1002 - 12 - 10^21 February 2^, 1961 7094

xJinth

Progress Report

on the

Ilechanisras of Fire Ignition and Extinguishment

by

T, G. Lee

Covering the period 1 July I960 to 31 Jan 1961

for

Bureau of Ships

Department of the '"avy

Code 633

Index Lumber x'S-l33-001

IISCIIAlilSES OF I IRE lONITIOi , AND EXTII^OUISIFIEfT

'C)y

T, r-, Lee

1. Summary

Studies of the effects of halogenated organic inhibitors

on the concentrations of electrons and ions in flames v;ere

continued. One of the characteristics of this class of inhibitors seems to be their ability to capture low energy

electrons and dispose of the acquired energy by dissociation

of the inhibitor molecule. Comparison of a normal (uninhibited) r, remixed flame with an inhibited flame shov/ed that

the maximum concentration of electrons occured about 1-1/2 ram upstream from the visible reaction zone in the normal flame

and about 1/2 mm downstream from the visible reaction zone in

a flame inhibited by CF^Bro

Information on the capture of electrons by halogenated

compounds are available for only a few compounds, which are

also known to be inhibitors . An attempt v/as made to extend

the list of such compounds by measuring the amount of inhibitor required to extinguish a glow discharge operating under

more or less standard conditions. The attem;'t was unsuccessful

probab.ly because the capture of low energy electrons is only

one of many processes v/hicli can extinguish such a discharge.

2c Position of )aximum Electron Concentra tion

When a conducting probe is placed in a plasma it is

bombarded by molecules, atoms, positive and negative ions,

and electrons. Charged particles may transfer their charges

to the probe in ’ loportion to the nu;'!iber of charged particles

colliding v/ith it. In a plasma, such as a flame, there are

equal numbers of positive and negative charge carrieis, but,

because of their higher velocities, electrons v’-ill tend to

make many more collisions than positive ions v/ith the result

that the charge acquired by the probe will, have a negative

sign. The magnitude of thf^ charge may be measured, '-lovided

the measuring equipment does not bleed the charge from the

probe at too high a rate. Cuch measurements v/ere made on a normal (unhibited) pro]!ane-air flame burning in an EdgertonPowling burner, and the position of the maxiraum concentration
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of electrons v/as found to be about 1-1/2 rarr. upstream fron

tile visible leaction zonec blien Cf' Br was added to the

mixture, the maximum negative probe-^potential was found

to be about 1/2 mm on the other side (downstream of the

visible reaction zone.

Interpretation of these results is difficult. One

explanation may be that electrons are cartured by the inhibitor to form Br ions wiiich are carried through the reaction

zone before liberating their _charges in some kind of recombination reaction, such as 2 Br Br^ + 2 . It_ma3

’' also be

that, because of their- high electron affinity, Br ions persist

aiid are carried into a region vrhich is deficient in ^'ositive

ions, so that the net charge transferred to the probe is

negative, but carried bj^ 3r ions' which were measured before

recombination , rather than by electrons. In the case of the

uninhibited flame, it is known that the concentration of

negative ions is low, sc the charge acquired by the probe can

be attributed to electrons, t.-e can, therefore, conclude only

that the position of the maximum negative riobe notential

shifts downstream as a result of tire addition of inhibitor.

It is not known v/hether there is any relation between this

effect and the mechanism of inhibition.

3« Bxtinguishment of Glovj Discharges

by Inhibitors

It v/as thought that tlie T:ro’''erty of electron car.ture by

inhibitors could be measured by their ability to extinguisxh a

lo\-j pressure glow disclrarge. A preliminary study by Paul D.

Burrow ('^BS Rep':^rt ’'"o. 5999) indicated the possibility of

relating the efficiency of halogenated organic corapounds in

quenching glov/ discharges to their efficiencies as extinguishing agents. A series of ten compounds, eigirt of them

containing halogen, and one known not to car ture electrons,

v/eie studied in glow discharges and no correlation found.

The lack of correlation could 'robably be attributed to the

difference in elctron energy distributions betv?een flames

and glow discharges. The lov/ average electron energ^^ in

flames is not sufficient to produce the same kind of phenomena

v/hich are oiesent in glovr discharges. The quenching of a glow discharge may, in addition, be attributed to reactions

which have nri thing to do with the immobilizing of elections.

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