What is gauge pressure in the context of SCUBA diving?

Gauge pressure in the context of SCUBA diving refers to the pressure being measured above ambient pressure. This means it is the measurement of pressure that indicates how much greater the pressure is compared to the surrounding atmospheric pressure. In diving, gauge pressure is important because it helps divers understand how much additional pressure they are experiencing due to water depth.

As divers descend, the water exerts pressure on them, and this pressure is measured above the ambient atmospheric pressure present at the water's surface. For example, if the ambient pressure at sea level is approximately 1 atmosphere (or 14.7 psi), and a diver is at a depth where the pressure gauge reads 3 atmospheres, the gauge pressure would only reflect the addition of pressure due to the water, which would be about 2 atmospheres in that case (3 atm total pressure - 1 atm atmospheric pressure).

Understanding gauge pressure is crucial for safety, as it allows divers to manage their breathing gas supply and prevent issues like decompression sickness by recognizing how their body is affected by the deeper water pressures.