What should you instruct a panicked diver at the surface to do first?

The best approach when dealing with a panicked diver at the surface is to have them completely fill their buoyancy control device (BCD). Doing this helps to provide immediate buoyancy and stability, allowing the diver to float and rest comfortably. This action reduces the risk of sinking and can help calm the diver, as they will have a more secure and buoyant position in the water.

By filling the BCD fully, the diver can focus on regaining composure instead of worrying about staying afloat. This is a crucial first step in handling panic in diving situations, as it prioritizes the diver's safety and comfort. Once the diver is stable, other actions, such as signaling for help or discussing subsequent evacuation plans, can be appropriately handled. These considerations make the immediate filling of the BCD the most vital first action.