If a diver performs a 30-minute dive to 40 meters (131 feet), what is the general recommendation for surface interval before subsequent dives?

The recommendation for a surface interval before subsequent dives depends on several factors, including the depth and duration of the previous dive, as well as the type of dive profile involved. In this scenario, the diver has completed a relatively deep dive to 40 meters (131 feet) for 30 minutes. Such a dive could result in significant nitrogen absorption, necessitating an adequate surface interval to allow for safe off-gassing of nitrogen from the body.

A surface interval of 60 minutes allows the diver to sufficiently reduce residual nitrogen levels, thereby lowering the risk of decompression sickness on subsequent dives. The duration of the surface interval is designed to help ensure that the diver is well within safe limits before entering the water again, especially after a dive at such a significant depth.

While other options suggest shorter or longer surface intervals, the 60-minute recommendation strikes a balance by providing enough time for off-gassing while still allowing the diver to engage in further activities later if they choose to dive again. This recommendation is in line with safe diving practices and guidelines provided by dive training agencies, making it a well-supported choice for this scenario.