What does two green lights on the HUD indicate?

Two green lights on the Heads-Up Display (HUD) of a Self-Contained Breathing Apparatus (SCBA) indicate that the air cylinder is full. This visual indicator serves as a quick reference for the user to assess the status of their air supply. In a high-stress environment, such as when responding to an emergency situation, it is crucial for a firefighter or emergency responder to have reliable and immediate feedback on their air supply.

The two green lights signal that the air tank is adequately filled, typically at or near its maximum capacity, allowing the user to focus on their tasks without the concern of running low on air. This feature enhances safety and operational effectiveness, ensuring that the user can perform their duties without the immediate risk of running out of breathable air.