The removal of flammable vapors by displacement for cleaning a storage tank can be accomplished...

The removal of flammable vapors by displacement for cleaning a storage tank can be accomplished by displacement with air, inert gas, and water. Water is a common method of displacing flammable vapors from tanks, as it is readily available, inexpensive, and non-reactive with most fuels. Water can be sprayed into the tank to create a water seal that prevents the vapors from escaping and reduces the oxygen concentration in the tank. Water can also be used to rinse the tank walls and remove any residual fuel. However, water displacement may not be suitable for some tanks that contain water-sensitive or water-soluble fuels, or for tanks that have limited drainage or disposal facilities.

References:ust permanent closure requirements - Nevada;A Guide to Safety in Confined Spaces - CDC Stacks;Fire Explosion Prevention – Visual Encyclopedia of Chemical Engineering …