The breaking of rock by explosives occurs so rapidly that the details of
the phenomenon cannot he observed by the unaided eye. High resolution
cameras and VCRs offer a means of slowing down the blasting action. A
high resolution super video camera with digital zoom and a variable
shutter speed was imported and used for the first time in India as a tool
for blast optimisation studies at Malanjkhand Copper Project. Slow motion play-back revealed that the gases vented out through the
fissures. The crest moved prior to the lower portion of the bench when
initiated with detonating cord. The delay timing between the rows was not
enough to provide sufficient relief and rock movement. This inadequate
delay timing resulted in flyrock from the back rows. Stemming ejection
was observed from practically all the holes. The muck profile was not
satisfactory. A trial was carried out using 450 ms in hole delays and 25 nis surface
delays. The front row holes were drilled based on the observations made
from the laser profiling survey system. The video of the monitored blast
showed that the rock started moving prior to the stemming ejection. It
could be clearly seen that the entire block was completely initiated
through the surface delays before the onset of the burden movement, thus
eliminating any chance of misfires. Viewing blasts in high quality slow
motion was useful to arrive at modified design parameters, resulting in
uniform fragment size distribution and controlled rock movement.