200901 Fire in palm seed cake cargo

 Fire in palm seed cake cargo
MARS Report 200901

Official report: Adapted from Australian Transport Safety Bureau (ATSB) Transport safety investigation report - Marine occurrence investigation no. 250

A dry bulk carrier was chartered to load a cargo of palm kernel expeller (PKE: see Editor's note, p 19) in bulk from a far eastern port for Australia. Before arrival at the load port, the master received by email the analysis report for the proposed cargo, declaring an oil content of 8.89 per cent and a moisture content of 7.93 per cent.

After consulting the Bulk Cargo (BC) Code, the master determined that the cargo was non-hazardous seed cake and therefore could be carried on board the ship. (The shipper had also provided the master with a certificate similarly stating that the cargo was 'non-hazardous seed cake'.)

Cargoes such as PKE are routinely fumigated en route to their destination port in order to destroy any pests that may be present in, or introduced, to the cargo. The fumigant used on board this vessel was aluminium phosphide, which produces phosphine gas when it reacts with the moisture in the cargo hold atmosphere.

Before the loading was completed a fumigation contractor added fumigant to each cargo hold at a rate of two grams of phosphine per cubic metre of cargo. The plan was to place socks containing aluminium phosphide tablets on the surface of each cargo hold. However, as it was raining at the time, the socks were buried in the cargo in an attempt to protect the fumigant from the rain.

The contractor who carried out the fumigation of the cargo provided the master with documentation that named the fumigant, defined the dosage rate, outlined the fumigation plan and the safety precautions to be followed during the voyage including when the cargo holds were to be ventilated. However, the correct method of application was not properly communicated.
The cargo hold hatch covers and ventilators were then closed. The ventilators were also wrapped in plastic and taped to ensure that the fumigant did not escape.

The day after sailing, the crew observed black smoke coming from no. 3 cargo hold, between the hatch coaming and the hatch cover. The master was informed and he instructed the crew to seal the cargo hold hatch covers with duct tape. He also reported the suspected cargo fire to the ship's manager and charterer.

The manager and the master discussed contingency plans that included diverting the ship to a place of refuge but, under advice from a contracted expert, it was decided to continue the voyage, with the ship sending regular reports of cargo temperatures at varying depths, concentration of carbon monoxide and oxygen for each hold.

The maximum cargo temperature measured was 44°C at a depth of 7.5 m in no. 3 cargo hold. As the temperatures were not increasing significantly, the consultant advised the master that it was safe for the ship to continue its voyage. The authorities at the port of destination were also advised about the suspected fire in the particular cargo hold.

On arrival off the port, an expert and two firefighters boarded the vessel along with the pilot. Observations confirmed the possible existence of a fire and, on berthing, more firefighters boarded the ship and rigged fires hoses. When the no. 3 hatch cover was opened, only two small areas of the cargo's surface, each less than two m in diameter, were smouldering. A small amount of water was sprayed on to each of the smouldering areas and the hold was thoroughly inspected to make sure there were no other hot spots. Soon afterwards, the two pockets of smouldering cargo were removed from the hold with a grab and placed on the wharf. The cargo was then spread out and hosed down to ensure that the smouldering material was extinguished. After the fire was declared extinguished, the ship proceeded to discharge the remainder of the cargo.

Both fire-affected areas had burned in a circular pattern that was centred on the location of a fumigation sock. However, the fires had not grown in size over the ensuing days because, as they developed, they had consumed the available oxygen in the vicinity. It is likely that the amount of oxygen in the cargo hold atmosphere quickly fell to a level that would not support flame (below 15 per cent). The fires then slowly smouldered until the cargo hold hatch covers were opened, when they were extinguished with water.

 

Circular pattern of burned cargo

 

When the fumigation socks were removed from the cargo, many of them were observed to have become charred.

During its reaction the fumigant, aluminium phosphide, releases phosphine gas, heat and diphosphine gas. Localised high concentrations of phosphine and diphosphine gases are likely if the reaction occurs too quickly; if too much fumigant is placed in the packaging; or if the packaging does not allow the gases to escape quickly enough. Furthermore, there will be localised 'hot spots' if the heat produced as a result of the reaction is slow to dissipate. As the socks containing the fumigant were buried in the cargo, the surrounding cargo would have slowed the dissipation of heat from the reacting fumigant tablets.

Pure phosphine gas has an auto-ignition temperature greater than 100°C. However, diphosphine gas has an auto-ignition temperature of about 90 to 100°C. As a result, it is likely that the local temperature rose to a level above the auto-ignition temperature of the diphosphine gas and that the gas subsequently ignited.

Root cause/contributory factors

The fumigation contractor buried the socks containing the fumigant in the cargo in an attempt to protect them from the rain;
The fumigation contractor and ship's crew did not sufficiently consider the risks associated with burying the aluminium phosphide fumigant in the cargo, especially that of heat build-up around each sock and auto-ignition of diphosphine.
Lessons learned

Shipowners, operators, masters and fumigation contractors should consider the safety implications of using aluminium phosphide;
The vessel must be given sufficient information to enable the ship's crew to effectively supervise the application of the aluminium phosphide fumigant.