In high altitude, the problem is with low atmospheric (barometric) pressure. In deep sea or mines, the

problem is with high barometric pressure. Increased pressure creates two major problems:

1. Compression effect on the body and internal organs

2. Decrease in volume of gases.


At sea level, the barometric pressure is 760 mm Hg, which is referred as 1 atmosphere. At the depth of

every 33 feet (about 10 m), the pressure increases by 1 atmosphere. Thus, at the depth of 33 feet, the pressure is 2 atmospheres. It is due to the air above water and the weight of water itself.


Narcosis refers to unconsciousness or stupor produced by drugs. Stupor refers to lethargy with suppression of sensations and feelings. Nitrogen narcosis means narcotic effect produced by nitrogen at high pressure. Nitrogen narcosis is common in deep sea divers,who breathe compressed air (air under high pressure). Breathing compressed air is essential for a deep sea diver or an underwater tunnel worker. It is to equalize the surrounding high pressure acting on thoracic wall and abdomen.

Eighty percent of the atmospheric air is nitrogen. Being an inert gas, it does not produce any known effect

on the functions of the body at normal atmospheric pressure (sea level). When a person breathes pressurized air as in deep sea, the narcotic effect of nitrogen appears. It produces an altered mental state, similar to alcoholic intoxication


Nitrogen is soluble in fat. During compression by high barometric pressure in deep sea, nitrogen escapes

from blood vessels and gets dissolved in the fat present in various parts of the body, especially the

neuronal membranes. Dissolved nitrogen acts like an anesthetic agent suppressing the neuronal excitability. Nitrogen remains in dissolved form in the fat till the person remains in the deep sea.


1. First symptom starts appearing at a depth of 120 feet. The person becomes very jovial, careless and does not understand the seriousness of the conditions.

2. At the depth of 150 to 200 feet, the person becomes drowsy

3. At 200 to 250 feet depth, the person becomes extremely fatigued and weak. There is loss of concentration and judgment. Ability to perform skilled work or movements is also lost.

4. Beyond the depth of 250 feet, the person becomes unconscious.


Nitrogen narcosis can be prevented by mixing helium with oxygen. Helium is used as a substitute for nitrogen, to dilute oxygen during deep water diving. Helium also produces some effects like nausea and dizziness. But, the adverse effects of helium are less severe than nitrogen narcosis. Nitrogen narcosis may be prevented by limiting the depth of dives. Effects of nitrogen narcosis may also be minimized by safe diving procedures such as proper maintenance of equipments and less work effort. In addition, alcohol consumption should be avoided 24 hours before diving.


Symptoms of nitrogen narcosis completely disappear when the diver returns to a depth of 60 feet. There

is no need for any further treatment since nitrogen narcosis does not have any hangover effect. However,

the physician should be consulted if the diver loses consciousness.

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