22 



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



When discoids are used, the fumigators are exposed to the gas 

 while they are opening the cans and distributing the contents. Good 

 gas masks are necessary and will prevent them from breathing poi- 

 sonous fumes, but there is also some danger from the direct absorp- 

 tion of hydrocyanic acid gas through the skin. Williams 3 has esti- 

 mated that a man protected by a good gas mask can remain in air 

 containing 2 ounces of hydrocyanic acid gas per 1,000 cubic feet for 



half an hour without 

 being affected; in a con- 

 centration of 4 ounces 

 per 1,000 cubic feet this 

 time should be reduced 

 to 15 minutes, and in 

 one of 8 ounces to 5 min- 

 utes. The same author 

 calculates that, in dis- 

 tributing discoids at the 

 rate of 8 ounces of hy- 

 drocyanic acid per 1,000 

 cubic feet, a fumigator 

 will be actually exposed 

 for the greater part of 

 the time to from 1 to 2 

 ounces per 1,000 feet. 

 Allowance is made for 

 the fact that the fumi- 

 gator is constantly mov- 

 ing away from the dis- 

 coids and that the full 

 quantity of the gas is not 

 given off immediately. 

 If the discoids are chilled 

 before being used, the 

 concentration to which 

 the fumigator is exposed 

 will be less. 



From the foregoing 

 data it is evident that, 

 where large quantities 

 of discoids are used, the 

 fumigating crew must 

 be large enough so that 

 the distribution of the 

 fumigant will be speedy and no one man is exposed to the gas for 

 a dangerously long period. 



Figuke 23. — Man, protected by gas mask, removing 

 the top from a tin can containing discoids im- 

 pregnated with liquid hydrocyanic acid. 



Disposing of Spent Discoids 



When the fumigation is finished and the building has been well 

 ventilated, the spent discoids and the empty cans can be gathered up 

 and thrown away. At the end of a 24-hour fumigation the discoids 

 will retain not more than a trace of hydrocyanic acid. 



3 Williams, C. L. fumigants. Pub. Health Repts. [U. S.] 46: 1018. 1931. 





