Frequently used Formulas for Nitrox Divers
Equivalent
Air Depth formula
This formula allows you to quickly calculate the exact equivalent
air depth for a given depth on a nitrox blend.
For example: To figure the exact EAD for 70 feet using a blend of 39% O2. Work it like this:
EAD = ((1-.39) x (70+33) / .79)
- 33
EAD = ((.61) x (103) / .79) - 33
EAD = (62.83 / .79) - 33
EAD = 79.53 - 33
EAD = 46.53 fsw
Partial
Pressure Formula
This formula allows you to compute the partial pressure
of oxygen in your mix for a given depth. (For safety,
remember 1.4atas for working load, 1.6atas at rest)
For example: What is the partial pressure for 76 fsw using a blend with 37% O2?
O2 Partial Pressure = ((76 fsw
+ 33) / 33) x .37
O2 Partial Pressure = (109 / 33) x .37
O2 Partial Pressure = 3.3 x .37
O2 Partial Pressure = 1.22 ata
