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DEPARTMENT OF THE ARMY FIELD MANUAL ----------------------------------------------------------------------------- Explosives and Demolitions extract. ----------------------------------------------------------------------------- HEADQUATERS, DEPARTMENT OF THE ARMY February 1971 Typed by:Death Jester. Chaper 2 FIRING SYSTEMS ----------------------------------------------------------------------------- Section I. NONELECTRIC FIRING SYSTEMS 2-1. Introduction Two types of systems for firing explosives are in general use--electric and nonelectric. Both have their individual priming methods and materials. In addition, detonating cord may be used with both systems to make them more efficient and effective, as described in paragraphs 2-10 through 2-16. 2-2. System Components and Assembly for Detonation A nonelectric system is one in which an explosive charge is prepared for detonation by means of a nonelectric blasting cap. The basic priming materials consist of a nonelectric blasting cap, which provides the shock adequate to detonate the explosives, and the time blasting fuse, which transmits the plame that fires the blasting cap. If more than one charge must be detonated simultaneously, the nonelectric system must be combined with a detonating cord (para 2-10 - 2-12) to insure simultaneous firing. The assembly of a basic nonelectric system follows. a. Cut and discard a 6-inch length from the free end of the time blasting fuse to prevent a misfire caused by the exposed powder absorbing moisture from the air (A, fig 2-1). Then cut off a three foot length of time blasting fuse to check the burning rate. Split the end of the fuse, insert a match head into the split, light the match with another match and note the time it takes for the fuse to burn. Then compute the burning rate per foot by dividing the time in seconds by the length in feet. b. Cut the time blasting fuse long enough to enough permit the person detonating the charge to reach a safe distance by walking at a normal pace before the eplosion. This cut should be made squarely across the time fuse. c. Take on blasting cap from the cap box, inspect it by looking into the open end. If any foreign matter or dirt is present, hold it with the open end down, and shake it gently or bump the hand holding it against the other hand. IF FOREIGN MATTER DOES NOT COME OUT, DISCARD CAP. NEVER TAP THE CAP WITH A HARD OBJECT OR AGAINST A HARD OBJECT. NEVER BLOW INTO THE CAP. DO NOT INSERT ANYTHING INTO THE CAP TO REMOVE AND DIRT OR FOREIGN MATERIAL. d. Hold the time blasting fuse vertically with the square cut end up and SLIP TH BLASTING CAP GENTLY DOWN OVER IT SO THAT THE FLASH CHARGE IN THE CAP IS IN CONTACT WITH THE END OF THE TIME FUSE; IF NOT IN CONTACT, IT MAY MISFIRE. NEVER FORCE THE TIME FUSE INTO THE BLASTING CAP BY TWISTING OR ANY OTHER METHOD. If the end is flattened or it is too large to enter the blasting cap freely, roll it between the thumb and fingers until the size is reduced to permit free entry. e. After th blasting cap has been seated, grasp the time blasting fuse between the thumb and third finger of the left hand and extend the forefinger over the end of the cap to hold it firmly against the end of the time fuse. Keep a slight pressure on the closed end of the cap with the forefinger (B, fig 2-1). f. Slide the second finger down the outer edge of the blasting cap to guide the crimpers (B, fig 2-1), and thus obtain accurate crimping, even in darkness. g. Crimp the blasting cap at a point 1/8 to 1/4 of an inch from the open end. A CRIMP TOO NEAR THE EXPLOSIVE IN THE BLASTING CAP MAY CAUSE DETONATION. POINT THE CAP OUT AND AWAY FROM THE BODY DURING CRIMPING (fig 2-2). Note. If the blasting cap should remain in place several days before firing, protect the joint between the cap and the time blasting fuse with a coating of a sealing compound or some similar substance. (As this sealing compound (para 1-50), a standard issue, does not make a waterproof seal, submerged charges should be fired immediately.) h. Pass the end of the time blasting fuse through the priming adapter. (The time fuse should move through the adapter easily.) Then pull the cap into the adapter until it stops, instert into the cap well of the the explosive, and screw the adapter in place. If no priming adapter is available, insert the blasting cap into the cap well and tie it in place with a string or fasten it with adhesive tape or some other available material. (For details of nonelectric priming of demolition blocks, see para 2-18). Note. For long lengths of time blasting fuse it may be more conveinent to pass the end of the fuse through the priming adapter before crimping the cap onto the the time fuse. i. Attach M60 weatherproof fuse igniter (para 1-57n) as follows: (1) Unscrew the fuse holder cap two or three turns but do not remove. Press the shipping plug into the igniter to release the split collet (fig 1-47), and rotate the plug as it is removed. (2) Insert the free end of the time fuse in place of the plug until it rests against the primer. (3) Tighten the cap sufficiently to hold the fuse in place and thus weatherproof the joint. (4) To fire, remove the saftey pin, hold the barrel in one hand, and pull on the pull ring with the other, taking up the slack before making the final strong pull. In the event of a misfire, the M60 can be reset quickly without disassembly by pushing the plunger all the way in and attempting to fire as before. (It cannot be reset underwater however, because water can enter the interior of the nylon case through the holes in the pull rod. The fuse igniter is reusable if the primer is replaced.) Note. The M2 weatherproof fuse igniter (fig 1-46) may be attached by sliding the fuse retainer over the end of the fuse, firmly seating it, and applying sealing compound at the joint betwwen the time blasting fuse and the igniter to protect the open end of the fuse from moisture. In firing, hold the barrel in one hand and pull on the other ring with the other. j. If a fuse igniter is not abailable, light th time blasting fuse with a match by splitting the fuse at the end (fig 2-3), placing the head of an unlighted match in the powder train, and then light the inserted match head with a flaming match or by rubbing the abrasive on the match box against it. 2-3. Nonelectric Misfires a. PREVENTION. Working on or near a misfire is the most hazardous of all blasting operations. A misfire should be extremely rare if these procedures are followed closely: (1) Prepare all primers properly. (2) Load charges carefully. (3) Place primer properly. (4) Perform any tamping operation with care to avoid damage to an otherwise carefully prepared charge. (5) Fire the charge according to the proper technique. (6) If possible, use dual firing systems (para 2-13 - 2-16). If both systems are properly assembled, the possibility of a misfire is reduced to a minimum. (7) Do not use blasting caps underground; use detonating cord. b. THE CLEARING OF NONELECTRIC MISFIRES. Occasionally, despite all painstaking efforts, a nonelectric misfire will occur. Investigation and correction should be undertaken only by the man that placed the charge. For a charge primed with a nonelectric cap and time blasting fuse, the procedure is as follows: (1) Delay the investigation of the misfire at least 30 minutes after the expected time of detonation. This should be ample time for any delayed explosion to take place because of a defective powder train in the fuse. Under certain combat conditions, however, immediate investigation may be necessary. (2) If the misfired charge is not tamped, lay a primed one-pound charge at the side of the charge, without moving or disturbing it, and fire. (3) If the misfired charge has no more than a foot of tamping, attempt to explode it by detonating a new 2-pound charge placed on top. (4) If the misfired charge is located in a tamped borehole, or if the tamped charge is so situated as to make method (3) above impractical, carefully remove the tamping by means of wooden or nonmetallic tools. Avoid accidentally digging into the charge. Also, the tamping may be blown out by means of a stream of compressed air or water if either is abailable. Constant checking of the depth of the borehole from the ground surface to the top of the charge during digging will minimize the danger of striking the charge. When the charge has been uncovered within 1 foor, insert and detonate a new 2-pound primer. Whenever possible, detonating cord should be used to prime underground charges and the blasting cap located above ground (see para 2-10 - 2-12). (5) An alternate method of reaching a deep misfire charge is to drill a new hole withing one foot of the old one and to the same depth a new 2-pound primed charge is then placed in the new hole to detonate the misfired charge. Extreme care is required in drilling the new hole to avoid striking the old misfired charge or placing the new charge too far away to induce detonation. Section II. ELECTRIC FIRING SYSTEMS 2-4. Components and Assembly for Detonation An electric firing system is one in which electricity is used to fire the primary initiating element. An electric impulse supplied from a power source, usually an electric blasting machine, travels through the firing wire and cap lead wires to fire an electric blasting cap. The chief components of the system are the electric blasting cap, firing wire, and the blasting machine. Detailed information about electric blasting equipment is contained in TM 9-1375-203-15. The preparation of the explosive charge for detonation by electric means is called electric priming. The proper methods and sequence of operations of electric priming are described below. a. Place Charges. Prepare and place all explosive charges as prescribed by the methods in chapter 3. (Details of preparing demolition blocks for electric priming are given in para 2-18.) b. Lay Out Firing Wire. (1) After locating a firing position a safe distance away from the charges, lay out the firing wire from the charges to the firing position. (2) Test the free ends of the firing wire together to prevent an electric charge from building up in the firing wire. (3) Twist the free ends of the firing wire together to prevent an electric charge from building up in the firing wire. c. Test Blasting Caps. (1) Test each blasting cap to be used in the electric firing system as described in paragraph 2-7. (2) After each cap has been tested, twist the free ends of the cap lead wire together or shunt them with the short circuit shunt provided to prevent an electric charge from building up in the cap lead wires. d. Connect Service Circuit. (1) If two or more electric blasting caps are used, connect their lead wires into one of the two series circuits described in paragraph 2-6. (2) If more than 10 blasting caps are used in the series circuit, or if the circuit is complicated, it should be tested with the test set or galvanometer (para 2-7). (3) Splice the free cap lead wire to the firing wire. e. Insert Caps Into Charges. Place the blasting caps into the explosive charges and fasten the caps securely to the charges (fig 2-4). (For details of electric priming of demolition blocks see para 2-18). f. Test Entire Circuit. (1) Move to the firing position and test the entire firing circuit with the test set or galvanometer as described in paragraph 2-7. (2) Twist the free ends of the firing wire together. g. Test Blasting Machine. Test operate the blasting machine several times as outlined in TM 9-1375-203-15 to insure that it operates properly. h. Connect Blasting Machine. (1) Untwist the free ends of the firing wire and fasten them to the two posts of the blasting machine. (2) Operate the blasting machine to fire the charges. i. Precautions. (1) TWO OR MORE CAPS. If two or more electric blasting caps are connected in the same circuit, be sure that they are of the same type and made by the same manufacturer. This is essential to prevent misfires, as blasting caps of different manufacturers have different electrical characteristics which can result in some caps in the circuit not firing because others fire more quickly and thus break the circuit before the slower caps have received enough electricity to fire. This is not true, however, of the M6 special electric blasting caps--all of which are made according to the same specifications. Blasting caps of the same manufacturer may be identical by the label, color of the cap, or shape of the shunt. (2) FIRING THE CIRCUIT. For safety reasons, only one individual should be detailed to connect the blasting machine to the firing circuit and to fire the circuit. He should be responsible for the care and security of the blasting machine at all times during blasting activities. He also should either connect the blasting wires in the circuit or check their connection by on-the-spot visual examination. 2-5. Splicing Electric Wires Insulated wires, before splicing must have the insulating material stripped from the ends. Expose about 3 inches of bare wire (fig 2-5), and remove any foreign matter such as enamel by carefully scraping the wire with the back of a knife blade or other suitable tools. The wires should not be nicked, cut, or weakened when the wires are bared, and multiple strand wires should be twisted lightly after scraping. a. SPLICING METHOD. Two wires, which have been prepared as described above, may be spliced as shown in figure 2-5. THis is called the Western Union "pigtail" splice. Two pairs of wires are spliced in the same manner as the two wire splice above. One wire of one pair is spliced to one wire of the other pair, and the process is repeated for the other two wires. b. PRECAUTIONS FOR SPLICING. A short circuit may ovvur very easliy at a splice if certain precautions are not observed. If pairs or wires are spliced, stagger the two separate splices and tie with twine or tape as in (1), figure 2-6. An alternate method of preventing a short circuit at the point of splice is shown in (2), figure 2-6. The splices are separated, not staggered, in the alternate method. Whenever possible insulate splices from the ground or other conductors by wrapping them with friction tape or othe electric insulating tape. This is particularly necessary when splices are place under wet tamping. Circuit splices, not taped or insulated, should not lie on moist ground. The splices should be supported on rocks, blocks, or sticks so that only the insulated portions of the wires touch the ground. THey may also be protected by inserting them to hold the splice firmly inside. Splices may be protected from damage from pull by tying the ends in an overhand or square knot, allowing sufficient length for each splice ((1), fig 2-5). 2-6. Series Circuits a. COMMON SERIES. This is used for connecting two or more charges fired electrically by a single blasting machine (A, fig 2-7). A common series circuit is prepared by connecting one blasting cap lead wire from the first charge to the once lead wire in the second charge and so on until only two end wires are free, then connecting the free ends of the cap lead wires to the ends of the firing. Connecting wires (usually annunciator wire) are used when the distance between blasting caps is greater than the length of the usual cap lead wires. b. "LEAPFROG" SERIES. The "leapfrog" method of connecting caps in series (B, fig 2-7) is useful for firing ditching charges or any long line of charges. It consists of ommitting alternate charges on the way and then connecting them to form a return path for the electric impulse to reach the other lead of the firing wire. This brings both end wires out at the same end of the line of charges, and thus eliminates laying a long return lead from the far end of the line charges back to the firing wire. 2-7. Testing Electric Wires, Blasting Caps and Circuits a. FIRING WIRE MAY BE TESTED AS FOLLOWS: (1) When using M51 blasting cap test set: (a) Check test set by connecting the posts with a piece of bare wire (para 1-54)(fig 2-8). Th indicator lamp should flash when the handle is squeezed. (b) Separate the firing wire conductors at bothe ends, and connect these at one end to the test set binding posts. Actuate test set. The indicator lamp should not flash. If it does, the firing wire has a short circuit (fig 2-9). (c) Twist the wires together at one end and connect those at the other end to the test set posts. Actuate test set. The indicator lamp should flash. If it does not flash, the firing wire has a break. (2) When using the blasting galanometer: (a) Check galvanometer by holding a piece of metal across its terminals (para 1-53, fig 2-8). If the batter is good, this should show a wide deflection of the needle, approximately 25 units (zero ohms). (b) Separate the firing wire conductors at bothe ends, and touch those at one end to the galvanometer posts. The needle should not move. If it does, the firing wire has a short circuit (fig 2-9). (c) Twist the wires together at one end and touch those at the other end to the galvanometer posts. This should cause a wide deflection of the needle (about 6.5 ohms or 23 to 24 units for a 500-foot length). (See note at end of d(2), below.) No movement indicates a point of break; a slight movement indicates a point of high resistance whcih may be cause by a dirty wire, loos wire connections, or wires with several strands broken off at connections. Note. Firing wire may be tested on the reel, but should be tested again after unreeling, which may separates broken wires unnoticed when reeled. b. Electric Blasting Caps May be Tested as Follows: (1) When using the M51 blasting cap test set: (a) Check the test set as described above. (b) Remove the short circuit shunt from the lead wires of the electric blasting cap. (c) Attach one cap lead wire to one binding post and tie other cap lead wire to the other post, and squeeze the test set handle. If the indicator lamp flashes, the blasting cap is satisfactory. If it does not flash, the cap is defective and should not be used. During the tes, ALWAYS POINT THE EXPLOSIVE END OF THE BLASTING CAP AWAY FROM THE BODY. (2) When using the blasting galvanometer: (a) Check the galvanomter as described above. (b) Remove the short circuit shunt. (c) Touch one cap lead wire to one galvanometer post and the cap lead wire to the other. If the galvanometer's needle deflects slightly less than it did when instrument was tested ((a) above) the blasting cap is satisfactory; if not, the cap is defective and should not be used. During the test, ALWAYS POINT THE EXPLOSIVE END OF THE CAP AWAY FROM THE BODY. Note. If the battery is fresh, the galvanometer should read 25 units (zero ohms) when the instrument is tested and about 24 units (about 2 ohms) when a good blasting cap is tested. c. Series Circuits May Be Tested as Follows: (1) Connect charges as shown in figure 208 (either method). (2) When using the M51 blasting cap test set, connect the free ends of the blasting caps lead wires to the test set binding posts. THe indicator lamp should flash. (3) When using the blasting galvanometer, touch the free ends of the blasting cap lead wires to the galvanomter posts. This should cause a wide deflection of the needle. d. The Entire Circuit May be Tested as Follows: (1) Splice firing wires to series circuit and move to firing position. (2) When using the blasting cap test set connect the free ends of the firing wire to the binding posts. The indicatior lamp should flash. If the lamp does not flash, the circuit is defective. Note. Since the M51 test set cannot discriminate between a firing circuit that is properly set up and once with a short in it, special care must be taken in wiring the circuit to avoid shorting. (3) When using the galvanometer touch the free ends of the firing wire to the galvanometer posts. This should cause a wide deflectction of the needle. The magnitude of the deflection depends upon the number of caps and the length of the firing wire. If there is no deflection, the circuit is defective. See appendix E for calculation of circuit resistance. Note. To get a "wide deflection of the needle" the galvanometer battery should be in good condition (para 1-53). (4) If the firing circuit is defective, shunt wires, Then go down range and recheck the circuit, repeating a and b above. If a splice is found defective, resplice the wires. If a cap is found defective, replace it. Continue to test all caps and wire in the circuit, then test the entire circuit again to make sure that all breaks have been located before attempting to fire the charge. 2-8. Electric Misfires a. PREVENTION OF ELECTRIC MISFIRES. In order to prevent misfires, make one individual responsible for all electrical wiring in a demolition circuit. He should do all splicing to be sure that-- (1) All blasting caps are included int the firing circuit. (2) All connections between blasting cap wires, connecting wires, and firing wires are properly made. (3) Short circuits are avoided. (4) Grounds are avoided. (5) The number of blasting caps in any circuit does not exceed the rated capacity of the power source on hand. b. CAUSE OF ELECTRIC MISFIRES. Common specific causes of electric misfires include-- (1) Inoperative or weak blasting machine or power source. (2) Improperly-operated blasting machine or power source. (3) Defective and damaged connections causing either a short circuit, a break in the circuit, or high resistance with resulting low current. (4) Faulty blasting cap. (5) The use in the SAME CIRCUIT of blasting caps (other than M6) made by different manufacturers. (6) The use of more blasting caps than the power source rating permits. c. CLEARING ELECTRIC MISFIRES. Because of the hazards of burning charges and delayed explosions, electric misfire must be cleared with extreme caution. A burning charge may occur with the use of electric as well as nonelectric caps. Misfires of charges primed with detonating cord fired by electric blasting caps are cleared as described in paragraph 2-12. If the charge is dual-primed electrically and below ground, wait 30 minutes before investigating to make sure that the charge is not burning; or if dual-primed above ground, wat 30 minutes before investigation because a burning charge can set off the second cap causing the main charge to detonate. On the other hand, if the electric misfire is above ground and the charge is not dual-primed, investigate immediately. If the system is below ground and not dual primed, proceed as follows-- (1) Check the firing wire connection to the blasting machine or power source terminals to be sure the contacts are good. (2) Make two or three more attempts to fire the circuits. (3) Attempt to fire again, using another blasting machine or power source. (4) Disconnect the blasting machine firing wire and wait 30 minutes before further investigation. Before moving on to the charge site, be sure that the firing wires at the power source end of the circuit are shunted to aboid any posible static electric detonation. (5) Check the entire circuit, including the firing wire, for breaks and short circuits. (6) If the faul is not above ground, remove the tamping material very carefully from the borehole to avoid striking the electric blasting cap. (7) Make not attempt to remove either the primer or the charge. (8) If the fault is not located by the removal of the tamping material to withing 1 foot of the charge, place a new electric primer and 2 pounds of explosive at this point. (9) Disconnect the blasting cap wires of the original primer from the circuit, and short the cap's lead wires. (10) Connect the wires of the new primer in their place. (11) Replace the tamping material. (12) Initiate detonation. Detonation of the new primer will fire the original primer. Note. In some cases it may be more desirable or expedient to drill a new hole withing a foot of the old one at the same depth to avoid accidental detonations of the old charge and then place and prime a new 2-pound charge. 2-9 Premature Detonation by Induced Currents and Lightning a. INDUCED CURRENTS. The premature detonation of electric blasting caps by induced curret from radio frequency signals is possibl. Table 2-1 showing the minimum safe distance in respect to transmitter power, indicates the distance beyond which it is safe to conduct electrical blasting even under the most adverse conditions. This table applies to operating radio, radar, and television transmitting equipment. Mobile type transmitters and portable transmitters are prohibited within 50 meters of any elctrical blasting caps or electrical firing system. If blasting distances are less than those shown in table 2-1, the only safe procedure is to use a nonelectric system, which cannot be prematurely detonated by RF currents. If however the use of the electric systme is necessary, follow precautions given in TM 9-1300-206. See also AR 385-63. Caution. If electric blasting caps are to be transported near operating transmitters or in vehicles (including helicopters) in which a transmitter is to be operated, the caps will be placed in a metal can, the cover of which must be snug fitting and lap over the body of the can to a minimum depth of one-half inch. Caps will not be removed from container in proximity to operating transmitter unless the hazard has been evaluated and estimated to be acceptable. b. LIGHTNING. Lightning is a hazard to both electric and nonelectric blasting charges. A strike or a nearby miss is almost certain to initiate either type of system. Lightning strikes, even at remote locations, may cause extremely high local earth currents. The effects of remote lightning strikes are multiplied by proximity to conducting elements, such as those found in buildings, fences, railroads, bridges, streams, and underground cables or conduct. Thus, the only safe procedure is to suspend all blasting activities during electrical storms and when one is impending. c. ELECTRIC POWER LINES. Electric firing should not be performed within 155 meters of energised power transmission lines. When it is necassary to conduct blasting operations at distances closer than 155 meters to electrical power lines, nonelectric fire systems should be under or the power lines deenergized (AR 385-63). table 2-1: ______________________________________________________________ Average or peak ! Minimum distance transmitting power ! to transmitter(meters) ______________________________________________________________ ! 0-30 ! 30 30-50 ! 50 50-100 ! 110 100-250 ! 160 250-500 ! 230 500-1000 ! 305 1000-3000 ! 480 3000-5000 ! 610 5000-20000 ! 915 20000-50000 ! 1530 50000-100000 ! 3050 _______________________________!______________________________ 2-10. Methods of Use Of all firing systems for explosives, a detonating cord firing system is probably the most versatile and in many cases the most easily installed. It is especially applicable for underwater and underground blasting because the blasting cap of the initiating system may remain above the water or ground. a. An electric system consisting of an electric blasting cap, initiated by a blasting machine or other power source, or a nonelectric blasting cap initiated by a fuse igniter and a length of time blasting fuse, is used to detonate the cord. b. The blasting cap, electric or nonelectric, is attached to a point 6 inches from the free end of the detonating cord by numerous wraps of string, wire, cloth, or tape. 2-11. Detonating Cord Connections A detonating cord clip (fig 1-33) or square knot pulled tight is used to splice the ends of detonating cord. At least a 6-inch length should be left free at both sides of the knot (fig 2-10). When fabric is used to cover the detonating cord, the fabric must not be removed. The knot may be placed in water or in the ground but the cord must be detonated from a dry end. a. BRANCH LINE CONNECTIONS. A branch line is fastened to a main line by means of a clip (fig 1-33) or a girth hitch with one extra turn (fig 2-11). The angle formed by the branch line and the cap end of the main line should not be less than 90 degrees from the direction from which the blast is coming; at a smaller angle, the branch may be blown off the main line without being detonated. At least 6 inches of the running end of the branch line is left free beyond the tie. b. RING MAIN. A ring main is made by bringing the main line back in the form of a loop and attaching it to itself with a girth hitch with one extra turn (fig 2-12). This will detonate an almost unlimited number of charges. The ring main makes the detonation of all charges more postitive because the detonating wave approaches the branch lines from both directions and the charges will be detonated even when there is one break in the ring main. Branch line connections should be made perpendicular to the ring main. Kinks in lines should be avoided, and curves and angles should not be sharp. Any number of branch lines may be connected to the ring main, but a branch line is never connected at apoint where the ring main is spliced. In making detonating cord branch line connections, avoid crossing lines. However, if this is necessary, be sure to have at least one foot of clearance at all points between the detonating cords; otherwise, the cords will cut each other and destroy the firing system. 2-12. Detonating Cord Misfires a. FAILURE OF NONELECTRIC BLASTING CAP. If a nonelectric blasting cap attached to detonating cord fails to function, delay the investigation for at least 30 minutes. Then cut the detonating cord main line between the blasting cap and the charge, and fasten a new blasting cap on the detonating cord. b. FAILURE OF ELECTRIC BLASTING CAP. If an exposed electric blasting cap fastened to detonating cord fails to fire, disconnect the blasting machine immediately and investigate. Test the blasting circuit for any breaks or short circuit. Short the firing wire leads before leaving firing position to correct the problem. If necessary, replace the original blasting cap. c. FAILURE OF DETONATING CORD. If detonating cord fails to function at the explosion of an exposed electric or nonelectric blasting cap, investigate immediately. Attach a new blasting cap to the detonating cord, taking care to fasten it properly. d. FAILURE OF BRANCH LINE. If the detonating cord main line detonates but a branch line fails, fasten a blasting cap to the branch line and fire it seperately. e. FAILURE OF CHARGE TO EXPLODE. If the charge is above ground, and the detonating cord leading to a charge detonates but the charge fails to explode, delay the investigation until it is certain that the charge is not burning. If the charge is intact, insert a new primer. If the charge is scattered by the detonation of the original charge as possible, place a new charge if necessary, and reprime. Make every attempt possible to recover all explosives scattered by misfire, particularly those used in training exercises. Section IV. DUAL FIRING SYSTEMS 2-13. Introduction There is always a certain amount of danger to personnel investigating misfires. Since dual priming increases greatly the probability of successful, firing, it should be used whenever possible. Dual priming consists of two complete systems independent of each other, and each capable of firing the same charge. It can be two electric systems, two nonelectric systems. Or an electric and nonelectric system. 2-14. Nonelectric Dual Firing Systems This consists of two independent nonelectric systems for firing a single charge or set of charges. If two or more charges are to be fired simultaneously, two detonating cord ring mains are laid out, and abranch line from each charge is tied into each ring main. Figure 2-13 shows the layout for a nonelectric dual firing system. 2-15. Electric Dual Firing System This dual firing system consists of two independent electric circuits, each with an electric blasting cap in each charge, so that the firing of either circuit will detonate all charges. The correct layout is shown in figure 2-14. The firing wires of the two circuits should be kept separated so that both will not be cut by a single bullet or a single shell fragment. The firing points also should be at two separate locations. 2-16. Combination Dual Firing System The combination dual firing system uses an electric and nonelectric firing system (fig 2-15). Each charge is primed electrically and nonelectrically. Both the electric and nonelectric systems must be entirely independent of each other. The nonelectric system must be fired first. Section V. PRIMING CHARGES 2-17. Introduction This section will show nonelectric, electric, and detonating cord methods of priming most basic explosives. Certain terminology should be clarified since it will appear frequently in this section. a. NONELECTRIC FIRING SYSTEM. A nonelectric firing system consists of a fuse igniter, a length of time blasting fuse, and a nonelectric blasting cap. (A, fig 2-16). b. ELECTRIC FIRING SYSTEM. An electric firing system consists of a blasting machine or some other means of producing current, the necessary number of reels of firing wire, and electric blasting cap(s) (B, fig 2-16). c. DETONATING CORD. Detonating cord can be used to fire several charges simultaneously. Charges in several locations can be detonated by a single blasting cap wehn detonating cord ring mains are used and the charges are primed with detonating cord (para 2-10 - 2-12). 2-18. Priming Demolition Blocks a. NONELECTRIC PRIMING. Demolition blocks may or may not have threaded cap wells. Priming adapters should be used, if available, to secure the nonelectric blasting cap and time blasting fuse to demolition blocks with threaded cap wells (fig 2-17, para 1-45 and 2-2). (1) If priming adapters are not available but the blocks have threaded cap wells, they are primed as follows:(method 1, fig 2-18) (a) Wrap a string tightly around the block and tie it securely leaving about 6 inches of loose string on each end after making the tie. (b) Insert a blasting cap with fuse attached into the cap well. (c) Tie the loose string around the fuse to prevent the blasting cap from being separated from the block. Note. Do not tie the string so tight that powder train is broken in the fuse. (2) If the demolition block does not have a cap well, proceed as follows: (a) Make a hole in the end of the block with a pointed nonsparking instrument or the pointed handle on the M2 crimpers large enough to contain the blasting cap (method 2, fig 2-18). (b) Using string, wrap several turns around the explosive and tie any knot. Position the tie so it will be at the top of the hole when the fused cap is inserted. (c) Insert fused cap into hole. Note. Never try to force a cap into an expedient cap well that is too small to admit it easily. Remove and enlarge hole. (d) Tie string around the time fuse at top of hole with two half hitches. b. ELECTRIC PRIMING. Here again demolition blocks may or may not have threaded cap wells. If the blocks have threaded cap wells, priming adapters should be used if available. Proceed as follows: (1) Untwist the free ends of the lead wire and fasten them to the firing wire (para 2-4). (2) Pass the lead wires through the slot of the adapter and pull the cap into place in the adapter (fig 2-19). (3) Insert the cap into the capwell of the explosive and screw the adapter into place. c. If a priming adapter is not available do the following: (1) If the block does not have a cap well, make one in the manner described in paragraph 2-18a and figure 2-18. (2) Untwist the free ends of the lead wire and fasten them to the firing wire. (3) Insert the electric cap into the cap well and tie the lead wires around the block by two half hitches or a girth hitch (fig 2-20). Allow some slack in the wires between the blasting cap and the tie to prevent any pull on the blasting cap. d. DETONATING CORD PRIMING. Demolition blocks may be primed with detonating cord in several ways. (1) The method which offers the greatest assurance of detonation is to affix a nonelectric blasting cap to the end of the detonating cord and place it in the demolation block similar to nonelectric priming methods (para 2-19a). The system is then intitiated by a nonelectric or electric assembly. (2) The common method (A, fig 2-21) lays one end of a 4-foot length of detonating cord at an angle across the explosive. The running end is tehn given three wraps around the block and the end laid at an angle. On the fourth wrap, slip the running end under all wraps parallel to the other end and draw tight. Initiate by an electric or nonelectric system. (3) Alternate method No. 1 is shown in B, figure 2-21. Tie the detonating cord around the explosive block (on top of the booster, if present) with a clove hitch with two extra turns. The cord must fit snugly against the blocks and the loops must be pushed close together. Use an electric or nonelectric firing system to initiate the charte. (4) Alternate method No. 2 places a loop of detonating cord on the explosive with four wraps around the block and loop. The running end is pulled through the eye of the loop and tightened (C, fig 2-21). This method is also initiated by an electric or nonelectric system. Note. Alternate method No. 2 is more applicable to short than to long detonation cord branch lines or primers. 2-19. Composition C4 and C3 Demolition Blocks a. NONELECTRIC AND ELECTRIC PRIMING. When ever whole blocks or portions of blocks of plastic explosives (Composition C4 and C3) are used, prime similarly to demolition blocks without cap wells (para 2-18). Plastic explosives can be cut with a knife and then formed into almost any shape. b. DETONATING CORD PRIMING. To prime plastic explosives with detonating cord, form either of the two knots shown in figure 2-22. Then inser the knot into a block of explosive or a molded piece of explosive as shown. In either case, insure that there is at least 1/2 inch of explosive on all sides of the knot. 2-20. Sheet Explosive (M118 and M186 Demolition Charges) a. NONELECTRIC AND ELECTRIC PRIMING. M118 and M186 demolition charges may be primed in the following ways: (1) Attach blasting cap holder M8 (para 1-46) to one end or side of sheet explosive. The blasting cap holder M8 (fig 1-25) is self-securing to sheet explosive by means of three slanted, protruding teeth which prevent withdrawl. Two dimpled spring arms firmly hold the blasting cap in the M8 holder (fig 2-23). Note. This holder is supplied in each M118 and M186 demolition charge of recent manufacture. It is also available as a separate item of issue in quantities of 4,000. (2) Cut notch approximately 1.5-inches long and 1/4 inch wide in sheet explosive and insert blasting cap to limit of notch; secure blasting cap with string, tape or strip of sheet explosive (fig 2-23). (3) Place blasting cap on top of sheet explosive and sevure with a strip of sheet explosive at least 3" x 3". (4) Insert end of blasting cap 1.5 inches between two sheets of the explosive. b. DETONATING CORD PRIMING. M118 and M186 demolition charge sheet explosive may be primed with detonating cord by attaching a nonelectric blasting cap to the end of the detonating cord and following the methods outlined in A above. The detonating cord is then attached to a nonelectric or electric initiating system. 2-21. Dynamite Dynamite can be primed at either end or the side. End priming is used when a whole case is fired or when the charges pclaced require no tamping. Side priming is used when the charge is placed in a tamped borehole to prevent damage to the prime during placement and tamping. a. NONELECTRIC PRIMING. (1) END PRIMING METHOD (A, fig 2-24). (a) Using the cap crimpers, make a cap well in the end of the dynamite cartridge. (b) Insert a fused blasting cap. (c) Tie the cap and fuse securely in the cartridge with string. (2) WEATHERPROOF END PRIMING METHOD. This method helps weatherproof the primed charge (B, fig 2-24). (a) Unfold the wrapping at the folded end of the dynamite cartridge. (b) Use the cap crimpers and make a cap well in the exposed dynamite. (c) Insert a fused blasting cap into the cap well. (d) Close the wrapping around th fuse and fasted securely with string or tape. (e) Apply weatherproof sealing compound to the tie. (3) SIDE PRIMING METHOD. (fig 2-25). (a) Use the cap crimpers and make a cap well about 1.5 inches from one end of the dynamite cartridge. Slant the cap well so that the blasting cap, when insterted, will be nearly parallel with the side of the cartridge and the explosive end of the cap will be at a point at about the middle of the cartridge. (b) Insert a fused blasting cap into the hole. (c) Tie a string securely around the fuse and then wrap it tightly around the cartridge making two or three turns before tying it. (d) The primed cartridge may be weatherproofed by wrapping a string closely around the cartridge, extending it an inch or so on each side of the hold to cover it completely. Then cover the string with weatherproof sealing compound. b. ELECTRIC PRIMING. (1) END PRIMING METHOD (A, fig 2-26). (a) Use the cap crimpers and make a cap well in the end of the cartridge and insert an electric blasting cap as shown in a(1) above. (b) Tie the lead wires around the cartridge with two half hitches or a girth hitch. (2) SIDE PRIMING METHOD (B, fig 2-26). (a) Make a cap well in the side of the cartridge and insert an electric blasting cap as outlined a(3) above. (b) Tie the lead wire around the cartridge with a girth hitch or two half hitches or fasten with string or tape. c. DETONATING CORD PRIMING. Dynamite cartridges may be primed with detonating cord by attaching a nonelectric blasting cap to the end of the detonating cord and following any of the methods for nonelectric priming outlined in A above. Dynamite may also be primed by lacing the detonating cord through it. This is used chiefly in boreholes, ditching, or removal of stumps. Punch four equally-spaced holes through the dynamite cartridge and lace the detonating cord through them as shown in figure 2-27. 2-22. 40-Pound Ammonium Nitrate Cratering Charge a. NONELECTRIC PRIMING (fig, 2-28). (1) Place a fused nonelectric blasting cap in the cap well on the side of the container. (2) Tie a string around the fuse and then around the cleat above the cap well. (3) Dual prime as outlined in D below. b. ELECTRIC PRIMING. (fig 2-28). (1) Place an electric blasting cap in the cap well on the side of the container. (2) Tie the lead wires around the cleat above the cap well. (3) Dual prime as outlined in D below. c. DETONATING CORD PRIMING (A, fig 2-29). (1) Pass the end of the detonating cord through the tunnel on the side of the can. (2) Tie an overhand knot on the portion passed through at least 6-inches from the end. (3) Dual prime as outlined in D below. d. DUAL PRIMING (B, fig 2-29). To insure positive detonation of the ammonium nitrate cratering charge all charges should be dual primed with a 1-pound brick of explosive taped to the side of the charge near the cap well or detonating cord tunnel to detonate the TNT booster in the center of the charge. This demolition block may be primed by the same method the cratering charge is primed. Both charges should be primed to detonate simultaneously. e. PRECAUTIONS. As ammonium nitrate is hygroscopic and becomes ineffective if it has absorbed moisture (para 1-33), the metal container must be carefully inspected for damage or rusting that would indicate that the ammonium nitrate had absorbed moisture. Damaged or rusted charges should not be used. For safety in priming use detonating cord whenever charges are placed underground. 2-23. Shaped Charges a. NONELECTRIC AND ELECTRIC PRIMING. The M2A3, M2A4, M3 and M3A1 shaped charges have a threaded cap well at the top of the rear cone. They may be primed by means of a blasting cap and priming adapter as shown in figure 2-30. If a priming adapter is not available, the primer may be held in the cap well with string, piece of cloth or tape. b. DETONATING CORD PRIMING. Shaped charges are primed with detonating cord by attaching a nonelectric blasting cap to the end of the detonating cord and following the procedure in A above. c. DUAL-PRIMING. As shaped charges must be detonated from the center of the rear of the cone for maximum effectiveness, conventional methods of dual priming are not applicable to shaped charges. 2-24. Bangalore Torpedo a. NONELECTRIC PRIMING. The bangalore torpedo may be primed by assembling alength of time blasting fuse and a nonelectric blasting cap in a priming adapter and screwing the assembly into the cap well of a torpedo section (A, fig 2-31). A section may also be primed nonelectrically by a pull type firing device, with a nonelectric blasting cap crimped on the base, screwed into the cap well (B, 2-31). b. ELECTRIC PRIMING. The bangalore torpedo may be primed electrically by assembling a blasting cap and priming adapter and screwing the assembly into the cap well of a torpedo section (C, fig 2-31). CHAPTER 3 CALCULATION AND PLACEMENT OF CHARGES ----------------------------------------------------------------------------- Section I. INTRODUCTION 3-1. Critical Factors in Charge Calculations The amount of explosive used in any demolition project is determined by formula calculations based on the critical factors listed below. a. TYPE AND STRENGTH OF MATERIAL. A demolition target may be constructed of timber, steel, concrete or some other material. Concrete may reinforced with steel thereby increasing its strength. Formulas for computing specific charges for timber, steel, concrete, and so on, are given in succeeding sections of this chapter. b. SIZE AND SHAPE OF TARGET. Consideration must be given to the size and shape of the target. For example, large targets, such as concreter piers, and oddly shaped targets, such as steel I-beams, may be more economically attacked by multiple charges than a single charge. c. DESIRED DEMOLITION EFFECT. The extent of demolition desired and other effects, such as direction of falling trees to construct an abatis, must be considered. d. TYPE OF EXPLOSIVE. The particular characteristics of each type of explosive make it applicable to certain demolition projects, in preference to others. The relative effectiveness of each type of explosive must be considered in each formula calculation. Explosive Charges used in military operation and their relative effectiveness factors are shown in table 1-2. e. SIZE AND SHAPE OF CHARGE. The amount of explosive is calculated by each demolition formula, but, in the absence of special placement techniques, when external charges are used, a flat square charge with a thickness to width ratio of 1 to 3 or more will give acceptable results. In general, charges less than 5 pounds should be 1 inch thick (one M112 demolition block; charges 5 pounds to 40 pounds should be 2 inches thick (one M5A1 demolition block); and charges 40 pounds or more should be 4 inches thick (one M-183 demolition assembly). A more detailed discussion of charge thickness is found in paragraph 3-2b. f. CHARGE PLACEMENT. (1) Charges should be placed at the position that will provide maximum effectiveness. For cratering, they are place in holes in the ground; for breaking or collapsing stone or concrete, they are properly located on the surface or in boreholes; for cutting timber they may be tied on the outside or placed in boreholes, whichever is the more practical. (2) Charges are fastened to the target by wire, adhesive compound, tape, or string; propped against the target by means of a wooden or metal frame made of scrap or other available materials; or placed in boreholes. Special accessories are issued for this purpose--adhesive compound, the rivet-punching powder-actuated driver, the earth auger, and pneumatic tools (para 1-58). g. METHOD OF INITIATION. Generally the method of initiation is not critical unless the demolition charge is of a special type such as a shaped charge or diamond charge. h. TAMPING. The detonation of an explosive produces pressure in all directions. If the charge is not completely sealed in or confined or if the material surrounding the explosive is not equally strong on all sides, the explosive force breaks through the weakest spot and part of the destructive force is lost. To retain as much of this explosive force as possible, material is packed around the charge. This material is called tamping material or tamping, and the process, tamping. On the other hand, an internal charge (one placed in the target to be destroyed) is confined by packing material in the borehole on top of the charge as is done in quarrying and cratering. This is called stemming. 3-2. Principles of Demolition a. EFFECTS OF DETONATION. When a high explosive detonates, the explosive changes violently into compressed gas at extremely high pressure. The rate of change is determined among other things by the type of explosive and the density, confinement, and dimensions of the charge. Thus the detonation releases tremendous pressure in the form of a compressive shock wave which, although it exist for only a few micro-seconds at any given point, may shatter and displace objects in its path as it proceeds from its point of origin. This shock wave is transmitted directly to any substance in contact with the charge, other characteristics being equal. A high explosive charge detonated in direct contact with a solid object produces three different easily detectable destructive effects. (1) CRATERING. The surface of the object directly under the explosive charge will be cratered. On a concrete surface the high pressure of the compressive shock wave crumbles that material in the immediate vicinity of the charge, forming the crater. On a steel target an indentation or depression with an are about the size of the contact area of the charge is made in the surface of the plate. (2) SPALLING. Providing that the charge is of sufficient size, the opposite side of the object will be spalled. The strong compressive shock wave transmitted into the material expands spherically losing energy as it moves through the material. If the target has a free surface on the side opposite the charge, the compressive shock wave will be reflected as a tensile shock wave from that free surface because of the difference in density between the target and the air. Reflection of the compressive shock wave as a tensile shock wave causes spalling of the target free surface, wherein a portion of the material is literally torn from the free surface. On a concrete wall, depending upon the relative size of the charge and thickness of the wall, the crater and spalls meet and form a hole through the wall. On a steel plate, usually only one spall, approximately the shape of the explosive charge, is thrown from the plate. (3) CRACKING. If the explosive charge is of sufficient size the high pressure gases from the explosive charge will create a pressure load on the object that will crack and displace the material beyond the extent of the crater and spall. These cracks will radiate from the charge position. On concrete walls, this craking may be extensive enough to break the wall into a large number of chunks which are projected away from the charge position. On steel plates, the material may be bent away from the charge position. b. SIGNIFICANCE OF CHARGE DIMENSIONS. The force of an explosion is proportional to the quantity and power of the explosive, but the destructitve effect depends, in part, on the manner that the explosive force is directed at the target. An optimum relation must exist between the area of the charge in contact with the target and charge thickness in order to transmit the greatest shock. If any given wight of explosive, calculated to cut a given target, is spread too thinly, there will be insufficient space for the shock wave to attain full velocity before striking the target. The shock wave will tend to travel more nearly parallel than normal to the surface over much of the area, and the volume of the target will be excessive for the strength of the shock wave. On the other extreme, a thick charge with a small contact area will transmit the shock wave over too little of the target with excessive lateral loss of energy. Test results have demonstrated that the optimum ratio of charge thickness to charge width is about 1:3 for contact steel cutting charges on structural steel 3 inches or less, and ranges from about 1:6 to 1:14 for rectangualar external untamped breaching charges for reinforced concrete from 1 to 7 feet thick. c. SIGNIFICANCE OF CHARGE PLACEMENT. The destructive effect of an explosive charge is also dependent upon the contact between the explosive and the target and the location of the charge in relation to target size and shape. (1) For the maximum destructive effect an explosive charge with a configuration and deimensions optimum for the size and shape of the target must be detonated in intimate contact with the target. Any significant air or water gap between the target and the explosive will not transmit the complete force of the shock wave into the target. Certain explosives, such as sheet explosive or plastic explosives, are more desirable for certain targets because they may be cut or molded to fit odd shaped targets. (2) Explosive charges are placed to act through the least dimension of the target whenever possible. In terms of the maximum destructive effect for the least amount of explosive, internal charges are the best. The tamping of external charges increases their destructive effect. 3-3. Types of Charges a. INTERNAL CHARGES. Internal charges are charges placed in boreholes in the target. These are confined by tightly packing sand, wet clay, or other material (stemming) into the opening. This is tamped and packed against the explosive to fill the hole all the way to the surface. In drill holes, the explosive (usually dynamite) is tamped as it is loaded into the hole. Refer to TM 5-332 for details of quarry practice. b. EXTERNAL CHARGES. These charges are placed on the surface of the target. They are tamped by covering them with tightly packed sand, clay or other dense material. Tamping may be in sandbags or loose. For maximum effectiveness the thickness of the tamping should at least equal the breaching radius. Small breaching charges on horizontal surfaces are sometimes tamped by packing several inches of wet clay or mud around them. This process is called mudcapping. 3-4. Charge Selection and Calculation a. CHARGE SELECTION. The selection of the optimum explosive charge for successful demolition operations is a balance between the important factors listed above and the practical aspects of the type of target, the type and amount of explosives available, the amount and type of material (such as sandbags) and equipment available, the amount of manpower available, and, probably most important, the time available to accomplish the mission. Formulas for computing specific charges and methods of their placement are given below. Formulas based on metric measurements are given in appendix B. b. CHARGE CALCULATION. The formulas in this chapter give the weight of explosive required for a demolition task P in pounds of TNT. If explosives other than TNT are used, the value of P must be adjusted according to the strength of these other explosives. The adjusted value of P corrected weight of explosive required, is computed by dividing the P value of TNT by the relative effectiveness factor for the explosive to be used. c. ROUNDING OFF RULE. When using explosives, NEVER use less than the calculated amount. Some explosives like plastic explosive (C4) and sheet explosive (M118 and M186) can be cut to the desired amount, while with other explosives the ability to size explosives is limited. For charges calculated by formula, use the following rounding off method: (1) Claculate the weight of a single charge for TNT using the selected demolition formula to at least two decimals. (2) Divide by the relative effectiveness factor, if required. (3) Round up answer for single charge to next package size. (4) Multiply answer for single charge by the number of charges to obtain the total amount of explosive required. Section II. TIMBER-CUTTING CHARGES 3-5. Size and Placement of Charge a. TYPE OF EXPLOSIVE USED. For tamped internal charges in boreholes, dynamite is generally used, as it is the most convenient to place because of the size of the cartridge and is powerful enough because it is confined. For untamped concentrated external charges, block explosive (TNT, Tetrytol, and Composition C4) is used, as it is easily tied or fastened on its effectiveness in relation to that of TNT (relative effectiveness factor). For untamped external ring charges, plastic explosive (Composition C4) or sheet explosive (M118 or M186) is used, as it is easily fastened to the target and molded around the target. It is impractical to attempt to cut all kinds of timber with charges of a size calculated from a single formula. THere is too much variation in different kinds of timber from locality to locality. Accordingly, test shots must be made to determine the size of the charge to cut a specific type of timber. Formulas for the calculation of these test shots are provided for tamped internal charges, and untamped external charges. They are as follows: b. FORMULA FOR TAMPED INTERNAL CHARGES. Tamped internal cutting charges may be calculated by the following formula: P = D²/250 or P = .004 D² where, P = Pounds of TNT required, D = diameter or least dimension of dressed timber, in inches, and 1/250 = .004 = constant The amount of explosive required to cut a 15-inch diameter tree, using tamped internal charges is determined as follows: P = D²/250 = 225/250 = .9 of 1 pound of TNT Note. See rounding off rule, paragraph 3-4c. c. INTERNAL CHARGE PLACEMENT. The charge is placed in a borehole parallel to the greatest dimension of cross section and tightly tamped with moist earth. If the charge is too large to be placed in one borehole, bore two holes side by side in dimensional timber. On round timber, bore two holes at approximately right angles to each other, but do not intersect (fig 3-1). Both boreholes are tamped and the charges are fired simultaneously. d. FORMULA FOR UNTAMPED EXTERNAL CHARGES. For cutting trees, piles, posts, beams or other timber members using explosives as an untamped external charge, the following formula is used: P = D²/40 or P = .025 D² where, P = pounds of TNT required, D = diameter of round timber, or least dimension of dressed timber, in inches, and 1/40 = .025 = constant. Adjustment for explosive other than TNT will be made by dividing by the relative effectiveness factor (table 1-2) that pertains to the particular explosive being used. The amount of explosive required to cut a round timber 30 inches in diameter using an untamped external charge is determined as follows: P = D²/40 P = (30)²/40 = 900/40 = 22.50 pounds of TNT. e. CONCENTRATED EXTERNAL CHARGE PLACEMENT. For maximum destructive effect concentrated charges should be of rectangular configuration, 1 to 2 inches thick and approximately twice as wide as they are high. Charges are placed as close as possible to the surface of the timber (fig 3-2). Frequently it is desirable to notch the tree or timber to hold the explosive in place. If the tree or timber is not round and the direction of fall is of no concern, the explosive is placed on the widest face so that the cut will be through the least thickness. The tree will fall toward the side where the explosive is placed, unless influenced by lean or wind. Charges on rectangular or square dressed timber are placed as shown in figure 3-3. f. RING CHARGE PLACEMENT. The ring charge (fig 3-4) is placed as a band of explosive completely circling the tree. The width of the explosive band should be as wide as possible, and a minimum of 1/2 inch thick for small diameter trees, and 1 inch thick for medium- and large- diameter trees up to 30 inches. This technique is used when the direction of fall is not important and the elimination of stumps is important, e.g., explosive clearing for a helicopter landing zone. The amount of explosive is calculated by the external charge formula. 3-6. Abatis a. FORMULA FOR PARTIALLY CUTTING TREES TO CREATE AN OBSTACLE OR ABATIS. When cutting trees and leaving them attached to the stumps to create an obstacle, the formula P = D²/ro or P = .02D² is used to compute the amount of TNT required for the test shot. The result of the test shot will determine the need for increasing or decreasing the amount of explosives required for subsequent shots. b. PLACEMENT OF ABATIS CHARGE. Charges for making fallen-tree obstacles are placed as a concentrated external charge the same as in paragraph 3-5c, except that they are placed approximately 5 feet above ground level. The tree will fall toward the side where the explosive is placed, unless influenced by lean or wind. To make the direction of fall more certain, a "kicker charge", a one pound block of explosive, placed about two-thirds of the distance up the tree on the opposite side may be used (fig 3-2). c. SPECIAL CONSIDERATIONS. To be effective these obstacles should be at least 75 meters in depth and the felled trees should extend at a 45 degree angle toward the enemy. The trees on one side of the road should not be cut simultaneously, followed by the cutting of the trees on the other side of the road. Delayed blasting of the second row of trees is necessary to provide time for the trees in the first row to fall and thereby eliminate the possibility of trees deflecting one another from their desired direction of fall. Likewise, in selection of trees to blast for abatis obstacles, the trees in a row should be selected spacing great enough to allow the trees to fall without interference from other falling trees in the same row. To make the obstacles more difficult to remove, they should be mined, boobytrapped, entangled with barbed wire or concertina, and covered by fire. Section III. STEEL-CUTTING CHARGES 3-7. Cutting Steel With Explosives a. IMPORTANT FACTORS. In the preparation of steel-cutting charges, the factors of type, size and placement of the explosive are important for successful operations. The confinement or tamping of the charge is rarely practical or possible. Formulas for the computation of the size of the charge vary with the type of steel--structural, high carbon, and so forth. Placement of the charge in direct contact with the target is more important with steel than with other materials. (1) FORMULA FOR STRUCTURAL STEEL. Charges to cut I-beams, builtup girders, steel plates, columns, and other structural steel sections are computed by formal as follows: P = 3/8 A or P = 0.375 A where, P = pounds of TNT required, A = cross-section area, in square inches, of the steel member to be cut, and 3/8 = 0.375 = constant (2) FORMULA FOR OTHER STEELS. (a) The formula below is recommended for the computation of block cutting charges for high-carbon or alloy steel, such as that found in machinery. P = D² P = pounds of TNT D = diameter or thickness in inches of section to be cut. (b) For round steel bars, such as concrete reinforcing rods, where the small size makes charge placement difficult or impossible and for chains, cables, and steel rods, of a diameter of 2 inches or less, use P = D P = pounds of TNT D = diameter in inches of section to be cut. Such steel, however, may be cut by "rule of thumb:" For round bars up to 1 inch in diameter, use 1 pound TNT. For round bars over 1 inch up to 2 inches in diameter, use 2 pounds of TNT. (3) RAILROAD RAIL. The height of ralroad rail is the critical dimension for calculating explosive required. Rails 5 inches or more in height may be cut with 1 pound of TNT. For rails less than 5 inches in height, 1/2 pound of TNT is adequate. (4) PROBLEM: Determine the amount of TNT required to cut the steel I-beam shown in figure 3-5. THe solution is given in the figure. (5) PROBLEM: How much TNT is needed to cut the steel chain in figure 3-6? The solution is given in figure 3-6. Notice that the link is to be cut in two places (one cut on each side) to cause complete failure. If the explosive is long enough to bridge both sides of the link, or large enough to fit snugly between the two links, use one charge; but if it is not, use two separately primed charges. (6) USE OF THE TABLE IN MAKING CALCULATIONS. Table 3-1 shows the correct weight of TNT necessary to cut steel sections of various dimensions calculated from the formula P = 3/8 A. In using this table: (a) Measure separately the rectangular sections of members. (b) Find the corresponding charge for each section by using the table. (c) Total the charges for the sections. (d) Use the next larger given dimension if dimensions of section do not appear in the table. (7) SOLUTION. The problem in figure 3-5 may be solved as folows: Charge for flanges: Charge for web: width = 5 inches height = 11 inches thickness = 1/2 inch thickness = 3/8 inch Charge from table = Charge from table = 1.0 pounds 1.6 pounds Total charge: 2 flanges = 2 x 1.0 = 2.0 pounds web = 1 x 1.6 = 1.6 pounds ---------- 3.6 pounds Use 4 pounds of TNT. b. FORMULAS FOR PLASTIC OR SHEET EXPLOSIVE CHARGES. When using plastic explosives (M5A1 or M112) charges or sheet explosive (M118 or M186) charges, which may be cut to fit the target and attached to the surface of the target with little or no air gap, the following formulas, based upon optimum charge configuration and optimum contact with the target, may be used. The following charge calculations are based upon the dimensions of the target, and with some practice these charges may be calculated, prepared, and placed in less time than the charges calculated by the formulas listed above. Thes charges may also be prepared in advance for transportation to the site by wrapping them in aluminum foil or heavy paper. The wrapper should be removed when the charge is attached to the target. When preparing these charges the explosive should be cut to the proper dimensions, not molded, as molding the explosive will reduce its density thereby decreasing its effectiveness. (1) RIBBON CHARGE METHOD. The charge, if properly calculated and placed, cuts stell with considerably less explosive than standard charges. It is effective on noncircular steel targets up to 3 inches thick (fig 3-7). Although this charge is based upon the used of C4 plastic explosive, sheet explosive may be used provided the 1/4- by 3 by 12-inch sheets of flexible explosive are used intact and complete charges are at least 1/2 inch thick. (a) CALCULATION. The effectiveness of the explosive depends upon the width and thickness of the explosive. THe thickness of the charge is one half the thickness of the stell. The width of the charge is three times the thickness of the charge. The length of the charge should be equal to the length of the desired cut. (b) EXAMPLE. Determine the thickness and width of a ribbon charge for cutting a steel plate 1 inch thick. Charge thickness = 1/2 steel thickness Charge thickness = 1/2(1) = 1/2 inch Charge width = 3 times charge thickness Charge width = 3(1/2) = 3/2 = 1 1/2 inches Charge is 1/2 inch thick and 1 1/2 inches wide. (c) DETONTATION. The ribbon charge may be detonated from the center or from either end. It may be necessary when the charge thickness is small (less than 3/4 inch) to place extra explosive around or over the blasting cap. (d) USE OF STRUCTURAL STEEL SECTIONS. The ribbon charge (computed by formula given in (b) above) has proven applicable to cutting structural steel sections (fig 3-8). On wide-flange or I-beams of less than 2 inches of steel thickness, a C-shaped charge is placed on one side to cut the web and half the top and bottom flanges. THe other sides of these flanges are cut by two offset ribbon charges, placed so that once edge is opposite the center of th C-shaped charge as shown in A, figure 3-8. For beams with steel thickness of 2 inches and over, the offset charges are placed so that one edge is opposite the edge of the C-shaped charge as shown in B, figure 3-8. FOr acceptable results, the charges must be detonated at the SAME INSTANT. This is accomplished by priming the charges with three exactly EQUAL LENGTHS of detonating cord with blasting caps attached and placed in the charges as shown in C, figure 3-8. The detonating cord primer may be initiated by an electric or nonelectric system. Simultaneous detonation may also be accomplished with M6 electric blasting caps wired in series in the same circuit. (2) CROSS FRACTURE METHOD (SADDLE CHARGE) FOR CUTTING MILLED STEEL BARS. This method of steel cutting utilizes the destructive effect of the end split or cross fracture formed in steel at the end of a charge opposite the end where detonation was initiated. This technique may be used on round, square, or rectangular milled steel bars up to 8 inches square or 8 inches diameter. The cross fracture method uses a charge cut in the shape of a triangle and is called a SADDLE CHARGE (fig 3-9). (a) CALCULATION. The dimensions of the saddle charge are computed from the dimensions of the target as follows: Thickness of charge = 1 inch (thickness of M112 block of plastic explosive). Base of charge = 1/2 circumference of target. Long axis of charge = Circumference of target. (b) EXAMPLE. Determine the dimensions of a charge for cutting a shaft 18 inches in circumference (may be measured with a string). Thickness = 1 inch Base = 1/2 x 18 = 9 inches Long axis = 18 inches Charge is 9 inches at base, 18 inches at long axis, and 1 inch thick. (c) DETONATION. Detonation of the saddle charge is by the placement of a military electric or nonelectric blasting cap at the apex of the long axis. (d) PLACEMENT. The long axis of the saddle charge should be parallel with the long axis of the target. THe charge should be cut to the correct shape and dimensions and then molded around the target, taking care to insure that the charge is in intimate contact with the target. This may be accomplished by taping the charge to the target. (3) STRESS WAVE METHOD (DIAMOND CHARGE). This method of steel cutting utilizes the destructive effect of tensile fractures induced through the interaction of two colliding shock wave fronts from an explosive charge simultaneously detonated at opposite ends. This techniquie may be used on high carbon steel or steel alloy bars either circular or square in cross section. The stress wave method uses a charge cut in the shape of a diamond, and thus called a diamond charge (fig 3-10). (a) CALCULATION. The dimensions of the diamond charge are computed from the dimensions of the target as follows: Thickness of charge = 1 inch (thickness of M112 block of plastic explosive). Long axis of charge = Circumference of target. Short axis of charge = 1/2 the circumference of the target. (b) EXAMPLE. Determine the size of a charge for cutting a steel alloy shaft 15 inches in circumference. Thickness = 1 inch Long axis = 15 inches Short axis = 1/2 x 15 = 7 1/2 inches Charge is 15 inches at long axis, 7 1/2 inches at short axis, and 1 inch thick. (c) DETONATION. The detonation of diamond charge must be done SIMULTANEOUSLY from both short axis ends. This may be done by priming with two pieces of detonating cord of the SAME LENGTH with nonelectric blasting caps crimped to the ends. The detonating cord primers may be detonated with an electric or nonelectric blasting cap. Simultaneous detonation may also be accomplished with M6 electric blasting caps wired in series in the same circuit. (d) PLACEMENT. Wrap the explosive completely around the target so that the ends of the long axis touch. It may be necessary to slightly increase the dimensions of the charge so this may accomplished. If necessary to insure complete contact with the target, tape the charge to the target. 3-9. Charge Placement a. STEEL SECTIONS. The size and type of a steel section determine the placement of the explosive charge. Some elongated sections may be cut by placing the explosive on one side of the section completely along the proposed line of rupture. In some steel trusses in which the individual memebers are fabricated from two or more primary sections, such as angle irons or bars separated by space washers or gusset plates, the charge must be placed with the opposing portions of the charge offset the same distance as the thickness of the section being cut to produce a shearing action (para 3-8b(1)(d)). Heavier I-beams, wide flange beams, and columns may also require auxilliary charges placed on the outside of the flanges. Care must be taken to insure that opposing charges are never directly opposite each other, otherwise they tend to neutralize the explosive effect. b. RODS, CHAINS, AND CABLES. Block explosive, often difficult to emplace, is not recommended for cutting steel rods, chains, and cables if plastic explosive is available. c. STEEL MEMBERS AND RAILROD RAILS. Charge placement for cutting these are found in figures 3-11 and 4-39. d. BUILT-UP MEMBERS. Built-up members frequently have an irregular shape, which makes it difficult to obtain a close contact between the explosive charge and all of the surface. If it is impractical to distribute the charge properly to obtain close contact, the amount of explosive should be increased. e. IRREGULAR STEEL SHAPES. Composition C4 is a good explosive for cutting irregular steel shapes because it is easily molded or pressed into place to give maximum contact. In the case of the M5A1 block charge, which uses C4, a light coating of adhesive compound or automotive grease (GAA) applied to the steel surface will help hold the explosive on the target. The M112 block, which also uses C4, and the M118 sheet explosive have an adhesive coating on one side, which makes placement easier. f. SECURING EXPLOSIVES IN PLACE. All explosives except adhesive types must be tied, taped, wedged in place unless they rest on horizontal surfaces and are not in danger of being jarred out of place. g. PRECAUTIONS. In cutting steel, the charge should be placed on the same side as the firing party, as explosive charges throw steel fragments (missiles) long distance at high velocities. Section IV. PRESSURE CHARGES 3-10. Size of Charge The pressure charge is used for the demolition of reinforced concrete T-beam bridge superstructures. Since it requires the use of more explosives than breaching charges, with comparable placement, it has been replaced by the breaching charge (para 3-12 - 3-14). a. FORMULA FOR TAMPED PRESSURE CHARGES. The amount of TNT required for a tamped pressure charge is calculated by the formula below. If explosive other than TNT is used, the calculated value must be divided by the relative effectiveness factor. P = 3H²T P = pounds of TNT required for each beam (stringer) H = height of beam (including thickness of roadway) in feet T = thickness of beam in feet. b. FORMULA FOR UNTAMPED PRESSURE CHARGES. The valure calculated for P by the above formula is increased by one-third if the pressure charge is not tamped to a minimum of 10 inches (P = 4H²T). 3-11. Charge Placement and Tamping a. PLACEMENT. The correct amount of explosive is placed on the roadway over the centerline of each stringer (fig 3-12) and alined between the ends of the span. If a curb or sied rail prevents placing the charge directly above the outside stringer, it is placed against the curb or side rail. This does not require an increase in the size of the explosive charge (See also para 4-22). b. TAMPING. Pressure charges should be tamped whenever possible. Effective tamping require a minimum of 10 inches of material. All charges are primed to fire simultaneously. Section V. BREACHING CHARGES 3-12. Critical Factors and Computation Breaching charges are applied chiefly to the destruction of concrete slab bridges, bridge beams, bridge piers, bridge abutments, and permanent field fortifications. The size and shape, placement, and tamping or confinement of the breaching charge are critical factors-- the size and confinement of the explosive being relatively more important because of strength and bulk of the material to be breached. High explosive breaching charges detonated in or against a target must produce and transmit enough energy to the target to crater and spall the material. THe metal reinforcing bars in reinforced concrete are not cut by breaching charges. If it is necessary to remove or cut the reinforcement, the necessary steel cutting formula is used after the concrete is breached. a. CALCULATION FORMULA. The size of a charge required to breach concrete, masonry, rock or similar material is calculated by the formula below. By proper adjustment of the P-value, the charge size for any explosive may be readily determined. P = R(cubed) KC where; P = pounds of TNT required, R = breaching radius (b below), K = material factor, given in table 3-4, which reflects the strength, hardness and mass of the material to be demolished (c below), C = a tamping factor, given in figure 3-13, which depends on the location and tamping of the charge (d below) b. BREACHING RADIUS R. The breaching radius R is the distance in feet from an explosive in which all material is displaced or destroyed. The breaching radius for external charges is the thickness of the mass to be breached. The breaching radius for internal charges is one-half the thickness of the mass to be breached if the charge is placed midway into the mass. If holes are drilled less than halfway into the mass, the breaching radius becomes the longer distance from center of the charge to the outside of the mass. For example, if a 4-foot wall is to be breached by an internal charge placed 1 foot into the wall, the breaching radius is 3 feet. If it is to be breached by a centered internal charge, the breaching radius is 2 foeet. The breaching radius is 4 feet is an external charge is used. Values of R are rounded off to the next highest 1/2-foot for external charges, and to the next highest 1/4-foot for internal charges. c. MATERIAL FACTOR K. K is the factor that reflects the strength and hardness of the material to be breached. Table 3-2, gives values for the factor K for various types and thicknesses of material. If the type of material in the object is in doubt, it is always assumed to be of the stronger type. Concrete is assumed to be reinforced, unless it is known not to be. TABLE 3-2. VALUES OF K(MATERIAL FACTOR) FOR BREACHING CHARGES. -------------------------!--------------------!------! MATERIAL ! BREACHING RADIUS ! K ! -------------------------!--------------------!------! Ordinary earth ! All values ! 0.07 ! -------------------------!--------------------!------! Poor masonry, shale, ! Less than 5 ft ! 0.32 ! hardpan: Good Timber ! 5 ft or more ! 0.29 ! and earth construction ! ! ! -------------------------!--------------------!------! Good masonry ! 1 ft or less ! 0.88 ! ordinary concrete ! 1.5-2.5 ft ! 0.48 ! rock ! 3.0-4.5 ft ! 0.40 ! ! 5.0-6.5 ft ! 0.32 ! ! 7 ft or more ! 0.27 ! -------------------------!--------------------!------! Dense concrete ! 1 ft or less ! 1.14 ! first-class masonry ! 1.5-2.5 ft ! 0.62 ! ! 3.0-4.5 ft ! 0.52 ! ! 5.0-6.5 ft ! 0.41 ! ! 7 ft or more ! 0.35 ! -------------------------!--------------------!------! Reinforced concrete ! 1 ft or less ! 1.76 ! (concrete only: Will not ! 1.5-2.5 ft ! 0.96 ! cut reinforcing steel) ! 3.0-4.5 ft ! 0.80 ! ! 5.0-6.5 ft ! 0.63 ! ! 7 ft or more ! 0.54 ! -------------------------!--------------------!------! d. TAMPING FACTOR C. The value of the tamping factor C depends on the location and the tamping of the charge. Figure 3-13 shows typical methods for placing charges and gives values of C to be used in the breaching formula with both tamped and untamped charges. In selecting a value of C from figure 3-13, a charge should be tamped with a solid material such as sand or earth or tamped by water is not considered full tamped unless it is covered to a depth equal to or greater than the breaching radius. e. USE OF FIGURE IN MAKING CALCULATIONS. Figure 3-14 gives the amount of TNT required to breach reinforced concrete targets. The amounts of TNT in the table were calculated from the formula P = R(cubed)KC. To use the figure: (1) Measure thickness of concrete. (2) Decide how the charge will be placed against the target. Compare the method of placement with the diagrams at the top of the figure. If there is any question as to which column to use, always use the column that will give the greater amount of explosive. (3) For explosive other than TNT, use the relative effectiveness factor (table 1-2). f. EXAMPLE. Using figure 3-14, calculate the amount of TNT required to breach a reinforced concrete wall 7 feet thick with an untamped charge placed at a distance R above the ground. From the figure the required amount of TNT is 334 pounds. g. USING FIGURE FOR MATERIAL OTHER THAN REINFORCED CONCRETE. The values given in figure 3-13 may be used to calculate breaching charges for obstacles of material other than reinforced concrete by multiplying the valure obtained from figure 3-14 by the proper conversion factor given in table 3-3. To use the table --- (1) Determine the type of material in the object. If in doubt assume the material to be of the stronger type, e.g. assume concrete reinforced, unless known otherwise. (2) Using figure 3-14, determine the amount of explosive that would be required if the object were made of reinforced concrete. (3) Using table 3-3, determine the appropriate conversion factor. (4) Multiply the number of pounds of explosive by the conversion factor. h. EXAMPLE. Using figure 3-14 and table 3-3, determine the amount of TNT required to breach an ordinary masonry pier 4 1/2 feet thick with an untamped charge placed 4 feet below the waterline. If the pier were made of reinforced concrete, 146 pounds of TNT would be required to breach it (fig 3-14). The conversion factor (table 3-3) is 0.5. Therefore 146 x 0.5 = 73 pounds of TNT are required to breach the pier. 3-13. Placement and Number of Charges a. PLACEMENT. In the demolition of piers and walls, the position for the placement of explosive charges are rather limited. Unless a demolition chamber is available, the charge (or charges) may be placed against once face of the target either at ground level, somewhat above ground level, or beneath the surface. A charge placed above ground level is more effective than one placed directly on the ground. When several charges are required to destroy a pier, slab, or wall and elevated charges are desired, they are distributed equally at no less than one breaching radius high from the base of the object to be demolished. In this manner, the best use is obtained from the shock waves of the blast. BREACHING CHARGES SHOULD BE PLACED SO THAT THERE IS A FREE REFLECTION SURFACE ON THE OPPOSITE SIDE OF THE TARGET. This free reflection surface is necessary for spalling to occur (see para 3-2). All charges are thoroughly tamped with damp soil or filled sandbags if time permits. (Tamping must be equal to or greater than the breaching radius.) For piers, slabs, or walls partially submerged in water, charges are placed equal to or greater than the breaching radius below the waterline (fig 3-13). b. CHARGE CONFIGURATIONS. In order to transmit the maximum destructive shock into the target, the explosive charge should be placed in the shape of a flat square with the flat side to the target. The thickness of the charge is dependent upon the amount of explosive and is given in table 3-4. TABLE 3-4. THICKNESS OF BREACHING CHARGES* ___________________________________________________ Amount of explosive ! Thickness of charge ____________________________!______________________ Less than 5 lbs ! 1 inch 5 lbs to less than 40 lbs ! 2 inches 40 lbs to less than 300 lbs ! 4 inches 300 lbs or more ! 5 inches ____________________________!______________________ *These are approximate values c. NUMBER OF CHARGES. The number of charges required to demolish a pier, slab, or wall is calculated be the formula: N = W/2R where, N = number of charges, W = width of pier, slab, or wall, in feet, R = breaching radius in feet (para 3-12b). 2 = constant If the calculated value of N is less that 1 1/4, use one charge; if it is 1 1/4 to less than 2 1/2, use 2 charges; if it is 2 1/2 or more, round off to nearest whole number. In breaching concrete beam bridges, each beam is breached individually. 3-14. Opposed (Counterforce) Charge This special breaching techniqure is effective against comparatively small cubical or columnar concrete and masonry objects 4 feet or less in thickness and wideth. It is not effective against piers or long obstacles. The obstacle must also have at least three free faces or be free standing. If constructed of plastic explosive properly placed and detonated, counterforce charges produce excellent results with a relatively small amount of explosive. Their effectiveness results from simultaneous detonation of two charges placed directly opposite eache other and as neer the center of the target as possible (fig 3-15). a. CHARGE CALCULATION. The size is computed from the diameter or thickness of the target in feet, as -- The amount of explosive = 1 1/2 x the thickness of the target in feet (1 1/2 pounds per foot). Fractional measurements are rounded off to the next higher foot prior to multiplication. Fot example, a concrete target measuring 3 feet 9 inches thick requires 1 1/2 x 4 = 6 pounds of plastic explosive (composition C4). b. PREPARATION AND EMPLACEMENT. Divide the calculated amount of explosive in half to make two identical charges. The two charges MUST be placed diametrically opposite each other. This requires accessibility to both sides of the target so that the charges may be placed flush against the respective target sides. c. PRIMING. The simultaneous explosion of both charges is mandatory for optimum results. Crimp nonelectric blasting caps to equal lengths of detonating cord. Prime both charges at the center rear point; then form a V with the free ends of detonating cord and attach an electric or nonelectric means of firing. Simultaneous detonation may also be accomplished with M6 electric blasting caps wired in series in the same circuit. Section VI. CRATERING AND DITCHING CHARGES 3-15. Critical Factors a. SIZE. Road craters, to be effective obstacles, must be too wide for spanning by track-laying vehicles and too deep and steep sided for any vehicle to pass through them. Blasted road craters will not stop modern tanks indefinitely, because repeated attempts by the tank to traverse the crater will pull loose soil from the slopes of the crater into the bottom reducing both the depth of the crater and angle of the slopes. Road craters are considered effective antitank obstacles if the tank requires three or more passes to traverse the crater, thereby providing sufficient time for antitank weapons to stop the tank. Road craters must also be large enough to tie into natural or manmade obstacles at each end. The effectiveness of blasted road craters may be improved by placing log hurdles on either side, by digging the face on the friendly side nearly vertical, by mining the site with antitank and antipersonnel mines. b. EXPLOSIVE. All military explosives may be used for blasting antitank craters. A special 40-pound cratering charge, ammonium nitrate, sued in a waterproof metal container, is used when available (para 1-4). c. SIZE AND PLACEMENT OF CHARGE. In deliberate cratering, holes are bored to specific depths and spaced according to computation by formula, as described below. In ditching, test shots are made and the diameter and depth are increased as required. d. CONFINEMENT OF CHARGE. Charges at cratering sites and antitank ditching sites are placed in boreholes and properly stemmed. Those at culvert sites are tamped with sandbags. e. BREACHING HARD-SURFACED PAVEMENTS FOR CRATERING CHARGES. Hard-surfaced pavement of roads and airfields is breached so that holes may be dug for cratering charges. This is done effectively exploding tamped charges on the pavement surface. A 1-pound charge of explosive is used for each 2 inches of pavement thickness. It is tamped with material twice as thick as the pavement. The pavemenmt may also be breached by charges placed in boreholes drilled or blasted through it. (A shaped charge readily blasts a small diameter borehole through the pavement and into the subgrade.) Concrete should not be breached at an expansion joint, because the concrete will shatter irregularly. f. BOREHOLES FOR CRATERING CHARGES. Boreholes for cratering charges may be dug by using motorized post hole augers or diggers. Boreholes may also be made by use of the earth rod kit (para 1-41) or by a mechanically drivin pin, widened with a detonating cord wick (para 3-27). g. BLASTING BOREHOLES WITH SHAPED CHARGES. Standard shaped charges may be used to blast boreholes in both paved and unpaved surfaces for rapid road cratering with explosives. The 15-pound M2A4 shaped charge detonated at 3 1/2 foot standoff and the 40-pound M3A1 shaped charge detonated at 5-foot standoff will blast boreholes of up to 9-foot open depths with 7-inch and larger diameters in both reinforced concrete pavements and gravel surfaced roads. For maximum effectiveness, M3A1 shaped charges should be used to blast boreholes in thick, reinforced concrete pavements laid on dense high-strength base courses. The M2A4 shaped charges may be used effectively to blast cratering charge boreholes in reinforced concrete pavement of less than 6-inch thickness laid on thin base courses or to blast boreholes in unpaved roads. Most any kind of military explosive, including the cratering charges, can be loaded directly into boreholes made by the M3A1 and the M2A4 shaped charges. Shaped charges do not always produce open boreholes capable of being loaded directly with 7-inch diameter cratering charges without removal of some earth or widening of narrow areas. Many boreholes having narrow diameters but great depth can be widened simply by knocking material from the constricted areas with a pole or rod or by breaking off the shattered surface concrete with a pick or crowbar. For road cratering on asphalt or concrete surfaced roadways, blasting the boreholes with shaped charges will expedite the cratering task by eliminating the requirement for first breaching the pavement with explosive charges (table 3-5). 3-16. Hasty Road Crater This method (fig 3-16) takes the least amount of time for construction, based upon number and depth of boreholes, but produces the least effective barrier because of its depth and shape. The method described below forms a V-shaped crater, about 6 to 7 feet deep and 20 to 25 feet wide extending about 8 feet beyond each end crater. The sides have slopes of 25 degrees to 35 degrees. Modern U.S. combat tanks (the M48 and M60) require an average of four passes to traverse hasty road craters. Craters formed by boreholes less than 5 feet deep and loaded with charges less than 50 pounds are ineffective against tanks. The following hasty cratering method has proved satisfactory: a. Dig all boreholes to the same depth; at least 6 feet. Space the holes 5 feet apart center-to-center across the road. The formula for the computation of the number of holes is : N = L-16/5 + 1, where L = length of crater in feet measured across the roadway. Any fractional number of holes is rounded off to the next highest number. b. Load the boreholes with 10 pounds of explosive per foot of depth. c. Prime all charges with detonating cord and connect them to fire simultaneously. Under ground charges should always be primed with detonating cord branch lines. A dual firing system should be used. d. If the standard cratering charge is used, place a 1-pound priming charge on the side of the charge for dual priming. For hasty cratering, if standard cratering charges are used, each charge must be supplemented with 10 pounds of additional explosive to total 50 pounds of explosive per borehole. Note. Each cratering charge must be carefully inspected for possible water damage prior to emplacement. e. Stem all boreholes with suitable material. 3-17. Deliberate Road Crater This cratering method (fig 3-17) produces road craters that are more effective than those resulting from the hasty method as they require an average of eight passes to be crossed by modern U.S. tanks. The crater produced is V-shaped, approximately 7 feet deep, 25 feet wide, with side slopes about 30 degrees to 37 degrees. The crater extends about 8 feet beyond the end holes. The method of placing charges is as follows: a. Bore the holes 5 feet apart, center-to-center, in a line across the roadway. The end holes are 7 feet deep and the others are alternately 5 feet and 7 feet deep. The formula for the computation of the number of holes is : N = L-16/5 + 1 L = length of crater in feet measured across roadway Any fractional number of holes is rounded off to the next highest number. Two 5-foot holes must not be made next to each other. If they are so calculated, one of them must be a 7-foot hole. The resulting two adjacent 7-foot holes may be placed anywhere along the line. b. Place 80 pounds of explosive in the 7-foot holes and 40 pounds of explosive in the 5-foot holes. c. Prime the charges as for hasty cratering. Dual priming of the 7-foot holes may be accomplished by independent priming of each of the two cratering charges, if used. d. Stem all holes with suitable material. 3-18. Relieved Face Road Crater This cratering method (fig 3-18) produces road craters that are more effective obstacles to modern tanks than the standard V-shaped craters. This technique produces a trapezoidal-shaped crater about 7 feet deep and 25 to 30 feet wide with unequal side slopes. In compact soil, such as clay, the relieved face cratering method will provide and obstace shaped as shown in A, figure 3-18. The side nearest the enemy slopes at about 25 degrees from the road surface to the bottom while that on the opposite side or friendly side is about 30 degrees to 40 degrees steep. The exact shape, however depends of the type of soil found in the area of operations. The procedure is as follows: a. On dirt or gravel surfaced roads, drill two rows of boreholes 8 feet apart, spacing the boreholes on 7-foot centers. On hard surfaced roads, drill the two rows 12 feet apart. The number of charges for the friendly side row can be calculated by the formula N = L-10/7 + 1, where L = length of crater in feet measured across the width of the road. Any fractional number of holes should be rounded off to the next highest number. Stagger the boreholes in the other row, as shown in B, figure 3-18. This row will always contain one less borehole than the other row. b. Make the boreholes on the friendly side 5 feet deep and load with 40 pounds of explosive, and those on the enemy side 4 feet deep and load with 30 pounds of explosive. c. Prime the charges is each row separately for simultaneous detonation. There should be a delay of detonation of 1/2 to 1 1/2 seconds between rows, the row on the enemy side being detonated first. Best results will be obtained if the charges on the friendly side are fired while the earth moved in the first row is still in the air. Standard delay caps may be used for delay detonation. d. Acceptable results may be obtained by firing both rows simultaneously, if adequate means are sufficient time for delay firing are not available. However the resulting crater will not have the same depth and trapezoidal shape as described above. e. To prevent misfires from the shock and blast of the row of charges on the enemy side (detonated first), the detonation cord mains and branch lines of the row on the friendly side (detonated last) must be protected by a covering of about 6 inches of earth. 3-19. Angled Road Crater Method This method is useful against tanks traveling in defiles or road cuts where the must approach the crater straightaway and is the most effective cratering method. The road crater is blasted using either the hast or deliberate cratering methods described in paragraphs 3-16 and 3-17, except the boreholes are drilled across the roadway at about a 45 degree angle as shown in figure 3-19. Because of the angle at which tanks must attempt to cross an angled crater, they tend to slip sideways and ride off their tracks. 3-20. Blasting Permafrost and Ice a. BLASTING PERMAFROST. (1) NUMBER OF BOREHOLES AND SIZE OF CHARGE. In permafrost, blasting requires about 1 1/2 to 1 times the number of boreholes and larger charges than those calculated by standard formulas for moderate climates. Frozen soil, when blasted breaks into large clods 12 to 18 inches thick and 6 to 8 feet in diameter. A the charge has insufficient force to blow these clods clear of the hole, they fall back into it when the blast subsides. Testing to determine the number of boreholes needed should be made before extensive blasting is attempted. In some cases, permafrost may be as difficult to blast as solid rock. (2) METHOD OF MAKING BOREHOLES. Boreholes are made by three methods--use of standard drilling equipment, steam pount drilling equipment, and shaped charges. Standard drill equipment has one serious defect--the air holes in the drill bits freeze and there is no known method of avoiding it. Steam point drilling is satisfactory in sand, silt or clay, but not in gravel. Charges must be placed immediately upon withdrawl of the steam point, otherwise the area around the hole thaws out and plugs it. Shaped charges also are satisfactory for producing boreholes, especially for cratering. Table 3-5 shows the size of boreholes in permafrost and ince made by M3A1 and M2A4 shaped charges. (3) EXPLOSIVES. A low velocity explosive like ammonium nitrate, satisfactory for use in arctic temperatures, should be used, if available. The heaving quality of low velocity explosives will aid in clearing the hole of large boulders. If only high velocity explosives are available, charges should be tamped with water and permitted to freeze. Unlesss high velocity explosives are thoroughly tamped, they tend to blow out of the borehole. b. BLASTING ICE. (1) ACCESS HOLES. These are required for water supply and determining the thickness of ice for the computation of safe bearing pressures for aircraft and vehicles. As ice carries much winter traffic, its bearing capacity must be ascertained rapidly when forward movements are required. Small diameter access holes are made by shaped charges. On solid lake ice, the M2A4 penetrates 7 feet and the M3A1, 12 feet. These charges will penetrate farther but the penetration distances were tested in only ice approximately 12 feet thick. If the regular standoff is used, a large crater formes at the top, which makes considerable probing necessary to finde the borehole. If a standoff of 42 inches or more is used with the M2A4 shaped charge, a clean hole without a top crater is formed. Holes made by the M2A4 average 3 1/2 inches in diameter, while those made by the M3A1 average 6 inches. (2) ICE CONDITIONS. In the late winter after the ice has aged, it grows weaker and changes color from blue to white. Although the structure of ice varies and its strength depends on age, air temperature, and conditions of the original formation, the same size and type of crater is formed regardless of the standoff distance. If the lake or river is not frozen to the bottom, the blown hole will fill with shattered ice and clearing will be extremely difficult. Under some conditions, shaped charges may penetrate to a depth much less than that indicated in table 3-5. (3) SURFACE CHARGES. Surface craters may be made with ammonium nitrate cratering charges or demolition blocks. For the best effects, the charges are placed on the surface of cleared ice and tamped on top with snow. The tendency of ice to shatter more rapidly than soil should be considered when charges are computed. (4) UNDERWATER CHARGES. (a) Charges are placed underwater by first making boreholes in the ice with boreholes in the ice with shaped charges, and then placing the charge below th ice. An 80-pound charge of M3 demolition blocks under ice 4 1/2 feet thick forms a crater 40 feet in diameter. This crater, however, is filled with floating ice particles, and at temperatures around 20 degrees F. freezes over in 40 minutes. (b) A vehicle obstacle may be cratered in ice by sinking boreholes 9 feet apart in staggered rows. Charges (tetrytol or plastic) are suspended about 2 feet below the bottom of the ice by means of cord with sticks bridging the tops of the holes. The size of the charge depends upon the thickness of the ice. An obstacle like this may retard or halt enemy vehicles for approximately 24 hours at temperatures around -24 degrees F. 3-21. Cratering at Culverts A charge detonated to destroy a culvert not more than 15 feet deep may, at the same time, produce an effective road crater. Explosive charges should be primed for simultaneous firing and thoroughly tamped with sandbags. Culverts with 5 feet or less of fill may be destroyed by explosive charges placed in the same manner as in hasty road cratering. Concentrated charges equal to 10 pounds per foot of depth are placed in boreholes at 5-foot intervals in the fill above and alongside the culvert. 3-22. Antitank Ditch Cratering a. CONSTRUCTION. In open country, antitank ditches are constructed to strengthen prepared defensive positions. As they are costly in time and effort, much is gained if the excavation can be made by means of cratering charges. To be effective, an antitank ditch must be wide enough to stop an enemy tank. It may be improved by placing a log hurdle on the enemy side and spoil on the friendly side. Ditches are improved by digging the face on the friendly side nearly vertical by means of handtools (para 3-15a). b. DELIBERATE CRATERING METHOD. The deliberate cratering method outlined in paragraph 3-17 is adequate for the construction of heavy tank ditches in most types of soil. c. HASTY CRATERING METHOD. An antitank ditch may be constructed by placing 50 pounds of cratering explosive in 5-foot holes, and spacing the holes at 5-foot intervals (fig 3-16). The ditch crater will be approximately 8 feet deep and 25 feet wide. 3-23. Blasting of Ditches In combat areas, ditches may be constructed to drain terrain flooded by the enemy or as initial excavations for the preparation of entrenchments. Rough open ditches 2 1/2 to 12 feet deep and 4 to 40 feet wide may be blasted in most types of soils. A brief outline of the method is given below. a. TEST SHOTS. Before attempting the actual ditching, make test shots to determine the proper depth, spacing, and weight of charges needed to obtain the required results. Make beginning test shots with holes 2 feet deep and 18 inches apart and then increase the size of the charge and the depth as required. A rule of thumb for ditching is to use 1 pound of explosive per cubic yard of earth in average soil. b. ALINEMENT AND GRADE. Mark the ditch centerline by transit line or expedient means and drill holes along it. When a transit or hand level is used, the grade of the ditch may be accurately controlled by checking the hole depth every 5 to 10 holes and at each change in grade. In soft ground, the holes may be made with a sharp punch, a quicksand punch (fig 3-20) or an earth auger. Holes are loaded and tamped immediately to prevent cave-ins and insure that the charges are at proper depth. Ditches are sloped at a rate of 2 to 4 feet per 100 feet. c. METHODS OF DETONATION. (1) PROPAGATION METHOD. By this method (fig 3-21) only one charge is primed-- the charge placed in the hole at one end of the line of holes made to blast the ditch. The concussion from this charge sympathetically detonates the next charge and so on until all are detonated. Only 50-60 percent straight commercial dynamite should be used in this operation. The propagation method is effective, however, only in moist or wet soils and may be effectively used in swamps where the ground is covered by several inches of water. If more than one line of charges is required to obtain a wide ditch, the first charge of each line is primed. The primed hole is overcharge 1 or 2 pounds. (2) ELECTRICAL METHOD. Any high explosive may be used in ditching by the electrical firing method which is effective in all soils except sand, regardless of moisture content. Each charge is primed with an electric cap and the caps are connected in leapfrog series (para 2-6b). Al charges are fired simultaneously. (3) DETONATING CORD METHOD. In this ditching method any high explosive may be used. It is effective in any type of soil, except sand, regardless of moisture content. Each charge is primed with detonating cord and connected to a detonating cord main or ring main line. d. METHODS OF LOADING. (1) The method of loading for a deep, narrow ditch is illustrated in figure 3-22. (2) The relief method of loading for shallow ditches is depicted in figure 3-23. Ditches 1 and 3 are blasted first to relieve ditch 2. (3) Figure 3-24 shows the posthole method of loading for shallow ditches in mud. (4) The cross section method of loading to clean and widen ditches is explained graphically in figure 3-25. Section VII. LAND CLEARING CHARGES 3-24. Introduction In military operations, construction jobs occur in which explosives may be employed to advantage. Among these jobs are land clearing, which includes stump and boulder removal, and quarrying. The explosives commonly used are military and commercial dynamite and detonating cord. The quantity of explosive used is generally calculated by rule of thumb. Charges may be placed in boreholes in the ground under or at the side of the target, in the target itself, or on top of the target. All charges should be tamped or mudcapped, which is a form of light tamping. 3-25. Stump Removal In certain military operations it may be necessary to remove stumps as well as trees. Stumps are of two general types, tap- and lateral-rooted (fig 3-26). Military Dynamite is the explosive best suited for stump removal. A rule of thumb is to use 1 pound per foot of diameter for dead stumps and 2 pounds per foot for live stumps, and if both tree and stump are to be removed, to increase the amount of explosive by 50 percent. Measurements are taken at points 12 to 18 inches above the ground. a. TAPROOT STUMPS. For taproot stumps, one method is to bore a hole in the taproot below the level of the ground. The best method is to place charges on both sides of the taproot to obtain a shearing effect (fig 3-26). For best results, tamp the charges. b. LATERAL-ROOT STUMPS. In blasting later-root stumps, drill sloping holes as shown in figure 3-26. Place the charge as nearly as possible under the center of the stump and at a depth approximately equal to the radius of the stump base. If for some reason the root formation cannot be determined, assume that it is the lateral type and proceed accordingly. 3-26. Boulder Removal In the building of roads and airfields or other military construction, boulders can be removed by blasting. The most practical methods are snakeholing, mudcapping, and blockholing. a. SNAKEHOLING METHOD. By this method, a hole large enough to hold the charg is dug under the boulder. The explosive charge is packed under and against the bould as shown in A, figure 3-27. For charge size, see table 3-6. b. MUDCAPPING METHOD. For surface or slightly embedded boulders, the mudcapping method is very effective. The charge is placed on top or against the side of the boulder wherever a crack or seam exists that will aid in breakage, and covered with 10 to 12 inches of mud or clay (B, fig 3-27). For charge size, see table 3-6. c. BLOCKHOLING METHOD. This method is very effective of boulders lying on the surface or slightly embedded in the earth. A hole is drilled on top of the boulder deep and wide enough to hold the amount of explosive indicated in table 3-6. The charge is then primed, put into the borehole, and stemmed (C, fig 3-27). Table 3-6. Charge Sizes for Blasting Boulders. ________________________________________________________________ ! Pounds of explosive required Boulder diameter (ft) !---------------------------------------- ! Blockholing ! Snakeholing ! Mudcapping -----------------------!-------------!-------------!------------ 3 ! 1/4 ! 3/4 ! 2 4 ! 3/8 ! 2 ! 3 1/2 5 ! 1/2 ! 3 ! 6 ---------------------------------------------------------------- 3-27. Springing Charges a. DEFINITION AND METHOD. A springing charge is a comparatively small charge detonated in the bottom of a drilled borehole to form an enlarged chamber for placing a larger charge. At times two or more springing charges in succession may be needed to make the chamber large enough for the final charge. Under these conditions at least 2 hours should be allowed between firing and placing successive charges for the boreholes to cool unless the sprung holes are cooled with water or compressed air. b. DETONATING CORD WICK. This is several strands of detonating cord taped together and used to enlarge boreholes in soils. One strand generally widens the diameter of the hole about 1 inch. (1) A hole is made by driving a steel rod approximately 2 inches in diameter into the ground to the depth required. According to the rule of thumb, a hole 10 inches in diameter requires 10 strands of detonating cord. These must extend the full length of the hole and be taped or tied together into a "wick" to give optimum results. The wick may be placed into the hole by an inserting rod or some field expedient. Firing may be done electrically or nonelectrically. An unlimited number of wicks may be fired at one time by connecting them by a detonated cord ring main or line main. (2) The best results from the use of the detonating cord wick are obtained in hard soil. If successive charges are placed in the holes, excess gases must be blown out andthe hole inspected for excessive heat. 3-28. Quarrying Quarrying is the extraction of rock in the natural state. Militarty quarries, generally of the open face type, are developed by the single or multiple bench method. See TM 5-332 for detailed information. Section III. DESTRUCTION TO PREVENT ENEMY USE 5-10. General a. The destruction of damaged or unserviceable explosives and demolition materials is accomplished by explosive ordnance disposal units as specified in AR 75-14, AR 75-15, TM 9-1375-200 and FM 9-16. b. Destruction of demolition materials, when subject to capture or abandonment, will be undertaken by the using of arm only when, in the judgment of the unit commander concerned, such action is necessary in accordance with orders of, or policy established by, the Army commander. The conditions under which destruction will be effected are command decisions and may vary in each case, dependent upon a number of factors such as the tactical situation, security classification of the demolition materials, their quantity and location, facilities for accomplishing destruction, and time available. In general, destruction can be accomplished most effectively by burning or detonation, or a combination of these. c. If destruction to prevent enemy use is resorted to, explosive and nonexplosive demolition materials must be so completely destroyed that they cannot be restored to usable condition in the combat zone. Equally important, the same essential components of sets and kits must be destroyed so that the enemy cannot assemble complete ones from undamaged components by cannibalization. d. If destruction of demolition materials is directed, due consideration should be given to (1) and (2) below. (1) Selection of a site that will cause greatest obstruction to enemy movement and also prevent hazard to friendly troops from fragments and blast which will occur incidental to the destruction. (2) Observation of appropriate safety precautions. 5-11. Destruction Methods Demolition materials can be most quickly destroyed by burning or detonation. The methods in A and B below, in order of preference, are considered the most satisfactory for destruction of demolition materials to prevent enemy use. For additional information on the destruction of explosives and ammunition see TM 9-1300-206 and TM 9-1300-214. a. METHOD No.1--BY BURNING. (1) GENERAL. Packed and unpacked high explosive items such as linear demolition charges, shaped demolition charges, block demolition charges, dynamite sticks, detonating cord, firing devices, time blasting fuse, and similar items may be destroyed quickly and effectively by burning. Blasting caps set aside for destruction by burning must be stacked in separate piles and not with other explosives. (2) METHOD OF DESTRUCTION. (a) Stack the explosives in a pile, if possible (not over 2,000 pounds to a pile), over a layer of combustible material. (b) Pour FUEL OIL over the entire pile. (c) Ignite the pile by means of a combustible train (excelsior or slow-burning propellant) of suitable length and take cover immediately. The danger area for piles being burned in the open is calculated from the safe distances given in paragraph 5-2 but never less than 400 meters. WARNING. COVER MUST BE TAKEN WITHOUT DELAY, SINCE DETONATION OF THE EXPLOSIVE MATERIAL MAY BE CAUSED BY THE FIRE. b. METHOD No.2--BY DETONATION. (1) GENERAL. Packed and unpacked high explosive items such as linear demolition charges, shaped demolition charges, block demoltion charges, dynamite sticks, detonating cord, blasting caps, firing devices, time blasting fuse, and similar items may be destroyed by placing them in piles and detonating them with initiating charges of TNT, or composition C series explosives, or other explosives having equivalent potential. (2) METHOD OF DESTRUCTION. (a) The explosives should be stacked in piles, if possible (not over 2,000 pounds to a pile). (b) Each 100 pounds of packed explosives (mine, blocks, etc.), require a 2-pound (minimum) explosive charge to insue complete detonation of the pile. For unpacked explosives, a 1-pound (minimum) explosive charge for each 100 pounds is sufficient. (c) Provide for dual priming as explained in chapter 2 to minimize the possibility of a misfire. For priming, either a nonelectric blasting cap crimped to at least 5 feet of time blasting fuse or an electric cap and firing wire may be used. (d) Detonate the charges. If primed with nonelectric blasting cap and time blasting fuse, ignite and take cover; if primed with electric blasting cap, take cover before firing charges. The danger area for piles detonated in the open is calculated according to the safe distance given in paragraph 5-2. APPENDIX D EXPEDIENT DEMOLITIONS ____________________________________________________________________________ D-1. Use of Epedient Techniques These techniques are not presented as a replacement for the standard demolition methods but for use by experienced blasters in special projects. Availability of trained men, time, and material will generally determine their use. D-2. Shaped Charges a. DESCRIPTION. Shaped charges concentrate the energy of the explosion released on a small area, making a tubular or linear fracture in the target. Their versatility and simplicity makes them effective against many targets, especially those made of concrete or those with armour plating. Shaped charges may be improvised (fig D-1). Because of the many variables, such as explosive density, configuration, and density of the cavity liner, consistent results are impossible to obtain. Thus experiment, or trial and error, is necessary to determine the optimum standoff distances. Plastic explosive is best suited for this type of charge. Dynamite and molten TNT, however may be used as an expedient. b. PREPARATION. Almost any kind of container is usable. Bowls, funnels, cone-shaped glasses (champagne glasses with the stem removed), and copper, tin, or zinc may be used as cavity linerse; or wine bottles with a cone in the bottome (champagne or cognac bottles) are excellent. If none of these is available, a reduced effect is obtained by cutting a cavity into a plastic explosive block. Optimum shaped charge characteristics are -- (1) Angle of cavity = between 30 degrees and 60 degrees (most HEAT ammunition has a 42 degree to 45 degree angle). (2) Standoff distance = 1 1/2 x diameter of cone (3) Height of explosive in container = 2 x height of cone measured from base of the cone to the top of the explosive. (4) Point of detonation = exact top center of charge. Cover cap, if any any part of it is exposed or extends above the charge, with a small quantity of C4 explosive. Note. The narrow necks of bottles or the stems of glasses may be cut by wrapping tem with a piece of soft absorbant type twine or string soaked in gasoline and lighting it. Two bands of adhesive tape, one on each side of the twine or string, will hold it firmly in place. The bottle or stemm must be turned continuously with the neck up, to heat the glass uniformly. Also, a narrow band of plastic explosive placed around the nexk and burned gives the same resulte. After the twine or plastic has burned, submerge the neck of the bottle in water and tap it against some object to break it off. TAPE THE SHARP EDGES OF THE BOTTLE TO PREVENT CUTTING HANDS WHILE TAMPING THE EXPLOSIVE IN PLACE. D-3. Platter charge This device utilizes the Miznay-Chardin effect. It turns a metal plate into a powerful blunt-nosed projectile (fig D-2). The platter should be steel (preferably round, but square is satisfactory) and should weigh from 2 to 6 pounds. a. CALCULATIONS. Weight of explosives = approximately the weight of the platter. b. PREPARATION. (1) Pack the explosive uniformly behind the platter. A container is not necessary if the explosive can be held firmly against the platter. Tape is acceptable. (2) Prime the charge from the exact rear center. Cover cap, if any part is exposed, with a small quantity of C4 explosive to insure detonation. (3) Aim the charge at the direct center of the target. c. EFFECT. The effective range (primarily a problem of aim) is approximately 35 yards for a small target. With practive, a demolitionist may hit a 55-gallon drum, a relatively small target, at 25 yards about 90 percent of the time. D-4. Grapeshot Charge This charge consists of a container, preferably a No. 10 can, projectiles (small pieces of steel), buffer material, an explosive charge, and a blasting cap. These are assembled as shown in figure D-3. a. COMPUTATION. The weight of the explosive is approximately 1/4 x the weight of the projectiles. b. PREPARATION. (1) Assemble the projectiles, a few inches of buffer material-earth, leaves, wood, felt, cloth, cardboard, etc., and the explosive charge. This should be C4, packed firmly. (2) Prime the charge from the exact rear center. Cover the cap, if any part is exposed, with a small quantity of C4 to insure detonation. (3) Aim the charge toward the center of the target. D-5. Dust Initiator This device consists of an explosive charge (powdered TNT or C3; C4 will not properly mix with the incendiary), an incendiary mix (2 parts of aluminum powder or magnesium powder to 3 parts ferric oxide), and a suitable finely-divided organic material (dust) or a volatile fuel such as gasoline called a surround. The dust initiator is most effective in an inclosed space, like a box car or a warehouse or other relatively windowless structure. At detonation, the surround is distributed throughout the air within the target and ignited by the incendiary material. a. COMPUTATION. (1) Charge size = 1 pound (1/2 explosive, 1/2 incendiary mix). (2) Cover size = 3 to 5 pounds of each 1,000 cubic feet of target. The one-pound charge will effectively detonate up to 40 pounds of cover. b. PREPARATION. Powdered TNT may be obtained by crushing it in a canvas bag. The incendiary mix must be thoroughly dispersed throughout the explosive. A great number of dust materials may be used as cover, among which are coal dust, cocoa, bulk powdered coffee, confectioners sugar, tapioca, wheat flour, corn starch, hard rubber dust, aluminum powder, magnesium powder, and powdered soap. If gasoline is used, 3 gallons is the maximum, as more will not disperse evenly in the air and thus give poor results. D-6. Improvised Cratering Charge This charge is a mixture of ammonium nitrate fertilizer containing at least 33 1/3 percent nitrogen and diesel fuel, motor oil, or gasoline at a ratio of 25 pounds of fertilizer to a quart of fuel. The ferilizer must not be damp. From this mixture, improvised charges of almost any sixe or configuration can be made. Proceed as follows: a. Pour the liquid on the fertilizer. b. Allow the mixture to soak for an hour. c. Place about half the charge in the borehole. Then place the primer, a primed 1-pound block of TNT, and add the remainder of the charge. (Never leave the charge in the borehole for a long period, as accumulated moisture reduces its effectiveness.) d. Detonate the charge. D-7. Ammonium Nitrate Satchel Charge Although the cratering charge (para D-6) is excellent, it is suitable only for cratering. A more manageable charge may be used by mixing ammonium nitrate fertilizer with melted wax instead of oil. The primer is set in place before the mixture hardens. a. PREPARATION. (1) Melt ordinary paraffin and stir in ammonium nitrate pellets, making sure that the paraffin is hot while mixing. (2) Before the mixture hardens add a half-pound block of TNT or its equivalent as a primer. (3) Pour the mixture into a container. Shrapnel material may be added to the mixture if desired or attached on the outside of the container to give a shrapnel effect. b. USE. Because the wax and fertilizer may be molded into almost any size or shape, it may be applied to agreat many demolition projects with satisfactory effects. _____________________________________________________________________________ Well, here it is, the file I spent 2 weeks typing up. It seems that it is "New and Improved by the U.S. Army!" (censored), chapters 1,4, almost all of 5, and at least 3 appendices have been eliminated. I'm sorry (yeah right) about no pictures, but what was I to do? I also eliminated lotsa tables cuz they wouldn't fit on the screen. Life's tough and you're just going to have to bear it! I'd pay close attention to the Appendix D, there is a lot of useful information in there. 'Til Next Time Death Jester. 12/01/90