Air contains approximately 78% nitrogen, when it is compressed and breathed under pressure the elevated partial pressure (Dalton’s Law) of nitrogen can have a narcotic type effect. Physiologically inert under normal conditions nitrogen can induce an anesthesia effect at raised pressures. How this effect occurs, is comparable to the way anesthesia gases operate, which is not clearly understood. All that is known is that gases affect the central nervous system in unique ways. The effects of nitrogen under pressure can be compared to the effects of alcohol. The relationship of nitrogen to alcohol is expressed by what has been called Martini’s Law. Simply put it is: that for every 1 ATM or 33 feet the diver receives the effect of one martini. At 99 feet the diver has the effect of 3 martinis and is typically unaware of reduced ability. Like alcohol the diver is unconcerned about how impaired he is and it is difficult to discern. Accomplishing such actions as figuring decompression, or reading gauges can be hindered. Reflexes, needed for emergency action, will be slowed.


33FT = 1 Martini

66FT = 2 Martinis

99FT = 3 Martinis

132FT = 4 Martinis

Martini’s Law: For each 33 fsw the effect is similar to one Martini

The effects of nitrogen fluctuate from day to day and diver to diver. Ill health, hard work, cold water, and being fatigue, all increase its effect. Most divers think of nitrogen narcosis as a sudden ”freaking out” by someone like giving a regulator to a fish but this does not happen until a great depth is achieved. Like drinking, you never feel drunk until it is to late. Sport divers should not exceed 130 feet and watch for the effects of nitrogen at around 100 feet, with the most serious symptoms below 150 feet.

One defense is to recognize the signs and ascend when present. It is characterized by a slowing of mental activity and a general feeling of euphoria. The greatest problem is it can prevent the diver from feeling about his own safety.

Ascending alleviates the effect but you may have to surface. When deep diving stay nearby your buddy in case one of you acquire symptoms that may bring on harm. If encountering someone, grab their arm, and signal up. If required, take him up with you by holding on to his arm, and ascending. Never send a conscious diver to the surface by making him positively buoyant. As pressure decreases, and air expands (Boyle’s Law) and his velocity of ascent will increase, to a conceivably uncontrolled rate. Over expansion injuries can transpire. After bringing the victim up, give 100% oxygen as needed. Training, preplanning, and declining dives greater than 100 to 130 feet can help avert narcosis.

Signs and Symptoms of Nitrogen Narcosis
Loss of judgment
False sense of well being
Lack of concern
Near unconsciousness at great depth
Unusual behavior
Stupor and/or coma

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