American tourist dies while diving Cozumel caves.....

[redacted]

What does a rebreather do with CO? Dilute it or concentrate it?

 

[Thalassamania]

Given the very high affinity of hemoglobin for CO I'd suspect that the blood in the lungs would scrub the CO out of the loop and it would be replaced only if diluent was added.

 

[Dive-aholic]

According to what Mr Dillehay posts, this has not, in fact, been shown to be a CO-related death.

I don't know Dillehay or how he would even get access to any of those records. It would seem that since he is associated with a dive shop in Cozumel that his statement could be just a bit biased. Also, no one ever confirmed what fill station the cylinder came from. Yes, someone stated it was Meridiano but that person was not on the trip so that information is also questionable. But even if it was and there were CO alarms and their response is to shut down the compressor, they need to be attentive to the inline analyzers and the alarms. On at least one occasion I witnessed one of the employees at the fill station sitting down with his eyes closed. At not time did I ever witness any of the employees tending to the compressors or monitors while they were operating. I'm also not sure what this "massive holding tank" is as all cylinders at the fill station were filled directly from the compressors not from any banks. Finally, the rebreather was examined after the incident. It was not a CO2 hit.

What does a rebreather do with CO? Dilute it or concentrate it?

In an SCR it would dilute it.

 

[Hatul]

What does a rebreather do with CO? Dilute it or concentrate it?

Presumably the CO comes from the diluent, while the O2 is pure. I think it would just sit in the loop, slightly diluted by the added O2.

In his book Mastering Rebreathers by Bozanic (p 119) he mentions the opposite phenomenon of smokers releasing CO into the loop from hemoglobin resulting in high levels of CO in the loop. Hence he advises avoiding smoking in CCR users.

Adam

 

[WSOPFAN]

I don't know Dillehay or how he would even get access to any of those records. It would seem that since he is associated with a dive shop in Cozumel that his statement could be just a bit biased. Also, no one ever confirmed what fill station the cylinder came from. Yes, someone stated it was Meridiano but that person was not on the trip so that information is also questionable. But even if it was and there were CO alarms and their response is to shut down the compressor, they need to be attentive to the inline analyzers and the alarms. On at least one occasion I witnessed one of the employees at the fill station sitting down with his eyes closed. At not time did I ever witness any of the employees tending to the compressors or monitors while they were operating. I'm also not sure what this "massive holding tank" is as all cylinders at the fill station were filled directly from the compressors not from any banks. Finally, the rebreather was examined after the incident. It was not a CO2 hit.




In an SCR it would dilute it.

Thanks for the additional info.
Would you care to address any of his other claims?
Such as the news articles are false, the coroner did no test, and a "homemade" rebreather was involved?
Thanks.

 

[DandyDon]

I always wonder what a poster really means in a CO discussion when they reference CO2...?

It may be a typo, but there is a vast difference.

 

[Thalassamania]

...

In an SCR it would dilute it.

I don't really know, but to follow the logic for a moment: an SCR bleeds in diluent at a constant rate, the diluent includes some level of CO, any oxygen that is added to the loop is basically "make up" and does not change the the concentration of CO, but the diluent coming in does replace some of the the CO that was lost as the CO flows out with the gas from the loop that flows out. Some more CO is lost to the blood.

I would infer that CO would stay pretty constant, unless a whole lot of oxygen was added.

Presumably the CO comes from the diluent, while the O2 is pure. I think it would just sit in the loop, slightly diluted by the added O2.

In his book Mastering Rebreathers by Bozanic (p 119) he mentions the opposite phenomenon of smokers releasing CO into the loop from hemoglobin resulting in high levels of CO in the loop. Hence he advises avoiding smoking in CCR users.

Adam

That doesn't make sense to me, CO has a very high potential to bind to hemoglobin, though some will diffuse out. CO that is in the loop, even CO that has diffused out of the blood, will still have a stronger than diffusivity potential to recombine with hemoglobin and thus leave the loop. Do keep in mind that Jeff is massively anti-smoking.

 

[DiverLaura]

I believe this is part of the primary issue with CO and CCR.

when the Hemoglobin finally does release the CO, it just goes into the loop and as you say another post, gets picked up again and back into circulation. I imagine part of what keeps people alive when they have excess CO is a function of high partial pressures and O2 in the mix pushing some O2 into plasma and Serum and allowing some circulation but i'm speculating.

Once you reduce the PPO2, the full magnitude of a CO event comes into play and even in topside CO poisoning many people need hyperbaric O2 to survive.

If CO is suspected/recognized on the dive, the difficulty is knowing if you have good gas in your bailout, and if you are pretty sure your bailout is clean, i'd go off loop immediately so as to stop recirculating and re-uptaking any residual CO. In a situation of bad CO poisoning in a remote area, a FFM and OC O2 at 20' might be the divers best hope, again i'm speculating here, just trying to think of what i'd do in similar situation tho, so take with a grain of salt.

I experienced bad gas once many many years ago, and it was simply wretched. i was knocked flat for a day or so after what a very mild episode by all accounts.

Given the very high affinity of hemoglobin for CO I'd suspect that the blood in the lungs would scrub the CO out of the loop and it would be replaced only if diluent was added.

 

[Hatul]

I don't really know, but to follow the logic for a moment: an SCR bleeds in diluent at a constant rate, the diluent includes some level of CO, any oxygen that is added to the loop basically "make up" and does not change the the concentration of CO, but the diluent coming in replaces some of the the CO that was lost, CO flows out at the rate that gas from the loop flows out. I would infer that CO would stay pretty constant.
That doesn't make sense to me, CO has a very high potential to bind to hemoglobin, though some will diffuse out. CO that is in the loop, even CO that has diffused out of the blood, will still have a stronger than diffusivity potential to recombine with hemoglobin and thus leave the loop. Do keep in mind that Jeff is massively anti-smoking.

The smoker example makes sense because even though the COHb levels in the blood of a smoker are small (<9%) the CO pool in blood is large while the circuit has relatively small volume. CO leaves the blood into the lungs and enters the loop and eventually a steady state will be reached where equal number of CO molecules leave the lungs as are taken up. The concentration of CO in the circuit at this point may be large. He mentions that concentrations as high as 810 ppm have been recorded. Once a steady state is reached the CO is trapped in the loop until diluent or O2 is added.

If the diluent should contain CO it will be trapped in the loop, that which is taken up will be replaced by more contaminated diluent.

 

[Thalassamania]

The problem with that analysis is that the transport of CO into the blood is not controlled by diffusivity alone, hemoglobin has a higher affinity for CO than it does for oxygen (that's the basis of the problem) and does not readily give it up.