5 - 3 5-1. INITIATING (PRIMING) SYSTEMS. The best way to prime demolition systems is with MDIs. These are blasting caps attached to various lengths of time fuse or shock tube. They can be used with a fuse igniter and detonating cord to create many firing systems. In the absence of MDI, field expedient methods may be used. a. Shock Tube. (1) Thin, plastic tube of extruded polymer with a layer of special explosive material on the interior surface. (2) Explosive material propagates a detonation wave that moves along the shock tube to a factory crimped and sealed blasting cap. (3) Detonation is normally contained within the plastic tubing. However, burns may occur if the shock tube is held. WARNING Burns may occur if the shock tube is held. (4) Advantages of shock tube: (a) It is extremely reliable. (b) It offers instant electric initiation, and it also prevents radio transmitters, static electricity, and such from accidentally causing an initiation. (c) It may be extended using leftover sections from previous operations. b. Blasting Caps. Five types of MDI blasting caps are available to replace the M6 electric and M7 non-electric blasting cap. Three are high-strength, and two are low-strength. High-strength blasting caps can prime all standard military explosives (including detonating cord) or and can initiate the shock tube for other MDI blasting caps. (1) M11. • Factory crimped to 30 feet of shock tube. • A movable "J" hook is attached for quick and easy attachment to det cord. • A red flag is attached 1 meter from the blasting cap and a yellow flag 2 meters from the blasting cap. (2) M14. • Factory crimped to 7.5 feet of time fuse. • May be initiated using a fuse igniter or match. • Burn-time for total length is about five minutes. • Yellow bands indicate calibrated one-minute time intervals. (3) M15. • Two blasting caps factory crimped to 70 feet of shock tube. • Each blasting cap has delay elements to allow for staged detonations. • Low-strength blasting caps. Used as a relay device to transmit a shock tube detonation impulse from an initiator to a high strength-blasting cap. (4) M12. This is factory crimped to 500 feet of shock tube on a cardboard spool. (5) M13. This is factory crimped to 1,000 feet of shock tube. c. Matches. If fuse igniter is unavailable, light the time (blasting) fuse with a match. Split the fuse at the end (Figure 5- 1), and place the head of an unlit match in the powder train. Light the inserted match head with a flaming match, or rub the abrasive on the match box against it. You may have to retry this in windy conditions. NOTE: High altitudes and colder temperatures increase burn time. d. M81 Fuse Igniter. This is used to ignite time blasting fuse or to initiate the shock tube of MDI blasting caps.