How can you tell if the Protective Breathing Equipment (PBE) runs out of oxygen?

The indication that the Protective Breathing Equipment (PBE) has run out of oxygen is that it will collapse and deflate. This physical change occurs because the container that holds the oxygen has been depleted, resulting in a lack of support for the structure of the device. When the oxygen supply is exhausted, the air pressure inside the PBE decreases, causing it to lose its shape, which is a clear sign to the user that the equipment is no longer functioning effectively and they should seek a new or alternative source of breathable air.

While other options might suggest different forms of malfunction or degradation, they do not accurately reflect the specific failure mode of the PBE. For instance, PBE does not emit an alarm, change color, or improve breathability as a sign of depletion. In fact, the structure and protective benefits of the PBE are compromised as the oxygen supply diminishes, which is crucial to ensuring the safety of users in environments where breathable air is not available.