Departure of FFU
CHAPTER TWO
3. TIMBER CUTTING:
a. Conventional Formula:
(1) Read the problem/gather information:
Example (a) Type of explosive TNT
M11
Det Cord M12, M13
M81
Det Cord M11
M14 M12, M13
M81
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(b) RE Factor 1
(c) Package Weight 1
(d) Number of Trees 3
(e) Formula
P=(D2/40) (External/Ring) P=(D2/50) (Abatis)
P=(D2/250) (Internal) (g) Tree diameter (D): 20 inches
D=(circumference/3.1416) (2) Solve Formula:
Example
P=(D2/40)=(202/40)
P=(400/40)= 10 lbs TNT
(3) Divide by RE Factor:
10 lbs TNT/1 = 10 lbs TNT (4) Divide by package weight and round up:
10 lbs TNT/1 lb = 1 PKG TNT (6) Number of Targets is 3
(7) Multiply by number of trees:
10 PKG TNT x 3 Charges = 30 PKG TNT b. Ring Charge Formula: For use with M112, M118, or M186. Max
diameter of tree can only be 30 inches.
2-5 D=(circumference/3.1415)
(g) Charge Thickness:
19.60 lbs TNT/1.25 lb PKG=14.62 lb C-4 (4) Divide by package weight and round-up:
(7) The Ring Charge is utilized when the direction of the fall of the tree is not important, there is no shortage of explosives and there is no need to clear the stump of the tree low to the ground.
This charge will place the remaining portion of the stump below the 8-inch Vehicle and Rotary Wing Aircraft obstacle clearance.
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This charge is mainly used to clear the way for roads, airfields, drop zones, and helicopter landing zones.
(a) Securing the Charge: Remove the bark from the tree.
Then, if adhesive face of explosive will not adhere to tree, wrap tree with tape. Use additional tape on outside of explosive if necessary.
(b) Charge Thickness:
0.5-inch thick for 10-inch diameter trees 1-inch thick for 10-30 inch diameter trees
Note: Only trees 30 inches or less can be cut with this charge. Trees larger than 30 inches should be cut using an external charge.
(c) Place charge as close to ground as possible
(d) Detonate with demo knot or blasting cap at center of charge with C-4 cover surrounding the detonator by at least 1 inch of explosive.
c. Land Clearing Charges:
(1) Stump Removal: Stumps are of two general types- Tap rooted and
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dead stumps and 2 pounds per foot for live stumps. If both the tree and stump are to be removed, increase the amount of explosive by 50 percent.
(2) Tap Rooted Stumps: The preferred method for tap rooted stumps is to bore a hole in the taproot below the ground level. The best
method is to place charges on both sides of the taproot to obtain a shearing effect. Tamp the charges for best results.
(3) Laterally-Rooted Stumps: In blasting laterally rooted stumps, drill sloping charge placements as close as possible under the center of the stump and at a depth equal to the radius of the stump base. If the root formation cannot be determined, assume that it is lateral type and proceed accordingly.
2-8 4. STEEL CUTTING:
a. Conventional Formula:
(1) Read the problem/gather information:
Example
(a) Type of explosive M112/C-4
(b) How many targets 4
(c) Which formula:
P= 3/8 A = 0.375 A
(d) Measurements/area calculation:
ATF 8 x 1 8 sq inches
ABF 8 x 1 8 sq inches
AW 10 x1 10 sq inches
TA = A = 26 sq inches (e) Package weight of explosive 1.25 lbs
(f) RE factor 1.34
(g) Draw a picture
(2) Solve for TNT:
P = 3/8 A
P = 3/8 (26 sq inches) P = 9.75 lbs TNT
10”
8”
1”
1”
1”
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Pounds C-4=(P/RE Factor)=(9.75 lbs TNT/1.34)=7.27 lbs (4) Divide by explosive’s package size and round up:
(7.27 lbs C-4 / 1.25 lbs/PKG)= 5.81 PKG C-4 (5) Number of target is 4.
(6) Multiply by number of charges:
6 PKGs x 4 Charges = 24 PKGs C-4
b. Advance formula (Ribbon Charge)- Only works with M112, M118, M186, and for steel up to 3 inches thick.
(1) Read the problem/gather information:
Example
(a) Type of explosive M118 Sheet
(b) Number of targets 4
(c) Measurements
TF Width = 10 Thickness = 1.5
BF 10 1.5
W 12 0.75
(d) Package size: L x W x H .75 x 3 x 12 (e) Draw a Picture:
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(f) Find the total charge volume (TCV):
CT x CW x CL = CV
CW = 3 times charge thickness Cl = Length of cut desired
(4) Total package volume divided by block size and round up:
Example
38.95 cu. in. = 4.32 Sheets M118 9 cu in
Round up to 5 sheets of M118 (5) Number of targets is 4.
2-11 Example
5 sheets of M118 x 4 Charges = 20 Sheets of M118 c. Ribbon Charge: (CT x CW x CL = CV)
(CV/EV = Number of Packages)
d. Diamond Charge: (CV/EV)
Thickness of charges is half the thickness of the target or a minimum of .5 inches Blasting cap or det cord
Width of charge is 3 times the thickness of the charge
Fuse
Primed at
Time fuse Length of charge
equals length of target
2-12 e. Saddle Charge: (CV/EV)
f. Steel Chain Cutting Charge:
P = D
P = Pounds of TNT Required
D = Diameter in inches of steel chain to be cut D = 1 inch
P = 1 pound of TNT, if block will bridge link. If not, use two blocks (one inch each side).
g. Rail Cutting Formula:
Rails are preferably cut at crossings, switches or curves. Cut at alternate rail splices for a distance of 500 feet.
Less than 5 inches high – use ½ pound of explosives Five inches or higher – use 1 pound of explosives Crossing and switches - use 1 pound of explosives
Tracks- The destruction of railroads with explosives should be done at vulnerable points. These are curves, switches, frogs and crossovers,
2-13 h. Charge Placement:
Steel Sections- The size and type of a steel section will determine the placement of the explosive charge. Cut extended sections by placing the explosives on one side of the section completely along the
proposed line of rupture. In some steel trusses with individual
members fabricated from two or more primary sections (such as angle irons or bars separated by spacer washers or gusset plates), place the charge with its opposing portions offset the same distance as the thickness of the section being cut to produce a shearing action.
Heavier I-Beams, wide-flange beams and columns can also require auxiliary charges placed on the outside of the flanges. Ensure that opposing charges are never directly opposite each other because this tends to neutralize the explosive effect.
Note: When cutting steel greater than 3 inches thick, use:
P= 3/8 x A
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2-15 5. BREACHING CHARGE
a. Breaching Charge Chart
Material R K
Earth All Values 0.07
Poor masonry, shale, hardpan, good timber and earth construction
Less than 1.5 m (5 ft) 1.5 m (5 ft) or more
0.32 0.29 Good masonry, concrete,
block, rock Dense concrete, first-class
masonry
(concrete only; will not cut reinforced steel) Values of C, the tamping factor, for breaching charges:
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(1) Read the problem/gather information:
Example
Type of Explosive TNT
RE Factor 1
Package Weight 1 lb
Type of Material Reinforced Concrete Breaching Radius (ft) (R) 3 ft
K Value (from chart) 0.80
Type Tamping Untamped, Ground Placed
C Value (from chart) 3.6
Width of Target 70 ft
(a) Formula:
P = R3 K C (b) Draw a picture:
(2) Solve formula:
P = R3 K C
P = (3 ft)3 (0.80) (3.6) = 77.76 lbs TNT (3) Divide by RE factor:
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(4) Divide by package weight and round up:
77.76 lbs TNT = 77.76 lbs TNT 1 lb TNT/PKG
77.76 PKGs rounds up to 78 PKGs TNT (5) Determine the number charges and round up:
N = W = 70 = 11.60 Charges 2R 2(3)
11.60 Charges rounds up to 12 charges
(6) Muliply amount of explosives by number of charges:
78 PKGs x 12 Charges = 936 PKGs TNT
b. Counter Force Charge Placement: Use 1½ pounds of explosive per foot of thickness. Round up to the next higher ½ foot before multiplying. Maximum target thickness is 4 feet.
Breaching Charge Thickness*
Charge Weight (lbs) Charge Thickness (inches) Less than 5
5 to less than 40 40 to less than 300 300 or more
1 2 3 4
* Approximate Values
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c. Boulder Blasting Charges:
(1) Block Holing Method: Drill a hole in the top of the boulder deep and wide enough to hold the amount of explosive required. Prime the charge, place into the borehole and stem.
(2) Snakeholing Method: Dig a hole large enough to hold the charge under the boulder. Pack the explosive charge under and against the boulder.
(3) Mudcapping Method: Place the charge on top or against the side of the boulder wherever a crack or seem exists that will aid in breakage. Cover the charge with 10 to 12 inches of mud or clay.
Notes
Charge Size (lbs) Boulder
Diamter (m)
Block-Hole Method
Snake-Hole Method
Mud-Cap Method
3 0.250 0.75 2.0
4 0.375 2.00 3.5
4 0.500 3.00 6.0
2-19 6. M122, DEMOLITION FIRING DEVICE
a. M122, General Data Chart M122, General Data
Transmitter:
Size (antenna collapsed) Length:
Without battery pack:
With battery pack
2.25 lbs (1.25 kg) 4.25 lbs (2.13 kg) Operating temperature -25° F to +125° F (-32° C to +52° C)
Without battery pack:
With battery pack:
1.1 lbs (0.5 kg) 1.4 lbs (0.6 kg)
Nominal capacity: Five M6 Electric Blasting Caps in series
Operating temperature: -25° F to +125° F (-32° C to +52° C) Number of caps able to be initiated: See table
Transmitter Battery Pack, M112 Type Battery:
2-20 Receiver Battery Pack, M112
Type Battery:
Life Expectancy at given temps:
Alkaline 1.5 volts BA 3030/U
6135-00-930-0030
General and Low temperatures TM 9-1375-213-12-3&P b. Firing Procedures:
(1) Before firing, allow 8 minutes to pass after the arming switch is set to ARM.
(2) Set the receiver’s code in the transmitter. Set letter using area code switch. Set numbers using the six button switches.
(3) Unscrew the transmitter antenna cap and extend the antenna to its full 47-inch length.
(4) Hold the transmitter in a vertical attitude. Life FIRE button cover and pus the FIRE button. Hold the FIRE button down for at lease five seconds.
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(6) Avoid contact with antenna when pressing fire button. A slight burn can result from touching the antenna when a signal is being transmitted, in addition to the transmission range being reduced.
(7) Operator will obtain greater transmitting range when operating transmitter by:
(a) Holding the transmitter against chest.
(b) In a kneeling position, placing the transmitter on the knee
(c) Placing the transmitter on ground or on top of large metal surface, such as the top of a vehicle, etc.
(8) To recover the receiver:
(a) Return to the receiver site only after it has been determined that the charge has been fired.
(b) Hold the receiver body steady and lift the arming switch and move it to the SAFE position.
(c) Disconnect the firing leads and antenna from the receiver.
(9) Misfire procedures:
(a) Check to ensure at least 8 minutes have passed since the receiver’s arming switch was ,oved to the ARM position.
(b) Check the transmitter’s code setting. Use a flat tip screwdriver to rotate are code switch back and forth through all positions five times. Reset the area code.
(c) If 8 minutes have passed since arming the receiver. Lift the FIRE button cover, and press the FIRE button.
(d) If the charge fails to fire, set the code to all zeros (any area code) lift the FIRE button cover, press and hold FIRE button for 5
seconds and observe lamp. If the FIRE SIGNAL lamp fails to light, secure another transmitter, if possible, and attempt to fire the charge with it.
(e) If the FIRE SIGNAL lamp lights, reset the transmitter with the proper code for the receiver being used, move closer to receiver if such movement can be safely undertaken from both a tactical and situation as well as to maintain a safe distance from the
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explosives. In addition to moving closer to receiver, relocate transmitter, if possible, so that its signal will reach the receiver from a different direction.
(f) From the new position, lift the FIRE button cover and push FIRE button once again.
(g) If above procedure again fails to initiate the explosives, secure another transmitter. Set the proper code, and attempt to fire the charge in the normal manner.
− Reset transmitter to zero at transmitter site.
− Wait ½ hour before approaching a misfired charge. When operator approaches a receiver after a misfire, it is
advisable that he take the transmitter with him in order to prevent the receiver from being inadvertently activated by someone else. The transmitter’s antenna should be collapsed.
− During the waiting time, attempt to use another receiver if available.
− After waiting ½ hour, approach the receiver, separate and cut the lead wires from the blasting cap binding posts one at a time without disturbing the receiver caps, or
connections.
− Strip an inch of insulation from the cut lead wires and shunt wires. Remove the remaining wire from binding posts.
− Remove the blasting caps from the firing circuit by cutting the det chord.
− Place the caps a safe distance away from the charges and personnel. Check cap circuit using M51 test set or
galvanometer. Check wires for visual damage in the process.
− Using a new receiver, repeat the hook-up sequence.
− If a new receiver is not available, check the current receiver as follows.
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− Ensure that the receiver’s battery cap is tightened to the index mark located on the receiver’s battery compartment.
− Ensure that the receiver’s antenna is properly connected and is NOT grounded.
− Ensure the firing circuit has been properly connected.
− If the problem is one of the above, correct as required and repeat arming and firing procedure.
− If the problem is not one of those listed above, use a standard blasting machine to complete the operation.