Editing Maximum operating depth (section)

{{Short description|Depth below which the partial pressure of oxygen (pO2) of the gas mix exceeds an acceptable limit}}
In [[underwater diving]] activities such as [[saturation diving]], [[technical diving]] and nitrox diving, the '''maximum operating depth''' ('''MOD''') of a [[breathing gas]] is the depth below which the [[partial pressure]] of [[oxygen]] (pO<sub>2</sub>) of the gas mix exceeds an acceptable limit. This limit is based on risk of [[central nervous system oxygen toxicity]], and is somewhat arbitrary, and varies depending on the [[diver training]] agency or Code of Practice, the level of underwater exertion expected and the planned duration of the dive, but is normally in the range of 1.2 to 1.6 [[Bar (unit)|bar]].<ref name="dan" />

The MOD is significant when planning dives using gases such as [[heliox]], [[nitrox]] and [[Trimix (breathing gas)|trimix]] because the proportion of oxygen in the mix determines a maximum depth for breathing that gas at an acceptable risk. There is a risk of acute [[oxygen toxicity]] if the MOD is exceeded.<ref name=dan/> The tables below show MODs for a selection of oxygen mixes. Atmospheric air contains approximately 21% oxygen, and has an MOD calculated by the same method.