While breathing air at fepths approachig 100 feet, you can experience an effect called nitorgen narcosis, which is an anesthetic quality nitrogen has under pressure. The deeper you dive, the more pronounced the narcotic effect becomes.

A diver affected nitrogen narcosis behaves as though he is intoxicated. He has impaired judgement and coordination, and may experience a feeling of false seurity and exhibit a lack of concern for safety. In short, he may behave folishly. Also, he may feel anxious or uncomfortable. These effects can be disastrous as a result of poor decisions by the diver.

Nitrogen narcosis affetcs individuals differently. You may be more or less susceptible than other divers. Also, the degree of susceptibility may vary from day to day and from dive to dive.

Nitrogen narcosis diminishes when you reach shallow water, with no aftereffects. If you begin to feel strange or intoxicated, immediately ascend to shallower depths to relieve the narcosis. It usually goes away quickly. If your buddy acts impaired, assist him to shallower water.

To prevent narcosis, simply avoid deep dives. Nitrogen narcosis is not dangerous or harmful in itself, but the impaired judgement and loss of coordination it causes can be quite hazardous.

 

This information was obtained from the Padi Open Water Diver Manual