The term gas poisoning summarizes all toxic effects on the human body caused by breathing gases at elevated partial pressures.
Basic knowledge for Open Water Diver* (OWD*)
Breathing nitrogen in depth has an narcotic effect. Although nitrogen is an inert gas and does not undergo chemical reactions in the body, but it can have a narcotic effect at higher partial pressures. A narcotic effect must be expected from a depth of about 30 m. The susceptibility to nitrogen narcosis varies greatly from person to person and you are not equally susceptible every day.
The effects are similar to alcohol and vary from disorientation, euphoria, changed vision, metallic taste in the mouth, anxiety, recklessness, etc. It can increase to panic and sudden loss of consciousness. Nitrogen narcosis is intensified through fear, physical effort, medication, intoxicants and stimulants. The partner's underwater hand signals are often ignored or no longer answered.
As a first measure, you must ascend controlled at least to a level until the symptoms subside. Depending on the severity of the symptoms, you have to support your diving partner with the ascent or bring him up – if necessary also against his will. After ascending to lower depths, the symptoms usually go away. However, effects on the mental performance can last for a few hours.