Excessive Carbon Monoxide Levels Discovered in Utila Nitrox Tanks

[swamp diver]

Very interesting story Don, but not surprising as we have identified similar CO contamination in multiple divers' tanks in Roatan, and also in Bali on a liveaboard over multiple days. Both incidents were with divers using Nitrox.

It certainly begs the question if the nitrox is produced using a membrane system or by continuous blending whether the higher percentage of oxygen leads to a higher risk of CO production via the compressor oil dieseling when sufficient heat is present?

On the other hand if the shop was partial pressure blending the CO concentration in the nitrox would have been diluted down by the CO-free oxygen. Those diving straight air would have had CO in their tanks even higher than that found in the nitrox.

It would be interesting to know the production method used for the nitrox and secondly whether or not the shop had a catalyst bed such as Hopcalite in the filter?

The type of compressor oil used is also a big factor in the risk for dieseling. One gains on average close to 30 C increase in flash point by switching from a mineral to synthetic oil. If one is producing nitrox using continuous blending or with a membrane system the compressor oil should be of the synthetic variety in order to take advantage of the higher flash point and lower risk of oil pyrolysis.

Of course we are assuming in this case there was no point source for external CO contamination (i.e. petrol-powered compressor, vehicular/boat exhaust, etc.)

 

[DandyDon]

Not surprising at all, with all that I already knew about the real risks, lack of information on DAN Accident Reports, lack of oversight, etc - but I had no idea how soon I'd have readings. I only wish I'd been there for the discovery - and shooting pics.

I got the story from the Instructor's wife who runs the store, don't get to talk with him often, but hope to soon. I'm told that he did inspect the resort's air compressor and found it acceptable enough with a suggestion of moving the air intake higher and the air from that compressor never had a reading. I don't know if he went into town to inspect the Nitrox compressor or not.

 

[swamp diver]

Personally I think the rate of CO contamination in the tropics is likely higher than the 3 percent level the labs have reported. We have good data to show that about a quarter of the shops when sending in a sample of air are maximizing their chances of passing the test and sampling under best case scenario conditions. This consists of switching out their filter cartridges, and sampling immediately afterwards while the compressor is still cold and under no load, both conditions which would minimize the risk of CO production.

We divers on the other hand are taking our air sample generally under the worst case scenario conditions as the tanks are often filled during the hottest part of the day and the compressor is run for hours on end filling tanks to full pressure one after another. The tanks filled first in a run will be at low risk for contamination when the compressor is cold while those later on in the fill sequence would be at higher risk if the compressor factors are sufficient to allow pyrolysis of the oil.

It would be very useful if CO is found in the diver's air/gas to answer the following and also very important take a picture of the compressor installation.

1. diameter and length of remote intake
2. any potential point sources for CO
3. if nitrox contaminated what production method used
4. electric or petrol-powered compressor
5. does purifier contain a catalyst such as Hopcalite
6. mineral or synthetic oil in use
7. individual tanks or storage banks in use.

If you look at the earlier DAN article (?1998) by Bob Rossier on CO contamination I think it reported a CO failure rate of 5 to 8 percent at 10 ppm? In those regions with high ambient heat and poor compressor installations this figure is likely a closer representation of the frequency of CO contamination. If this turns out to be the case then it is time for DAN to take their head out of the sand and start to look seriously at this CO contamination problem from poorly installed and maintained compressors.

 

[DandyDon]

Oh sure, I can certainly see that...

• I suspect that many if not most that do sample would sample for testing under best conditions - new filter, compressor not yet hot;
• With 3% of those submitting for tests failing, one has to wonder if the ones who do not bother are the same, better, or worse - and I think somewhat worse would be a given;
• And in the tropics, we divers are not likely to get our air from those who do bother to test since few do, right after a filter change, before the compressor gets hot - we'll get the next tank in line.

It amazes me how long I accepted air & Nitrox on faith that the responsibility was surely being handled, by someone.

If you look at the earlier DAN article (?1998) by Bob Rossier on CO contamination I think it reported a CO failure rate of 5 to 8 percent at 10 ppm? In those regions with high ambient heat and poor compressor installations this figure is likely a closer representation of the frequency of CO contamination. If this turns out to be the case then it is time for DAN to take their head out of the sand and start to look seriously at this CO contamination problem from poorly installed and maintained compressors.

I have wondered if DAN could do anything, since they have no controls over the operators - but I guess they could publicize the risks and failures to comply with even the basic standards more than they have.

And now that DAN accepts ads, I wonder if KWJ Engineering might be interested in advertising there? I'll suggest it. They are open to ideas; I suggested today in a phone chat that they really should add a question on the order form asking for the customer's focus of interest in purchasing, i.e. truck driver, pilot, scuba diver, etc - and he liked that idea right away. I know a Flight Attendant who ordered one after she learned that the planes do not have CO monitors.

 

[swamp diver]

I have wondered if DAN could do anything, since they have no controls over the operators - but I guess they could publicize the risks and failures to comply with even the basic standards more than they have.

And now that DAN accepts ads, I wonder if KWJ Engineering might be interested in advertising there? I'll suggest it. They are open to ideas; I suggested today in a phone chat that they really should add a question on the order form asking for the customer's focus of interest in purchasing, i.e. truck driver, pilot, scuba diver, etc - and he liked that idea right away. I know a Flight Attendant who ordered one after she learned that the planes do not have CO monitors.

There are lots of proactive steps DAN could take if the will was there. If sufficient divers start testing their air/gas for CO and a widespread problem is identified then DAN could lean on the training agencies, particularly PADI with the largest market share, to insist their shops and resorts install a $US600 inline CO tester.

If DAN is reluctant to do this then I think one must look at who their largest corporate donors are remembering that DAN is an organization which wears several hats. One hat is to corporate DAN and the other is to the membership. Corporate DAN is there to ensure the organization remains financially viable while the membership hat is to ensure the mission statement regarding the promotion of dive safety through education and research is adhered to. At times these two hats may not see eye to eye and conflicts of interest can arise.

Secondly DAN could develop a diving fatality protocol which would include carrying out both a mandatory tank gas analysis and a blood carboxyhemoglobin (COHb) level for all global dive fatalities. We know from their own study that a COHb concentration is only done in about 15 percent of fatalities here in Canada and the USA. Likely in the tropics this rate approaches zero percent. A fatality protocol could be circulated to all its regional offices and sent to the coroners/medical examiners in those countries where a significant amount of diving is done. Until a tank analysis and COHb is done for every dive fatality we really have no idea as to the extent and significance of the problem. No testing for contaminants at the time of death will ensure these issues remain under the radar and this status quo is where some in the industry may prefer things to remain.

 

[wve]

Thanks, Don.

We just got back from Roatan where we dove Nitrox. No one had any problems. In fact, we all felt great. But we are planning a trip to Utila. Not sure yet whether we plan to dive Nitrox, but I just ordered a CO tester anyway.

It does not seem like a bad idea to test any tank that your life depends upon.

The issue does raise some interesting questions since you mention that there may be a higher risk of CO contamination with Nitrox.

One question is whether Nitrox users are really at higher risk for carbon monoxide poisoning, or is it just that Nitrox users are already thinking about the composition of the gas in their tanks and more likely to discover a problem?

A corollary question is, even if Nitrox users are at higher risk of having carbon monoxide in their tanks, are they really at higher risk for carbon monoxide poisoning? I ask because they also have higher levels of oxygen in their tanks. The treatment for CO poisoning is hyperbaric oxygen -- which is the same effect that diving with oxygen-enriched air will have.

Thus, one could postulate that, to some extent, a Nitrox user might be able to tolerate a higher level of carbon monoxide.

But I suggest that this would be wrong. Poison is still poison. And considering that carbon monoxide binds 240 times more tightly to hemoglobin (the stuff in red blood cells that carries oxygen) than does oxygen, the carbon monoxide under pressure will win over the oxygen under pressure.

The reason hyperbaric oxygen works is because you are breathing a higher partial pressure of oxygen WITHOUT a higher level of carbon monoxide, allowing the oxygen to nudge the carbon monoxide off the red cells a little more quickly. A Nitrox tank contaminated with carbon monoxide doesn't do that.

By the way, those interested in this issue might also be interested to know that non-smokers can have carboxyhemoglobin levels as high as 3% just from breathing the air around them. (Carboxyhemoglobin is hemoglobin with carbon monoxide attached.) Smokers have levels up to 15%. And that's before they go diving. Just one more reason NOT to smoke if you dive.

 

[DandyDon]

My home bud and I were discussing this a bit today and I mentioned some trips where I wished I'd had this gadget then "Especially for that awful one we had in Belize in 2004, except I used Nitrox from a different Op whom I trust (saw their test results, etc) for all of my dives." He then reminded me of how sick much of the group got the first day, puking from the boat, etc. - including him and his GF. I then dismissed that as a combination of dehydration, motion sickness, and psychosomatic suggestion after the first one puked but now he can't remember if he & she were on boat provided air or Nitrox from the trusted Op?

Now we're wondering if we had a close call with disaster that first day?

 

[vanisleboy]

Hi Don,

Thanks for posting info on pocket CO tester. After reading about the unfortunate incident in the Maldives, I've been looking at CO testers, particularly the Nuvair Pro CO.
This seems like a much cheaper and more practical solution.

Question, how are you using the unit to test you tank, particularly, how are you isolating the tank gas from ambient? From what I read on the web site the unit samples gas from both sides and exhausts through the back. Testing in and area where there are no exhaust fumes seems straight forward, but I'm thinking about a live aboard situation where there quite often is exhaust gas from the boat. TIA

Rob

 

[DandyDon]

I just today got mine as I had it shipped to my Inst for this trip. I think he use my suggestion on taking tests...
1-Turn on and drop into one gallon clear plastic bag - and I prefer the tall bags to the zip locks, altho I have not done a hands-on test yet;
2-Compress bag to push all air out, then fill bag half full from tank, twist neck with monitor face down to expose all three inlets to air, and hold for 2 minutes - use second counter on watch or whatever I think so you won't rush this.
3-Then read.

Keep in mind that there is going to be 1 to 5 ppm background CO in everyday air, maybe more - but scuba air is always supposed to be below 10 ppm.

If we can get enough divers carry these, running the tests and reporting on SB, we can get a better idea of the real situation in the tropics. Even DAN doesn't know.

I just got a PM from a friend just back from Fantasy Island Beach Resort on Roatan who'd asked the manager about their air quality control, and he was happy to show the compressor and the quarterly test results from TA: Compressed Air Testing Specialists - Makers of the AirCheck Air Sampling System - Trace Analytics I was pleasantly surprised that they do theirs, but I don't know if they have an inline monitor or scrubber?

 

[peterbj7]

Is there any evidence to suggest whether the CO is sucked into the intake for the compressor, or produced within the compressor (probably by "dieseling")?

If the former than using air from an electric-powered compressor should be a lot safer than if it were powered by an internal combustion engine, unless the air intake were located in an area of high vehicular traffic....?

If the latter than there could be a variety of contributing factors - wear state of the bores/pistons/rings, age/state/type of the compressor oil, operating temperature of the compressor, design/type/state of the filters. Anything else?