§ 35. Mr. DAVID DAVIESasked the Secretary for Mines the number of samples taken of coal dust during 1932 and 1933, in each of the inspectorate divisions, giving results of the content of incombustible matter and the content of matter injurious to mine workers?
§ Mr. E. BROWNDuring the year 1932, 3,864 samples of the dust on underground roadways in coal mines were taken by the inspectors, and 87 per cent. of these samples were found on analysis to contain 50 per cent. or more of incombustible matter. Details for each of the inspection divisions will be found on page 73 of the Annual Report of the Chief Inspector. The corresponding figures for 1933 are not yet available. The measures taken to prevent the use of stone dust which would be injurious to health are based on a consideration of the character of the stone dust itself rather than of the mixed dusts on the roadways and no general statistical information on this point is available.
§ 38. Mr. BANFIELD (for Mr. DAGGAR)asked the Secretary for Mines whether he can state the amount of coal dust, minimum and maximum, per cubic foot of air space, necessary to propagate an explosion in a mine?
§ Mr. E. BROWNThe amounts vary considerably with the character of the coal and the fineness of the coal dust. The finest dusts of the most inflammable coals are the most explosive and the least quantity that will propagate flame, when raised in a cloud under experimental conditions, is rather less than one tenth of an ounce per cubic foot of air. The greatest quantity is difficult to determine, but explosions have been produced experimentally with as much as two ounces of such coal dust per cubic foot of air.