At what depth is the limiting partial pressure of oxygen set to 1.40?

Prepare for the SSI Decompression Diving Test with challenging multiple choice questions, detailed explanations, and in-depth study materials. Boost your chances of success!

The limiting partial pressure of oxygen (PPO2) is an important consideration in diving, particularly to prevent toxicity that can occur at elevated pressures. Under water, the partial pressure of a gas is influenced by the surrounding depth, due to the increase of pressure as you go deeper.

The concept of limiting PPO2 is generally understood to be around 1.4 ATA (atmospheres absolute) for recreational diving. This occurs at depths where the accumulation of oxygen in the breathing gas reaches this safe threshold.

To calculate the depth at which the PPO2 reaches 1.40, you can use the formula:

PPO2 = (depth in meters / 10) + 0.79 (the atmospheric pressure at sea level is 1 ATA, and every 10 meters adds 1 ATA)

In this case, you're looking for the point where PPO2 equals 1.40 ATA, which typically corresponds to a depth around 135 feet (approximately 40.5 meters). At this point, the ambient pressure exerted by the water combined with the atmospheric pressure creates a total pressure that, when multiplied by the fraction of oxygen in the air (usually around 0.21 for air), gives a PPO2 of approximately 1.

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