Before introducing hydrocarbons (CH4 Methane) in a system (vessels, drums, pipe lines) it's mandatory to free the system from oxygen before introducing the gas.
For this purpose Nitrogen is used, High accuracy LEL (lower explosivity limit) & oxygen meters are used to monitor oxygen value at the outlet of system which is being flushed with nitrogen,
In the same way before opening the cover of a vessel it is mandatory to free the system from hydrocarbons before introducing the air in the system.
Otherwise explosion can occur at any time.
Gas quality may an issue, as our country is facing energy crices, our gas distribution companies are not providing the gas as per agreed BTU value, they are only providing gas volumes.
There are many distribution networks, every network may have different BTU value gas .