Apeks - DSX

The long held conventional wisdom, based on early work by Bühlmann, has been that tissues take up helium faster than nitrogen; thus requiring deeper stops and longer decompression. This idea that more helium yields more decompression, sometimes referred to as the "helium penalty", is incorporated to varying degrees in most decompression algorithms used by technical divers. However, based on recent work of decompression physiologist David Doolette, Ph.D. and the team at the Navy Experimental Diving Unit (NEDU) there is no such thing as a helium penalty. Essentially, for the bounce dive profiles of technical diving and comparing trimix to heliox, their research found the controlling factor for decompression is the amount of oxygen in the mix (inversely, the total amount of inert gas), not the amount of helium specifically.

This has some implications for the future of technical diving: Improved deco algorithms for helium rich mixes will probably begin to appear over time as the amount of helium may not be as critical a factor in decompression as previously assumed. However, this does not mean you should start diving trimix on nitrox tables or lie to your dive computer about your mix. (It's entirely possible the current algorithms are giving you the "right" amount of required decompression for the "wrong" reasons!) It does mean that other than cost, there is reason to take the advantages of helium at every opportunity even to the point of using heliox instead of trimix. While the increasing cost of helium in open circuit continues to be a concern, in closed-circuit you may be better off to just use heliox as the US Navy does.