Why is surface interval time important between dives?

Surface interval time is critically important between dives primarily because it helps eliminate nitrogen from the body. After spending time at depths where the pressure is higher, divers absorb nitrogen from the breathing gas due to the increased partial pressures. As a diver ascends and experiences a decrease in pressure, this nitrogen needs to be off-gassed to prevent decompression sickness, commonly known as "the bends." The body naturally eliminates nitrogen, but this process is more efficient with adequate surface interval time.

During this time, the diver's body can safely reduce the levels of nitrogen within tissues before embarking on subsequent dives. Surface intervals also allow the body to stabilize and return to pre-dive conditions. Just as important, divers can use this interval for hydration and review of dive plans; however, the most critical factor concerning safety and physiological status is the elimination of nitrogen.

It’s essential for divers to be aware of the importance of these intervals to ensure safe diving practices and minimize the risk of decompression illness.