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BUREAU OF STANDARDS REPORT

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S. DEPARTMENT OF COMMERCE

MECHANISMS OF FIRE IGNITION AND EXTINGUISH! PINT

1.

SUMMARY

A preliminary study was undertaken on the electrical

effects during application of dry powders to fires.

Technical difficulties seem to make continuation of this

work inadvisable at present. Measurements were made of

ionization present in fuel mixtures in gases just prior to

ignition. The results seem to indicate that preflame

reactions do not result in ion formation.

2.

EXTINGUISHMENT BY POWDERS

Scaling studies relating the effectiveness of several

dry powder extinguishing agents to the area of the fire,

were concluded with thejpublication of a report, No* 6^31,

"Extinguishment Effectiveness of Some Powdered Materials

on Hydrocarbon Fires" by T. G. Lee and A. F. Robertson,

dated 8 September 1959* These results were presented at

the National Research Council Symposium on the Use of Models

in Fire Research, on November 1959*

Preliminary work on halogenated organic extinguishing

agents has indicated that the inhibition of the flame reactions may be connected with ionization effects. A preliminary study of electrical effects in dry powders was made,

but was dropped because of the difficulties involved. It

proved to be very difficult to distinguish between charges

on the powder particles induced by the electric field

required for measurement, and charges produced by frictional

effects, and charges adsorbed on the particles as a result

of passing through the plasma in the flame. A sufficient

number of interesting effects were observed that it is probable the work will be reactivated at some future date, when

It appears that some of the measurement difficulties can be

resolved.

3.

IONIZATION STUDIES

Since Ionization appears to be an almost universal

effect in flames and the addition of inhibitors seems to

have very profound effects on the steady state concentrations

of ions and electrons, it was of interest to try to find out

whether preignition reactions can be connected with ionic

processes. A pair of concentric tubes were built into a furnace so that a gaseous fuel and air could be heated to the
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same temperature priosr to mixing. It the exit of the

furnace , fuel and air were* sjlxed and the mixture explored

with Langmuir profees for the presence of ions end electrons.

The temperature was raised slowly until self-ignition occurred

however, no ions could be detected at temperatures dese to

the self-ignition temperature and at times within 0.2 second

of visible ignition, the indications are, therefore, that

preignition flame reactions are fee tween neutral species and

my even occur between free radicals formed as a result of

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