Bob Engelhardt fired this volley in
:

Introduced air in the tank cannot create a bomb condition. A good old
whoosh for sure, but not a bomb. Pure oxygen would have to be added
for
that.

Bob, please take this from someone who knows something about explosive
mixtures -- Approximately any mixture of air and propane that would
create a good blue flame will constitute a mixture that will explode with
force sufficient to fragment the tank.

I'm not guessing or theorizing. I do this for a living -- making
explosives (and machines to make explosives) for stage and film. Propane
is one of our "staple" items. I have experience (deliberately) creating
both flame and explosion effects with propane. The lower and upper
explosive limits of propane/air mixtures are pretty broad. It doesn't
have to be stoichiometric mixture to explode. (acetone is worse... look
it up)

One machine I designed mixes pure oxygen and propane under PLC control to
create "tuned" explosions for noise-making, with differing mixtures for
differing noise levels. Another less expensive system (in terms of
expendables) does the same thing with compressed air. The difference is
one of total acoustic pressure -- oxygen being the more "efficient",
since the entire mass of mixture is explosive, where with air only about
30% of it is (the rest being nitrogen and trace gasses).

You seem to be working from the stance of "it hasn't killed me yet",
which is a fatal flaw in blasters, fireworkers, and stage
pyrotechnicians. We (who still survive) work from the posture of "what I
don't know will kill me."

You're welcome to cut into all the propane tanks you want, and I wish you
no harm when you do. Please don't recommend this practice to others who
might not end up as lucky as you.

LLoyd