At what depth is the partial pressure of oxygen at 2.5 ATA?

To determine at what depth the partial pressure of oxygen reaches 2.5 ATA, it's important to understand how partial pressure and depth are related in diving. The total pressure experienced underwater increases with depth due to the weight of the water above.

In the case of air, which is composed of approximately 21% oxygen, the relationship between depth (measured in feet of seawater or FSW) and atmospheric pressure is governed by the following:

At sea level (0 fsw), the atmospheric pressure is approximately 1 ATA. For every 33 feet of seawater, the pressure increases by 1 ATA. Therefore, at a depth of 33 fsw, the total pressure is 2 ATA, where 1 ATA is from the atmosphere above and 1 ATA from the water itself.

To find the partial pressure of oxygen at a given depth, you multiply the total pressure in ATA by the fraction of oxygen in air (0.21). Therefore, the equation for finding the depth at which the partial pressure of oxygen is 2.5 ATA can be derived from the total pressure (depth) required.

To achieve a partial pressure of oxygen of 2.5 ATA, we rearrange the information as follows:

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