Is it safe to use aluminium phosphide tablets to fumigate my stored grain?

Please be very careful here. Aluminium phosphide tablets release phosphine gas, which is highly toxic and is a restricted, hazardous chemical. It is responsible for many accidental and fatal poisonings every year, including from grain stores that were re-entered too soon or sealed homes nearby. For these reasons it is not a do-it-yourself home product. It should only be used by a trained or authorised person, in a properly sealable structure, following the label dose, exposure time, ventilation and safety rules exactly, and with the area kept locked and clearly warned off during fumigation and aeration. Never place tablets loosely in a house store where people sleep or cook, never open the sealed space early, and never reuse the spent residue. For an ordinary farm and home, the far safer route is non-chemical: dry the grain to safe moisture, clean out old grain and cracks, and store in hermetic or airtight bags or sealed bins, which controls insects without any poison. If you genuinely have a large commercial stock that needs fumigation, hire a trained, licensed pest control operator rather than doing it yourself. Confirm the legal and safe options with your agriculture department.