In diving terminology, what does fsw stand for?

• A. Feet of Submerged Water
• B. Feet of Seawater
• C. Feet of Surface Water
• D. Flowing Seawater Width

Answer: (B)

fsw stands for feet of seawater. It’s a depth unit used by divers to express how deep you are based on the pressure produced by seawater. Because seawater is denser than freshwater, depth is commonly spoken of in terms of the equivalent water column that creates the same pressure rise—about 33 feet of seawater corresponds to one additional atmosphere of pressure. This helps with gas planning and decompression calculations, since pressure and gas behavior depend on how deep you are. Other phrases like submerged water, surface water, or flowing seawater width aren’t standard depth terms in diving, so they don’t fit. The widely accepted term is feet of seawater.