I've been waiting for someone to identify the "gray spongy stuff"
that fills nearly 100% of the interior of an acetylene cylinder,
but since no one has, I thought I'd throw this in.....
My first "real" job was as a traveling salesman for Selpac SE,
selling Sherwood high pressure compressed gas valves; (oxygen,
nitrogen, argon, nitrous oxide, etc,) as well as propane and
acetylene valves. I sold primarily to the welding industry in the
SE, USA. If you check the valves on your tanks you stand a better
than a 50/50 chance of having a Sherwood valve on one of them.
One of our accounts, Union Carbide, was a major acetylene
manufacturer/filler. Right after I was hired on, my boss took me way
back to the back of one of the Union Carbide plants for an
education from an OLD-timer that he knew. The old fellow began his
lecture by telling me that the gas is manufactured from the
mineral, carbide; a rock. This is the stuff that is mixed with
water to create the flame that was (and sometimes still is) used to
illuminate the old miners' and spelunkers' helmets. I was told that
acetylene was SO unstable that if it were not mixed with acetone
and cushioned by the "gray spongy stuff" in the cylinder, that as
little as a small coffee cup of the pure acetylene, if dropped on
the floor would have exploded and killed the 3 of us outright and
that a whole cylinder's worth would have leveled the 50' x 150'
plant that we were standing in (that always sounded a bit
far-fetched to me, but I was never inclined to experiment!). Then
he went on to explain that the "gray spongy stuff" that filled the
bottle was, in fact, ASBESTOS!!! They actually had an in-house
supply of a ground asbestos slurry which they injected into new
cylinders then baked into a solid mass. SCARY stuff!!!!! I can still
remember that little educational session to this day!
That was over 25 years ago and they may not be using asbestos in
acetylene cylinders anymore, but I wouldn't bet on it. This is just
another good reason why suppliers should only EXCHANGE acetylene
cylinders. It is set up that way so that only qualified personnel
in a suitable facility are responsible for filling/maintaining what
is not only essentially a bomb, but is also a MAJOR carcinogen!!!
Having said all that, keep in mind that gas
welding/brazing/soldering has a LONG (over 150 years) and
essentially SAFE history. If a person of reasonable intelligence
gets a little training and uses simple common sense they should
have nothing to worry about.
As for laying an acetylene cylinder on its side, its not a really
good practice, but as long as you allow plenty of time for the
contents to settle (overnight, to err on the long side!), it
shouldn't ever cause you any problems.
Personally, I prefer propane (LPG), because it is cheaper, so much
cleaner to use, and is sold in 20 lbs. tanks nearly everywhere.
Propane, though, has its own set of limitations and drawbacks!!