Explosions aboard bulkers loaded at Grande Do Sul, Brazil, are believed to have involved phosphine fumigants, warns the North of England P&I club, Nepia. Those vessels undergoing fumigation at Rio Grande Do Sul should contact the local agents or P&I correspondents for advice on the current situation with respect to fumigants.
Most incidents involving phosphine tablets, colloquially known in Latin America as ‘tablets of love‘,
One potential cause of a phosphine fumigant explosion may be contaminated tablets of aluminium phosphide or similar fumigants. Tablets react with moisture to produce phosphine gas, PH3, which has an autoignition temperature of 38 Celsius However, the presence of impurities, particularly diphosphine, often causes PH3 gas to ignite spontaneously at room temperature and to form explosive mixtures at concentrations greater than 1.8% by volume in air. The spontaneous ignition behaviour of PH 3 gas is very unpredictable.
Investigations into the bulkers covered by Nepia are yet to be published but a comparable incident occurred in 2012 involving the bulk carrier Theofylaktos. In that case high humidity led to a larger evolution of gas, the temperature above the cargo reached the autignition temperature of phosphine which was made worse by the close proximity of the tablets to each other, the uneven distribution of the tablets and the location of the suction pipe which was supposed to distribute the gas evenly prevent it from doing so effectively given the high production of phosphine.
Podcast: The Tablets of Love