If more than 4 surD periods are required, what is the next depth used?

In the context of diving and undersea rescue operations, the concept of "surD periods" refers to the duration that a diver must spend at a specific depth to allow for proper acclimatization and minimize the risk of decompression sickness. When a diver exceeds the standard surD limits, a deeper stop is often necessary during ascent to ensure safety.

When more than four surD periods are needed, the next standard depth typically employed in diving procedures is 30 feet of seawater (fsw). This depth serves as a common threshold within diving protocols that allows for effective decompression while providing a balance between safety and logistical efficiency. The choice of 30 fsw is grounded in practices that prioritize diver health and adhere to established decompression tables, which detail the requisite time spent at increasing depths based on the duration and depth of the dive.

Other depths such as 20 fsw, 40 fsw, and 50 fsw may not align as closely with established safety protocols for situations requiring extended surD periods, making 30 fsw the optimal depth to manage and mitigate risks during ascent and ensure voluntary compliance with safety standards.