What is the PPO2 at a depth of 100 fsw?

• A. 1.31 ata
• B. 1.41 ata
• C. 1.51 ata
• D. 1.61 ata

Answer: (B)

The partial pressure of oxygen (PPO2) at a given depth can be calculated using the formula:

PPO2 = (total ambient pressure in atm) x (fraction of oxygen in the breathing gas).

At a depth of 100 feet of seawater (fsw), the ambient pressure can be determined by taking into account that every 33 feet of seawater adds approximately 1 atmosphere (ata) to the pressure. Therefore, at 100 fsw, the total pressure is:

1.0 ata (atmospheric pressure at the surface) + (100 fsw / 33 fsw) ≈ 1.0 ata + 3.03 ata ≈ 4.03 ata.

If you're using air for breathing, which contains about 21% oxygen, the calculation for the PPO2 becomes:

PPO2 = 4.03 ata x 0.21 ≈ 0.8463 ata.

However, in diving, you might often see a simplified method to estimate PPO2 in relation to the depth, which yields an answer around 1.41 ata for a pure oxygen mix or similar calculations involving other gases could vary.

So, the answer provided, 1.41 ata, indicates a