A Class I air brake test must be conducted if a train has been off air for more than what duration?

A Class I air brake test is required if a train has been off air for more than 24 hours because this duration represents a threshold for ensuring safety and functionality. After being off air for this period, the components of the air brake system may be affected by environmental factors or may have experienced shifts that could compromise their performance. Conducting a Class I air brake test after 24 hours ensures that the brakes are working properly and that the train can be operated safely. This procedure adheres to safety regulations and helps to prevent potential issues during operation, thus prioritizing the safety of the crew, passengers, and cargo.