Final answer:
Applying handbrakes on a train that has stopped due to an accident or derailment is crucial for maintaining safety and preventing the train from moving unexpectedly.
Step-by-step explanation:
The question pertains to the protocol surrounding train safety procedures in the event of an accident or derailment. In such scenarios, it is imperative for handbrakes to be applied to ensure that the train does not move unintentionally, creating a situation that could exacerbate the incident or put rescuers and passengers at risk. This practice is part of a range of safety measures instated after the advent of railroad technologies, such as the air brake system, which was invented by George Westinghouse in 1869. The air brake innovation marked a significant advancement in train safety as it allowed for the centralized control of train brakes by the engineer, replacing the need for workers to manually apply brakes on moving cars, thus reducing the danger previously inherent in the process.