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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 = D<>/250 or P = .004 D<> 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 = D<>/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 = D<>/40 or P = .025 D<> 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 = D<>/40
P = (30)<29>/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 = D<>/ro or P = .02D<EFBFBD> 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 = D<>
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 = 3H<33>T
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 = 4H<34>T).
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

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