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Considerations on the Safety of Electric Caps Based on Measured Electrical Resistivity of Rock Samples  

Choi, Byung-Hee (한국지질자원연구원)
Ryu, Chang-Ha (한국지질자원연구원)
Shin, Seung-Wook (한국지질자원연구원)
Kim, Soo-Lo (한국광해관리공단)
Publication Information
Explosives and Blasting / v.34, no.4, 2016 , pp. 19-27 More about this Journal
Abstract
Much care should be taken when electric caps are used in blast site than when non-electric initiation systems are used. This is because electric caps can cause premature firing or misfires if stray currents of high magnitude flow into the blasting circuit. If the rock has higher electrical conductivity or lower electrical resistivity, such risks will be increased because the rock will provide more passages for the stray currents to flow into the blasting circuit. In this study, several rock samples obtained at a blast site were tested for electrical resistivity to decide whether electric caps could be used or not in the site. The measured electrical resistivity was $39{\sim}47{\Omega}{\cdot}m$ for the rock samples that had a higher content of metal sulfides. Contrary, the resistivity was $15000{\sim}21000{\Omega}{\cdot}m$ for ordinary rocks. Especially, in the case of the rock of electric resistivity of $39{\Omega}{\cdot}m$, only 2-V electric potential enables a stray current to flow through the rock of 1-m length, which can cause the premature firing of a detonator whose initiation current is 0.4 A. This result shows that electric initiation system should not be used in the site because rocks containing much amount of metal sulfides are widely distributed there.
Keywords
electric cap; stray current; premature firing; misfire; electrical conductivity; electrical resistivity;
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