Under what condition should a train not move in relation to a blue flag?

A train should not move when men are working on or about the train equipment due to safety protocols that are in place to protect the workers. The blue flag serves as a visible signal, indicating that the equipment or train is being worked on, and no movement should occur to ensure the safety of those workers. This regulation safely isolates work areas, preventing accidents that could result from a train departing while personnel are present.

The other conditions listed may not directly impose the same level of immediate danger as the presence of workers. While flashing lights can indicate caution or signaling requirements, they do not inherently indicate restricted movement unless specified by operational protocols. A delayed train does not involve any immediate safety concern that would prevent movement, as it may simply require waiting time for operational reasons. A horn signal might indicate that the train is about to move, but does not provide a safety warning like the condition of workers being physically present. Thus, the presence of workers necessitates that the train remains stationary for their safety.