What must be established when employees are unable to obtain authority and need to foul or occupy a main track?

When employees find themselves in a situation where they need to foul or occupy a main track and have been unable to obtain authority, it is essential to establish flag protection in accordance with the specified rule. Flag protection provides a critical safety measure to safeguard both the workers and any approaching trains by ensuring that there is clear communication and visual signals in place for the protection of personnel on the track. This proactive step mitigates the risks associated with working close to active tracks.

The other choices touch on procedural elements that could be relevant in different contexts, but they do not directly address the immediate safety requirement when authority cannot be obtained. While obtaining authority from the dispatcher is generally necessary for track occupancy, the focus here is on the actions taken when that authority cannot be secured. Similarly, a safety briefing and a written request, although important elements of overall safety culture and communication, do not replace the immediate need for flag protection in this urgent scenario.