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Nitrogen Narcosis Nitrogen Narcosis is the effect that breathing compressed air has on our central nervous system. It starts at shallow depths and becomes significant at depths greater then 30 msw/ 100 fsw. The symptoms are impaired judgement, altered perception, and decrease in reaction speed. Nitrogen narcosis stops as soon as we ascend to shallower depths. The danger lies in the combination of having a temporarily decreased brain-function in a for us unnatural and dangerous environment. Possible mistakes made while under the influence of nitrogen narcosis are: forgetting about depth and time limits, failure to monitor our air supply, reacting slow or the wrong way when a problem arises, or being unaware of our buddy. Each of these examples can cause diving "accidents" that would not have happened if we avoided to become "narced". The deeper we go, the stronger the effect of the nitrogen narcosis gets, which can result in unconsciousness at extreme depths. Hypercapnia Hypercapnia is also called CO2 retention, and means that the level of CO2 in our body is higher then normal. In diving there are some possible causes for hypercapnia: -skip-breathing, skipping breaths or breathing very slowly to conserve air. -using a faulty regulator with a high breathing resistance. -exerting ourselves at depth, where the density of the air we breath is higher. The deeper we dive on air, the higher the density of the air we breath, and the higher the risk of hypercapnia becomes. CO2 is a highly narcotic gas and therefore hypercapnia also increases your levels of nitrogen narcosis. Signs and symptoms of hypercapnia are: shortness of breath and rapid heart beat, disorientation and panic, hyperventilation, and finally, unconsciousness. Oxygen Toxicity In diving, there are two types of oxygen toxicity: central nervous system oxygen toxicity (CNS) and pulmonary oxygen toxicity. When deep air diving our concern is CNS. Some of the signs and symptoms of CNS are: muscle twitching, dizziness, irritability, fatigue, tunnel vision, nausea, anxiety and convulsions. These convulsions almost invariably lead to death by drowning. The normal air-diving limit where you can get CNS starts is 66 MSW / 218 FSW, the depth where you have a partial pressure of O2 of 1,6 ATA. But this depth-limit is not exact. It varies from person-to-person, from day-to-day, and is also influenced by other factors. A higher level of CO2 gives a higher chance of a CNS problem, for example. This means that when you dive shallower then 66 meters on air you have a smaller chance of getting CNS, but you do not have a guarantee against getting CNS. These phenomena: nitrogen narcosis, hypercapnia and oxygen toxicity, cause "accidents" by putting the diver under stress. They can cause divers to lose consciousness and drown. When you read about another diver who has died during a deep air dive then at least one of these factors has played a role. These "accidents" can easily be avoided, by following good diving practices and using the right gas-mixture for the planned depth of your dive.
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