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November 2022    Download the Entire Issue (PDF) Available to the Public Vol. 48, No. 11   RSS Feed for Undercurrent Issues
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Instructor Killed by Blasted Tank Valve

from the November, 2022 issue of Undercurrent   Subscribe Now

After Undercurrent reported an exploding tank in Australia in the mid-October email, a Dutch diving instructor died from a different sort of tank incident while conducting a class at a swimming pool in Amstelveen on October 16. The pressure in the tank blew out the valve, which hit and killed him. According to Divernet, some of his students later reported on social media that he had seen the man "launched into the air" by the force of a blast.

Authorities concluded the accident was caused by a mismatched tank valve and tank threads, an insidious accident that should never happen.

When being fitted, parallel threaded valves should screw in smoothly without binding or feeling loose. However, a European M25-mm thread valve stem, if inserted into a G3/4 inch cylinder neck (an older tank still used in the U.S.) with a slightly different thread pitch, will feel very loose until the valve is screwed in about halfway. At this point, the threads begin to bind, and one must use excessive force to finish screwing the valve home.

To the inexperienced person fitting the valve, the connection would appear robust. But, after many fills, the connection may fail, releasing energy equivalent to approximately 1,300,000 foot/pounds, turning the valve into a deadly missile.

When in doubt due to lack of any proper cylinder marking, do not fill it but send it for inspection.

By the way, the Special Permit (SP) is expired as of 9/30/22. This means that any cylinder stamped with that SP9791 or E9791 is no longer valid for use, fill or transport in the US by law. It means that regardless if the cylinder still contains gas, or is still within its current hydro or inspection period, it is still not valid for fill, use or transport.

- John Bnatin

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