How do you identify if a fire extinguisher has been discharged and needs replacement?

A pressure gauge reading in the red zone is the definitive indicator that a fire extinguisher has been discharged and needs replacement. The pressure gauge on a fire extinguisher is designed to provide a clear visual representation of the internal pressure required for effective operation. If the needle is in the red zone, it signifies that the extinguisher is either empty or has fallen below the required pressure levels necessary for use. This condition indicates that the extinguisher is no longer functional and should be replaced or serviced.

Other indicators, while they may suggest some issues with the extinguisher, are not as reliable for confirming that it has been discharged. A burnt smell might indicate that the extinguisher has been used, but it is not a definitive measure of its functional status. Similarly, the external temperature of the extinguisher being cold does not inform you about its contents or pressure status. Lastly, having a full external appearance may give the impression that the extinguisher is fully operational, but it does not guarantee that it is pressurized adequately for use. The most reliable method remains checking the pressure gauge reading.