Drilling Blast timing

Re. Shabecoff s report in the New York Times, who drilled the blast holes, where did the equipment come from, and why are there once again no witnesses to this considerable amount of work Why is no trace of any of this visible on the air photos ... 

To ensure adequate breakage at the intended toe of the bench, the blast hole should be drilled some distance below the depth of the bench to the correct toe elevation. This process is termed subdrilling and should be between 0.2 and 0.5 times the burden distance. 

The blasting wholes were drilled in the coal roof of monitoring areas in work face 182106. The explosive parameters can be seen at Table 1. Because the arriving time of wave P (longitudinal wave) was used in plotting wave emission source, the speed and structure of wave P are interested. 

A part-time helper had drilled and loaded a series of blast holes. His mother and sister were there to observe the blasting. After preparing for the blast, his mother and the other workers left the area. The sister wanted to take pictures of the blast, so she remained. They backed off ISO feet from the blast site to take pictures. When the blast was detonated, the helper was hit on the head by a large piece of flyrock and was killed instantly. His sister suffered massive chest injuries and a punctured lung. 

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