Tank explosion kills one - Cozumel

[redacted]

I doubt if we will see any more specific information on this incident, so maybe we should back off and take a more general look at this rare problem.

Does Mexico have any federal requirements for scuba tank inspection or re-qualification? I took a quick look and found nothing!!! If not, then why are there additional hydro markings on any tanks in MEX and what do they mean? What does the "H" mean in the middle of those re-qualification markings? That is quite different than the US markings format.

The 'bones' of retired scuba tanks are easily found in Cozumel (piers and underwater) so something happened that caused them to be removed from service. What was it?

You really don't hear of these kinds of problems very often. The only other one I can recall was the Parrots Landing dive op (I think that was the name) in Grand Caymen that had their bank tank explode. That was the end of that operation.

 

[flots am]

Back to my question--how are you to know? Are you going to say, "Were these tanks certified by a qualified, unbiased, properly trained inspector using the right equipment?"

I trust the tank inspectors at the SCUBA shop because I've watched them do a lot of inspections and know that the bad tanks are condemned, the good tanks are passed, and the process is always he same no matter who owns the tank.

I've seen the neck cracks on the failed tanks in person and on the Eddy Current Tester's screen.

I trust the tank inspectors at the other hydro/fill place in town because they're a huge medical & industrial gas supplier, and send out truckloads of tanks every day and are hard-asses about everything. They also have a lot to lose and nothing to gain by passing a bad tank.

Places I don't trust: "Everywhere else"

If I don't know how the last tank inspection was done, and when and by who, and trust the work, I'm not going to fill it.

Unfortunately, in Mexico, if the employee had refused to fill unknown tanks or had a low level of trust in the inspection process (if any), he would be replaced before the next sunset.

As a diver, I don't much care, since I don't beleive a tank has ever blown up on a boat (although I could be wrong) and I bring my own O2 and CO analyzers, so I know what I'm breathing is OK to breathe.

flots.

---------- Post added September 4th, 2014 at 04:08 PM ----------

Just wondering, if anyone can tell me. Metal fatigue in airplanes is highly related to the number of "cycles", i.e., takeoffs and landings, because of the effects of expansion and contraction resulting from repeated pressurization and depressurization of the fuselage. These cycles of expansion and contraction result in metal fatigue in the aluminum skin of the airplane fuselage, resulting in cracks and fractures in the skin. Don't Scuba tanks expand (very slightly) upon being completely filled, then contract upon being emptied down to 200-500 psi? Have there been any studies on the effect of "cycles" on scuba tanks? If repeated cycling of Scuba tanks does increase metal fatigue, it seems that places like Cozumel, where the tanks are cycled pretty much daily, ought to use a more frequent inspection standard, based upon usage rather than simply time.

SCUBA cylinders get metal fatigue just like anything else, and the amount of fatigue is related to the pressure change between empty and full and the number of cycles (and I believe the fill rate).

A tank that goes from 3000PSI->2000PSI every day will have a longer life than a tank that goes from 3000PSI to 100PSI every day.

This is supposed to be caught in the tank inspection process, particularly hydro, where the elasticity of the metal is supposed to be compared to REE numbers the manufacturer expects to see.

flots

 

[nadwidny]

Just wondering, if anyone can tell me. Metal fatigue in airplanes is highly related to the number of "cycles", i.e., takeoffs and landings, because of the effects of expansion and contraction resulting from repeated pressurization and depressurization of the fuselage. These cycles of expansion and contraction result in metal fatigue in the aluminum skin of the airplane fuselage, resulting in cracks and fractures in the skin. Don't Scuba tanks expand (very slightly) upon being completely filled, then contract upon being emptied down to 200-500 psi? Have there been any studies on the effect of "cycles" on scuba tanks? If repeated cycling of Scuba tanks does increase metal fatigue, it seems that places like Cozumel, where the tanks are cycled pretty much daily, ought to use a more frequent inspection standard, based upon usage rather than simply time.

The number 10,000 comes to mind but I can't remember if that was for aluminum or steel tanks.

 

[grf88]

Luxfer states in excess of 100,000 cycles. Can't imagine that steel would be any less.

 

[redacted]

As a fill station operator, I trust the tank inspectors at the SCUBA shop because I've watched them do a lot of inspections and know that the bad tanks are condemned, the good tanks are passed, and the process is always he same no matter who owns the tank.

flots

What kind of a dive shop are you with that you "condemn" tanks? Or did you mean to say "fail" them.

 

[grf88]

Looks like Faber may be 10,000 cycles to 4000 psi.

 

[flots am]

What kind of a dive shop are you with that you "condemn" tanks? Or did you mean to say "fail" them.

The kind that does hydrostatic testing? What's the problem?

flots.

 

[Mike]

Just wondering, if anyone can tell me. Metal fatigue in airplanes is highly related to the number of "cycles", i.e., takeoffs and landings, because of the effects of expansion and contraction resulting from repeated pressurization and depressurization of the fuselage. These cycles of expansion and contraction result in metal fatigue in the aluminum skin of the airplane fuselage, resulting in cracks and fractures in the skin. Don't Scuba tanks expand (very slightly) upon being completely filled, then contract upon being emptied down to 200-500 psi? Have there been any studies on the effect of "cycles" on scuba tanks? If repeated cycling of Scuba tanks does increase metal fatigue, it seems that places like Cozumel, where the tanks are cycled pretty much daily, ought to use a more frequent inspection standard, based upon usage rather than simply time.

I believe the entire reason for having to be concerned with metal fatigue in scuba tanks is exactly because of the cycles of filling over and over again, that the elements effect on them.

I'd also think that the number of fills is hugely conservative in the 5 calculation. A huge number that could probably never actually be physically attained. That's typical for things like this where there is usually a huge conservative factor built in.

 

[nadwidny]

Looks like Faber may be 10,000 cycles to 4000 psi.

That's the one I was thinking of. And 100,000 for luxfer.

---------- Post added September 4th, 2014 at 09:13 PM ----------

The kind that does hydrostatic testing? What's the problem?

flots.

It's been my experience that any operation that is accredited to do a certain type of testing isn't allowed to make an interpretation ie "condemning". They can only report on the results and whether or not the analysis meets standards ie "fail" (actually it should be "Fails to meet standards" since "fail" alone is apparently an interpretation). I believe this holds true for hydrostatic testing.

Of course since there is no such thing as accreditation for visuals, or for dive shops doing them, then they can do whatever they want and be wrong doing it.

 

[redacted]

The kind that does hydrostatic testing? What's the problem?

flots.

Not a problem. Just not at all common. I have seen some DIVE shops that were not DOT testers that bought divers new tanks when they "condemned" a tank that "failed" a visual inspection.