Section 161(4) in The Coal Mines Regulations, 2011
(4)Every connection between a main intake airway and a main return airway shall until it is no more required and has been sealed off, be provided with at least two doors so spaced that whenever one door is opened, the other door can be kept closed and steps shall be taken to ensure that at least one of the doors is always closed.Provided that any such connection which is no more required shall be effectively sealed;
