NEXT-GENERATION FIRE SUPPRESSION TECHNOLOGY PROGRAM (NGP): 

TECHNICAL HIGHLIGHTS 

Richard G. Gunn 

Building and Fire Rescarch Laboratory 

Nationit1 Institute of Standards and Technology 

Gaithcrsburg, MD 20X99-X650 USA 

INTRODUCTION 

The Department of Defense (DoD) is entering the third year or its Ncxt Generation Fire 

Suppression Technology Program (NGP). The NGP goal is to demonstrate. by 2005. 

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

tcchniques. and fluids that meet the operational requirements currently satisfied by Halon I30 I 

systems in aircraft. ships, land combat vehicles. and critical mission suppon facilities. If 

successful, the NGP could eliminate DoD dependence on a harmful substance no longer in 

national production, minimize any readiness impacts that could result if Halon 1301 use 

restrictions were imposed in thc future, and achieve these at greatly reduced cost. 

The potential fire locations for which alternatives to Halon 1301 itre sought include aircraft 

engine nacelles, dry bays. cargo bays. and fuel tanks; ground vehicle crew compartments; and 

shipboard machinery spaces and storage compartments (Figure 1 ). The hazards to be avoided 

include harm to people, thermal damage. post-fire corrosion. loss of visibility, and overpressure. 

Successful candidates must thus do well in the following: the fire suppression efficiency and 

reignition quenching, ODP, GWP, atmospheric lifetime. suppressant residue level, electrical 

conductivity, metals non-corrosivity and polymeric materials compatibility. long-term storage 

stability. low toxicity of the chemical and its combustion and decomposition products. speed 01' 

dispersion, and safety and occupational hcalth requirements. To be cost-effective, the suppressant and storage/delivery systcm must be of light weight and low volume, as well as compatible 

with the host designs of existing platforms. 

Points of contact and additional information on the strategy and status of the NGP can he found 

at the NGP web site: www.dtic.mil/ngp/. 

PROGRAM STATUS 

Support for the NGP comes from DoD funding and cost sharing from the participating 

laboratories. To date, most of the DoD support has come from the Strategic Environmental 

Research and Development Program (SERDP), with additional support from the Army Tank and 

Automotive Command (TACOM). To date. thc NGP will have expended about 15% of the 

planned resources. 

Halon Oplions Tcchnicd Worhing Confcrcncc Z7-2 April 1994 87 
NGP 

Figure 1. NGP research for retrofitable fire suppression technologies. 

TECHNICAL HIGHLIGHTS 

The achievements of the NGP research team have been numerous, significant and stimulating. 

The following describes the highlights. 

New Flame Suppression Chemistry 

An easy way to effect economical retrofit of a fire suppression system is with a new chemical 

that perfornis as well as CF3Br, but without the environmental drawback. Limited searches have 

turned up a number of new chemicals for consideration, so it is likely that there are more worthy 

candidates. The NGP is developing both improved methodologies for doing the search as well as 

identifying candidates worthy of further consideration. 

In the published literature on flame inhibition and suppression are a number of chemicals that are 

far more efficient at quenching flames than is CF3Br. If any of these interfere with flame 

propagation chemistry in a manner different from the way Halon 1301 does. it., depleting the 

free radical (H, OH, 0) pool that propagates combustion, this would provide additional guidance 

for the search through the world of chemistry. 

NGP laboratory studies with opposed flow diffusion flames have demonstrated a direct 

relationship between the degree of reduction of the OH concentration in the flames and 

suppressant efficiency for a range of additive chemistries. This measurement for a candidate 

chemical should enable rapid identification of similarity to or difference from Halon 1301 

flame suppression. 

88 Halon Oplions Technicul Working Conlcrence 21-21) April I949 
An NGP-developed reduced propandair chemical kinetics mechanism will serve 11s the basis 

for understanding better the suppression activity of a chemical. Flame speed and species 

concentration predictions compare well with published data. A contract has been let to 

- generate flame reaction rate data for additives of known high supprcssion efficiency. 

NGP research has developed two devices (an electrostatic atomization system and an 

inductively couplcd plasma nebulizer) for seeding the air streams of laboratory burners with 

fine droplets of an additive compound. For several applications, water mists and other 

multiphase systems are under consideration. The ability to vary the droplet size makes it 

possible to study both chemical effects. after droplet vaporization, and the physical effects of 

the droplets. 

Using published data, quantitative structure-activity relationships. and laboratory screening tests, 

NGP chemists have examined families containing thousands of chemicals to identify those with 

desirable properties: high fire suppression efficiency. short atmospheric lifetime, low toxicity, 

and boiling point sufficiently low that an extinguishing concentration can be achieved within a 

specified time following discharge. 

The presence of a bromine atom and a chemical feature that makes a molecule prone to rapid 

decomposition in the troposphere are a winning combination. Eight (8) bromolluoroalkcnes 

appear to have flame extinguishment concentrations not far from that of CFIBr. Inhalation 

toxicity screening data for these compounds should be available soon. An additional 8 

bromofluoroamines appear promising and have been targeted for synthesis or acquisition. 

A number of liquid and solid phosphorous-containing chemicals (PCC) are used as flame 

retardant additives in plastics. For many of those, the retardancy occurs in the gas phase. and 

PCCs thus merit serious consideration as fire suppre 

lifetimes of these chemicals are expected to be sufficiently short (on the order of days) that 

thcy will not create any global environmental problems. NGP research indicates that lor 

most binding states of phosphorus, the flame suppression effectiveness is high and largely 

determined by phosphorus loading, so candidates can be selected on the basis of physical or 

toxicological properties. (There is a range of toxic potency, with a general tcndency to 

increase as the oxidation state of the phosphorus decreases. Most PCCs also have high 

boiling points, so to be used as total-flooding agents, they would need to be carricd on a 

powder or dispersed using a solid propellant gas generator.) Possihle exceptions to this are 

the phosphorus nitrides, for which conflicting fire suppression efficiency data exist. 

Approximately a dozen PCCs are being examined more closely. 

Many organosilicon materials are stable, inert, and have low toxicities. Those with an 

oxygen linkage should have low atmospheric lifetimes. This suggests that adding bromine 

could provide a compound with good fire suppression capability while maintaining good 

environmental characteristics. Some fluorination is needed to reduce the boiling points. A 

small sct of thcsc chemicals is being prepared for screen testing. 

Fluorinated amines and ethers are reported to be nonflammable and, in some cases, to act 21s 

fire extinguishants. Most have boiling points too high lor total-flooding use. However, NGP 

calculations on CJF~~OCHI indicate an extinguishing concentration near that of Halon I30 I, 

combined with a short atmospheric lifetime. This compound is EPA-approved for use as a 

solvent. 

This indication for C~FUOCH~ is an example of a broader finding, that is, there are compounds that manifest reasonable flame quenching efficiency with little chemical interference 

in flame propagation. Examination of over IS00 potential thermal agents identified ‘I b out 

25 compounds that might be suitable as firefighting agents, and in fact some are already 

ints. Moreover, the atmospheric 
being used as halon replacements. A variety of families including ethers, furans, amines, and 

straight-chain hydrocarbons are represented. Almost all are highly fluorinated. 

Suppressant Screening Tests 

Of the large number of chemicals to be considered in the search for replacement suppressants, 

many have been and will be discarded from further consideration based on available information. 

For the rest, screening tools are needed to enable rapid identification of those relatively few 

agents whose propriety should be investigated aggressively. These tools should be quick, 

inexpensive, and require little of the agent. 

A measure of fire suppression efficiency is mandatory. The NGP has developed the first benchscale suppression screen for comparing the flame extinction performance of both gases and 

liquids. The suppressant, added to the air flow past a cylindrical porous plug burner, sharply 

blows off the leading edge of the flame. The flow facility and the burner may also be made 

suitable as a screening tool for powders. Fabrication drawings and an operations manual are 

being prepared for distribution to interested laboratories. 

A second apparatus is being developed for screening the effectiveness of a short burst of 

suppressant (such as would emerge from a solid propellant gas generator), both in quenching 

open flames and those stabilized behind an obstruction. 

Of comparable interest is the development of a screening protocol and screening methods for the 

compatibility of agents with (I) people (toxicity). (2) materials used in the storage container for 

the agents and that the agent might contact after discharge, and (3) the environment. NGP 

research staff convened the experts in these fields, compiled a hierarchical roadmap through the 

maze of properties of interest, and identified the best screening tests for the key properties. 

New and Improved Aerosol and Powder Suppressants 

For some applications, clean (volatile) suppressants are not essential. While fine water mist and 

efficient powders have been the subjects of real-scale testing, the approaches to date have not 

met with universal success. As with gaseous and vapor suppressants. NGP research is directed at 

finding new approaches to condensed phase candidates and ways to improve the use of current 

suppressants. 

Prior information about the effect of particle properties on flame suppression effectiveness has 

been obtained empirically. NGP research is determining the mechanics of how particles interact 

with flames. The alkali metal atoms released when sodium or potassium bicarbonate powders 

decompose in and near a flame participate in the chemical tie up of reactive flame radicals. The 

surface area of the powder particles controls the rate of release of these species into the flame and 

the subsequent decomposition and flame temperature reduction. The powder particle size and 

density dictate how closely the particles follow the flame gas velocity streamlines and thus how 

efficiently the particles reach the most chemically sensitive locations in the flame reaction zone. 

In storage facilities and machinery spaces, the quenching of flames from liquid and solid fuels is 

of concern. NGP research has characterized the flame spread over polymethylmethacrylate 

(PMMA) as a surrogate fuel. The flame speed decreases as the opposing air speed increases, and 

the flame speed is greater over thinner samples than over thicker ones. Experiments are now 

underway with water droplets injected over these flames to provide correlations for the optimum 

drop sizes and velocities for effective extinguishment. 

90 Halon Options Technical Working Conference 27-29 April 1999 
When a liquid droplet with high momentum impacts a burning liquid fuel surface, splashing of 

the fuel will likely occur. The splashing may generate satellite fuel droplets. which may create 

an additional fire hazard. There is no published information on this phenomenon. Measurements 

are in progress to provide a map of the velocity/drop size distributions that are capable of penetrating fires to reach the surface of the combusting material, and calculations are showing the 

magnitude of suifiice cooling that can he expected. 

Interpreting most of these results and performing the model calculations require thcrmophysical 

property data for the tluids. A unique set of computer programs for estimating these properties is 

now operational. As the NGP examines new tluids, some not commercially available, and as 

solutions emerge as serious candidates (e.g., aqueous sodium lactate), these estimates will 

become pivotal. 

The NGP is examining whether a highly efficient. but otherwise undesirable (e.g., high toxicity 

or atmospheric contamination) chemical can be stored and transported safely to the fire on an 

inert carrier. The criteria are stability of adhesion of the agent to the host powder at ambient 

temperatures, sufficiency of loading of the agent on the powder, and rapidity of release in the 

tlame zone. 

Guidance is emerging on the volatility of organometal complexes that are highly efficient 

with the order of volatility generally being as follows: AI < Cu < Mo < Mn < Ni < Cr < Sn < 

Ti < Fe < Co < Sb < Pb < Ge. For the organic moiety. the order of increasing volatility was 

generally the following: oxalate < acetate < acetylacetate < methoxide < cthoxide < 

trifluoroacctylacctate < hcxatluoroacetylacetonate. Encapsulation of the compounds in 

matrices. such as alumina, decreased the volatility of the compound sharply. suggesting that 

it is unlikely that these would he very effective as fire suppressants. 

NGP researchers have examined the possibility of using dendritic ("tentacled") polymers ;is 

fire suppressants, perhaps with chemically active atoms bonded to the structure. Preliminary 

analysis shows that the "pure" dendrimers showed fire suppression effectiveness very similar 

to water, indicating that the polymer carrier is essentially inert and not detrimental to fire 

suppression properties. The dendrimer-alkali salt solutions were only about 20% more 

effective than pure water or small molecule salt controls. 

nts, but often are toxic. Their relative volatility is dependent on the central atom, 

Viability of New Suppression Technologies 

The success of new NGP technologies requires (I ) that the lnhoratory research replicate the 

suppression phenomena in real-scale fires and (2) that the NGP he able to demonstrate that 

candidate fire suppression methods are quenching flames as they would under the threats 

experienced in the field. Meeting both of these needs entails improved instrumentation in the 

test articles already owned by the military department laboratories. 

Making these measurements of concentrations of fuel, oxygen, suppressant, and harmful 

combustion hyproducts during and after the fire suppression process requires groundbreaking 

advances in instrumentation. In many of these tests. the fire may be ignited by explosion of a 

shell, requiring both rapid data acquisition during a period of shock and vibration. High temperatures and rapidly changing flow patterns further complicate the measurements, Fortunately. 

industrial and academic researchers have developed new instrumental capahilities. NGP staff ire 

building on these and adapting them to the harsh environments experienced during fires in 

aircraft, ships, and ground vehicles. 
For the first time, near-infrared tunable diode laser absorption spectroscopy (NIR-TDLAS) 

has been used for measurements during suppression of crew and engine compartment fires in 

ground vehicles. Oxygen concentrations have been measured during the 250 msec time-tosuppression of the fireball, providing the first glimpses of the mixing processes during this 

violent event. 

HF is a corrosive and toxic degradation product of any of the fluorinated fire suppressants 

(eg, HFC-227ea and HFC-12.5) currently under consideration as replacements for Halon 

1301. Excessive generation of HF is a principal deterrent to the deployment of these agents. 

The first in-situ, time-dependent measurements of the concentration of HF, its dissipation, 

and its amelioration by additives to the suppressant have now been recorded. 

Improving the spatial resolution of such measurements will require a fiber optic probe system 

capable of operation at elevated temperatures. NGP scientists have designed a probe for use 

at temperatures up to 1200 K in the presence of powder, smoke, and fine water mist. Using 

commercially available components where possible, a prototype design contains integrated 

diode laser fiber optics. Laboratory tests have shown that the probe provides an adequate 

signal for monitoring species concentration. 

The NGP team has also developed a cell for use in measuring the high temperature (5 1000 K) 

infrared properties of candidate suppressants. This information enables finding spectral lines for 

NIR-TDLAS detection and developing calibration curves for the temperature-dependent 

sensitivity of the measurements. 

Measurement of the distribution of the suppressant is essential, initially to characterize the fire 

extinguishment process and later for certification of a suppression system. Since there are likely 

to be a multiplicity of candidate agents, with potentially different capabilities of being 

monitored. the NGP is developing two methods of detection, based on two distinct principles. It 

is expected that at least one of these will be suitable for each agent and each weapons system 

application. 

Laser-induced breakdown spectroscopy (LIBS) involves shattering the suppressant molecule 

and monitoring the breakdown products. NGP laboratory capability has established detection 

limits for Halon 1301 and several candidate halon alternatives. 

Improvements are being made to the prototype Differential Infrared Agent Concentration 

Sensor (DIRRACS) developed under a prior DoD program. A new design overcomes flow 

velocity effects on the measured concentration and on vibrations of the IR source and other 

optical components. 

Better Suppressant Delivery 

Fire suppression tests in the military departments’ real-scale simulators show that Halon I301 

was so effective and inexpensive that extra suppressant was used to compensate for the engineering simplicity of the delivery and dispersion systems. In searching for retrofit alternatives for 

situations where storage weight and volume are limited, it is likely that some solutions will arise 

from improving the delivery system. This would enable use of an agent of only moderate 

efficiency. 

Two principal reasons for overdesigning the Halon 1301 systems are the transient release of the 

suppressant and the presence of numerous obstructions or clutter. NGP engineers are determining the penalties imposed by these. They find that extinguishing concentration decreases with 

increasing injection period (longer residence time at proportionately lower concentration). The 

92 Halon Options Technical Working Confercnce 27-29 April 1995, 
extinguishing concentration and injection period decrease as the air flow increases. At high 

flows, there is a minimum agent mole fraction below which no extinction occurs; there is a 

minimum injection period, below which the flame can not he extinguished, even at high concentrations. These rcsults will both quantify the potential gains from redesigning distribution 

systems and assist in screening for the effectiveness of candidate suppressants. 

Replacement fluids must function within the cxisting distribution plumbing. Replacing the 

piping is a major cost in rctrofit and is to be avoided. Thereforc one has to know how a new. 

multiphase chemical will behave in ii long run of bent pipe. A new computer code for prediction 

of two-phase fire suppre 

RELAPS, a computer program used to predict such flows, primarily for nuclcar plant transient 

and accident analyses. It solves field equations for seven primary variables as a function of time 

and distance: pressure, phasic specific internal energies, vapor volumc fraction or void fraction. 

phasic velocities. and noncondensable quality. The modified code was successfully tested 

against previous expcriniental data for Halon I30 I dischargc. The code, portable to a variety of 

commonly used operating systems, will soon he modified to handle dissolved gas. 

Construction of the facility to verify the suppressant flow and discharge predictions has been 

completed. The advanced instrumentation redefines the state-of-the-art in measurements of the 

instantaneous mass flow of fluid during transient discharge from the source vessel, fluid 

temperatures along the discharge pipe using film thermocouples with response times in the order 

ofmilliseconds, and the void fraction. using a capacitance sensing probe. Upon completion of 

the instrumentation, the apparatus will be tested under a wide range of operating conditions, 

generating parametric data for both Halon 1301 and HFC-227ea. 

While several weapons systems incorporate :I two-shot capability, there has always been reliance 

on the use of a singlc suppre nt. One of the new concepts the NGP is exploring is the use of a 

dry powder (NaHC02 or KHCO?) to suppress the fuel spray deflagration in a combat vehicle 

crew compartment, followed by a discharge of water mist to mitigate the inhospitahlc environment produced by the dry chemical discharge. Tests showed that the fireball could he extinguished near the 250 msec required and that modest quantities of water mist could effectively 

remove the dry chemical particles from suspension. 

lilt flows during discharge is now operational. It is derived from 

WHAT LIES AHEAD? 

There is a broad spectrum of research yet to he performed if the NGP is to meet its goal of 

providing weapons platform managers with feasible alternative approaches for the retrofit of 

Halon I301 -based fire suppression systems. 

All of the currently selected candidate chemicals will undergo screening to identify those 

with truc potcntial. and the emerging subset will he subjected to more rigorous evaluation. 

The search for additional replacement chemicals (tluids and powders) will continue until the 

full range of possibilities has been considered. 

Research will hesin on the use of novel ways of storing, generating and dispensing 

suppressants, such as solid propellant gas generators. Empirical tests have shown great 

potential for these. hut have also revealed serious flaws. e.g., excessive temperature. 

int jetting, and compartment overpressure. 
The research effort into the science of agent and air distribution in the fire compartment will 

increase. This will provide information on the potential for minimal modifications to 

dispersion hardware. 

Data gathering and research will hegin on retrofit technologies for fuel tank inerting. 

Ignition prevention or quenching phenomenology differs from flame extinguishment. 

Real-scale experiments with new suppression approaches will he carried out in the military 

department test fixtures, which will have been outfitted with enhanced measurement 

capability. These experiments will examine the variables involved in optimizing the new 

technologies, to verify the predictions from the models of fire suppression performance, and 

to identify what additional factors need research emphasis. 

The system for evaluating the relative desirability (total cost and performance) of changes to 

fire suppression systems and procedures will be completed. Input data for the best new 

technologies will be obtained, and comparative appraisals of the new technologies will be 

prepared. 

Throughout the research, the NGP Technical Coordinating Committee will continue to maintain 

close contact with the platform managers and the testing and evaluation facilities in the military 

departments. As appropriate research questions arise, they will become the subjects of NGP 

investigation. 

94 Halon Options Technical Working Conference 27-29 April 1999