Development Face Ventilation

To maintain a ventilation circuit it is necessary to have an intake and a return airway to the innermost point to be ventilated. As roadways are mined, the last section has only a single roadway so another arrangement has to be made.
At one time this was done by erecting a temporary "wall" along one side of the roadway by hanging a flexible, airtight material known as brattice on timber props and extending the brattice across the last completed cut-through so air was forced to flow up to the face.
This system works quite well and is still in use in some mines where ventilation is not too arduous (e.g. bord and pillar mining). The brattice wall tends to be leaky and it is difficult to get good flow at the face for distances over 80m. The brattice also restricts the working width or the width of the return path (or both).
The adoption of longer pillar centres (>100m) in longwall mines coupled with higher in situ gas regimes experienced in deeper mines has necessitated that mines utilize a more effective ventilation system comprising electrically powered auxiliary fans attached to ventilation ducting to course air through the working areas. Auxiliary fans add another complication and another piece of machinery, but give more positive flow and more flexibility in sequencing.
A common misconception among operators is that face ventilation can be improved by increasing the airflow to a panel. This is true for brattice ventilation, but for fan ventilation the face flow depends entirely on what the auxiliary fan will pull. Extra air to the panel will not improve face ventilation quantity.
It is essential to have more airflow in the panel than the auxiliary fan is capable of pulling otherwise recirculation will occur and if there is any gas make the concentration of gas in the air will gradually increase. It is usual to maintain more flow than the open circuit capacity of the fan, typically 30% more than the open circuit capacity added as a safety factor.
Because an auxiliary fan has a pressure rise through it, it is possible for the ventilation pressure at the start of the return to be slightly higher than the intake and recirculation through a stopping or door is possible. This can be avoided by erecting a baffle behind the auxiliary fan outlet to cause a pressure drop at that point.