What does the term "fail-safe" mean in reference to spring brakes?

Answer: B — They automatically engage when the air pressure is lost

The term "fail-safe" in reference to spring brakes indicates that these brakes are designed to automatically engage when the air pressure is lost. This is a crucial safety feature in vehicles equipped with air brake systems, especially large commercial vehicles. The purpose of this design is to ensure that if there is a failure in the air brake system, such as a loss of air pressure due to a leak, the spring brakes will activate to bring the vehicle to a stop. This mechanism helps prevent accidents that could occur if the driver loses braking ability due to an air pressure loss, thereby enhancing overall safety on the road. The automatic engagement of spring brakes serves as a reliable backup system, ensuring that the vehicle can still be controlled even in adverse conditions, reinforcing the importance of safety in heavy vehicle operation.