The influence of some blasting techniques on the probability of ignition of firedamp by permissible explosives.

The ignition of firedamp by permissible explosives is assessed by means of gallery testing conducted by the Bruceton up-and-down method. Six test series were made in order to analyze the influence of several blasting practices in long-holes coal blasting, namely: use of slotted PVC pipes, detonating cord, salt cartridges and double (top and bottom) initiation. The parameters of the distributions of the probability of ignition are determined by the maximum likelihood method; normal, logistic, lognormal and Weibull distributions have been used. Confidence bands for the probability points are obtained both from the asymptotic standard errors of the parameters and by a bootstrap-like technique. The four distributions used give similar results in a rather ample probability range; discrepancies in the probability points are within 2% and in the confidence limits within 10% in a range of probability [0.1, 0.9] in most of the cases. The use of detonating cord is found to affect significantly the probability of ignition; the double initiation does also have an influence though not statistically significant at a 95% level; the use of salt cartridges, in the amount tested, has little effect in the ignition probability; the use of PVC pipe shows no effect.