CO problem in tanks

[Minion_Diver]

I've been reading on here lately that many people have seem to be having issues with CO in their tanks after a full and diving on them. I was wondering, has this become a more recent problem or has it always been there and not brought out before.
I know some places are just looking for your dollar and will fill your tank with equipment that has not been maintained properly and this could be a source of the CO.
I am curious to how often CO comes into play with all the accidents that are occurring.

 

[tbone1004]

you'll find a whole lot of reasons, but like a lot of things, you are just hearing about the incidents more often. If you have an oil-less compressor that is electric drive with an intake properly isolated, use tanks that you know 100% have never had any salt water inside of them and are rust free, and the compressor has a CO filter on it, the odds of you having a CO problem are so close to 0 it isn't worth worrying about.

Conversely, if you have an oiled compressor that is gas driven and the intake isn't isolated properly the odds are pretty high that at some point the wind will shift to the point that you get exhaust going into the intake, or you run trimix through it and it overheats, that's bad and one of those two situations will most likely cause a CO problem.

Most of the professional fill stations are electric drive with remote mounted intakes and temperature alarms on each of the stages that will shut the compressor off or at least make one helluva racket if the temp gets to the point that the oil will start causing CO to go into the line. Many of them also have CO monitors on the outlet that will either shut the system off or sound alarms to get the operator to shut it off. If you get fills at these types of stations, the odds of CO are again, so close to 0 it isn't worth worrying about.

If you suspect you will be getting fills from a gas drive compressor and/or will be using rental tanks that you aren't 100% confident are clean, then I'd get a CO sensor and test those tanks.

that's my 2c. Other divers are very passionate about testing every cylinder after every fill regardless of where it comes from. The fill stations I use are state of the art and have sensors and auto-shutoffs. I do my own VIP's and make sure my bottles are clean and never let them get so empty that water can get into them which can generate CO in the tank. This happened to someone in the caribbean relatively recently using rental tanks. I don't CO check my bottles when they come from the fill stations I regularly use, but will use one in the circumstances described above. Any gas compressor, any rental tanks.

 

[boulderjohn]

We certainly are hearing about it more than before, in my experience by a very wide margin. Does this mean it happens more? I would be surprised to find that it was happening more than in the past. I have no idea, therefore, why we are hearing about it more, but there are several possibilities.

1. Some proponents of CO testing are very vocal about it these days. Perhaps testing advocates were not so vocal in the past.

2. We have much better networking of information. Details such as this are finding their way into the media with greater frequency than in the past.

3. Better detection is also a possibility. If you go through the old DAN fatality reports carefully enough to read their explanations, you will find that in many cases the only thing they know about a fatality is that the diver died and was ruled to have drowned. No autopsy was performed because it was obvious he drowned. There as no checking of gear or analysis of gas. It is very possible that at least some of these cases involved CO, but we will never know. It is possible that it is more likely today that the necessary tests will be done.

4. Because we are hearing about it more, we are much more aware of it and more prepared to act. We are testing for it more and more. Tanks with low levels may in the past have given you a headache that you dismissed as just one of those things--today a detector might pick that up before you get in the water. It may also be something you check into later. There is a current thread on ScubaBoard in which someone talks about the symptoms he felt after the dive, and he was immediately wisely advised to get the tank checked. That might not have happened in the past.

In my mind, it may be similar to the sudden and dramatic rise in the numbers of children with autism. Although it is possible that their true numbers actually are rising, better detection and more widespread information are definitely factors. My wife's entire career was in special education, and for the last years she was a specialist in diagnosing autism. A few decades ago someone was just a "quirky kid" with odd habits. today that "quirky kid" is being tested for autism, and they are finding he is on the spectrum. They have also expanded the definition considerably. There are families today whose children have autism, and when you look at the characteristic behaviors of the parents, you can't help but think think they are probably on the spectrum a bit themselves and might have been so diagnosed if they had grown up in this era.

 

[dreamdive]

One thing that seems to be overlooked as a cause of CO in your tanks is partial pressure blending. You can have electric run compressors, clean intake and filters, proper compressor lubricants, avoidance of running the compressor "hot", in-line CO detectors and still get a CO in your tank.

This was brought to my attention after listening to a very prominent cave diver and rebreather manufacturer who almost died. Post-accident analysis led back to a partial oxygen fire that occurred during the fill. It would not have been detected with an in-line CO detector.

Considering that a lot of the previous causes of CO fills have been attempted to mitigate against, the total number of incidences are probably low (total personal guestimate) and having the above described situation occur, is rare, too.

We partial pressure blend and are checking our tanks - to avoid Murphy's law.

Key to remember though is: If you are getting a headache mid to end of a dive without having increased work loads, suspect it! If you suspect it, get off the tank you are breathing! The more shallower you get, the more severe the symptoms will get. BTW: peripheral "floater" are another common symptom.

So, get off the tank and get on another (a buddy). When still not feeling well, go to 100% O2 and to the hospital.

 

[grf88]

The more shallower you get, the more severe the symptoms will get.

That part may seem counter-intuitive until you realize that the bloods ability to carry oxygen has been compromised and reducing the partial pressure of O2 means the body receives less oxygen

 

[dreamdive]

That part may seem counter-intuitive until you realize that the bloods ability to carry oxygen has been compromised and reducing the partial pressure of O2 means the body receives less oxygen

The "bloods ability to carry oxygen" has already been compromised by CO disabling hemoglobin from releasing its remaining oxygen molecules. However, with depth more oxygen is dissolved in plasma due to the increase in partial pressure. Likewise, as one emerges, partial pressure decreases and with it, the amount of oxygen dissolved. Now cells really "starve" for O2.

 

[dshorwich]

To the OP: if you haven't seen it already, this thread is worth reading.

 

[imjustdave]

you'll find a whole lot of reasons, but like a lot of things, you are just hearing about the incidents more often. If you have an oil-less compressor that is electric drive with an intake properly isolated, use tanks that you know 100% have never had any salt water inside of them and are rust free, and the compressor has a CO filter on it, the odds of you having a CO problem are so close to 0 it isn't worth worrying about.

Conversely, if you have an oiled compressor that is gas driven and the intake isn't isolated properly the odds are pretty high that at some point the wind will shift to the point that you get exhaust going into the intake, or you run trimix through it and it overheats, that's bad and one of those two situations will most likely cause a CO problem.

Most of the professional fill stations are electric drive with remote mounted intakes and temperature alarms on each of the stages that will shut the compressor off or at least make one helluva racket if the temp gets to the point that the oil will start causing CO to go into the line. Many of them also have CO monitors on the outlet that will either shut the system off or sound alarms to get the operator to shut it off. If you get fills at these types of stations, the odds of CO are again, so close to 0 it isn't worth worrying about.

If you suspect you will be getting fills from a gas drive compressor and/or will be using rental tanks that you aren't 100% confident are clean, then I'd get a CO sensor and test those tanks.

that's my 2c. Other divers are very passionate about testing every cylinder after every fill regardless of where it comes from. The fill stations I use are state of the art and have sensors and auto-shutoffs. I do my own VIP's and make sure my bottles are clean and never let them get so empty that water can get into them which can generate CO in the tank. This happened to someone in the caribbean relatively recently using rental tanks. I don't CO check my bottles when they come from the fill stations I regularly use, but will use one in the circumstances described above. Any gas compressor, any rental tanks.

How can water in the tank cause CO?

Could a tank that is drained right before a fill also cause an issue? In theory the air inside should be dry so draining shouldn't cause condensation.

 

[tbone1004]

salt water inside tanks cause oxidation which can offgas CO. Someone died in the caribbean because of it and the root cause was determined by inches of standing water in the bottom of the tank that had caused the tank to start rusting. Bad news bears. This is unfortunately somewhat common when idiot divers run the tanks dry and then water gets into them while they're on the way up, dive op doesn't pay attention when they get to the surface and just fill the tank. It doesn't "feel" empty because of the water weight so they don't think anything of it. This is a nonissue if you never run your tanks dry though, the little bit of water that can get in if the valve isn't properly blown off isn't going to cause enough of a problem to hurt you though.

 

[dreamdive]

Hey tbone, I don't understand the chemistry. CO is produced because of incomplete oxydation of fuel. Do you mind explaining how CO is formed from salt water in an aluminum tank? Thanks