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March 10, 2010
How Not to Do It: Liquid Oxygen Cylinders
We haven't had a How Not to Do It around here in a while, so here's a companion piece to the famous Sealed-Up Liquid Nitrogen Tank. This incident happened (as far as I can tell) about ten years ago. It's been used in a number of safety presentations then, thanks to the Airgas Corp., whose safety officer assembled a number of photos (and this is the time to emphasize that they had nothing to do with the accident itself, because people who work for a pressurized-gas company actually know how to handle pressure vessels.
As opposed to the two guys who scavenged a liquid oxygen Dewar from a scrap metal yard and decided to put it back into service. According to the most detailed report, they tried to rig up a connection to refill the cylinder, but found that it vented immediately through the pressure-relief valve. So. . .well, yeah, you know what's coming next: they took the darn thing off and plugged it shut. No more pesky venting! They filled up their cylinder, which was loaded on the back of their pickup truck, and went rolling down the interstate at lunchtime. Whereupon they had a flat tire, and pulled over for a while to fix things. . .
OK, you can look out from behind your hands now. Although I can't imagine how, neither of these two cowboys managed to get themselves killed, nor did they take out anyone else, through what appears to be sheer blind luck. According to the report, one member of the Cylinder Kings ended up being blown across five lanes of traffic, while his partner was launched forty feet in another direction. You can see from the photo how the truck weathered things. I can't imagine that a pressure wave of straight oxygen hitting tank of gasoline can end well; it's a perfectly reasonable mixture to put a payload into low-earth orbit.
Which is a good note on which to take inventory here. We have the owners of the oxygen cylinder accounted for, and their truck. What about the cylinder itself? Well, similar to the nitrogen tank referenced above, it had failed at the bottom weld and thus departed the scene of the accident like an artillery shell. It re-entered the affairs of the world a quarter of a mile away, plunging through the roof of an apartment, completely trashing the place (and severing a natural gas line in the process). As I said, how a dozen people didn't end up killed by all this is a complete mystery to me. (The red circle in that photo is where the pressure-relief device used to be. )
So the moral of this story is, I suppose, that Pressure Relief Devices Are There For A Reason. Or maybe it's "don't scrounge gas cylinders from the scrap yard and try to get them to work". Or perhaps "just because you haven't seen a pressure vessel explode yet, it doesn't mean that they can't". Or "Gegen der Dummheit kämpfen Götter selbst vergebens." Or something.
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