At a depth of 99 fsw / 30m, how much of the surface volume will a flexible container be?

At a depth of 99 feet of seawater (fsw) or 30 meters, the pressure increases significantly due to the weight of the water above. For every 10 meters (or approximately 33 feet) of depth, the pressure increases by about one atmosphere. Therefore, at 30 meters, the pressure is roughly four times atmospheric pressure, or about 4 ATA (atmospheres absolute).

In the case of a flexible container submerged at this depth, the increased pressure compresses any gas contained within the container, which affects its volume. The principle that governs the behavior of gases under pressure is Boyle’s Law, which states that the volume of a gas is inversely proportional to the pressure exerted on it, provided the temperature remains constant.

At greater depths, because the pressure increases, the volume of the gas will decrease. Specifically, a flexible container that begins with a defined volume at the surface will have its volume reduced at depth. In practical terms, many would find that at a depth of 30 meters, the volume of gas in a flexible container is reduced to about one-fourth of its original volume at the surface. This is due to the significant compression under high pressure, which leads to the conclusion that a