Ventilation. The picture on the left above shows an iron hook driven into the wall to hold up an air duct. The rock has been cut away by hand to make space for the duct. On the right, a duct has been drawn in to show how the passage may have appeared while it was being mined. There is no wood on the floor here so the duct was probably removed once the through route for fresh air had been made. (Picture above courtesy of Peter Clewes in the Probationers' Series.)
(Left) This engraving from Agricola shows a large air blower of the type which might have been used in the Alderley Mines when working a "blind heading", a passage with no other means of ventilation. Once the mines were established, routes were developed to encourage air to flow naturally through the mines using ventilation shafts, forced ventilation with fire baskets and internal air circuits.
(Right) Reconstructed air door. This reconstructed air door in Wood Mine has been built in the place where evidence strongly suggests there was previously an air door to assist in the management of ventilation of the mine.