FIGURE M.1 Electric detonator. A, metal shell; B, base charge; C, primer charge; D, ignition charge; E, bridge wire; F, ends of leg wires; G, H, plugs and/or filling; I, leg wires. SOURCE: Adapted from materials presented to the committee by Paul Horowitz, JASON Program, March 3, 1997.

There are two general types of detonators: electric and nonelectric. Electric detonators are activated by passing an electrical energy pulse through a bridge wire that is embedded in the ignition charge or primer spot. Electric detonators may be further classified as electric instantaneous, electric delay, electronic, toroid-type, and exploding bridge wire. All are produced with numerous delays, wire lengths, wire colors, and wire configurations.

Nonelectric detonators are initiated by other than electrical means. These include safety fuses, shock tubes, miniature detonating cords, and gas-initiated systems. As with electric detonators, nonelectric detonators are produced with a great variety of tubing or cord lengths, types of plastic closures, and so on. The gas-initiated system is no longer used in the United States, although stocks of these devices may still be found in blasters' magazines.

Until approximately the mid-1970s, the prevailing means of initiating explosives in the United States were by cap and fuse, electric detonators, and detonating cord. Since then, cap and fuse systems have virtually disappeared, but the other methods are still used, with technological improvements. In spite of vast improvements in electric detonator technology and manufacturing quality, nonelectric shock-tube detonators are now the product of choice for the majority of explosive initiation applications. The shock-tube system, invented in Sweden, appeared in the United States in the mid-1970s and quickly spread to all types of blasting. It has virtually taken over civil tunneling and is dominant in most underground mining except coal mining.

The U.S. market is split nearly evenly between electric and nonelectric (mainly shock-tube) detonators, but as described above, the nonelectric shock-tube systems are ascendant. Most detonators in use in the United States are produced domestically or in Canada. The cap and fuse detonators still being used (mainly in small mining operations, avalanche control, and agricultural applications)

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