Coal is categorised according to the hazards associated with it. Whenever coal is shipped from any place, the history of the previous shipments must be known, so as to be aware of the hazards of the particular type of coal.
Coal may have any or all of the following hazards:
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Spontaneous heating:
Coal is very liable to spontaneus heating. Freshly mixed coal absorbs oxygen, forming peroxides which break up into carbon monoxide and carbon dioxide. This is an exothermic reaction and the heat produced causes further oxidation and more heat.
Co (carbon monoxide) has a large flammable range (12% to 75%) by volume and besides is also highly toxic. If this heat is not dissipated then spontaneous combustion can occur.
Oxidation depends on the surface area available for absorbtion of oxygen, hence breakage of coal into smaller pieces while it is being loaded is to be prevented.
If conciderable breakage occurs the smaller pieces shall accumulate in the centre of the hold while the larger pieces shall roll to the sides, this action aggravates the situation as the large pieces of coal give way for the air to flow to the smaller pieces where spontaneous combustion is most likely to occur.