Prevention of Spontaneous Combustion on board

Marine Operations Prevention of Spontaneous Combustion on board

By Captain Delson Roche

In the 3rd Century AD, the Chinese philosopher Chang Hua in a book called ‘Record of the Investigation of Things’ narrates about stored oil being ignited spontaneously, setting fire to an arsenal belonging to Emperor Wu. In 1834, the ship ‘Earl of Eldon’, which had loaded cotton in Bombay, caught fire due to the spontaneous combustion of her cotton cargo, resulting in the loss of the vessel.

Painting of ‘Earl of Eldon’ on fire, after her cotton cargo spontaneously caught fire. Vessel Roxburgh Castle is rescuing the crew. Source: Wikimedia commons Spontaneous combustion is not a new observation- written history has records of things spontaneously catching fire. On board a vessel today, both oil and cotton are commonly found mixed, especially in the form of oily rags. Both these substances, as exemplified earlier, have a notorious history of spontaneously catching fire; most of us are aware of this. It is our responsibility on board the ship to eliminate the potential for spontaneous ignition by taking all the necessary safety precautions and through proper housekeeping. So, why does spontaneous combustion occur? Chemically, fire is - any substance trying to bond itself with oxygen, in a process called ‘oxidation’, which is followed by liberation of heat. Different substances oxidise at different temperatures. The substances that spontaneously combust, have a low oxidation temperature. Let us look into some of the instances on board that can cause spontaneous combustion. Seed oils: Other than fuel soaked rags, lesser known, but much more susceptible to combustion are rags soaked in linseed oil. Linseed oil is frequently used these days - linseed oil soaked brushes are used to coat the warping drums of winches and wood on embarkation ladders, and rags are used to clean the work area – so brushes and rags in contact with this oil need to be handled carefully. ISGOTT recommends stowing any linseed oil-soaked rags and paper in waterfilled metal cans until they can be disposed of. The same is the issue with lard soaked rags; lard is used in some vessels for greasing of wires. In either case, oil or lard-soaked rags should be stored in fully closed containers, which ensures that no oxygen is available for combustion. Sawdust: Sawdust is one of the most effective means of cleaning up oil spills on deck. ISGOTT has now recommended avoiding using sawdust on board because moist sawdust is susceptible to spontaneous combustion. If any sawdust is used to clean up spills, then ISGOTT recommends storing it in airtight drums, away from the hazardous areas. The same procedure should be followed for oilsoaked granules and adsorbent pads. Galley aprons and towels: In recent years, there have been incidents of fire when freshly laundered clothes have caught fire! In all instances, the oil-stained clothes were washed and then dried in the tumble drier. The clothes were then immediately folded and kept in storage. A few hours later smoke was noticed coming from the storage area. Investigations have determined the fire to be caused by spontaneous combustion of the oil-soaked clothes, triggered by the heat of the laundry drier. Fool’s gold: Those on tankers know it as ‘Pyrophoric Oxidation’. Rust on the tank bulkheads reacts with the sulphur in hydrogen sulphide, commonly found in many crude oils. This results in the formation of various types of iron sulphides, one of which is called pyrite or fool’s gold. The compound has a brass or gold-like colour when it occurs naturally and has fooled people into thinking that they have discovered gold. On tankers, though, this could be deadly because iron sulphides in the presence of oxygen can self-ignite and become red hot incandescent. This is one of the reasons why crude oil ships cannot discharge cargo if there is no inert gas available.

Iron Sulphide or fool’s gold- In a ship’s cargo tank, iron sulphide can glow red hot in the ‘Pyrophoric Oxidation’ process. Source: Wikimedia

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Coal: Certain coals can ignite spontaneously when exposed to oxygen. Why this happens is not well understood and there are many theories behind it. However, before ignition, coal starts to heat up and gives off carbon monoxide (CO). It is for this reason that it is important to monitor CO levels and the temperature of the cargo hold, whenever coal is carried. Soybean: Soybean is covered with a layer of mould, which is usually in a dormant stage. However, in the presence of the right amount of moisture and the right temperature, this mould can become active and start to grow. This increased mould activity causes heat generation, consequently leading to burnt soybean and cargo damage. This problem usually occurs in vessels engaged in the South America to China run, where the long voyage provides sufficient time for mould to grow. Hence, it is important to verify moisture content in soybean before loading and keep a close watch for signs of burn marks on the soybean being loaded.

Soybean being fumigated- the fumigation is performed to avoid insect infestation and does not prevent the mould from developing.

Boiler chemicals: ISGOTT cautions us that some of the oxidising chemicals used for boiler water treatment have the potential to spontaneously catch fire. Hence, it is important to keep the chemicals in their original container and have the cap closed at all times except while they are being used. There are many other products which can spontaneously combust but these are not found in sufficient quantity on board to be of concern. Some interesting ones, which are not chemicals are pistachio nuts, milk powder, hay, sugarcane bagasse, oil cakes and human beings - the last one, though, has mainly been reported in stories.