TT Talk - Fumigation risks in containerised and bulk cargoes
The Hazworld.com website recently carried an article on the problems that can arise when cargoes are fumigated. Readers with good memories may remember that TT Talk addressed this issue in Editions 17 and 19, published in January and March 2002 respectively. The Hazworld article was prompted by a circular issued by the TT Club's sister club, the UK Pandi Club, following a survey of containers that had recently been carried out in Rotterdam.
The Hazworld article reads:
Fumigation risks in containerised and bulk cargoes
China's recent enactment of a law requiring the fumigation of all wooden packaging used in shipments to the country is another indication of the increasing prevalence of this cargo treatment practice. Yet fumigation poses risks that are easily underestimated. The UK P&I Club has advised its shipowner and operator members to ensure that adequate warnings are posted on containers under fumigation and that proper procedures are followed when entering such units. As experience has shown, contact with residual fumigants can lead to permanent disability, severe injury or even death.
The Club issued its warning following a recent survey in Rotterdam which found that 21 per cent of 300 containers chosen at random for inspection contained methyl bromide, formaldehyde or phosphine. Only three units displayed the required "Under Fumigation" warning label. Fumigants are typically used to protect foodstuffs from rodents, insects, mould and fungi. Of nine leading fumigants, the three most commonly used in containers are phosphine, sulphuryl fluoride and methyl bromide. Phosphine is readily absorbed by inhalation and through the gastrointestinal tract. At low levels of inhalation, symptoms include headache, weakness, faintness and pains in the chest. At high levels, nausea, vomiting and pulmonary oedema can occur. Contact with methyl bromide through inhalation and absorption through the skin can cause damage to the brain, nervous system, skin, lungs and possibly kidneys.
While the high toxicity of phosphine gas has long been recognised, its flammability risk is not widely appreciated. Its lower flammability limit is only 1.8 per cent by volume in air. If an air/phosphine mixture in which the phosphine concentration exceeds this limit is ignited in a confined space, it is highly probable that an explosion will occur.
Phosphine gas is generated from aluminium phosphide tablets when the aluminium phosphide reacts with moisture in the air. This process, in addition to liberating phosphine, produces aluminium oxide as a byproduct and, occasionally, small quantities of diphosphine gas. Unlike phosphine, diphosphine is spontaneously combustible. Diphosphine is more likely to be generated if the aluminium phosphide tablets contain amounts of phosphorous in excess of that specified in an acceptable formulation. Aluminium phosphide tablets are routinely used in fumigation and a very large number of shipments are fumigated annually without any problems. It appears that fumigant explosions have only occurred when cheaper brands of aluminium phosphide tablets produced in developing countries were used.