What is a critical reason to monitor atmospheric pressure while diving?

Monitoring atmospheric pressure while diving is essential primarily because of the effect of pressure on breathing gas. As a diver descends, the surrounding water pressure increases, which in turn compresses the breathing gas in the tank and affects the way gases behave. Under increased pressure, the volume of gas decreases, and the diver must consider the partial pressure of each gas in the mixture they are breathing, particularly nitrogen and oxygen.

This understanding is crucial for avoiding problems such as nitrogen narcosis, oxygen toxicity, and decompression sickness. For instance, the relationship between pressure and gas volume is described by Boyle's Law, indicating that as a diver descends and pressure increases, the volume of the gas decreases, leading to changes in buoyancy and gas absorption into the body tissues. Thus, monitoring atmospheric pressure allows divers to manage their ascent and descent rates safely, ensuring that they remain within safe operational limits for their breathing gas. Recognizing these effects ensures divers can plan their dives more effectively, manage their air supply, and prevent dangerous situations related to pressure changes.