Fumigation
The hazard
Fumigants are highly toxic gases that must stay confined. Typical products: methyl bromide (soil and commodity, heavily restricted), chloropicrin, 1,3-dichloropropene, metam sodium/potassium (soil), sulfuryl fluoride (structural), and metal phosphides (aluminum and magnesium phosphide) that release phosphine gas on contact with moisture. Fumigant labels impose fumigation management plans, buffer zones, posting, monitoring, and strict aeration and clearance procedures.
Sealing, temperature, and dose
The enclosure must be gas-tight; leaks defeat the treatment and endanger neighbors. Temperature and moisture drive speed of action - fumigants move faster and escape faster in warm, porous conditions. Soil fumigation requires proper soil moisture, temperature, and tarping. Structural fumigation requires taping, sealing, locking out occupants, posting, and clearance monitoring before reentry.
Phosphine specifics
Metal phosphide products are restricted-use, react with atmospheric moisture to release phosphine, and are used in gas-tight structures or sealed containers. Phosphine is flammable and can explode at certain concentrations; keep it away from water lines and never allow gas to migrate into occupied spaces. Sulfuryl fluoride is a structural fumigant, not a commodity phosphine substitute.
Traps
Treating an unsealed structure; skipping clearance monitoring; confusing phosphine and sulfuryl fluoride uses; assuming a respirator alone suffices (supplied-air is required for many tasks); ignoring buffer zones and occupied adjacent units.
Rule of thumb: no fumigation begins until the enclosure is sealed, the area is secured and posted, monitoring equipment is calibrated, and the label's plan has been followed.