The first set of images shows the explosion unsuppressed; there is no barrier or any stone dust in the gallery, only coal dust. The quantity of dust distributed in the gallery would give a concentration of about 150grams/m3 if all of it became airborne inside the gallery at the same time.
Note the density of the dust cloud that develops before the flame exits the gallery and the intensity and extent of the flame travel outside the gallery.
The next set of images shows a similar explosion to the one shown above but with a series of bag barrier bags suspended inside the gallery.
Note that the colour of the dust ejected from the gallery is much lighter that in the previous unsuppressed explosion due to the presence of the stone dust from the bags, and most importantly there is no sign of flame.
It should also be noted that although the explosion appears to be quite violent, the barrier has suppressed the flame and therefore will prevent the propagation of the explosion.
This last series of images shows details of how the explosion pressure wave bursts the bags and disperses the stone dust ahead of the explosion flame.
A number of bags have been placed in the mouth of the 200m gallery so that they can been easily seen from outside.
A small explosion of about 50m3 of 9% methane normally used to initiate a coal dust explosion is used to break the bags.
There is no coal dust in the gallery so that the breakage action of the bags can be seen.
Note how, as soon as the pressure wave reaches the end of the gallery the bags react and within an extremely short time the stone dust has dispersed into the airflow cause by the pressure wave (frame 2)