Narcosis & Toxicity
The body is affected in several ways by increased gas pressures at depth. High pressures of nitrogen, carbon dioxide and oxygen often lead to narcosis and toxicity.
Nitrogen Narcosis: Breathing air below 100ft leads to an intoxicated drunken state referred to as nitrogen narcosis, due to the increased concentrations of nitrogen in the body and its anesthetic quality under pressure.
Oxygen Toxicity: While breathing pure oxygen relieves the symptoms of decompression sickness and nitrogen narcosis, oxygen has a toxic effect on the brain at high pressures. Toxicity occurs at partial pressures above 1.4 atmospheres (at the earths surface the partial pressure is 0.21 atmospheres). This problem can be resolved by using air tanks with a mixture of helium and oxygen.