Page 427 - Advanced Mine Ventilation

396 Advanced Mine Ventilation

23.4 Stone Dust Barriers for Explosion Propagation
Prevention

The most effective way of controlling coal dust explosion is to minimize them at the
sourcedthe initial ignition. But this is not always possible. The second step in this direc-
tion is to make the coal dust inert by mixing it with noncombustible dust discussed earlier.
The third line of defense is the use of stone dust barriers. They consist of a number of
plankssuspended fromthe roofthat are loadedwith veryfinestone dust, suchaslimestone
orgypsumpowder. Theshock wavethatleadsthe flame front ina detonationofgasordust
knocks the plank off its support. The resulting cloud acts as a barrier to the forward prog-
ress of the flame by quenching it on the spot or only a short distance away from it. The
explosion is thus contained in the section and minimizes widespread destruction. Many
countries require stone dust barriers by law in coal mines. Water can be used in place
of dust to considerably cut down the cost. Such barriers are called passive barriers. Cybul-
ski [12] did extensive work on the design and effectiveness of such barriers.
Fig. 23.10 shows the effectiveness of these barriers. They appear to work if they are
kept close to the working face, where an explosion is likely to initiate. Thus, they must
be moved inby as the development entries are driven inby. By contrast, there are some
barriers that are activated by remote sensors on the mining machines or in the nearby
areas.
Besides limestone and gypsum, marble, dolomite, and anhydrites have been used,
but gypsum (calcium sulfate) and rock phosphates appear to do a better job with

Figure 23.10 Effectiveness of a stone dust explosion barrier [12].