Section 143(2) in The Coal Mines Regulations, 2017
(2)For the purposes of this regulation, a place shall not be deemed to be in a harmless state for person to work or pass or remain therein if the eight hours time-weighted average concentration of airborne respirable dust in milligrams per cubic meter of air sampled by dust sampler of a type approved by and determined in accordance with the procedure as specified by the Chief Inspector by a general or special order, exceeds two, where working is being made wholly in a coal seam or where free respirable silica present is less than five per cent. and the value arrived at by dividing the figures of ten with the percentage of free respirable silica present in other cases.
