Initiator Firing Times and Their Relationship to Blasting Performance

摘要

Commercially produced electric and non-electric ms delay initiators, period 0-19 (0-1000 ms), from the four principal U.S. manufacturers were tested to determine mean and standard deviations of firing times. Deviations from nominal firing times given by the manufacturer were noted for all manufacturers' initiators. A predictive statistical model has been developed to describe the behavior of these initiators in actual practice. Application of this model to the test data reveals that, at present, the probabilities of successful shots (no sequencing errors and separation of adjacent periods by 8 ms or more) are low. Observations of production blasting operations in several aggregate quarries, using high-speed cinematography, confirm the results of the test and the statistical model in field practice. Relationships between deviations from nominal firing time and problems with relief, fragmentation, flyrock, and backbreak were established. In addition, data from the high-speed films suggest that currently used timing guidelines for designing properly relieved shots (1 ms/ft of burden) are too short, and that delay times up to 3.5 ms/ft are needed. The low probabilities of success predicted by the model potentially affect vibration and airblast control.