SUBCOURSE MM2605
EDITION 4
US ARMY AMMUNITION SPECIALIST MOS 55B SKILL LEVELS 1 AND 2
DEMOLITION FIRING SYSTEMS
US ARMY MISSILE AND MUNITIONS CENTER AND SCHOOL
US Army Ammunition Specialist MOS 55B Skill Levels 1 and 2 Course
DEMOLITION FIRING SYSTEMS SUBCOURSE MM2605
US Army Missile and Munitions Center and School Fort Lee, Virginia
MM2605
This publication is provided for nonresident instruction only. It reflects the current thought of this school and conforms to published Department of the Army doctrine as closely as possible. Users of this publication are encouraged to recommend changes and submit comments for its improvement. Comments should be keyed to the specific page and line of the text to which the change is recommended. Reasons will be provided for each comment to insure understanding and complete evaluation. Comments should be prepared using DA Form 2028 (Recommended Changes to Publications and Blank Forms) and forwarded directly to Missile and Munitions, United States Army Combined Arms Support Command, Fort Lee, Virginia 23801-1809.
ii
MM2605 CONTENTS INTRODUCTION, v DEMOLITION FIRING SYSTEMS (Tasks 093-400-1257 and 093-400-1258), 1 Preparing a Nonelectric Firing System, 1 Step 1: Test the Burning Rate of the Time Blasting Fuse, 3. Step 2: Inspect the Nonelectric Blasting Cap, 6. Step 3: Install and Crimp the Nonelectric Blasting Cap to the Time Blasting Fuse, 8. Step 4: Insert the Time Blasting Fuse in the Priming Adapter, 10. Step 5: Attach the Fuse Igniter to the Time Blasting Fuse, 10. Step 6: Prime the Charge, 10. Preparing an Electric Firing System, 12 Step 1: Test the Blasting Cap Test Set or the Galvanometer for Serviceability, 14. Step 2: Test the Firing Wire for Shorts and Continuity, 15. Step 3: Test the Electric Blasting Cap for Serviceability, 18. Step 4: Splice the Electric Blasting Cap to the Firing Wire, 19. Step 5: Prime the Charge, 20. Step 6: Test the Firing Circuit, 21. Step 7: Test Operate the Blasting Machine and Connect It to the Firing Circuit, 22. Preparing a Detonating Cord System, 22 Step 1: Lay the Ring Main, 24. Step 2: Lay the Branch Lines and Connect Them to the Ring Main, 26. Step 3: Prime the Charges, 28. Step 4: Attach the Firing System, 29. REVIEW EXERCISES, 31 EXERCISE SOLUTIONS, 37
iii
MM2605 INTRODUCTION An ammunition specialist may be required to help destroy unserviceable ammunition by detonation. In a combat situation, an ammunition specialist may have to perform emergency destruction of ammunition to prevent enemy use. In both of these situations, you will need a means of ignition to detonate primed charges. Both electric and nonelectric firing systems serve this purpose. The detonating cord system is used to initiate explosive charges as a component of an electric or nonelectric firing system. If the nonelectric firing system is being used with more than one charge, the detonating cord system must be used to assure that the charges fire at the same time. In this subcourse, you will learn how to prepare a nonelectric firing system, an electric firing system, and a detonating cord system. The destruction of ammunition is hazardous and requires special instructions. Instructions that could lead to personnel injury or death if not followed are emphasized by warnings in the text. Tasks. This subcourse Demolition Firing Systems, consists of one lesson in support of the following tasks from soldier's manual FM 9-55B1: 093-400-1257, Perform Emergency Destruction of Ammunition in an ASP by Burning. 093-400-1258, Perform Emergency Destruction of Ammunition in an ASP by Detonation. Objectives. When you have completed this subcourse, you should be able to identify the correct procedures for preparing a nonelectric firing system, an electric firing system, and a detonating cord system for the destruction of ammunition. Conditions. You will have this subcourse book and work without supervision. supplementary requirements in material or personnel for this subcourse.
There are no
Standard. You must score at least 70 on the end-of-subcourse examination (answer 9 of the 12 questions correctly). Credit Hours. Three credit hours will be awarded for the successful completion of this subcourse.
v
MM2605 DEMOLITION FIRING SYSTEMS
PREPARING A NONELECTRIC FIRING SYSTEM A nonelectric firing system (figure 1) consists of a fuse igniter, time blasting fuse, and a nonelectric blasting cap. Upon activation, the fuse igniter initiates the time blasting fuse, which transmits the flame that fires the blasting cap. The blasting cap provides a shock adequate to initiate the explosive charge into which the cap has been installed. The tools and equipment needed to assemble the system--a crimper, a computing tape, a watch, time blasting fuse, a fuse igniter, and a nonelectric blasting cap-are shown in figure 2. A threaded priming adapter (figure 3) is required when the system is used with a demolition block that has a threaded cap well. There are six steps in assembling a nonelectric firing system with a demolition block: 1. 2. 3. 4. 5. 6.
Test the burning rate of the time blasting fuse. Inspect the nonelectric blasting cap. Install and crimp the nonelectric blasting cap to the time blasting fuse. Insert the time blasting fuse in the priming adapter (if required). Attach the fuse igniter to the time blasting fuse. Prime the charge.
Figure 1. Nonelectric Firing System. 1
MM2605
Figure 2. Tools and Equipment for Assembling a Nonelectric Firing System.
Figure 3. M1A4 Priming Adapter. 2
MM2605 Step 1: Test the Burning Rate of the Time Blasting Fuse You test burn the time blasting fuse to find out how much fuse you will need to give you time to reach safety after you have activated the firing system. Using the cutting (inside) jaws of the crimper, cut off a six-inch length of fuse from the free end of the roll of time blasting fuse (figure 4) and discard it. This is done to prevent a misfire occurring because moisture has been absorbed from the air by exposed powder in the fuse. Make sure that you cut the fuse square across. Next, use your computing tape to measure three feet of time blasting fuse. Cut it off square across with your crimper. This is the piece you will use to determine the burning rate of the time blasting fuse. Warning: A time blasting fuse with a rough, jagged cut across the end can cause a misfire of the blasting cap.
Figure 4. Cutting Time Blasting Fuse. 3
MM2605
Loosen the fuse holder cap on the M60 fuse igniter and remove the shipping plug (figure 5). Then, insert the three-foot length of time fuse into the fuse igniter as far as it will go and tighten the fuse holder cap. To activate the fuse igniter (figure 6), remove the safety pin and then pull hard on the pull ring. You will hear a snap, which indicates that the fuse igniter has functioned. Use your watch to start timing the burning of the time fuse. (Check the fuse to make sure that it is burning. You should see a little smoke coming from the fuse and smell a burning odor.) When you see flame at the free end of the time blasting fuse (figure 7), stop timing.
Figure 5. Removing the Shipping Plug from the M60 Fuse Igniter.
Figure 6. Activating the M60 Fuse Igniter. 4
MM2605
Once you know how much time it takes to burn a three-foot length of time blasting fuse, you can compute the burning rate. Divide the total burning time by the length of the fuse. This will give you the burning rate per foot. For example, if it took 135 seconds to burn 3 feet of fuse, divide 135 by 3 to get a burning rate of 45 seconds per foot.
Figure 7. Timing the Burning of the Time Blasting Fuse. After you have determined the burning rate of the time blasting fuse, you can determine the length of fuse that will be required for your demolition. To do this, take the time in seconds required for you to walk to the shelter, or someplace a safe distance away from your demolition, and divide it by the burning rate of the time fuse. For example, you need 6 minutes to walk to the shelter. Multiply 6 minutes by the number of seconds in a minute, 60, to get the total time in seconds, 360. Divide 360 seconds by 45 seconds per foot (the burning rate), and you get 8 feet for the length of time blasting fuse you must use in your firing system. Two types of time blasting fuse are presently in use. They are fuse, blasting, time (orange color), which has a burning rate of 30 to 45 seconds per foot, and fuse, blasting, time, M700 (olive drab color, with a single yellow band every 18 inches and a double yellow band every 90 inches), which has a burning rate of 36 to 44 seconds per foot. When you test burn the fuse, any significant difference in the burning rate is cause to discard that roll of fuse and use another one. Warning: Test burning time blasting fuse and crimping a blasting cap to the fuse must be done downwind at a minimum distance of 25 feet from blasting caps or other explosives.
5
MM2605 Step 2: Inspect the Nonelectric Blasting Cap The standard Army nonelectric blasting cap is the cap, blasting, nonelectric, M7 (figure 8). The open end of the M7 blasting cap is flared to make the insertion of fuse easier. Dirt or other foreign matter in a blasting cap can cause a misfire. Remove one nonelectric blasting cap from the cap box, holding the cap by the open end (figure 9). Inspect the cap by looking into the open end. If the cap contains any dirt or foreign matter, hold the cap with the open end down and shake it gently, or follow the procedure shown in figure 10. If the dirt or foreign matter does not come out, dispose of the cap by placing it with the material to be detonated. When handling blasting caps, observe the following safety rules: •
Do not expose caps to heat, flame, or sunlight.
•
Do not drop caps or handle them roughly--by tapping them with a hard object or against a hard object, for example.
•
Never blow into a cap.
•
Do not insert anything into a cap to remove dirt or foreign matter.
•
Do not carry caps loose in pockets--always use a cap box.
Figure 8. Cap, Blasting, Nonelectric, M7. 6
MM2605
Figure 9. Removing a Blasting Cap from the Cap Box.
Figure 10. Removing Dirt or Foreign Matter from a Nonelectric Blasting Cap. 7
MM2605 Step 3: Install and Crimp the Nonelectric Blasting Cap to the Time Blasting Fuse Hold one end of the time blasting fuse up at about eye level and at arm's length away. Gently slip the blasting cap down over the fuse (figure 11) so that the explosive in the cap is in contact with the end of the fuse. Warning: Never force the fuse into the blasting cap. If the fuse is not in contact with the explosive in the cap, a misfire may occur. When the time fuse is properly seated within the blasting cap, grasp the fuse just below the cap with the thumb and middle finger of your less-favored hand (left or right) and place the forefinger over the closed end of the cap. Keep a slight pressure on the closed end of the cap with your forefinger to keep the cap in position. Position the crimper's crimping (outside) jaws (see figure 2) around the cap not more than a quarter of an inch from the open end. Warning: A crimp too near the explosive in the blasting cap may cause detonation. Start the crimp (figure 12) at this time by crimping--tightening the crimping jaws--just enough so that the fuse will not fall out of the cap. After you start the crimp, remove the hand holding the blasting cap. Then, holding the cap and fuse by the crimper at arm's length from your side, complete the crimp
Figure 11. Placing a Blasting Cap over Time Fuse.
8
MM2605 (figure 13). Warning: When crimping a blasting cap, always keep your head turned away from the cap so as to avoid injury if a detonation occurs. Never point the cap toward other personnel or explosives.
Figure 12. Starting the Crimp.
Figure 13. Completing the Crimp.
9
MM2605 Step 4: Insert the Time Blasting Fuse in the Priming Adapter If a priming adapter (figure 3) is used, pass the free end of the time fuse through it so that the threads of the adapter are facing the blasting cap (toward the charge) (figure 14).
Figure 14. Priming Adapter Placement.
Step 5: Attach the Fuse Igniter to the Time Blasting Fuse To attach the M60 fuse igniter to the free end of the time fuse, follow the instructions in step 1 (page 4). Step 6: Prime the Charge Priming the charge consists of attaching the nonelectric firing system to the demolition block to be detonated. Demolition blocks may or may not have threaded cap wells. If they are available, priming adapters should be used to secure nonelectric blasting caps and time blasting fuse to demolition blocks with threaded cap wells. When priming a demolition block that has a threaded cap well and using a priming adapter, carefully place the priming adapter over the blasting cap until the adapter stops (figure 15). Insert the assembly into the threaded cap well of the demolition block (figure 16). Then, screw the priming adapter into the threaded cap well hand-tight to complete priming the charge (figure 17). When priming a demolition block that has a threaded cap well without using a priming adapter, wrap a string around the demolition block tightly near the cap well end and tie it securely. Leave about six inches of loose string on each end after making the tie. Insert the assembly into the threaded cap well of the demolition block. Then, tie the loose ends of the string around the time fuse near the blasting cap. Be careful not to tie the string so tightly that the powder train in the time fuse breaks.
10
MM2605
Figure 15. Priming Adapter Pulled over a Blasting Cap.
Figure 16. Inserting a Nonelectric Firing System into a Demolition Block.
Figure 17. Primed Charge. 11
MM2605
When priming a demolition block that has no cap well, use the pointed leg of the M2 crimper to make a hole in the end of the demolition block large enough to contain the blasting cap (figure 18). Wrap string several turns around the demolition block. Tie it leaving about six inches of loose string on each end. Then, insert the assembly into the cap well you have made. Never try to force a blasting cap into an expedient cap well. If the hole is too small to admit the cap easily, remove the cap and enlarge the hole. Tie the loose ends of string around the time fuse near the blasting cap at the top of the hole with two half hitches.
Figure 18. Making a Cap Well in a Demolition Block with a Crimper.
PREPARING AN ELECTRIC FIRING SYSTEM An electric firing system (figure 19) consists of an electric blasting machine, the firing wire and reel, and an electric blasting cap. When the blasting machine is activated, it generates an electric impulse that travels through the firing wire and cap lead wires to fire the electric blasting cap. Initiation of the cap detonates the explosive charge into which the cap has been inserted. The tools and equipment needed to assemble the electric firing system--a penknife, an M2 crimper, the firing wire and reel, an electric blasting cap, an electric blasting machine M32 or M34, and a blasting galvanometer or the M51 blasting cap test set--are shown in figure 20. There are seven steps in assembling an electric firing system to a demolition block: 1. 2. 3. 4. 5. 6. 7.
12
Test the blasting cap test set or the galvanometer for serviceability. Test the firing wire for shorts and continuity. Test the electric blasting cap for serviceability. Splice the electric blasting cap to the firing wire. Prime the charge. Test the firing circuit. Test operate the blasting machine and connect it to the firing circuit.
MM2605
Figure 19. Electric Firing System.
Figure 20. Tools and Equipment for Assembling an Electric Firing System. 13
MM2605 Step 1: Test the Blasting Cap Test Set or the Galvanometer for Serviceability Either of two instruments can be used to test the electric firing system, the blasting galvanometer or the M51 blasting cap test set. These instruments are used to check circuit continuities by checking the electric blasting cap, the firing wire, the firing wire connections, and any firing wire splices. This test is required to reduce the possibility of misfires. Blasting Galvanometer. The blasting galvanometer consists of a meter with a needle and a scale, a small special silver-chloride dry-cell battery, and two external terminals. When the two external terminals are connected in a closed circuit, the flow of current from the dry-cell battery moves the needle across the scale. To test the blasting galvanometer for serviceability, hold a piece of metal across its two terminals. You can use the crimper for this (figure 21). If this procedure does not cause a wide deflection of the needle on the meter (23 to 25 units), the battery is weak and should be replaced. The galvanometer must be handled carefully and kept dry. It is delicate and must not be opened except to replace a weak battery.
Figure 21. Testing the Blasting Galvanometer.
14
MM2605
The two types of dry-cell batteries authorized for use with the blasting galvanometer are the BA-245/U special silver-chloride dry-cell, 0.9 V total voltage, and the BA-2245/U special silver-chloride dry-cell, 0.9 V total voltage. Warning: Before using the galvanometer, make sure that only the appropriate silver-chloride dry-cell battery is installed. Any other battery may produce enough voltage to detonate blasting caps. Test Set, Blasting Cap, M51. This test set was developed to replace the blasting galvanometer for testing electrical firing circuits. It is a self-contained unit with a magnetotype impulse generator, an indicator lamp, two binding posts, and a handle to activate the generator. To test the M51 blasting cap test set (figure 22), connect a piece of bare wire to the two binding posts. Depress the handle sharply while observing the indicator lamp. If the set is serviceable, the lamp will flash. (Note: Since the M51 blasting cap test set can not discriminate between a firing circuit that is properly set up and one with a short, you must take special care in wiring a circuit to avoid shorting.)
Figure 22. Testing the M51 Blasting Cap Test Set.
Step 2: Test the Firing Wire for Shorts and Continuity The firing wire could be tested on the reel. It must be retested after unreeling, however, because uncoiling may separate broken wire that was undetected when reeled. To preclude testing the firing wire twice for shorts and continuity, unreel the firing wire and lay it from the location of the charges to be detonated (blasting site) to the firing site. 15
MM2605
When using the M51 blasting cap test set to test for shorts, separate the firing wire conductors at both ends. Connect the conductor wires at one end to the test set binding posts and actuate the test set (figure 23). The indicator lamp should not flash. If the indicator lamp does flash, the firing wire has a short circuit. Locate it and repair as required. To test for continuity, twist the firing wire conductors together at one end and connect those at the other end to the test set binding posts. Actuate the test set (figure 24). The indicator lamp should flash. If the indicator lamp does not flash, there is a break in the firing wire. If this happens, locate it and repair as required.
Figure 23. Testing for Shorts Using the M51 Blasting Cap Test Set.
Figure 24. Testing for Continuity Using the M51 Blasting Cap Test Set. 16
MM2605
When using the blasting galvanometer to test for shorts, separate the firing wire conductors at both ends. Touch conductor wires at one end to the galvanometer posts. The needle in the meter should not move (figure 25). If the needle does move, the firing wire has a short circuit. Locate it and repair as required. To test for continuity, twist the firing wire conductors together at one end and touch those at the other end to the galvanometer posts (figure 26). This should cause a wide deflection of the needle (about 23 to 24 units for a 500-foot length of wire). A slight movement of the needle indicates a point of high resistance, which could be caused by several broken strands of multistranded wire or by dirty wires. If there is no movement of the needle, a break in the firing wire is indicated. If this happens, locate and repair the break as required. When testing has been completed, twist the conductor wires together at each end of the firing wire.
Figure 25. Testing for Shorts Using the Blasting Galvanometer.
Figure 26. Testing for Continuity Using the Blasting Galvanometer. 17
MM2605 Step 3: Test the Electric Blasting Cap for Serviceability Each electric blasting cap to be used in an electric firing system must be tested individually for continuity. The cap, blasting, electric, M6 (see figure 27) is the standard Army electric blasting cap and will initiate any standard demolition charge. It is electrically uniform, so any lot of M6 caps may be mixed with any other lot in a firing circuit without fear of misfires. Carefully extend the cap lead wires to their maximum length. Make sure not to disturb or remove the shorting clip. Place the electric blasting cap in a hole, behind a barricade, or under a sandbag, with the lead wires fully extended. You are then ready to test the blasting cap for continuity using either the M51 blasting cap test set or the blasting galvanometer. Warning: When uncoiling blasting cap lead wires, do not hold the cap directly in your hand. Hold the cap by the wires about six inches from the cap. Straighten out the lead wires by hand. Do not throw, wave, or snap the wires to loosen them. Always point the explosive end of the blasting cap away from yourself, other personnel, and explosives. Personnel must use available protective cover and keep their backs toward the blasting cap when caps are being tested for continuity. The distance between personnel and the blasting cap will be the maximum allowed by the length of the lead wires. When using the M51 blasting cap test set, remove the shorting clip from the blasting cap lead wires. Connect the lead wires to the two binding posts on the test set. Squeeze the test set handle. If the indicator lamp flashes, the blasting cap is satisfactory. If the indicator lamp does not flash, the cap is defective and should not be used. Shunt (short) the lead wires by twisting their ends together immediately after testing. Keep them shunted until you connect them to the firing circuit. When using the blasting galvanometer, remove the shorting clip from the blasting cap lead wires. Hold one cap lead wire to one post of the galvanometer and touch the other lead wire to the other
Figure 27. Cap, Blasting, Electric, M6, with Lead Wires and Shorting Clip.
18
MM2605
post. If the blasting cap is satisfactory, the galvanometer needle will deflect slightly less than it did when the instrument was tested (23 to 25 units). Shunt lead wires by twisting their ends together immediately after testing. Step 4: Splice the Electric Blasting Cap to the Firing Wire The ends of the firing wire and the blasting cap lead wires must have the insulation material stripped from them so that the splice can be made. Use a penknife to expose about three inches of bare wire from each end. Remove any foreign matter by carefully scraping the wire with the back of the knife blade. The wires should not be nicked, cut, or weakened when they are bared. Multiple-strand wires of the firing wire should be twisted lightly after scraping. Point the free ends of the lead wires and the free ends of the firing wire in opposite directions (figure 28a). Join the opposite-facing wires with a few tight twists around each other. Bend the remaining ends up, away from the joint (figure 28b). Twist these ends together to form a pigtail at right angles to the connected wires (figure 28c). Push each pigtail to one side so it will lie along one of the wires (figure 28d). Tape each connection to insure complete insulation. If pairs of wires are spliced, stagger the two separate splices. Tie with twine or wrap with friction tape or electrical insulating tape. See figure 28e.
Figure 28. Splicing the Electric Blasting Cap to the Firing Wire.
19
MM2605
Circuit splices that are not insulated should not lie on moist ground. They should be supported on rocks, blocks, or sticks so that only the insulated portions of the wires touch the ground. Warning: Shunt the firing wire at the initiating point before connecting the blasting cap wires to the firing wire. The person making the connection must work as far from the blasting cap as the cap lead wires allow, keeping their back turned to minimize injury in case of a premature detonation.
Step 5: Prime the Charge Basically, the procedures for priming the electric firing system to the demolition charge are the same as those for priming the nonelectric firing system. As with the nonelectric firing system, a priming adapter (figure 3) should be used, if available, to secure the blasting cap to the demolition block. When using a blasting cap with a priming adapter, pass the electric blasting cap lead wires through the slot of the priming adapter, making sure the threaded end of the adapter is toward the cap. Pull the blasting cap into place in the adapter. Then, insert the cap and the priming adapter into the cap well and screw into place (figure 29). When using a blasting cap without a priming adapter, insert the electric blasting cap into the cap well of the demolition block and tie the cap lead wires around the block by two half hitches (figure 30). Allow some slack in the wires between the blasting cap and the tie to prevent any pull on the cap. As an alternate method, use tape to secure the blasting cap inside the demolition block (figure 31). Warning: Never try to force a cap into a cap well that is too small to admit it easily.
Figure 29. Priming a Charge Using a Blasting Cap with a Priming Adapter.
20
MM2605
Figure 30. Priming a Charge Using a Blasting Cap Without a Priming Adapter.
Figure 31. Alternate Method of Priming a Charge Using a Blasting Cap Without a Priming Adapter.
Step 6: Test the Firing Circuit When using the M51 blasting cap test set, move to the firing position and separate the free ends of the firing wire. Connect the free ends of the firing wire to the binding posts of the test set. Depress the handle. The indicator lamp should flash. If it does not, the circuit is defective. Recheck the circuit for shorts or defective splices or wires. (Note: The M51 blasting cap test set will react the same way-lamp will flash--when testing either a properly set-up circuit or a shorted circuit.) When using the blasting galvanometer, move to the firing position and separate the free ends of the firing wire. Touch the free ends of the firing wire to the two terminals on the galvanometer. This should cause a wide deflection of the needle. The degree of deflection will depend upon the number of caps and the length of the firing wire. If the test indicates a break (the needle does not move) or a high resistance (slight movement of the needle), shunt the firing wire and repair wire or connections as required. 21
MM2605 Step 7: Test Operate the Blasting Machine and Connect It to the Firing Circuit The standard blasting machines currently in use are the M32 and the M34 (figure 32). The M32 can initiate 10 electric blasting caps, and the M34 can initiate 50 electric blasting caps. Both machines are the same in size and operation. Testing procedures are also the same. To test either blasting machine for serviceability, free the D ring holding the plunger handle against the machine's body. The plunger is spring-loaded, so the handle is in the ready-to-fire position when freed from the D ring. Give the handle three or four strokes. The neon indicator lamp located within the plastic housing between the two terminals should glow briefly. Connect the blasting machine to the firing circuit by fastening the ends of the firing wire to the two terminals of the blasting machine. To prevent a misfire, before connecting the blasting machine, make sure that all blasting caps are included in the firing circuit; that all connections between the blasting cap wires, connecting wires, and firing wire are properly made; and that the number of blasting caps in any circuit does not exceed the rated capacity of the blasting machine being used. Warning: Do not connect the blasting machine to the firing wire until all prefiring tests have been completed and a signal is received from the supervisor that the area has been cleared of all personnel and equipment.
Figure 32. M32/34 Blasting Machine.
PREPARING A DETONATING CORD SYSTEM A detonating cord system (figure 33) consists of two or more branch lines of detonating cord primed to demolition charges that are connected to the ring main.
22
MM2605
Figure 33. Detonating Cord System. A detonating cord system is used to initiate explosive charges as a component of an electric or nonelectric firing system. If a nonelectric firing system is being used with more than one charge, the detonating cord system is required to insure that the charges fire at the same time. Detonating cord is usable underground or underwater. The initiation of the detonating cord is achieved by an electric or nonelectric blasting cap located above ground or above water. In addition to general safety requirements, the precautions listed below must be followed strictly when using detonating cord: •
Avoid kinks and sharp bends.
•
Handle with special care to avoid breaking the outside covering or the explosive train inside.
•
Lay out lines as straight as possible, but not stretched taut. Detonating cord forms a spiral as it is unwound from the spool. It must be straightened out carefully before firing to avoid a misfire.
•
Do not remove any part of the outer covering.
•
Insure that branch lines and the ring main touch only at the connections when making branch line connections.
•
Make the angle formed by the branch lines and the cap end (initiating point) of the ring main at least 90 degrees. At a smaller angle, the branch lines may blow off the ring main without detonating.
There are four steps in assembling a detonating cord system: 1. 2. 3. 4.
Lay the ring main. Lay the branch lines and connect them to the ring main. Prime the charges. Attach the firing system. 23
MM2605 Step 1: Lay the Ring Main Use the cutting jaws of the M2 crimper to cut six inches from the free end of the detonating cord. Discard it. This will prevent misfires caused when exposed explosive absorbs moisture from the air. To lay the ring main, place the main line (detonating cord on the ground) from the point of initiation (where either firing system will be attached) and pass it near each charge to be detonated. Then, bring the main line back to the point of initiation in the form of a loop. If you do not have enough detonating cord left on the spool to complete the ring main, get another spool of cord and splice it to the ring main using one of the methods that follow. Splice Using the Clip, Cord, Detonating, M1. The M1 detonating cord clip (figure 34) is a steel device used to hold two strands of detonating cord together parallel or at right angles to each other. Connections are made more quickly with these clips than with knots. Cut and discard 6 inches from the ends of the detonating cords to be joined. Overlap the free ends of the cords by 12 inches. Take two detonating cord clips and place the overlapping ends of the detonating cords in the tongues, making sure the clips are separated by 6 inches (figure 35). Bend the tongues over both ends firmly. The connection is made secure by bending the troughs back over the tongues.
Figure 34. Clip, Cord, Detonating, M1.
Figure 35. Splice Using Detonating Cord Clips.
24
MM2605 Splice Using the Connector, Detonating Cord. The detonating cord connector (figure 36) is a cylinder made of either white or blue plastic molding material. It may be used to connect detonating cords end to end or at right angles. It may also be used to fasten a blasting cap, either electric or nonelectric, to the detonating cord. Pass one free end of detonating cord through the connector from the slotted end, leaving six inches of cord extending beyond the opposite end. Take the other detonating cord and bend its free end back parallel with the rest of the cord. Insert it through the connector from the opposite end until it is all the way through and its free end extends at least six inches beyond the end of the connector (figure 37). Splice Using a Knot. If detonating cord connectors or clips are not available, the splice can be completed with a square knot. When a square knot is used, at least six inches of detonating cord should be left free beyond the tie (figure 38).
Figure 36. Connector, Detonating Cord.
Figure 37. Splice Using the Detonating Cord Connector. 25
MM2605
Figure 38. Splice Using a Square Knot.
Step 2: Lay the Branch Lines and Connect Them to the Ring Main Lay the branch lines (detonating cord) from where the charges are located to the ring main. Leave enough line so that the charge can be primed and the connection made to the ring main. The branch lines should be positioned so that the angle formed when they are connected to the ring main will be 90 degrees (a right angle). When making branch line connections to the ring main, never connect at a point where the ring main has been spliced. Connecting the branch lines to the ring main may be accomplished by any of the methods that follow. Detonating Cord Clip Method. Pass the free end of the branch line through the trough of the M1 detonating cord clip so that the line extends six inches beyond the tongue. Slide the ring main into the tongue of the clip. Secure the connection by bending the trough and the tongue of the clip against the cords (figure 39). Detonating Cord Connector Method. Pass the free end of the branch line through the unslotted end of the connector. Wrap the branch line around the ring main and reinsert the free end back through the connector from the slotted end. Place the ring main in the detonating cord holes. Pull the branch line tight against the ring main, making sure that the free end extends six inches beyond the end of the connector (figure 40). Knot Method. If detonating cord connectors or clips are not available, the connection can be made with a girth hitch with one extra turn (figure 41). At least six inches should be left free beyond the tie. The free end of the girth hitch should be on the opposite side of the branch line from the initiating point on the ring main.
26
MM2605
Figure 39. Branch Line Connection Using the M1 Detonating Cord Clip.
Figure 40. Branch Line Connection Using the Detonating Cord Connector.
Figure 41. Branch Line Connection Using a Girth Hitch with One Extra Turn. 27
MM2605 Step 3: Prime the Charges The charges may be primed by a capped detonating cord (above-ground charges only) or by wrapping the charge directly with noncapped detonating cord using one of the three methods shown in figure 42 and described on page 29. (The procedures for using capped detonating cord are the same as those used for capped time blasting fuse. Handling and inspecting nonelectric blasting caps and priming charges having a threaded cap well with or without a priming adapter have also been covered earlier in this subcourse.)
Figure 42. Noncapped Detonating Cord Priming. 28
MM2605 Method 1. Tie the detonating cord securely around the charge using a clove hitch with two extra turns. Fit the cord snugly against the charge and push the loops close together. Method 2. Place a loop of detonating cord on the charge and wrap detonating cord around the charge four times. Draw the free end of the detonating cord through the loop and pull until tight. Method 3. Lay detonating cord at an angle across the charge. Wrap the free end over the cord and around the charge three times. At the fourth turn, slip the free end under the three wraps and parallel to the cord laid at an angle. Draw tight. Step 4: Attach the Firing System The detonating cord system is initiated by an electric blasting cap when an electric firing system is used, and by a nonelectric blasting cap when a nonelectric firing system is used. The blasting cap of either firing system is attached to the detonating cord system at the initiation point using one of the methods described below and on page 30. Using the M1 Detonating Cord Clip. Place the blasting cap in the tongue of the clip. Then, place the free end (initiation point) of the detonating cord system in the tongue beside the cap. Make sure the free end of the detonating cord extends six inches beyond the crimped or wire end of the blasting cap. Press down firmly on the tongue. Secure by bending the trough over the tongue. See figure 43.
Figure 43. Attaching a Blasting Cap to the Detonating Cord System Using an M1 Detonating Cord Clip. Using the Detonating Cord Connector. Pass the free end (initiation point) of the detonating cord through the connector from the slotted end. Then, bend the free end back parallel with the rest of the cord and pass it back through the connector to extend six inches beyond the end of the connector. Insert the blasting cap into the connector from the slotted end. This will secure the connection. See figure 44.
29
MM2605
Figure 44. Attaching a Blasting Cap to the Detonating Cord System Using a Detonating Cord Connector. Using Electrical or Friction Tape. Bend the free end (initiation point) of the detonating cord back parallel with the rest of the cord and place the blasting cap on top of the two parts. Secure the blasting cap by making several wraps around the two strands of cord and the blasting cap with electrical or friction tape. Make sure that the free end of the cord extends six inches beyond the tie. See figure 45.
Figure 45. Attaching a Blasting Cap to the Detonating Cord System Using Tape. 30
MM2605 REVIEW EXERCISES Circle the letter of the correct answer to each question. 1. What are the three components of the nonelectric firing system? a. Fuse igniter, time blasting fuse, and electric blasting cap. b. Fuse igniter, time blasting fuse, and nonelectric blasting cap. c. Fuse igniter, priming adapter, and electric blasting cap. d. Fuse igniter, priming adapter, and nonelectric blasting cap. 2. How many feet of time blasting fuse are required for timing the burn rate? a. Three feet. b. Four feet. c. Five feet. d. Seven feet. 3. When a priming adapter is used with the nonelectric firing system, in which direction should the threaded end be? a. Away from the charge. b. Toward the charge. c. Behind the charge. d. To the left of the charge. 4. You are inspecting a nonelectric blasting cap and you find foreign matter inside that will not come out. How should you dispose of the cap? a. Place the cap with the material to be detonated. b. Place the cap in water and burn it. c. Detonate the cap immediately upon discovery of the foreign matter. d. Place the cap in a solution of sodium sulfide and detonate it. 5. When crimping a nonelectric blasting cap to time fuse, how do you hold the time fuse? a. With the thumb and middle finger of favored hand. b. With the thumb and middle finger of less-favored hand. c. With the thumb and index finger of less-favored hand. d. With the thumb and index finger of favored hand. 31
MM2605
6. What are the two testing instruments used in testing the electric firing system? a. Blasting machine and dry-cell battery. b. Test set AN/TJM-1A and blasting galvanometer. c. Blasting galvanometer and M51 blasting cap test set. d. Test set A/E 24T-80 and blasting galvanometer. 7. What is indicated if the indicator lamp does not flash when you are testing the firing wire for shorts using the M51 test set? a. Separated conductors. b. Loose conductors. c. There are no shorts in the firing wire. d. A break in the firing wire. 8. Can any lot of M6 electric blasting caps be mixed in a firing circuit without fear of a misfire? a. Yes. b. No. c. Maybe. 9. How many inches of bare wire must be exposed on the ends of the electric blasting cap lead wires to make a splice? a. About two inches. b. About three inches. c. About four inches. d. About five inches. 10. What is the alternate method of priming a charge with an electric blasting cap without a priming adapter? a. Use tape to secure the blasting cap to the cap well to prevent blasting cap withdrawal. b. Use tape to secure the blasting cap outside of the demolition block. c. Use the blasting cap holder, M8 to secure the blasting cap to the demolition block. d. Use detonating cord clip, M1 to secure the blasting cap to the demolition block.
32
MM2605
11. What type of knot is used when making a branch line connection to the ring main in a detonating cord system? a. A square knot. b. A clove hitch. c. Two half-hitches. d. A girth hitch with an extra turn. 12. When using the detonating cord connector to attach an electric or nonelectric firing system to the detonating cord system, in which end of the connector is the blasting cap inserted? a. Slotted end. b. Open end. c. Flared end. d. Smaller end. Go back over the questions and recheck your answers. When you are satisfied that you have answered every question to the best of your ability, check your answers against the Exercise Solutions. If you missed four questions or more, you should retake the entire subcourse, paying particular attention to the areas in which your answers were incorrect.
33
MM2605 EXERCISE SOLUTIONS
1. b (see page 1) 2. a (see page 3) 3. b (see page 10) 4. a (see page 6) 5. b (see page 8) 6. c (see page 14) 7. c (see page 16) 8. a (see page 18) 9. b (see page 19) 10. a (see page 20) 11. d (see page 26) 12. a (see page 29)
37
