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  • #16
    I guess some research is in order. I was told a certain volume of acetylene can become unstable. I have seen a spontaneous ignition of acetylene in open air. A gas bottle valve was cracked to show the tank was not empty, and somebody stuck their hand in front of it to feel the flow. It detonated. I ran to get a welding glove and turned off the valve which was still spewing flame.

    *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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    • #17
      Acetylene is well known to be unstable. The method described was a very poor idea, I have wondered many times if a acetylene tank was empty or how much it had in it, its a simple matter to just screw a regulator on and open the tank, the gauge gives a accurate true reading. Cracking the valve open yielded no meaningful information on the tanks fill. 300 psi is full and I have found once it gets below 50 psi it may not work well, especially in cold conditions and if a larger tip is used which needs more flow. I suspect that is because the acetylene is dissolved in the tank and does not vaporize well when nearing empty.

      The fact that acetylene is dissolved in acetone in the tank along with a fibrous filler of some sort attests to its instability and pretty well answers your original question. Its unstable in any volume.

      Lot of horror stories about use of acetylene out there but many come down to poor practices. Lets face it, oxy/acetylene has been used forever and considering the numbers in use problems are very rare if used properly. Not used properly, it is very unforgiving !

      In the case cited, there is no doubt that a certain volume will mix with air to form a perfect ratio to detonate with the slightest ignition source. In this case it could have been as simple as a static electricity spark. Also, the standard limit of keeping the pressure under use to 15psi or lower was ignored, the flow out of the tank was at tank pressure into the room. Does flow from the tank at over 15psi create a unstable situation? I don't know but was never tempted to find out, I have too much respect for the stuff.
      Last edited by Sparky_NY; 04-13-2021, 07:27 AM.

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      • #18
        The old school way to test if any tanks were not empty was to put your thumb over the opening on the tank and quickly open and close the valve. It was said that if held tightly it would take over 250 psi to blow your thumb off the opening.
        Some places require check valves and flash back or spark arrestors at the gauges. Even if they are not required it is good practice to have them on.

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        • #19
          I have never understood trying to tell if a cylinder is full by opening the valve. The correct nipple, coupling and gauge is not that hard to get.
          At 70 degrees an acetylene cylinder is considered full at 225 psi.

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