Garn Pit, Blaenavon. June 21st 1890. Showing furnace ventilation stack.
The fan house at Big Pit is agruably the most important building on site. The giant fan housed here provides fresh air for ventilation, pulling out 'foul' air from underground: gases, dust and fumes.
Before mechanical fans were used underground furances or fires would often do the job of ventiating a mine - warming the stale air which travelled up the shafts. But, this brought the obvious danger of explosion if any gas was present underground.