Which step comes first when using the fixed breathing air system on an aerial device?

Answer: B — The responder dons a facepiece with a supply hose

The first step when using the fixed breathing air system on an aerial device is for the responder to don a facepiece with a supply hose. This is crucial because it establishes a secure connection between the user and the breathing air system. By putting on the facepiece first, the responder ensures their airway is protected and ready for use, which is essential in environments where air quality may be compromised or where toxic fumes are present. Prior to engaging with the fixed air system, the responder must ensure their personal safety. After donning the facepiece, they can then proceed to connect to the air supply through the suitable fittings, ensuring they have a secure and uncontaminated source of air. This sequence emphasizes the importance of personal protective equipment in hazardous environments and prioritizes the responder's safety before interacting with the apparatus.