MOD - maximum operating depth

Listen to this article MOD (Maximum Operating Depth) – for a given mixture, the maximum depth expressed in metres at which the mixture can be used. The MOD value is closely related to oxygen toxicity. Reaching the maximum MOD value means reaching the maximum allowable partial pressure of oxygen, previously established for the given mixture.

ByAdam Sieczkowski

Published: April 29, 2011 - 16:47

Updated: February 9, 2023 - 01:24

Listen to this article

MOD (Maximum Operating Depth) – for a given mixture, the maximum depth expressed in metres at which the mixture can be used. The MOD value is closely related to oxygen toxicity. Reaching the maximum MOD value means reaching the maximum allowable partial pressure of oxygen, previously established for the given mixture.

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MOD is calculated from the formula below:

where:
FO2- oxygen fraction
ppO2 max- maximum assumed partial pressure of oxygen

The MOD value is used when diving on nitrox mixtures, most often in technical diving. Each diving cylinder containing a mixture with increased oxygen content should clearly display the MOD.

In technical diving, each side cylinder has a sticker with a number indicating the MOD of the gas in it.

Maximum vapour pressure is usually set between 1.2 and 1.6, depending on the activity you plan to carry out with the gas. For decompression gases, values higher than 1.6 may be adopted. For bottom gases, more restrictive values of 1.2 or 1.4 are usually used. Very rarely, usually in the military, high ppO2 max values of even 2.0 can be found.

Typical MOD values:
Air – 56m
EAN50 – 21m
Oxygen – 6m