Chugh, J.C. (1983) Gassiness of coal seams-criteria for categorisation. Journal of Mines, Metals & Fuels, 31 (2). pp. 41-47. ISSN 0022-2755

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Abstract

All the coal seams in underground mines are now statutorily regarded as gassy and have been classified into three categories of gassiness on the basis of either the concentration of methane in the general body of the ventilating air and or on the basis of a relative index derived from statistical records of general body methane concentration and quantity of air flowing at a measurement station, the location of station and the time of measurement are not prescribed either statutorily or otherwise. Gas surveys are required to the carried out in workings of all coal seams according to a prescribed procedure laid down by relevant circulars from D.G.M.S. for placing the coal seam in its appropriate degree of gassiness. Gas surveys in coal mines are being carried out by C.M.R.S. for the past five years or so and in this paper some of the points which have been overlooked for laying down not only the criterion for categorisation but also the procedure for determining the appropriate degree of gassiness of a coal seam have been discussed. One of the most vital points is the variations not only in the quantity of air with time, place person, instruments etc. etc., but also in the general body methane concentration, and the latter could be due to variations in air quantity or in the make or rate of emission of methane with time and points of emission. The above stated variations are because neither are properly trained persons available for not only taking air and or methane measurements at specified stations underground but also for analyzing air samples subsequently in a laboratory nor are properly calibrated or standardized equipment for air and methane measurements or analysis available. The measurements and sampling points are also not properly defined or fixed. Frequency of sampling and measurements and the time interval between subsequent samples or measurements are either not defined or are too long to take care of the variations in concentration of methane. Also precautions which should be taken during the said measurements or samples for ensuring accuracy and consistency of measurements are also not specified. Coal seams in the I degree of gassiness might be recategorised to a higher degree of gassiness on the basis of methane concentration in the samples of gas-air mixtures drawn from shallow (1.5 m deep) boreholes drilled into the coal seam at an active face of a heading or in the adjacent rib pillar, and at uniform spacing of I m between adjacent holes, the boreholes are sealed at their mouths, and the gas-air mixture samples from the boreholes are drawn through a pipe left in the borehole 1 hour and one week after sealing. The above stated procedure for categorization to higher degree is not, in the opinion of the author, correct because the boreholes are too shallow either to cover the full seam thickness of a coal seam thicker than 3 m, and or go far deep into the roof or floor of the seam beyond the already fractured, relaxed and degasified zone. Sealing at the mouth might not be effective, and might get disturbed due to strata movements and or blasting etc. etc. The sampling interval is too large to give a correct5 picture of gassiness. Some of the important sampling locations, and important periods of sampling are not specified statutorily or otherwise. Also coal seams might sometimes be placed into a higher degree of gassiness because of past history of gas emission (occurrence of incidence of ignition explosion in the past, occurrence of gas pockets, blowers, outburst etc. etc.). The author is of the opinion that categorization of coal seams according to gassiness on the basis of the said indices is not appropriate, and too general to meet effectively the long-term requirements of safety, production, planning etc. etc. Determination of such parameters as indicates propensities of ignition/explosion hazards (like the layering number and/or the layering index with normal and disturbed ventilation) in a mine or district or indices like residual (total) gas contents of coal samples, or total gas contents of coal samples drawn from different depths along deep boreholes (10 to 20 m) as is done in some of the countries abroad (France, W. Germany, Poland, U.S.S.R and U.S.A.) might be more relevant and appropriate for purposes of categorization of coal seams according to gassiness.

Item Type:	Article
Subjects:	Thick Seam Mining
Divisions:	UNSPECIFIED
Depositing User:	Dr. Satyendra Kumar Singh
Date Deposited:	04 May 2012 10:43
Last Modified:	04 May 2012 10:43
URI:	http://cimfr.csircentral.net/id/eprint/1120

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