How is SEV (surface equivalent value) calculated?

The correct option relates to the calculation of the Surface Equivalent Value (SEV), which is a measure used in diving to estimate how the physiological effects of pressure experienced underwater equate to surface conditions. Specifically, SEV is calculated using the partial pressure of oxygen (ppO2) at a given depth and comparing it to normal atmospheric pressure (1 atmosphere or ATA).

In this context, the SEV reflects the relationship between the actual pressure diver experiences and the pressure at the surface. By using the partial pressure of oxygen, divers can determine how much effective oxygen is available for respiration at depth and understand the implications for safe diving practices and limits regarding exposure to elevated oxygen levels.

Understanding this formula is essential for divers to manage the risks of oxygen toxicity and to plan dives in a safe manner, ensuring that the physiological impact of the environment at depth is accounted for as if it were occurring at the surface.