Peter,
Acetylene has a much higher rate of dissipation in air, so leaked acetylene tends to quickly spread out within a given air space, and it takes a good deal of initial leak before you reach an explosive mix at all.
Acetylene is definitely less dense than propane and in fact is close
to the density of air, but unless there is air movement in the
studio, caused by good ventilation, both acetylene and propane will
tend to hang around in that room as they really have no place to
dissipate to. True, the propane will want to accumulate near the
floor, but the rate of dissipation is really controlled by
ventilation rather than by a property of the propane or the acetylene
itself. Also, propane will not plummet to the floor instantly as if
it was a solid poured out of a bottle. It is a gas and will float
around the room with a tendency to pool on the floor but at any given
time there will be some concentration of propane on the floor, a
lower concentration of propane in the middle of the room and maybe an
even lower concentration of propane floating up around the ceiling. I
am about 5"10" tall. When there is a propane leak near the floor of a
room, I can always smell it standing up ie over 5 feet above the leak
near floor level.
My totally unverified intuition would be that the most dangerous situations would be where there is already a pretty steady source of ignition, and all that's needed is for the gas to reach the lower level before things go boom. If it hasn't ignited yet at 10 percent, why would it somehow be more likely to ignite at 50 percent, for example.
The more gas that has accumulated prior to being ignited, the bigger
the explosion. Therefore, having a source of ignition close to your
gas leak can actually be a good thing as the gas will reach the
ignition source prior to accumulating significantly in your studio
and flash off and potentially cause a fire rather than an explosion.
The worst explosions typically occur when a gas has been leaking for
a long time and does not find a source of ignition. So the gas sits
there and waits until you come into your studio and flip on a light
switch.
I can't say I'm all that concerned with the fact that acetylene remains explosive through a higher concentration range than propane.
I have to disagree with you here. If you released an amount of
propane into a poorly ventilated room and an equal amount of
acetylene into another identical poorly ventilated room and then
provided each room with an ignition source, the room with the
acetylene will have a higher chance of experiencing an explosion
simply because it has much a higher explosive range.
Propane tanks, while also usually well made, are generally lower priced, and mass marketed. That might suggest a greater chance of manufacturing defects. Plus, they're engineered with an overpressure release mechanism in the valve that can actually intentionally let gas out if the tank gets warm.
A propane BBQ tank should never ever be placed inside a home or a
studio, for the exact reason you describe. If they are overfilled at
the gas station, they will later overpressure as they warm up in the
studio and the relief valve will do what it is supposed to do, and
that is open up and release a substantial amount of propane into
your studio. The only propane tank I would ever bring indoors is the
small 1 pound disposable bottle. The relief valve on this bottle
will probably never open as the bottle is filled carefully under
controlled conditions. In addition, if the valve does open up, the
most it could ever release is the 1 pond of propane in the bottle.
Less leaked gas means less fuel means a smaller fire or explosion.
To avoid problems, you have to pay attention to your procedures, the maintenance of your equipment and the tanks, and to making sure you're working safely
I agree with you completely on this point!
Regards
Milt Fischbein