/

.'

Optical Measurement of Toxic Gases Produced during

Firefighting Using Halons

KEVIN L. McNESBY,* ROBERT G. DANIEL, ANDRZEJ W. MIZIOLEK, and

STEVEN H. MODIANO

u.s. Army Research Laboratory, Aberdeen Proving Cround, Maryland 21005-5066 (K.L.M., R.C.D., A. W.M.); and Aberdeen Test

Center, Aberdeen Proving Cround, Maryland 21005-5059 (S.H.M.)

Several optical techniques (FT-IR emission and absorption spectroscopy, mid- and near-infrared tunable diode laser absorption

spectroscopy) have been used to measure toxic gases produced during inhibition of flames by halogenated hydrocarbons (Halons). Fire

types studied include low-pressure premixed flames, counterflow

diffusion atmospheric-pressure flames, open-air JP-S (turbine fuel)

fires, and confined JP-S fires. Spectra are presented and analyzed

for these fires inhibited by CF3Br (Halon 1301) and C3F1H (FM200). For low-pressure premixed flames, spectra are presented

which show production of the CF3 radical in methaneJoxygenlAr

flames inhibited by CF3Br. For large-scale fire testing, it is shown

that the type and amount of toxic gases produced during fire inhibition are highly dependent on fire conditions and temperatures and

that some species not considered important (CF20) are often produced in significant amounts. Finally, it is shown that HF production, during inhibition of vehicle fires using FM-200, is highly dependent on time to suppression.

Index Headings: Halon; Flame inhibition; Toxic gas production; HF;

CF20.

INTRODUCTION

The investigations at the Army Research Laboratory

(ARL) into halogenated hydrocarbon (Halon) inhibition

of flames began several years ago as a projectt to elucidate mechanisms of suppression using low-pressure

premixed flames. This investigation was expanded to include atmospheric-pressure counterflow diffusion flames

and was further expanded by an ongoing collaboration

with the Aberdeen Test Center (ATC) to evaluate new

test methods and equipment for suppression of real fires

occurring within the crew compartment of combat vehicles. Results of these studies have recently appeared in

the literature.1.2 Since beginning these investigations, we

have also been measuring production of toxic gases during Halon inhibition of flames.

The purpose of this paper is to describe how the fireinhibitant testing methodology in our lab changed as our

focus expanded from controlled laboratory-scale fires to

large-scale real fires. We also present some recent results,

using laser-based diagnostics, of measurements of toxic

gas production, and measurements of precursors to toxic

gases, during Halon inhibition of laboratory-scale fires

and real fires in ordinary and demanding environments.

To our knowledge, this is the first report of optical measurement of the CF, radical in inhibited, premixed, lowReceived 28 May 1996; accepted 4 October 1996.

* Author to whom correspondence should be sent.

t The project was originally funded under the auspices of the Strategic

Environmental Research and Development Program (SERDP) of the

U.S. Department of Defense.

pressure flames and is the first report of quantitati ve, in

situ, real-time measurements of HF gas production during

large-scale fire fighting by Halons.

The fire types investigated for production of toxic gases during inhibition by Halons range from laboratoryscale controlled flames to air-fed turbine fuel (lP-S) pan

fires. Laboratory controlled flames include low-pressure

premixed CH4/Oi Ar and CH4/air flames and atmospheric-pressure CHiOz and CH4/air counterflow diffusion

flames.I,2 Real fires include open-air lP-S pan fires3 and

confined lP-S pan fires. Gas production was measured by

using optical dignostics including mid-infrared tunable

diode lasers (MIR- TDLs), near-infrared tunable diode lasers (NIR- TDLs), and Fourier transform infrared (FT-IR)

absorption and emission spectroscopy. Inhibitants investigated include CF,Br (Halon 1301), C3F7H (FM-200),

C3F6H2(FE-36), C2FSH(FE-25), CF3H (FE-13), and CF4,

For this report, inhibition only by CF3Br (Halon 130 I)

and C3F7H (FM-200) will be discussed.

EXPERIMENTAL

Details of the experimental apparatus and equipment

used in some of these measurements have been previously published'-3 but will be summarized in what follows.

Laboratory-Scale Fires. Low-Pressure Premixed

Flames. The experimental apparatus consists of a lowpressure flat flame burner (McKenna Industries, Inc.)

mounted on translational stages inside an evacuable

chamber. The evacuable chamber is equipped with apertured LiF windows (1.5 mm diameter) to allow passage of infrared laser radiation. Since the infrared laser beam

or modulated FT-IR beam used to probe the burner flame

remains fixed in position relative to the low-pressure

burner chamber, different parts of the flame are examined

by moving the burner within the chamber. Typical gas

flow rates were 0.95 Umin CH4, 1.9 Umin O2, and 3.0

Umin Ar. Argon was used as a diluent in order to lower

the peak flame temperature to the working range of

Pt-Pt/Rh thermocouples (~2000 K). Inhibitant flow was

typically less than 2% of the total (fuel plus oxidizer)

flow, although the low-pressure flames could withstand

inhibitant (CF3Br) levels up to 15% of total flow without

being extinguished. Fuel, oxidizer, and inhibitant were

mixed together prior to their entering the final mixing

section immediately below the burner frit. Typically, an

Ar shroud (3 Umin) was flowed around the flame to minimize absorption by cold gas in the line of sight. Gas

flow was controlled by a MKS Instruments Inc. Type

147B gas flow controller. Total pressure within the burner

678 Volume 51, Number 5, 1997 0003-7028/97/5105-0678$2.00/0

© 1997 Society for Applied Spectroscopy APPLIED SPECTROSCOPY
chamber was maintained near 20 Torr, although stable

flames could be maintained from near-atmospheric to less

than 2 Torr.

Mid-infrared laser radiation used to probe the lowpressure, premixed flames was provided by a liquid nitrogen-cooled tunable diode laser (cryogenically cooled

Pb-salt laser source and monochromator system from Laser Photonics, Analytics Division, Inc.) and detected by

using a liquid nitrogen-cooled HgCdTe narrow-band infrared detector. Laser output is frequency modulated (1

kHz) and is collimated and mode-selected prior to its entering the low-pressure chamber. After passing through

the flame region, the mid-infrared laser beam is focused

onto the liquid nitrogen-cooled HgCdTe detector. Lock-in

detection at the modulation frequency effectively discriminates against emission from the flame. Entrance and

exit apertures mounted on the evacuable burner chamber

restrict the maximum beam diameter through the flame

to 1.5 mm.

FT-IR absorption measurements through low-pressure

premixed flames were made by using a Mattson Sirius

FT-IR spectrometer. The collimated beam from the infrared spectrometer was taken externally to the instrument,

apertured to 1 mm diameter, brought to a focus above the

center of the burner, and then refocused onto a liquid

nitrogen-cooled HgCdTe wide-band infrared detector.

FT-IR emission measurements used a Midac Model

G-500 I-FH spectrometer system modified in-house to

measure radiation emitted from the flame. Because of the

modular nature of the Midac spectrometer, modification

of the instrument to measure emission spectra was

straightforward, and consisted of repositioning of the interferometer "brick" and liquid nitrogen-cooled In-Sb

detector to accommodate the burner flame as the source

of radiation.

Atmospheric-Pressure Counterflow Diffusion Flames.

The atmospheric-pressure counterflow diffusion burner

assembly was fabricated at NIST2 and consists of two

opposing, wire-screen-covered gas ports (2.5 cm diameter). Gas port separation was adjustable but was typically

several centimeters. Fuel (methane) is flowed into the

flame region through the lower port. Oxidizer (oxygen or

air) and inhibitant are flowed into the flame region

through the upper port. The flame appears as a thin, flat,

luminous disk (with slight edge curvature pointing up

towards the exhaust shroud) located between the fuel and

oxidizer ports. All gases are exhausted from the flame

region through an exhaust port, which forms a shroud

around the oxidizer port. Typical flow rates were 600

mL/min oxygen and 500 mL/min methane. When air was

used as the oxidizer, the air flow rate was 2.2 L/min and

the methane flow rate was 1.1 L/min. Inhibitant was always added on the oxidizer side only, and inhibitant flow

varied up to a maximum of 1.3% of the total flow for

each system investigated. These flow parameters were selected because they gave the most stable flame for that

particular fuel/oxidizer combination.

Fuel and oxidizer flow was controlled by a MKS Instruments Inc. Type 147B gas flow controller. Although

the burner exhaust shroud was connected to a high-volume vacuum pump, it was necessary to contain the atmospheric-pressure counterflow diffusion burner within a

large box equipped with optical ports and a chimney attached to a fume hood. This arrangement was made to

prevent toxic gases (HF and CF20) from entering the

main laboratory.

Real-Scale Fires. Two types of lP-S fuel pool fires

were investigated. The first fire investigated was a lP-S

fuel pool fire burning in air. Infrared spectra of gases

removed from the flame environment were measured by

using a Midac Corporation Model G-5001-FH Fourier

transform spectrometer system operating at 0.5-cm-1 resolution. Detection of infrared radiation was by a liquid

nitrogen-cooled HgCdTe detector. The interior of the

spectrometer was purged with dry nitrogen, and the spectrometer system was ruggedized, by the manufacturer, for

outdoor use. This ruggedization consisted of kinematic

mounting of all optical components and manufacture of

all transmissive optics (including the beamsplitter) from

ZnSe.

Samples of gases were removed from the flame environment and flowed through a lO-m-pathlength multipass

optical cell (internal volume approximately 2300 cm3) at

a flow rate of 6 L/minute. The gas manifold and the

10-m-pathlength multipass optical cell contained within

the instrument were maintained at 400 K to prevent condensation. The tubing leading from the stainless steel

probe (0.25-in.-o.d. 304 stainless steel tubing) to the instrument gas manifold was of Teflon® and was unheated.

No condensation was observed within the Teflon® tubing

leading from the probe to the spectrometer, but a small

amount of black soot formed on the interior surface of

the Teflon® tubing during testing. It is assumed that measured concentrations of gases normally highly soluble in

water (e.g., HF and CF20) were always less than actual,

because of reactions of these gases with water condensed

on the walls of the probe. Fires were fueled by 3 gallons

of lP-S fuel placed in a 20-cm-deep square pan approximately I m on a side. The stainless steel probe, approximately 3 m in length, was located at the edge of the pan,

approximately 1 m above the surface of the liquid fuel.

Prior to ignition of the fuel (accomplished with an oxygen-acetylene torch), gas flow to the multipass cell was

begun, a background scan set was measured, and a series

of sample scan sets was begun. Each scan set consisted

of 10 coadded scans measured at 0.5-cm-1 resolution.

Collection of these scan sets continued throughout the

course of the experiment. Three minutes after ignition of

the fuel (to allow the fire to stabilize), chemical inhibitant

(either CF3Br or C3F7H) was sprayed into the fire with a

hand-held extinguisher. The inhibitor [CF3Br (Halon

1301, DuPont) or C3F7H (trade name FM200, Great

Lakes Chemical)] was applied to the fire from the side

opposite to the location of the probe, with the inhibitor

stream directed toward the lower portion of the fire.

The second type of fire investigated was a lP-S fuel

pool fire burning in the crew compartment of the ballistic

hull of a Bradley Fighting Vehicle. For these tests, a 0.3-

m2 pan was filled to a depth of approximately 1 cm with

lP-S fuel. All doors and hatches were closed, and the fire

was ignited through a small access port with an oxygenacetylene torch. After approximately 15 s, the onboard

fire suppression system, consisting of a bottle filled with

approximately 3 kg inhibitant and pressurized with N2 to

SOOpsi, was deployed. Full inhibitant release and fire

extinguishment (when successful) occurred in less than 1 s.

APPLIED SPECTROSCOPY 679
C02

17 torr CH4/02 l1ame

Inhibition by 3% CF3Br

I I I I 1000 2000 3000 4000

Wavenumbers (em-I)

.6

.2

4000

Counterflow Diffusion CH4/02

Flame Inhihited By 1.3% CF3Br

CH4

3000 2000

Wavenumbers (em-I)

1000

FIG. 1. The FT-IR emission spectrum of gases present 10 mm above

the burner surface of a 17 Torr, stoichiometric, premixed gas, CHiO,

flame to which 3% CF3Br has been added.

Placed within the crew compartment of the vehicle (see

Fig. 6) was a GRIN-lens tipped fiber optic, emitting laser

radiation at 7665 cm-I. The source of the near-infrared

laser radiation was a tunable diode laser spectrometer

system (thermoelectrically cooled InGaAsP distributed

feedback laser source) manufactured by Southwest Sciences, Inc. The laser radiation was detected by a roomtemperature InSb photodiode detector (distance from fiber-optic source = 10 cm). This frequency corresponds

to the frequency of the P(2) line of the first overtone of

the fundamental HF vibration. The laser was scanned at

50 Hz over the spectral region of interest (approximately

0.05 cm-I on either side of 7665 cm-I) and frequency

modulated at 50 kHz during each scan through the spectral region of interest. Detector output was demodulated

at 100 kHz (SRS Inc. Model 850 lock-in amplifier), and

digitized with the use of an oscilloscope (Lecroy 9360).

Data collection was initiated prior to ignition of the fire.

Each data point (Figs. 7 and 8) corresponds to one scan

over the spectral region near 7665 cm-I, at to a time

resolution of 20 ms. A new data point was measured

every 2 s, for the duration of the experiment.

RESULTS

Laboratory-Scale Fires. Fourier Transform Spectroscopy. Initial measurements in our laboratory2 using FT-IR

spectroscopy to investigate low-pressure (20 Torr) premixed CH4/02 flames inhibited by up to 15% CF3Br

showed no evidence of CF20 formation, even though calculations indicated4 that CF20 should be formed in small

amounts. As an example, Fig. 1 is an FT-IR emission

spectrum of gases present 10 mm above the burner surface (spatial resolution approximately 1 mm) of a 17 Torr

premixed CH4/02 flame to which 3% CF3Br has been

added. This spectrum is similar in appearance to an absorbance spectrum measured through the flame at a similar height above the burner surface.3 Emission spectroscopy was used because experiments using absorption

spectroscopy to measure combustion products in flames

are often complicated by absorption of radiation by cold

gas species outside of the flame zone. Although significant amounts of HF are detected near 4000 cm-I, there

is no evidence of CF20 gas (strongest feature near 1900

cm-I) at any height within the flame.

680 Volume 51, Number 5, 1997

FIG. 2. The FT-IR absorbance spectrum measured through an atmospheric-pressure counterflow diffusion CH)air flame inhibited by 1.3%

CF3Br.

Figure 2 shows the FT-IR absorption spectrum measured through an atmospheric-pressure counterflow diffusion CH4/air flame3 inhibited by 1.3% CF3Br. In this

spectrum, formation of CF20 gas is measured near 1900

cm-I, as well as CO (2100 cm-I), HBr (2700 cm-I), and

HF (4000 cm-I). More species are observed in the atmospheric-pressure counterflow diffusion flame than in

the low-pressure premixed flame, because the peak temperature in the counterflow diffusion CHiair flame is

several hundred Kelvins lower3 than in the low-pressure

CH4/02 flame. Species generated in the lower-temperature flame have a longer residence time than do those in

the low-pressure CHi02 flame, allowing measurement of

CF20 and HBr in the counterflow diffusion CH4/air

flame.

These initial studies using FT-IR spectroscopy provide

spectroscopic evidence that gas production during Halon

inhibition of fires is highly dependent on the fire type and

conditions. In our investigations aimed at validating

flame modeling calculations,5 we use low-pressure flames

because, at low pressure, flame zones are expanded, and

more information is available from optical measurements

with the use of our finite spatial resolution (typically 1

mm). However, for measurements of some species present at low concentrations within the low-pressure flame,

we are limited by the optical resolution of most commercial FT-IR spectrometers (usually on the order of 0.5

cm-I).

Tunable Diode Laser Spectroscopy. To measure species at concentrations below the detection limit of our

Fourier transform spectrometer, we employ tunable diode

laser absorption spectroscopy using phase-sensitive detection. The instrumental methods employed in using

such derivative-based spectroscopies have been well

characterized in the literature.6 The principal advantages

of the technique are high resolution (typically better than

0.0005 cm-I); increased sensitivity, because of the use of

phase-sensitive detection; and, at high laser modulation

frequencies, low source noise.

Figure 3 shows second-derivative mid-infrared tunable

diode laser absorption spectra measured through rich and

lean 21 Torr CHi02/Ar flames doped with 5% CF3Br.

These spectra were measured by using a probe beam

waist of 1.5 mm, with the beam center axis 3 mm above
I

1264.55

*

I I

1264.6 1264.65

Wavenumbers (em-I)

*

Rich Flame

I

1264.7

FIG. 3. Second-derivative mid-infrared tunable diode laser absorption

spectra measured through rich and lean 21 Torr premixed CH4/02 flames

inhibited by 5% CF,Br. Spectra for each flame were measured 3 mm

above the burner surface. The asterisks indicate the position of an absorption feature due to CF20. Double-headed arrows indicate positions

of CF, absorption. Note that CF20 absorption is greater in the lean

flame, while CF, absorption is greater in the rich flame (see text).

the burner surface. The spectral region of interest was

determined by the reported frequencies of CF3· and CF20

absorptions,? by the spectral structure of the reference gas

(N10), and by the output range of our diode laser system.

The spectral region selected was from 1264.3 to 1264.7

cm-I. In addition to encompassing several absorption

lines of CF3 and CF20, this spectral region was selected

because it was free from absorptions from the reference

gas (N20), as well as CH4, CF3Br, CO2, and H20, and

because the CF20 absorption features present in this region, although dense, were recognizable, and they had a

weak temperature dependence as calculated with the use

of the HITRAN8 database. Because of the low anticipated

concentrations of the CF3 radical, we did not consider

interferences from C2F6, although for higher concentrations of the CF3' radical it has been shown that absorption

from C2F6 may be important.? The CF2· radical has no

reported absorbance in this region.9 The main experimental difficulty in detecting CF3 in flames inhibited by Ha1-

ons is that the spectral features from the radical are usually obliterated by the dense spectral structure of CF20.

Several features may be noted from the spectra shown

in Fig. 3. Most importantly, features due to absorption of

radiation by CF10 (marked with an asterisk) are seen to

be more intense for the lean flame (1.9 Llm 02' 0.76 Urn

CH4, 1.0 Urn Ar) than for the rich flame (1.7 Urn 02'

1.0 Urn CH4, 1.0 Urn Ar). This is because excess oxygen

in the lean flame may compete with the H atom for reactions with the CF3· radical and CFz' radical, increasing

CF20 formation relative to that occurring in a rich (oxygen-poor) flame.lo We have found that comparing richand lean-flame infrared spectra of flames with similar levels of fluorocarbon inhibitant is a useful way of aiding

the identification of lines arising from absorption of infrared radiation by CF20. This observation reflects the

different way the inhibitant participates in rich and lean

combustion environments and may provide insight into

controlling amounts of HF and CF20 in combustion gases.

Figure 4 shows measurements of second-derivative

spectra, over the same spectral region shown in Fig. 3,

FIG. 4. Second-derivative mid-infrared tunable diode laser absorption

spectra measured through a premixed, rich, CHiO,/Ar flame to which

5% CF3Br has been added, measured as a function of laser beam height

above burner (HAB) surface. The asterisks indicate the position of an

absorption feature due to CF20. Arrows indicate positions of CF3 absorption. Note how CF3 absorption first increases, then decreases, with

increasing height above burner surface, in agreement with flame modeling calculations.

through the rich, 21 Torr, premixed CH4/0iAr flame

doped with 5% CF3Br (and shown in Fig. 3), as a function of height above the burner surface. As in Fig. 3,

absorption by CF20 is indicated by asterisks. Arrows indicate the position of absorption of infrared radiation by

CF3• For Fig. 4, two features, at 1264.557 and 1264.604

cm-I, corresponding to absorption by CF3', are not obscured by absorption by CF20. The absorption at

1264.557 cm-I is more intense than the absorption at

1264.604 cm-I, and first appears at 1 mm above the burner surface. The absorption at 1264.557 cm-I disappears

as height above the burner surface is increased. The

smaller absorption near 1264.604 cm-I appears approximately 3 mm above the burner surface, and vanishes at

approximately 4 mm above the burner surface.

We believe the absorption features seen in the spectra

of Halon 1301-inhibited flames at 1264.557 and 1264.607

cm-I are the first optical measurement of the CF3· radical

in Halon-inhibited low-pressure flames. The successive

spectra show an increase, followed by a decline, with

height above the burner surface, for the two features at

frequencies previously assigned to the CF3' radical. This

spatial dependence is consistent with predictions from

flame model calculations of fluorine-inhibited flames.lO

The intensity of these two features, in proportion to CF20

absorption, changes in qualitative agreement with flame

modeling calculations. However, it may be seen from Fig.

4 that there remain many unassigned features in each

spectrum, so an unambiguous assignment of these weak

features to CF3· cannot be made until more than two transitions have been identified.

Real-Scale Fires. Fourier Transform Spectroscopy.

Measurement of gases produced during real-scale fire

testing was performed at the Aberdeen Test Center. All

fires investigated used JP-S as fuel. JP-S is a turbine engine fuel composed of long-chain (Cn, n > 5) hydrocarbons. Figure 5 shows the FT-IR absorbance spectrum of

gases removed from the vicinity of the fire during inhibition of the fire by Halon 1301 (CF3Br). Evident from

this spectrum are features due to HF, HC1, HBr, CO, and

APPLIED SPECTROSCOPY 681
HF Production - Crew Compartment

FIG. 7. A graph of HF production (ppmm) vs. time after release of

C3F7H inhibitant (FM-200) for a JP-S fuel pool fire occurring within

the crew compartment of an Army combat vehicle. For this test, the

inhibitant extinguished the fire.

1400

1200

]' 1000 0.. 800 8 600

~400 ••••••

20: tl ~~~f--~~-+-~~--=:~~--;:-~~~ 20 40 60 80 100

Time After Release (s)

o

:1

JP8 Fuel Fire During Inhibition By !Won 1301

ICF3Br

HF I I~A 

;J .4CF20

!:~~~~~~,~;II',:~w_1 \::.1~~::':".llIr) -----r---

3000 2 1

FIG. 5. The FT-IR absorbance spectrum of gas removed from the vicinity of a JP-S fuel pool fire during inhibition by CF3Br (Halon 1301).

CF20, as well as other species participating in the combustion. Most noticeable is the difference between species present in this fire vs. those observed in the laboratory-scale fires. Most significant are the prominent features due to HBr and CF20. We believe the HCI present

in the flame arises from chlorine impurities in the CF3Br,

although no effort was made on our part to verify impurities present in any of the inhibitants used in these

experiments. The optically determined concentrations of

gases present during inhibition of open-air JP-S pan fires

by CF3Br (Halon 1301) and C3F7H (FM-200) have recently been reported by us elsewhere.3

Tunable Diode Laser Spectroscopy. Results from measurements using Fourier transform spectroscopy (Fig. 5)

showed significant lethal concentrations of HF and CF20

gas produced during inhibition of open-air JP-S fuel pan

fires by CF3Br. For testing of fire inhibition by Halons in

occupied areas, it is important to measure in situ the time

evolution of any toxic gases produced during the inhibition event. This is important for measurement of HF,

since we have observed that HF reacts rapidly with most

surfaces, especially in the presence of moisture. For this

reason, tunable diode laser spectroscopy was chosen to

be one of the diagnostics employed during testing. HF

was selected as the most important gas to monitor, since

HF typically has the highest partial pressure of any of

the Halon-inhibited flame toxic gas products.

Figure 6 shows a schematic diagram of the facility for

measuring gases produced during suppression of JP-S

fires occurring within the crew compartment of a ballistic

hull and turret of an Army combat vehicle. The HF diagnostic uses a near-infrared tunable diode laser operating at 7665 cm-I. This frequency corresponds to the frequency of the P(2) line of the first overtone of the fundamental HF vibration. There are several reasons to use

diode lasers operating in the near-infrared. For HF diagnostics, however, the most important is that mid-infrared

diode lasers operating at the fundamental frequency (near

4000 em-I) are not yet available. Other reasons for using

a near-infrared tunable diode laser-based diagnostic include the ease of transmission of the laser radiation

through optical fibers, the operation at temperatures attainable with thermoelectric coolers (~270 K), the low

cost of detectors, and the ability to significantly reduce

laser output noise through the use of kHz modulation

techniques. II

Figure 7 is a graph of HF gas production (in ppmm,

parts per million meter), measured with the use of the

near-infrared tunable diode laser, vs. time immediately

after release of 3.4 kg of C3F7H (FM-200) into a JP-S

fuel pan fire (area ~0.3 m2) burning within the closed

crew compartment of the ballistic hull and turret of a

Bradley Fighting Vehicle. The Halon was dispersed into

the fire in approximately 1 s. Fire extinguishment occurred during dispersal of the inhibitant. Figure S is a

graph of HF gas production (in pptm, parts per thousand

HF Production - Crew Compartment

Detector

Assembly

~

I I

Test Vehicle

Inhibitant

Reservoir

70

60 1..' ~50

S

;:;:' ~!5:: 30402010 0 0

.

.....".

••••••••••••" ••••••••"i'••••• 50 100 150 200 250

Time After Release (s)

JP-8 Fire

FIG. 6. A schematic diagram of the test facility for measuring gases

produced during suppression of JP-S fuel pool fires occurring within

crew compartments of Army vehicles. The detector assembly consists

of an extractive FT-IR probe and an in situ NIR diode laser emitterdetector assembly.

FIG. S. A graph of HF gas production (pptm) vs. time immediately

after release of C3F7 (FM-200) into a JP-S fuel pool fire burning within

the closed crew compartment of an Army combat vehicle. Unlike the

data shown in Fig. 7, for this test the fire was not extinguished by the

inhibitant. The dip in HF concentration near 40 s is due to activation

of the back-up CO2 extinguisher system.

682 Volume 51, Number 5, 1997
meter), measured with the use of the near-infrared tunable

diode laser, vs. time for an identical test, except that the

fire was not extinguished by the Halon. The only difference between tests is a slight change in position of the

nozzle of the cannister from which the Halon is dispersed. From Figs. 7 and 8, it may be seen that peak HF

production in the fire not extinguished by the Halon is

approximately 50 times higher than in the fire in which

extinguishment by the Halon occurred immediately. The

dip in HF concentration in Fig. 8 near 40 s marks the

time at which the back-up CO2 extinguishment system

was used to put out the fire. These results indicate that

time to suppression, when Halon-based fire inhibitants

are used, is a critical factor in determining the amount of

toxic gas (HF) produced during fire fighting. We believe

these results are the first real-time, quantitative, in situ

measurements of HF production during inhibition of realscale fires using Halons.

CONCLUSION

Optically based measurements can provide valuable diagnostic information necessary for determination and

analysis of mechanisms and efficiencies of Halon fire inhibitants. We have shown that production of toxic gases

associated with fire inhibition by Halons, particularly HF

and CF20, is dependent on the type and conditions of the

fire being investigated. We have measured differences in

concentrations of CF3 produced in rich and lean flames

inhibited by CF3Br. Finally, we have shown that the time

evolution of HF gas produced during inhibition is dependent on whether fire suppression is accomplished immediately after application of Halon inhibitant. We are

currently exploring the application of the diagnostic techniques mentioned in this report to more types of fires and

extending the methods described here to even more extreme environmental conditions.

ACKNOWLEDGMENTS

We would like to acknowledge support from Mr. Steve McCormick

at TACOM and also from the SERDP program of the 000. We also

wish to acknowledge the support of Craig Herud, Bill Bolt, and Stan

Poly anski of the Aberdeen Test Center (ATC), who were responsible

for overseeing the running of the tests and of the testing facility, and

without whom these tests would have been impossible.

I. K. L. McNesby, R. G. Daniel, and A. W. Miziolek, Appl. Opt. 34,

3318 (1995).

2. K. L. McNesby, R. G. Daniel, J. M. Widder, and A. W. Miziolek,

Appl. Spectrosc. 50, 126 (1996).

3. S. H. Modiano, K. L. McNesby, P. E. Marsh, W. Bolt, and C. Herud,

Appl. Opt. 35, 4004 (1996).

4. A. W. Miziolek, A. E. Finnerty, R. G. Daniel, K. L. McNesby, W.

Tsang, V. 1. Babushok, M. R. Zachariah, P. R. Westmoreland, and

D. R. F. Burgess, Jr., "Fundamental Studies of Fire Extinguishment

for Predicting Halon Alternative Compound Behaviour", in Proceedings of the 1994 Army Science Conference, Orlando, Florida

(1994 ).

5. R. G. Daniel, K. L. McNesby, and A. W. Miziolek, Appl. Opt. 35,

4018 (1996).

6. P. L. Varghese and R. K. Hanson, J. Quant. Spectr. Rad. Transfer

24, 279 (1980).

7. C. Yamada and E. Hirota, J. Phys. Chern. 78, 1703 (1983).

8. L. S. Rothman, R. R. Gamache, R. H. Tipping, C. P. Rinsland, M.

A. H. Smith, D. C. Brenner, V. Malathy Devi, J.-M. Flaud, C.

Camy-Peyert, A. Perrin, A. Goldman, S. T. Massie, L. R. Brown,

and R. A. Toth, J. Quant. Spectrosc. Radiat. Transfer 48, 469 (1992)

(1992 HITRAN database).

9. P. B. Davies, W. Lewis-Bevan, and D. K. Russell, J. Chern. Phys.

75,5602 (1981).

10. V. Babushok, D. F. R. Burgess, Jr., G. Linteris, W. Tsang, and A.

W. Miziolek, "Modeling of Hydrogen Fluoride Formation From

Flame Suppressants During Combustion", in Proceedings of the

1995 Halon Options Technical Working Conference (New Mexico

Engineering Research Institute, Albuquerque, 1995), pp. 239-250.

II. D. S. Bomse, D. C. Houde, D. B. Oh, J. A. Silver, and A. C.

Stanton, "Diode Laser Spectroscopy for On-Line Chemical Analysis", in Optically Based Methods For Process Analysis, SPIE Vol.

1681 (SPIE, Bellingham, Washington, 1992), p. 138.

APPLIED SPECTROSCOPY 683