Firedamp explosion

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By sculptor Wilhelm Wulff created memorial in the cemetery Bochum - Hamme to commemorate the miners who in 1936 at the Schlagwetterexplosion on the 9th floor of the United Mine president died

In mining, a firedamp explosion is the explosion of striking weather . The firedamp explosion is most violent when 1/11 of the ignited gas mixture, which corresponds to 9.5%, consists of methane . Under certain conditions, a firedamp explosion can lead to a coal dust explosion as a secondary reaction . The miner describes a weak firedamp explosion with a low-concentration gas-air mixture as a firedamp explosion .

History

Firedamp explosion on a panel in the main entrance of the administration of the Union, AG for mining, iron and steel industry

The first firedamp explosions occurred in the German coal mining industry in the second half of the 19th century. While initially only a few miners were killed in a firedamp explosion due to the low staffing of the operating points, more than 100 miners died in a firedamp explosion at the Neu-Iserlohn colliery in 1868 . The reason for the first firedamp explosions was the use of open light . In the period from 1878 to 1894 there were at least eleven mine accidents with several deaths almost every year due to bad weather . Due to the many firedamp explosions, the Prussian firedamp commission was founded in the 1880s. At the beginning of the 20th century there was a firedamp explosion followed by a pit fire at a mine in Hamm , killing 349 miners. The worst firedamp explosion in the Ruhr mining industry occurred in 1946 at the Grimberg colliery in Bergkamen, killing 405 miners. On February 7, 1962, the worst firedamp explosion occurred in the Saar mining industry. 299 miners died at the Luisenthal mine near Völklingen. The pressure of the explosion was so strong that it threw the two 20 t heavy cover plates about 10 m into the air in the Alsbach shaft, which was about 3 km away, whereby one plate wedged itself in the headframe. In 1968, 17 miners died in a firedamp explosion at the Minister Achenbach colliery . In 1986 there was a firedamp explosion at the Camphausen mine in the Saar district , killing seven miners.

Beginning and course of the explosion

If an explosive mixture of methane and oxygen comes into contact with an ignition source, the two gases will burn:

Whether this gas-air mixture can explode, however, initially depends on its concentration. The limits of the ignitability of this mixture are between five and 14 percent methane. Another prerequisite for a firedamp explosion is the energy content of the ignition source. Since the firedamp mixture only ignites with a delay, the ignition source must also act on the gas mixture for a certain minimum time. For the ignition process, this means that the ignition source has a minimum temperature of 650 degrees and must act for at least ten seconds. As the ignition temperature rises, the required exposure time drops to less than one second. After the firedamp mixture has been ignited, the gas temperature increases to over 2000 degrees. Due to the increase in temperature, the gas mixture expands significantly. The detonation effect is increased by the spatial delimitation of the mine workings. The explosion propagates through the mine. Once the explosion has started, gas mixtures with lower concentrations of methane can also be ignited. There is also the possibility that a firedamp deflagration could initiate a powerful firedamp explosion. The deflagration can push further firedamp before the pressure wave of the weak explosion and this compressed mixture can then be ignited by the trailing flame of the deflagration at a branch or in a location. Shortly after the explosion, the explosion gases cool down again and contract. Since the water vapor produced by the explosion condenses, the volume of the remaining gases drops below the volume of the gases before the explosion.

Possible sources of ignition

Open flames, such as those found in mine fires or open light, serve as the ignition source. In the 19th century, weather ovens were used in the weather shafts for ventilation . In 1883, 41 such ovens, which were a possible source of ignition, were being used in the Ruhr mining industry. A frequent source of ignition and thus the cause of firedamp explosions were also the weather lamps used up until the 20th century . These were often opened without authorization and then caused the firedamp to ignite. In addition to the open flames, high-energy sparks that are produced by hitting steel on stone can also be a possible source of ignition. The sparks produced when hard layers of rock collapse can also act as an ignition source. If components made of aluminum or other light metals hit rusty iron parts, sparks with great ignitability are created. This reaction, known as the thermite reaction, also occurs when there is rust film on the aluminum parts and z. B. is hit with a hammer. Another source of ignition can be underground blasting . Internal combustion engines that are operated underground can act as possible ignition sources. Ultimately, however, electrical switching devices and damaged electrical cables and devices can also develop ignitable sparks.

Effects of the firedamp explosion

The effects of the firedamp explosion are very different. In most cases the explosion has a very destructive effect. People who are in the area of ​​the explosion are seriously injured or killed. In the case of some firedamp explosions, the effect is often only minor. Even with larger explosions, the effects can be weak at certain points. Depending on how severely a mine is affected by the explosion, it can happen that hardly any damage occurs. Particularly intense explosions generate pressures of over 100 bar . In such violent explosions, trucks are deformed and thrown through the air. Fractions of a second after the explosion, the explosion gases cool down again. The cooling leads to a contraction of the explosion gases and thus to a negative pressure and a kickback in the direction of the explosion source. Due to the negative pressure, non-breathable residual gases, in particular nitrogen and carbon dioxide, flow into the mine construction concerned. In addition, at higher temperatures methane can reduce the carbon dioxide to toxic carbon monoxide :

The effect of the explosion of the mine gases concentrated in this way, in which a pressure surge occurs first in one direction and then a kickback in the other, gave the gases their name "firedamp".

Avoidance and reduction of the effects

There are various options for reducing the risk of a firedamp explosion. First of all, the concentrations of methane in the weather will be reduced by suitable measures, such as dilution of the gases through increased ventilation. The methane concentrations are monitored by suitable weather measuring devices. Another option is to extract the methane from the seams . Another possibility is to avoid ignition sources. So were z. B. At the beginning of the 20th century in the Ruhr mining industry the operation of the open light underground was prohibited. In underground coal mining, electrical systems are only operated in firedamp and explosion-proof versions. So-called safety explosives are used during blasting work. Machines are monitored for overheating and cutting tools are cooled by means of nozzles. Should a firedamp explosion nevertheless occur, the effects are reduced by suitable measures such as rock dust barriers or water trough barriers.

See also

Individual evidence

  1. a b c d e Walter Bischoff , Heinz Bramann, Westfälische Berggewerkschaftskasse Bochum: The small mining dictionary. 7th edition, Verlag Glückauf GmbH, Essen 1988, ISBN 3-7739-0501-7 .
  2. ^ A b c d e f g h Heinrich Otto Buja: Engineering handbook mining technology, deposits and extraction technology. 1st edition, Beuth Verlag GmbH Berlin-Vienna-Zurich, Berlin 2013, ISBN 978-3-410-22618-5 .
  3. a b c d e f g h i Michael Farrenkopf: Mine accidents as disasters in mining: on the methodology of the investigation from a technical and socio-historical perspective. In: Ferrum, News from the Iron Library, Georg Fischer AG Foundation. Tape. 69, 1997, pp. 24-35.
  4. a b Dirk Proske: Catalog of Risks - Risks and their presentation. 1st edition, self-published, Dresden 2004, ISBN 3-00-014396-3 .
  5. a b c d e f g h i j Ernst-Ulrich Reuther: Textbook of mining science. First volume, 12th edition, VGE Verlag GmbH, Essen 2010, ISBN 978-3-86797-076-1 .
  6. ^ A b c d Carl Hellmut Fritzsche: Textbook of mining science. First volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1961.
  7. a b c d e 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.
  8. ^ A b c Heinrich Winter: Physics and Chemistry: Guide for Mountain Schools . Springer-Verlag, 2013, ISBN 3-662-36403-4 , p. 115 ( limited preview in Google Book search).
  9. 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 .
  10. Technical rules for operational safety, TRBS 2152 Part 3. Dangerous explosive atmosphere - Avoiding the ignition of dangerous explosive atmosphere.