Do You Analyze Your Gas for CO?

OSHA standards limit exposure to less than 50 ppm over an 8 hour period. The 10 ppm scuba standard would equate to 50 ppm at 5 atmospheres or 130 fsw. I haven't been able to find any rhyme or reason to the 10 ppm other than this correlation. 50 m is equivalent to 165 ft so limiting exposure to 3 ppm is taking a conservative approach. I've personally seen 8-10 ppm in tanks. I've heard of 17 ppm in 100% O2 from a reliable source. None of that will kill you unless you're doing a very long saturation dive. And then only maybe. But all the other cases I've heard of have resulted in pretty severe sickness or death. I'm guessing those samples were in the hundreds. For some reason I've never heard or seen any ranges in between. The only exception was at a fill station testing tanks when a minivan with lousy exhaust pulled up. I could smell the nasty exhaust before I saw the minivan and when it was within 50 ft of me the readings on my CO analyzer jumped up into the 50 ppm range. That was from 50 ft away! Oh, and another time a friend put his CO analyzer right by the exhaust of a vehicle and it jumped to over 200 ppm. It took his analyzer most of the day to calibrate back to zero. He was a little concerned about having done that to his analyzer. ;)

I am in no way shape or form an expert on this stuff however this is my take and concern with CO. It bonds to our hemoglobin not allowing us to carry oxygen and other gases. Lets take the example of 10ppm being acceptable because it relates to acceptable limits on the surface at 1 ATA. It is not the deepest part of the dive that concerns me it is when moving towards the surface. Time at depth has increased the amount of CO that is bonded. Now that I am moving shallower my body needs to off gas and still exchange in my lungs to get oxygen to my brain. Having the CO will put a lot of pressure on my circulatory system namely my heart and lungs while reducing the amount of O2 getting to my brain. Diving is a dynamic environment that adds stress to our bodies. Stacking on top of that CO is adding more stress that is not acceptable for me. For me a dive is not worth that type of added risk so I set my limit at 3ppm. I figure that carries all the fudge factor I am willing to accept.

By fudge factor I mean that I look at CO testing the same as O2 as having error either way. If I see 4ppm that could easily be 5-6 in my eyes and it is now time to call the dive.

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Originally Posted by Bobby

It is not the deepest part of the dive that concerns me it is when moving towards the surface.

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I'm no expert either, but this makes sense to me. At depth the partial pressure of CO increases, as does the partial pressure of O2 and whatever other gases may be in your mix. So the ratio of CO to O2 and other gases is the same at depth as it is at the surface. But since CO has a much greater affinity for hemoglobin than O2, the longer you are exposed to CO, the more of your hemoglobin has the O2 it's carrying replaced by CO and becomes carboxyhemoglobin. Then as you get shallower, the partial pressure of all the gases in your mix drop, but the CO hangs on to the the hemoglobin, so your elevated carboxyhemoglobin percentage stays the same as your ppO2 drops.

I may be FOS on this - if so, I hope that someone with a better understanding of diving physiology will clarify it.

Mike

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Originally Posted by Bobby

I am in no way shape or form an expert on this stuff however this is my take and concern with CO. It bonds to our hemoglobin not allowing us to carry oxygen and other gases. Lets take the example of 10ppm being acceptable because it relates to acceptable limits on the surface at 1 ATA. It is not the deepest part of the dive that concerns me it is when moving towards the surface. Time at depth has increased the amount of CO that is bonded. Now that I am moving shallower my body needs to off gas and still exchange in my lungs to get oxygen to my brain. Having the CO will put a lot of pressure on my circulatory system namely my heart and lungs while reducing the amount of O2 getting to my brain. Diving is a dynamic environment that adds stress to our bodies. Stacking on top of that CO is adding more stress that is not acceptable for me. For me a dive is not worth that type of added risk so I set my limit at 3ppm. I figure that carries all the fudge factor I am willing to accept.

By fudge factor I mean that I look at CO testing the same as O2 as having error either way. If I see 4ppm that could easily be 5-6 in my eyes and it is now time to call the dive.

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and the only treatment is a chamber ride, hoping to flood any remaining Hemogolbin IF You Have Any Clean Hemoglobin let. If not SOL

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Originally Posted by MORGAN

... I hope that someone with a better understanding of diving physiology will clarify it.

Mike

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I think you are exactly correct!

Yeah, it would be great if someone who were really knowledgable were to chime in. I am stuck on the notion that CO bonds to the hemoglobin in the blood, preferentially. So I think those CO molecules bond as fast as they encounter hemoglobin. That seems like a numbers game. Parts per million. I'm having trouble understanding why increased partial pressure would affect that. But I don't know.

I remember reading about the 2011 Cozumel incident that greater depth might have helped him - that the shallow depth led to his death because higher PPO2 would have helped the oxygen bond with the hemoglobin. I'd also like someone to address this.

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Originally Posted by Slüdge

I remember reading about the 2011 Cozumel incident that greater depth might have helped him - that the shallow depth led to his death because higher PPO2 would have helped the oxygen bond with the hemoglobin. I'd also like someone to address this.

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Just my opinion. In the accounts of OW CO toxicity I 've read, the survivors using same breathing gas reported they quit diving earlier and shallower than the deceased victims. Because hemoglobin has a higher affinity for CO than O2, I believe increased depth with the CO tainted gas means increased blood ppCO . Chamber treatment has a clean gas supply, so high ppO2 is beneficial.

Look at it this way. You have a tank of air at sea level. The percentage of O2 in that tank is 21%, the PPO is .21 ATA. Take that tank to 33 ft. The % is still 21% the PPO in the tank is still .21 Untill you take a breath. The PPO in that breath thru a demand valve is.42. Take the same tank and add 10 PPM Co at the surface then take it to 33 ft, the PPM in the tank is still 10 but the PPM in your breath is 20 PPM. The amount of hemoglobin in your blood is the same at depth as at the surface. If you double the amount of CO to the same amount of hemoglobin, twice as many hemoglobin are filled with Co. Co is 200% more coherent to hemoglobin then O2. In a direct contest between O2 and Co for hemoglobin, Co wins. Increase the amount of Co and O2 equally in each breath Co wins faster. The only way increasing depth helps is if you remove the Co, Aka a chamber ride on pure O2. Keep in mind this does not remove Co from hemoglobin but rather fills any uninfected hemoglobin with O2 if any are left uninfected. Therefore the best cure for Co poisoning is to not breath it.

Ata or ppm are both just ways of measuring a gas. A container at sea level with 10PPM of a gas the same as saying .00001 Ata. Or .21ata of a gas same as 210000PPM? No matter how you measure it the components of a gas are all subject to the same laws of physics.