What does a yellow disc indicate in the fire extinguishing system?

In a fire extinguishing system, a yellow disc serves as an indicator of a specific condition within the system. When the yellow disc is present, it indicates that one of the fire extinguisher containers has discharged its contents. This visual cue allows flight engineers and crew members to quickly assess the status of the fire suppression system, ensuring they can take appropriate action if needed, such as preparing for a potential fire event or replacing the discharged cylinder.

The other conditions listed do not align with the indication provided by the yellow disc. For instance, normal operation of containers would not trigger a yellow disc, and neither would overheating of containers nor low pressure warnings typically be signified by this visual indicator. Each of these cases represents different system statuses that require different monitoring and responses, emphasizing the usefulness of the yellow disc in the context of fire safety management.