What is the time of descent required for a controlled ascent after scuba diving?

After scuba diving, a diver should allow a recommended waiting time before ascending to altitude to avoid decompression sickness, often referred to as "the bends." This waiting time is necessary because while scuba diving, nitrogen is absorbed into the body tissues under pressure. If a diver ascends to altitude too soon after completing a dive, the reduction in atmospheric pressure can cause the nitrogen that was absorbed to come out of solution and form bubbles, leading to potentially serious health risks.

The general guideline for a controlled ascent after scuba diving suggests waiting at least 24 hours. This duration allows sufficient time for nitrogen levels within the body to decrease to a safe level, minimizing the risk of decompression sickness. Therefore, the correct recommendation is to wait 24 hours after the last dive before flying or ascending to a higher altitude. This is a standard procedure agreed upon in many diving and aviation safety guidelines.