What action should be taken if a diver signals that they need to share air?

When a diver signals that they need to share air, the primary and immediate action is to provide an alternate air source. This response is crucial because it allows the diver in need to maintain a safe and adequate air supply while ensuring their safety and that of their buddy. The alternate air source could be a secondary regulator or octopus, which is typically part of the buddy's dive gear for such emergency situations.

Sharing air is a fundamental skill that divers must practice, as it enables them to manage situations of low or depleted air supply effectively. By offering an alternate air source, both divers can continue their dive safely and plan to ascend together while maintaining a controlled buoyancy.

Changing to a different tank would not address the immediate need for air and could complicate the situation further. Preparing for a buddy rescue may be necessary if the situation escalates, but it wouldn't be the first response if an alternate air source is readily available. Rapidly ascending to the surface is dangerous and could lead to serious consequences, such as decompression sickness, so this option is not advisable in response to an air-sharing request.