As gassy , even fire-damp , formerly detonirende [ sic ] weather , wild fire or fiery plume is called in the underground mining a special gas mixture of methane and air , which under normal pit conditions by ignition source can be made to ignite. The term firedamp comes from the fact that a firedamp explosion is always oscillating, i.e. initially with a pressure surge and then with a kickback.
Occurrence and formation of firedamp
Fire weather is caused by the concentration of methane that flows into the mine workings from the mountains . Methane occurs predominantly in the coal seams and the bedrock of coal mines, but also in other mountain formations, e.g. B. in Zechstein from Kaligruben. There it is contained under a certain excess pressure. The gas can now enter the mine workings in three different ways. Through regular outflow from the coal and the surrounding rock, through so-called blowers and through gas eruptions . The amount of gas flowing out is also influenced by the atmospheric depression. When the air pressure rises, the resistance increases and thus the amount of gas escaping decreases. When the air pressure falls, the amount of gas escaping increases again. The methane flows out of the rock either very quietly or noisily. It can flow out of the rock with a quiet but distinctive noise. Since the noise is also reminiscent of the scraping of crabs , the French and Belgian miners refer to this emission of methane as "crabs". Gas that has accumulated in cavities can suddenly flow into the pit from the cavity. The escaping gases are irreversibly mixed with the air by turbulence. These gas mixtures are distributed in parts of the mine building due to the draft . If these gas mixtures reach a volume fraction of methane between 5 and 14 percent, they are referred to as firedamp.
Local firedamp can also accumulate at certain points, which the miner calls firedamp accumulations. However, the gas concentrations are not the same across the entire cross-section of the mine. The accumulations take place in so-called gas magazines. There are three types of this. Due to the fact that the gas is lighter than normal air, striking weather mainly collects at higher points in the mine, e.g. B. in the area of overheating or in the ridge area of routes . If there are cavities behind the expansion of the route, firedamp can build up there. The miner also calls such accumulations a gas bag. The expansion of the route prevents such accumulations from being washed away by the stream of fresh weather. Likewise, firedamp accumulations can form in higher-lying and discarded stretches and tunnels . Firedamp can also accumulate in the old man . These areas are considered to be the most dangerous gas magazines because they cannot be reached by continuous ventilation. In addition, due to the higher temperature, further methane outgassing can occur through distillation processes from existing coal residues. Due to the crime of the hanging wall , large amounts of gas can suddenly be pushed out of these cavities into the routes at great speed.
Striking weather is non-toxic to humans, but it makes it difficult for miners to breathe. In addition, firedamp can lead to chest tightness in humans. With a volume fraction of 5 to 14 percent, firedamp is explosive. These gas mixtures are ignited when they come into contact with an appropriate ignition source. Depending on the volume fraction of methane, a flame, a deflagration or an explosion occurs. The most effective gas mixture has a methane content of 9.5 percent. If the volume fraction of methane is greater than 9.5 percent, the oxygen required for complete conversion is missing. If the volume fraction of methane is less than 9.5 percent, there is not enough fuel available. Weather with a volume fraction of more than 14 percent methane are no longer ignitable under normal mine conditions. An open flame goes out in this gas mixture. It is therefore wrong to call pure methane a firedamp. However, these limits, methane content 5 to 14 percent, only apply with atmospheric air and normal air pressure . Mixtures above and below the stated concentrations are also dangerous under certain conditions. By increasing pressure, e.g. B. by a shock wave during blasting or by a previous explosion, the upper explosion limit can be higher. Likewise, a more concentrated gas mixture can be mixed back into the explosive area by being swirled with fresh weather. The addition of unsaturated hydrocarbons can make gas mixtures with methane contents higher than 14 percent explosive again. Swirled coal dust or a shock wave can lower the explosive limit below 5 percent methane. The explosiveness of the firedamp can also be impaired by the addition of other gases such as carbon dioxide or nitrogen or the associated lack of oxygen .
Until the second half of the 19th century, it was common practice to torch accumulations in the mine workings from bad weather. To do this, a miner had to drive up before the start of the shift and ignite the gas accumulations from as far away as possible. In order to be able to burn off the accumulation of firedamp in the roof, the miner crawled to the place with the accumulation of firedamp. He carried a long pole with an open light attached to one end. Another possibility, especially for mines located above, was the use of a special construction: A small roller was attached to a rod, over which a cord was passed. On this cord was a small board to which a lit open light was attached. From a safe location, the miner moved the light into the gas accumulation. With all methods he used the open light to ignite the beating weather. This usually resulted in a slight explosion. After the gas had burned off, the workforce could drive off. However, this procedure was not without risk, so that serious burns or even firedamp explosions occurred time and again. A safer method of flaring was lighting with so-called wildfire. There were also devices with which the gas was ignited at certain time intervals. There was also the option of installing open lighting in the areas where firedamp regularly accumulated and thus burning off the accumulated gas mixture.
Another possibility is the improvement of the ventilation through artificially generated weather draft. In order to achieve greater ventilation, two shafts , one pulling in and one pulling out, are required in underground pits . In England two shafts were already prescribed by law in 1862; in Prussia a uniform regulation lasted until the end of the 19th century. Here the arrangement of a second shaft was regulated by the mining authorities on a case-by-case basis until 1887 . Today it is stipulated by law that the methane content of the mine weather in the mine workings must not exceed one percent methane anywhere. In addition, innovations were introduced in the 19th century to prevent firedamp explosions. For example, when the first signs of firedamp accumulation due to breathing difficulties, increased safety measures were planned. In this case, the use of open lights was prohibited and safety lights were prescribed. The use of weather ovens was also discontinued, these were then replaced by pit fans . From the beginning of the 20th century , electric mine lamps protected from fire weather were used. The amount of gas flowing out can be reduced by targeted gas suction . Another measure is the control of the weather through weather measurements . Every shift supervisor has a weather measuring device on his man during the shift in order to check the weather for methane at certain predetermined points. The respective weather measurements are entered on a weather board.
- Karl Behrens: Contributions to the firedamp question . Baedeker, Essen 1896 ( digitized version ).
- Michael Farrenkopf (Ed.): Firedamp and coal dust. The risk of explosion in industrial Ruhr mining (1850–1914). Verlag Deutsches Bergbau-Museum, Bochum 2003, ISBN 3-937203-04-4 .
- Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining encyclopedia. 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .
- Explanatory dictionary of the technical terms and foreign words that occur in the mining industry, in metallurgy and in salt works. Falkenberg'schen Buchhandlung publishing house, Burgsteinfurt 1869.
- Carl von Schauroth: Die Grubenwetter. at JCB Mohr, Heidelberg 1840.
- Tilo Cramm, Joachim Huske: Miners' language in the Ruhr area. 5th revised and redesigned edition, Regio-Verlag, Werne 2002, ISBN 3-929158-14-0 .
- Ernst-Ulrich Reuther: Textbook of mining science. First volume, 12th edition, VGE Verlag GmbH, Essen 2010, ISBN 978-3-86797-076-1 .
- Fritz Heise, Fritz Herbst: Textbook of mining science with special consideration of hard coal mining. First volume, fifth improved edition, published by Julius Springer, Berlin 1923.
- Franz Ritter von Rziha: Schlagende Wetter . Lecture from February 10, 1886.
- A. von Wurstemberger: Firedamp explosions and sudden barometric depressions. In: Glückauf, Berg- und Hüttenmännische magazine. Association for mining interests in the Oberbergamtsiertel Dortmund (Ed.), No. 4, 16th year, Essen January 12, 1895.
- Carl Hellmut Fritzsche: Textbook of mining science. First volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1961.
- R. Vandeloise: occurrence and release of mine gas. In: Commission of the European Communities (ed.): Research books coal. Issue No. 35, Luxembourg 1971.
- Carl von Scheuchenstuel : IDIOTICON of the Austrian mountain and hut language. kk court bookseller Wilhelm Braumüller, Vienna 1856.
- Friedrich Alexander von Humboldt: About the underground types of gas and the means to reduce their disadvantage. Bey Friedrich Vieweg, Braunschweig 1799.
- Aloys Wehrle: The pit weather. Publisher by Franz Tendler, Vienna 1835.
- Walter Buschmann: Collieries and coking plants in the Rhenish coal mining industry, Aachen district and western Ruhr area. Gebr. Mann Verlag, Berlin 1998, ISBN 3-7861-1963-5 .
- Heinrich Otto Buja: Engineering manual mining technology, deposits and extraction technology. 1st edition, Beuth Verlag GmbH Berlin-Vienna-Zurich, Berlin 2013, ISBN 978-3-410-22618-5 .
- Dirk Proske: Catalog of Risks - Risks and their presentation. 1st edition, self-published, Dresden 2004, ISBN 3-00-014396-3 .