John Spedding invented the "air coursing"
procedure around 1760. Fresh air travelled along the mine roadways and
faces by means of doors and stoppings before leaving the mine.
Airdoors are set to avoid air passing directly from the downcast to
the upcast shaft. Normally there were two or even three doors as the
opening of a single door would short-circuit the workings and the
pressure on the door would be such that it would be almost impossible to
open.
Stoppings are built from masonry and debris to block a space
originally occupied by coal.