What should a diver do immediately upon realizing they are out of air?

When a diver realizes they are out of air, signaling their buddy to share air is the most appropriate and safe response. This mutual assistance is vital because both divers can utilize the air that the buddy has remaining, allowing them to ascend safely and avoid the risks associated with a rapid ascent or becoming separated underwater.

Additionally, the buddy system is a cornerstone of diving safety; divers are trained to be aware of each other’s air supply and have practiced emergency protocols, which include sharing air when necessary. This action helps maintain a calm environment and allows both divers to ascend together, prioritizing safety and communication.

The other choices present significant risks. Swimming to the surface quickly can lead to decompression sickness and other serious conditions. Performing a safety stop is not feasible when a diver is out of air and requires immediate assistance. Panic not only hinders rational thought but increases the risk of making poor decisions underwater that can exacerbate the situation.