What role do visual notification appliances play in a fire alarm system?

Visual notification appliances are crucial components of a fire alarm system, serving the primary role of alerting occupants in the event of a fire alarm activation. These devices, which may include flashing lights or strobe signals, are designed to attract attention and ensure that individuals—especially those who may be hearing impaired—are made aware of an emergency situation. The effectiveness of visual notifications is particularly important in environments where audible alarms might be difficult to hear or not sufficient to capture the attention of all building occupants.

The other options relate to functions that are not directly associated with visual notification appliances. For instance, system diagnostics, power supply, and remote monitoring are responsibilities that fall to different parts of the fire alarm system. Thus, option B accurately represents the essential function of visual notification appliances in ensuring the safety and awareness of building occupants during a fire emergency.