Following on from recent controversy on tank failures we interview prominent members of the dive industry, and manufacturers, for their thoughts.



Are Aluminium Cylinders Safe?


Interview with Guy Kidd, The Dive Centre, Auckland


By Dave Moran


Guy, how long have you been involved in the dive industry, and how long have you been testing dive cylinders?


I’ve been earning my living through diving for close to 40 years now. We started testing cylinders right from the word go, before there were any rules and regulations, just for our own peace of mind because we were the fellows that had to fill them. When I was in the Navy we tested them at the light machine shop. They had a pump that could hydraulically pump cylinders in those days. We ended up getting an engineer by the name of Jack Hanson, who was entrepreneurial in the mid ‘60s – who built a hand pump that we purchased which enabled us to pump tanks hydraulically. In those days they were steel tanks with a working pressure of 2250psi. We would pump them to 1.5 times their working pressure, in other words 3375psi, and measure the stretch. We used to do that once every five years. Eventually this became the recognised standard and the Department of Labour got in on the act and formalised it all. Since those days we’ve more or less followed Australia, whatever has been good enough for the Aussies the NZ Department of Labour just copycatted. That’s why we’ve ended up with a strong formula for testing cylinders.


Has there been some concern in recent years about some of the problems you’ve seen in the cylinders that you’re testing?


Very much so, to the point where I even faxed OSH (Occupational Safety and Health) safety inspectors quite recently, asking for a meeting because I’m very, very seriously worried that somebody is going to become a statistic. My reasons for this are that the cylinders in question, the Luxfer E6498, SP6498 and DOT3AL all have the same metal, and we believe all had the same manufacturing process. Now, these tanks are developing structural failures well inside the test regime that this country has put in place, ie one year for visual and two years for hydro. We have now proven that these cylinders can be perfectly acceptable to the trained eye during a visual, or the visual that goes with a hydro, and you must remember that we are visualising before and after a hydro in case the test pressure is making the cylinders crack. They are passing happily, and then inside three or four months they’re failing. We really, really started getting pedantic with these tests after Brian Schmidt lost his leg in Tairua. If there was any doubt whatsoever whether a cylinder was suspected to have a crack, other qualified staff would reinspect it, acid etch the neck region again if necessary, and if there was still any doubt we would condemn the cylinder. Then within three months we have had the same cylinder that has passed happily develop horizontally opposed cracks to the point where they become porous and we know that if the pressure had been kept pumped into them, they would have let go. They would have turned into a bomb. Now, that’s happened twice in my own filling bay.


So these tanks are being filled and all of a sudden you’re hearing air escaping from the tanks.


Correct. Not only us, but we’re starting to get reports in from other people. For example one of the dive operators in Rarotonga recently said that because he filled in air (he’s not wet filling), he heard this hiss and bent over to try and find out where it was coming from, and ascertained that it had horizontally opposed cracks in the neck of the cylinder, and he took off!

Now we wet fill, but when you start filling an aluminium tank it’s buoyant and it tends to float in the water. The first time it happened here I was filling a tank, talking to the owner of the cylinder, it got up to about 2800psi or 180 bar and I heard this rapidly increasing hiss. So thinking it was the blow-off disk vibrating loose or something, I just pushed the tank an extra inch under water to ascertain where the leak was coming from, and it was coming from two horizontally opposed cracks either side of the valve. That was at 2800psi. Now luckily our system has a rotational valve, one way to fill, the opposite to bleed off the air in the filling hose. And of course if the tank valve is still open you bleed the air out of the cylinders, so I just spun that valve, told the fellow he should do something about sex and transport in a big hurry, and cleared the building. We stood outside and listened to it vent until it was empty.

Now OSH came, said ‘Oh my God,’ and took it away. Six weeks later the exact same thing occurred on another cylinder that was only three months into its test period. So that’s two in my establishment. Same series, they’ve all been E series and the SP and AL. Even though Luxfer tell us that it is a user problem, in other words the cylinder is being damaged by the owner, that is an absolutely incorrect statement. The reason for this is that divers aren’t stupid. They realise it’s a high pressure vessel, they do transport them carefully, they do tie them into their boats, they don’t have them thrashing around, and the other thing is we’re not talking about user damage. We are talking, in my opinion, about a stress crack which has been in the metal from day one. When the neck area was formed, something, maybe the temperature that they were heated to, because they’re cold drawn and then the top of the barrel is heated to form the neck area, maybe that heat was incorrect. That meant that as it was formed the metal actually had cracks, and those cracks in the centre of the metal have been travelling. Some of them travel inwards and some have travelled outwards. When they travel both ways you get a porous area. This is one of the reasons why I fill in water. It’s no safer, because the water will just transfer the pressure as quickly if not quicker than air. It just means that as you get your head blown off you get wet as well!

The cracks have been there and they are growing. But everyone says, ‘Oh yeah, but they only grow very very slowly.’ My experiences and my gut feeling is that they are growing much quicker than people realise. They are minute one moment, and then they are catastrophic the next.


A lot of divers, after their tanks are filled, put them in their garage. These filled tanks could sit for a couple of months before their next dive. Is this part of the problem?


No, I don’t think it is a problem. The safety factor of these pressure vessels is huge. The half life and the number of cycles they’re supposed to be able to handle defies all reasoning that they should be kept empty until immediately before they’re used. I believe it is nothing to do with the pressure they are designed to handle. I believe it has everything to do with the manufacturing process being incorrect for the type of alloy that was used in the forming of the neck. Now, we’re not getting cracks in the base. They get tested to 1.67 times their working pressure, that’s over 5000 psi, and no, it’s not leaving them filled. It is a manufacturing problem, I am convinced. Regardless of what the manufacturers say about washing them down, drying them down, where you store them, that’s not the issue. The issue is they’re letting go, they’re failing. If it is a diver-produced problem, how come we have never had a failing of the English Luxfer, the HOAL2 cylinder? We just have not had one, in over 28 years of testing on these premises, we haven’t had one HOAL2 fail. How come they are all this particular group of one company’s cylinder?


So what would you like to see happen in the industry to safeguard against the possibility of a disaster, someone losing their life?


Well, if you buy a car for $30,000 you get three years’ guarantee. Anything that happens after that time, you pay for, not the manufacturing company. Luxfer’s system at the moment is if it gets a crack they’ll replace it, which I believe is magnificent. I believe that an owner of a cylinder who has had possibly 20 years or more use out of the cylinder is totally delighted at the public relations of Luxfer in giving him a new cylinder once the crack has been found. If they had a blanket condemnation and just pulled the plug on these cylinders, and that was it, ie these tanks would not be allowed to be presented for testing or filling, they were all trashed, then the diver, being who he is, would possibly be offended. A few would be philosophical, but the majority of them in my opinion would be offended. I would like to see some sort of a business deal done by Luxfer where the divers present the suspect cylinders and are given some sort of a reduction on the price of a new cylinder.


So you’d like to see these cylinders completely removed from the market?


Oh yes, they must be. They will be, the day after they kill somebody. I am sure of that. But I would prefer that the plug gets pulled prior to that happening, rather than as an after effect of a fatality. They say they will give you a new cylinder, but they might have to give it to your widow. This is why I went public with OSH and I believe the plug should be pulled on them.

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