Breathing contaminated gas at depth amplifies the effective exposure. A surface reading of 16 ppm during a 60\u2011foot (18-m) dive (about 2.8 ATA) corresponds to an effective exposure of just under 50 ppm for the duration of the dive. While this is concerning, it is below clinically significant toxic levels. The threshold for symptomatic CO toxicity is substantially higher than the level to which this diver was likely exposed, but tolerance to CO toxicity can vary from diver to diver.<\/p>\n\n\n\n
Why are we concerned about elevated CO levels? Hemoglobin inside red blood cells carries almost all the oxygen in our system. When CO is introduced, it binds to hemoglobin and displaces oxygen, forming carboxyhemoglobin (COHb), one of the indicators of CO toxicity. The greater the CO, the more toxic the effect and the more rapidly we become hypoxic. <\/p>\n\n\n\n
As we dive deeper, oxygen in the breathing gas dissolves directly into plasma, the liquid component of blood. This dissolved oxygen partially offsets the reduced oxygen\u2011carrying capacity caused by COHb, but as we ascend, COHb levels remain high for several hours while dissolved oxygen rapidly decreases. A diver becomes more hypoxic, not less, during ascent and after the dive.<\/p>\n<\/div>\n\n\n\n
![\"Carbon](\"https:\/\/world.dan.org\/wp-content\/uploads\/2026\/08\/Q3_109_Safety101-450x543-1.webp\")
The expected limit for CO in the environment is zero. If levels are above this, as 16 ppm in our example implies, there is a source somewhere. We need to know what it is, where it is, and whether it can suddenly introduce a large amount of CO near the compressor intake. A gasoline engine or generator powers the compressor on a boat, so we have a ready source of CO, even when the boat engines are not running.<\/p>\n\n\n\n
A sample is not the same as continuous monitoring. <\/strong>While one batch of cylinders may read 16 ppm, another could be much higher. Without additional sampling, we can\u2019t know unless we observe a diver feeling unwell or worse.<\/p>\n\n\n\n Breathing\u2011air compressors \u2014 especially those located in environments where CO may be present, such as on a boat \u2014 should always have filters with a CO catalytic converter. The catalyst continuously converts CO to carbon dioxide, yielding an expected result of 0 ppm. <\/p>\n\n\n\n There are limits, however. When CO entering the compressor exceeds the filter\u2019s overload limits \u2014 usually 50 to 100 ppm for a properly sized filter \u2014 some CO will pass through. The filter\u2019s ability to convert CO further decreases in humid environments. The CO\u2011removal process generates heat, related to the amount of CO. Excessive heat degrades the catalyst, further reducing its effectiveness.<\/p>\n\n\n\n A reading of 16 ppm in a cylinder likely indicates the catalytic converter is being overloaded due to a significant amount of CO in the air near the compressor intake. If levels rise further, the filter\u2019s effectiveness drops even more. When breathing gas contains any amount of CO, either the filter does not contain a catalytic converter or it is overextended by moisture, heat, oil, or volatile compounds. There must also be a significant CO source nearby.<\/p>\n\n\n\n This recent event is a serious reminder of the toxic killer: the tasteless, colorless, and invisible contaminant that we strive to eliminate completely. Toxicity from breathing gases remains an essential component of the differential diagnosis and is particularly relevant to dive medicine physicians assessing potential dive injuries.<\/p>\n\n\n\n The following are some useful safety considerations for all filling\u2011station operators working in environments where elevated CO levels may exist, such as near a gas\u2011powered engine or generator on a boat. <\/p>\n\n\n\n Divers have the right to expect that the operator has things under control, especially where CO may be present. If you are unsure or want to take added precautions, you can test a cylinder\u2019s purity in less than a minute with a small, handheld analyzer.<\/p>\n\n\n\n One added benefit of a portable CO analyzer in your dive kit is that it\u2019s useful in a liveaboard\u2019s sleeping quarters for alerting occupants to even small CO levels. A suitable, inexpensive analyzer with a range of 0 to 100 ppm should provide early warning of trouble on board.<\/p>\n\n\n\n \u00a9 Alert Diver<\/em> \u2013 Q3 2026<\/p>\n\n\n\n <\/p>","protected":false},"excerpt":{"rendered":" Explore the effects of carbon monoxide in breathing air on divers’ well-being and the significance of gas quality testing.<\/p>","protected":false},"featured_media":36077,"template":"","dan_alert_diver_categories":[83],"dan_alert_diver_issues":[526],"class_list":["post-36076","dan_alert_diver","type-dan_alert_diver","status-publish","has-post-thumbnail","hentry","dan_alert_diver_categories-safety-101","dan_alert_diver_issues-q3-2026"],"acf":[],"yoast_head":"\n\n
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