Which statement about surface air consumption rate is true?

The surface air consumption rate (SAC) is defined as the volume of air consumed at the surface divided by the duration of the dive. It serves as an important metric for divers, allowing them to estimate their air supply needs at various depths and conditions.

The correct assertion indicates that the SAC is assumed to be constant under controlled conditions, such as at the surface. While individual factors like exertion level, dive profile, and physiological responses can affect air consumption during a dive, the SAC itself is typically measured and reported as a standard rate. This means that for consistent dive conditions, divers can use this rate for calculating their air needs effectively.

Other options may confuse the understanding of how SAC operates. For example, while it is true that SAC might appear to change with depth due to the effects of pressure on air density and breathing resistance, the rate itself as a measure does not vary in a straightforward manner with depth. Instead, divers often refer to their SAC as a baseline measurement that helps in planning dives based on their experience and dive profile. Hence, while conditions may impact actual usage, the base measurement of SAC is treated as constant for analysis and planning purposes.