Section 144(3)(a) in The Coal Mines Regulations, 2017
(a)with fine incombustible dust in such manner and at such intervals as will ensure that the dust on the floor, roof and sides and any support or structure shall always consist of a mixture containing not less than 75 per cent. of incombustible matter in case of coal seams containing less than 30 per cent. volatile matter (on dry ash free basis) and 85 per cent. of incombustible matter in case of coal seam containing more than 30 per cent. of such volatile matter; or