If it wasn't for scuba cylinders that give us the possibility to breathe underwater, we wouldn't be able to enjoy the wonderful marine life. However, that is no reason to blindly trust your breathing gas.

There are various kinds of contaminations that can turn your underwater life support into pure poison.

The slogan "Safety is in the air" wants to make divers attentive to the risk of contamination in the breathing gas.

Better safe than sorry! That is why DAN Europe's focal point is prevention. We provide divers with first aid instructions and treatment for intoxication, but our main goal is to prevent people from diving with contaminated air in the first place. To achieve this goal we inform divers on the possibility of getting intoxicated and how risks can be reduced.


Carbon monoxide is an odourless, colourless and tasteless gas, usually produced by the incomplete combustion of carbon containing compounds.

It is absorbed 200 times more by haemoglobin than oxygen is. This reduces the Oxygen carrying capacity and can eventually lead to hypoxia and even death. The severity of CO poisoning depends on its concentration in the breathing gas and the exposure time. A long exposure to relatively low concentrations can therefore result in serious CO intoxication.

In diving, the partial pressure of CO will increase with depth and even a low concentration of CO contamination which at normal atmospheric pressure and after a prolonged exposure time would have no toxic effect will become dangerous with increasing depth. When descending the haemoglobin can get overloaded with CO, impairing its ability to bind with oxygen, but the increased oxygen partial pressure may also result in enough oxygen in the blood keeping cells oxygenated. During the dive, the decreased oxygen transportation (through the haemoglobin) is also partially compensated by the amount of dissolved oxygen in the blood plasma. But during the ascent, when the partial oxygen pressure is reduced, and the amount of dissolved oxygen also reduces, this can lead to hypoxia. This might be the reason why the symptoms of poisoning may become worse during or after ascent.

CO poisoning is potentially the most dangerous contamination of breathing gas. However, there are other forms of contaminations, which we would like to bring to your attention.

There are three levels of contaminants that could contaminate your breathing gas:

  1. Those most commonly found in compressed gas like Carbon Monoxide (CO): Carbon dioxide (CO2), moisture (H2O), condensed oil, particles and odour
  2. Those found in certain geographic locations: volatile hydrocarbons and organic compounds, such as methane (CH4)
  3. Relatively rare but reported toxic substances: for example vapours from cleaning products and halogenated solvents, emissions from motor vehicles, suphur and nitrogen-based products and fumes

Carbon dioxide (CO2) in excessive quantities increases the rate of breathing and in deeper diving causes respiratory risk. It also leads to minor perceptive changes, discomfort, dizziness or stupor and in extreme cases it may cause unconsciousness and even death.

Excessive moisture can make regulators freeze or fail to open. It also enhances corrosion and rust of the cylinders, thus interacting with filtration elements reducing filtration efficiency and generating chemical odours causing nausea and respiratory irritation.

As for oil, especially the smaller particles create health concerns as they will not be removed by the bodys' clearance mechanisms, as happens to the larger particles. The retained oil particles can cause inflammation. Oil mists may also cause a significant fire hazard.

Dust is hazardous to both our lungs as well as to fine regulator parts.

All these contaminations imply awareness by the diver, diligence by the dive station and knowledge by all!

Symptoms and treatment
What are the signs and symptoms of a CO intoxication?

Typical signs and symptoms of carbon monoxide poisoning are:

  • Headache and sensation of pressure inside the head;
  • Vertigo
  • Nausea;
  • Breathlessness with exertion;
  • Confusion;
  • Vomiting;
  • Paralysis; and/or
  • Unconsciousness;
  • Cherry-red lips, cheeks and fingernails (specially at the early stage).

When you experience a symptom of CO intoxication or you notice these signs in a fellow diver it is extremely important to follow the following procedure to avoid unconsciousness, incapacitation or even death:


The diver should stop breathing from the contaminated cylinder and end the dive. The dive buddy can provide his alternative air source to provide the diver with uncontaminated air, although if filled using the same compressor this air supply may also be contaminated.


Basic Life Support (BLS) and 100% Oxygen should be administered as soon as possible. Call DAN for medical advice and arrange transportation to an emergency medical facility (preferably with a hyperbaric chamber) for assessment and appropriate treatment. A quick response is vital in cases of CO intoxication but better still than curing the symptoms is to avoid them in the first place by having a good prevention strategy.

How to reduce the risk of CO intoxication during diving?

CO contamination usually arises from impurities in the air taken into the compressor or from contaminants generated by the compressor itself. The air compression process can only introduce large amounts of CO and CO2 to your breathing air when they are directly available in the environment of the compressor. Therefore, it is important to make sure to check the compressor that fills your air cylinders and its location. Let us go a little bit more into detail and find out what you can do to prevent CO intoxication, whether you are the person filling the air cylinders or whether you are the diver using them.

What can the dive centre, club or dive shop do?
Make sure the air inlet from compressors is upwind of the exhaust, and away from any source of contamination such as motor vehicles, diesel generators or other gas exhausts. Also make sure nobody is allowed to smoke or burn any materials near the air inlet.


Make sure the correct compressor oil and filters are used, and regularly check that the air intake hose is not damaged and couplings are not loose (which is usually caused by vibrations).


Ensure proper maintenance of the compressor, as excessive wear can lead to overheating and these high temperatures may decompose the lubricating oil into toxic products such as CO.


Regular check the quality of the air: this can be done by using detector tubes and other non-reusable devices, or with electronic analysers. Alternatively, and required in some regions, air testing by accredited laboratories can be done.
What can the diver do?
If using your own compressor, respect the recommendations as stated above.


Only obtain air or breathing gas fills from a reputable dive centre, club or dive shop.


Ask the air supplier how often they check the quality of their air and if they periodically perform compressor maintenance and have a compressor log.


If possible, check the location of the air intake of the compressor when getting a cylinder filled at an unknown filling station, especially when on a dive holiday.


Avoid smoking immediately prior to the dive as cigarette smoke also contains CO.


Check your air cylinder for the presence of CO using a personal CO detector device, especially if you have concerns about the quality of the air supplier or when you can not determine how the dive cylinders where filled. While electronic sensors may be rather expensive for the single diver, products such as the CO - Pro™, which can detect the presence of CO in the breathing gas are inexpensive, making them accessible to all divers and they allow to analyse the air in real time and on site.