28 CIRCULAR 3 6 9, U. S. DEPARTMENT OF AGRICULTURE 



pounds net. The natural pressure of the gas is sufficient at room tem- 

 perature so that both cans and cylinders are self-emptying when 

 opened. However, the pressure in the cylinders is increased slightly 

 by the manufacturers to facilitate the rapid removal of the gas. 



Methyl bromide is relatively cheap, highly toxic to all stages of 

 insects including their eggs, noninflammable at concentrations used 

 in commercial practice, and can be used successfully at comparatively 

 low temperatures. It has remarkable powers of penetration and is 

 undoubtedly the most efficient fumigant known for the treatment of 

 warehouses filled with bagged commodities. It is useful, however, only 

 in buildings of modern concrete or brick construction. As it does not 

 kill quickly, it is useless in loosely constructed buildings, where leakage 

 is high. Lacking a distinctive odor, this gas is but faintly noticeable 

 in small amounts, a feature that creates a hazard that is not present 

 with some of the rapidly toxic gases that possess distinctive warning 

 properties. 



As a general fumigant for mills or warehouses of modern tight con- 

 struction methyl bromide can be applied through a piping system in 

 much the same manner as described for liquid hydrocyanic acid. Each 

 cylinder of methyl bromide is equipped with a siphon tube so that it 

 can be emptied without inverting the cylinder. Preparatory to liber- 

 ation of the gas the pressure in the cylinder is usually increased with 

 compressed air to 150 pounds. The cylinder is then connected by the 

 single outlet to the manifold of the piping system of the mill or ware- 

 house being fumigated, and the valve is opened. The pressure forces 

 the fumigant from the cylinder into the fumigation line at the rate 

 of about 10 pounds per minute. In cool weather the pressure in the 

 cylinder must sometimes be built up with compressed air a second time 

 to speed up the emptying of the cylinder and the application of the 

 gas. A three-wav connection between the cylinder, the manifold, and 

 the air compressor will facilitate this operation. 



Small warehouses that do not have a piping system can be fumigated 

 by distributing the requisite number of cylinders uniformly over the 

 warehouse floor and releasing the gas by opening the valves. Since 

 the gas is heavier than air. the valve opening of each cylinder should 

 be connected to %-inch copper tubing of sufficient length to reach 

 nearly to the ceiling. By plugging or pinching shut the exit openings 

 of the copper tubes and boring holes through the tubes near the ends, a 

 better distribution of the fumigant will be obtained. 



Exposure periods are similar to those used for hydrocyanic acid 

 fumigation, and the same precautions should be taken in applying 

 the fumigant as well as in ventilating the fumigated buildings. In 

 referring to the human hazard connected with the use of methyl 

 bromide for fumigation, the United States Public Health Service 5 

 states that, "while methyl bromide is less toxic to man than certain 

 fumigants, all persons fumigating with methyl bromide or mix- 

 tures containing methyl bromide, or persons entering fumigated 

 rooms, cars, or sheds to open ventilators or to unload fumigated 

 materials, observe precautions used with other toxic fumigating 

 gases. Experience indicates that adequate precaution will 

 obviate danger of injury by this gas." 



5 PRELIMINARY RECOMMENDATIONS TO FUMIGATORS USING METHYL BROMIDE OR MIXTURES 



containing methyl bromide as a fumigant. I'. S. Pub. Health Serv., Natl. Inst. Health, 

 Division of Industrial Hygiene. Mimeographed Leaflet. May 16, 1938. 



