Road and workshop
Page 44
If you've noticed an error in this article please click here to report it so we can fix it.
Combustibles and spontaneous heating
Safe and unsafe storage (3)
by Handyman
• Quite often one finds a corner of a transport warehouse or transit shed reserved for damaged goods—one or more claims may be pending—and often a mixed assortment of goods, scarred, bent or leaking may be held in "limbo" until settlement is agreed.
I remember such a corner where a fire started for no apparent reason. Then a visiting fire officer asked to see an inventory. The c,lairris list showed that one of the earlier bent and very wet 40gal drums had contained an incomplete or reactive oil; what had happened was that in contact with other material it began to heat up, ending in ignition.
Of the many oils that are used today, animal and vegetable oils are mostly incomplete chemically, therefore on exposure to air they are liable to oxidation; also they can absorb other substances if placed in contact with them and a reaction can set in that generates heat. Drying oils and semi-drying oils come within this category. Where such an oil is brought into contact With rag, cotton waste, Hessian, etc, and spread over a wide area of the material, a reaction will begin that can raise the temperature enough to cause spontaneous combustion.
Where the same oil is spilled over a non-porous, non-fibrous surface the heat generated from contact with air is rapidly dispersed through the surface and there is no risk of combustion.
Chemical compounds known simply as driers which are prepared for the purpose of speeding up the drying and hardening of paint are transported and stored in quite large quantities. The drier considerably speeds up the oxidation of an unsaturated oil, thus the oil that contains a drier has a much greater spontaneous heating potential than the straight oil.
The critical features of vegetable and animal oils are usually expressed by a measurement known as the iodine value this simply means the amount of iodine that can combine with a given amount of oil and only indicates the tendency of an oil to spontaneous heating; it does not necessarily give a figure for safe and unsafe, as factors such as spillage, air pressure or temperature, contact with other materials, all have a bearing on the reaction. However, for those concerned with movement and storage I will list common oils in use, their top iodine value, and place them in order of high risk first: Linseed oil 204, cod liver 181 tung 175, cotton seed 115, castor 86, olive 94 and palm 84.
While it is true to say that below 75 there is little risk, care should still be taken to store safely and sensibly. Avoid stacking baled or bagged materials on top of a layer of drums full of the above oils, as saturation of the sack material could generate heat.