Alma, the answer to what size fuel tank is legal indoors depends upon
the laws of each state. The state in which you and I reside
prohibits all but the disposable size propane canister indoors but
allows much larger acetylene tanks.
As to the actual volatility of propane, my fire marshall and fuel gas
dealer, (poor men, I grilled them mercilessly) stated that leaked
propane does lay in low pockets and any tiny spark (phone, motors or
any other source of ignition) could quickly separate my body and soul.
If we use and store larger, illegal propane tanks indoors we are in
violation of state fire codes and in doing so, are pretty much
assure the voiding of our home- owners’ insurance in the case of
fire or explosion.
Large tanks of propane are not a problem ONLY if the gas is piped
into the building and are inspected and certified.
Kinda made me think…and be a VERY careful person!