O2 tank explosion

[Puffer Fish]

When I saw this image, I was immediately reminded of several images as seen in this YouTube video:




The video has about 20 seconds of black screen, in the beginning, as the incident is narrated. (Obviously) the causes are different, but some similarities may be drawn. Perhaps SLC was a cause? I will re-think many of the common practices we use with our deco bottles.


All the best, James

I would like to thank you for posting that video. I have found this accident extremely troubling, first because of the terrible nature of the event and second because I have had difficulty understanding exactly what happen, and how anyone could have done something differently to prevent the event.

The video you posted, for all practical purposes is, as best I can tell an almost identical event. The only difference being what cause the initial leak.

Why would a O2 tank explode from a valve leak? Well, if you look for video's of people shooting tanks, compressed air tanks just shoot around, while even low pressure O2 tanks explode. Obviously O2 is not explosive, and is not a fuel, and yet if you shoot one, you get an explosion. I believe it is because even tiny amounts of metal, dust or anything that can act as fuel, will react so quickly that the expanding gas is faster that the container (even a container with a hole now in it). It expands to the point where the tank blows apart, and now there is lots of fuel to continue the flash.

But what provided the energy to ignite the fuel? O2 is a much thicker gas than air, and going thru the tiny opening must have heated some of the tiny particles. In the case of the video, just breaking the seal on the valve provided enough material to explode the tank. I believe the tank dropping on the value would have actually released a lot more fuel.

I found that there have been several reported cases of Large O2 tanks blowing up and/or igniting inside the regulator from falling over and then just opening the valve at a later date. It is the reason for the OSHA requirement to have the tanks secured. Any fall off from the inside of the tank can be very dangerous.

I had no idea just how dangerous compressed O2 can be. IF I had one fall off a table onto the floor, my reaction would have been to reach down and pick it up. If I had a tank get knocked around on a dive trip, I would not have thought to drain the tank away from anyone and have it inspected.

I find it very sad to have learned this from such an event.

 

[mitsuguy]

Why would a O2 tank explode from a valve leak? Well, if you look for video's of people shooting tanks, compressed air tanks just shoot around, while even low pressure O2 tanks explode. Obviously O2 is not explosive, and is not a fuel, and yet if you shoot one, you get an explosion. I believe it is because even tiny amounts of metal, dust or anything that can act as fuel, will react so quickly that the expanding gas is faster that the container (even a container with a hole now in it). It expands to the point where the tank blows apart, and now there is lots of fuel to continue the flash.

But what provided the energy to ignite the fuel? O2 is a much thicker gas than air, and going thru the tiny opening must have heated some of the tiny particles. In the case of the video, just breaking the seal on the valve provided enough material to explode the tank. I believe the tank dropping on the value would have actually released a lot more fuel.

This is exactly what I've mentioned like a half dozen times during this thread.

in that video, you can definitely see that there was fire around the valve assembly - those black markings are definitely from fire... and this was caused from just opening the valve slightly - sounds similar to my theory that when the tank fell that something happened to the valve and that caused the fire (whether it was loosened from the fall by spinning it, or maybe, perhaps, with this new video in mind, that it opened the valve just slightly)

 

[oxyhacker]

The valve-to-tank interface on an aluminum tank is an excellent place to start a fire, because the valve threads come to a sharp point, and are generally rough and abraded, all of which makes excellent "kindling" to initiate combustion. This is not ordinarily a problem, since there isn't ordinarily enough heat there to take advantage of it, but when someone take a wrench to the valve and tries to force it all bets are off.

When a valve is forced, the friction as it breaks loose can create very localized, very high temperatures. One can notice the same effect when undoing a nut - I have burnt my fingers picking up nuts after undoing them with a hand wrench. In the case of a valve on an O2 tanks the localized heating as it is loosened will be accompanied by a blast of O2 over the threads, so that all the elements of the combustion triangle are fulfilled.

My suspicion is that this is also the mechanism in some of these mysterious knocked over tank events - that a small blow at just the right spot can create a one-in-a-million (or one-in-ten-million, whatever it takes) event. The only predictable thing about high pressure O2 is that it is unpredictable.

There are also reports of leaking aluminum tanks combusting just from the heat caused by the friction of the escaping gas abut they are harder to nail down. I was told some years ago that this was the reason why Linde doesn't use any aluminum tanks for O2.

Why would a O2 tank explode from a valve leak?

 

[Zodiacdiverdave]

One more possible source of ignition would be from the static electricity generated by the very dry O2 escaping from either the valve being opened accidentally or from a leak at the threads. The static electricity can create sparks, the O2 causes the AL to burn rather then the O2 itself burning. The kindling could also be dust or dirt of any kind. When the AL starts to burn the tensile strength is rapidly lost and the cylinder ruptures. In the video it is the top part of the cylinder that came apart and it is also the area of the fire.
ZDD

 

[John C. Ratliff]

Charles and I have been discussing this accident, and our disagreements, off line. I have done quite a bit of reading, and found a number of references. I will be sharing these here, and probably starting another thread about this potential for oxygen to cause this kind of accident. My reading included: NASA, the Myth Busters Blog, Air Products and Luxfer.

The short answer is that the simple shock of the fall is enough to ignite the fuel (any contaminants) inside a cylinder. It is apparent that many, many sports divers are unaware of these problems, and this includes people with a lot of education. Sources of ignition, according to NASA, include frictional heating, adiabatic compression, mechanical impact, particle impact, mechanical stress or vibration, static discharge, electrical arc, chemical reaction, and resonance. Luxfer states this:

12. Question: Can dropping or striking a scuba tank containing pressurized oxygen start a fire?
Answer: If a contaminant (fuel) is present and the oxygen inside a cylinder is under sufficient pressure, impact from a fall or blow can indeed be the ignition source for an oxygen-fed fire. Although ignition of this type occurs very rarely, it’s still a good idea to handle a pressurized cylinder with care at all times. Always follow all applicable DOT guidelines when transporting cylinders. Secure cylinders when transporting them so that they will not roll around, rattle about or strike other cargo or hard surfaces. Protect cylinders from falling and impact by using chain restraints, padding, straps and dollies during transportation and use. Also, always exercise great caution when hand-carrying all pressurized scuba cylinders, especially those containing oxygen or oxygen-enriched mixtures.

There is another source, the US Department of Veteran's Affairs, which states:

• Rapidly opening a valve on a compressed gas cylinder can cause particle impact ignition resulting in a fire (this is why aluminum regulators are not permitted - aluminum is a combustible metal).

I have done a lot of accident analysis over the years (30+ years in the professional safety and industrial hygiene fields). All the evidence from this accident, and others, is that there was ignition and explosion. I now know that there are multiple potential ignition sources, and sufficient fuel, for this to have happened. I am hoping that this information will become more prevalent in the sport diving field, and especially recommend the information developed by NASA and Luxfer above.

John

 

[Zodiacdiverdave]

John, this sounds like it may be a good thread to be discussed in a tech. diving forum. O2 is used often by techies and the potential hazards of this gas may be under estimated by allot of people out there. For myself, I only have O2 for accidents and I have a membrane system for making nitrox and tend to use steel tanks but not always.
ZDD

 

[Puffer Fish]

This has been a tremendous eye-opener for me, thanks Mitsu, Oxyhacker, Zodiac and John.

Mitsuguy, Yes you have, but in all honesty, the concept that just dropping a tank or having a valve leak could cause a tank to blow up was difficult to wrap my head around. I don't think I am alone in that, by the way.

I've done a limited amount of fire accident investigation, but it has been mostly boiling vapor explosions and dust (chemical engineer). Only once, a very long time ago, was I involved in a O2 tank fire. But this was a welding system, and the fire started in the regulator. The determination was that it was cause by "contaminants", with no specific source. Today, I would look at how the tank had been handled. That same event, with a scuba tank (without the regulator) would have been an explosion.

Thanks guys, and yea, this subject might make a good sticky in Tech.

 

[2 Big 2 Fail]

If it was a matter of the aluminum tank burning, I suspect it's most unlikely that every detail of the event can be determined after the fact. Aluminum has some peculiar properties and can be difficult or easy to ignite, depending on the circumstances. Generally, it's difficult. Thermite normally requires some kind of burning metal secondary ignitor, the classic being magnesium ribbon. Metals generally burn without cooling vapors and have high boiling points and so make good ignition sources.

It seems unlikely to me that friction of gas passing through a fissure could reach the necessary temperature. I'm not sure about that or even if it's possible to generate any appreciable heat from friction alone. Objects entering the atmosphere might get hot enough, but that's air compression, not friction. But if another substance is present, it might be one that would require relatively little heat to react in an almost total oxygen environment. Once ignited, it might well act as an ignitor for the aluminum which, as has been pointed out, is already formed in a more easily ignited form by threading or, perhaps more likely, aluminum powder, which is far more easily ignited. It wouldn't take much at all of an ignitor substance or aluminum powder to get the aluminum fire going instantly. And the evidence of what exactly happened would disappear.

Once ignited, aluminum under the influence of high-pressure oxygen would surely produce a fearful jet of flame hot enough that

 

[sharksdelight]

While I see that there is a 'Donate to ScubaBoard's Legal Defense Fund' under Puffer Fish's post, may I remind everyone that this thread is really about helping Rick and Cindy Allen as they are dealing with the horrible results of this accident. Donations from this thread should be made to them which they very much need at this time.
Steve

 

[falcon125]

Prayers sent for Rick & Cindy.
I will make a donation soon.