What gas mixture is recommended for a dive to 125 feet with oxygen partial pressure limit of 1.40?

To determine the appropriate gas mixture for a dive to 125 feet while adhering to an oxygen partial pressure limit of 1.40, it is crucial to understand how to calculate the partial pressure of oxygen based on depth and the mixture's oxygen content.

At a depth of 125 feet, the ambient pressure is approximately 4.0 atmospheres absolute (ATA), as deep-sea diving typically adds 1 ATA for every 33 feet of seawater. Given this pressure, you can calculate the partial pressure of oxygen with any gas mixture.

For each option, the percentage of oxygen in the gas mixture needs to be converted from a percentage to a decimal. This decimal value is then multiplied by the absolute pressure to find the partial pressure of oxygen.

When using EAN 29, which contains 29% oxygen (or 0.29 in decimal), the partial pressure of oxygen is calculated as follows:

Partial pressure of O2 = %O2 (as a decimal) × total pressure

= 0.29 × 4.0 ATA

= 1.16 ATA

This value is below the limit of 1.40, making EAN 29 a suitable option for the dive.

Analyzing the other options shows