"Ventilation" or "pit ventilation" is understood to mean the planned ventilation of a mine with "fresh weather" (fresh air) from above ground.
The word "weather" is an umbrella term for gas mixtures occurring in the pit. If it is oxygen-rich, breathable air, one speaks of "fresh weather". If the gas mixture is no longer breathable due to excessive CO2 levels, it is called "dull weather". If the gas mixture contains gases that are toxic to humans, such as CO or nitrogen oxides, one speaks of "bad weather". Finally, “beating weather” are gas mixtures that contain explosive gases such as methane or carbon monoxide.
The task of ventilation is to supply the pit with the oxygen it needs to breathe and to dilute dull, bad or pounding weather to such an extent that it no longer poses a danger to people. Human air consumption fluctuates between 8 l/min at rest and 70 l/min during the heaviest work, depending on the amount of work done.
Ventilation can either be "natural" due to temperature differences between the pit and the surface of the day, or "artificial" using fans.
Figure 1: Natural ventilation, scheme, 2005, from Wulz "Bleiberger mining"
There is "natural ventilation" in the main line systems. The main air flow can be "incoming" or "outgoing" depending on whether it is colder or warmer on the surface than in the pit. In the pit, the temperature of the weather remains the same all year round, whether summer or winter. In the salt mines, the pit temperature is around 8 - 10°C.
in the In summer, the outer, warmer air is cooled by that in the mine and, due to the resulting greater density, sinks from the upper, higher tunnels down to the deeper ones, only to exit again in the deepest tunnel. In winter, on the other hand, the air penetrating the pit is heated and, because of the lower density, rises from the deepest tunnel to the highest tunnel. In autumn or spring it can happen that the outside temperature is the same as the inside temperature and so no natural weather draft can develop, one speaks of "standing weather".
In the pit, you can control the weather currents caused by the respective ventilation through built-in “weather doors”. Closing weather doors blocks the shortest path for the draft so that it can escape to other areas of the pit.
At the Ischler Salzberg, in winter, the cold air draws in over the Franz Josef Erbstollen at 503m above sea level, heats up, rises over the two shafts (central and Distler shaft) and over the open pits, to over the highest one that is still open tunnel, the Amalia tunnel located at 851 m above sea level. In summer, the weather takes the opposite path.
"Artificial ventilation" is used for tunneling or when blowing out factory rooms, since natural ventilation is not possible due to the lack of route connections.
In the case of artificial ventilation, a distinction is made between "blowing ventilation", in which fresh air is blown into the track, and "sucking ventilation", in which, conversely, the used air is sucked out of the track.
Windfocher and bellows:
With "blowing ventilation", the air flow was generated via "Focher" or "Windfocher". A focher was a wooden chest in which was a round cylinder with wooden wings, which, turned over by human hands, brought fresh air to the houses where they worked. Focher could also be large bellows operated by humans. The fresh air was brought on site from the pressure side of the focher through "air ducts" or "air separation lines" (tubes).
Figure 2: Bellows and Windfocher, M. Kefer, 1836, Archiv Salinen Austria
Figure 3: Sucking Windfocher, M. Kefer, 1836, Archiv Salinen Austria
Figure 4: Windfocher, Salinen manipulation description, 1807 – 1815, Archiv Salinen Austria
Figure 5: Bellows, description of manipulation of salt works, 1807 – 1815, Archiv Salinen Austria
Figure 6: Section with duct, rods and stretchers, M. Kefer, 1836, Archiv Salinen Austria
"Air machines" or "water drums" were used for tunneling from above ground. In 1836, Michael Kefer described such a water drum in his “Objects to be manipulated”.
Figure 7: Water drum, M. Kefer, 1836, IGM archive
The water drum (see Figure 3) consisted of a standing barrel (No. 4) open at the top with a discharge pipe (No. 6) on which stood a tub (No. 3) open at the bottom. At the top of the vat, a funnel (No. 2) tapered downwards and was 5 – 6 m high. Water flowed into the tub through the funnel. Through the narrowing funnel, the water flow sucked in air on the way down, atomized on the stone (No. 7) and reached the outflow pipe (No. 6). The air released during atomization collected in the vat (No. 3) and was blown away through a trachea (No. 5). The outflow pipe (No. 6) had to be attached at such a height that the stone (No. 7) always protruded above the water.
The efficiency of a water drum was relatively low, but the advantages were the simplicity and the low investment costs. Water drums were used successfully on the Ischler Salzberg, for example when driving the Franz and Leopold tunnels.
Figure 8: Water drum, around 1840, Archiv Salinen Austria
Today, two types of fans are used for artificial ventilation. Vertical sections, such as shafts, are ventilated with centrifugal or centrifugal fans, in which the fan blades move radially. "Luttenventilator" is used for horizontal stretches. With this type of fan, the fan blades move axially. A duct line is laid from the duct fan to the site. In the case of suction ventilation, this consists of galvanized sheet metal pipes and, in the case of blowing ventilation, mostly of flexible plastic hoses with a length of up to 8 m and a diameter of up to 1200 mm.
Figure 9: Duct fan with duct, Hall salt mine, around 1935, Nussbaumer archives
Figure 10: Tunneling with air line, Hallstatt salt mine, 2020, Kranabitl archive
Ventilation fans are used for the "special ventilation" of mine workings that cannot be included in the continuous ventilation because they only have one connection point. These mine workings include almost all roadway driving, tunnel driving, hewing and demolition. Special suction ventilation is used when a lot of dull or bad weather is to get into the outgoing weather stream without further ado.
All mine rooms serving the operation are to be ventilated in such a way that accumulations of pounding, bad or dull weather as well as excessive heat are avoided. Every workplace that is not sufficiently ventilated by natural weather exchange must be supplied with such large quantities of air that each man gets at least 2 m³/min. The amount of air in pits where diesel engines are in operation must be at least 6 m³/min per engine horsepower.
Regular weather checks are required by the mining authorities. The amount of weather and the prevailing temperatures as well as the direction of flow of the weather must be measured and noted in certain, regular periods. In addition, the oxygen content of the mine air must be determined during these investigations.
Figure 11: Weather station, 2015, IGM archive
The path of the mine ventilation is shown on weather cracks. These show the opposite direction of the mine weather in summer and winter as well as the weather measuring points and weather doors and facilities for artificial ventilation.
Figure 12: Bad Ischl salt mine weather forecast, 1979, Salinen Austria archive
Carl Schraml "The Upper Austrian Salt Works from 1750 to the time after the French Wars", Vienna 1934
Carl Schraml "The Upper Austrian Salt Works from 1818 to the end of the Salt Office in 1850", Vienna 1936
L. Janiss "Technical help book for the Austrian salt mining company", Vienna 1934
Alois Fellner "Mining Dictionary", Vienna, 1999
G. Köhler "Textbook of Mining Science", Leipzig, 1903
Stefan Wulz "The Development of the Bleiberg Mining", Bad Bleiberg, 2005