[76834]

That is iffy deal.
You might get away with it numerous times but you are "Pulling the Dragon's Tail".

Dragons have a tendancy to turn around and bite your head off...

[tacticalogic]

I've done it, but I don't make it a habit, and I had a D7 between me and the tanks at the time.

Anyway it seems like there has to be more to it than just pressure. The bulk of the acetylene is dissolved in acetone sitting in the clay in the bottom of the tank, and bubbles out into the space above the clay. When I turn on the valve, the pressure gauge tells me there is approx 200psi of gas pressure if the tank is full. That gas has to be acetylene, in a free gaseous state. And it doesn't go boom.