What is the maximum operating depth (MOD) for Nitrox 36 to keep the partial pressure of oxygen below 1.4 ATA?

To determine the maximum operating depth (MOD) for Nitrox 36, we need to understand how to calculate it based on the mixture's oxygen content and a safe partial pressure of oxygen limit.

Nitrox 36 means the gas mixture contains 36% oxygen and 64% nitrogen. The maximum safe partial pressure of oxygen for recreational diving is typically set at 1.4 ATA (atmospheres absolute). This partial pressure can be calculated using the formula:

MOD = (Depth in meters + 10) / (Fraction of oxygen) - 10

To find the MOD for Nitrox 36 with a fraction of oxygen of 0.36, we can rearrange the equation. First, we need the partial pressure of oxygen:

Desired PO2 = 1.4 ATA

Taking the ratio of the partial pressure of oxygen to the percentage of oxygen in the mixture gives:

MOD = (1.4 / 0.36) - 10

Calculating this:

1.4 / 0.36 = approximately 3.8889

Multiplying this by the atmosphere pressure at sea level (1 ATA):

3.8889 - 1 = 2.8889

Now, converting this value from ATA