Portable CO monitor

[suprane]

2) When should I be alarmed and refuse the tank, at a measurement just different from 0 ? at 5ppm ?

The first thing you need to think about is the fact that for every atmosphere that you descend the partial pressure of all gasses in the mixture you are breathing increases by a factor of one. That is to say that if you are a breathing 21% O2 mix (ie: compressed air) at 10 metres/33 ft it has the same effect on your body as breathing 42% O2. And at 20 meters/ 66 ft it now exhibits the effects of 63% O2. More simply, it is the fraction of the individual gas multiplied by the number of atmospheres of depth.

The same applies for all gasses in the mix. Therefore, as you descend the toxicity of the CO increases correspondingly. The other thing to keep in mind is that with CO it is not just a matter of how much but also for how long the exposure lasts! The longer you are exposed to it the more hemoglobin it has a chance to occupy. So, a long exposure at a moderate level may prove more toxic than a very brief exposure to a higher concerntration.

For healthy adults, CO becomes toxic when it reaches a level higher than 50 ppm (parts per million) with continuous exposure over an eight hour period.. When the level of CO becomes higher than that, a person will suffer from symptoms of exposure. Mild exposure over a few hours (a CO level between 70 ppm and 100 ppm) include flu-like symptoms such as headaches, sore eyes and a runny nose. Medium exposure (a CO level between 150 ppm to 300 ppm) will produce dizziness, drowsiness and vomiting. Extreme exposure (a CO level of 400 ppm and higher) will result in unconsciousness, brain damage and death.

The following figures come from wikipedia.com:

Concentration Symptoms
35 ppm (0.0035%) Headache and dizziness within six to eight hours of constant exposure
100 ppm (0.01%) Slight headache in two to three hours
200 ppm (0.02%) Slight headache within two to three hours; loss of judgment
400 ppm (0.04%) Frontal headache within one to two hours
800 ppm (0.08%) Dizziness, nausea, and convulsions within 45 min; insensible within 2 hours
1,600 ppm (0.16%) Headache, tachycardia, dizziness, and nausea within 20 min; death in less than 2 hours
3,200 ppm (0.32%) Headache, dizziness and nausea in five to ten minutes. Death within 30 minutes.
6,400 ppm (0.64%) Headache and dizziness in one to two minutes. Convulsions, respiratory arrest, and death in less than 20 minutes.
12,800 ppm (1.28%) Unconsciousness after 2-3 breaths. Death in less than three minutes.

I am not aware of any reliable, well tested crtieria that says do not dive a tank with greater than (fill in a number) ppm CO. At this stage of our working knowledge of CO poisoning as applied to diving I think each individual sort of has to determine what degree of risk (within reasonable limits!) that he/she is willing to accept.

I, personally, would be very reluctant to dive any tank with greater than 10 ppm to any depth greater than 3 atmospheres. And I really get pretty uncomfortable when the number creeps above 7 or 8 ppm.

I hope this helps your knowledge and decision making somewhat.

I currently use a ToxiRae 3 analyser to test all of my tanks. And, will continue to do so! It is calibrated with 10 ppm prior to each trip.

 

[DandyDon]

Until you get to the ascent complication. You feel bad from bad air at depth so you ascend, but the partial pressure of O2 goes down while the CO is bound - and things get much worse on the surface.

 

[suprane]

Until you get to the ascent complication. You feel bad from bad air at depth so you ascend, but the partial pressure of O2 goes down while the CO is bound - and things get much worse on the surface.

True!! That is why it is critical that if CO poisoning is even remotely suspected that you get the victim on 100% O2 immediately and keep them on it while transporting them promptly to hospital (and possibly hyperbaric facility!).

 

[manus]

Always looking forward to your posts, DD. Thanks !
Thanks a lot to Suprane as well !

I clearly remember the drama detailed by Leeaf on the Maldive accident and I want to report some data: http://www.scubaboard.com/forums/accidents-incidents/236596-memory-roman-rudakov-baani-adventurer-incident-22-may-2008-a.html

Lee's buddy started having symptoms while ascending, around 12m, after a dive of 37 min, max 32.9m, arrived semi-conscious at the surface. Poor Roman, may he rest in peace, had a dive time of 21 min, max depth 35m. His bottle measured 115 ppm of CO (which is the max readable, so who knows how much CO there was...) and "most tanks showed 80ppm carbon monoxide".
Lee also says: "easy dive, no exertion at all. There was just a slight current and we drifted with it. Vis was 15-20m, water temp 29C."
So yes, all perfectly matches with theory.

 

[DandyDon]

Always looking forward to your posts, DD. Thanks !
Thanks a lot to Suprane as well !

I clearly remember the drama detailed by Leeaf on the Maldive accident and I want to report some data: http://www.scubaboard.com/forums/accidents-incidents/236596-memory-roman-rudakov-baani-adventurer-incident-22-may-2008-a.html

Lee's buddy started having symptoms while ascending, around 12m, after a dive of 37 min, max 32.9m, arrived semi-conscious at the surface. Poor Roman, may he rest in peace, had a dive time of 21 min, max depth 35m. His bottle measured 115 ppm of CO (which is the max readable, so who knows how much CO there was...) and "most tanks showed 80ppm carbon monoxide".
Lee also says: "easy dive, no exertion at all. There was just a slight current and we drifted with it. Vis was 15-20m, water temp 29C."
So yes, all perfectly matches with theory.

Yeah, after being to 35 meters/over 4 atmospheres with air tainted with at least 115 ppm CO, the effect would be like around 460 ppm or more at surface - and if that's all there was, then he may not have felt ill effects until he started ascending with about a 60% reduction in PPO, yet with his blood already bound by CO poisoning. As they may have been breathing tainted air all thru the trip, his blood may have had some residual CO loading before the fatal dive. Lots of speculating here, but thinking about whatever could go wrong?

The others on the 80 ppm CO tanks were also injured to some degrees as I recall, yet gallantly did all they could to help him when the dive staff seemed useless in the emergency. Forgive me and correct me if I remember incorrectly, but that's how I remember the story from that long thread. Anyway, the others on 80 ppm CO tanks, diving to 4 atmosphers for the effect of 320 ppm CO, in addition to possible residual CO already in their blood from earlier dives - it all adds up. I would not want to dive even one tank like that, but as part of a bigger problem - scary.

It's sad that we have to figure all this out ourselves with little help from the industry as the agencies, instructors, and operators don't want to talk about it - other than to claim they never have any problems. None that we can find on google anyway, huh?

I've been told that the Honduran government took the tanks from the Roatan accident with two deaths some years ago for testing, but how knows? Does the Honduran government have the capacity to test? If they did and did, they kept the results well hidden. There's more I'd like to share from reputable resources I've lucked into, but I guess if they wanted their stories and names out here - they'd do so themselves, so I won't. It just makes me more resolved to not trust.

 

[manus]

The others on the 80 ppm CO tanks were also injured to some degrees as I recall, yet gallantly did all they could to help him when the dive staff seemed useless in the emergency. Forgive me and correct me if I remember incorrectly, but that's how I remember the story from that long thread.

You remember pretty well the sad story. And also from there, which results came out of official investigations? None!

Keeping talking about risks and danger of bad air and the importance of testing for CO presence will rise awareness ..... We should start working inside our diving associations as well.
In the training I am giving to the students I already introduced an emphasized dedicated lecture about CO (and bad air in general) effects. I find that the baseline courses are not enough informative on the subject; yes, it is covered, but not stressed enough, at least for PADI and BSAC, I do not know about others.

Looking forward to that day when the test of tanks for CO will be as natural and common as test of O2 in Nitrox bottles, both for the single individual and for operators.

Maybe a device like the EII CO will greatly help, as many people are already familiar with the Analox O2 analyser. Also the fact that it looks very similar, in my opinion, will help.

 

[bleeb]

True!! That is why it is critical that if CO poisoning is even remotely suspected that you get the victim on 100% O2 immediately and keep them on it while transporting them promptly to hospital (and possibly hyperbaric facility!).

How exactly does hyperbaric treatment of CO poisoning work? I mean what is the physiological mechanism? Does it actually help in the long term, or is it just a temporary aid? While a patient is under pressure, is there actually more O2 in their blood stream? It's not like the amount of hemoglobin is changing, whether or not said hemoglobin is permanently bound to CO, and I thought the amount of O2 carried dissolved in plasma was relatively small, so would a high PPO2 change this enough to be helpful?

 

[bleeb]

How exactly does hyperbaric treatment of CO poisoning work? I mean what is the physiological mechanism? Does it actually help in the long term, or is it just a temporary aid? While a patient is under pressure, is there actually more O2 in their blood stream? It's not like the amount of hemoglobin is changing, whether or not said hemoglobin is permanently bound to CO, and I thought the amount of O2 carried dissolved in plasma was relatively small, so would a high PPO2 change this enough to be helpful?

At the risk of answering my own post, co-incidentally most of my questions were just answered in another thread.

On room air, the half-life of carboxyhemoglobin (CO bound to hemoglobin) is about 300 minutes; on 100% oxygen therapy, it is about 60 minutes. Hyperbaric treatment decreases this to about 20 minutes.

Similarly, from the paper cited, roughly 1/3 of body requirements for O2 may be met by dissolved oxygen while breathing 100% O2, while some studies suggest almost all needs can be supplied through dissolved oxygen at 2.5-3 ata and 100%.

 

[suprane]

How exactly does hyperbaric treatment of CO poisoning work? I mean what is the physiological mechanism? Does it actually help in the long term, or is it just a temporary aid? While a patient is under pressure, is there actually more O2 in their blood stream? It's not like the amount of hemoglobin is changing, whether or not said hemoglobin is permanently bound to CO, and I thought the amount of O2 carried dissolved in plasma was relatively small, so would a high PPO2 change this enough to be helpful?

Let me add a bit more to what you have already learned.

First, CO forms a reversable bond with hemoglobin. This means that if you are removed from the CO exposure source that over a period of time the CO will be "kicked off" of the HGB molecule. The insidious thing about CO is that its affinity for hemoglobin (HGB) is 230 to 270 times greater than O2. Therefore it easily displaces oxygen from HGB and locks up the molecule so that it can not carry O2. The organ systems most effected by lack of O2 are the brain and heart.

Hyperbaric O2 has the ability to greatly increase the amount of dissolved O2 in the plasma. And, in fact, hyperbaric O2 at 3 atm can raise the plasma level to 6.8%. This is enough to support cerebral metabolism and prevent any additional brain damage. It may also reduce the elimination half-life of CO to as little as 15-23 minutes. Keep in mind that what CO causes is essentially a hypoxic state (lack of sufficient O2 for normal organ functioning). So any damage that it causes may possibly be permanent! This is known as Delayed Neurological Sequelae (DNS) This can be deficits in mental capacity, vision, balance, memory, cardiac function, etc. The list goes on and on. So it is critical to stop the progression of any additional damage as quickly as possible. This is where hyperbaric oxygen (HBO) may prove invaluable. Not only does it speed the immediate recovery, it may also help to prevent any long term sequelae.

If you would like, we can get into much more depth and detail about this..... Like maybe a discussion of the oxyhemoglobin dissociation curve, or the Henderson-Hasselbalch Equation, or cytochrome oxidase impairment. LOL Naaa, we'll save that for another day!

 

[Patti Analox]

Gentlemen, great discussion and very good information. Very good point to begin working on the various certifying organizations and also insuring/advising organizations (we are). Whether it is my the Analox EIICO or any other Carbon Monoxide analyzer, checking your gas should and hopefully will be standard operating procedure. The "smell and taste your air" just doesn't cut it.