Are you aware of fumigation?
Fumigation is is a method of pest control that completely fills an area with gaseous pesticides or fumigants to suffocate or poison the pests within. There are different method to fumigate. The US Gulf ports prefers the use of gas pellets (Aluminum Phosphide), are distributed/scattered uniformly on top of the leveled stow of bulk grains by private companies which are certified applicators.
Process involved in Fumigation:
- Gas pellets are placed on the surface
- The pellets will react with atmospheric moisture and dissolve over time creating phosphine gas
- Initially there is a rapid buildup of gas in the void space on top of the cargo
- The reaction process generates heat as the pellets dissolve.
- The speed of the reaction increases depending on higher temperatures and/or relative humidity of the air locked inside the void space.
- All that is left after the pellets are converted into gas is a gray-white powdery ash.
How does it explode?
Aluminum phosphide is not flammable by itself. When aluminum phosphide is wet through contact with moisture in the air or water, hydrogen phosphide gas will be created. This gas can ignite spontaneously in air at concentrations above its lower flammable limit. Ignition of a high concentration of phosphine gas can result in explosions.
What will be the severity of explosion?
- The steel hatch covers can get lifted up out of their sealed position, resulting in deformed hatch panels, torn off cleats, etc..
- Vessels can be damaged so hard that it has to discharge its cargo at the load port in order to carry out required repairs prior to being allowed to reload their grain cargoes.
Why does such explosions occur?
Investigations reveal that the reason was uneven distribution of the gas pellets on top of the bulk stow. It was ascertained that the gas pellets had been piled in small heaps along the inside of the hatch coaming square. The piling of the pellets resulted in a concentrated/accelerated release of phosphine gas which filled the void space to the point that it reached its lower flammable limit and spontaneously combusted / exploded.
Lesson Learnt:
- The crew must have a watchful eye on the cargo holds which are being fumigated
- The gas pellets must be evenly distributed / scattered across the top of the stow
- The gas pellets must not be dumped in large piles
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Source: Skuld
