I recently came across a statistic examining scuba diving-related deaths in Australia from 2014 to 2018. Such statistics often seem rather dull, but occasionally contain remarkable details - like this one.
The study reports a total of 42 deaths, 38 of which were attributable to scuba diving and 4 to surface-supplied breathing apparatus (SSBA). These included three deaths from carbon monoxide poisoning, an underestimated risk.
The maximum diving depth in the cases investigated was 39 meters. The risk of carbon monoxide poisoning increases with depth, as its partial pressure also increases with diving depth, meaning that even small amounts of carbon monoxide (CO) can have a toxic effect while diving. It is particularly striking that two of the reported CO deaths were associated with SSBA. These are particularly susceptible to CO poisoning as they can potentially aspirate exhaust gases, e.g. from ships, and thus expose divers to danger.
It is alarming that the quality standards for breathing gas were not met in a quarter of all gas samples analyzed. In one case, potentially lethal CO values were found and in another case, elevated CO₂ values.
The Divers Alert Network (DAN) recommends a CO concentration of less than 5 ppm for recreational dives and even lower values for technical dives at greater depths for safe breathing gas.
The production of nitrox using methods such as the membrane separation process can be problematic. This can concentrate existing CO in the final breathing gas. It is also less well known that CO can also be produced within a compressor - for example through the breakdown of lubricating oil under heat (pyrolysis). This does not even require an external CO source. For these reasons, the proper and regular maintenance of compressors is essential to ensure the safety of the breathing gas.
Divers should choose their breathing gas suppliers carefully and know their reliability. As conventional gas-analyzers cannot detect the CO content, it is advisable for divers traveling to remote regions to carry a special CO analyzer with them. This allows them to check the quality of the breathing gas themselves, rule out CO contamination even in places with precarious infrastructure and dive safely.
You can find out more about carbon monoxide in this blog post.
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