Section 7 in The Static And Mobile Pressure Vessels (Unfired) Rules, 1981
7. Purging of pressure vessels used for flammable gases .-(1) Before using any new vessel or before the refilling of any existing vessel which has been made gas-free, air contained therein shall be purged by an inert gas or by the gas for which the vessel is to be used.
(2)If the vessel is purged by means of a flammable gas, the flammable mixture so formed shall be vented from the vessel only after taking adequate precautions to prevent its ignition.
