CONTROL OF INSECTS IN TOBACCO 21 



ceiling, such as windows, doors, ventilators, eaves, skylights, and ele- 

 vator shafts, must be closed and the building made gastight. 



One method of sealing warehouses, which has been followed for 

 some time, utilizes gastight paper (such as sisal kraft paper), paste, 

 asphalt, elastic roofing cement, calking compound, and masking tape. 

 Large openings are closed with heavy paper sealed with paperhanger's 

 paste or, in the case of eaves and flashings, with tarred paper and 

 asphalt. Cracks are filled with a mixture of 4 parts of asbestos fiber 

 to 1 part of calcium chloride and enough water to form a stiff dough. 

 Kecently a new method of sealing has been adopted which consists in 

 spraying a vinylite plastic over cracks around windows, ventilators, 

 and other openings. The plastic is applied with a paint-spray gun 

 operated by compressed air. In the old method of sealing the cost of 

 materials is low but the charge for labor is high. The cost of sealing 

 by means of plastic spray under 1948 conditions Avas approximately 

 two-thirds the cost of the older method because of the smaller re- 

 quirement for labor. However, the use of plastic calls for spray guns, 

 and air compressor, air hose, and other equipment. Companies hav- 

 ing many warehouses can afford such equipment, but the cost is pro- 

 hibitive for firms with only one or two storages. Sealing with plastic 

 has one big advantage — -it can be done very rapidly. Sometimes the 

 need for fumigation develops quickly and speed in preparing the 

 building is important. Sections of tobacco warehouses sealed for 

 fumigation are shown in figures 15. 16, and IT. 



For best results in fumigation, the warehouse should be piped with 

 %-inch copper tubing. Small brass spray nozzles should be so dis- 

 tributed as to provide the proper dispersion of gas— one for each 

 15,000 to 25,000 cubic feet. The piping system should be so arranged 

 that the gas pressure is about the same on all nozzles. Large ware- 

 houses with several floors require branch lines with separate risers. 

 From 10 to 18 nozzles may be used to a riser. Detailed plans for 

 piping warehouses can usually be obtained from any fumigating 

 company after a survey of the building. 



Unpiped warehouses can be fumigated with hydrogen cyanide by 

 means of temporarily installed rubber hose and nozzles. 



For many years hydrogen cyanide has been the fumigant most 

 generally used in tobacco warehouses. Liquid hydrogen cyanide in 

 steel pressure cylinders is used. A small air compressor pumps air 

 into the cylinder through an intake valve until a pressure of about 

 100 pounds per square inch is reached. The pressure forces the air 

 through the piping system and out of the spray nozzles. When only 

 part of a cylinder of gas is required, the amount may be weighed 

 from the cylinder on portable platform scales. 



The operator should read the safeguards at the end of this cir- 

 cular and be certain that all persons and animals are out of the 

 building before beginning introduction of gas. When the required 

 dosage has been forced into the building, the valve on the cylinder 

 should be closed and the piping system blown clear of gas by air 

 pressure. The inlet pipe into the warehouse should then be 

 capped. 



The amount of hydrogen cyanide needed varies somewhat with 

 the tightness of the warehouse. A dosage of 16 ounces per 1,000 cubic 

 feet, with an exposure of 72 hours, is considered more or less standard. 

 However, in warehouses with floors of cinders or crushed rock, or 



