The biggest problem with propane is that it is heavier than air.
If it leaks it will fill up basements, floor drains and any other low spots. That means a pool of propane gas sitting there waiting to be lit.
That is one reason why it must not be inside any structure or even near basement windows.
Tho other reason is that you don't want exploding propane tanks if there is a fire in your house.
(Natural gas is lighter than air and just floats away, but you still don't want it inside a building.
EDIT: If you google natural gas and propane gas explosions you will see why.)


The reasons they dont apply that to one pound cannisters is that they don't figure a pound of propane is enough to do any harm, and it would be impossible to enforce anyhow.

I don't know what the leaky small propane canister problem is from except cheap manufacturers.