Overview of the use of different gas mixtures in self-contained diving

With the development of the so-called "technical diving" techniques the depth capability of untethered divers took a major step downward, providing access for scientists and explorers to a depth range formerly available only to commercial and military divers with massive equipment systems. Dives to depths of 80 to 100 msw are now routine for many divers. A major aspect of this capability is the creative application of the properties of different inert gases and gas mixtures and the judicious use of oxygen to hasten decompression. The leading benefit of alien gases is the use of helium to reduce narcosis; narcosis makes diving to such depths with air both unsafe and ineffective. Diving beyond the "air range" of 40 or so msw immediately invokes the need for sophisticated decompression techniques; it was the development of procedures for managing these decompressions that opened up this category of diving. Decompression involves not only calculating or otherwise determining the profile to be followed, but also managing the necessary gas logistics, oxygen exposure, thermal protection, and other endurance factors, and having a place to do the decompression. The latter task may be assisted by a variety of semi-dry stations or "habitats" or by drifting in a controlled way in the open sea. Future developments are sure to include more efficient decompressions by the incorporation of empirical findings such as the benefit of deeper stops