Methyl Bromide as an Extinguishing Agent
Recently several small fire extinguishers have been put on the market in this country in which the extinguishing agent was Methyl Bromide. None of these extinguishers has been listed by Underwriters Laboratories. The effective quality of this material as an extinguishing agent was recognized during the war; systems were installed in aircraft which would spray the liquid as a mist or vapor in the engine space to put out fires. It is the general opinion of those best informed that due to its high toxicity it should not be used in fire extinguishers available to the general public. Food brought in contact with Methyl Bromide should be discarded.
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Below is given the principal information on Methyl Bromide as taken from data issued by Underwriters Laboratories:
“Methyl bromide (CH3BR) (when pure) is a colorless, transparent volatile liquid. SP. GR. 1.73, boiling point 4.6 C. (40.3 F.), vapor density 3.29 (air = 1).
Toxic Hazard. Methyl bromide in concentrations of the order of 0.7 to 1.0 per cent by volume in air for durations of exposure of the order of 1/2 hr. has been shown to be lethal to guinea pigs. Its odor is not distinctly unpleasant and it cannot be said to give definite warning of its presence in dangerous concentrations Underwriters’ Laboratories’ test data confirm opinion that methyl bromide. like many other toxic products, may not manifest its poisonous effects immediately.
Methyl bromide readily decompose into toxic products in the presence of flame or heated surfaces at high temperatures. These products include hydrobromic acid (Hllr) and small amounts of bromine (BR2).
Fire Hazard is very small and the material is classified as “weakly flammable.” Weak flame propagation within the narrow range of 1 per cent (13.5 to 14.5 per cent by volume) in the presence of an intense source of ignition is recorded in technical literature.
Uses. Methyl bromide is effective as a fire extinguishing agent in certain concentrations and has also been used as a refrigerant. In both instances, however. its use has been limited on account of the high toxic hazard. Methyl bromide finds its principal use as a fumigant and is listed by the Laboratories for this purpose, both alone and mixed with COe, in Section II of the List of Gas, Oil and Miscellaneous Appliances. For use alone it is supplied in steel cylinders under pressure of 11 lb. per sq. in. at 70 F.
Listed mixtures of methyl bromide and carbon dioxide for use as fumigants are supplied in steel cylinders under a pressure of 820 lb. per sq. in. at 70 F. These mixtures are classed as nonflammable and are characterized by toxicity of a comparatively low order when used in proportions of 15 to 28 lb. per 1,000 cu. ft. and in accordance with the procedure recommended by manufacturers.—-N.B.F.U. BULLTIN No. 251.