Close to 100% nitrogen in an old tank?

[Kurtis Clark]

Hi All,

Had a friend pass from a diving accident last fall. The coroner just got back to his family with info. I didn't speak to the coroner directly and this information is second hand.

However, I have been told that his aluminum pony bottle was filled with almost 100% nitrogen and I can't make sense of how that would happen?

I believe he hadn't used that bottle for a couple of years but don't know that for sure. Is there anyway anyone could think a pony bottle could accidentally get filled with nitrogen? Or if there is some type of oxidization process on the inside of a tank after a long period of time that could increase nitrogen levels?

I will be following up to see if I can read the report to confirm this information. It would obviously make a lot more sense if it were filled with 100% O2 and he didn't realize it and switched gasses too deep.

Thanks for any information in advance

 

[O-ring]

Sorry about your friend. Do you know where he got the tank filled? Oxidation could theoretically cause the o2 content to drop, but in an AL tank? I've seen some rusted tanks, but I can't imagine the kind of oxidation it would take to consume all the o2. What did the inside of the tank look like?

 

[wnissen]

Wow. Inert gas asphyxiation is pretty scary. I don't think anyone in the SCUBA world uses compressed nitrogen, though in the chemical / industrial world those green cylinders (not O2 green) are pretty common. I was always under the impression that aluminum oxide was a thin, fast-forming, protective coating, and would not corrode like steel. If I had a few minutes I could work out how much mass of oxidized aluminum that would require.

Sorry about your friend, hope you get some answers.

 

[jeff h]

I wonder if the dive shop mistook the tank for an inflation bottle and it was filled with argon instead of air? Then maybe the coroner only checked the O2% and did not verify what was the inert fraction? I've had tanks sit a full hydro cycle untouched and were still breathable (not advisable).

Independent of cause, very sorry to hear this. Condolences to you and the family.

 

[tech_diver]

How was it determined that the bottle had 100% nitrogen? Who did the analysis?
Generally, nitrogen level is checked by measuring the oxygen and assuming the rest is nitrogen. Do we know it was nitrogen in the bottle and not argon?

Even if the tank sat for a couple of years, it should be possible to make an educated guess as to where it was filled.
Very, very few operations keep 100% nitrogen on hand. The NASA Neutral Buoyancy Lab blends breathing gas from liquid O2 and liquid N2. This is not something you see in regular diving.

 

[Kurtis Clark]

As far as I know it's the BC Coroners Service doing the investigation. I believe they would use a proper lab test on the gas. Especially if they found it had minimal O2 in it. But to be honest I don't know very much about their process. I don't have any additional information at this point as it's just some second hand information from the family that don't have diving background so don't know the right questions to ask.

I just wanted to make sure I wasn't missing something obvious as to how a tank could get filled with nitrogen.

I'll let you know what I find out in the next couple weeks.

 

[tech_diver]

One other remote possibility to check on...

Some paintball gun systems are pressurized with nitrogen. There are differences in the valve outlets but some paintball suppliers might pump nitrogen. It would be more likely to get nitrogen from a paintball fill than a scuba fill.

Thank you for sharing the information with us.

 

[rjack321]

Ask for the gas analysis report from the lab.

This isn't just some diver's O2 nitrox analyzer - proper gas analysis should have been conducted on something like a gas chromatograph by a laboratory certified for gas analysis.

 

[Stoo]

I didn't speak to the coroner directly and this information is second hand.

Given that this is "second hand" information AND that it was a pony bottle, I can't help but think the information passed along had been misunderstood. If the report was that it was 100% O2, that would be entirely believable as it may have been used as a deco bottle.

The other piece of critical information that's missing is whether the victim was breathing from the pony bottle. If he wasn't, then none of this even matters. If he was, then why?

What did the Coroner list as COD?

 

[Kurtis Clark]

Hey Stu, COD is lack of oxygen.... Not super helpful.

Nobody is sure if he was breathing from his pony bottle or not.