Ronda Cross Tank CO Test cause of Death

[John C. Ratliff]

DandyDon,

It is my understanding that there is no carbon monoxide within the body under normal circumstances; any found there is a result of breathing air contaminated with CO, which includes most of our city air, or air behind a vehicle such as a boat or fire engine. I have measured CO levels of over 500 ppm in the eddy of a fire truck where the firemen stand--my recommendation was to keep their noses up in the air stream. CO is the result of incomplete combustion, usually from a fire or internal combustion engine.
http://en.wikipedia.org/wiki/Respiration_(physiology)

Here is an interesting PowerPoint presentation I found on sources of CO:
http://www.colorado.edu/physics/phy...ectureNotes/nagle_phys3070_fa08_lecture35.pdf

Human respiration produces CO2 exclusively, which is good as CO has a 250:1 greater association with our hemoglobin than oxygen.

Carbon monoxide combines with hemoglobin at the same point on the hemoglobin molicule as does oxygen; it can therefore displace oxygen from the hemoglobin, thereby decreasing the oxygen carrying capacity of blood. Further, it binds with about 250 times as much tenacity as oxygen, which is demonstrated bythe carbon monoxide-hemoglobin dissociation curve, except that the carbon monoxide partial pressures, shown on the abscissa, are at a level 1/250 of those for the oxygen-hemoglobin dissociation curve of Figure 40-8. Therefore, a carbon monoxide partial pressure of only 0.4 mm Hg in the alveoli, 1/250 of normal alveolar oxygen (100 mm Hg PO2), allows the carbon monoxide to compete equally with the oxygen fdor combination with the hemoglobin and causes half the hemoglobin in the blood to become bound with carbon monoxide instead of with oxygen. Therefore, a carbon monoxide pressure of only 0.6 mm Hg (a volume concentration of less than one part per thousand in air) can be lethal.
Guyton, Arthur C., M.D. and John E. Hall, Ph.D., Textbook of Medical Physiology, Eleventh Edition, Elsevier Saunders, 2006, pages 509-510.

The American Conference of Governmental Industrial Hygienists sets Threshold Limit ValuesTM for substances, and for CO that level is 25 ppm. So why is it important to keep CO levels in our scuba breathing air at below 10 ppm? That is because of Dalton's Law of Partial Pressures. If we dive to 132 feet, that's five atmospheres absolute pressure, and therefore the air is compressed that we breath by a factor of five. This means that in the same space that at the surface has 10 ppm CO, at 132 feet it will have the equivalent of 50 ppm CO on the surface. At 165 feet, which we now see sport divers attaining, which is 6 atmospheres absolute, the equivalent on the surface for air actually containing 10 ppm CO would be 60 ppm CO (our bodies react to it as if there are 60 ppm in the air).

Most direct-reading instruments are accurate within a certain percentage points. The Analox EII CO instrument appears to be accurate within plus or minus 30%. Detector tubes, an older CO detection technique, are plus or minus about 25%. This is not a big deal in detecting CO, but it is not a reliable method for quantitative analysis which would be required for legal purposes. Divers can use this easily to determine contamination, but this technique has limitations for accident investigation. I hope this clarifies things a bit.

John (SeaRat)
John C. Ratliff, CSP, CIH, MSPH

 

[DandyDon]

Gawd, I hate it when I post during the 15 minutes of down time here and lose what I said.

Briefly, it think the 10 ppm having an effect of 50 ppm at depth is more complicated than that alone. With the CO binding to the blood and remaining bound on ascent when the PPO2 drops, I think the damages are greatly increased. How much might vary with variables and details, and possibly open to debate?

The portable Analox CO unit and others similar may not be more accurate than you described, but that's about the best we can hope for, technology not available only a few yeas ago, and still close enough for me, as well as my only defense. If I bump test, field calibrate, then find 5 or 10 ppm CO that should not be there - I don't want to dive it. Who knows how much can be in another tank filled a few minutes later when the compressor is hotter.

The portable units are certainly not going to give results useable in court. Sampling supplies can be obtained from labs qualified to give expert results, but I don't expect to find those in Mexico or many other dive destinations, nor a hospital with the equipment to measure CO in blood. Besides, bribes still change stories in Mexico easily.

 

[ajduplessis]

I do believe that you can get 1900ppm from a compressor oil flash.

Can you smell a oil flash in the breathing gas?

 

[swamp diver]

DandyDon,

It is my understanding that there is no carbon monoxide within the body under normal circumstances; any found there is a result of breathing air contaminated with CO

This is incorrect. The human body produces carbon monoxide endogenously (from within) from the breakdown of heme in hemoglobin. We also produce nitric oxide (NO) and hydrogen sulfide (H2S) and the three of these gaseous molecules make up a new class of compounds known as 'gasotransmitters' which allow rapid cell to cell signalling, far more rapid than a hormone released into the bloodstream will act.

A non-smoking healthy person will always have ~ 1 to 3 ppm of CO in their breath. A smoker will have considerably more depending on amount smoked and last time of smoke. Most smokers I've checked have 6 to 10 ppm of CO in their breath. The insurance industry now uses this to test the veracity of people's claims as to whether or not they smoke. Most forms of lung disease will also lead to elevated carbon monoxide in the breath.
Exhaled carbon monoxide in airway diseases: fro... [J Breath Res. 2010] - PubMed - NCBI
Breath carbon monoxide as an indication of s... [Singapore Med J. 2004] - PubMed - NCBI

I'm not sure where your figure of a 30% accuracy came from for Analox's EII CO, but it is listed by the manufacturer as 0.5 ppm +/- 5% of the reading. This is much more accurate than any colorimetric tube test (i.e. Drager, Gastec, Sensidyne) and the accuracy and resolution of these hand held detectors is very adequate for determining CO contaminated compressed dive air < 5 ppm as long as the unit is kept calibrated as per manufacturer's recommendations.
http://www.analox.net/product-docs/datasheet-91.pdf

---------- Post added January 2nd, 2014 at 08:02 AM ----------

Can you smell a oil flash in the breathing gas?

Normally not if the filters have been changed out at the manufacturer's recommended interval. The activated charcoal bed in the cartridge will remove any odor leaving only the odorless CO in the breathing gas assuming there is no catalyst in the filter which normally would oxidize small amounts of CO to CO2.

This activated charcoal effect was seen in the Maldivean CO fatality incident.

 

[rjk75]

...snip, snip...
I'm not sure where your figure of a 30% accuracy came from for Analox's EII CO, but it is listed by the manufacturer as 0.5 ppm +/- 5% of the reading....snip, snip...

The PDF you mentioned says, "Accuracy: ± (0.5ppm CO ± 5% reading)*" is "After factory calibration." Could this accuracy change considerably after some usage or time?

It'd be interesting to know how one of those rental Analox EII's (per DandyDon) compares to a brand new one. After reading through the earlier discussions of test findings of CO in N. Am. scuba sources, I really am considering buying one this year.

 

[John C. Ratliff]

Swamp Diver,

Thanks for the links. I'm studying them now. But a preliminary reading shows that those with CO (non-smokers) were in some way under a lot of stress (asthma, respiratory disease, etc.). I'll look more closely though.

Concerning the accuracy, I was going by the results of the bump test, which the manufacturer said a good test was between 7 and 13 ppm for a calibrated 10 ppm test gas.

This technical discussion is only to better understand the instrument. I would urge others to go ahead and buy the CO instrument, and use it. Lives are more important than a tech discussion.

For those interested in a good description of a CO incident, I would recommend reading Captain J.Y. Cousteau's Silent World, Chapter 5, "Cave Diving." The Cousteau team almost did not survive one of their first adventures after breathing 500 ppm CO at 165 feet. 1/2000 CO was reported by Jacques Cousteau in their cylinders after a new compressor was sucking its own exhaust fumes.

---------- Post added January 2nd, 2014 at 05:15 PM ----------

The PDF you mentioned says, "Accuracy: ± (0.5ppm CO ± 5% reading)*" is "After factory calibration." Could this accuracy change considerably after some usage or time?

It'd be interesting to know how one of those rental Analox EII's (per DandyDon) compares to a brand new one. After reading through the earlier discussions of test findings of CO in N. Am. scuba sources, I really am considering buying one this year.

rjk75,

The short answer is "Yes." You need to follow the manufacturer's directions, and zero the unit in fresh, uncontaminated air. Then run the bump check on the unit. If those two things are done, you are good to go in your test. As with any new tool, we need to learn how to use in correctly to get valid results. The new Analox EII and a rental one should actually read approximately the same (+ or - 30%); that should not matter if the units are maintained well.

Once done, if you get any readings of CO, the air is somewhat suspect. If that reading is above 10 ppm, then the tank should be rejected.

The portable Analox CO unit and others similar may not be more accurate than you described, but that's about the best we can hope for, technology not available only a few yeas ago, and still close enough for me, as well as my only defense. If I bump test, field calibrate, then find 5 or 10 ppm CO that should not be there - I don't want to dive it. Who knows how much can be in another tank filled a few minutes later when the compressor is hotter.

DandyDon, I agree, and a diver using it as a screening tool doesn't need a high end instrument like those used for confined space entry by Haz-Mat teams. My concern is that it seems people do not sometimes realize the need to zero and bump test the Analox CO Unit immediately before testing the air, and that can lead to misleading results. In my line of work, not only did we do the zeroing and bump testing, we recorded the findings (including the times when the zeroing and bump testing were accomplished) for use later if we ever got significant readings. Maybe this could be an added block for someone's electronic dive log.

John (SeaRat)

John C. Ratliff, CSP, CIH, MSPH

 

[ianr33]

Unless a person is a smoker, there should be no CO (carbon monoxide) in a person's breath,

.....manufacturer states that the acceptable range is 7 ppm to 13 ppm; this is a 30% factor each way, which indicates that this is not an especially sensitive instrument to use

A quick Google search indicates the CO concentration in exhaled breath of non smokers is in the range 1-6ppm. Low,but not zero. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1742317/

If the acceptable range of the measurement is 7ppm to 13ppm, that indicates poor PRECISION , not poor SENSITIVITY.

Best, Ian

 

[John C. Ratliff]

A quick Google search indicates the CO concentration in exhaled breath of non smokers is in the range 1-6ppm. Low,but not zero. Breath analysis to detect recent exposure to carbon monoxide

If the acceptable range of the measurement is 7ppm to 13ppm, that indicates poor PRECISION , not poor SENSITIVITY.

Best, Ian

Ian,

I'm still not convinced the CO was produced by internal human physiology. I'm also still researching it, so my mind is open to this. But look at your paper's abstract:

Results: The range of carbon monoxide concentrations obtained in the non-smoking group was 0&#8211;6 ppm and in the smoking group was 1&#8211;68 ppm. Smokers had a mean breath carbon monoxide concentration of 16.4 ppm and non-smokers had a mean of 1.26 ppm (95% confidence interval (CI) for difference 13.6 to 16.8 ppm). Male sex and frequent motor vehicle use were associated with slightly higher carbon monoxide concentrations (by 0.40, 95% CI 0.18 to 0.63 ppm, and 0.38, 95% CI 0.13 to 0.63 ppm, respectively) in the non-smoking group. Mean breath carbon monoxide concentrations increased in direct proportion to the number of cigarettes smoked (p<0.001) and there was a negative correlation between carbon monoxide and time since last smoking a cigarette (p<0.001). Altogether 23% of smokers had breath carbon monoxide concentrations in the range 1&#8211;6 ppm.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1742317/

Note that the non-smokers range was 0-6 ppm. How would someone get a 0 ppm if everyone produced CO internally? A more likely scenario is that there are other sources of exposure. For instance, in the air in my area, there is CO. This comes from the cars which drive by on Highway 26, less than a quarter mile away. I have a gas stove in my house, and we don't always use the fan. Those are two external sources of CO that can affect me. For your theory to be true, all the people would have to have some CO in exhaled breath. At least that is my thought.

John (SeaRat)
John C. Ratliff, CSP, CIH, MSPH

 

[uwxplorer]

The American Conference of Governmental Industrial Hygienists sets Threshold Limit ValuesTM for substances, and for CO that level is 25 ppm. So why is it important to keep CO levels in our scuba breathing air at below 10 ppm? That is because of Dalton's Law of Partial Pressures. If we dive to 132 feet, that's five atmospheres absolute pressure, and therefore the air is compressed that we breath by a factor of five. This means that in the same space that at the surface has 10 ppm CO, at 132 feet it will have the equivalent of 50 ppm CO on the surface. At 165 feet, which we now see sport divers attaining, which is 6 atmospheres absolute, the equivalent on the surface for air actually containing 10 ppm CO would be 60 ppm CO (our bodies react to it as if there are 60 ppm in the air).
John (SeaRat)
John C. Ratliff, CSP, CIH, MSPH

John,

note that the pp of O2 (and any other gas present in the mix) will be multiplied by 5 as well, so the respective binding propensity (or whatever you want to call it) of the different gas present in the mix will not change. In other words, if 10 ppm of CO at 1 ata is OK IN THE PRESENCE OF AIR as the diluent gas, 50 ppm of CO at 5 ata will have the same effect IN THE PRESENCE OF THE EXACT SAME AIR FRACTION.
It is a competition thing. 1 big guy against 10 tiny ones will have the same effect as 5 big ones against 50 tiny ones.

 

[John C. Ratliff]

John,

note that the pp of O2 (and any other gas present in the mix) will be multiplied by 5 as well, so the respective binding propensity (or whatever you want to call it) of the different gas present in the mix will not change. In other words, if 10 ppm of CO at 1 ata is OK IN THE PRESENCE OF AIR as the diluent gas, 50 ppm of CO at 5 ata will have the same effect IN THE PRESENCE OF THE EXACT SAME AIR FRACTION.
It is a competition thing. 1 big guy against 10 tiny ones will have the same effect as 5 big ones against 50 tiny ones.

uwxplorer,

Yes, it is a competition thing, but realize that for every oxygen that binds with the red blood cell's hemoglobin, 250 CO molecules will bind. The CO out-competes the oxygen 250:1. Here again is the quote from above:

Carbon monoxide combines with hemoglobin at the same point on the hemoglobin molicule as does oxygen; it can therefore displace oxygen from the hemoglobin, thereby decreasing the oxygen carrying capacity of blood. Further, it binds with about 250 times as much tenacity as oxygen, which is demonstrated bythe carbon monoxide-hemoglobin dissociation curve, except that the carbon monoxide partial pressures, shown on the abscissa, are at a level 1/250 of those for the oxygen-hemoglobin dissociation curve of Figure 40-8. Therefore, a carbon monoxide partial pressure of only 0.4 mm Hg in the alveoli, 1/250 of normal alveolar oxygen (100 mm Hg PO2), allows the carbon monoxide to compete equally with the oxygen fdor combination with the hemoglobin and causes half the hemoglobin in the blood to become bound with carbon monoxide instead of with oxygen. Therefore, a carbon monoxide pressure of only 0.6 mm Hg (a volume concentration of less than one part per thousand in air) can be lethal.
Guyton, Arthur C., M.D. and John E. Hall, Ph.D., Textbook of Medical Physiology, Eleventh Edition, Elsevier Saunders, 2006, pages 509-510.

Now, think of a volume of air at the surface, and a similar volume of air at 5 atmospheres (132 feet of sea water). The volume has 5 times the number of molecules within it as it does at the surface. The U.S. Navy, in their March 1970 U.S. Navy Diving Manual, showed it graphically this way:

At 5 atmospheres, or 132 feet, the oxygen in the air by Dalton's Law of partial pressures exerts the same effect as pure oxygen at the surface. This is where with a volume of air, oxygen's partial pressure becomes one atmosphere, equivalent of breathing pure oxygen at the surface. At 196 feet (6 atmospheres) the oxygen in the air becomes toxic (equivalent of breathing pure oxygen at 33 feet).

This is also why Nitrox divers have to be very careful about their depths, because breathing enriched air (with a higher oxygen content) affects the depth at which oxygen becomes toxic.

Now, think about a contaminant like carbon monoxide being in the air the diver breaths. At the surface, there is 10 ppm. But at 5 atmospheres, lung full of contaminated air will have 5 times the number of CO molecules trying to compete with the oxygen to get a ride on the red blood cell's hemoglobin. But they compete at 250:1 ratio. The effect is the same as breathing a lung full of air with a CO contamination of 50 ppm at the surface.

The U.S. Navy Diving Manual, 6th Edition (2008) also states what DandyDon has a concern about:

3-5.8.2 ...Carbon monoxide poisoning is particularly treacherous because conspicuous symptoms may be delayed until the diver begins to ascend. While at depth, thegreater partial pressure of oxygen in the breathing supply forces more oxygen into solution in the blood plasma. Some of this additional oxygen reaches the cells and helps to offset the hypoxia. In addition, the increased partial pressure of oxygen forcibly displaces some carbon monoxide from the hemoglobin. During ascent, however, as the partial pressure of oxygen diminishes, the full effect of carbon monoxide poisoning is felt.

Note that this effect is because of oxygen saturated in the plasma, not attached to the red blood cells (RBCs). As soon as the pressure is released, this oxygen becomes unavailable, and the CO in the RBCs becomes even more devastating.

John (SeaRat)
John C. Ratliff, CSP, CIH, MSPH