A Simple Method of Determining Site-Specific Safe Decking Procedures in Order to Avoid Dynamic Pressure Issues When Decking

摘要

Determining the minimum amount of inert material that can be used between explosive columns is acomplex problem. Using too little inert material can result in detonator/primer failure, either bysympathetic detonation of or failure to fire of the subsequent explosive column(s). Propagation typefailure results when inert material length between charges is small enough that the subsequent (delayed)deck fires more or less instantly. In this situation, the primer, detonator, or bulk product is initiated bythe shock wave from the earlier firing deck. This type of failure may be un-noticed until thevibration/airblast report is examined. Alternatively, failure to fire results in undetonated explosives inthe muck-pile. Either of these failures modes likely happens with more regularity than suspected.Whether using electric, non-electric, or electronic detonators, the delay train can be interrupted by shockeven after initiation of the delay mechanism within the detonator shell has commenced.Published literature recommends that inert decking length be 14 x charge diameter (ISEE, 2011).Because this rule of thumb is intended to be comprehensive, it is necessarily restrictive. For example,when using a 7.875 inch hole diameter, 9.2 feet of inert decking material is the minimum amountrecommended between explosive columns. In many situations, using such a large deck is not practical.The determination of a site-specific decking plan to reduce/eliminate this type of detonator failure isadvised in situations where the typical recommendation is not practical. A better method of comparingscenarios (than merely the amount of inert stemming material between decks) is to use the minimumdetonator separation. This method takes into account all material (both explosives and inert decking)which is between the end of the first deck to fire and the second deck primer, thus is partially dependenton the direction of initiation (top down or bottom up decking delays). This is the distance that the shockwave has to pass to reach the second detonator in order to damage it.Current methods for determining minimum separation distances involve the use of VOD analysis andequipment required for such analysis. This paper describes a novel method for establishing site specificseparation distances that allows for top down initiation and a seismograph as the sole analysis tool.