What is the maximum operating depth for using a mix of 40% oxygen to maintain a partial pressure below 1.4 ATA?

To determine the maximum operating depth for a mix of 40% oxygen while keeping the partial pressure of oxygen below 1.4 ATA, it's essential to understand the relationship between depth, ambient pressure, and the percentage of oxygen in the breathing gas.

At sea level, the atmospheric pressure (ATA) is 1.0. As you descend in water, for every 10 meters of seawater, the pressure increases by approximately 1 ATA due to the water. Therefore, at a depth of 10 meters, the total pressure would be 2.0 ATA, at 20 meters it would be 3.0 ATA, and so on.

For a gas mixture containing 40% oxygen, the partial pressure of oxygen can be calculated by multiplying the total ambient pressure (in ATA) by the fraction of oxygen in the mix. To ensure the partial pressure remains below 1.4 ATA, the formula can be rearranged:

[ \text{Max Total Pressure} = \frac{1.4 \text{ ATA}}{0.40} = 3.5 \text{ ATA} ]

Now, to find the corresponding depth, we determine the depth at which the pressure equals 3.5 ATA. Sub