Owing to the expense of helium, heliox is most likely to be used in deep commercial diving. It is also sometimes used by diving enthusiasts, particularly those using rebreathers. These conserve the breathing gas at depth much better than open circuit scuba. Trimix is another cheaper alternative which can be used.
The proportion of oxygen in a diving mix depends on the maximum depth of the dive plan. It is often hypoxic and typically 10%. Each mix is bespoke and is created using gas blending techniques. These often involve the use of booster pumps to achieve typical diving cylinder pressures of 300 bar (4351 psi ) from lower pressure banks of oxygen and helium cylinders.
Because sound travels faster in heliox than in air, voice formants are raised. This results in divers’ speech being very high-pitched and hard to understand to people not used to it. Surface personnel often employ a piece of communications equipment called a “helium de-scrambler. This electronically lowers the pitch of the diver’s voice as it is relayed through the communications gear, making it easier to understand.
Trimix is a slightly less expensive alternative to heliox for deep diving. Commercial diving and technical diving will often use Trimix. In 2015, the United States Navy Experimental Diving Unit showed that bounce dives using trimix are not a more efficient decompression than dives on Heliox.