On Sat, 18 Aug 2007 14:12:03 -0400, Bob Engelhardt
wrote:

Shaun Van Poecke wrote:
... The cyllinder ruptured in
an unusual way, splitting right down the side. ... the safety release valve
did not operate, ...

... the Co2 filled up the copper pot ... the welder climbed into the pot
... once he was
inside the pot he was overcome pretty quickly by dizziness and was unable to
get out. ...

Shaun - thanks for the real-world input. Too many of our posts are
speculation, sometimes not based on much knowledge.

While accepting that CO2 is more dangerous than I believed, I'm still
going to store my cylinder in the cellar. It's a probability thing
(like most things in life). The probability that there'll be a fire AND
the safety will fail is small enough for me. Likewise the probability
that my cylinder will leak fast enough to fill up my drafty basement is
small enough. It's a small cylinder.

Bob

Wouldn't worry about it for the normal 5-pound or 10-pound CO2
cylinder you'd have for home shop use - you can't flood a room that
well unless it's a full-size 50-pound tall bottle with several hundred
CF of gas inside and a really small basement.

Oh, and it may not be a pop-type resetting relief valve, they use a
rupture disc relief on some cylinders, once it pops it fully vents.
Ask the supplier what you have on any particular bottle.

As that fire proved, even if the cylinder relief valve vents, it may
not vent fast enough to prevent cylinder rupture in a fire. But I'll
bet there was a time delay between venting and popping, and everyone
had a chance to get out of the way.

-- Bruce --