Unfortunately, from time to time, carbon monoxide kills a diver or causes serious injury. Due to the low incidence of carbon monoxide accidents each year, few divers think or know what to do if they encounter a carbon monoxide situation. Although, we cannot officially tell you what to do, we can advise you on the signs, symptoms and possible treatment.

What is the carbon monoxide?

It is an invisible, tasteless and odorless gas that is formed when fuels like gas, oil, coal and wood are not completely burned. It is very poisonous and has an immediate harmful effect on our respiratory system, being life threatening if it enters our air bottle. The real problem with carbon monoxide is that it has the unfortunate ability to bind to the bloodstream faster and better than oxygen. By doing so, it greatly reduces our ability to transport oxygen through our bodies. A situation that, if not dealt with quickly, can lead to serious injury and death. However, at mild to moderate levels, this can be offset by an increase in blood flow, so that although the blood contains less oxygen, the oxygen supplied remains. It appears that carbon monoxide also has other effects on cells within tissues (particularly the brain) and that these effects produce toxic symptoms.

Where does it come from?

The carbon monoxide that affects divers generally comes from:

  1. The oil in the pistons is leaking and partially burned by friction, contaminating the air that is pumped through a compressor. This has the double problem of carbon monoxide and oil droplets entering the air tanks. Due to poor compressor maintenance (unchanged / damaged filters, poor piston care), this is why it is always important to ask to see a compressor if you are unsure.

  1. A misplaced compressor inlet, near a parking area or places where vehicles are idle; in this case, these are exhaust gases that the filters cannot trap.

  1. Someone burning plastic / rubber (or general trash) near a compressor inlet. If you smell smoke in the dive shop, ask where the compressor air inlet is.analizador monóxido de carbono

How can it get into an air bottle?

Carbon monoxide can enter an air bottle while it is filling, if there is an engine leak near the compressor air inlet. The source could be the exhaust from the compressor’s own motor if it is broken or misplaced. In a life on board, it could be fumes from the ship’s own engine. On land, carbon monoxide could just come from a car with the engine running parked near the compressor room of the dive center.

How will you know if there is carbon monoxide in your air bottle?

To be honest, without using any analyser, you won’t know, at least until it’s too late. Currently there are analyzers that can be used to detect the presence of carbon monoxide. For about a hundred euros, you can buy one and use it before a dive to verify that the air is not polluted. The first indication that you have carbon monoxide in your air bottle will be that you start to feel bad during the dive. If there is carbon monoxide in your air bottle, the deeper you dive, the more you will inhale with each breath.

What are the symptoms?

Symptoms are headaches, irritability, dizziness, vomiting, confusion, and difficulty breathing. Confusion is a complicated factor, of course, because it means that your judgment can be affected and you cannot take the necessary corrective action on time.

Underwater, divers have explained the symptoms as “feeling bad” and some have been described as having effects similar to narcosis on their dive buddies. With any of these signs, the diver must finish the dive. If unconsciousness has occurred, you should make a sign about an emergency ascent. On the surface, you’ll see the most telltale sign: cherry red lips, cheeks, and nail edge. Carbon monoxide has the opposite effect of anoxic cyanosis; It causes a bright red redness. If you observe this, and the person has lost consciousness, things are wrong. CPR (cardiopulmonary resuscitation) may also be required.


Oxygen. Put the affected person on O2 as fast as you can. If you have nitrox that was not filled from the same station as the contaminated bottle, this may be a suitable substitute.

Fresh air if you don’t have anything else. Due to the highly effective bonding of carbon monoxide forms with hemoglobin, the victim needs a constant high-oxygen gas to breathe. Immediate transportation to a hospital and professional medical treatment is a requirement here, not an option, due to the numerous and serious internal injuries and brain damage that can occur from exposure to carbon monoxide.

Due to the rarity of these incidents, few divers think about it. As we discussed earlier, we cannot officially advise you what to do in these circumstances, but what we have described in this article are very good ideas in these circumstances. All that said, it is a rare and unlikely occurrence; But knowing how to recognize it and what to do about it can make a difference.

Dive safely.

Simon Pridmore article for Diver magazine issue May 2020.

Translation and adaptation by Maribel Martin