Gas Narcosis vs Decompression sickness

During the Open water course we always have students who have questions about gas narcosis, formally known as nitrogen narcosis, and decompression sickness. During the Divemaster training we go a little more in-depth, but there always seem to be questions about these 2 topics.  Gas narcosis and decompression sickness have very different symptoms and must be treated in very different ways. 

What Is Gas Narcosis?: Gas narcosis is an altered state of awareness caused by breathing a high partial pressure of breathing gas. The deeper a diver goes, the greater the partial pressure of the gas, and the stronger the diver’s narcosis will be. Some divers have compared the feeling of gas narcosis to being pleasantly drunk, while others find it terrifying. Gas narcosis is caused by breathing a concentration of gas which can result in  a mild anesthetic. The gas causing the narcosis remains partly dissolved in a diver’s tissues and does not form bubbles.

Gas narcosis is one of the factors that will limit the depth of your dives.  It can change, all depending on your physical condition. Due to its perception-altering effects, the onset of narcosis may be hard to recognize. Narcosis results in relief of anxiety – a feeling of tranquility and mastery of the environment. These effects also resemble (though not as closely) the effects of alcohol or marijuana. Such effects are not harmful unless they cause some immediate danger not to be recognized and addressed. Once stabilized, the effects generally remain the same at a given depth, only worsening if the diver ventures deeper.

Narcosis may be completely reversed in a few minutes by ascending to a shallower depth, with no long-term effects. The most dangerous aspects of narcosis are the impairment of judgment, multi-tasking and coordination, and the loss of decision-making ability and focus. The relation of depth to narcosis is sometimes informally known as “Martini’s law”, the idea that narcosis results in the feeling of one Martini for every 10 m (33 ft) below 20 m (66 ft) depth.

What Is Decompression Sickness?: Decompression sickness is a physical condition caused by the formation of gas bubbles in a diver’s blood and tissues. Although they are generally quite tiny, these bubbles can block blood flow to various parts of the body and may irreversibly damage tissues. Decompression sickness is caused by gas coming out of solution and forming bubbles. During every dive, a diver’s body absorbs nitrogen and/or other inert gasses by breathing from his tank. As the diver ascends, the gas expands. Normally, the gas travels in the diver’s bloodstream until it reaches his lungs, where it is exhaled. However, if a diver stays underwater too long (past the limits), or ascends too quickly, his body cannot eliminate the gas effectively, and the excess gas trapped in his body forms bubbles. Like gas narcosis, the symptoms of decompression sickness may include confusion and impaired thinking, but also may include pain, loss of feeling in an isolated area of the body, tingling, visual disturbances, vertigo, and paralysis (among many other symptoms). A bubble may even block blood flow to the point that body tissues and organs are permanently damaged. Divers typically experience decompression sickness a few hours to one day after a dive, or during ascent from a very deep or long dive. Unlike gas narcosis, the symptoms of decompression sickness are not noticeable during the deepest part of the dive. The first treatment for this is 100% oxygen and transport the patient to a hospital / hyperbaric chamber as soon as possible.


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