What occurs to the indicator lights in a PBE as oxygen supply diminishes?

In a Portable Breathing Equipment (PBE), the indicator lights serve as visual cues to indicate the status of the oxygen supply. As the oxygen supply diminishes, the correct response is for the red and green lights to alternate flashing. This alternating pattern is designed to alert the user that the oxygen levels are insufficient and that the equipment may soon become non-functional. It is essential for the effective use of the PBE that users are immediately aware of this critical change in status, allowing them to take necessary actions to ensure their safety.

The other options do not accurately represent the indicators' function during a decrease in oxygen supply. A solid green light would typically signify that the system is functioning properly, while a flashing red light would indicate an urgent issue, not specifically tied to diminishing oxygen. If the lights were to go out, it could signal a complete failure of the equipment but not necessarily provide a warning during an oxygen shortage.