PADI Divemaster Certification Practice Exam

How does breathing gas at depth affect its toxicity compared to breathing the same gas at the surface?

1. It has no effect

2. It increases toxicity

3. It decreases toxicity

4. It makes toxicity unpredictable

The correct answer is: It increases toxicity

Breathing gas at depth can significantly affect its toxicity due to the increased pressure underwater. As a diver descends, the partial pressure of the breathing gas increases, which can raise the concentration of specific gas components—most notably, oxygen and nitrogen—within the body. When the partial pressure of oxygen increases, it can lead to a condition known as oxygen toxicity. Elevated levels of oxygen can cause central nervous system (CNS) toxicity, which can result in symptoms such as visual disturbances, tinnitus, nausea, twitching, and potentially seizures, especially when exposed to pressures exceeding a certain threshold, commonly around 1.4 ATA (atmosphere absolute) or higher. Similarly, an increased partial pressure of nitrogen at depth can contribute to nitrogen narcosis, a state that impairs cognitive functioning and can be likened to being intoxicated. The effects of nitrogen narcosis vary among divers and can start to be noticeable at depths as shallow as 30 meters (100 feet), emphasizing how depth not only influences the physiological effects of the gas but also contributes to potential hazards. Therefore, it is essential to understand that as a diver descends, the toxicity of the breathing gas increases due to the higher partial pressures of its components, leading