How do you preflight the fixed halon fire extinguisher in the lavatory of the CRJ 700/900?

To effectively preflight the fixed halon fire extinguisher in the lavatory of the CRJ 700/900, the key action is to check that the thermometer sticker is not black. The thermometer sticker is designed to indicate if the extinguisher has been exposed to excessive heat, which can compromise its effectiveness. If the sticker has turned black, it signifies that the extinguisher may have been subject to conditions that could make it unserviceable, hence, it is critical to ensure the sticker remains a normal color, indicating that the extinguisher is likely functioning properly.

This action helps maintain safety standards by ensuring that the equipment will function correctly in the event of a fire emergency. The other options do not directly assess the integrity and readiness of the halon fire extinguisher for use: ensuring the gauge is in red would imply a pressure issue, and testing the pressure is not applicable for a fixed system, while observing a color change in the label does not provide relevant information about the extinguisher's operational readiness.