Introduction to Nitrogen Narcosis

Scuba diving is pretty unique as far as a leisure activity goes, and for lots of reasons. Not the least of which is that it takes place in an environment completely foreign, and hostile, to human existence. It's also the only sport that I know of in which you literally have to pay for the air you breath. But perhaps the most unique aspect of diving is that even if we do everything right we can still fall victim to life threatening disorders. Furthermore, the deeper we go, the greater the risk we incur. This is in stark contrast to almost every other sport or recreational endeavor in which you'll normally have to do something wrong before you get into any kind of trouble. Not so for divers, though. We're exposed to hazards merely by being underwater.

At the root of almost every problem a diver faces is the fact that the air he or she breathes is under continually varying pressure. On ascent, when the pressure decreases, problems can arise when the air-filled spaces of our body, most notably our lungs, aren't vented and expand to a point beyond their maximum capacity. The result is a lung expansion injury such as an air embolism. In parlance of scuba instructors, we sometimes refer to this as the “direct” effects of pressure. Yet, other problems can result from the simple absorption of the inert component of our breathing gas mixture.

Unlike the mechanical nature of injuries caused directly by changes in the volume of bodily air spaces, like the lungs, ears, and sinuses, these more subtle consequences are what we term the “indirect” effects of pressure.

In recreational diving, the inert component of our breathing gas is nitrogen, although for technical divers it can also be helium. On ascent, the disorder of concern is decompression sickness which is caused by dissolved inert gas (nitrogen or helium) escaping our tissues too quickly to remain in solution and, thus forming bubbles. However, there is also another indirect effect of pressure that's associated only with descent and it's almost as familiar to non-divers as is the “bends”. It's formally call nitrogen narcosis, but scuba's own inventor, Jacques Cousteau, gave it the much more lyrical name, l'ivresse des grandes profondeurs (“rapture of the deep”). As Cousteau once wrote, “The chief symptom of this phenomenon, to put it bluntly, is the sensation of becoming as drunk as a hoot owl.”

Without exception, every scuba training course covers nitrogen narcosis, but usually teaches only that it's cause by breathing nitrogen at high pressure; its effects increase with depths, normally becoming quite noticeable around 100 feet; and ascending to a shallower depth will relieve the symptoms. Case closed.

While these are certainly the highlights, this is anything but an in-depth explanation of this important condition. Additionally, the growing popularity of technical diving has made recreational divers more aware and curious about diving to much greater depths than our own limit of 130 feet. But whether you're interested in learning more about the challenges of deep diving as a bridge to technical diving, or just want a better understanding of what goes on inside your body at any depth, a more thorough insight into narcosis isn't a bad idea.