Section 144(4) in The Coal Mines Regulations, 2017
(4)The incombustible dust used for the purpose of sub-regulation (3) shall be-(a)such that it does not contain more than 5 per cent. of free silica;(b)of such fineness and character, that it is readily dispersible into the air and that, when used in places which are not directly wetted by water from the strata, it does not cake but it is dispersed into the air, when blown upon with mouth or by a suitable appliance; and(c)as far as practicable light in colour.
