An auxiliary fan in a mine is a smaller ventilation fan used to provide local airflow in headings, stopes, crosscuts and other blind workings that are not directly served by the primary ventilation airways. While main mine fans move large volumes of air through shafts and main drifts, auxiliary fans and ducts extend that airflow into the development and production faces where miners and equipment are actually working.
Auxiliary fans are typically axial flow fans, chosen for their compact size, high volume at relatively low pressure, and ability to connect to flexible or steel ducts. They are installed close to intake airways or return airways depending on whether the auxiliary system is “forcing” or “exhaust.” In a forcing system, the auxiliary fan blows fresh air into the duct, which delivers it to the heading or stope. In an exhaust system, the fan pulls contaminated air through the duct from the working area to a return airway, drawing fresh air in from the intake side.
The main purpose of auxiliary fans is to deliver sufficient fresh air to the face to dilute gases, dust and diesel fumes, and to control temperature and humidity. Regulations often specify minimum airflow at faces and around diesel machines, and auxiliary ventilation is the practical means of meeting these requirements where the primary airflow alone is not enough. Properly designed auxiliary systems also help clear blasting fumes quickly so that re-entry times can be minimized without compromising safety.
Auxiliary fans in mines must be selected and installed with attention to performance and safety. Fan capacity and pressure must match the duct length, diameter and resistance so that the required airflow reaches the face. In gassy or coal mines, auxiliary fans and their motors may need explosion-proof or flameproof construction and non-sparking materials. Fans are usually fitted with guards and may have quick-disconnect couplings or suspension systems for easy relocation as headings advance.
Because auxiliary fans and ducts are moved frequently, there is a constant risk of damage and leakage. Tears in flexible duct, poorly sealed joints, crushed sections and sharp bends can all reduce airflow at the face. Regular inspection and maintenance are essential, and ventilation personnel must check that actual face air quantities match the design values. Good housekeeping—keeping ducts off the floor, away from sharp edges and protected from vehicle impact—helps maintain performance.
In modern mines, auxiliary fans may be integrated into ventilation on demand systems. Variable speed drives and remote controls allow airflow to be increased when the face is occupied or production is high, and reduced when the area is idle, saving energy while still respecting minimum safety requirements.
In summary, an auxiliary fan in a mine is a local ventilation fan used with ducts to bring fresh air to, or remove contaminated air from, working places beyond the reach of primary airways. It is a critical component of secondary ventilation and day-to-day mining safety.
