West of England P&I Club issued a Loss Prevention bulletin, regarding fires and explosions, due to aluminium phosphide fumigation. Recently, the Club has experienced several similar incidents in cargo holds, on-board bulk carriers, where aluminium phosphide tablets had been applied to fumigate agricultural products.
Aluminium phosphide tablets are designed to react with moisture in the air and release phosphine (hydrogen phosphide, PH3), a colourless, highly toxic and flammable gas, to kill off any insect infestation in the cargo. As phosphine gas is slightly heavier than air, it will slowly sink down through the cargo filling the hold. Depending on the composition of the fumigant product, the tablets may also release ammonia and carbon dioxide to reduce the potential for ignition of a phosphine gas / air mixture. Pure phosphine gas is odourless; however, where impurities are present, as is usually the case with aluminium phosphide tablets, it may smell of garlic, decaying fish or carbide.
When the tablets have completed releasing phosphine gas, the remaining residue consists of aluminium oxide or aluminium hydroxide, a grey /white powder which, although non-toxic, the dust can present a hazard to health when handling residues. However, it needs to be considered that if the tablets are not fully reacted then there remains the potential for phosphine to be produced.
Problems have been encountered when aluminium phosphide tablets have not been evenly distributed across the cargo either on the surface or sub-surface; instead they have been piled on the cargo surface in a handful of locations, usually when the fumigation is rushed. When aluminium phosphide tablets react with moisture in the air and in the cargo, they produce heat as well as releasing phosphine gas.
When a flammable phosphine / air atmosphere forms, it can be ignited by:
- The presence of an impurity such as diphosphine in the aluminium phosphide tablets, which will spontaneously ignite moist phosphine at ambient temperatures.
- The heat of the reacting tablets or a smouldering cargo fire igniting pure moist phosphine gas (without impurities) which has an auto-ignition temperature of 38˚C.
- The heat of the reacting tablets or a smouldering cargo fire igniting moist phosphine gas (with impurities) which has an auto-ignition temperature of 150˚C.
- Glowing combustion or sparks from a smouldering fire, or flames from a flaming fire, which could ignite phosphine at ambient temperatures.
- Non-intrinsically safe cargo hold lights which have been left switched on.
- Non-intrinsically safe internal re-circulation fans or blowers fitted by the fumigation team.
Recommendations Further information may be found by reading the full report: Source: West of England P&I Club