PADI Divemaster Certification Practice Exam

When breathing a gas mixture at depth compared to the surface, what is expected?

1. The effect of the gas is equal

2. The gas has lesser effect

3. The effect of the gas is greater at the surface

4. The gas has no effect

The correct answer is: The effect of the gas is greater at the surface

When breathing a gas mixture at depth, the pressure surrounding the diver increases due to the weight of the water above. This increased pressure causes the gases in the mixture (typically nitrogen and oxygen) to behave differently than they do at the surface. Based on Dalton's Law, at any given depth, the partial pressure of each gas increases proportionally to the surrounding pressure. As the diver descends, the partial pressure of oxygen increases, which enhances its effects on the body. This means that the body can become more saturated with the gases, leading to potential effects such as narcosis from nitrogen or oxygen toxicity at greater depths if the concentrations are high enough. Therefore, the physiological effects of the gas mixture are indeed greater at depth because of the increased pressure which amplifies the effects of each gas component within the mixture. This understanding is essential for divers to manage their exposure to the effects of breathing gases while diving.