Scuba Cylinder kills fire fighter

[tridacna]

It sounds like the writer got some facts wrong. Fireman use SCBA bottles, not SCUBA. I've only seen two tanks, both Alu80, blow a burst disk after a hot fill and some hours in the hot sun on a hot day. The tank didn't go anywhere, it just made a lot of noise. The second tank was in a water bath IIRC at a fill station and again, it just made a bang when it blew--but didn't go anywhere.

Not that it couldn't happen...but with the quality of journalism these days, I have to question the "missile" aspect. Maybe if the entire valve somehow cracked out...but not a burst disc, and I've yet to see firemen using recreational SCUBA bottles. I wouldn't be that conventional SCBA valves would fit in them.

https://www.firerescuemagazine.com/content/dam/fire-rescue/downloads/face201810.p

 

[johndiver999]

Is it possible they initially tried to vent the tank by spinning the valve out just a little. You know just enough to allow the neck oring too spit and fizz? This would eventually drop the pressure.

Perhaps they initially tried this and failed, but in the process of cranking on it, exerted excess torsion and actually cracked the brass valve slightly. A prior weakening of the valve might make shearing it off more likely?

 

[Basking Ridge Diver]

Is it possible they initially tried to vent the tank by spinning the valve out just a little. You know just enough to allow the neck oring too spit and fizz? This would eventually drop the pressure.

Perhaps they initially tried this and failed, but in the process of cranking on it, exerted excess torsion and actually cracked the brass valve slightly. A prior weakening of the valve might make shearing it off more likely?

I am sure I am coming across as a numbnut - so let me try this slowly. Firefighters are not going to mislead, leave out, embellish, forget to mention, or straight out lie in a death of a fellow firefighter. They are going to tell the story the way they remember it and they will get the story straight.
Why? So this does not happen again.
This was a tragic accident - no more - no less. There is a story here if you read it and listen - you don't have to try to come up with alternate scenarios. The story is told - reviewed - re-interviewed and documented so that approximately 3 million other firefighters will not make this same mistake.
If it is fun for you to disregard the facts and come up with a conspiracy theory - then have at it.

Otherwise the facts and the eye witnesses (there were several) all told NIOSH what happened and NIOSH pieced together the story for you and others to learn from... No need to wonder or guess or otherwise interpret the report...

Peace Out...

 

[fish149]

RIP.....

 

[Bob DBF]

Perhaps they initially tried this and failed, but in the process of cranking on it, exerted excess torsion and actually cracked the brass valve slightly. A prior weakening of the valve might make shearing it off more likely?

More likely cranked on it hard and sheared off the burst disc nut, or its threads, which vented the tank. I've done it but not with a full tank, it's small and brass so I can't imagine it holding up enough to cause a valve body to crack.


Bob

 

[Rred]

Reading further down the original URL...FD dive rescue team members purchased the tanks, so SCUBA vs SCBA is not an issue, they were SCUBA for SCUBA use. But that page shows a link to the original NIOSH report--which requires a UID and password to access it. So we don't(?) have ready access to the NIOSH report.

I don't think anyone doubts NIOSH had some reason for their findings, or that firefighters conspired or lied about anything. But has anyone actually seen a tank with a blown burst disk, even a full tank, literally go airborne? The two I've seen didn't go anyplace.

And yes, I've seen the old 50's or 60's b&w photo that shows steel 72's in a car trunk after one "exploded"...apparently one tank is equal to three sticks of dynamite (not tnt, not dynamite)...but the burst disk usually directs air out at least 3 ways to spread the force around. Launching it? Just sounds like we're not getting the whole picture.

NIOSH? Well, sure. Think of what the DoD said about syphilis experiments. Or radiation tests. Or what the Navy said about the USS Pueblo. Or the totally fabricated Gulf of Tonkin incident. Or even the FAA, who reluctantly 'fessed up and said oh, yeah, Boeing tested the new 737 by themselves really, we couldn't be bothered.

There's just something either badly wrong with burst discs, or something missing in that story. If burst discs really can launch a tank, maybe the industry needs to reconsider how burst discs should be made.

 

[Bob DBF]

There's just something either badly wrong with burst discs, or something missing in that story.

Nothing missing, some of the valves were frozen shut, the burst disc nut was being loosened to drain the tank. Somehow during the process the burst disc nut came out or was sheared off which gave a catastrophic release of gas. No burst disc, no three holes, a direct hole from a pressurized tank to the atmosphere. Along the way the tank valve sheared off.

I'm always up for a good conspiracy theory, however this seems like a straightforward accident. Unfortunately one man died.


Bob

 

[michael-fisch]

Assume the hole in the valve body under the burst disk is a 1/8" hole. That works out to a surface are of about 1/100 square inches.
3000 Lbs per square inch divided by 100 only exerts a force of 30 Lbs for a fraction of a second before the pressure drops. Since the tank weighs about 30lbs I find it hard to imagine that it went airborn without sliding and impacting something else before it was up in the air losing energy the whole time.
Put the tank on a table, have it fall off because its spinning and when the valve hits a sharp corner it could fracture. The hole through the now missing top part of the valve is less than 1/4" and the gas now flowing through the 1/4" hole could cause 120lbs of force, which is quite a bit - I'm not sure that I can punch a sandbag with 120 lbs of force.
That kind of force can destroy a dryboard wall, cause very litte damage to a hollow cinderblock wall but appearantly enough force to kill an unprepared firefighter.
Sad, not sure what we'll learn from this as divers, but may he RIP.

Michael

 

[TrimixToo]

Assume the hole in the valve body under the burst disk is a 1/8" hole. That works out to a surface are of about 1/100 square inches.
3000 Lbs per square inch divided by 100 only exerts a force of 30 Lbs for a fraction of a second before the pressure drops. Since the tank weighs about 30lbs I find it hard to imagine that it went airborn without sliding and impacting something else before it was up in the air losing energy the whole time.
Put the tank on a table, have it fall off because its spinning and when the valve hits a sharp corner it could fracture. The hole through the now missing top part of the valve is less than 1/4" and the gas now flowing through the 1/4" hole could cause 120lbs of force, which is quite a bit - I'm not sure that I can punch a sandbag with 120 lbs of force.
That kind of force can destroy a dryboard wall, cause very litte damage to a hollow cinderblock wall but appearantly enough force to kill an unprepared firefighter.
Sad, not sure what we'll learn from this as divers, but may he RIP.

Michael

Hmmm.

Pi (R**2) yields the area of a circle. 1/8" is .125".

3.14(.125 * .125) = .049 sq. in.

.049 sq in * 3000 PSI yields 147 lbs of thrust*. When the tank has emptied by 1/3, there is still nearly 100 lbs of thrust. When there's 1000 PSI left, there's still nearly 50 lbs of thrust. That takes at least several seconds.

147 lbs of thrust, at the end of a tank, perpendicular to its axis, *will* make the tank fall over, where if unrestrained it will roll until the thrust is about parallel with the floor, upon which it will spin up *very* quickly on a smooth surface. Like, say, smooth concrete. Or, as I think I posted earlier in the thread, a tiled floor. Clearly, it is likely to stay on the floor unless it hits something, but if it does hit something it is not at all hard for me, at least, to imagine it bouncing into the air with lots and lots of stored rotational energy just waiting for whatever will happen when it hits the next solid object.

Am I missing something somewhere?

* It's actually less than this, most likely, because the flow through the hole is imperfect, with edge effects that reduce the effective "nozzle" size, but this seems like a reasonable first approximation. Also, if the thrust is reduced, it's because the flow is reduced, which means the thrust continues for a longer time. Either way, that sucker is spinning fast on the floor.

 

[michael-fisch]

Hmmm.

Pi (R**2) yields the area of a circle. 1/8" is .125".

3.14(.125 * .125) = .049 sq. in.

.049 sq in * 3000 PSI yields 147 lbs of thrust*.

Slight error in the calculation, you calculated the area of the circle using the diameter of the hole instead of the radius.
should have been
3.14(0.0625 * 0.0625) = 0.01226 sq inches
3000 / 0.01226 = 36.79 pounds pounds of thrust which is a lot less than a slowly moving light bowling ball.

Doesn't really matter though, somebody died unnecessarily and it didn't really have to happen.

Michael