Which of the following is NOT a trigger for an Emergency brake application?

The correct answer identifies the Passenger Door Mechanism as something that does not trigger an emergency brake application. In the context of train operations, emergency brakes are typically invoked by safety mechanisms designed to respond to critical situations.

An overspeed relay is a system that detects when a train exceeds its safe speed and activates the emergency brakes to prevent accidents. The deadman's device is a safety feature that requires the operator to continuously control the train; if they become incapacitated, it triggers the emergency brakes. The emergency stop button allows staff or passengers to manually activate the brakes during an emergency.

In contrast, the passenger door mechanism primarily deals with the opening and closing of doors and is not a safety feature aimed at controlling train motion. While it is essential for operations and passenger safety, it does not contribute to implementing emergency brake protocols. Hence, it is correct to identify it as not being a trigger for activating the emergency braking system.