Section 64(4)(e) in The Indian Electricity Rules, 1956
(e)Where a sub-station or a switch-station with apparatus having more than 2000 litres of oil is installed, whether indoor or out-doors, the following measures shall be taken, namely:-(i)The baffle walls [of 4 hour fire rating][shall be provided between the apparatus in the following cases:- [Substituted by G.S.R. 843, dated 23.7.1985 (w.e.f. 7.9.1985). ](A)single phase banks in the switch-yards of generating stations and sub-stations;(B)on the consumer premises;(C)where adequate clearance between the units is not available.(ii)Provisions shall be made for suitable oil soakpit and where use of more than 9000 litres of oil in any one oil tank, receptacle or chamber is involved, provision shall be made for the draining away or removal of any oil which may leak or escape from the tanks, receptacles or chambers containing the same, special precautions shall be taken to prevent the spread of any fire resulting from the ignition of the oil from any cause and adequate provision shall be made for extinguishing any fire which may occur. Spare oil shall not be stored in any such sub-station or switch-station.(iii)[ All the transformers and switchgears shall be maintained in accordance with the maintenance schedule given in the relevant Code of Practices of BIS and the authorised person shall keep a record thereof as required under rule 3(6).(iv)Notwithstanding anything contained in rule 64(2)(d) and rule 64(2)(f)(ii), only dry type of transformers shall be used for installations inside the residential/commercial buildings.]