INDUSTRIAL FUMIGATION AGAINST INSECTS 55 



chloropicrin is sprinkled on burlap sacks spread out on the floor, 

 6-quart sprinkling cans being convenient for this purpose. 



Care should be taken not to spatter the liquid on the hands or 

 feet, since it might cause blistering of the skin. 



Where conditions in the mill do not warrant a general fumigation, 

 satisfactory results can sometimes be obtained by fumigating the 

 machinery only. For this type of fumigation the chloropicrin is 

 applied directly into the machines in accordance with the dosage 

 table. The dosage for the reels and purifiers should be increased in 

 proportion to the quantity of stock left in the machinery. In gen- 

 eral, at least 1 pound should be used in each machine. 



Considerable time is required to ventilate a building that has 

 been fumigated with chloropicrin, as evaporation is slow and the 

 fumigant clings to commodities with great tenacity. When present 

 in flour, chloropicrin has a deleterious effect on its baking quality, 

 but this effect disappears when the flour is aerated. 



METHYL BROMIDE AS A MILL FUMIGANT 



For fumigation with methyl bromide the mill should be prepared 

 in the same manner as for an open-space fumigation with hydrocyanic 

 acid except that it is unnecessary to clean out the stock from the 

 milling units. In fact, better results are obtained if the milling 

 stock is left. This is a distinct advantage in that the cost of clean- 

 ing out and removing the stock is avoided. 



As far as practical each floor should be treated as a separate unit, 

 doors between floors and to stair wells and freight elevators being 

 closed. Some interchange of gases through the slide spouts and 

 elevator legs is unavoidable. 



The gas should be used at the rate of 1 pound per 1,000 cubic feet 

 of space, and it should be applied through the same type of piping 

 system employed with liquid hydrocyanic acid in open-space fumi- 

 gation. If the floors of a mill can be closed off, the dosage should 

 be divided equally. Otherwise slightly more of the gas should be 

 applied to the upper floors, since the gas is heavier than air. As 

 previously described, the gas is applied from cylinders that are 

 connected to a manifold on the outside of the mill. The pressure 

 in each cylinder is increased to 150 pounds with compressed air, the 

 valve is opened, and the gas flows rapidly through the piping sys- 

 tem into the mill. 



After a 16- to 24-hour exposure the mill can be opened up for 

 aeration. Workmen opening up the mill should wear masks 

 equipped with a canister designed to protect against the vapors 

 of methyl bromide. Ordinarily the vapors clear out rapidly. 



Owing to the absorption and retention of the methyl bromide by 

 the milling stock, it is well to set aside the first 24 bags of flour 

 for each 500-barrel unit after the mill is started. Later this flour 

 can be gradually fed back into the mill. 



LOCAL FUMIGATION 



A general fumigation once or twice a year does not entirely solve 

 the insect problem in a flour mill, since small infestations are con- 

 tinually developing here and there throughout the milling system. 



