Bad air originating in tank and not compressor

[Ayisha]

OMG Glenn, I'm so glad you tested the tanks. Thanks for sharing. Who would have thought?

 

[Stoo]

It's been a lot of years since I studied chemistry, but as far as I know CO can not come from rust. So unless someone knows something different, I have to cry "error". I'm not saying that there wasn't CO in the tank, but the rust and water can't be the source of it. More likely, the tank was already contaminated from a previous fill, and you happened to be the individual who got that tank. As mentioned above... how fortunate... and how odd... that the only person with the analyzer got that tank...

A quick Google verified my understanding... the only byproducts of a "rusting reaction" are Ferric Oxide (Fe2O3) and hydrogen.

CO is the result of combustion, pure and simple.

I have carried and used a CO analyzer for many years, and have never had an unsafe reading.

If CO had an aroma, I'd say something smells...

 

[Johnoly]

First a quick review of where CO comes from when we are talking specifically about inside scuba tanks.
1) Thru the compressor's fresh air intake hose.
In many remote compressors they are driven by fossil fuel engines. If the fresh air intake hose is too close to the fossil fuel drive engine, then most of the tanks filled during that condition will have an elevated CO (not just a single tank)

2) The single tank was from a previous or outside batch of tanks or was already mostly full and they just topped it off.
Existing bad air combined with a small amount of good air, resulting in still mostly bad air.

3) Compressor Flash over
Remember that CO is the result of an incomplete burn of a combustible product (ie lubrication, orings, even metal bearings)

These are pretty much the only ways CO can get into a scuba tank. I guess you could light a piece of paper or matches and toss them inside followed by installing the valve, but we'll leave the whacked out methods off the table for this discussion.

... just recently installed a new compressor......

I think most SB members can tell you stories of rental equipment failure where the staff swore up and down it was just rebuilt( boat engine/regs/bc infllators/pressure guages/etc). If you didn't see the shiny new compressor and that single tank was being filled by it, then you have to trust that same guy's word that just gave you a bad tank too. I wouldn't.

.... Meter read 81 ppm which I thought was damned near impossible so I tested my own tank again and every other tank that was set up for the divers. Sure enough none of the other tanks registered more than 1 ppm. Tested my son's tank yet again and it still read 81 ppm,.....

Above we talked about bad batch and most people understand that. Garbage in, garbage out
But what about "Compressor Flash Over". Flash over occurs usually when the lubricant used in the compressor is so hot from running that it self ignites. Just like when you are trying to light your charcoal coals and they only burn a little bit(incomplete), this incomplete "flash over" generates CO. This flashover is usually On-Off, On-Off and occurs inside the compression cylinder so you can't see it happen. The flashover could last 5 seconds or 5 minutes. There is no way to tell that it is happening unless you have an inline tester with auto shutdown. That's why one tank can be bad and the very next tank after it is good.

....It also goes to show that an inline tester on the compressor would not have prevented this incident....

If the inline tester with auto shutdown was correctly working on all of it's features, then the bad gas would probably not reached the tank. How many people here want to admit they kept driving their car with the check engine light on?? Just because the alarm keeps ringing doesn't mean you can't ignore it. Keep in mind less than one tenth of one percent of all compressors have an inline tester. You might have better odds picking the lotto numbers than finding a true functional working inline auto shutdown CO tester for scuba tanks (Hospitals are the direct opposite with almost all doing it)

Thank you for telling your story!!! It helps prove to people to never trust any tank you dive and every tank should be tested for CO. $300 for a tester versus $15,000 for a funeral. I'd book another dive trip with the money you just saved.

 

[kafkaland]

Does anyone know of an analyzer that gives me both CO and O2, can be used easily on the boat, and preferably doesn't cost too much?

 

[grf88]

The compressor is about 4 months old as are the new steel tanks, some of the aluminum tanks are older. The compressor is a nice new shiny Poseidon that is fully enclosed; yes, I looked at it. I checked about 30 different tanks, mostly steel, and the only reading I got was from one of the aluminum tanks that registered 1 ppm. They have not had a lot of dive groups through since the compressor was installed. If they had been pumping bad air I would expect some of the other tanks to have some residual CO which although diluted would probably have registered if they ever had high concentrations of CO in them. I plan on contacting Analox to see if there is anything else to explain what might have happened and if it is possible that the sensor is sensitive to any other compounds. In addition they have no other compressors on site or probably within 100 miles of the facility.

 

[Ken T]

Just a curious thought.....the tank had seawater in it...are there any sea life bacteria or algae that produces CO as a metabolism by-product?

 

[Stoo]

Just a curious thought.....the tank had seawater in it...are there any sea life bacteria or algae that produces CO as a metabolism by-product?

No. Not unless they're on fire...

The water and rust in the tank had nothing at all to do with any CO in it. There is simply no chemical reaction possible that can account for it. It's like seeing a red car crash into a bridge. The logical conclusion is that because the car is red, it crashed into the bridge... which is wrong. There is no causal relationship.

The tank had water in it. And the tank had CO in it. It does not mean the water caused the CO, any more than it means that the CO caused the water.

The shop' compressor was not working properly... either the old one, or the new one. Johnoly very clearly explained all of the possible sources of carbon monoxide in the tank. It's also possible that that tank was kicking around for a bit and not used, so might have been contaminated for days or even weeks...

Does anyone know of an analyzer that gives me both CO and O2, can be used easily on the boat, and preferably doesn't cost too much?

Nope... they use different sensors. Analox makes a nice set, that can be fit into a small Pelican case, or even a little Tupperware container. They should be protected from moisture, and shock, and in the case of the O2 analyzer, kept in a sealed vessel, since the sensor basically decays in the presence of oxygen. Use the plug, and keep it in an airtight container and it will last 2 or 3 times as long as it would otherwise.

 

[grf88]

Maybe clutching at straws here but I am wondering if an aggressive rusting process could strip oxygen atoms from CO2 as the atmosphere contains about 300+ ppm of CO2 which I don't believe is removed by hopcalite which only converts CO to CO2. Any chemists out there?

 

[DandyDon]

Yeah, I doubt that rust produced the CO. Puzzling, but again - drives home the need to check every tank, even as boring as it can be when you get all zeroes, until your first one.

Does anyone know of an analyzer that gives me both CO and O2, can be used easily on the boat, and preferably doesn't cost too much?

Nope. It's been proposed, but I just feel lucky that we now have the technology and it's affordable. It would have been nice if my sometimes dive trip buddy had split the purchases with me, but nope - so I carry one of each in my backpack boarding. I have seen divers given nitrox by mistake for deeper dives too, so I test every tank for both. Oh well, he's taken care of my vacuum cleaner needs at his cost, fixed my daughter's sewing machine for free, this & that - and his sainted mom is wonderful to me too.

Just a curious thought.....the tank had seawater in it...are there any sea life bacteria or algae that produces CO as a metabolism by-product?

Worth a thought, but I can't think of any that would produce that much. Dive Ops in tourist destinations juggle tanks so much, trading them out, loaning & borrowing, etc. that you really have no idea when & where a tank was used last.

Maybe clutching at straws here but I am wondering if an aggressive rusting process could strip oxygen atoms from CO2 as the atmosphere contains about 300+ ppm of CO2 which I don't believe is removed by hopcalite which only converts CO to CO2. Any chemists out there?

No, air does not contain 300 ppm CO in normal circumstances, not even 30 - 3 maybe in some cities. And your problem tank defies explanation, know knows where it's been and how it's been treat.

 

[Stoo]

Worth a thought, but I can't think of any that would produce that much.

Where on earth does the concept that sea life or algae could contain or produce carbon monoxide come from? It's ridiculous. If it isn't, we had all better run out and test our dogs... 'cause if algae can emit CO enough to hurt you, God only knows what the CO from the family dog could do.

The only way an animal or plant can produce CO is if you set it on fire... and I'm not even sure about that unless it was a duck found floating beside the Exxon Valdez.

Here's a question... would a CO analyzer detect methane? In theory, decaying plants or animals could produce methane CH4???

Nope... simplest explanation is almost certainly the correct one... faulty compressor.