Many accidents and mining disasters in the Middle Ages were due to inadequate ventilation. That’s why new devices were developed again and again to improve the air underground. One of them was the bellows: it sucked used air out of the mine chambers while at the same time blowing fresh air into the mine. Depending on its size, it was powered by hand, by horse power, or by water wheels.

As early as around 400 years ago, alum shale was mined intensively in the area of today’s Feengrotten. The search for valuable ores probably led to the accidental discovery of a sought-after raw material – black alum shale. For the arduous mining deep inside the mountain, light and fresh air were indispensable.

Fresh air was essential for the miners: they needed it to breathe and so their pit lamps could burn. Used, oxygen-poor air was called “dead air”. If it contained only little oxygen and a lot of carbon dioxide, it was referred to as “suffocating air”, which could become life-threatening. In addition, there were poisonous or explosive mine gases that had to be removed from the mine as quickly as possible.

Two shafts ensured that fresh air could reach the mine from the surface. Underground, they were connected to each other. In addition, vertical air ducts at the entrance to the adit distributed the fresh air into the mine chambers. Just like in a building above ground, natural air currents also arise in a mine due to differences in temperature and air pressure. You can clearly feel the draft here in the mine.

To check whether there was enough fresh air, miners often took canaries or small animals such as mice underground. If an animal became unusually quiet or motionless, that was a warning sign: the air had become dangerous and had to be replaced as quickly as possible with fresh ventilation.