What is the surface interval a diver must observe after a first dive to 18 m/60 ft for 24 minutes before making a second dive?

The surface interval a diver must observe after completing a dive is crucial to minimizing the risk of decompression sickness, also known as "the bends." After conducting a dive, particularly one to 18 meters (60 feet) for a duration of 24 minutes, divers refer to dive tables or dive computer recommendations to determine the appropriate surface interval for a subsequent dive.

In this scenario, the dive to 18 meters for 24 minutes typically leads to a specific nitrogen absorption level in the body. The diver needs to allow enough time on the surface for the nitrogen to safely off-gas, reducing the risk of forming bubbles in the bloodstream during the next dive.

Based on the typical nitrogen loading associated with such a dive, a surface interval of 32 minutes is often recommended. This duration allows the body’s tissues to eliminate excess nitrogen effectively, making it safer for the diver to descend again.

Choosing shorter surface intervals can increase risk, as the body may not have completely off-gassed nitrogen, potentially leading to decompression sickness on subsequent dives. Thus, the decision rests on ensuring that adequate time is allowed between dives to maintain safety.