After the primer has been lowered to its proper location in the blasthole, the detonating cord is cut from the spool. About 0.75 to 1 m cord should extend from the hole to allow for charge settlement and tying into the trunkline. When the entire shot has been loaded and stemmed, the trunkline is laid out along the path of desired initiation progression.
Trunkline-to-trunkline connections are usually made with a square knot. A tight knit, usually a clove hitch, a half hitch or a double-wrap half hitch is used to connect the downline to the trunkline. Any excess cord from the downline should be cut off disposed. The cord lines should be slack, but not excessively so.
If too much slack is present, the cord may cross itself and possibly cause a cut off. Also, if the lines are too tight and form an acute angle, the downline may be cut off without detonating.
Two of the primary advantages of detonating cord initiation systems are their ruggedness and their insensitivity. They function well under severe conditions such as in hard, abrasive rock, in wet holes and in deep, large diameter holes.
The system is not susceptible to electrical hazards, although lightning is always a hazard while loading any blast. Detonating cord is quite safe from accidental initiation while initiating cap or delay connectors are attached. Available delay systems are extremely flexible and reasonably accurate.
There are several disadvantages that may be significant in certain situations. Systems employing only surface connectors for delays present the hazard of accidental initiation impact. Detonating cord trunklines create a considerable amount of irritating, high frequency airblast (noise). In populated areas the cord should be covered with fine material such as drill cuttings.
The means of checking the system is visual examination, in hot holes standard cord containing PETN explosive be replaced by cord containing explosives such as RDX. Detonation cord downlines present the problem of charge or stemming disruption.
Author: Sushil Bhandari
