Scuba Cylinder kills fire fighter

[JackD342]

Since it seems this thread will be going on for a while, I think I should add in another thought about preventing valves from ever getting to the point where one has to figure out the safest way to open and empty one past a frozen valve.

*** regular scheduled maintenance ***

I know both Sherwood and Thermo/XS Scuba state that a valve overhaul and complete change of burst disk assembly are required every 5 years - so at time of hydro is a natural cycle. Also, inspection and a check for trouble free operation at each annual visual inspection - perhaps requiring service work sooner than 5 years. I strongly suspect that guidance is common to all valve manufacturers.

I also suspect that valves that finally freeze up after going 10, 15, 20 or more years without an overhaul might also be far more likely to have a burst disk assembly that also resists removal, and may be more easily sheered off while attempting to remove under pressure.
K
(Yes, I know in this instance they were used cylinders recently acquired, and so they were not in control of the fire department as they aged and the valve deteriorated.)

 

[rjack321]

As for the actual incident, I have been trying to get information on whether the top of the PRD sheared off while being removed resulting in a direct exhaust path, if the threads failed, resulting In the PRD bolt being ejected, or if the PRD was unscrewed to the point that it was ejected from the cylinder.

At the bottom of page 6 on the pdf
https://www.firerescuemagazine.com/content/dam/fire-rescue/downloads/face201810.pdf

It explains that the venting cylinders with loose burst disks were set out on the floor. Nobody was working the one that failed at the time it turned into a missle. So it seems that the plug either ejected or the head of the plug sheared off due the force of the escaping gas. It would help if the burst plug side of the valve were illustrated but alas not.

 

[guruboy]

At the bottom of page 6 on the pdf
https://www.firerescuemagazine.com/content/dam/fire-rescue/downloads/face201810.pdf

It explains that the venting cylinders with loose burst disks were set out on the floor. Nobody was working the one that failed at the time it turned into a missle. So it seems that the plug either ejected or the head of the plug sheared off due the force of the escaping gas. It would help if the burst plug side of the valve were illustrated but alas not.

It says they were left standing upright, though upright or laying down probably didn’t affect the outcome much.

 

[rjack321]

It says they were left standing upright, though upright or laying down probably didn’t affect the outcome much.

Yes the way its written strongly suggests that nobody was actively removing or breaking the burst plug at the time it broke. It sounds like the venting pressure popped the nut head off the burst plug

 

[guruboy]

Yes the way its written strongly suggests that nobody was actively removing or breaking the burst plug at the time it broke. It sounds like the venting pressure popped the nut head off the burst plug

Yes, it sounds like the plug was loosened, started venting, and was left standing.

Not sure if plug broke or just came out.

 

[clownfishsydney]

Really strange idea to remove the burst disk holder. I would not have thought the cylinder would have went that far and high, especially after hitting many things. Sad accident.

 

[rjack321]

I have never seen the head break off a burst plug from venting. But I sheared one off once and it was not hard at all with an 8" long socket wrench. The valve is pretty corroded in the picture so I am guessing the plug was corroded in place like the rest of the brass. They put a socket on it and the plug turned a little but required some force. The head started to shear off from that extra force with one or two of the connecting bits of brass ripping. But the socket didnt completely rip it free. The cylinder was then set with the others to vent and less than a minute later the sustained force of the gas popped the head off plug and turned the multiport outlet into a single outlet. Based on the overall level of corrosion on the valve I would say the odds of the burst plug just spontaneously unscrewing and falling out are slim.

 

[fsardone]

Really strange idea to remove the burst disk holder. I would not have thought the cylinder would have went that far and high, especially after hitting many things. Sad accident.

Well the forces from venting through the burst disk orifice made the cylinder spin and roll until the impact on the valve caused valve/cylinder separation. The force is proportional to the ejected mass of air and the speed. The greater orifice increases mass a lot (speed remains the same since it will be no more than speed of sound due to the approximation of a convergent /divergent ejection hole) hence the huge propulsion force.

 

[Bob DBF]

From my best guess, wtshtf the only person that knew what actually happened is the deceased. They talk about how they processed the tanks, but while man 1 was standing the tanks to drain, man 2 could be starting the next tank with no one observing.

I am supprised that men who work with HP air, and dangerous situations, did not consider what could happen in the worst possible case and proceed accordingly.



Bob

 

[guruboy]

I have never seen the head break off a burst plug from venting. But I sheared one off once and it was not hard at all with an 8" long socket wrench. The valve is pretty corroded in the picture so I am guessing the plug was corroded in place like the rest of the brass. They put a socket on it and the plug turned a little but required some force. The head started to shear off from that extra force with one or two of the connecting bits of brass ripping. But the socket didnt completely rip it free. The cylinder was then set with the others to vent and less than a minute later the sustained force of the gas popped the head off plug and turned the multiport outlet into a single outlet. Based on the overall level of corrosion on the valve I would say the odds of the burst plug just spontaneously unscrewing and falling out are slim.

If you really want to know you can request a copy of the valve analysis lab report. See last page of the pdf.