INDUSTRIAL FUMIGATION AGAINST INSECTS 39 



Procedure 



The commodity to be fumigated is loaded into the vacuum tank, 

 the doors are closed, and air is removed until the vacuum gage regis- 

 ters 28 or 29 inches. The proper dosage of fumigant is then admitted 

 through the vaporizer or accumulator. 



If the tank is equipped with multiple gas inlets and a gas-circu- 

 lating system, the fumigant should be pumped from the accumulator 

 tank into the vacuum tank through the circulating system. When 

 all the fumigant is in the tank, the valve to the accumulator tank 

 should be closed and the necessary valve adjustments made to allow 

 the gas to be circulated in the vacuum tank. The gas should be cir- 

 culated for 15 minutes. By holding the remaining vacuum without 

 change for the duration of the fumigation, better results are ob- 

 tained than by breaking the vacuum with air. If the instrument 

 panel is equipped with a recording device, a chart record (fig. 31) 

 can be made of each fumigation for future reference. 



The dosage is usually measured by weighing the fumigant into 

 the tank or vaporizer, by measuring it volumetrically, or by dropping 

 the vacuum a given number of inches with the fumigant. The first 

 two methods are accurate. The third method cannot be used indis- 

 criminately, since with a given quantity of gas the drop in vacuum 

 will vary both with the quantity and the type of commodity being 

 fumigated and with the temperature of the gas and of the com- 

 modity in the tank. It is convenient for commercial fumigations, 

 however, and if proper allowance is made for these variations it 

 will be sufficiently accurate for ordinary work. 



At the end of the fumigation the gas is pumped out of the tank 

 and the vacuum is broken with air. If desired, the fumigated prod- 

 ucts can be "air-washed" several times by alternately drawing and 

 breaking a vacuum of about 27 inches. 



When large tanks filled with commodities of an absorbent nature 

 are being unloaded, the residual gas is quite noticeable. Workmen 

 should be equipped with gas masks having canisters designed to 

 protect against the gas being used before they are permitted to 

 unload the tank. It is a wise policy to keep the pump in operation 

 during the unloading process so that a stream of fresh air will be 

 drawn constantly through the tank, thus reducing the concentration 

 to which the workmen are exposed. 



The temperature of the commodity is an extremely important 

 factor in vacuum fumigation. Cold commodities, particularly highly 

 absorbent materials such as flour products, cannot be treated suc- 

 cessfully unless large dosages are used. A temperature of 70° F. or 

 above is desirable. If possible, commodities taken from cold storage 

 should be allowed to come to room temperature before being treated. 



FUMIGATION OF VARIOUS COMMODITIES 



Since it is impossible to discuss here in detail the fumigation of 

 all the many types of commodities that become infested with in- 

 sects, only those commodities most often fumigated in commercial 

 establishments are included in this circular. The fumigation of dried 

 beans and grain in bulk on the farm and in the terminal elevator is 



