Nitrogen Narcosis - Prevention

Prevention

The most straightforward way to avoid nitrogen narcosis is for a diver to limit the depth of dives. If narcosis does occur, the effects disappear almost immediately upon ascending to a shallower depth. Since narcosis becomes more severe as depth increases, a diver keeping to shallower depths can avoid serious narcosis. Most recreational dive schools will only certify basic divers to depths of 18 m (60 ft), and at these depths narcosis does not present a large risk. Further training is normally required for certification up to 30 m (100 ft) on air, and this training should include a discussion of narcosis, its effects, and cure. Some diver training agencies offer specialty training to prepare recreational divers to go to depths of 40 m (130 ft), often consisting of further theory and some practice in deep dives with close supervision. Scuba organizations which train for diving beyond recreational depths, may forbid diving with gases that cause too much narcosis at depth in the average diver, and strongly encourage the use of other breathing gas mixes containing helium in place of some or all of the nitrogen in air—such as trimix and heliox—because helium has no narcotic potential. The use of these gases forms part of technical diving and requires further training and certification.

While the individual diver cannot predict exactly at what depth the onset of narcosis will occur on a given day, the first symptoms of narcosis for any given diver are often more predictable and personal. For example, one diver may have trouble with eye focus (close accommodation for middle-aged divers), another may experience feelings of euphoria, and another feelings of claustrophobia. Some divers report that they have hearing changes, and that the sound which their exhaled bubbles make becomes different. Specialist training may help divers to identify these personal onset signs, and these may then be used as a signal to ascend to shallower depths. Although severe narcosis may interfere with the judgment necessary to take preventive action, a diver who remains calm and is alert to the danger will be capable of resolving these problems at an earlier stage.

Deep dives should be made only after a gradual training to gradually test the individual diver's sensitivity to increasing depths, with careful supervision and logging of reactions. Diving organizations such as Global Underwater Explorers (GUE) emphasize that such sessions are for the purpose of gaining experience in recognizing the onset symptoms of narcosis for an individual, which are somewhat more repeatable than for the average group of divers. Scientific evidence does not show that a diver can train to overcome any measure of narcosis at a given depth or become tolerant of it.

Equivalent narcotic depth (END) is a commonly used way of expressing the narcotic effect of different breathing gases. The National Oceanic and Atmospheric Administration (NOAA) Diving Manual now states that both oxygen and nitrogen should be considered equally narcotic. Standard tables, based on relative lipid solubilities, list conversion factors for narcotic effect of other gases. For example, neon at a given pressure has a narcotic effect equivalent to nitrogen at 0.28 times that pressure, so in principle it should be usable at nearly four times the depth. Argon, however, has 2.33 times the narcotic effect of nitrogen, and is not suitable as a breathing gas for diving (it is used as a drysuit inflation gas, owing to its low thermal conductivity). Some gases have other dangerous effects when breathed at pressure; for example, high-pressure oxygen can lead to oxygen toxicity. Although helium is the least intoxicating of the breathing gases, at greater depths it can cause high pressure nervous syndrome, a still-mysterious but apparently unrelated phenomenon. Inert gas narcosis is only one factor which influences the choice of gas mixture; the risks of decompression sickness and oxygen toxicity, cost, and other factors are also important.

Because of similar and additive effects, divers should avoid sedating medications and drugs, such as marijuana and alcohol before any dive. A hangover, combined with the reduced physical capacity that goes with it, makes nitrogen narcosis more likely. Experts recommend total abstinence from alcohol at least 12 hours before diving, and longer for other drugs. Abstinence time needed for marijuana is unknown, but due to the much longer half-life of the active agent of this drug in the body, it is likely to be longer than for alcohol.