Graham's Ratio
In any Under ground coal mine,even at normal temperature some oxidation of coal takes place.In this process,some O2 is consumed and CO is produced.The ratio CO produced/O2 consumed,known as Graham's Ratio or Graham's Index,for a mine remains more or less constant.If spontaneous heating occurs there is steady rise of the ratio with increase of temperature.The ratio can,therefore be used as a guide to detect heating. Regulation prescribe that the return air of every depillaring distt.Shall be analysed at least once in every 30days to determine the Graham's Ratio.If successive tests show steady increase in the ratio,steps shall be taken to determine the site of heating and to deal with it. Incubation period : This is the period between the time when coal is first subjected to condition favourable for heating develop when the first Major roof fall occurs, because fallen/Crushed coal starts heating but the heat does not escape as coal...