Loss Prevention Bulletin Aluminium Phosphide Fumigation – Fires and Explosions

Recently the Club has experienced several fires and explosions in cargo holds on-board bulk carriers where aluminium phosphide tablets had been applied to fumigate agricultural products.

Fumigation using Aluminium Fires and Explosions caused by the cargo surface, water ingress via PhosphideTablets Aluminium Phosphide Tablets nonweathertight hatch covers or from ship or cargo sweat can substantially Aluminium phosphide tablets are Problems have been encountered hasten the reaction of the tablets, designed to react with moisture in the when aluminium phosphide tablets increasing the rate at which heat and air and release phosphine (hydrogen have not been evenly distributed phosphine gas are produced still phosphide, PH3), a colourless, highly across the cargo either on the surface further. The heat produced by a pile of toxic and flammable gas, to kill off or sub-surface; instead they have been reacting aluminium phosphide tables, any insect infestation in the cargo. As piled on the cargo surface in a handful particularly in the presence of free phosphine gas is slightly heavier than of locations, usually Aluminium water, can in some cases be sufficient air it will slowly sink down through Phosphide Fumigation – Fires and to start a smouldering cargo fire. the cargo filling the hold. Depending Explosions when the fumigation is The heat from reacting tablets or the on the composition of the fumigant rushed. When aluminium phosphide presence of a smouldering cargo fire product the tablets may also release tablets react with moisture in the can ignite a flammable phosphine / air ammonia and carbon dioxide to air and in the cargo, they produce atmosphere in a cargo hold. reduce the potential for ignition of heat as well as releasing phosphine a phosphine gas / air mixture. Pure gas. Clusters of fumigant tablets Phosphine gas has a Lower Explosive phosphine gas is odourless; however, can result in localised elevated Limit (LEL) in air of 1.8%, (the Upper where impurities are present, as concentrations of phosphine and Explosive Limit (UEL) has not been is usually the case with aluminium high temperatures, increasing the determined.) phosphide tablets, it may smell potential for the ignition of cargo and of garlic, decaying fish or carbide. the formation of a flammable mixture When the tablets have completed of phosphine and air. The presence of releasing phosphine gas the remaining free water, such as from rain lying on residue consists of aluminium oxide or aluminium hydroxide, a grey /white powder which, although non-toxic, the dust can present a hazard to health when handling residues. However, it needs to be considered that if the tablets are not fully reacted then there remains the potential for phosphine to be produced. Loss Prevention Bulletin

Where tablets are grouped together Aluminium phosphide fumigant tablets there is a greater likelihood of the will usually start reacting 2 to 4 hours atmosphere near the tablets being after being set. The generation of flammable due to the quantity of phosphine gas can typically continue phosphine gas produced. When a for between 48 and 72 hours. Although flammable phosphine / air atmosphere most fumigant explosions occur within forms, it can be ignited by: 24 hours of the tablets being set, there have been occasions when explosions The presence of an impurity such have occurred several days after as diphosphine in the aluminium fumigation commenced. phosphide tablets, which will spontaneously ignite moist Where the cargo grains have an phosphine at ambient temperatures. excessive moisture content or have The heat of the reacting tablets or been wetted, they will expand, clump a smouldering cargo fire igniting together and restrict the migration of pure moist phosphine gas (without the phosphine gas through the cargo, impurities) which has an auto- possibly concentrating the gas in the ignition temperature of 38˚C. upper reaches of the stow and in the headspace between the cargo and The heat of the reacting tablets or a the hatch covers. Such a restriction on smouldering cargo fire igniting moist the movement of phosphine gas may phosphine gas (with impurities) increase the probability of a flammable which has an auto-ignition phosphine / air mixture forming. temperature of 150˚C. The size of any explosion will depend Glowing combustion or sparks from on the quantity of flammable gas a smouldering fire, or flames from ignited; in some cases, the explosion a flaming fire, which could ignite of a phosphine gas / air mixture has phosphine at ambient temperatures. been of sufficient force to cause Non-intrinsically safe cargo hold lights access hatches or hatch covers to be which have been left switched on. blown upwards and displaced whilst Non-intrinsically safe internal re- hatch cleats, hatch coamings and circulation fans or blowers fitted by the hatch covers have been severely the fumigation team. damaged, presenting the potential Explosions because of aluminium risk of serious injury to personnel and phosphide tablets having been delays to the voyage. The passage incorrectly set may not only be of the flame through the flammable caused by the ignition of a flammable atmosphere within the hold can also phosphine gas / air mixture. There cause blackening of the surface of the have been cases where smouldering cargo and the steel structures within cargo fires have been started by the cargo space. piles of aluminium phosphide tables creating considerable heat when reacting with moisture. A smouldering fire can cause thermal decomposition of the agricultural product producing a flammable combustion product Loss Prevention Bulletin

Precautionary Measures Vessels should be provided with gas detection equipment, instructions The fumigator’s written instructions for its use and adequate spare concerning the use of the fumigant parts to enable the measurement of product and the conduct of the concentrations of phosphine gas. An fumigation after their departure from infrared handheld thermometer can the vessel must be followed precisely. also be useful for checking for hot The guidance contained in the spots on suspect hold steelwork. Material Safety Data Sheets (MSDS) In addition, at least four sets of suitable for the tablets and their residue must respiratory protective equipment be left with the vessel and must be should be available onboard. reviewed and understood. If cargo hold fire alarms are activated, It will be seen from the foregoing smoke / vapour (considering that guidance that problems with phosphine gas is colourless) is seen aluminium phosphide tablets can issuing from hold openings, or if hatch arise when they are not spread evenly covers, coamings or the main deck in cargo holds, instead being placed in way of the holds are found to be in piles on the cargo surface. The warmer than normal, then the cause problem is further exacerbated by of the problem must be investigated the presence of free water in contact whilst always taking all necessary with the tablets. Therefore, tablets safety precautions. Where smoke should be evenly spread over the tube fire alarms are fitted, it needs to surface of the cargo or evenly placed be considered that the system will be sub-surface; the tablets should not be continuously drawing phosphine gas heaped together in one or a handful from the holds and venting this outside of locations. When the tablets are the accommodation superstructure, evenly spread, there is less likelihood therefore the risk of using the system of excessive heat being generated should be fully evaluated prior to and it is unlikely that sufficient fumigation commencing. phosphine gas to form a flammable atmosphere with the air in the hold will If problems develop it is recommended be produced. Piles of tablets usually that expert advice be sought at the / air mixture which is subsequently occur when the fumigation operation earliest opportunity as some actions, ignited by the smouldering fire, is rushed by the fumigators; therefore, such as opening a hold access hatch, causing what is known as a “smoke where practicable, it must be ensured may cause the situation to deteriorate. explosion”. The introduction of fresh that the fumigators are reminded to In the event of a problem, it is air into what might be an oxygen take their time to properly distribute recommended that, where possible, deficient environment in the closed the required number of tablets over gas monitoring for oxygen, carbon hold, by opening an access hatch or in the cargo, and that clusters of monoxide and flammable gases (% or vent, can feed the fire and allow tablets are not set. LEL) is conducted on the problematic for the formation of a flammable hold using a suitably calibrated gas atmosphere. detector to support the expert with their provision of assistance. Loss Prevention Bulletin

As noted earlier, the presence of If it is necessary for crewmembers to The long-term exposure limit (8-hour free water in contact with aluminium handle the residue of spent aluminium Time Weighted Average (TWA)) for phosphide tablets will speed up the phosphide tablets; then the fumigator’s phosphine is 0.1 ppm (parts per million) reaction causing higher temperatures instructions in this regard should be / 0.14 mg/m3 and the short-term and the production of more phosphine followed as well as the guidance exposure limit (15 minute TWA) is 0.2 gas, heightening the possibility of a contained in the MSDS for the spent ppm / 0.28 mg/m3, the corresponding flammable atmosphere being formed product. Appropriate safety measures figures for hydrogen sulphide are 5 ppm in the hold. The cargo surface must should be followed and personal / 7 mg/m3 and 10 ppm / 14 mg/m3. therefore be kept dry, protected from protective equipment, which will The “Recommendations on the Safe precipitation during loading and, it usually be cloth gloves and a dust use of Pesticides in Ships Applicable should be considered that sweat may mask, should be worn. to the Fumigation of Cargo Holds”, form on the cargo or on hold steelwork It must also be noted that when contained in MSC.1/Circ.1264 and while the holds are sealed whilst aluminium phosphide residues are MSC.1/Circ.1396 (Amendment) fumigation is in progress. collected and stored together, they should also be followed by all vessels It must also be ensured that the vessel may spontaneously ignite due to the undertaking the fumigation is cargoworthy, with weathertight hatch presence of unspent chemical. of cargo holds. covers, vents and access hatches, to The toxicity of phosphine gas must Members requiring any further prevent water ingress into the holds. As never be underestimated; it is guidance or advice on this topic an additional precautionary measure to worthwhile considering the Workplace should contact the Loss Prevention reduce the potential for moisture laden Exposure Limits (WEL) for phosphine department. air to enter the hold, Ram-nek tape or compared to another well-known toxic expanding foam can be added to hatch The Club would like to thank gas, hydrogen sulphide. cover joints although the creation of Burgoynes for assisting with the a fully airtight hold could potentially preparation of this Bulletin. present problems of overpressure or a vacuum forming in the hold because of temperature changes.

The West of England Ship Owners Mutual Insurance Association (Luxembourg)

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