In what scenario would a train operator use two blasts of the whistle?

The use of two blasts of the whistle is primarily intended as a warning signal, especially in scenarios where safety is a concern. When a train operator gives two blasts of the whistle, it serves to alert individuals, such as shop employees or workers near the tracks, about the train's impending approach. This is vital for ensuring that people working in close proximity to the railways can take necessary precautions to avoid any potential accidents.

In contrast, using the whistle to greet passengers or signal departures does not typically involve specific blast patterns, as these situations usually utilize different or single blast signals. Announcing arrival at a station often involves a formalized communication method and does not rely solely on whistle signals. Therefore, the scenario that specifically aligns with the established protocols for train operations is the warning to shop employees, making it the correct response.