What is the significance of the key marked 'FIRE SERVICE' in Phase One of Elevator Recall?

The key marked 'FIRE SERVICE' is significant because it cancels all registered elevator calls. This function is critical during fire emergencies as it allows firefighters to take control of the elevator system. When fire personnel engage the elevator in fire service mode, it prevents the elevator from stopping at floors where alarms may be triggered, ensuring that firefighters can reach the fire floor efficiently while minimizing the risk of the elevator stopping at potentially dangerous or crowded levels.

By canceling all registered calls, the key ensures that the elevator operates only in a manner dictated by the fire service, allowing for safer access to the scene of the emergency without interference from other elevator functions or passenger calls that might still be in the system.