Carbon Monoxide - essential knowledge for ALL divers

[Aotus]

Surprisingly some of them like the Analox had very stable sensors where you could store it for six months, turn it on again, bump check the unit with calibration gas and find that it was bang on. Initially I'd calibrate my Analox unit every 6 months but found that a one year calibration was fine. Unfortunately Analox has discontinued production of their CO E11 so unless you can find one real cheap I wouldn't go that route. The sensors will be available though until July 2016.

Here are the other options.

1) Oxycheq

Good unit which they claim does not need calibration which is not the case. I'd at least put some calibration on the sensor once a year in order to ensure it has not drifted and remains accurate.
OxyCheq - OxyCheq Expedition CO Analyzer w/ Alarm


The SensorCon was a unit previously available but the manufacturer has discontinued the scuba option. This unit's sensor was very sensitive to over-pressurization and one had to find a way to deliver gas at a flow of only 0.5 lpm to the sensor. Higher than that and one would get a false positive reading.

On my trip I used an Analox to double check the readings from my oxycheq. That's a shame to hear the Analox is out of production, it's a handy, super easy to use unit. Also, regarding the oxycheq. I called them about calibration before my trip because I ran out of bump gas too quickly and couldn't calibrate my new sensor. They DO advocate calibrating a new sensor, but in my case (1 day before my trip) recommended I calibrate the sensor for a zero/near-zero reading for air in an open clean area. I did that, but couldn't get it quite down to zero. When I tested good fills, the number stayed the same (<1) or went down to zero. When I found the bad fill it went right up to 20 and alarmed. So, I borrowed a friend's Analox and double checked a good fill and the suspect fill, they both matched - 0 and 20 respectively.

Lastly, that's a shame to hear the sensorcon tester isn't good. I bought one once and returned it before use because it felt cheap in my hand. The oxycheq is solid, but it's a shame that means there may not be a cheap option for a CO tester. Maybe every OW diver should start with some of those tester strips, so at least they have SOMETHING.

 

[Peter69_56]

Having had bad gas in Bali and surviving it, its not a pleasant experience. My wife was that ill, she had to lay on the jetty for 20 minutes to recover. The bad gas was reported, however as it was borrowed gas from an independent (perhaps back yard) supplier, little will probably be done other than the LDS not using them again.

I have also had bad gas in Australia (oil contaminated).

I guess the main point being, you will never know when contamination happens. We all assume everything will be fine, and when Murphy strikes, we all look with amazement. We all (I hope) test Nx when we buy it, why not test for CO.

As a tech diver I was taught to test ALL tanks, not just the Nx ones. What happens when the air tanks you are so sure are air turn out to be 40%Nx. In that thought I test all my tanks for CO as well.

I am going to Santo to dive the Coolidge and will be testing my tanks for sure given previously reported incidents on the wreck.

It just makes sense to check the most important thing you have underwater, your gas!

 

[Aotus]

Having had bad gas in Bali and surviving it, its not a pleasant experience. My wife was that ill, she had to lay on the jetty for 20 minutes to recover. The bad gas was reported, however as it was borrowed gas from an independent (perhaps back yard) supplier, little will probably be done other than the LDS not using them again.

did you ever find out what the CO levels were? or was it something else?

 

[dreamdive]

The scariest one, to me, is that not only does CO become increasingly deadlier as you go deeper, it then starts getting deadlier again as you go shallower. So, the partial pressures of the gases you're breathing gos up as you descend and go down as you ascend, right? That means that your ppCO is going up as you go down. The physiology of that is that the CO is getting absorbed more rapidly into your bloodstream. CO in your blood prevents O2 from bonding. But at those depths, your ppO2 is elevated as well. When you start ascending, your ppO2 drops dramatically.....but the CO attached to your blood cells stays there. This makes you less tolerant of the CO in your system, making ascent the deadliest time of a CO hit, if you haven't died already.



---------- Post added April 20th, 2015 at 09:35 AM ----------

As you said, it is almost a biphasic event. As we go deeper the partial pressure of CO increases disabling more hemoglobin, but since the partial pressure of oxygen increases, as well, more is dissolved in plasma and oxygen delivery is less dependent on hemoglobin. Then as we come up, we still have disabled hemoglobin but our dissolved oxygen drops and symptoms become more pronounced.

It is less of an issue with "CO getting absorbed into the bloodstream" and CO does not prevent oxygen bonding as much as it changes the conformation of the hemoglobin preventing oxygen molecules from being released. Hemoglobin has 4 oxygen binding sites and the attachement of one CO molecule on one of those sites reduces the other oxygen molecules from coming off the hemoglobin rendering it ineffective for oxygen transport.

 

[victorzamora]

As you said, it is almost a biphasic event. As we go deeper the partial pressure of CO increases disabling more hemoglobin, but since the partial pressure of oxygen increases, as well, more is dissolved in plasma and oxygen delivery is less dependent on hemoglobin. Then as we come up, we still have disabled hemoglobin but our dissolved oxygen drops and symptoms become more pronounced.

It is less of an issue with "CO getting absorbed into the bloodstream" and CO does not prevent oxygen bonding as much as it changes the conformation of the hemoglobin preventing oxygen molecules from being released. Hemoglobin has 4 oxygen binding sites and the attachement of one CO molecule on one of those sites reduces the other oxygen molecules from coming off the hemoglobin rendering it ineffective for oxygen transport.

That's certainly a more accurate.....I was just trying to keep it more basic for the "Basic Scuba Discussions" forum.

 

[Aotus]

I love when someone with much greater understanding of a subject really lays it out like that. Thanks dreamdive!

 

[Peter69_56]

did you ever find out what the CO levels were? or was it something else?

No we never found out. I was relatively new at the time to diving. We realised at the time we could taste the oil in the gas. I suspect that the filters were well and truly past their replacement date as well as a crap worn compressor.

Now I would test before I used, and have a reasonable indication of the gas state as well as reject it if I could smell or taste oil.

 

[dreamdive]

That's certainly a more accurate.....I was just trying to keep it more basic for the "Basic Scuba Discussions" forum.

Thanks Victor! Just trying to educate a little

Claudia

 

[knotical]

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[DandyDon]

I suspect Dandy Don, our resident CO cognoscente will add to this thread.

Sorry, I missed this thread before. I am no expert or authority on the subject, but I do try to watch for these discussions - and add to them if I can help. I can help at times because so many divers know so little about the real risks, a failure of our agencies and DAN as well, IMO.

How sensitive are the CO meters to storage? Do they easily go out of calibration? I'm not lucky enough to be a frequent diver. A few times a year is all I can do. I'm wondering if buying a meter would still be smart or would it be unreliable after a few uses and long storage periods.

They do need to be calibrated at times, and sensors replaced. There is no cheap solution. I looked at the CO test strips when I first got interested, as I hoped for a cheap solution, but they were out of production then. They have been brought back since after new interests have been developed, but they really suck. So the need is for an expensive solution, but - what's it worth to finish every dive alive?

The scuba option is a total waste, it absolutely sucks. The hardware in it is absolute garbage. However, the overpressure sensitivity is real. There are ways around it, but it's certainly an issue. It's good for as cheap as it is, $119 from Sensorcon directly, but I'm currently looking elsewhere to replace mine.

I like the Sensorcon as it is a low cost solution. I never did like their now discontinued scuba adapter kit, but use mine like I did my first portable tester (which failed in experiences) - in a gallon zip lock bag. Just pack a supply of those, enough to have a new one every day of a dive trip - and I like the slider zips for ease of handling.

The Cootwo Dual-Gas Analyzer is more expensive, but super. It quickly gives you O2 and CO readings. I have seen divers who thought they were on air but had been given Nitrox for their deeper dives. No harm, but there was fright.

Maybe every OW diver should start with some of those tester strips, so at least they have SOMETHING.

As I mentioned above, they suck. They give a vague and undependable indication.