Mine Explosion Mitigation
Methane gas and coal dust explosions have been ever present in the process of coal mining operation. The first reported explosions can be dated back to the 19th century. The risk of a methane gas and/or a coal dust explosion is still present in coal mining operation. In December 2018 an unsuppressed methane gas explosion killed 9 miners in a mine the Czech Republic. In April 2017 an unsuppressed methane gas explosion killed 8 miners at the Stepnaya mine in the Ukraine. In February 2016, 36 miners were killed by an unsuppressed methane gas explosion at the Severnaya coal mine in Vorkuta, Russia. In November 2016, 33 miners were killed due to an unsuppressed explosion in Jinshangou Coal Mine in Chongqing. The risk of a methane gas and/or a coal dust explosion is clearly still present in coal mining operations. Over the years a number of methods have been investigated and developed to either prevent or suppress a coal mine explosion. Figure 1 depicts the currently accepted categorization of explosion mitigation controls. The focus is, and should remain, the prevention of an event leading to methane gas or coal dust explosion. In this case, a mine would typically address aspects such as diluting the methane concentration in the atmosphere by adequately ventilating the area, using water spray to mitigate coal dust at the cutting face or utilizing flameproof or intrinsically safe equipment to mitigate the source of an ignition. Although the 100% prevention of both a combustible atmosphere and high enough energy source to spark an explosion remains the obvious goal, it is currently still accepted that it is not possible to fully prevent an explosion in a coal mining operation. One of the reasons is e.g. the continuous increase of mechanized and automated cutting of coal. As a result, mines look towards means to suppress an explosion in the case it should occur. In this case a mine would investigate the use of constructive measures. These mitigating controls are, according to Michelis (1999), categorized into “explosion stopping”, “special structure” or “explosions barriers”. The constructive measures such as “explosion stopping” and “special structures” are physical, purpose-built walls or shelters. The explosion barriers on the other hand are equipment introduced into an area that only react once the event of an explosion occurs. The explosion barriers are in turn separated into passive barriers and active barriers. The meaning of passive and active in this case relate to the use of an external power source. Passive barriers therefore do not require a source of energy to detect an explosion but are activated by the pressure wave that leads any explosion. Active barriers are equipment that require a source of energy to detect an explosion. Unlike the passive barrier they are then however independent of the physical dimension of an explosion and will rather react based on the logic and mechanism that has been set for this particular device.
Active explosion suppression barriers have clear advantages in modern mining operations (Spaeth and Belle, 2018). These barriers can be adopted to optimally react on an event such as a methane gas or coal dust explosions. Considering the successful testing done at Kloppersbos (van Dyk 2005) and that six methane gas explosions have been suppressed by active barriers in South Africa since 2001, it can be said that the effectiveness of these systems has been proven in the field. As mining operation get more mechanized and automatized, the requirement for active barriers to adapt increase. The core functional requirement to stop an explosion remains.