Apparatus used in method is commercially available, powder-deposition type oxy-acetylene torch that has been modified to provide electronically timed operations and more uniform powder flow; usual torch tips are replaced by burner head with pilot flame

Altman, R. L.

English

NASA Technical Reports Server

February 1975	
.	 B75-10027 
NASA TECH BRIEF 
Ames Research Center	
-	 £ 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Method for Evaluating Effectiveness of Dry

Fire-Extinguishing Chemicals 
.
The effectiveness of dry powdered chemicals for 
extinguishing fires can be evaluated by a method 
which is based on the observation that the powders 
cannot put out fires in a pure oxygen atmosphere. 
The method involves determination of the "oxygen 
index," that is, the upper limiting ratio of oxygen to 
oxygen-plus-nitrogen (02/02 + N2) below which a 
specific dry chemical is capable of extinguishing a 
premixed propane-oxygen-nitrogen flame. The ap-
paratus used in the method is a commercially avail-
able, powder-deposition type oxy-acteylene torch that 
has been modified to provide electronically timed 
operations and more uniform powder flow; the usual 
torch tips are replaced by a burner head with a pilot 
flame. 
It has been observed that the torch flame can be 
reproducibly extinguished so long as extinguishment 
time is limited to about one second. If the flame is not 
extinguished within the first second after commencing 
powder injection, then the probability for such occur-
rence within the next half-second is less than 1 in 10, 
and within the last ½ second of a 2-second time 
period about 1 in 100. 
Extinguishment data are plotted as oxygen index 
(0.1.) vs. the equivalence ratio (E.R.), which is the 
stoichiometric ratio of propane to oxygen. As an ex-
arñple, when data for oxygen flow rates are arranged 
in order of increasing 01. vs. extinguishment success, 
it is found that a definite yes-no cutoff for 1-second 
extinguishment occurs in the case of sodium bicar-
bonate at 0.1. = 0.33 and E.R. 2.8 in one run, at 
0.1. = 0.36 and E.R. = 2.8 ii a second run, and 
0.1. = 0.39 and E.R. = 3.6 in a third run. In other 
words, extinguishment in one second or less always 
takes place with 0.1. <0.36 ±0.03, and never seems
to occur for 0.1. >0.39. The examination of many 
data points indicates that this 0.1. extinguishment 
limit is relatively insensitive to equivalence ratio. 
Also noted is that the oxygen flow rate must exceed 
3300 cc/min for extinguishment success; rates up to 
4500 cc/mm (experimental limit) were used in the 
determinations. 
Potassium bicarbonate is rated about twice as 
effective as sodium bicarbonate by Underwriter's 
Laboratories on the basis of pan-fire extinguishment 
tests. Qualitative agreement with this rating was ob-
tained for several commercial products containing 
potassium bicarbonate, i.e., 0.1. = 0.49, 0.49, and 
0.47 vs. 0.36. Other dry chemicals which are report-
edly superior to potassium bicarbonate (containing 
phosphate, nitroprusside, cryolite) were found to be 
little different than sodium bicarbonate; chromate-
containing powders are apparently slightly more 
effective than sodium bicarbonate. 
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: TSP .75-10027 
Patent status: 
NASA has decided not to apply for a patent. 
Source: Robert L. Altman

Ames Research Center

(ARC-10869) 
Category 04 
This document was prepared under the sponsorship of the National
	
Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United Stales
	
information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	
will be tree from privately owned rights.
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Method for evaluating effectiveness of dry fire-extinguishing chemicals

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