Section 126(2)(c) in The Indian Electricity Rules, 1956
(c)all apparatus, including portable and transportable apparatus used at any place within 90 metres of any working face or goaf in case of a second degree gassymine and within 270 metres of any working face or goaf in case of third degree gassymine or at any place which lies in-bye of the last ventilation connection or in any return airways shall be flame-proof;