What is the recommended air pressure for safe operation of air brakes?

Answer: C — Above 90 psi

The recommended air pressure for the safe operation of air brakes is above 90 psi. This standard is crucial because air brakes rely on compressed air to function effectively, and operating below this pressure can compromise the braking system's performance. When air pressure in the brake system drops below 90 psi, it may not provide adequate force to activate the brakes reliably, increasing the risk of brake failure during critical driving situations. Keeping the air pressure at or above this level ensures that the brake components, such as the brake chambers and valves, can operate properly. This pressure threshold is essential for maintaining safety on the road, as it ensures that the brakes will engage firmly and efficiently when needed, thereby helping to prevent accidents and ensure smoother stopping power for large vehicles like trucks and buses.