Ventilation is the process of bringing fresh air to the underground mine workings while removing stale and/or contaminated air from the mine.
In many industrial mineral mines, the total volume of the underground mine is huge. Often in potash or salt mines, they are larger than a typical city. The distances from the ventilation fan to the current mine workings can be up to 10 kms or greater.
Booster fans are often deployed to effectively move large quantities of air and often more than the primary fans can deliver. This condition will cause air recirculation which can potentially increase the level of harmful gas concentrations.
In addition, ever increasing energy costs and the need to conserve energy have prompted many mines especially industrial mineral producers, to examine their operations and identify potential saving methods. Recirculating a fraction of ventilating air may enable these mines to reduce winter heating costs. Studies indicate that the mine pollutant concentrations in many of these mines are low and stable. Recirculation experiments returning between 20-40% of the exhaust air into the fresh air airway did not cause significant increases in mixed intake pollutant levels.