In warehouses that have been recently sealed prior to fumigation, good results 

 are usually obtained, whereas in warehouses, in which the sealing work was done 

 more than 6 months previously, checking and injury permit cracks to develop and 

 thus the effectiveness of fumigation is correspondingly reduced. The Bureau 

 of Entomology and Plant Quarantine recommends a fumigation period of 72 

 hours and it is obvious that a perfect seal must be maintained for that period. 



The use of paper, mineral asphalt, and other materials has not been entirely 

 satisfactory. Paper has a tendency to dry with age and is easily torn. Drafts 

 and vibration tend to loosen the seal. Some sealing compounds lose their ad- 

 hesive qualities and become hard and brittle. Careful inspection of the sealing 

 at the beginning of each fumigation season will disclose a certain amount of 

 injury, but it is impossible to ascertain and entirely eliminate the effects of aging 

 and resulting leakage of gas. 



N 10129 



Figure 2. — Interior of closed-type tobacco-storage warehouse showing suction light 



trap and screened door. 



Vinylite Plastic (Strippable) Coating 



The Department of Agriculture, in its study of sealing tobacco warehouses, 

 was anxious to find a material which would retain its elastic and adhesive qualities 

 over long periods of time. Plastic materials were considered and were found to 

 have these characteristics, and, in addition, were readily removable (strippable). 



Vinylite plastic strippable film is a material the basis of which is a plasticized 

 vinyl chloride-acetate copolymer resin. It is made sprayable for pressure spray- 

 gun equipment by the addition of volatile solvents, such as methyl ethyl ketone 

 and acetone. The resulting material after the volatile solvents have evaporated, 

 forms a durable, flexible film which is tough and weather-resistant. 



In addition to being volatile, the solvents used in plastic are highly inflammable 

 and explosive where a sufficient concentration of fumes exist. Although there 



