Explosives and Explosions – Blog 2 by Eric Eaton
Firing off solid
When firing any explosives they tend to go to the weakest point, and that is why the old miners when it was hand got used a cutter to undercut/middlecut/overcut the coal seam before they fired the coal, thus the shots which would explode all at once, would go to the weakest point which is where the cutter had taken a section out of the coal seam.
When it isn’t an option to undercut/middlecut/overcut we have to “fire off the solid”. In headings we start off by boring a “box” this is in the centre of the heading, it is what it says, you would bore a box shape of holes in the stone/coal and then bore the whole heading around the box.
In this situation we would use what are called delayed detonators’ and these are numbered as such, so in the box you would put 0 detonators in the gun powder and place these in the box holes. You would then place No. 1 detonators’ in the first holes closest to the box and the No. 2 detonators in the next row and so on until you have all the holes of the heading filled with gunpowder and numbered detonators.
When the shot-firer fired the shots the 0 detonators in the box would go off first and then all the other delayed detonators would go off in sequence, it would only be a split second for each detonator to explode one after the other.