What is the Maximum Operating Depth (MOD) for a Nitrox blend of 36%?

The Maximum Operating Depth (MOD) for a Nitrox blend is determined by calculating the depth at which the partial pressure of oxygen (O2) in the gas mixture becomes too high for safe diving. For a Nitrox blend of 36%, the calculation involves using the formula for partial pressure of oxygen, which is:

MOD = (Max Partial Pressure of O2 / Fraction of O2) - 10

In this case, the maximum safe partial pressure of oxygen is typically set at 1.6 ATA (atmospheres absolute) for recreational diving.

First, calculate the partial pressure for 36% Oxygen:

• The fraction of oxygen in the blend is 0.36.
• Using the safe limit of 1.6 ATA: MOD = (1.6 / 0.36) MOD = 4.44 ATA

Since we need to convert ATM to depth in feet, we know that at sea level, atmospheric pressure is approximately 1 ATA, and every 33 feet of seawater adds about 1 ATA.

Thus, at a depth (in feet) of MOD = (4.44 ATA - 1 ATA) * 33 feet/ATA = 3.44 ATA