What unit is used to express ambient pressure in the diving data?

• A. psi
• B. atm
• C. ATA
• D. bar

Answer: (C)

Ambient pressure in diving data is expressed as atmospheres absolute (ATA). This provides a single, intuitive way to represent the total pressure acting on the diver, including the atmospheric pressure at the surface plus the pressure from the water above. Using ATA makes gas partial pressures and decompression calculations straightforward because it’s a direct multiple of surface atmospheric pressure. For example, at 20 meters of seawater, the ambient pressure is about 3 ATA (1 ATA at the surface plus ~2 more ATA from depth). While other units like psi, bar, or atm exist, diving data standardize on ATA to keep depth-related pressure comparisons consistent across dives and equipment.