Combat Dive Closed Circuit Diving Fundamentals Practice Exam

Time at a given depth is limited by a planning threshold that prevents decompression obligations. As you go deeper, more inert gas dissolves into your tissues, so the amount of time you can stay under without needing decompression decreases. The depth range of 21–40 fsw is the band where the standard TWE limit is 15 minutes, meaning you can perform your underwater work there for up to 15 minutes before decompression considerations come into play. At shallower depths, you’d typically have a longer allowable bottom time, while deeper ranges shorten the limit, so they wouldn’t be 15 minutes. This is why that particular depth range is the correct choice for a 15-minute TWE limit.