Fumigant Application Methods, Dosage, and Calculation
Methods and their constraints
Structural fumigation is delivered by tent/tarp, sealed-building, or chamber systems; commodities by chamber or vacuum. Methyl bromide is typically released through a vaporizer or as a gas distributed through tubing; sulfuryl fluoride is released as a gas from cylinders; phosphine comes from tablets or sachets that generate gas over hours, depending on temperature and humidity, with magnesium phosphide releasing faster than aluminum phosphide. The release method, number and placement of release points, and circulation all affect whether the intended concentration is achieved throughout the space.
Dosage fundamentals
Label rates are usually expressed per 1,000 ft³, per 1,000 bushels, or per 1,000 lb, paired with a required exposure period. Efficacy is a function of concentration multiplied by time (the CT product), so cutting exposure cannot simply be offset by raising the rate - labels set both. Temperature, sorption, leakage, and load factor all require adjustment within the rate range the label allows.
Calculating
Total product = (structure volume ÷ 1,000) × label rate, then convert units carefully and round within the labeled range.
Worked example: a 24,000 ft³ structure at a label rate of 1 lb per 1,000 ft³ needs (24,000 ÷ 1,000) × 1 = 24 lb, which is 384 oz.
Useful equivalences: a rectangular volume is length × width × height; 1 ft³ of air holds roughly 0.075 lb; and 1 lb of methyl bromide per 1,000 ft³ produces approximately 0.4 percent by volume (about 4,000 ppm).
Traps
Mixing units (ounces vs. pounds, cubic feet vs. cubic meters), forgetting to subtract unusable space or add attached volumes, and applying a rate without the matching exposure time.