An emergency brake must be able to activate due to...

An emergency brake is designed to engage automatically in the event of a loss of air pressure. This is a critical safety feature for air brake systems. When air pressure drops below a certain threshold, the emergency brake system operates to bring the vehicle to a stop, preventing potential accidents caused by brake failure.

This automatic engagement is essential, as it ensures that the vehicle can be safely stopped even if the primary braking system fails due to an air pressure drop. It provides a fail-safe mechanism that helps maintain control and safety on the road, which is paramount when operating large commercial vehicles that rely heavily on air brakes for effective stopping power.

The other factors listed, such as the driver’s intervention, high brake temperatures, and electrical failure, do not trigger the emergency braking system directly in the context of air brakes. Instead, the focus of the emergency brake's operation lies specifically in the maintenance of necessary air pressure levels to ensure safe vehicle operation.