When should all employees be evacuated from the mine after the fan stops?

All employees should be evacuated from the mine if ventilation is not restored within 15 minutes after the fan stops because maintaining adequate ventilation is critical for ensuring a safe working environment in a mine. Proper ventilation is essential for providing fresh air and dissipating harmful gases, such as carbon monoxide or methane, which can accumulate quickly in a confined space. If the fan stops and ventilation is compromised, the air quality can deteriorate rapidly.

The 15-minute time frame is significant because it provides a clear, actionable guideline for foremen and workers to follow in emergency situations. This timeframe allows for a brief assessment and, if conditions remain unsafe, ensures prompt action to ensure the safety of all personnel in the mine.

Other options, while they indicate situations that also require caution, do not provide the same immediate and specific directive related to ventilation. For example, while losing lighting could be a concern, it does not directly correlate with hazardous air conditions. Similarly, rising temperatures and smoke detection are serious issues but might not require an evacuation as rapidly as the failure of ventilation would necessitate. Hence, the priority placed on ventilation underscores its fundamental role in mine safety protocols.