Us Marines - Explosives And Demolitions Techniques From Vietnam.pdf - archive - wojak.aon

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Field Manual: Explosives and Demolitions

by U.S. Army

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DEPARTMENT OF THE ARMY FIELD MANUAL

Explosives and Demolitions extract.

HEADQUATERS, DEPARTMENT OF THE ARMY

February 1971

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.

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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.)

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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).

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(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

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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

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