**2. History**

The poisoning caused by air inhalation in a high-pressure environment was first described by Junod in 1835 [2]. In 1861, Green made a dive with divers with 48 m of compressed air, observing that the divers developed to sleep, their decision-making powers were impaired, and they saw hallucinations. Paul Bert stated that divers were poisoned at high depths in 1878. In 1903, Hill and McLeod described the intellectual functions of tunnel workers as inadequate at 5.5 ATA pressure. In 1930, Damant reported that memory problems had developed in 10 ATA. In 1932, Hill and Phillips thought these effects could be claustrophobic or psychological. According to a report by the British Navy in 1933, the section entitled "Loss of semiconsciousness" states that divers who have dived at 60–106 m have received hand signals sent to them, but no one remembers it when it comes to the surface [1].

In 1935, Behnke and his colleagues described the currently accepted theory of nitrogen narcosis. Narcosis is caused by an increase in partial pressure of nitrogen, which is an inert gas. The enthusiasm (euphoria) developed at the 30-m compressed air dive; accompany slowing of the mental capacity and deterioration of the nerve-muscle communication. Attention was paid to the fact that this effect was further enhanced by the depth of the dive. At diving, drowsiness occurs at 90 m and loss of consciousness occurs at 90–140 m. Behnke and Yarbrough reported that this effect could be reduced by replacing nitrogen to helium in the dive inhalation gas [1].

According to the Deep Dive Committee Report in 1933, this was also related to the accumulation of carbon dioxide during the dive. In 1941, Case and Haldane showed that, when carbon dioxide was mixed in the diving air, the mental symptoms became more intense. However, In some studies clearly denied the carbon dioxide theory. They showed evidence of narcotic symptoms despite normal levels of carbon dioxide in the alveolar air. In subsequent years of studies has been found that direct anesthesia is responsible for the nitrogen between the air and dive with helium/oxygen [2].
