Nitrogen is commonly painted as the bogeyman gas for divers, but there are two other gases that can cause scuba divers problems. Carbon dioxide (CO2) and carbon monoxide (CO) are the real black gases of scuba diving.
By Simon Pridmore
Simon is the best-selling author of Scuba Confidential – An Insider’s Guide to Becoming a Better Diver and Scuba Professional – Insights into Scuba Diver Training & Operations. Both books are available from Oceanic Ventures. Simon has also just published a new book for divers-to-be and absolute beginners called Scuba Fundamental – Start Diving the Right Way.
The dangers of CO2 in particular have come to attention in sport diving recently with the increasing popularity of rebreather diving, where it has been a factor in many accidents. However, it is important to appreciate that open circuit divers are also at risk. CO2 build up is a major contributor to one thing that, above all else, causes divers to come to harm – panic!
The risk of CO2 poisoning is something that all divers should be aware of but its importance is often understated in basic training manuals, where headaches are commonly given as the only adverse effect. Divers therefore often do not think of it as a threat at all.
How CO2 can affect us all
CO2 is a waste product of the metabolic process and is potentially toxic. Usually, we automatically regulate the level of CO2 in our bodies just by breathing. If there is too much, our brain detects what is happening and causes our breathing rate to increase in order to to flush out the excess.
Divers tend to develop higher-than-normal levels of CO2 during a dive. This is because when we are underwater we do not eliminate enough of the CO2 that our body is producing, especially when we are deep and exerting effort.
This is due to a number of factors, including: –
- Water pressure on the chest;
- The extra resistance to breathing imposed by the our equipment, and
- The increased density of air at depth.
A high level of CO2 in the bloodstream produces a condition called hypercapnia. Hypercapnia does indeed give you a headache but it can also make you confused, dizzy, disorientated, light-headed, short of breath and panicky.
How to Prevent and Combat CO2 Poisoning
The key strategies to deal with the threat posed by hypercapnia are awareness and prevention. Know that it is a risk, anticipate situations where it is likely to occur and avoid such situations. CO2 build up happens mainly when you descend fast, head down, or when you swim hard at depth, perhaps when you are swimming against a strong current or hurrying to get back to the boat because you are low on air.
Because the deeper you go, the more dense your air becomes, working hard on deeper dives carries a greater risk of CO2 build up. So, if you are deep and find yourself fighting a current, change direction and go with the flow. Or ascend to a shallower depth so you are not dealing simultaneously with the twin challenges of both depth and exercise.
If you know beforehand that your dive might involve a long, hard swim at depth, always ensure your regulator is set to give you the least breathing resistance possible. Consider using specialized equipment such as a scooter to help reduce your workload.
Carbon Monoxide
The other black gas is carbon monoxide, which is completely invisible and odorless, but potentially fatal if it is present in your scuba cylinder in even small quantities.
How does it get into the scuba cylinder?
Carbon monoxide usually gets into the cylinder because there is an engine exhaust close to the compressor intake. The source might be a permanent fixture such as the exhaust from the compressor engine itself or a dive boat engine. It could also be something temporary. Perhaps a car was parked with its engine running close to the compressor intake while your cylinder was being filled.
How will you know?
Analyzers are available which can be used to detect the presence of carbon monoxide in a scuba cylinder. They work in much the same way as an oxygen analyzer. Otherwise, you will not know until you start feeling unwell during a dive. The initial symptoms are headache, fatigue, irritability, dizziness and confusion. Carbon monoxide poisoning causes oxygen deprivation that leads to loss of consciousness, cell damage and death. As you probably know, carbon monoxide is a threat in the home as well, for instance, if you run a car engine in a confined space such as a closed garage or if your heating system is poorly maintained or poorly ventilated.
What Can You Do?
If you ever feel unwell during a dive then you should immediately abort the dive and ascend slowly WITH your buddy. Do not just go up on your own in case your situation becomes worse during the ascent. Make yourself positively buoyant at the surface, remove your regulator and take a few long deep breaths. Do NOT resume your dive, even if you start to feel better. Once you are safely back home, let the folk at the dive center that filled your cylinder know what happened, so that they can test the air in your cylinder and check their systems. The problem might have been carbon monoxide. It might have just been something you ate. But they should be told, just in case.
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