Dive Cylinder Explodes - Sydney

[KevinNM]

contrary to what wookie suggests, my instinct tells me that if the outside of the tank stays cool-ish, the inside won't be as warm as when dry filled.

I don't think he claimed it wouldn't be as hot. I think the argument was there would be higher stress on the tank due to the heat differential. Don't know myself.

There is a fill station in FL that (does or did, not sure) fill in an ice bath. Occasionally, in a hot car, people would get their burst disk blowing out, or so people who had that happen told me.

 

[Patoux01]

No I know it was not about heat, but aluminium (not its oxyde) is supposed to be very good at dissipating heat (at least, IIRC from my materials engineering courses, which I'll happily admit I wasn't interested in...), so I'm unsure the gradient would be as large as implied.

Yes that story comes pretty close to this article http://www.cochranescuba.com/forms/Case for Dry Filling Scuba Tanks.pdf

 

[Diving Dubai]

@Patoux01 @KWS

A couple of points that may relieve your concerns.

Firstly the working pressure of a scuba cylinder is referenced to a temp - so 200bar @ 20C (3000 PSI @ 70F as a round number) However Scuba cylinders are rated up to a maximum working temperature of 65C (150F). So as long as the pressure is relative to the temperature (i.e the pressure increases with temperature) all is okay)

Regarding fills, as you can imagine here in the Middle East, we get very high air temps and high humidity (well over 110F and 70% humidity. All the shops have air driers and air chillers to cool and dry the air before is enters the compressor (I believe the air chillers get the air down to 5C (41F).

Standard practice when I was filling was to simply fill the tank to the working pressure, take it off the whip and let it cool and then top off the pressure (rather than over filling). Our club had an air drier but no chiller.

Regarding cooling a cylinder. The tank walls are quite thick meaning it's a big heat sink. The external surface area isn't that big, to cool it effectively you'd need heat sink fins around the exterior. If you got the outside cold, and assumed the inside was hot from the compressed air, you would induce thermal stress. Better to allow the tank to change temperature gradually.

It may be already done, but I don't see why you can't reduce the air charge temp by putting an inter-cooler after the compressor to cool the air and make the charge more dense as used on vehicle engines

 

[Wookie]

No I know it was not about heat, but aluminium (not its oxyde) is supposed to be very good at dissipating heat (at least, IIRC from my materials engineering courses, which I'll happily admit I wasn't interested in...), so I'm unsure the gradient would be as large as implied.

Yes that story comes pretty close to this article http://www.cochranescuba.com/forms/Case for Dry Filling Scuba Tanks.pdf

No reason to take my word for it, here is the industry standard: PSI-PCI - Filling Cylinders In Water - Time to Review

What I find most interesting is that there is a huge argument from laymen (tank fillers, dive shop owners, scuba divers) about how a tank should have a better fill (stay cooler, more pressure, etc) if filled in a water bath, yet there is not one piece of published data anywhere that backs up this theory. Oh, sure, there are a million articles written by very intelligent people about how a cylinder should never be filled in a water bath, and how it would never help in a cylinder explosion, and that the water bath itself becomes part of the flying debris, and these articles set the industry standard, but there are no articles that back up the myth of filling in a water bath.

Even important topics like the Existence of God and/or Global Warming have articles written on both sides of the argument, but there is not one single published paper touting the benefits of filling in a water bath. Not one. The cylinder manufacturers, the compressor manufacturers, the gas houses, the training agencies, nobody has written such a report. Go to an industrial gas house someday. Watch them fill bottles of welding or medical O2. You'll note that they strictly observe filling rates, but never submerge their cylinders. I think someone above implied that scuba shops can't afford to take a safety precaution like that.

But don't mind me, I'm just parroting the acknowledged experts.

 

[BoltSnap]

No reason to take my word for it, here is the industry standard: PSI-PCI - Filling Cylinders In Water - Time to Review

What I find most interesting is that there is a huge argument from laymen (tank fillers, dive shop owners, scuba divers) about how a tank should have a better fill (stay cooler, more pressure, etc) if filled in a water bath, yet there is not one piece of published data anywhere that backs up this theory. Oh, sure, there are a million articles written by very intelligent people about how a cylinder should never be filled in a water bath, and how it would never help in a cylinder explosion, and that the water bath itself becomes part of the flying debris, and these articles set the industry standard, but there are no articles that back up the myth of filling in a water bath.

Even important topics like the Existence of God and/or Global Warming have articles written on both sides of the argument, but there is not one single published paper touting the benefits of filling in a water bath. Not one. The cylinder manufacturers, the compressor manufacturers, the gas houses, the training agencies, nobody has written such a report. Go to an industrial gas house someday. Watch them fill bottles of welding or medical O2. You'll note that they strictly observe filling rates, but never submerge their cylinders. I think someone above implied that scuba shops can't afford to take a safety precaution like that.

But don't mind me, I'm just parroting the acknowledged experts.

LOL, you took the words out of my mouth.

Perhaps it is a conspiracy by PSI-PCI to overtake the universe

If it is OK by you @Wookie , I'd like to quote your post in a FB page please??

 

[Diving Dubai]

@Wookie @BurhanMuntasser

Good post by Wookie and interesting article from PSI.

Out of interest I looked at their courses, and noted that they offer Eddy current courses for $195 which only take 2 hours. For anyone wishing to sign up for these believing that in 2 hrs you'll have enough knowledge and practice to safely carry out a Eddy current test and accurately be able to decide if there is a defect or not. Please send me $150 and I will guarantee that within 2 weeks I'll make you a millionaire

@KWS Out of interest as I believe you are qualified to VIP tanks. Are you (or others) that VIP tanks required to carry any indemnity or Public liability insurance if a mishap happens on a tank you certified being filled by others? (A genuine question out of interest)

 

[BoltSnap]

@Wookie @BurhanMuntasser

Good post by Wookie and interesting article from PSI.

Out of interest I looked at their courses, and noted that they offer Eddy current courses for $195 which only take 2 hours. For anyone wishing to sign up for these believing that in 2 hrs you'll have enough knowledge and practice to safely carry out a Eddy current test and accurately be able to decide if there is a defect or not. Please send me $150 and I will guarantee that within 2 weeks I'll make you a millionaire

@KWS Out of interest as I believe you are qualified to VIP tanks. Are you (or others) that VIP tanks required to carry any indemnity or Public liability insurance if a mishap happens on a tank you certified being filled by others? (A genuine question out of interest)

Perhaps you are thinking of much larger range of testing than what they intend their students to be able to do. Also, The Eddy current course is part of a sequence of courses AFAIK.

At any rate, why don't you correspond with PSI and present your point of view.

If you are able to deliver a better, and relevant, course than they do, please package it and start offering it and I'll sign up for sure.

 

[Wookie]

LOL, you took the words out of my mouth.

Perhaps it is a conspiracy by PSI-PCI to overtake the universe

If it is OK by you @Wookie , I'd like to quote your post in a FB page please??

Of course. Use it as you like. You don't even have to credit me...

 

[Wookie]

@Wookie @BurhanMuntasser

Good post by Wookie and interesting article from PSI.

Out of interest I looked at their courses, and noted that they offer Eddy current courses for $195 which only take 2 hours. For anyone wishing to sign up for these believing that in 2 hrs you'll have enough knowledge and practice to safely carry out a Eddy current test and accurately be able to decide if there is a defect or not. Please send me $150 and I will guarantee that within 2 weeks I'll make you a millionaire

@KWS Out of interest as I believe you are qualified to VIP tanks. Are you (or others) that VIP tanks required to carry any indemnity or Public liability insurance if a mishap happens on a tank you certified being filled by others? (A genuine question out of interest)

Somehow I got KWS's quote in here also. So, first off, the easy one. I do not VIP outside cylinders. My cylinders do not get filled anywhere but at my fill station. I do carry liability insurance in case one of my cylinders blows up and wipes out a diver's leg. If I worked for a dive shop, they would carry liability insurance for my VIPs that I performed for them for outside cylinders. I am also a trained valve repair technician and O2 cleaning technician. And I have all of the tools to work on alloy 6061 cylinders. I got rid of my 6351 cylinders many years ago.

As far as eddy current testing training goes. I agree that becoming a QA technician and having the ability to perform different types of NDT takes a ton of time and a mountian of school to become certified. Being an eddy current technician, however, using one specific tool to check one specific part of one specific cylinder is a different animal. I can see a 2 hour course as being sufficient.

 

[Peter69_56]

Part of my current life is throwing b ombs overboard to shock test Navy destroyers. According to the website How Stuff Works Is it worse to be near an explosion on land or in water? you'd sustain far more damage from a water blast than an air blast. Now, I'm no expert on explosions, (I'm just the ship's engineer), but the shock wave is not dissipated by the water except by distance, because the water in not compressible. Air is compressible, so some of the energy is used by compression of air and not transferred to the person. This assumes that shrapnel isn't a factor.

Back in the day when torpedoes were actually contact weapons, if you could fight the water coming in the boat, there would be little further damage inside the hull because of the compression effects of the air inside the hull. I have seen examples of this when diving on the U-2513. The U-boat was sunk during a navy exercise by hedgehogs, which opened a hole in the bow in the forward torpedo room. Hedgehogs were depth charges, and they were a "close enough" weapon. A fairly small charge, they were designed to produce a pressure wave which would transfer through the water and strike the hull. Since the outer hull is just ballast tanks, usually full of water, the pressure wave would be transferred to the pressure hull, or people tank. Assuming the people tank was full of air, damage would be limited to the hull. That was the idea, to fill the people tank full of water. The U-2513 is almost in perfect condition. All except that big hole in the torpedo room.

I understand and agree that its far worse to be IN the water with an explosion compared to on land, however we are talking about both here so somewhat different. I also agree with you that having it in a tank of water will not prevent injury or death.

However If I had to chose to stand in a room with tank in water to its neck (with distance, thus air between the water tank and me, or same position with the tank free standing in air, I would take the first option. Thats based on my "amateur" understanding of where a lot of the energy will go (remembering there is a water tank wall assuming its steel holding the water in). In both cases energy will go out as well as up. In the first case however, the water absorbs much of it going out and thus with the air space as well, the damage "generally" speaking would be less, and the water "tends" to contain the energy somewhat thus forcing more of it upward. In the second case the energy travels in the direction of failure with nothing really to stop it except distance. I am not saying you would be safe, nor would I say you would not be hurt, but the potential for damage would be reduced.

I also spoke to a dive tech who had one explode on him while filling. He had it in a tank (out the back of the shop), and his comment was that he would have been hurt had the water tank (and steel containment wall) were not there.

Now I am NOT an engineer or have experience in explosions and containment but thats my thinking and I guess the only way someone could change my mind is to do a test or show me the maths. Its not to say you dont know what you are talking about wookie, but I cant get my head past the logic above (sorry). You are an engineer, and I am just an amateur and where I dont have the skills I operate on what seems logical to me anyway (correct or not). If you can direct me to some studies or whatever, I am more than willing to change my "logic".

I suppose the main point I would make though is that so many dive shops fill in the shop in front of customers. Mainly so they can minimise staff and have one person do everything during week days. And they paint a yellow line 1 m around the tank fill area as apparently the yellow paint contains exploding tanks! This should not be allowed ever as its stupid at best.

With regard to getting water in tanks while filling, yes standing them in water tanks increases risk, but if one is anal, it should not happen. How many times have I seen a tank brought in, immediately connected to a fill line and filled, without clearing the connecting point on the tank first. Onlt takes one drop of salt water! If you accept more risk but the method you use, you have to be more methodical in how you do it. Yes, reducing risk is always better, however that may increase risk in other areas to an unacceptable level.