A bulk carrier had loaded yellow corn in all cargo holds up to the hatch coamings. After the loading, fumigation technicians came on board and fumigated the cargo with fumitoxin pellets.
According to the cargo documentation, the fumigation pellets needed to be applied subsurface. In this case the technicians poured the pellets from flasks while walking on the hatch coamings or hatch covers. This work took a little more than an hour and after that all the cargo hatches were closed and the vessel sailed.
A couple of hours later an explosion took place in one of the holds. The crew saw that the hatch covers had moved slightly and blue gray smoke was coming from under the edges. About an hour later another explosion occurred in a second hold, and a couple of minutes later a third explosion happened. There were explosions in the remaining holds shortly afterwards.
According to the Swedish Club, the fumigant pellets in each hold had not been distributed across the entire cargo surface, or applied to the subsurface. They had been applied by simply pouring the pellets on top of the cargo.
This method of application had allowed the gathering of the pellets in limited areas and promoted a relatively rapid reaction of the pellets with moisture, leading to concentrations of phosphine gas over the lower flammable limit, which caused the explosions.
After the incident, the following lessons are to be learned:
- Fumitoxin pellets and similar fumigants are made up of around 55% aluminium phosphide which reacts with water to produce phosphine, an extremely toxic and effective fumigant. Phosphine gas will form an explosive mixture when mixed with air at a concentration exceeding around 1.8% to 2% by volume (the lower flammable limit). The concentration of phosphine in the air in each of the holds exceeded this lower flammable limit;
- The manager should ensure that the crew is aware of the requirements and procedures for the fumigation operation and the crew need to ensure that the fumigation pellets are distributed as per the cargo documents.