The History of Nitrogen Narcosis
While we call the condition nitrogen narcosis, almost any gas can have a narcotic effect when breathed under enough pressure. The condition produces a state like alcohol intoxication or breathing nitrous oxide (“laughing gas”) at surface pressure. The good news is that, unlike decompression sickness, the effects of narcosis are completely resolved by ascending to a shallower depth, and with no long-term consequences. Therefore, provided a diver is aware of its symptoms and ascends to manage it, narcosis rarely develops into a serious problem.
Another interesting fact is that, aside from inert gases, it appears that we can also succumb to narcosis from high enough levels of that vital gas, oxygen. The reason is that too high a level of oxygen within the tissues can leave some of it metabolized, thus enabling oxygen to behave like an inert gas.
We've known about nitrogen narcosis for about as long as technology has enabled people to breathe air under pressure. In 1834 a French researcher, Victor Junod, was the first to describe it, noting “the functions of the brain are activated, imagination is lively, thoughts have a peculiar charm and, in some persons, symptoms of intoxication are present.” As a cause, he proposed that narcosis resulted from high-pressure gas causing increased blood flow, therefore stimulating nerve centers.
A bit later, in 1881, a physician named Walter Moson proposed that pressure forced blood to inaccessible parts of the body and the stagnant blood somehow caused emotional changes. Others believed it was a result of psychological factors, such as latent claustrophobia.
It wasn't until 1935 that a diving physiologist named Albert Behnke — the father figure of the U.S. Navy's diving program — suggested that it was the nitrogen component of air responsible for the narcotic symptoms. In 1939, Behnke and his colleagues were also the first to demonstrate that gases other than nitrogen, such as helium, could cause narcosis.
That year was also auspicious for yet another reason. On May 23, 1939, the U.S. Navy submarine, Squalus, suffered a catastrophic valve failure during a test dive off New Hampshire's Isle of Shoals. Fortunately it came to rest in just 240 feet of water, rather than the crushing depths just offshore. Only a quick salvage-and-rescue operation would save the lives aboard, but the depth made air diving operations less than ideal due to the effects of nitrogen narcosis. The situation provided the Navy with its first opportunity to try the then-experimental gas mixture heliox (helium-oxygen) to complete the rescue; and the Squalus salvage operation went down as one of the most famous and successful in U.S. Naval history.