Which of the following statements is true in relation to ppO2 at greater depths?

The increase in partial pressure of oxygen (ppO2) with depth is a fundamental concept in diving physiology and gas laws. As a diver descends, the ambient pressure surrounding them increases due to the weight of the water above. Since the partial pressure of a gas is directly related to the total pressure of the gas mixture, the ppO2 in a gas mixture will also increase with depth when using air or nitrox.

For example, at a depth of 10 meters in seawater, the pressure is approximately 2 ATA (atmospheres absolute), meaning that the air you breathe is under double the atmospheric pressure at sea level. If the gas mixture contains 21% oxygen (like air), the ppO2 would effectively double because it is influenced by the total pressure.

Understanding this principle is particularly important for divers using enriched air nitrox, as breathing higher ppO2 levels can increase the risk of oxygen toxicity, especially at depths where greater partial pressures are present. Thus, the assertion that ppO2 increases with depth highlights the relationship between depth, pressure, and gas properties, which is crucial knowledge for safe diving practices.