Which of the following is vital for maintaining safety underwater?

Regularly checking air levels is vital for maintaining safety underwater because it directly impacts a diver's ability to manage their ascent and surface safely. A diver must continuously monitor their air supply to ensure they have enough for the planned duration of the dive, including a safe ascent and any potential delays. Failing to keep track of air levels can lead to dangerous situations such as running out of air, which increases the risk of panic and emergencies while underwater.

Being aware of air supply allows divers to plan their dive, ensuring they can safely execute their dive profile and return to the surface with adequate air remaining. This proactive approach enhances overall safety and helps avoid potentially life-threatening situations.

In contrast, only looking ahead while diving may prevent a diver from being aware of their surroundings and important cues like the air gauge, using a single dive light limits visibility and can create hazards in the absence of adequate light, and diving in complete silence does not facilitate communication with dive buddies, which is essential for safety.