Section 148(2) in The Coal Mines Regulations, 2011
(2)Every return airway as lies within two hundred metres of the last working face and every haulage, tramming or conveyor roadway which is not naturally wet throughout, sha11 be divided into zones not longer than one hundred and fifty metres each:Provided that where in a mine some parts are being treated with water and others with incombustible dust, the zones shall be so formed that in each zone only one system of treating coal dust is being followed.
