For a team diving into a cave that descends to 20 m, what is the equivalent ATA at that depth?

To determine the equivalent ATA (Atmospheres Absolute) at a depth of 20 meters in water, it’s helpful to understand the concept of pressure under water. At sea level, the atmospheric pressure is approximately 1 ATA.

As a diver descends, the pressure increases due to the weight of the water above them. The rule of thumb for calculating the pressure is that for every 10 meters of seawater, the pressure increases by approximately 1 ATA. Therefore:

• At a depth of 0 meters (at the surface), the pressure is 1 ATA (atmospheric pressure).

• At 10 meters depth, the pressure increases to 2 ATA (1 ATA for atmosphere + 1 ATA for water pressure).

• At 20 meters depth, the pressure further increases to 3 ATA (2 ATA at 10 meters + 1 ATA for the additional 10 meters of water pressure).

This means that at a depth of 20 meters, the total pressure experienced by the diver is 3 ATA. This is why the correct answer is 3 ATA, which accounts for both the atmospheric pressure and the water pressure at that depth.