Soldier Combat Skills

Chapter 14-2 – Demolition Firing Systems

The moderized demolition initiator (MDI) is a suite of initiating components used to activate all standard military demolitions and explosives (Figure 14-8). The MDI consists of nonelectric blasting cap assemblies (M11/12/13/14/15/16/18) each with an integral time-delay initiator; a time fuse or shock tube; and a “J” hook for attachment to a detonating cord. These MDIs will eventually replace all electric and nonelectric firing systems for conventional forces, while maintaining compatibility with existing Army systems.

Note: Information on the preparation and placement of demolition charges for electric and nonelectric firing systems separate from MDI is in FM 3-34.214.

BOOSTER ASSEMBLIES

14-11. The MDI includes a pair of booster assemblies (M151/M152), consisting of a detonator (det) and a length of low-strength detonation cord, were added to MDI. Since they contain no sensitive initiating element, they can be used to safely initiate underground charges. The MDI’s blasting cap assemblies consist of five high-strength blasting caps and two high strength booster assemblies. These cap assemblies can be used to prime standard military explosives, or to initiate the shock tube or detonation cord of other MDI components. MDI also contains an igniter (M81) that can activate either time fuse or shock tube. With MDI, you can successfully complete demolition missions in a safe, quick, and easy manner. It is also flexible enough that any unit conducting demolition activities can use it. Timing can be set to fire immediately or up to a 20-minute delay. It is nonelectrical, so it is impervious to EMP.

PRIMING OF EXPLOSIVES

14-12. The two methods of priming explosive charges are nonelectric (MDI) and detonating cord. MDI priming is safer and more reliable than the current nonelectric cap priming methods. However, detonating cord is the most preferred method of priming charges since it involves fewer blasting caps and makes priming and misfire investigation safer.

14-13. MDI blasting caps are factory-crimped to precut lengths of shock tube or time-blasting fuse. Because the caps are sealed, they are resistant to moisture and will not misfire in damp conditions. Splicing compromises the integrity of the system, and moisture will greatly reduce reliability. Also, the human factor in incorrect crimping is removed, making MDI blasting caps extremely reliable.

PRIMING OF NONELECTRIC MDI

14-14. Use only high-strength MDI blasting caps (M11, M16, M14, M15, or M18) to prime explosive charges. M12 and M13 relay-type blasting caps have too little power to reliably detonate most explosives. Use them only as transmission lines in firing systems. You can use MDI blasting caps with priming adapters, or you can insert them directly into the explosive charge, and then secure them with black electrical tape. If you use priming adapters, place them on M11 blasting caps as follows:

Priming Plastic Explosives with Nonelectric MDI–(See Figure 14-9.)

  1. Use M2 crimpers or other nonsparking tools to make a hole in one end or on the side (at the midpoint) of the M112 (C4) demolition block. The hole should be large enough to hold an M11, M16, M14, M18, or M15 blasting cap.
  2. Insert an M11, M16, M14, M18, or M15 blasting cap into the hole produced by the M2 crimpers.

WARNING

If the blasting cap does not fit, do not force it!
Instead, make the hole larger.

  1. Anchor the blasting cap in the demolition block by gently squeezing the C4 plastic explosive around the blasting cap.
  2. Use tape to secure the cap in the charge M112.

PRIMING OF DETONATING CORD

1. Form either a uli knot, double overhand knot, or triple roll knot as shown in Figure 14-10.

  1. Cut an L-shaped portion of the explosive, still leaving it connected to the explosive. Ensure the space is large enough to insert the knot you formed (Figure 14-11).
  2. Place the knot in the L-shaped cut.
  3. Push the explosive from the L-shaped cut over the knot. Ensure there is at least 1 centimeter (1/2 inches) of explosive on all sides of the knot.
  4. Strengthen the primed area by wrapping it with tape.


Note: Do not prime plastic explosives by wrapping them with detonating cord, since wraps will not properly detonate the explosive charge.

CONSTRUCTION OF NONELECTRIC INITIATING ASSEMBLY WITH MDI

1. Turn the end cap of the M81 fuse igniter a half-turn counterclockwise, and remove both the shipping plug and the shock tube adapter from the igniter (Figure 14-12).

  1. Cut off the sealed end of the M14 time-delay fuse (Figure 14-13), and insert it into the end cap of the M81. Tighten (finger-tight) by turning the end cap clockwise.
    1. Attach the blasting-cap end of the M14 time-delay fuse to the existing detonating-cord ring/line main using either an M9 holder or adhesive tape. If using tape, ensure it is at least 6 inches from the end of the detonating cord.
      1. Attach the M14 blasting cap using the M9 holder (the preferred method).
      2. Open both hinged flaps of the M9 holder.
      3. Insert the blasting cap into the M9 holder and close the small hinged flap.
      4. Form a bight 6 inches from the end of the detonating cord, lay it in the M9 holder, and close the hinged flap.
      5. Secure the detonating cord into the M9 holder (Figure 14-14). Secure the door with adhesive tape.


Note: Do not loop more than two shock tubes in the M9 holder.

4. Construct a nonelectric initiating assembly using the M11 branch line and the M12 transmission line.

  • a.
    Place the M11 branch line’s blasting cap under a sandbag near the detonating-cord firing system.
  • b.
    Attach the M11 branch line to the M12 transmission line by forming a bight at the end of the M11, laying it in the attached M9 holder on the M12, and closing the hinged flap. Tape and secure the M11 into place. Place the M9 holder, along with the M12, under the same sandbag as the M11 blasting cap.
  • c.
    Retrieve the M11 blasting cap from under the sandbag. Attach it to the detonating-cord firing system using an M9 holder as described above using either the M14 or adhesive tape. Ensure the tape is at least 6 inches from the end of the detonating cord.
  • d.
    Secure the transmission line to a nearby anchor point and run the M12 transmission line back to the initiating point.

5. Cut the sealed end of the M12 transmission line at the initiating point, and attach an M81 fuse igniter as described above for the M14 time-delay fuse (Figure 14-15).

Note: MDI systems come with short clear plastic tubes used for repair. The shock tube repair procedure is outlined in TM 9-1375-213-12, Army Demolition.

6. Firing procedure for a nonelectric initiating assembly with MDI.

  • a.
    Squeeze the spread legs of the safety cotter pin together.
  • b.
    Use the safety pin’s cord to remove the safety cotter pin from the igniter’s body.
  • c.
    Grasp the igniter body firmly with one hand, with the pull ring fully accessible to the other hand. To actuate, sharply pull the igniter’s pull ring. The igniter can burn at extremely high temperatures.
  • d.
    Ensuring that smoke is coming from the fuse (or out of the vent hole in the igniter), remove the igniter and withdraw to a safe distance or to appropriate cover.

WARNING

When using MDI in extreme cold temperatures and/or high altitudes, dual prime and dual initiate the charges.

MISFIRES

14-15. The most common cause of a misfire in a shock-tube firing system is the initiating element, usually an M81 igniter. However, the most common failure with the M81 is primer failure to fire. To correct this, recock the M81 by pushing in on the pull rod to reengage the firing pin and then actuate the igniter again. If, after two retries, the M81 does not result in firing, cut the shock tube, replace the igniter with a new one, and repeat the firing procedure.

14-16. Another misfire mode with the M81 is the primer fires but blows the shock tube out of its securing mechanism without it firing. (This is usually due to the shock tube not being properly inserted and secured in the igniter.) To correct this problem, cut about 91 centimeters (3 feet) from the end of the shock tube, replace it with a new igniter, and repeat the firing procedure.

Note: Your supervisor needs to be involved to identify and correct any additional misfire problems. The correct procedure to implement for all possible misfires is in FM 3-34.214.


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