User's Manual

87
RIOTRONIC X+
User Manual
9.2.4. Lead holes
The first few holes to fire often cause the highest air blast. This is thought to be because they
are working the hardest and have no free faces developed by the holes beside them. In some
situations, it has been seen that firing the first couple of holes a bit slower can significantly
reduce peak air blast. For example, if the optimal timing was 18/55, the first couple of holes
could be timed at 25/30 milliseconds between them. The following air blast trace shows signs
of lead hole peaks (Figure 115).
Figure 115. Air blast trace from a blast suffering from lead hole peaks
9.2.5. Vibration
The change from pyrotechnic detonators to RIOTRONIC X+ detonators will make a
difference to ground vibration simply because of the much greater accuracy. Holes will fire
at the designed timing separation rather than a spread of times around the chosen delay. In
decking operations, a single deck per delay can be fired with confidence. The eight-
millisecond window that has crept in as an industry standard should be looked at with
caution. Depending on the ground conditions and the distance from the blast to the
monitoring point the optimum window may range from 4 to 40 milliseconds. The following
graphic illustrates the decrease in vibrations over time after a blast (Figure 116).
Figure 116. Vibration over time after a blast