Mining Publication: Overlap Probability for Short-Period-Delay Detonators Used in Underground Coal Mining

The Bureau of Mines investigated coal-mine-type short-delay electric detonators marketed by three domestic manufacturers to determine the accuracy of delays and the probability of overlap between adjacent delay periods. The Winzer index was computed and compared with the probability of overlap. A close agreement between the winzer criterion and overlap probability was demonstrated. A permissible blasting unit capable of delivering a maximum firing energy of 4.0 J and a digital oscilloscope were used to measure the delay time with an accuracy of plus or minus 0.25 Ms. Another oscilloscope and a pulse transformer were used to record firing current. Experimental data indicated negligible overlap probability in detonators of shorter delay periods: periods 1 to 4, which correspond to 25 to 250 ms. However, a significant probability of overlap was detected in some detonators of longer delay periods: periods 5 to 9, which correspond to 300 to 500 ms.