 With a mixture of three gases it is possible to create mixes suitable for different depths or purposes by adjusting the proportions of each gas.Oxygen content can be optimised for the depth to limit the risk of toxicity, and the inert component balanced between nitrogen (which is cheap but narcotic) and helium (which is not narcotic and reduces work of breathing, but is more expensive and increases heat loss).The mixture of helium and oxygen with a 0% nitrogen content is generally known as Heliox.