Oxygen Clean Tank

[Crazy Fingers]

If the only issue at stake here is the "small amount of hydrocarbon" present in the cylinder, we would have no problem. However, what actually happens is much more catastrophic. Those "small amount of hydrocarbons" only begin the fire. The pressure and temperature elevate so fast at the beginning of the fire that the metal in the cyinder starts to become the fuel. In a matter of nano-seconds, the whole process gets out of control.

Hmm... so it seems like very slowly bringing the pressure up would at least reduce the risk of this occuring.

I couldn't find the ignition temperature of aluminum plate or rod (only powder), but I found the melting temperature of aluminum sheet to be 1220F. I would imagine that it probably has to melt before it can burn, since evaporation is much easier than sublimation, and combustion can only occur in the gas phase. But that doesn't seem to be unreasonable temperature to have in a localized combustion area inside a tank with a few hundred PSI of O2.

If you all are the guys that "wrote the book" on this stuff, then I guess I am not going to bash heads with you. But, again, I would like to see documented instances (such as a fire inspector's report) of SCUBA cylinder failure due to oxygen fire. And not when the user is compressing O2, only a transfill. As authorities on the subject, you should be able to give this information.

 

[in_cavediver]

Hmm... so it seems like very slowly bringing the pressure up would at least reduce the risk of this occuring.

I couldn't find the ignition temperature of aluminum plate or rod (only powder), but I found the melting temperature of aluminum sheet to be 1220F. I would imagine that it probably has to melt before it can burn, since evaporation is much easier than sublimation, and combustion can only occur in the gas phase. But that doesn't seem to be unreasonable temperature to have in a localized combustion area inside a tank with a few hundred PSI of O2.

If you all are the guys that "wrote the book" on this stuff, then I guess I am not going to bash heads with you. But, again, I would like to see documented instances (such as a fire inspector's report) of SCUBA cylinder failure due to oxygen fire. And not when the user is compressing O2, only a transfill. As authorities on the subject, you should be able to give this information.

First, yes it is all about fill rates. NASA I belive has done testing and claimed to light any hose up with o2 given a suitable rate. Many others fill 'safely' with questionable air/tanks at very low fill rates. Generally, a good idea to keep the low rates with clean tanks and clean air anyway. Why rush it.

WHY CHANCE IT WITHOUT 02 CLEANING A TANK????

Its something YOU can do and its not that difficult. Get the Oxyhacker book and READ IT. Vance is an excellent resource.
High pressure gas handling isn't rocket science but it does take respect.

 

[FishDiver]

An aluminum cylinder that is constantly refilled with clean air gets progressively less clean. While our ultra clean scuba air has greatly reduced hydrocarbons, it doesn't have zero. Therefore, the more you fill and use a scuba cylinder, the more it progressively gets contaminated.....no matter WHO makes the air and no matter HOW CAREFUL they are. Those are the facts. So, frequent recleaning is required.

I never contested the fact that O2 cleaning made sense. My original statement was that annual hydro testing is excessive and I questioned the need to to reclean a tank after each hydro.

Ignoring arbitrary legal requirements, after how many FILLS, on average, should a tank be O2 cleaned?

 

[Dive-aholic]

Looks like an interesting book... I will see if the Library has it or can get it. Thanks.

You probably won't find it in the library. And you definitely won't find a used one out there for sale. When people buy it, they keep it. It's that good.

 

[PhilEllis]

I never contested the fact that O2 cleaning made sense. My original statement was that annual hydro testing is excessive and I questioned the need to to reclean a tank after each hydro.

Ignoring arbitrary legal requirements, after how many FILLS, on average, should a tank be O2 cleaned?

If your original question was "why should a cylinder be cleaned after hydro inspection", that is a very easy one.

In the hydrostat process, the cylinder is filled with water. The source of that water varies, depending on the set-up at the local hydro facility. The one we use here recycles the water used for the test. I am told that the same water is also used in the circulating system to cool the test equipment. Given that we don't know the level of cleanliness of the water, NOT cleaning an oxygen cylinder that will be used for breathing air after hydro would be utterly foolish. Scuba diving operations have no valid test for "inspecting" the oxygen clean status of a cylinder. Short of using milipore tests or some other type of lab test to determine the presence of hydrocarbons, we depend upon the "validity of the cleaning process" as our only proof of cleanliness. The short answer......the only way to have confidence that the cylinder is as hydrocarbon-free as possible is to clean it. Thanks.

Phil Ellis

 

[oxyhacker]

That, alas, is the nature of O2 incidents - they usually make such a mess that one never can quite figure out the exact cause or even the order of events. You are left with a burnt-out garage, shop, or house, and not a clue to why. So wise mixers do everything they can to eliminate potential sources of fuel or ignition, while fools quibble and conjecture to try and explain away the need.

2) No one on that thread really knew what happened anyways since there is no explanation.

 

[pescador775]

About the Diesel fuel: Diesel fuel will not normally ignite at high pressures. Fuel ignites in a Diesel engine because of heat generated by almost instantaneous compression of the air-fuel mixture, correctly referred by another poster as "stoichiometric". In cold weather, additional means are needed to ignite Diesel fuel.

Carbon monoxide is not a typical byproduct of combustion in an oxygen environment.

Aluminum cylinders will always be suspect for the purpose of containing oxygen. They should be cleaned more frequently than steel. The main danger is possible presence of loose particles of metal.

The word "adiabatic" is most frequently used by those who have no clue.

NASA can prove anything at any time. They have the resources and the contractors willing to do it for a price.

Organizations like NASA and the EDU can only obtain more funding if they spend existing moneys. In order to expend leftover funds, contracts are sometimes awarded to chase obscure objectives. The resulting reports can be picked up by the diving community to answer questions which nobody asked and may be expensive to implement. The "certifying" agencies" have a similar need to show "results" and when they come into possession of one or more of these nebulous reports may take the opportunity to publish new "safety" rules or guidelines. If these new guidelines require the purchase of more equipment the diving equipment companies, to which these agencies are satellites, are in full agreement.

 

[MSilvia]

I want to see a documented instance of a SCUBA cylinder (which was always filled with a BREATHING GAS, not some filthy pressure vessel that used to have oil in it or something) being filled via PPB with O2 that catastrophically exploded due to conflagration. Surely if it is so dangerous someone can provide this information.

Show me REAL evidence and I will shut my mouth about the O2 issue forever.

Here's one for you. It didn't kill anyone or burn any buildings to the ground, but it left Chickdiver with a blown up, brand new, "nitrox compatable" tank valve and a hand badly peppered with valve shrapnel.

http://thedecostop.com/forums/showpost.php?p=5426&postcount=1

 

[pescador775]

I assume most divers know that the valve can be a problem. Silicone grease is a hazard as are solvents. However, I appreciate the reference. The valve was not "new". No manufacturer lubes or cleans a valve with flammable material. Since the valve exploded and did not simply burn it suggests that the valve was cleaned with gasoline.

 

[Thalassamania]

The word "adiabatic" is most frequently used by those who have no clue.

Love it<G> But really:

1. DOT has no jurisdiction of scuba tanks, that's an industry standard with on weight of either regulation or law.
2. Visual inspection is the same story.
3. Oxy-clean is even less of a story.

Not that I'd do without any of the three.