What should a diver do if they notice a rapid ascent?

When a diver notices a rapid ascent, the appropriate action is to stop ascending immediately and hold depth. This response is essential because a rapid ascent can lead to decompression sickness, also known as "the bends," which occurs when nitrogen bubbles form in the body due to rapid reduction in pressure. By halting the ascent, the diver can stabilize their depth, allowing their body to off-gas the excess nitrogen more safely and reducing the risk of injury.

Holding depth provides the diver the opportunity to monitor their condition and assess any symptoms that might indicate a need for further action, such as ascending slowly or performing other safety measures. It also allows for a controlled ascent, which is usually accompanied by the use of proper decompression procedures to enhance safety.

In contrast, continuing to ascend quickly would only increase the risk of complications associated with rapid pressure changes. Descending back to the previous depth might offer another chance to off-gas but could create confusion in the diver's buoyancy control and does not address the immediate danger of the rapid ascent. Increasing the ascent rate completely disregards safe diving practices and heightens the risk of decompression sickness. Thus, stopping and holding depth serves as the safest and most prudent course of action in such a situation.