Rock dust barrier

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A rock dust barrier is made of a plurality of stages and board with rock dust explosion barrier behäufte for mining underground . The barrier has the task of preventing both a firedamp explosion and a coal dust explosion from spreading further in the mine . In 1926, the use of rock dust barriers was made compulsory in German coal mining. Today the rock dust barrier has been replaced by the water trough barrier.

Basics and history

In the rock dust barrier, the behavior of an explosion, in which the pressure wave runs ahead of the explosion flames, is exploited. If a sufficiently high amount of rock dust is distributed in the cross-section of the route , the ignition energy of the explosion flame can be significantly reduced and the explosion can be prevented from spreading further. Rock dust barriers develop their extinguishing effect better in coal dust explosions than in firedamp explosions. This is because in a coal dust explosion the ignition propagates from one coal dust particle to the next and this chain of reactions can be interrupted by the shielding rock dust particles. As early as the beginning of the 20th century, rock dust was used in the English coal mining industry to combat coal dust explosions. In the following years, attempts were made in the German hard coal mining industry to limit the effects of underground explosions by using rock dust. The effect of rock dust barriers was re-examined in the 1960s after a severe coal dust explosion had occurred at the Luisenthal mine, despite numerous rock dust barriers. Later investigations showed that the severity of an explosion cannot be predicted. Tests have also shown that it is better to divide the required extinguishing agent into several small barriers rather than a few large ones.

Lock types

A basic distinction is made between main barriers and secondary barriers depending on the amount of dust used. In addition, there are intermediate barriers and hiking barriers. Main barriers serve to seal off entire weather departments, both in the incoming and outgoing weather stream . They also serve to separate the shafts and the fittings and fixtures from the other pits . In the case of main barriers, an amount of 400 kilograms of rock dust is used per square meter of the cross-section of the route. Secondary barriers are used to seal off the dismantling operations of a building leaf from one another. They are also used in the mining stretches where local shooting is taking place . In the case of secondary barriers, an amount of 100 kilograms of rock dust is used per square meter of the cross-section of the route. However, due to the small amount of rock dust per square meter of the cross-section of the route, secondary barriers are unsafe in their effect. Intermediate barriers were used to seal off mining stretches against the local crosscut or the Bremsberg . In söhliger storage they can be used to the degradation routes against the conveyor line to seal off. In the case of intermediate barriers, a dust volume of 200 kilograms of rock dust per square meter of route cross-section is used. Wandering barriers were used to initially have a smaller barrier when the site or mining area advanced, until a larger barrier could then be erected. The distance between the hiking barrier and the location could not exceed 20 meters. A dust amount of 60 kilograms of rock dust per square meter of cross-section of the route was used for hiking barriers.

Designs

Over the years, different designs for rock dust barriers have been developed and used in practice. The rock dust was loosely piled on various wooden structures. Depending on the design of a barrier, the rock dust is deposited in hordes, mats, boxes or barriers. With the hordes, several boards at different heights are attached to the track extension . The rock dust is piled up on the paved boards. In the design with mats, mats made of strong paper or fabric strips are provided with a cross piece of wood at the two head ends. These crossbars are then attached to the caps with wires . The rock dust was then piled on the mats. Boxes were used as ridge boxes with a side wall height of a maximum of ten centimeters. However, box-shaped containers and platforms with edge strips have not proven themselves in practice. Ultimately, the type 1, also known as the Dortmund stage, and the type 2, also known as the Polish stage, were able to prevail in practice. There are also single-board platforms that are suitable for a maximum load of 100 kilograms. The main difference between the Dortmund stage and the Polish stage is that on the Polish stage the dust boards are mounted lengthways and on the Dortmund stage across the line. The stages consist of several loose boards supported by two girders. The Polish stage uses higher supporting beams than the Dortmund stage. The supporting beams in turn lie loosely on spars. The entire stage construction is relocated to the track extension using brackets or support brackets. The Dortmund stage may be loaded with a maximum of 300 kilograms. While these platforms can be used for main barriers, the single board barriers are used for building secondary barriers or to supplement main barriers.

Function and conditions

Due to the blast of air hurrying ahead of the explosion flame, the stage and the rock dust on it are overturned. This creates a dust cloud of rock dust, which cools the explosion flame that rushes behind. The explosion flame now cools down until it goes out. Whether a rock dust barrier can develop its full effectiveness depends primarily on where and how the barrier was installed. Only if the barrier is hit in good time, before the explosion flame arrives and with sufficient force by the pressure surge, it can develop a sufficient extinguishing effect. For this, the barrier must be set up so that the barrier is hit by the full explosion force. To achieve this, there must be a distance of at least 75 meters between the explosion source and the barrier, within which the explosion wave can propagate in a straight line. It is also very important that all of the rock dust in the barrier can be thrown off freely and that the discharge is not hindered.

Individual evidence

  1. ^ A b c 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 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.
  3. ↑ a b c d e f g h i Standing Committee for Industrial Safety and Health Protection in Hard Coal Mining (ed.): Flammable Dusts . Luxembourg 1968.
  4. ↑ a b c d e f g h i Carl Hellmut Fritzsche: Textbook of mining science. Second volume, 10th edition, Springer Verlag, Berlin / Göttingen / Heidelberg 1962.
  5. ↑ a b c d e f g Ernst-Ulrich Reuther: Textbook of mining science. First volume, 12th edition, VGE Verlag GmbH, Essen 2010, ISBN 978-3-86797-076-1 .
  6. ^ F. Friedensburg: The fight against coal dust explosions by rock dust and the implementation of this process in the English coal mining industry . In: Glückauf, Berg- und Hüttenmännische magazine. Association for Mining Interests in the Upper Mining District Dortmund (Ed.), No. 6, 49th year, February 8, 1913, pp. 201–209.
  7. ↑ C. Beyling: Experiments with rock dust to combat mine explosions, carried out in the test section of the Knappschafts-Berufsgenossenschaft in Derne . In: Glückauf, Berg- und Hüttenmännische magazine. Association for Mining Interests in the Upper Mining District Dortmund (Ed.), No. 25, 55th year, June 21, 1919, pp. 457–466.
  8. ↑ Steffenhagen, Meerbusch: Explosion tests with barriers and dams II . In: Commission of the European Communities (Ed.): Research books coal. No. 30, Luxemburg 1970, pp. 9-33.

See also