What should be checked immediately after applying the brake handle in FULL SERVICE position to ensure safety?

After applying the brake handle in the FULL SERVICE position, it is essential to check the air compressor switches to ensure safety. This is crucial because the air compressor is responsible for maintaining the necessary air pressure in the brake system. A proper air supply is vital for the braking system to function effectively; if there are issues with the air compressor, it may result in insufficient braking power, risk of brake failure, or delayed response times when stopping the train.

By confirming the state of the air compressor switches, the engineer can ensure that the compressor is operational and able to replenish air pressure as needed. This proactive step helps maintain safety not just for the current operation but also for future brake applications.

While awareness of crew presence, emergency protocols, and fuel levels is important for overall operational safety, these factors are not as immediate or critical to the braking system’s performance immediately after applying the brakes. The air compressor's functionality directly impacts the braking system, making it the priority check in this situation.