In the last 24 months amongst our group of divers we have had the following incidents only found by using reliable CO detector technology. There was no indication (odour, taste, or irritant) of a problem otherwise. The liveaboard was a Tier A well known company and the resort also a popular one. There will be no further information as to the location of these incidents, but they do provide some insight into the type of problems out in the industry.
1) Liveaboard CO problem
First day all nitrox tanks contaminated with carbon monoxide between 1 and 18 ppm. Compressor's intake was well placed with no external sources of CO present. Compressor was located in very tiny room with only small door and no cross ventilation and due to noise operator was in the habit of closing the door during operation. Once door was opened and compressor was run in cooler evening they managed to keep CO levels between 0 and 5 ppm for the week. There was no catalyst in the cartridge to convert CO to CO2. Other than sitting on deck and not diving there was no other way to reduce exposure to zero. Group leader tried to keep divers shallower when he saw increased CO levels for the day.
Cause: pyrolysis of compressor oil secondary to poor installation, lack of compressor room ventilation, and lack of catalyst to convert CO to CO2.
2) Roatan CO problem
First day at resort and all 12 tanks were checked for CO on way out to dive site. Concentrations varied from 0 to 30 ppm carbon monoxide. Group leader refused to allow dive and boat went back to shore. The tanks were emptied and filters changed on the compressor after discussion with dive shop manager. Again intake was well placed with no potential for CO entrainment. Source was traced to poorly installed compressors running simultaneously in same room with poor ventilation. This time there was catalyst in the purifier however the filters had been run past their end of service life and the catalyst no longer functions to convert CO to CO2 when wet. After the filter change all tanks remained CO free for balance of week.
Cause: pyrolysis of compressor oil secondary to poor installation, lack of ventilation, and wet filter media (catalyst) which could not convert CO to CO2
Once one starts to look for CO on a regular basis particularly in the high heat tropical areas often with poor compressor installations, no ventilation, and no catalyst in the filters it is surprising how often carbon monoxide contamination crops up. When a bit of oil is burned intermittently there may be no odour as that is removed from the air stream by the activated charcoal. At the lower levels one may just think they have a bit of sea sickness, flu, food poisoning, hang over, etc. and I suspect much of this low level CO contamination remains under the radar as we are not checking on a regular basis. As mentioned previously the compressed breathing labs in the USA which receive thousands of samples a year from all over the planet report a failure rate for CO at three percent which gives good insight into the extent of the problem.
This problem of CO contamination is a very real but sporadic one, and difficult to identify without some sort of detector unless of course there is an injury as we saw in the Maldives incident when often at that point in time the air quality is verified after the fact. If you are unsure about the quality of the air, particularly if presenting with the new onset headache or nausea, check your air for CO contamination.
At least 3 times now on pre-paid tropical dive trips when bad air has been detected we have been able to salvage the trip by increasing ventilation to the compressor, pumping at the coolest part of the day, and convincing the operator to switch out the filters ahead of his schedule. These remedial solutions have rectified problems originally identified using detectors and taste (oil in air).
