Final answer:
Hand brakes are applied in conjunction with air brakes to enhance safety and prevent unintended vehicle movement. This redundancy ensures compliance with safety regulations and adds an additional layer of security should the air brake system fail or lose pressure.
Step-by-step explanation:
The primary reason for applying hand brakes when using air brakes in vehicles, particularly in trains or heavy trucks, is to ensure additional safety and to prevent the vehicle from rolling when stationary. While air brakes are incredibly effective during travel, when a vehicle is not in motion, there could still be a risk of it moving due to a failure in the air brake system or a loss of air pressure. Hand brakes act as a mechanical backup to hold the vehicle stationary, making it a critical safety feature.
Air brakes utilize compressed air to apply pressure to the brake pad, thereby stopping the vehicle. The invention of the air brake by George Westinghouse increased safety, as it allowed trains to be stopped by the engineer from the locomotive rather than manually by workers jumping between cars. And while air brakes are efficient, relying solely on them while stationary could be risky without the added security of mechanical hand brakes.
Using hand brakes also ensures compliance with transportation safety regulations which require stationary vehicles to be secured against unintended movement. This layered braking approach provides redundancy, reducing the likelihood of potential accidents due to system failures or unexpected loss of brake pressure.