Page 425 - Moving the Earth_ The Workbook of Excavation

BLASTING AND TUNNELING

BLASTING AND TUNNELING 9.25

FIGURE 9.17 Insertion of fuse in cap.

FIGURE 9.18 Priming dynamite with fuse cap.

In shallow holes, and in blockholing or mudcapping, it is practical to simply insert the cap in
the cartridge end, without fastening, as the primer need not go out of reach. Friction will hold it
in place against a moderate pull, but not against yanking.
Electric Cap Primer. Figure 9.19 illustrates the most common method of priming a small-diameter
stick of dynamite. The cap is pushed into the navel-like end of the wrapper, and the wires are caught
in a half hitch around the center. If the dynamite is hard, a hole may be made in the end with a
wood peg to make it easier to insert the cap securely so that it will not slip out during loading.
Large-diameter sticks are best primed by this sequence: the cap is inserted in the top, and a
loop of wire is pushed through a slanting hole and is caught around the middle.
In each case the cap is entirely inside the dynamite, cannot work into a position where it might
scrape the side of the borehole, and its direction of explosion, away from the wires, is directed
into the dynamite.
Detonating Cord. To make up a primer, Primacord is fastened to a large stick of dynamite by
being threaded through and secured with tape and to a small one by being tied tightly. The resulting
primer is usually the first explosive to be put in the hole. This puts the detonating cord in contact
with the entire charge. See Fig. 9.20.

Placing Primers. If one primer is to be used in a borehole, it is best to place it at the top, or one
cartridge down from the top. This keeps to a minimum the danger of damage to fuse or wires while