Dive Cylinder Explodes - Sydney

[KevinNM]

Just a question on the side, since filling tanks has its risks, could they put the tank being filled in a protection enclosure?

I remember that they now fill truck tires in a sort of cage because they had explosion in the past. Maybe it could be applied to scuba tanks?

There is a lot of energy in a 3000 psi tank. I suspect you'd be better off arranging thick concrete walls such that the tanks are away from people and equipment while being filled. OTOH, I know someone who found a cracked tank while filling it by observing something "odd" going on with a label, which wouldn't have happened if they were not near it during the fill.

 

[kelemvor]

They make safety cabinets for scuba and scba tank filling. They are big, take up a lot of space and expensive. Here is an example. Just wait and see what it would cost to get your fills if they had to buy these at you LDS.

High Pressure Fill Stations And Containment Systems - Compressors - Fill Stations - For Fire Service and Scuba Diving - Poseidon Air Systems - Colchester Vermont

They're not that big. Clearwater Marine Aquarium where I used to volunteer has a fill station with a containment box. I bet pricing would come down if it became a government requirement and therefore the things would be sold at a much higher volume. Certainly rules have been enacted (often) for things that have killed fewer people.

I'm sure diveshops would complain at first. But in the end, everyone would be safer for it. The funny thing about that is that the diveshop owners and employees who would be most likely to complain would be the ones who saw the most benefit.

The only place I can think of off the top of my head where it might be a problem is on LOBs. I suspect space is at a premium on boats.

 

[EricTheDood]

I bet pricing would come down if it became a government requirement and therefore the things would be sold at a much higher volume. Certainly rules have been enacted (often) for things that have killed fewer people.

Government intervention is a slippery slope. That's why people fight new legislature so vehemently.

Anyone have stats on cylinder explosion rates? A quick and dirty Google search seems to reveal that one is more likely to get fatally attacked by shark, which is less likely than getting struck by lightning.

 

[Shotmaster]

The best fill station I ever saw was in Monterey, CA in the early 80's which had used old naval gun barrels cut down and set at an angle for easy loading and unloading. They sat below the waterline in a large water bath tank. Those tubes were probably 2 inches thick! It was outside and you could pull right along side it and drop off cylinders.

 

[2airishuman]

Government intervention is a slippery slope. That's why people fight new legislature so vehemently.

Anyone have stats on cylinder explosion rates? A quick and dirty Google search seems to reveal that one is more likely to get fatally attacked by shark, which is less likely than getting struck by lightning.

SCUBA cylinders specifically, or high pressure gas cylinders in general? Either way, there aren't very many explosions, and statistics are hard to find. In the U.S., and other places where cylinders get inspected regularly, explosions are rare. I haven't been able to find any statistics, just anecdotal reports.

There were something like 5 or 6 explosions of aluminum SCUBA cylinders, attributed to sustained load cracking, before the visual eddy requirements were put in place. I don't believe there have been any since.

There have been a number of oxygen related explosions of SCUBA cylinders. I'm not sure how many. All the ones I've seen reported have involved aluminum cylinders.

There are many reports of valves separating from cylinders, either due to thread failure, or because the tank fell over and hit something.

I've yet to see a report of a steel SCUBA cylinder exploding in the U.S. for any reason, since the annual VIP became a thing.

 

[Rooster59]

Poking around the web's attic, I came across this at Aluminum Tank Controversy Continues: Undercurrent 08/2000

The leading manufacturer, Luxfer, has just issued a new policy statement requiring that every Luxfer 6351-T6 aluminum scuba cylinder be visually inspected at least every 2.5 years and that the cylinder neck be(using electromagnetic waves to detect cracks in tank threads that might not be visible to the naked eye) or equivalent non-destructive testing equipment. These requirements are in addition to DOTmandated VIP and hydro tests. For cylinders in heavy use (for example, those filled five or more times a week), Luxfer recommends visual inspection every four months.

This was dated August of 2000, 16 years ago.

 

[rjack321]

You are spreading lies and innuendo. You are right, not an expert. The failure mode of the 6351 cylinder is sustained load cracking, not brittle fracture. That means the crack forms and propagates under a sustained load instead of a sharp blow. A sustained load like putting 3,000 lbs per square inch inside the cylinder, specifically in the neck, not by placing a hydro stamp on the shoulder of the cylinder.

Yes BUT
there is a hydro station and dive shop in NC (or there was) who has on several occasions VIPed a tank, hydroed it, and found a brand new obvious neck crack post hydro. This phenomenon was confined to 6351 tanks as far as I know. The owner posted about it on TDS more than once and after the 2nd or 3rd time decided he never wanted a 6351 tank in his shop again regardless of who VIPed or visual eddied it or when. I forget his name and don't know if his facility is still in business or not. I will try to find a link for you but I don't frequent TDS anymore.

Another hydro facility (in AK, I think it might have been Anchorage) has sent me pictures of neck cracks in 6061 cylinders, something which isn't "supposed" to happen. Since 6061 is immune to SLC these can only be inferred to be brittle fractures. I will look for those in my email when I get a chance. (They were big and I may have discarded them) I have no way to verify the actual tank composition just looking down the neck though.

I only bring up this issue because Ali tanks of both types definitely appear capable of experiencing what is effectively a brittle fracture during use or hydro.

 

[rjack321]

There were something like 5 or 6 explosions of aluminum SCUBA cylinders, attributed to sustained load cracking, before the visual eddy requirements were put in place. I don't believe there have been any since.

Worldwide there's one every few years (so total way more than 5 or 6), but fewer and fewer 6351 tanks are getting filled at all because many shops refuse them. Around here only 1 in about 9 shops will fill them and the costs of an eddy current test at the hydro facility almost doubles the hydro price. So the combination of those two factors mean they are effectively retired from service and (thankfully) getting recycled. The last 6351 tank was made in about 1989 so at a minimum they are 27 yrs old now.

 

[Diving Dubai]

@rjack321

Not to be facetious but, why someone is surprised when a crack appears after hydro amazes me.

Hydro stretches the tank, so much the the tank never returns to its pre hydro dimensions. So if there is a defect the hydro us just going to make it worse.

All Aluminum tanks IMO should be eddy current inspected ( with steel it gets more complicated, it can be done though)

Visual can't be used to confirm and eddy current detection at eddy current is able to find defects that the eye can't

The visual plus Eddy current tester is a piece of crap and is best used as a door stop.

Clearly the people who devise the testing procedures and frequency of scuba tanks are fools ad don't understand the science.

6351 tanks are perfectly safe if subjected to a proper inspection method. After all you all fly in aircraft that are inspected for cracks, and indeed fly with cracks that are within an allowable limit.

 

[Wookie]

Trucks used two piece rims, if the steel band slipped off it became a room clearing missile. Hence the safety cage required.

They make safety cabinets for scuba and scba tank filling. They are big, take up a lot of space and expensive. Here is an example. Just wait and see what it would cost to get your fills if they had to buy these at you LDS.

High Pressure Fill Stations And Containment Systems - Compressors - Fill Stations - For Fire Service and Scuba Diving - Poseidon Air Systems - Colchester Vermont

Yes, they are officially known as containment fill stations, and are good engineering practice for any fill station that fills 6351 alloy cylinders. 49 CFR 173.302 (e) states:

DOT 3AL cylinders manufactured of 6351-T6 aluminum alloy. Suitable safeguards should be provided to protect personnel and facilities should failure occur while filling cylinders manufactured of aluminum alloy 6351-T6 used in self-contained underwater breathing apparatus (SCUBA), self-contained breathing apparatus (SCBA) or oxygen service. The cylinder filler should allow only those individuals essential to the filling process to be in the vicinity of the cylinder during the filling process.

That should keep bystanders from getting hurt. Sadly, most fill stations do not follow either safe engineering practices or the law. But the scuba police won't be there to stop them.