My bet, arc from the light switch. Most fire codes these days say
propane tanks have to be 10' from the house, even if they are buried


Heck, it should be "ESPECIALLY" if they are buried. Gas has a funny way of
traveling underground and entering basements.

The NFPA calls for 10' for tanks over 125gallons [and under
2001gallons]. My 100gallon tank is adjacent to the house and meets
all codes.

I'm not sure just how big a 125 gallon tank is but I suspect it's the one
that's about 5' high and a little more that 3' in diameter. I have seen
BANKS of them put right outside of restaurants and two put next to a home.

Maybe they use the BANKS just so they can keep them closer in. Once the
fuel truck comes in it's only a little more trouble to fill several tanks
one after the other.