Under what condition should the power to the auxiliary fan be switched off?

The condition that necessitates switching off the power to the auxiliary fan is when methane levels exceed one percent. This is critical for maintaining safety in underground mining operations. Methane is a highly flammable gas and can lead to explosive conditions when present in sufficient quantities. By turning off the fan when methane concentrations rise, you mitigate the risk of igniting an explosive atmosphere which could jeopardize the lives of workers and the integrity of the mine.

Ensuring that ventilation systems do not exacerbate the concentration of harmful gases is integral to mining safety protocols. In this scenario, the fan may inadvertently circulate methane-laden air, worsening the situation. Therefore, the immediate action of switching off the fan is a vital safety response.

While other conditions, such as malfunctioning fans or insufficient airflow, are also important to address, they do not pose an immediate and critical safety risk to the same extent that elevated methane levels do. Inadequate airflow may require a fan to be adjusted or repaired rather than shut off entirely, and the completion of a work shift would also not necessitate immediate action regarding the fan unless there were other safety concerns present. Hence, prioritizing the response to methane levels is essential in ensuring a safe working environment.