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.