a fixed gas generator load (mass of propellant), the smaller pellet size had a larger total surface 

area, resulting in faster pressurization (peak pressure of 17.7 MPa) and a discharge time of 0.1 s, which

can be seen in Figure 9–47. The large tablets had a smaller surface area (per unit mass) that produced a

very uneve

out to almost 1 s. 

In an attempt to improve discharge characteristics of the larger tablet size, the gas generator orifice area

was reduced by ≈ 50%. This reduction in area results in a less than two times higher internal pressure and 

a more regular and well-behaved pressurization curve, while retaining the longer discharge time desired.

extinguish the fire in the FTF. 

Figure 9–48 portrays the temperatures measured using Type K thermocouples tack-welded to the SPGG 

surface. Measured temperatures appear to peak at about 120 °C. While different tablet sizes do yield 

different perfo
990 Powder Panel and Propellant Discharge Technologies 

Figure 9–47. Chamber Pressure for Different Propellant Surface Areas (CA-04). 

Figure 9–48. Housing Temperatures for Different Propellant Surface Areas (CA-04). 
Solid Propellant Gas Generators 991

Effects of Propellant Temperature on Burn Rate 

Besides pr

burned. High

essure, the burn rate is also dependent on the initial temperature at which the propellant is 

er temperatures generally result in increased burn rates, as is typical for activated processes. 

ature sensitivity of burn rate, the derivative of the 

linear burn rate with respect to ber 

pressure it on the nature

of the p e

are defined as follows:48

Given that most propellant applications require functioning of the propellant device over temperature 

extremes as wide as -50 °C to 75 °C, a low sensitivity of burning rate on temperature is desirable. Two

parameters are typically used to describe this temper

temperature at fixed pressure, σp, and the variation in combustion cham

w h temperature at fixed propellant geometry, πk. These parameters are dependent

rop llant composition, its burn rate and the combustion mechanism of the given propellant, and

T T P T P ⎝ r 1 − 0 ⎠ ⎝ ∂ ⎠

and 

p = ⎜ ⎟ ⎟

⎟ ⎜ σ = ⎜

⎛ 1 r1 − r0 ⎞ ⎛ ∂ ln r ⎞

n n K K

k T

P

T T

P P

P ⎟

⎠

⎞ ⎜

⎝

⎛ = ⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

−

− = ∂

∂

π

1 ln

1 0

1 0 , 

where r is the linear burn rate, r0 and r1 are the burn rates at T0 and T1, respectively, and Kn is defined as 

Ab/At. For conventional propellants, σp ranges 

between 0.002/K to 0.008/K; for AP-based propellants, σp is typically ≈ 0.0015, while for AN-based

the ratio of burning surface area to exit orifice area,

propellants, σp is often in the vicinity of 0.002/K. 

These two parameters can be related to each other through the pressure exponent defined previously, n. 

K P n π σ − = 1

1

Note that in the case of n approaching 1, πk can become very large even for small σp; i.e., large changes in

chamber pressure can be expected with even small temperature variations. 

rn rate increases with temperature in a predictable 

manner. 

Baseline Propellant, FS-0140. 

Table 9–13 shows the measured burning rates at various initial temperatures for the baseline propellant 

composition used in the current study, along with the derived temperature sensitivity parameters and

pressure exponent. These findings reveal that the bu

Table 9–13. Temperature Dependence of Burn Rate for 

T, °C BR1000 (mm/s) Pmax (MPa)

-25 12.7 7.83

25 14.0 10.3

75 15.2 12.8 

σp = 0.13 %/°C πk = 0.48 %/°C n = 0.73
992 Powder Panel and Propellant Discharge Technologies 

9.3.5 Results: Cooled Propellant Formulations 

The hot exhaust gases of typical solid propellant compositions are not efficient suppressants for 

combustion reactions. Additionally, the quantity of gases required for suppression may result in overThis research explored three different routes towards achieving cooler solid propellant fire extinguisher 

• seeking faster-burning solid propellant compositions, to which one could add coolant to 

ame temperatures was explored. The selection of 

fuels focused on those with nitrogen-nitrogen bonding in the fuels’ molecular structure. N–N bonding 

ts in a cooler solid propellant exhaust composition. 

etics, or burn rate. 

able; it and its derivatives are 

used in several commercially viable automotive airbag formulations. Many of the other fuels considered 

have limited commercial availability. Preliminary evaluations suggested that bis(5-aminotetrazolyl) 

tetrazine (BTATZ) would be an attractive candidate for further study because of its high nitrogen content. 

pressurization conditions when released in enclosed bays, as well as resulting in greater concerns for 

materials compatibility for the structure surrounding the suppressor. For these reasons and others, cooler 

solid propellant fire extinguisher compositions are highly desired. 

compositions: 

• reducing the enthalpy of the combustion process through selection of various fuels/oxidizer 

blends; 

• altering the stoichiometry and enthalpy of the propellant reactions through various 

fuel:oxidizer ratios; and 

reduce the overall exhaust gas temperature. 

Solid Propellant Combustion Thermodynamics 

The impact of different fuels upon calculated adiabatic fl

was considered to provide two distinct advantages: N–N molecular bonds are often kinetically labile and 

therefore susceptible to rapid reaction with an oxidant; and additional nitrogen atoms in the fuel increases 

the production of the molecular nitrogen in the exhaust. 

Several high-nitrogen fuels were considered. (See Figure 9–49.) A more negative enthalpy of formation 

generally leads to cooler exhaust products; however, one must also consider the enthalpy of the 

equilibrium products that are formed. In particular, a higher N:C and N:H ratio in a fuel results in the 

formation of a greater proportion of N2 vs. CO2 and H2O gas; the lesser enthalpy associated with N2 (vs. 

CO2 or H2O) resul

Thermodynamic equilibrium calculations of the adiabatic flame temperature (typically conducted at 

6.9 MPa) are precise and straightforward. On the other hand, predictive solid propellant kinetics 

modeling is very poorly developed and unreliable. Hence, characterization of viability of cooler 

propellant compositions requires complementary thermodynamic modeling together with experimental 

measurement of combustion kin

The effect of different fuels upon exhaust gas temperatures was determined for a common oxidizer in a 

stoichiometric mixture. The calculations were performed using the NAWC PEP40 computer code, and the 

results are shown in Table 9–14. A review of these data shows that all but the GAZT (bisguanidinium 

azotetrazole)/strontium nitrate blend exhibit adiabatic combustion temperatures well in excess of 2000 K. 

Among the fuels studied, 5-amino-tetrazole (5AT) is the most readily avail
Solid Propellant Gas Generators 993

N N

N N

NH

N

N

N

NH

HN

N

N

N

HN

N N

N

N

N

N

N

H

N

N

N

N

N

N

N

N

H

N

N

N

N

N

N

N

N

N

NHNH2

H2NHN NHNH2

+

NH2

H2N NH2

+

2-

2

- NH2

H2N NH2

+

N O3

-

Guanidinium

Bitetrazole

(GBT)

Bisguanidinium

Azotetrazole

(GAZT)

N

H N

Triaminoguanidinim

Nitrate(TAGN)

Bitetrazole(BT)

Bis(aminotetrazolyl)tetrazine

(BTATZ)

N

N

N

H

N

NH2

5-Aminotetrazole

(5AT)

Figure 9–49. High-nitrogen Fuels Used in China Lake/Aerojet Propellant Development. 

BTATZ was discovered recently by Hiskey et al.49,50 at Los Alamos National Laboratory (LANL). Its

promise as a high-nitrogen, highly reactive fuel led to an extensive NGP effort to explore its utility for

solid propellant compositions, and to work to scale up synthesis of this material from the several gram, 

laboratory level to kilogram quantities.
994 Powder Panel and Propellant Discharge Technologies 

Table 9–14. Adiabatic Temperatures of High Nitrogen Propellant Fuels in Stoichiometric 

Mixtures with Sr(NO3 2) Oxidizer.

Fuel 

Molecular 

Formula ∆H (J/g) Density (g/cm3

) Tc (K) 

5AT CH3N5 2450 1.65 2650 

BTATZ C4H4N14 3560 1.74 2750 

TAGN CH9N7O3 -290 1.54 2680 

BT C2H2N8 3350 1.79 2750 

GBT C3H7N11 1540 1.57 2520 

GAZT C4H12N16 -1110 1.66 1930 

GN CH6N4O3 -3530 1.39 2250 

NQ CH4N4O2 -880 1.73 2720 

BTATZ is synthesized from commercially availa p procedure furnished by 

LANL and outlined in Figure 9–50.49,50 Reaction of guanidine hydrochloride with three equivalents of 

hydrazine hydrate yields triaminoguanidine hydrochloride (TAG•HCl) in almost quantitative yield. 

Reaction of TAG•HCl with 2,4-pentanedione leads to dihydroDMPTZ which upon oxidation with N2O4 

gives DMPTZ. Very careful control of the reaction conditions is required for the final step. The solvent 

time. The reaction mixture is allowed to cool to 70 °C 

and ethanol is added to prevent the mixture from freezing upon further cooling. BTATZ is collected on a 

d 

by trituration with dimethylformamide (DMF) or ethanol, with ethanol giving a higher recovery but 

providing slightly less pure material. The yield for this last step in a typical experiment is in the 70 % to 

75 % range with ethanol purification versus ≈ 50% when DMF is employed. The synthesis of BTATZ 

were reviewed by a panel of 

experienced energetic materials researchers before any scaling up of the synthesis was permitted. 

Using these guidelines NSWC staff preceded through the 1 g, 5 g, 25 g, 100 g, 250 g and 450 g levels. 

Al d 

in a 12 L flask. On the 4 ale, the produ d by filtr porosity 

filter funnels. In order to carry out the synthese cribed above we needed a large amount of the 

immediate precursor DMPTZ (C12H14N8). This material is not an energet terial and is not subject to 

the scale-up limitations described for the synthesis of BTATZ. NSWC staff used a published procedure 

to carry out the synthe ately 4.5 rial. A fu kg were supplied by the 

Los Alamos National Laboratory. Modifications to the purification process provided material with 

acceptable properties but in higher yield than that using the standard method. 

ble ingredients in a four-ste

used for the reaction (sulfolane) is a solid at room temperature (melting point 28 °C). The solvent is 

heated to 40 °C and DMPTZ and 5AT are added. This temperature is maintained for 2 hours and then the 

temperature increased over a six-hour period to 135 °C and held at that temperature for 18 hours. BTATZ 

precipitates from the reaction mixture during this 

medium porosity glass frit and is washed with copious amounts of ethanol. The crude product is purifie

was carried out initially at quantities of about 1 g for review by the safety committee, as is common for 

the synthesis of energetic materials. The results and procedures used 

Typically, if upon review, the procedures are deemed safe and the material itself has no hazardous 

properties that cannot be mitigated through the use of appropriate handling techniques, the reaction can be 

scaled up by a factor of five. Several results at each level were required for review. 

l of these reactions were carried out in a laboratory fume hood. At this level, 6 L of solvent were use

50 g sc ct was collecte ation on two 3 L medium

s des

ic ma

sis of approxim kg of this mate rther 4.5 
Solid Propellant Gas Generators 995

NH N

N

N CH3

NMP N N

N

N CH3

∆

N N

N

N

N

NH

bis(aminotetrazolyl)tetrazine, BTATZ

NH N

N

N CH3

NO2 N N

N

N CH3

N

NH2

N N

N

N

N

NH

2

CH3

CH3

H2N

CH3

CH3

N N

NH

NNH2

N

N

CH3

NH NH

NH

CH3

4 .HCl 2 + +

c initiation. When formulated into a molding powder 

with poly(ethyl acrylate) (3 % as a binder) electrostatic sensitivity is still a concern, even when 0.5 % 

In order to assess the effect of the choice of oxidizer on exhaust gas temperatures, thermodynamic 

O

H2NNH2

NH2 NH .HCl 2 NHNH2 H .HCl 2NHN

CH3

dioxane, ∆

NNH2 O O NH N N

CH3

NHNH2 HN .HCl NH N

N CH3 STEP II

N CH3

STEP III

STEP IV

STEP I

Figure 9–50. Synthetic Route to BTATZ. 

Further safety data on BTATZ itself has been obtained. BTATZ shows acceptable friction and impact 

sensitivity but is somewhat sensitive to electrostati

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. However, shipments of these new energetic materials is

still limited to small quantities. 

calculations were performed using the NAWC PEP40 computer code, with different oxidizers and a 

common fuel (5-aminotetrazole, or 5AT) in stoichiometric proportions. Combustion was assumed to be 

complete. The results are compiled in Table 9–15. 
996 Powder Panel and Propellant Discharge Technologies 

Am test exhaust 

gases. erature, has

poor th

ith 

ong the oxidizers considered, strontium nitrate and potassium perchlorate produced the hot

 The ammonium nitrate/5AT blend, while it produces a lower adiabatic flame temp

ermal stability, rendering it impractical for use in a fire extinguisher on DoD weapons platforms. 

Table 9–15. Adiabatic Temperatures of Oxidizers in Stoichiometric Mixtures w

5-aminotetrazole. 

Oxidizer Molecular Formula ∆H, J/g Density, g/cc Calculated Tc, K 

Strontium Nitrate Sr(NO3)2 -4610 2.99 2650

Potassium Nitrate KNO3 -4880 2.12 2150

Potassium Perchlorate KClO4 -3210 2.52 2970

Ammonium Nitrate NH4NO3 -4980 1.72 2390

High Nitrog

While fuel and oxi opriate solid 

propellant co es that it be 

kinetically

For different ver a 

broad range, y 

applications. bays. 

The chem to the nth

build to

≈ 6.9 MPa to 

 typically in 

the range of generator and 

biting pressure 

exponents gr

For this proj odeled and 

sted. A summary of several cooler propellant compositions is presented in Table 9–16. The baseline

so

combustion temperature (1450 K), a moderate burn rate (1.27 cm/s), and a moderate pressure exponent 

en Propellant Burning Characteristics 

dizer thermodynamic studies provide a useful means of predicting appr

mpositions having cooler exhaust gases, actual use of a composition requir

 robust; i.e., the composition must burn at an appropriate rate. 

DoD fire suppression applications, agent discharge rates can be expected to extend o

from 50 ms to 500 ms for aircraft dry bay applications, to 0.5 s to 5 s for aircraft engine ba

The focus of this NGP research was the shorter timeframe associated with aircraft dry

ical reaction proceeds with a rate that is directly proportional to the pressure raised

power. When taking place inside a closed vessel – e.g., a gas generator – pressures typically

34 MPa in order to produce consistent performance. The burn rate at 6.9 MPa (1000 psi) is

often used as a standard condition for comparison of different solid propellants; this BR1000 is

5 mm/s to 15 mm/s. For the sake of ease of manufacturability (of both the gas 

enclosed propellant grains), n is preferred to be less than 0.6. Propellant compositions exhi

eater than unity were not considered for further evaluation, as this pressure dependence is not

suitable for practical applications. 

ect, several different combinations of fuels, oxidizers and coolants have been m

te

lid propellant fire extinguisher composition (FS-0140) can be seen to have a moderately high

(n ≈ 0.5). Most of these compositions contain, low levels of the processing/combustion aids including

PBA (poly(butyl acetate) binder), C-black (carbon black combustion aid) and mica (a lubricant); oxidizers 

were typically KP (potassium perchlorate) or KN (potassium nitrate). 
Solid Propellant Gas Generators 997

Table 9–16. Development Propellant Compositions and Burning Parameters. 

Temperature 

(K) Propellant Composition 

(wt %

Exhaust Species, 

) vol % @ Tc Tc, Texh

Calculated

Density 

Gas

Output 

(mol/100

Measured 

BR1000

(g/cm3) 

g (cm/s) )

Measured 

Pressure 

exponent, 

n 

Baseline: 5AT, 21

Sr(NO3)2 19.1, M 0 N2 45, H2O 20 14 000 2.55 2 0.5 .9,

gCO3 60. CO2 35, 50 1 1.27

5AT: 5AT 86.0,

PBA 3.0, C-blac

Mica 0.5 

N2 6 3, 

CH4 3, KCl(s) 5.3 g 1667 874 1.68 4.41 0.80 

KP 10.0, 

k 0.5, 1, H2 29, CO 0.43

BTATZ-1: BTAT

PBA 2.0, C-black 0.5

Mica 0.5

N2 75, H

CO, C 2349 1151 1.72 3.66 0.51 

Z 97.0,

,

2 24,

H4 5.44 

BTATZ-2: BTAT ,

KP 10.0, PBA 3.0 

C-black 0.5, Mica

N2 6 9 2290 1135 1.76 3.68 0.55 

Z 86.0

0.5

8, H2 23, CO 5.46

BTATZ-3: BTATZ 86.0, 

KN 10.0, PBA 3.0, 

C-black 0.5, Mica 0.5

N2 69, H2 23, CO 8 2085 1088 1.74 3.72 4.57 0.57

5AT/BTATZ-1: 5AT 48.0 

BTATZ 48.0, PBA 3.0, 

C-black 0.5, Mica 0.5

N2 68, H2 29 1939 908 1.66 4.14 1.40 

1.6 

(3.45-6.89

MPa)

5AT/BTATZ-2: 

BTATZ 72.0, 

5AT 24.0, PBA 3.0 

C-black 0.5, Mica 0.5

N2 70, H2 28 2118 995 1.69 3.94 4.52 0.71 

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 

1961 967 1.72 4.01 3.85 

0.7 

(6.89-18.9

MPa)

5AT/BTATZ-4: 5AT 43.0, 

BTATZ 43, KN 10.0, 

PBA 3.0, C-black 0.5,

Mica 0.5

N2 65, H2 29, CO 4 

K2CO3(s) 5.3 g 1799 965 1.70 4.10 1.55 1.6 

GAZT: GAZT 33.6, 

KP 62.4 , PBA 3.0 

C-black 0.5, Mica 0.5

N2 28, CO2 13, H2O 28

H2 26, CO 24, 

KCl(s) 32.6 g 

1723 964 1.92 2.51 >6.4 ND

BT: BT 33.6, KP 62.4, 

PBA 3.0, C-black 0.5,

N2 31, CO2 12, 

H2O 10, H2 13, 2479 1761 1.92 2.13 

Mica 0.5 CO 29, KCl(s) 32.6 g 

>6.4 ND 

GBT: GBT 33.6, KP 62.4,

PBA 3.0, C-black 0.5,

Mica 0.5

N2 28, CO2 10, 

H2O 9, H2 23, 

CO 29, KCl(s) 32.6 g 

2000 1457 1.88 2.19 >6.4 ND 

TAGN: TAGN 33.6,

KP 62.4, PBA 3.0, 

C-black 0.5, Mica 0.5

N2 21, CO2 17, 

H2O 30, H2 11, 

CO 13, KCl(s) 32.6 g 

2646 1421 1.86 2.44 >6.4 ND 
998 Powder Panel and Propellant Discharge Technologies 

In addition to its high nitrogen content, BTATZ has a high burn rate with a low pressure exponent and 

burns well even without any added oxidizer. This is attractive because addition of oxidizer leads to a 

much hotter effluent gas mixture as the product. In contrast, 5AT does not sustain combustion at 

atmospheric pressure and requires added oxidizer and significant pressure to a burn steadily. 

BTATZ was included in several formulations in combination with 5AT in an attempt to increase the 

efficiency of combustion while keeping oxidizer content to a minimum. A composition with 10 % KP 

has a very low dependence of burn rate on pressure, with a calculated combustion temperature of 

app 00 K, and yields over 4 mol gas/100 g, nearly 60 % of which is N2. 

A concern in most of these compositions is the high fraction of un-oxidized gases in the exhaust. 

Hydrogen levels are typically in the 10 % to 30 % range, with CO levels 5 % to 10 %. Although these 

gases are always diluted in N2-dominated exhaust, their presence would seem to represent a challenge in 

suppression applications. The CO levels would render their use unattractive in occupied spaces. 

Over the range 6.89 MPa to 18.9 MPa the pressure exponent for formulation 5AT/BTATZ-3 is 0.5 and 

decreasing. This formulation is a promising candidate as the burn rate is relatively high at low pressures 

and has a decreasing pressure dependence of the burn rate. Formulations BTATZ-2 and BTATZ-3 also 

exhibit ideal bu cteristics for gas generator applications with pressure exponents around 0.5 and 

with relatively high burn rates. 

BTATZ and its blends offer the potential for SPGG formulations with higher gas output and cooler 

effluents at low pressure. Low-pressure operation offers the possibility of constructing hardware from 

lighter mass materials resulting in an overall significant reduction in mass of the system. Evaluation of 

these compositions did not result in truly applicable, cooler solid propellant fire extinguisher 

compositions. However, several of these compositions offered promise for applicability when additives 

are used to promote cooler exhaust gases. 

Additives and Formulations for Cooler Exhausts 

The temperature of an otherwise hot solid propellant exhaust can be reduced if it is intermixed with a heat 

sink or cooling agent. This cooling agent can be included within the fuel-oxidizer blend, or it can be 

plemented externally to the combustion chamber. These two approaches are considered, in order, in 

this section. 

The effect of different coolants upon calculated adiabatic combustion temperature for fully-oxidized 

 Magnesium carbonate was selected for the baseline 

propellant mixture because of its strong cooling performance. The benefits of other coolants are not 

roximately 17

rning chara

im

Coolants are materials that undergo an endothermic reaction (or phase change) upon exposure to heat. 

Several endothermically active agents were considered, including MgCO3, Al(OH)3, CaCO3 and hydrated 

clays. When dispersed within a propellant blend, these solids absorb heat and decompose 

endothermically, producing inert gases such as CO2 and H2O. The combination of lower temperatures 

from heat absorption and inert gas production contributes directly to more effective fire suppression. 

stoichiometric blends was calculated using the NAWSC PEP40 thermodynamics code. The fuel-oxidizer 

blend (5AT- Sr(NO3)2) and mass fraction of coolant (40 %) were maintained constant for the different 

coolants. Relative effectiveness for heat absorption of the different coolants can be seen in Table 9–17 

through the lowered adiabatic flame temperature. 
Solid Propellant Gas Generators 999

always realized in propellant formulation; aluminum hydroxide, for instance, while offering attractive 

cooling properties has the unattractive feature of excessive reduction in propellant burn rates. The 

calculated adiabatic flame temperature for calcium carbonate should be lower than that of MgCO3; this 

discrepancy suggests there are gaps in the thermodynamic reference data used in the PEP code. Note 

that an 

approach 80 % that of water in the case of

Table 9–17. Effect of Different Co n Ad Fla empera f 5AT-Sr(NO3)2

Propellant Mixture. 

relative heat absorption capabilities are less than the evaporative cooling from water, but c

 calcium carbonate. 

olants o iabatic me T ture o

Coolant 

Molecular 

Formula 

Endothermic 

Process ∆H, J/g Density, g/cm3 Tc, K 

Magnesium 

carbonate 

MgCO3 decomposition 90 3.05 1440 

to MgO 

13

Aluminum 

Hydroxide 

Al(OH)3 decomposition 

to Al2O3

970 2.42 1480 

Copper(II) 

Oxalate 

Cu(C2O4)•0.5H2O decomposition 

to Cu 

83 2.21 1910 

Calcium 

Carbonate 

CaCO3 decomposition 

to CaO 

1780 2.71 1440 

Water H2O evaporation 2260 1.00 not determined 

The benefits of decreased exhaust temperatures are often offset by a decrease in the burn rate of the 

propellant, which in turn decreases the rate of suppressant delivery. This is illustrated in Figure 9–51, 

where ln(BR1000) is plotted as a function of 1/T for five proprietary formulations. The linear relationships 

indicate that an Arrhenius-type activated process is occurring, as might have been anticipated. 

Propellant Burn 

Rates for Different 

A number of high nitrogen component formulations based on BTATZ have been evaluated for their 

uitability in agent generation devices as a function of the amount of coolant added (MgCO3). The results 

are presented in Table 9–18 and in Figure 9–52. These data again illustrate the falloff in burn (agent 

generation) rate with decreased adiabatic combustion temperature. 

Figure 9–51. 

Temperature 

Dependence of 

FS01-40/additive 

Combinations. 

s
1000 Powder Panel and Propellant Discharge Technologies 

Tab nt: 

Composition g Parameter

le 9–18. High Nitrogen Content Developmental Propellants with MgCO3 Coola

s and Burnin s. 

Temperature

(K ) Propellant Composition 

(wt %) 

Exhaust 

species 

(vol % @ Tc) T , c Texh

Calculated 

Density 

(g/cm3)

Gas o ut utp

(mol/100 g) 

Measured 

BR1000

(cm/s) 

Measured 

Pressure 

exp nt, one

n 

Baseline: 5AT, 21.9, 

Sr(NO3)2 38.1, 

MgCO3 40.0 

N2 45, CO2 35, 1450 1000 2.55 2 1.27 0.5 H2O 20 

BTSN-00: BTATZ 36.0, 

5 

 26, Sr(NO3 2) 63.0, PBA 3.0, 2770 1590 2.38 2.27 2.77 nd 

C-black 0.5, Mica 0.

N2 59, CO2

H2O 13 

BTSN-10: BTATZ 32.4, 

Sr(NO3)2 56.6, PBA 3.0, C- 25 2 2. T N2 56, CO2 30, 

H2O 12 black 0.5, Mica 0.5 

60 1460 .43 12 BD nd 

BTSN-20: BTATZ 28.8, 

A 3.0, 

.5 H2O 13 Sr(NO3)2 50.3, PB 22 2 2.

C-black 0.5, Mica 0

N2 55, CO2 34, 60 1440 .49 00 0.75 nd 

BTSN-30: BTATZ 25.1, 

Sr(NO3)2 43.9, PBA 3.0, C 2 33, 

2

- 18 2 1. T N2 54, CO

H O 12 black 0.5, Mica 0.5 

90 1410 .55 8 9 BD nd 

BTSN-40: BTATZ 21.4, 

, PBA 3.0, 

.5 

N 49, CO2 40, Sr(NO3 2) 37.6 15 2 1.

C-black 0.5, Mica 0

2

H2O 11 00 1140 .61 79 0.89 nd 

BTSN-50: BTATZ 17.8, 

3.0, 

5 

N2 42, CO2 48, Sr(NO3)2 31.2, PBA 1444 964 2.67 1. 0.38 

C-black 0.5, Mica 0. H2O 9 54 nd 

Figure 9–52. Effect 

of Coolant 

Percentage on 

Burning Rate (in./s) 

and abati

Temperature of 

High Nitrogen 

Propellants Listed 

in Table 9-18. 

he cooler, high gas output propellant compositions described in Table 9–18 represent an important step 

towards increased efficiency SPGG fire suppression devices. Gas temperatures were reduced in some 

 Adi c 

T
Solid Propellant Gas Generators 1001

cases by up to 20 % when compared to the current baseline. The findings of increased burn rate 

compositions, while maintaining relatively low gas temperatures, provides a means for further increases 

in agent cooling when these compositions are further modified with endothermic chemical coolants. In 

general, the most successful energetic fuels were high in nitrogen, based upon BTAZ, with atomic N:C 

ratios of at least 3:1, as well as significant levels of unsaturation. These features combined to enable the 

ant fire extinguisher 

compositions was not evaluated in this program due to excessive costs associated with addressing US 

nts to validate these have not yet been conducted. 

8). Many other bromine- and iodine-containing compounds 

vely due to significantly higher boiling 

ride, CrO2Cl2, and tetraethyl lead, Pb(C2H5)4. These agents have very high boiling points 

ates 

cooler exhaust temperatures and N2-dominated exhaust gases at the expense of the more exothermic CO, 

CO2, and H2O. 

The relative fire suppression effectiveness of some of these new, cooled solid propell

Department of Transportation (DoT) restrictions on the shipping of energetic BTATZ materials from 

where they were prepared (China Lake, California) to where they were to be tested in the FTF (Redmond, 

Washington). A DoT classification requires several kg of propellant for testing, with its associated costs, 

plus the fees for DoT witnessing and licensing. 

Further testing of BTATZ blends in the FTF is certainly warranted due to the potential of these materials 

to produce lower temperature products. In addition, it is necessary to confirm that, because of the 

relatively high hydrogen levels in the exhaust of some of these blends, the presence of H2 does not 

diminish suppression effectiveness. China Lake presented calculations that the H2 did not promote 

additional combustion; experime

9.3.6 Results: Chemically Active Fire Suppressants 

Candidate Active Agents 

The great fire suppression effectiveness of halon 1301 is due largely to its combination of high chemical 

activity and ease of dispersion (Chapter 

would have similar chemical effectiveness, but disperse less effecti

points. 

In addition, there are other compounds known to be effective fire suppressants, including some 

"superagents" which exhibit fire suppression effectiveness much greater than halon 1301 (Chapter 3).51

The foremost example of these agents is iron pentacarbonyl, Fe(CO)5, but other examples include 

chromyl chlo

and are highly toxic, and so are not used in general suppression applications. 

Solid propellant compositions offer a potent means of delivering such chemically active materials to a 

fire. These chemicals can be incorporated directly into the propellant composition. Upon combustion of 

the solid propellant, its product gases carry the additive and its radical-trapping reaction products into the 

fire zone. To enable testing of this concept in SPGG formulations, a broad review of potential candid

was undertaken in this project, including the examples presented in Table 9–19. 

Among halide-containing species, Br- and I-containing compounds were considered to offer the most 

promise. Among these compounds, the alkali-metal salts offered appealing combinations of availability, 

and volatility; further, those potassium-based halides appeared to offer the most suitable levels of 

hygroscopicity – where low moisture-affinity is desired. 
1002 Powder Panel and Propellant Discharge Technologies 

Table 9–19. Candidate Chemically Active Agents. (Data from References 52, 53)

Compound 

Active 

Species MP (°C) BP (°C) Comments 

HALOGEN VEHICLES 

NaI I 660 1304 deliquescent powder

KI I 681 1330

KIO3 I 560 sometimes used as propellant oxidizer;

partial decomposition at MP, releasing O2

NaBr Br 747 1390 forms a dihydrate - NaBr≅2H2O 

KBr Br 734 1435

C12Br10O Br 294 unknown

NaCl Cl 801 1413

KCl Cl 770 1500 sublimes 

KClO4 Cl 610 

lle

on

d freque a propellant er;

(contro decom at 400 °C 

conditi

d

s)

use ntly as oxidiz

poses

ALKALI VEHICLES 

CaCl2 Ca 772 anhy nhy rms mono- etra-, & hex tes;

highly hygroscopic 

1935 a fo , di-, t ahydra

LiBr Li 550 1265 forms mono-, di-, and trihydrates 

LiCl Li 605 1360

LiI Li 449 1180 forms mono-, di-, and trihydrates 

RbBr Rb 693 1340

RbCl Rb 718 1390

RbI Rb 647 1300

Na2CO3 Na 851 decomposition forms mono- and deca

loosen CO2 w

hydrates; begins to

ell before melting

K2CO3 K 891 decomposition

Li2CO3 Li 723 1310 (decomp.) 

Rb2CO3 Rb 837 900 (decomp.) very hygroscopic; readily forms 

monohydrate 

NaHCO3 Na 50 (decomp.) begins to lose CO at 50 °C; converts to

Na2CO t 100 °C 

2

3 a

KHCO3 K >100 Decomposition 

LiHCO3 Li no data No data

RbHCO3 Rb no data No data

NaNO3 Na 308 380 

KNO3 K 334 400 (decomp.) evolves O2 at decomposition 

LiNO3 Li 264 600 (decomp.) hygroscopic 

RbNO3 Rb 305 

NOAC Na 58 decomposition, forms trihydrate 

KAc K 292 deliquescent crystals

LiAc Li 70 decomposition

RbAc Rb 246 hygroscopic 

Na2SO4 Na 884 forms a decahydrate; hygroscopic 

K2SO4 K 1069 1689

Li2SO4 Li 845 subl forms a monohydrate 
Solid Propellant Gas Generators 1003

Compound 

Active 

Species MP (°C) BP (°C) Comments 

Rb2SO4 Rb 1050

TRANSITION METAL (Iron) VEHICLES 

FeO Fe+2 1377 readily oxidizes to Fe3O4; insoluble in H2O 

Fe2O3 Fe+3 1565 insoluble in H2O 

Fe3O4 Fe+2 1594 insoluble in H2O 

Fe(C2H5)2 “Fe” ferrocene

Fe2(CO)9 100 (decomp.) iron nonacarbonyl; toxic

Fe3(CO)12 140 (decomp.) iron dodecacarbonyl; toxic 

FeCl2 Fe

+2 677 1023 forms di- and tetrahydrate; hygroscopic 

FeCl3 Fe

+3 306 315 (decomp.) hygroscopic

Fe(CO)5 was considered too hazardous for handling in the Aerojet test fixture due to its toxicity and the

tu s were

n, 5H5)2, shown here: 

ining ered included several oxides and the oxalate. At 

e oxalate 

t ) , 2 4 3 ⎯ ⎯ →⎯ + 2 . 

Decabromodiphenyl ether (DBPE) was also investigated: 

O tion,

C-Br bond breakage results in formation of volatile Br compounds. 

Suppression Effectiveness of Entrained Chemicals 

Some of the candidate chemical agents were tested in the FTF to evaluate the

suppression for a controlled JP-8 fire. The agents were delivered into the fir slow

discharge SPGG displayed in Figure 9–40, whereby powdered candidate agents were entrained by highlarge scale of the test fix

iro

re. Alternative vehicle for the iron atom considered, including ferrocene,

bis(cyclopentadienyl) and Fe(C

Additional iron-conta compounds that were consid

elevated temperatures, th is known to decompose according to 

Fe (C O FeOx CO CO hea

This material has been used in many plastic formulations as a flame inhibitor. n thermal degrada

ir effectiveness in fire

e zone using the

CO Fe

CO

CO

CO

CO

H

HC C

H

CH

H

C C

``HC

HC C

H

CH

H

C

Fe

Iron P

Fe

entacarbonyl

(CO)5 Ferrocene

Fe(C5H5)2
1004 Powder Panel and Propellant Discharge Technologies 

temperature exhaust gases produced by a neutral-burning solid-propellant gas generator producing a blend 

of CO2, N2, and H2O with constant discharge rate of exhaust gases to carry the candidates into the fire. 

ischarge rates for this testing were purposefully slow in order to minimize strain and mixing effects 

associated with rapid SPGG discharges. A representative discharge (pressure-time) profile for these tests 

Active Agents. 

ered candidate agents 

were supported on a metal grid in the downstream chamber that formerly housed the coolant bed. Upon 

 thru the chamber and entrain the powder 

and carry it to the fire. Test results using the latter method are shown in Table 9–20. 

PGG Fire Suppression Testing with Chemically Active Agents. 

D

is presented in Figure 9–53. 

Initial tests of this type used a coolant bed to support the candidate agents. Aqueous solutions of the 

candidate were mixed with the coolant material (magnesite, 6 mesh to 10 mesh) and heated until the water 

had evaporated. This yielded loadings of ≈ 20 % candidate agent on magnesite. The fraction of agent 

carried to the fire could again be controlled by varying a downstream orifice leading to ambient. 

Figure 9–53. 

Representative SPGG 

Pressure-time Curve 

Obtained During Delivery 

of Candidate Chemically 

An alternate approach gave more reproducible performance. In this case, powd

activation of the gas generator, the resultant exhaust would pass

Table 9–20. Summary of S

Agent Mass, g Test No. Result Agent Mass, g Test No. Result 

KI 20 027-06 fire not out Fe2O3 40 038-01 fire not out 

40 027-07 fire not out 80 038-02 fire not out 

40 027-05 fire out 

60 027-04 fire out 

KBr 40 032-02 fire not out Ferrocene 40 039-01 fire not out 

60 032-03 fire not out 80 039-02r fire not out 

60 032-01 fire not out 

K2CO3 20 035-03 fire not out Iron Oxalate 40 040-01 fire not out 

40 035-02r fire out 

60 035-01 fire out DBPE 60 041-01 fire not out 

The iron-based agents and DBPE were less effective than KI and K2CO3, at least within Aerojet's FTF. 

The results also indicated that K2CO3 and KI were more effective than KBr. The threshold amount for 
Solid Propellant Gas Generators 1005

successful fire extinguishment seemed to be around 40 g of neat K2CO3 or KI powder used in each solid 

propellant extinguisher. 

The similarity in performance between the iodide and th

54

e carbonate reflects the observations in turbulent 

spray burner testing; those data were interpreted as reflective of the greater role of the potassium ion in 

suppre acile 

vaporization of the ally relevant potassium species from the K2CO3. This is inconsistent with the 

hig poi 3 vs. KI (891 °C vs. 681 °C), but may be consistent at higher temperatures 

where K2CO3 decomposes before boilin out decomposing at 1330 °C. Another 

possib c interactio een the halogen cies in the 

flame region. 

Testing with ferrocene yielded some unexpected results. Ba n 

pentacarbonyl, ferrocene would be cted to be a t suppressan

powdered ferrocene was swept into hot solid pro t exhaust did not result in fire suppression when 

loads were increased to levels well in excess of the KI, KBr, or K2CO3 suppression loads. Furthermore, 

ferrocene delivery was accompanied by growth of les of ferrocene crystals on the exit port of the 

delive be. These findings imp at the f ite stable in air/combustion conditions, and 

further that this material could no ntrained for a ufficient le n 

oxide, likewise, was ineffectiv ive suppressant. While only alate was 

attempted with a 40 g load, th pound could reach 

superagent status in this mode of o n

The lesser performance of the iron- and decabro ntaining species, known to be excellent flame 

inhibi n other circumstances, indicates that equate agen be 

carefu esigned an mplement the solid p ant fire exti e the 

chem pabilities uch agent

Burning Characteristics of Active Propellant Compositions 

Chem itives selected from Table 9–19 were incor ed in ly 

active agent is liberated upon comb n of th nt, the exhaust consisting of inert gases plus 

entra itives. se additiv their blended directly into the propellant, or the 

addi recurso as blende a hybr al comp that a 

common composition family evolved having different levels of additive. Bur s of several of 

thes itions a umm le 9–21. positio rs 

were demonstrated to burn efficiently and were subsequently shown to be effective in fire suppression. 

The incorporation of species to suppress fires did not event combustion of t

ssion effectiveness rather than the anion. A possible explanation for this trend is the more f

 chemic

her melting nt of K2CO

g whereas KI melts with

ility is that there is an antagonisti n betw and alkali metal spe

sed on its chemical similarity to iro

 expe poten t. However, multiple tests in which 

 the pellan

 need

ry tu ly th errocene is qu

t be e

e as an act

e results did

 s ngth of time into the flame zone. Iro

one test with iron ox

 not indicate that this iron-containing com

peratio . 

mo-co

tors i an ad t delivery me anism needs to ch

lly d d i ed in ropell nguisher in order to fully utiliz

ical ca of s s. 

ical add porat to formulations wherein the chemical

ustio e solid propella

ined add The es (or precursors) were

tive (or p r) w d into id fluid. Sever ositions were developed, such 

ning propertie

e compos re s arized in Tab Com ns incorporating combustion inhibito

pr he propellant. 
1006 Powder Panel and Propellant Discharge Technologies 

Table 9–21. Chemically Active Developmental Propellants. 

Temperature

(K) Propellant Composition

(wt %)

Exhaus

Tc, Texh

Calculated 

Density

(g/cm3) 

Gas output, t species

Measured

BR1000

(vol % (cm/ @ Tc) mol/100 g s)

Measured

Pressure 

exponent, n

Base 21.9,

Sr(NO

MgC

N2 45, C

H2O 20 1450 1000 2.55 2.00 1.27 0.5 

line: 5AT,

3)2 18.1,

O3 40.0 

O2 35, 

CA-0 .2,

Sr(NO3)2 30.0, 

MgCO KI 21.3,

Graphi

N2 47

H2O 22 1.47 1.27 0.55 

1: 5AT 17

3 30.0,

te 0.5

, CO2 31, 1450 970 2.66 

CA-02 0.8 ,

Sr(N

Mg CO3 5.0

N2 47, C

H2O 22 

KI 21.3 g 

0.13

1440 1200 2.54 0.48 

: 5AT 2

O3)2 36.2,

CO3 38.0, K2

O2 31, 

mol K

1.67 1.40

CA 0,

Sr(NO ,

MgCO 2CO3 8.9 

N2

H2O 22, 

K2CO3 9.

0.13 mol

1450 1210 2

-03: 5AT 20.

3)2 34.7

3 36.4, K

47, CO2 31 

0 g 

K

.54 1.78 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 

1440 1110 2.54 1.75 1.27 0.44

CA-05: 5AT 17.52, 

Sr(NO3)2 30.5, 

MgCO3 32.0, K2CO3 20.0 

N2 47, CO2 31 

H2O 22 

K2CO3

0.30 mol K 

1480 1180 2.52 1.55 0.64 0.77 20.0 g 

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 

1440 1100 2.44 1.61 1.04 0.66 

CA-07: 5AT 22.1, 

Sr(NO3)2 22.9, 

MgCO3 40.0, KNO3 15.0 

N2 47, CO2

H2O 22 

K2CO3 10.0g 

0.15 mol K 

0 1090 1.78 1.62 0.52 

31, 

144 2.42

CA-08: 5AT 22.1, N2 47, CO2 31 

Sr(NO3)2 22.9, 

MgCO3 40.0, KNO3 30.0 

H2O 22 

K2CO3 20.0 g 

0.30 mol K 

1470 990 2.30 1.79 .68 1.77

CA-09: 5AT 21.9, 

Sr(NO3)238.1, 

MgCO 34.5, Fe O 5.0 

N2 48, CO2 29, 

H2O 33, Fe2O3 5g 1470 1100 2.59 1.88 1.62 0.62 3 2 3

Graphite 0.5 (0.06 mol Fe) 

C

5

A-10: 5AT 81, KP 10, DBPE 

.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) 5.4 g 

1630 874 1.71 4.24 0.25 1.0 

CA-11: 5AT 19.7, N 42, CO 30 Sr(NO3)2 34.3, 

MgCO3 36.0, DBPE 10.0 

2 2

H2O 11, H2 6 1440 853 2.57 1.76 nd nd 
Solid Propellant Gas Generators 1007

Potassium-Containing Compositions 

I O OH H combustion quench

KI aerosol K I flame

+ → −

− ⎯ ⎯ →⎯ +

• / /

• •

N2, H2O inert gas blend, to the fire, the KI then dissociating in the flame to

produce combustion-radical-trapping I• species according to: 

Several potassium-carbonate-containing blends were made, where the m CO3 in the blend was 

varied from 5 % to 20 %. The rationale for the varied levels of K2CO3 was to probe this effect upon fire

suppression effectiveness; i.e. varying the extent of chemically active agent within an otherwise nearlycommon inert gas blend. All of these blends had acceptable burning properties, although at 20 % K2CO3, 

BR1000 was dropping to unattractively low levels at the same time that the pressure exponent, n, was 

increasing to unattractive levels. As such this propellant, as formulated eally suited for

commercial application. These compositions were expected to obtain ering

K2CO3 aerosol, entrained in a CO2, N2, H2O inert gas blend. The K2CO3 me to

produce combustion-radical-trapping I• species according to: 

ally either the oxide, 

K O, or the carbonate, K CO : 

For the cooled p blends under 

to be K2CO3. Hence for K-containing blends based on KN K2CO3 aerosols can also be expected, with

KN offering the possibility of circumve rates obtained in the higher percentage 

K2C lends. One caveat necessary mind when comparing the carbonate and the nitrate 

blends is that the use of KN requires that its oxidizing power be offset by mpa ount of fuel in 

Three different approaches were used to incorporate potassium-containing species into propellant blends. 

These approaches built upon the agent testing efforts already described. The first blended potassium 

iodide directly into a propellant; the second blended potassium carbonate directly into a propellant, and

the third used potassium nitrate blended into a propellant. 

One potassium iodide-containing blend was made, labeled CA-01. This blend had an acceptable BR1000

and pressure exponent n. This composition was expected to obtain chemical activity by delivering KI

aerosol, entrained in a CO2,

ing

KI aerosol

CO N H O CA

+ − − → , , 01 2 2 2

ass of K2

, would not be id

chemical activity by deliv

would dissociate in the fla

In an attempt to counteract the fall-off in BR1000 observed in the 20 % K2CO3-containing blends, an

alternative approach to potassium incorporation was investigated. Instead of direct incorporation of 

K2CO3 into a propellant blend, we incorporated potassium nitrate (KNO3, or KN). When blended into a

propellant, KN is an oxidizer for fuels; the potassium product of this reaction is typic

2 2 3

KO O OH H combustion quenching

K CO aerosol KO CO

K CO aerosol

CO N H O CA

flame

+ → −

− ⎯⎯ →⎯ +

+ − − →

• / /

•

, , 02,3,4

2 3 2

2 3

2 2 2

. / 2O K

, , 2 N2 etic.. fue

2 3

2

K CO

CO H O

nerg l

+

KNO3 + e →

ropellant consideration here, the dominant K-containing species is expected 

,

nting the undesir

to keep in

able burn 

O3 b

a co rable am
1008 Powder Panel and Propellant Discharge Technologies 

order to maintain the de O2, nert gas exhaust blend; this offset is minim l and 

straightforward to achieve. 

The KN-containing blends are listed as CA-6, CA-7, and CA-8 in Table 9–21. At lower levels, these KN 

lends yielded materials having suitable burning parameters. Unfortunately, attempts to obtain usable 

ntaining formulations do not have the drawbacks of iron pentacarbonyl and ferrocene 

. These formulations were evaluated thermodynamically but 

emically Active Propellant Compositions 

Chemically active propellant compositions were prepared in kilogram quantities to provide sufficient 

2.7 mm diameter x 6.4 mm thick 

 unsuccessful 

suppression event using the CA-04 propellant formulation. 

sired C N2, H2O i a

b

quantities of blends containing higher levels of KN (e.g., CA-8) were repeatedly thwarted by a 

combination of poor burning characteristics and/or poor processability. 

Iron-Containing Additives 

As mentioned previously, iron pentacarbonyl Fe(CO)5, was not blended into any propellant formulations 

because of its high toxicity. Ferrocene and its derivatives have been reportedly used in various 

propellants as burn rate modifiers with great success. However these formulations displayed unsuitable 

thermal stability. The ferrocene derivatives tended to migrate to the surface of the propellant, where they 

are oxidized to ferrocinium compounds. Ferrocinium derivatives in combination with propellant 

ingredients give friction sensitive materials. This limits the use of ferrocene derivatives to hybrid systems 

where the propellant and the additive are stored separately. 

Iron oxide co

mentioned above. Although definitive results were not obtained in this project, the routes explored to 

date involving iron oxide containing discharges have yielded burning characteristics that suggest further 

study is warranted. 

Decabromodiphenyl Ether 

Propellant compositions were formulated both with and without decabromodiphenyl ether (DBPE), added 

as a chemically active flame inhibitor, and these formulations underwent preliminary burning 

characterization. Composition CA-11 in Table 9–21 did not have suitable burning properties, with the 

effect of the DBPE to slow the burn rate and increase the pressure exponent. DBPE was also formulated 

into a 5AT-Sr(NO3)2-MgCO3 blend (CA-11)

not reduced to practice due to lack of resources and because of concerns with regard to DBPE handling 

during propellant processing and corrosivity during DBPE application. 

Suppression Effectiveness of Ch

material for repeated testing. Propellant was typically pressed into 1

tablets. The tablets were loaded into heavy mass, refurbishable gas generators, with some booster 

propellant ignition aid added, and then fitted with pyrotechnic initiators. Upon activation, the initiator 

ignites the booster propellant and then the main propellant. The internal pressure rises (Figure 9–54) until 

it exceeds the burst pressure of the material sealing the orifices of the device; this occurs at approximately 

6.9 MPa. Internal pressures continue to rise, reaching a maximum of up to 10 MPa before the propellant 

completes its burn. Complete discharge of the agent from the SPGG is achieved within about 200 ms of 

initiation. Acceptable discharge times were achieved provided the pressures were maintained in the 

6.8 MPa to 13.6 MPa range. Representative FTF pressure-time curves showing the impact of the SPGG 

discharge on the fixture pressure are shown in Figure 9–55 for two successful and one
Solid Propellant Gas Generators 1009

Figure 9–54. 

Representative P-t 

e for SPGG 

Chamber 

Pr

er pres low 6.8 MPa not ible discharge behavior, 

ressures much above 10.2 MPa in general yielded too rapid a discharge event and sometimes 

surizatio e). The target peak pressure was 10.2 MPa, which yielded a 

e of ≈ 100 ease of tes ar SPG rifices aintaining this sort of 

mode designs used in the V-22/F-18 fire suppression 

ice diameters ranging from 2 mm to 4.8 mm with burst 

 aluminum al e are s 168 2 for a test . 

d smaller SPGG size

Figure 9–55. 

esen 

P-t Curve for 

Fire Test 

Fixture 

sure 

before, during, 

and after 

G 

discharge. 

rizes the test results and shows how the test configurations compare on a total agent 

mass basis and also on a K-molar basis. FTF testing with various inert and chemically active solid 

propellant compositions demonstrated that incorporation of 0.1 % additive (expressed as a fraction of the 

gaseous molar output) into inert fire suppressants has a dramatic positive effect on fire suppression 

Curv

essure. 

Peak SPGG chamb sures be did in general yield reproduc

and peak p

SPGG over pres n (and ruptur

discharge tim ms. For t turn ound, G o for m

discharge rate were led after Aerojet proprietary

systems. These designs use several different orif

seal material consisting of 0.1 mm . Tot orific

s. 

a wa mm 210 g SPGG

This total area is scaleable to larger an

Repr tative

Pres

SPG

Figure 9–56 summa
1010 Powder Panel and Propellant Discharge Technologies 

efficiency. The otherwise similar propellant c examined during this testing indicated a 50 % 

to 70 % uctio ading f ppress ntical fires when the p

co little as 0.1 % On equimo r ba assium carbona ea

more effective chemical additive t potassium iodide. Table 9–22 summarizes the threshold values of 

e threshold is defined as the amount of agent needed to extinguish

eas three tim Typ ly, th sts we nducte he threshold 

hree addition conducted at an agent load greater than the threshold amount. 

ndicate that KI yield significantly im ed sup ion ef iveness en

t propellant composition. For a composition containing 0.1 mole KI per 100 g

ropellant, the threshold propellant load was ≈ 45 % that of the baseline inert propellant composition, 

ass flows. A composition containing a similar amount of K2CO3 

red only 30 % of the mass of the baseline propellant. 

were greater than a factor of

three over the inert baseline propellant. A comparison of the suppression findings for CA-02 and CA-03

indicate that suppression effectiveness increased with higher levels of potassium content. CA-03 and

CA-06, with comparable molar levels of potassium, appear to have similar suppression effectiveness. On 

the contrary, comparison of CA-01 with CA-02 suggests that the KI-containing composition (CA-01) 

may have some canceling contributions from the K and I portions of the additive. 

ompositions

 (by mass) red

mposition contained as 

n of agent lo or su ion of ide ropellant

. an la sis, pot te app rs to be a

han 

the most promising active

the fire in the FTF at l

amount and t

agents. Th

t two out of es. ical ree te re co d at t

al tests were

The results i K2CO3 and prov press fect wh

compared to the iner

p

given similar discharge conditions and m

(0.1 mole K per 100 g propellant) requi

Figure 9–56. Threshold Mass of Inert Propellant Plus Potassium Compound for 

Suppression in the FTF. 

The defined threshold level criterion of agent required for suppression (two out of three fires suppressed) 

was met for the baseline, CA-01, and CA-02 compositions; for CA-03 and CA-06, this criterion was 

exceeded and the fires were always suppressed, down to the minimum load capable for our equipment. 

This suggests that actual performance improvements for C-03 and CA-06
Solid Propellant Gas Generators 1011

Table 9–22. Threshold Mass of Propellant and Potassium-based Additive for Fire 

Suppression in the FTF. 

Agent/Additive

Baseline/ 

none 

CA-01/ 

KI 

CA-02/ 

K2CO3

CA-03/ 

K2CO3

CA-06/ 

K2CO3

(from KN) 

Gas Fraction 50 % 50 % 50 % 50 % 50 % 

MW, g/mole 30 30 30 30 30 

Mole active (K)/100 g 0 0.127 0.073 0.145 0.145 

Mole active (K) discharged 0 0.199 0.114 0.152 0.152 

Threshold gas generator Load, g 347 157 157 105 105 

Powder discharge mass, g (Threshold) 173.5 78.5 78.5 52.5 52.5 

Table 9–22 and Figure 9– to the nature of large-scale fire tests. 

The threshold quantity m re-out and fire-not-out, 

but more of a band due to variations in test parameters. 

Larger pellets of the chemically active decabromodiphenyl ether formulation were burned and the 

Extinguishers 

n outlet for the fluid; there were typically eight 3.1 mm to 3.4 mm orifices 

ur sides to ensure non-propulsive behavior) sealed with 0.05 mm thick Al 

ew propellant-fluid configurations underwent

of threshold level loads for the hybrid extinguisher testing was found to be best

accomplished using various combinations (single and/or different hybrid extinguisher sizes) mounted 

upstream of the flame in the test fixture, as shown in Figure 9–58. The results of hybrid extinguisher

testing are presented in two separate categories: fluorocarbon systems and aqueous systems. 

56 are subject to some uncertainty due

ay not be a sharp line separating the regions between fi

temperature of the gaseous products measured. The SPGG outlet temperature was approximately 675 °C, 

which was in good agreement with the temperature predicted from thermochemical calculations. The 

chemically active formulation was found to be impact, friction and electrostatically insensitive. The 

PBDE formulations was able to successfully suppress a JP-8 pool fire in a small vented box, but was not 

able to suppress the JP-8 flame in the FTF at a loading of 60 g. 

9.3.7 Results: Hybrid Fire 

Hybrid Fire Extinguisher suppression effectiveness tests employed a set of re-usable “workhorse” 

generators, with size varying from 56 mL to 110 mL internal volume. A schematic of this test article is 

shown in Figure 9–57. 

Exhaust orifices provided a

(oriented 90° apart on all fo

1100-T1 shim material. Propellant loads were typically 10 g to 20 g, and the nominal propellant:fluid 

mass loading ratio was 1:6 to 1:10. 

The tests were conducted on combinations of the fluid suppressants listed in Table 9–23 with the 

following propellants: Baseline (FS-0140, inert); CA-01 (chemically active – KI); and CA-04 (chemically

active – K2CO3). Halon 1301 was not tested, but is included in Table 9–23 for reference. 

In order to ensure safe operation within the test fixture, all n

functional testing first to ensure proper performance of the propellant/fluid combination. These tests

consisted of the assembly of the desired propellant/fluid combination, mounting the hybrid extinguisher 

unit in a vise anchored to a bench, and operating the hybrid extinguisher. 

Accurate definition
1012 Powder Panel and Propellant Discharge Technologies 

(102 mL)

(76 mL) 

(52 mL) 

3.4 mm orifice 

3.2 mm orifice 

3.2 mm orifice 

Figure 9–57. Schematic of Hybrid Extinguisher Workhorse Hardware Configuration. 

, 0.05 mm

Figure 9–58. Mounting Configuration of Multiple Hybrid Extinguishers Used to Bracket 

Threshold Levels. 
Solid Propellant Gas Generators 1013

Table 9–23. Properties of Hybrid Fluid Candidates. 

Property Halon 1301 HFC-125 Water HFC-227ea HFE-7100 HFE-1230 CF3I 

Chemical formula CF3Br C2F5H H2O C3F7H C4F9OCH3 C6F12O CF3I 

Molecular wt. 149 120 18 170 250 316 196 

Boiling pt.(°C) -58 -48 100 -16 61 49 -21 

Freezing point (°C) -168 -102.8 0 -131 -135 -108

Density @25o C (g/cm3) 1.55 1.19 1.00 1.4 1.52 1.6 2.1 

Vapor pressure (kPa) @ 25 6 538 o C 1510 1370 3 460 27 

Specific heat (kJ/kg°C) 1.26 4.18 1.184 0.89 

(J/g) Heat of vaporization 117 113 2255 134 201 88 113 

Cup-burner (vol %) fire

extinguishing concentration 3.1 8.7 25# 6.5 6 5 3.1 

Fire extinguishing design

concentration (g/m3) 305 516 590 776 401 

Ozone depletion potential

(relative to CFC-11) 12 0 0 0 0 0 0.0001

Global warming potential

(relative to CO2) 5400 2800 0 2900 320 1 <5 

Atmospheric lifetime (yr) 65 33 n/a 37 4.1 0.014 <0.005

Cardio-sensitization LOAEL 

(vol%) 10 10 n/a 10.5 10 0.4 

Cardio-sensitization NOAEL 

(vol%) 7 7.5 n/a 9 10 0.2 

EPA SNAP approved for

unoccupied No Yes Yes Yes Yes Yes Yes 

# assumes full recovery of enthalpy of vaporization 

Fluorocarbon Hybrid Extinguishers 

The fluorocarbon test results are listed in Table 9–24. The threshold values were determined for the 

hybrid extinguisher initially at ambient temperature. The baseline hybrid extinguisher against which the 

other propellant/fluids were compared consisted of the FS-0140 propellant (21.9 % 5AT, 38.1 %

Sr(NO3)2, 40.0 % MgCO3) with HFC-227ea fluid. The threshold suppression level for this baseline 

hybrid extinguisher was 358 g. (The fire suppression number (FSN) reported in the table is the ratio of

the threshold determined for the other hybrid extinguisher combinations normalized by the baseline 

base system, with no particular advantage. In addition, measurements in the test fixture revealed higher 

bay pressures than the norm and the flame seemed to be enhanced by the fluid discharge. 

mass.) Replacing the HFC-227ea with HFE-1230 led to a similar threshold level. Interestingly, this

threshold level value is nearly identical to the value obtained for testing of the FS-0140 propellant alone

in a standard SPGG. 

Hybrid extinguisher tests with HFE-7100 and a total load of 358 g did not extinguish the fire. Further

testing with this agent was suspended since the amount of agent needed would have been more than the
1014 Powder Panel and Propellant Discharge Technologies 

Table 9–24. Hybrid Extinguisher Fluorocarbon System Data Summary. 

Agent 

FS-0140/ 

HFC227ea 

FS-0140/ 

HFE 

1230

FS-0140/ 

HFE7100

CA-01/ 

HFC227ea 

CA-04/ 

HFC227ea 

FS-0140/ 

HFC-227ea + 

KHCO3

FS-0140/ HFC227ea + 

NaHCO3

FS0140/ 

CF3I 

Active 

additive 

- - - K2CO3 K2CO3 KHCO3 NaHCO3 CF3I 

MW, g/mol 170 316 250 170 170 170 170 196 

Load, g 358 358 - 228 228 265 228 98b

Discharge

mass, g 

340 340 - 217 217 252 220 93 

Mole (K or I)

discharged

0 0 - 0.040 0.046 0.040 0.052 0.429 

FSN 1 1 >1a 0.637 0.637 0.740 0.637 0.274 

a.

b. ted

everal combinations of chemically active hybrid extinguishers were tested. Combinations of the

chem 0 %

enhancement in performance when co extinguisher. This finding indicates 

that significant reductions in hybrid extinguisher agent levels can be achieved by combining chemically

Testi ost

effective hybrid combination, with an 25 % of the baseline propellant/fluid

combination. This represents an approximate threshold value since two test using 130 g 

(both fires out) and two tests were conducted using 98 g (one fire out not op e

standard two- cessful fire supp n event ed to define the threshold. Fire extinction 

ation of brilliant purple smok usting of the

ental iodine, I2, fumes during the suppression pro

with CF3I proved problem cause ent te disso mmon 

fluids lik C-227e ecause leakag gent ar /through

ng th sts, th st shim re moved to outsid hybrid

xtinguisher, thereby minimizing exposure of the adhesive to CF3I. 

Tests conducted using 358 g (same agent mass as the FS01-40/HFC-227ea system) did not extinguish the fire.

Testing was suspended since the amount of agent needed would be more than the baseline system. 

Anticipated threshold value: two tests were conducted using 130 g (both fires out) and two tests were conduc

using 98 g (one fire out, one fire not out).

S

ically active propellants CA-01 and CA-04 with HFC-227ea were found to yield ≈ 4

mpared to the baseline hybrid

active solid propellant compositions with inert fire suppression agents. 

Chemically active hybrid extinguishers were also constructed using the FS-0140 propellant with HFC227ea plus the chemically active powders KHCO3 and NaHCO3 (potassium bicarbonate and sodium

bicarbonate, respectively). These systems exhibited performance enhancement of about ≈ 40 %, similar

to the results from the CA-01/HFC-227ea and CA-04/HFC-227ea tests. Note that each of these

chemically active hybrid extinguisher combinations maintained similar levels of chemically active

additive (0.04 mol to 0.05 mol), implying that in each case the benefit of this chemical activity is 

independent of the form in which that additive is delivered. 

ng of the inert FS-0140 propellant with the chemically active suppressant CF3I resulted in the m

approximate threshold value ≈

s were conducted 

, one fire out), as posed to th

out-of-three suc ressio s us

coincided with the form e exha from the test fixture, evidence

formation of elem cess. 

Hybrid extinguisher testing atic be this ag nded to lve co

adhesives not affected by other e HF a. B some e of a ound

the Mylar burst tape occurred duri ese te e bur s we e the

e
Solid Propellant Gas Generators 1015

An additional test of the 130 g FS-0140 propellant/CF3I hybrid extinguisher was conducted after cold 

soaking; the fire was successfully extinguished. In this test the hybrid extinguisher was conditioned to 

–65 °C; however, the CF3I temperature rose to –27 °C before the extinguisher was operated. 

Aqueous Hybrid Extinguishers 

The results of the aqueous-based hybrid extinguisher combinations are summarized in Table 9–25. 

Table 9–25. Hybrid Extinguisher Aqueous System Data Summary. 

Agent 

CA-01/ 

Water 

CA-04/ 

Water 

Baseline/ 

Water:KOAc:Soapb

Acti e additive v KI K2CO3 KC2H3O2

MW, g/mol 18 18 30 

Load - - 228 

Discharge mass, g - - 217 

Mole (K) discharged - - 0.96 

FSN (Baseline/HFC-227ea) >1a >1a 0.637 

a. Testing conducted using 358 g (same agent mass as the FS01-40/HFC-227ea system) did not extinguish the fire. Testing was 

suspended since the amount of agent needed would be more than the baseline system. 

b. 48:48:4 mass ratio of water:potassium acetate:soap. 

not successfully 

extinguish the fire with agent loads up to the baseline mass. Substituting a water-potassium acetate-soap 

 chemically active agent to the 

suppressant mix. The improved performance of these KOAc blends vs. pure water is presumably due to 

Testing of aqueous hybrid extinguishers was often plagued by poor performance/distribution of the agent. 

A frequent occurrence was the collection of puddles of water upstream of the flame zone in the FTF. 

While this means that flame suppression was accomplished with less than the full hybrid extinguisher 

load, it also means that the given test articles would benefit from design modifications to yield improved 

distribution, e.g., through use of screens to improve mixing of the SPGG exhaust with the fluid, or by 

varying the ratio of propellant to fluid. 

Summary of Hybrid Extinguisher Results 

A summary of the hybrid extinguisher testing is presented in Figure 9–59. On a mass-to-mass basis, the 

inert hybrid extinguisher and SPGG systems appear to provide similar suppression protection, requiring 

Tests conducted at ambient temperature using pure water with a total load of 358 g (same agent mass as 

the FS-0140/HFC-227ea system) did not extinguish the fire. Testing of hybrid extinguishers charged with 

chemically active CA-01 and CA-04 propellants in conjunction with pure water also did 

(surfactant) blend (48:48:4 mass ratio) for pure water, and pressurizing with the CA-04 chemically active 

propellant did yield successful flame extinction at levels approximately 60 % that of the Baseline hybrid 

extinguisher. Potassium acetate, KO2CCH3, or “KOAc,” is a well known freezing point suppressant for 

aqueous solutions, and as it contains potassium ions, also contributes a

the chemical activity contributed by the potassium; assuming this is the case, one would expect to see a 

range of performance thresholds for this hybrid extinguisher given variations in KOAc levels. However, 

testing of different levels of KOAc in water was not attempted in this effort as the focus was on KOAc 

loadings suitable for meeting typical low temperature performance requirements of -40 °C. 
1016 Powder Panel and Propellant Discharge Technologies 

≈

 active 

n. 

on m

uids

opport

em 

Hy

found t ilar 

of the 

hy

based h be 

provement found from the addition of chemically active species to the propellant mixture in the

hybrid ext n

tha r

the SPGG configuration, but only 14 % of the total agent mass for the hybrid extinguisher configuration,

 the

a 

 360 grams to suppress the 1 MW FTF fire. The higher molar efficiency of the hybrid testing reflects 

the higher molecular mass of the HFC-227ea. As in the pure SPGG, incorporation of chemically

species into the propellant improves the suppression efficiency for the hybrid extinguisher configuratio

Testing conducted with KHCO3 added into the hybrid fluid of the system produced results similar (based

oles of K) to results with active agents (KI, K2CO3) added into the propellant. This indicates that 

active additives in the hybrid fluid may be just as effective as active additives in the propellant. 

Testing hybrid extinguishers with HFE-7100 and HFE-1230 did not lead to reductions in total propellantplus-fluid mass (when compared to HFC-227ea), but it did demonstrate that higher boiling point fl

could be successfully discharged when pressurized by a solid propellant gas generator. This opens

unities for alternate suppression fluids that, on the basis of vapor pressure alone, would not appear 

to be desirable candidates as fire suppressants. 

The lowest hybrid extinguisher agent loads were found when using CF3I as the hybrid fluid. Coupling 

this agent with a solid propellant gas generator also overcame the low temperature dispersion probl

encountered in previous testing with conventional pressurized fire bottles.55

brid extinguisher testing with aqueous agents provided additional insight into necessary levels of 

active agent required for suppression. Tests using an inert propellant configuration with pure water were 

o require agent loads in excess of threshold levels of inert propellants and HFC-227ea. Sim

findings were obtained when the active CA-04 propellant was used in conjunction with pure water. This 

relatively poor performance of the water hybrids is likely a function of insufficient distribution 

brid stream into the fire compartment of the FTF. However, while poor dispersion in the case of waterybrid extinguishers probably resulted in their lackluster performance, this effect was found to

offset by blending in potassium acetate. 

The im

inguisher systems (an approximate 36 % reduction in suppressant mass) appears to be less tha

t found in the SPGGs (70 %). Note, however, that the propellant is 100% of the total agent mass fo

thus limiting the molar fraction of chemically active additive to ≈ 2 volume %. It is likely that if

amount of active additive in the hybrid extinguisher systems were optimized, these systems would show 

mass reduction similar to the SPGG systems. 
d Propellant Gas Generators 1017

brid Extinguisher Propellant/fluid Combinations.

Hybrid

rs Extinguishe

Hybrid

Extinguishers 

Figure 9–59. Effectiveness of Various Hy

Soli
1018 Powder Panel and Propellant Discharge Technologies 

9.3.8 Su

The t/NAW GP ces d pr t-b e hn ude

Developing a me y r scre nd opel

Developing a medium scale Fire Test Facility to evaluate alternative SPGG fire suppression 

chno s for a cluttered space such as a dry or engin elle. 

Scaling up the n of the h itrog opellan l, BTATZ half kil m 

quantities. 

Calculating exhaust temperature and composition of new, high nitrogen propellants. 

rning rate and ese new, high nitrogen pr

• Tabulating the effect of different coolants on t ct of propellant burni and t 

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

llant compositions, to which one 

could add coolant to reduce the overall exhaust gas temperature. Cooler propellant compositions have 

production capability plus the attractive burn 

rate and pressure sensitivity of BTATZ formulations make them good candidates for future work, 

 solid propellant compositions 

demonstrated that incorporation of 0.1 mole % additives into inert fire suppressants can have a dramatic 

ide) 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. 

mmary of Solid Propellant Gas Generator Research 

 Aeroje SC/N advan in soli opellan ased fir suppression tec ology incl : 

•

•

thodolog fo ening ca idate pr lants. 

te logie bay e nac

• productio igh n en pr t fue , to ogra

•

• Measuring bu pressure exponent for th opellants. 

he effe ng rate exhaus

temperature. 

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

effectiveness of SPGG fire extinguishers. 

aqueous fluids. 

Three different paths to cooler propellant compositions were demonstrated: by reducing the enthalpy of 

the combustion process through selection of various fuels/oxidizer blends; by altering the stoichiometry 

of the propellant reactions; and by seeking faster-burning solid prope

been used in conjunction with chemically active additives, or combustion radical scavengers. Adding 

radical traps to the exhaust provides means for cooling, dilution and chemical termination of the 

combustion process, hence increasing the overall effectiveness of the fire suppressant. 

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

provide increased means for reducing propellant combustion temperatures. The preparation of BTATZ 

has progressed to the half kilogram scale. This increased 

including re-formulation with additional chemical coolants, as well as suppression effectiveness testing in 

the FTF. Direct incorporation of coolant species into the propellant composition reduced exhaust 

temperatures by as much as 30 % vs. current baselines. 

Testing of propellant compositions containing potassium iodide and potassium carbonate as chemically 

active additives demonstrated enhanced effectiveness in the FTF as compared to chemically inert 

compositions. FTF testing with various inert and chemically active

effect upon suppression efficiency. The otherwise similar propellant compositions examined during this 

testing indicated a 50 % to 70 % reduction (by mass) of agent loading for suppression. On an equimolar 

basis, potassium carbonate appears to be a more effective chemical additive than potassium iodide. The 

greater effectiveness of potassium carbonate (vs. potassium iod
Solid Propellant Gas Generators 1019

Fire testing with chemically active compositions indicate that the CA-04 composition (20 % 5AT, 34 % 

Sr(NO3)2, 36 % MgCO3, 10 % K2CO3) is the most effective. This composition is three times more 

effective per unit mass than the inert baseline propellant (22 % 5AT, 19 % Sr(NO3)2, 60 % MgCO3), with 

no K2CO3. Testing with compositions of lower active-agent loading resulted in less effective 

 additive loading in CA-04 is below (or at) the saturation level 

reported in sub-scale testing with numerous other chemically active suppressants. 

Testing of hybrid SPGGs with HFE-1230 indicates that high boiling point, low vapor pressure agents can 

be delivered e Suppression 

tests with HFE-7100 were not as encouragin n fact resulted in flashback in fire tests. Both the 

HFE-1230 and HFC-227ea gave comparable results (on a basis) in fire suppression tests. 

In F3I into a hybrid extinguisher proved conveni vercoming po perature 

dispersion. The water-based hybrid extinguishers did not perfo

hy ishers; however, blending potas acetate into the water was shown to significantly 

im suppression effectiveness in the FTF. 

On nert hybrid extinguisher and SPGG systems pear to provide si suppression 

pr chemically active ies into the h d extinguisher propellant improves 

e 

t as effective as active additives in the propellant. 

evices using 

chemically active, water-based hybrid extinguishers have moved from development to production and 

performance. This indicates that the

fficiently to the fire zone by heating and pressurizing the liquid with an SPGG. 

g, and i

mass 

corporation of C ent for o

 as well as the fluorocarbon-based 

or cold-tem

rm

brid extingu sium

prove 

 a mass basis, the i ap milar 

otection. Incorporation of spec ybri

the suppression efficiency. Testing conducted with additives incorporated into the h luid of th

system produced results similar to results with active agents added into the propellant. This indicates that

ybrid f

active additives in the hybrid fluid may be jus

Since initiation of this research 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 advanced additives 

have been demonstrated, developed and manufactured for three new platforms.56,57 Developments in 

improved, chemically active SPGGs are being implemented over the course of 2005-2008 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 from ballistic events upon the US Army’s M1114 

HMMWV. 

Figure 9–60 summarizes how the performance of SPGGs, as measured by suppression effectiveness, has 

improved over this period. This research has enabled system mass reductions by over a factor of two, 

with still greater reductions possible by optimizing the findings. 

Finally, SPGG technology has also crossed over from military to civilian applications. D

integration in commercial automobiles manufactured for the Ford Motor Company’s Crown Victoria 

Police Interceptor.58 A conceptual flow of this evolution and application is presented in Figure 9–61. 

(Note that in Figure 9–60 and Figure 9–61, the term "SPFE" for Solid Propellant Fire Extinguisher is used 

to distinguish these systems from a Hybrid Fire Extinguisher or "HFE.") 
1020 Powder Panel and Propellant Discharge Technologies 

Figure 9–60. Relative Effectiveness of Various SPGG Fire Extinguishers over the Span of 

the NGP Research. Blue bars: inert effluent; yellow bars: 1st generation Chemically 

Active Systems; green bars: 2nd generation Chemically Active Systems. 

Figure 9–61. Evolution of SPGG Fire Suppression Application Technologies. 
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