Accidental 100% O2 in non O2 clean regs - real risk?

[miketsp]

Although I've been diving EAN now for over 10 years, over the last 24 months in order to analyse tanks I've hooked up my reg set (with my analyser attached to BC hose) to quite a few tanks partially filled with 100% O2. The tanks had been partially filled with O2 but the compressor operator had then failed to top off with air. I'm seeing this mistake becoming very common at various operators and various sites - probably due to EAN becoming more widely available.

I assume that there have not been any serious consequences because the tank pressure would normally be low - even for a target mix of 40% the undiluted initial O2 would only correspond to the tank at about 1/4 pressure.

But it does raise a couple of questions:

Is there any risk of putting 100% O2 at 50 bar into a non-O2 prepared/clean reg set?

By repeatedly doing this is there any risk of causing premature failure of o-rings or other parts during a dive?

Does it justify only using the type of analyser that you hold directly against the cylinder valve - eliminating the need to hook the regs up to an unknown cylinder - although personally I've always found found this type of analyser a pain to use, slower to stabilize and less accurate?

 

[PfcAJ]

If you're going to be doing it like that, I think it would behoove you to make sure your reg is cleaned and assembled with o2 compatible components and lubrication.

That said, I think the real risk is putting a reg on a cylinder that hasn't been analyzed. IMO, you're better off getting a dedicated reg with just a BC hose for the purpose. They can be had for ~80USD, so its not a huge investment. Putting a reg on a tank, walking away, and having that reg and tank end up somewhere it shouldn't could be read bad. I make a point to not put a reg on any tank that hasn't been analyzed.

As far as accuracy of one method vs another, they're both equally accurate in my experience, and one takes a little longer for the numbers to stabilize while the other takes longer to hook up to the tank. Six on one, half a dozen on the other.

 

[miketsp]

..snip..
IMO, you're better off getting a dedicated reg with just a BC hose for the purpose. They can be had for ~80USD, so its not a huge investment.
..snip

I do have some spare 1st stages and BC hoses - but it's not quite as simple as that. I'd want to add an SPG (I also have a couple of spares) and some way to bleed off the pressure after the measurement so I'm going to add a setup that adds some impractical weight issues - I fly to a lot of my diving and weight restrictions on both cabin and checked baggage seem to be getting ever tighter.
If it really is a safety issue then probably the best is to invest in a press-on analyser - at least to get the initial reading.

 

[PfcAJ]

You can use an allen wrench to bleed the pressure from the BC hose, they're almost free

 

[maniago]

Is there any risk of putting 100% O2 at 50 bar into a non-O2 prepared/clean reg set?...
By repeatedly doing this is there any risk of causing premature failure of o-rings or other parts during a dive?

I just finished the O2 cleaning and gas blending class yesterday. The tanks pressure is immaterial. The presence of pure O2 with non-O2 compatible grease is your issue. The fact that you haven't had any issue could be luck or could be that your gear was assembled with O2 grease. If you don't know, then you can consider it non-O2 and when used with pure O2, you should consider yourself playing Russian roulette. You might get lucky, and you might not. But relying on luck sure isn't a proven method of surviving to old age. The age old horror story goes that some guy dove non-O2 clean gear with a high O2 mix and got to 100' before his second stage ignited and blew his lips off. Why not before 100', who knows. Whether the story is accurate as told, who knows. But point made is a point taken.

As far as premature failure, again that depends on whether your orings and such are O2 compatible. Most new scubagear these days is made that way, though always check the mfg literature. That said, if not, yes the parts will deteriorate more rapidly than their expected life span. How fast? Well, get out your 45 and take a spin....

 

[rhwestfall]

if you build a test stage, something like the "quick shot bag inflator' by (IIRC) HOG may be the relief valve you seek.... SPG on a 6" hose is pretty simple to find (couple in classifieds right now).

 

[manni-yunk]

The tanks pressure is immaterial.

Generally speaking...is this true when it comes to 100% O2 - ??? I didnt think so. Are there not PSI limits based on % of o2?

 

[maniago]

Its the concentration that is material, that will cause a blow out ie explosion. Assisting factors for fire are pressure (ie constant flow), restrictions, adiabatic heating, blocking debris, poor gear design (ie tight bends) and such...Obviously a fast fire in your face is as good as an explosion Id think.

 

[Diver0001]

Is there any risk of putting 100% O2 at 50 bar into a non-O2 prepared/clean reg set?

In the time I've been reading scubaboard I recall reading about two incidents involving O2 and regulators catching fire. If I'm not mistaken one incident involved a titanium regulator, I believe from Apollo but I'm not 100% sure anymore. I don't know if it was clean or not but titanium and oxygen are never a good combination, clean or not. It caught fire when the tank was opened and I believe the diver was injured.

Another incident involved a rebreather that caught fight after being turned on. I believe this happened onboard a boat and they threw it overboard. I don't recall hearing if they recovered it or if there was a clear link made between the fire and the O2 (although I can hardly imagine what else could have caused a rebreather to catch fire).

R..

 

[The_Aviator_1]

The real risk comes with any presence of hydrocarbons (or any other substance which readily likes to ignite) inside either your hoses or regulator. This would include lubrication, or debris, as well as certain materials used in construction of older regulator set ups. The presence of 100% O2 significantly increases the chance of a flash fire. To give you an idea of how serious the danger is, in hyperbaric chambers, you are required to remove all your clothing and put on cleaned scrubs without shoes, because if any asphalt from the parking lot got stuck in your shoe sole, it could potentially have catastrophic consequences.