Equipment Exploding tank shrapnel injures boy - Ploče beach, Montenegro

[iain/hsm]

I had some troubles at one dive centre and thought this was exactly what had happened to them. The physics didn’t make sense to me, so I tested it. I mention this because I generally do trust government reports, but in this case the report might not be the best out there.

I am not a great fanboy of the HSE lets just say I know them from there previous shallow work experience
and skills Those that do vs those that don't teach and those who cant do either get a desk job and work for standards jobsworth.Poacher turned gamekeeper is a term I recall we used for them.

When I started diver training we were issued with twin inverted cylinders a full Admiralty Pattern Full face mask and an Avon dry bag and a knife for up to 50MSW depth on air.
You used one cylinder open and one cylinder closed. And would check that the 2nd valve was closed by a process known as "Heared to equalise" You used up the one cylinder then opened the second and equalised. You would do this twice before surfacing. (Standard Royal Navy Practice)
I had similar concerns regarding fast filling of the 1st cylinder over and over again diving multiple dives 7 days a week for the 12 weeks training with same result as you on inspection dry as a bone. The cylinders were however non magnetic Aluminium. Thus making the difference being all in the detail.

 

[iain/hsm]

I assume the case you quoted is the 3 litre pony bottle that exploded in June 2011 in the UK. If memory serves, the cylinder ingested freshwater from a lake rather than contaminated compressor air. It was also an oxygen rebreather bottle, and the high oxygen content rapidly increased corrosion.

If I recall correctly, the bottle was just under 2 years old, not 6 months. That is, if we are talking about the same incident.

Both of our examples are problematic. If a diving cylinder UK/Europe requires a Hydro test every 5 years and Visual Inspection every 18 months. However in your example as an oxygen cylinders above this would require O2 cleaning every 15 months. Hence a 2 year old cylinder from new used for oxygen back then (2011) could have had an internal inspection and cleaning 6 months prior to it's explosion.

 

[iain/hsm]

Well, I just assumed that salt water causes more corrosion than sweet water. Publishing an assumption is a way to ask for more detail. Hence, verification. No need to take that personally.

A chemist would answer this much better but its the salt in salt water that creates a battery effect electrolysis and this in turn dissolves the metal more rapidly. I cant say it causes more corrosion but certainly oxidises ferrous metal more rapidly when measured against time.

Add pressure and then add oxygen and the reaction time is even faster.

In addition the real problem is crevice pitting creating a localised wall thickness reduction and a pin hole leak. Now if the pin hole is akin to a balloon being pricked with a pin you get a burst and a fragmenting cylinder. If however you stick a small piece of sellotape over your party ballon you can prick it with a pin and it won't burst it just leaks slowly. (This is the area compensation design aspect we discussed earlier)

This is the concept of the no burst design with new cylinders but it cannot compensate for the crevice localised corrosion hence the bright shine metal comments made. Not a cratered surface of the moon wall as seen in the photo I posted. Which is why the cylinder failed in an explosive fragmentation.

 

[DandyDon]

Serbian arrested after dive-tank explosion

A 45-year-old man from Belgrade in Serbia, identified only by the initials ‘MB’, has been arrested by Montenegrin police in connection with the scuba-tank

divernet.com

 

[iain/hsm]

What I didn't realise until today was that they carried this kids hand away with him separately in a bag. Any wonder the local medical centre couldn't cope.

In addition two others were also injured making a total of three people injured.

The cylinder fragment hit him on the wrist severing the hand. The boy was from Serbia but lived with his family in Germany.

From the local medical centre he was transferred to the main hospital while his hand was transported by car. He was then transferred to the another hospital in Podgorica. For there he was then taken by aircraft to a specialist centre in Belgrade where surgeon's undertook an 11 and a half hour operation to re attach the hand.
The surgery was reported successful and they reported that the lad is commutative cheerful and smiling. The operation to re attach using microsurgery was undertaken at the Major Clinical Surgical Centre in Belgrade.

 

[Kay Dee]

Exact in Europe (and most of the world) valves (and tanks) don 't have burst disk

Most of the world? Australia, Asia and many of the Pacifc islands (less French possesions I assume?) use cylinders with burst discs, although not sure if it is mandatory in all (as it is in Australia).

 

[NetG]

Most of the world? Australia, Asia and many of the Pacifc islands (less French possesions I assume?) use cylinders with burst discs, although not sure if it is mandatory in all (as it is in Australia).

I don't see burst disk in indonesia, philippines, thailand, maldivia , red sea ....

Perharps mandatory with DOT cylinder ?

 

[Kay Dee]

I don't see burst disk in indonesia, philippines, thailand, maldivia , red sea ....

Perharps mandatory with DOT cylinder ?

Not sure re DOT. But like I said I wasn't sure if mandatory - but from what you say seems its not - in some of the regions I mentioned (as it is in Oz, and NZ I believe). I guess I was either lucky or chose wisely as who I dived with outta Singa's, in Indo, Sols, PNG, Fiji, Guam and the Marshals all used cylinders with burst discs.

 

[TooCold]

That HSE article isn’t one of their best pieces either. I emailed them long ago about this statement, I think they published this around 2013 or so? I did get no reply...:

"Do not charge cylinders (such as delayed SMB cylinders) that have been emptied underwater, by decanting from your main cylinder – water from the empty cylinder may enter the 'charging cylinder' when they equalise."

I had some troubles at one dive centre and thought this was exactly what had happened to them. The physics didn’t make sense to me, so I tested it.
I added a litre of water to an S80 and decanted from it: no water transferred. I repeated with around 5 litres, same result: not a single drop entered the whip or second cylinder.

@Tanks A Lot , did you really mean to say you decanted FROM the cylinder you added water to? That's baclwards.

 

[Tanks A Lot]

Yes, that's exactly what I mean.

The flow of gas is from high pressure to low pressure. How would water from inside the lower-pressure cylinder enter the higher-pressure cylinder?

I tried exactly what they suggested and, even with an "empty cylinder" full of water well past the dip tube, not a single drop transferred. Equalisation was just really quick, pretty much exactly as I would have expected.
The gas moves from the higher pressure to the lower pressure, but no water travels back against the gas flow.

The other way round seemed to make at least some sense to me, which is why I tested it that way. I imagined that some of the water might theoretically get drawn up into the flowing gas, but that proved difficult.

Clearly I have a blind spot here, as that is exactly what confused me in their statement. Would you mind explaining how that would happen?