For treatment tables involving sustained nitrogen exposure, what is the general recommended surface interval?

The recommendation for a surface interval of 18 hours following treatment tables that involve sustained nitrogen exposure is based on the need to allow sufficient time for the elimination of nitrogen from the body and to reduce the risk of decompression sickness (DCS) during subsequent dives. After a dive that involves significant nitrogen absorption, the body requires adequate time to off-gas the nitrogen and return to a normal physiological state before engaging in further diving activities.

This 18-hour surface interval is a guideline intended to ensure a safe transition between dives by allowing for proper recovery and minimizing the likelihood of bubbles forming in the body's tissues as pressure changes occur. It is particularly crucial after saturation dives or repetitive dives that result in accumulated nitrogen in the body.

In contrast, shorter intervals might not allow for complete off-gassing, leading to increased risks of DCS. Thus, adhering to the recommended 18-hour surface interval plays a vital role in promoting diver safety and health.