Toby

[Bubble Boy]

seahunter once bubbled...
Did I miss something??

We just sold our Visual Eddy machine since it is not an essential service and was adding nothing to the safety of the visual exam.

Thats a wide open question but I will behave. You did miss something. Eddy current testing is not a substitute for a visual inspection, it is a tool to assist in a visual inspection. False positives are a lack of training or failure to use the equipment properly. If you can do a visual in the time it takes to do an eddy current test then you are doing neither correctly.

On recreational "SCUBA" cylinders the testing is not required but strongly recommended for the older alum cylinders. It can detect a crack prior to them being visible as well. The are not for use with steel cylinders.

Don't forget that the units should be recalibrated annually---ooops is there no one servicing the visual plus units in Canada?! I have had my eddy current machine calibrated regularly but I doubt that it is the norm.

Yes they do add safety to the scuba industry.

 

[Groundhog246]

Bubble Boy once bubbled...
Don't forget that the units should be recalibrated annually---ooops is there no one servicing the visual plus units in Canada?! I have had my eddy current machine calibrated regularly but I doubt that it is the norm.

Yes they do add safety to the scuba industry.

My LDS sent theirs out for calibration this year (I think they do every year). I know because it went 3 days before I dropped my tanks off (one is the old alloy) and it was almost a month before it came back. Wasn't an issue in the middle of winter and I have 2 steels which weren't due yet available for pool play.

I can't see how any extra level of scrutiny can be bad. During my equipment course, the Eddy machine was demonstrated on both good and known bad tanks (bad tank was rendered permanently unfillable and saved for demo). Yes the crack was barely visible, but quite obvious with the Eddy test.

 

[seahunter]

I don't want this to be a 'He said - I said' debate so let's see if we can agree on some basic technical points and also on some well-understood if not appreciated human characteristics.

1. A proper visual will detect any cracks. A poor visual will miss cracks and, it's safe to assume, other problems.
2. A Vis Ed must be accompanied by a proper visual as well so the time factor is longer than for a proper visual alone. In the time required to set up, calibrate and conduct a Vis Ed AND then a proper visual , you can complete a thorough, proper visual.
3. Vis Eddy machines have a history of false positives and missed cracks. This may well be due to operator error but the operators in the study were trained in the use of the machine so these 'mistakes' will occur in the general, proper use of the machines.
4. Human nature dictates that a safe condition on the Vis Ed display creates a false sense of security. The operator will seldom if ever check the threads manually or question the validity of the reading. That is, in my experience, if the machine shows a crack the operator will re-check to be sure BUT, if the machine shows no cracks he will not.
5. Again, human nature is such that when supplied with assurances from a Vis Eddy salesman that tank problems are 'solved' by it's use, he will be believed. Now the inspector does a Vis Eddy plus a cursory visual and sends the tank on it's way. What the tank gets is a quick Vis Ed with it's inherent errors and a sloppy visual.

My basic point is that a proper visual is the solution and the addition of the Vis Ed may not help. It may in fact hinder the process.
I'm of the opinion that Vis Ed is simply an application of the old magnaflux technology in a new form which has been sold to the dive industry. All these types of non-destructive testing are very operator sensitive. This opinion is based on lengthy discussions with an industrial stress engineer on my staff.

No, Visual Eddy testing is not bad.

Why not do both?
Human nature as described above. It is the same process that has led to the exclusion of 'buddy breathing' from basic scuba classes or to the extinction of the J Valve. I loudly protested those moves but now understand the rationale and absolutely support the dropping of both these seemingly supportive safety measures. Human nature often contradicts logic.

Perhaps these two changes in scuba are another topic for discussion. I think I still have my notes from 1970 (for the J Valve) and 1989 (for the Buddy Breathing). We might as well jump to another unrelated topic. I'm having fun.

I'm know you're well aware that the accident in Toby was not remotely related to recreational scuba tanks or their inspection.
You're right that it may have raised sensitivities but it's illogical to relate the two actions - Human nature again?

 

[Groundhog246]

seahunter once bubbled...
Perhaps these two changes in scuba are another topic for discussion. I think I still have my notes from 1970 (for the J Valve) and 1989 (for the Buddy Breathing). We might as well jump to another unrelated topic. I'm having fun.

I'm know you're well aware that the accident in Toby was not remotely related to recreational scuba tanks or their inspection.
You're right that it may have raised sensitivities but it's illogical to relate the two actions - Human nature again?

I think we mostly agree on the inspection issue then. perhaps we should insist on 2 different people inspecting. One doing the Eddy test and one the visual, without being able to discuss before both are done. With 2 people, each determined not to miss something that the other might find, you'd have an extra margin of care. Of sourse, the cost of inspection might become an issue. :wacko:

My LDS still trains buddy breathing, almost wonder why when you've an octo and it was the advent of the spg that killed the J valve, whose demise I am agreed with.

And yes, I am aware that the tank explosion in Toby was an error by the fill operator, not a faulty tank. In fact, if you look at the info from Luxfer, the number of crack related failures, worldwide, is really very low when placed against the number of cylinders they made. I've also wondered, how many of those have been repeated overfilling. While some may complain if they get to a dive site and they've only got 2900PSI, I'm just as happy if that's the case. The very few minutes that 100PSI (or 200) will make to my dive is less important than extending the life of MY cylinders. Most of my buddy's use more air than me anyway, I often end up with 1000PSI left, maybe I should have saved weight and bought 63's.

 

[seahunter]

Divers are pretty funny. They seem to think that they must get 3000 psi or they've been ripped off even though every one will agree they usually come up with between 500 and 1000 psi anyway.
That's been another good side effect from our policy of free air for divers. Certainly no one can claim we ripped them off.
We don't take advantage of it however. Our posted air fill policy states that a 3000 psi fill will require at least 30 minutes. If they can't wait, they will likely lose 200 to 500 psi. Their choice. Many do come in and ask us to overfill (3300?) so the tank will be full at the dive site. It's against policy and we tell them that stores who do that are not doing them, their tank or scuba any favor. Fill it right or go home!

When the octopus first became popular the skill(?) of buddy breathing was still taught because older divers and instructors felt (rightly) that a diver out of air would grab the main reg from his buddy's mouth and the skill of BB might be useful.
Research has since shown that it is the teaching of the skill of buddy breathing that gives the new diver the idea of grabbing his buddy's main reg.
New divers now never even think about doing that. They are taught to instinctively find and use the octopus. Theoretically, if you went diving with a new diver and you did not have an octopus, he would drown looking for it but would not grab your main reg. He's has never even considered that as an option! Theory and practice may differ somewhat but it seems to be working just fine.

For me personally who was trained on two hose and how to buddy breath on two hose (quite a trick I'll tell you!), I would not buddy breath with another diver in an emergency. If he runs out of air, he can damn well go to the surface. I have no intention of increasing the number of 2-diver deaths in the accident reports at my own expense.

 

[Bubble Boy]

From the UHMS' web pages:

One tank has the explosive potential of a stick of Forcite. This tank was 13 1/2 feet long, 18 inches in diameter and fully charge to 3000 psi. The blast was heard miles away. A map showed the original location of the tanks and where some of the pieces and other tanks ended up. the tanks had been in a pyramid stack with a row of 4 on the bottom, three on top of them and 2 in the upper tier. The lower outside tank that was against a wall blew up. One piece ended up on the road to Big Tub and another was near the lighthouse. Two intact tanks were on the lawn, one on the patio of the resort next door. The one victim was standing beside the wall the tank was against and was literally blown away. Another person standing nearby was not injured. One tank ended up in the lake. All the tanks were ripped from their moorings. People described the tanks having "blue flames" coming out of their broken off stems but it was likely just condensation of the air rushing out. It was very luck that the accident happened in early June because there were no visitors at Tobermory yet. Last know date of inspection of the tanks was in 1989. They were war surplus torpedo charging air tanks. The owners had the air checked regularly but there were no tank inspections done by regulatory authorities and that issue needs to be resolved. The explosive capacity of the tanks was equal to three stick of dynamite. The interior walls of the tank were heavily pitted and the tank probably blew up because of corrosion inside. The wall thickness varied greatly

 

[TAM Dive]

Toby charters???...........yes the enforcement of the coast gaurd rules and regs has weeded out the charter boats with not quite up to standards worthyness, so ya!! less charter boats available presently...........meaning, you may have to book early to get on one..............weekends in Toby are still a zoo, so if you just show up, you take your chances??

VIS Eddy?? if you check out the Luxfer site, you'll read that the VIS Ed machine was designed for a specific material, Luxfer does not recommend the machine to be used on the 6061 aluminums or steel tanks, and even comments about the high number of tanks sent back to them as failed, which should have never been removed out of service.

Unless you own a compressor, you are at the whim of the diveshop, they are the ones who are filling the tanks, in consideration of the fact that the few tank explosion accidents that have been documented ( I think last count was less then a dozen) have happened in the dive shop while the tank is being filled.

With regards to getting that FULL Fill 3000psi?? everyone one is in a hurry these days, hurry up fill my tank, well I'm sure we can get into a whole physics thing about heat of compression yada yada!!! best way to get that full fill is to plan on leaving the tank at the dive shop, let them fill it slowly (low heat build up) and then a top off after it cools...................but understand.......you take the tank out from the room temp of the shop to say the 5C temp of the water today, that tank is NOT going to read 3000 anymore......hmmmm there's that physics thing again??.......you are pretty much splitting hairs over a couple of hunder pounds??

mho
j

 

[sparky30]

I keep my tanks in the car if I'm going to dive them in the next few days.. They go out even before I get tehm filled.. When I haul them into the shop to get filled they are nice and cold.. Even with a quick fill, the increae in temperature is minor... I let them sit for a while and top them up.. Then they go back into the car..
By the time they hit the colder water they are already cold, so I usually end up with 3000psi.. Works very nicely
They were basically filled at the same temperature (or as close as I could get it) as the water the will be used in..

 

[cat]

the laws of physics...
Ignoring the Joule-Thompson effect for now (the heat of compression/expansion thing) you can calculate what your tank should read in the water like this:

Pressure in the water = pressure in the dive shop x (water temp in C + 273)/ (temp in diveshop in C + 273)

The 273 is the conversion to the absolute temperature scale (aka Kelvin)

Example: a tank that shows 3000 psi in a 20 C dive shop (assuming it is at equilibrium and not a hot, just-filled tank) should have just under 2850 psi in 5 C water.
The same tank filled to 3000 psi on a hot, 30 degree C day will only read around 2800 in 10 degree water or 2740 in the 4 degree water at the bottom.

 

[seahunter]

Thanks for the graphic details bubble boy. I'm not entirely sure if much was gained by reading that anymore than we are more careful drivers by hearing how a person's head was torn off in a car accident.

Some technical deatils that are not common knowledge might be more interesting. I am not defending nor attacking anyone by stating these things.

1. Stationary compressed air bottles are not required to be visually inspected. Even the storage ones in every dive store are NOT inspected each year. A visual is unique to portable bottles and particularly to scuba for a variety of reasons which you may be able to guess - marine environment and private (read sloppy) care.
2. Most stationary bottles require a Hydro test every 10 years.

The submarine bottles (that's the common name for the one in Toby that exploded because they were used as storage of air on submarines) were not covered by any government inspection regulation. That is, when TSSA went to inspect the TOBY system, they found no standards for the inspection of those bottles. Whether it was neglect on the part of the owner or the regulating body is for the courts to decide but there were no care and inspection guidelines for the owner to follow.