Another safety rule I was taught, is to ALWAYS leave the tank wrench on the acetylene valve. Usually there is even a small chain connecting the wrench to the tank so your co-worker cannot borrow your gas wrench while you are busy welding. In the event of a broken hose, fitting, a fire or whatever, you don't want to be looking for who took the wrench so you can stop the gas flow. Some of the old timers I worked with also insisted on only opening the acetylene valve about 1 or 2 turns - enough not to restrict the gas flow, but less turns to close in an emergency. I have never had a problem, but apparently some of these old timers had been through some panic situations (involving confined spaces or on high structural steel.
As far as operating pressure of the gas, it helps me to know why it is limited to 15 psi. Pure acetylene pressurized above about 29 psi is capable of violent explosions when the acetylene breaks down into benzene and vinylacetlylene (and maybe some other stuff). This reaction releases lots of heat and does not require any oxygen to proceed. The 15 psi max acetylene gas pressure gives you a safety factor of 2:1 in staying away from the explosive range. As pointed out below, the acetylene is absorbed in acetone when stored in the tank so that solution is stable. Plus, the inside of the tank looks something that looks like a solid cinder block which keeps the solution from slopping around. (There is a fancy name for the cinder block stuff, but I don't recall what it is). While you are burning gas, the acetylene is boiling out of the acetone solution at the same rate you are consuming gas. The gas has to find its way through up the cinder block to get out of the tank.
Like others have pointed out below, you typically run at gas pressures well under the 15 psi limit.
Terry S.
uch:
