Section 146(2) in The Coal Mines Regulations, 2011
(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 8 hours time-weighted average concentration of airborne respirable dust in milligrams per cubic metre 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 seam or where free respirable silica present is less than 5 percent and the value is arrived at by dividing the figures of ten with the percentage of free respirable silica present in other cases; or
