For a maximum depth of 25 fsw, what is the allowed oxygen exposure time according to Single-Depth Limits?

The allowed oxygen exposure time for a maximum depth of 25 feet of seawater (fsw) is based on the physiological effects of oxygen at increased pressures and the guidelines provided in diver safety manuals. At 25 fsw, the pressure experienced is greater than that at the surface, which increases the partial pressure of oxygen.

When considering oxygen toxicity, particularly around levels of 1.6 ATA (atmospheres absolute) or higher, exposure times need to be carefully managed to prevent potential toxic effects. The Navy Dive Manual outlines that at 25 fsw, the exposure limit can be much longer than at deeper depths because the partial pressure of oxygen is not as elevated.

In this case, the correct answer reflects the guidelines for oxygen exposure times at this depth. The maximum allowable exposure time of 240 minutes is designed to provide a safe buffer for divers, allowing them to complete longer dives without significant risk of oxygen toxicity, as long as they adhere to the guidelines provided for planning dives. This extended time helps account for variables such as dive profile, activity level, and individual physiological responses.

The other options reflect shorter exposure times that are not aligned with the recommended standards for that specific depth, thus making them less suitable in this context. Understanding