Demolitions

The breaching charge formula is the most-tested calculation in Sapper School. Memorize it. Practice it until you can solve problems in your sleep.

The Breaching Formula:

P = R x K x C

Where:

• P = Pounds of TNT equivalent needed
• R = Thickness (in feet) of the material to be breached
• K = Material factor (see table below)
• C = Breaching factor (see table below)

Material Factor (K):

• Earth, loam, sand = 0.3
• Concrete (unreinforced) = 0.5
• Concrete (reinforced) = 0.6
• Rock, shale = 0.8
• Steel = 1.0
• Timber = 0.2 (rarely breached, usually cut)

Breaching Factor (C):

• External charge, tamped = 1.0
• External charge, untamped = 1.5
• Internal charge, uncased = 1.0
• Internal charge, cased = 0.5

Practice Problems:

1. Breach 4-foot reinforced concrete wall with external untamped charge:
   P = 4 x 0.6 x 1.5 = 3.6 lb TNT. Round up to 4 lb or 3 M112 blocks (3.75 lb equivalent).
2. Breach 2-foot steel door with cased internal charge:
   P = 2 x 1.0 x 0.5 = 1.0 lb TNT. Use 1 M112 block (1.25 lb equivalent).
3. Breach 6-foot earthen berm with external tamped charge:
   P = 6 x 0.3 x 1.0 = 1.8 lb TNT. Use 2 M112 blocks (2.5 lb equivalent) or round up to 2 lb.

Converting to C4:

To convert required TNT to C4: C4 = P / 1.34

Example: Need 4 lb TNT equivalent. 4 / 1.34 = 2.99 lb C4. Round up to 3 lb or approximately 2.4 M112 blocks.

Testing Notes:

• Calculations are tested without calculators — practice mental math
• Show all work — partial credit may be available for correct method
• Always round UP — insufficient explosive fails the mission
• Units matter — R must be in feet, not inches

Breaching creates holes; cutting severs materials. Different formulas apply for cutting timber and steel structural elements.

Timber Cutting Formula:

P = (D² / 40) x K

Where:

• P = Pounds of TNT equivalent needed
• D = Diameter of timber (in inches)
• 40 = Constant for timber cutting
• K = Material factor (Timber = 1.0 for most species)

Timber Cutting Examples:

• Cut 12-inch diameter tree: P = (144 / 40) x 1 = 3.6 lb TNT. Round up to 4 lb or 3-4 M112 blocks.
• Cut 24-inch diameter timber: P = (576 / 40) x 1 = 14.4 lb TNT. Use satchel charge approach.
• Cut 6-inch diameter pole: P = (36 / 40) x 1 = 0.9 lb TNT. 1 M112 block sufficient.

Steel Cutting Formula:

P = 3/8 x A

or P = 0.375 x A

Where:

• P = Pounds of TNT equivalent needed
• A = Cross-sectional area in square inches
• 3/8 (0.375) = Constant for steel cutting

Steel Cutting Examples:

• Cut steel beam with 6 sq in cross-section: P = 0.375 x 6 = 2.25 lb TNT. Use 2 M112 blocks.
• Cut steel rod with 2 sq in cross-section: P = 0.375 x 2 = 0.75 lb TNT. Use 1 M112 block.
• Cut I-beam with 12 sq in cross-section: P = 0.375 x 12 = 4.5 lb TNT. Use 4 M112 blocks.

Charge Placement for Cutting:

• Timber: Place charge on side of tension (the side that will pull apart when cut)
• Steel: Center charge on cross-section for even cutting
• Multiple charges: For large cuts, use multiple smaller charges rather than one large charge

Ring Charges:

For cutting circular steel or timber, construct a ring charge using detonating cord. The cord is wrapped around the target and secured. The simultaneous detonation around the circumference creates a clean cut.

Building effective charges requires understanding charge types, proper construction techniques, and placement principles for maximum effect.

Charge Types:

• Standard Charge: Bulk explosive placed in contact with or near the target. Used for breaching and cratering.
• Shaped Charge: Directional explosive with a conical liner that focuses energy. Used for penetrating armor, concrete, and steel.
• Cutting Charge: Explosive configured to sever material. Timber and steel cutting charges.
• Expedient Charge: Improvised from available materials. Sappers must be able to construct effective charges from scratch.

Charge Construction Principles:

• Contact: Charge should be in direct contact with target when possible
• Shape: Follow target contour for even distribution of explosive force
• Security: Charge must remain in place during firing
• Accessibility: Must be able to prime the charge after placement

M112 Block Charge Construction:

1. Determine required number of blocks from calculations
2. Arrange blocks to cover target area evenly
3. Use adhesive backing or tape to secure blocks to target
4. Ensure continuous contact between blocks if using multiple
5. Prime at center or designated priming point

Satchel Charge Construction:

1. Place required explosive in a canvas or nylon bag
2. Distribute evenly within the bag
3. Secure bag opening (tie, Velcro, or tape)
4. Attach carrying straps if needed
5. Prime charge through bag material at designated point

Shaped Charge Employment:

• M5A1, M2A4, and M3 charges come pre-constructed
• Standoff distance is critical — follow specifications (typically 2-4 charge diameters)
• Must be perpendicular to target surface for maximum penetration
• Secure to prevent movement during firing
• Prime at designated initiation point

Expedient Charge Construction:

When standard charges are unavailable, sappers construct charges from raw C4 or other explosives:

1. Calculate required explosive weight
2. Form explosive into appropriate shape for target
3. Use container (sandbag, cloth, tape) to hold shape if needed
4. Ensure density and consistency of explosive mass
5. Prime at center of mass

Priming is the process of initiating the main explosive charge. Understanding blasting caps, detonators, and priming methods is essential for safe and effective demolitions.

Blasting Caps:

• M6 Electric Blasting Cap: Initiated by electrical current. Color-coded wires (yellow = positive, blue = negative for military caps).
• M7 Nonelectric Blasting Cap: Initiated by burning time fuse or detonating cord.
• Commercial Blasting Caps: Various types, use only if military caps unavailable.

Priming Methods:

• Direct Priming: Blasting cap inserted directly into the explosive charge. Used for small charges and when det cord is unavailable.
• Indirect Priming (Det Cord): Detonating cord attached to charge, blasting cap initiates the det cord. More reliable for large or multiple charges.

C4 Priming Procedure:

1. Identify priming point (usually center of charge)
2. Create cavity in C4 using sharp object or finger
3. Insert blasting cap into cavity
4. Pinch C4 around cap to ensure good contact
5. Secure cap in place (do not remove once inserted)
6. If using det cord, insert det cord end into cavity with cap

Detonating Cord (Det Cord):

• Flexible plastic tube containing high explosive (PETN)
• Burns/detonates at approximately 20,000 feet per second
• Can be used to prime charges or create ring charges
• Initiated by blasting cap attached to end
• Knots: Uli knot or square knot to join sections

Time Fuse (Safety Fuse):

• Burns at approximately 40 seconds per foot
• Used with nonelectric caps for non-electric initiation
• Provides time delay for personnel safety
• Must test burn rate before use (environment affects burn rate)

Priming Safety:

• Never insert blasting cap into explosive until ready to fire
• Handle caps gently — they are sensitive
• Keep caps away from all radio transmitters (can cause premature detonation)
• Electrical caps: Check circuit with galvanometer before connecting to firing device

Firing systems provide the initiation energy to the blasting cap. Understanding electrical and nonelectrical firing systems is critical for mission success and safety.

Electrical Firing Systems:

• M57 Firing Device (Clacker): Hand-powered generator. Squeezing handle generates electrical current. Most common for field demolitions.
• M40 Test Set: Used to test electrical circuits before firing. Ensures continuity and proper resistance.
• Battery Firing: Uses military or commercial batteries. Simple but requires fresh batteries.

Electrical Firing Circuit Components:

1. Firing device (power source)
2. Firing wire (conducts current to charge)
3. Blasting cap (converts electrical energy to explosive initiation)
4. Main charge (explodes when cap detonates)

Electrical Circuit Types:

• Series Circuit: All blasting caps connected in a single line. One break disables entire circuit.
• Parallel Circuit: Each cap has independent path to power. More reliable for multiple charges.
• Series-Parallel: Combination for large numbers of charges.

Nonelectrical Firing Systems:

• Time Fuse: Provides time delay. Used when electrical systems unavailable or when radio silence required.
• Command Detonation: Immediate initiation via pull-wire or other mechanical means.
• Tripwire: Victim-activated initiation for booby traps and obstacles.

Firing Procedure (Electrical):

1. Construct and place charges
2. Prime charges with blasting caps
3. Connect firing wire to blasting caps
4. Test circuit with M40 test set (resistance should be 1-3 ohms per cap)
5. Secure all connections
6. Connect firing device only when ready to fire
7. Clear area and sound warning
8. Fire by actuating firing device

Firing Safety:

• Never connect firing device until ready to fire
• Keep firing device on person or secured until firing
• Clear minimum safe distance (based on charge size)
• Account for all personnel before firing
• Have backup firing method if primary fails

Explosives are inherently dangerous. Strict adherence to safety procedures protects personnel and ensures mission success. There are no shortcuts with explosive safety.

General Safety Rules:

• Never point blasting caps at anyone, including yourself
• Never attempt to disarm or recover a misfire yourself — report to EOD
• Never use radio transmitters near electrical blasting caps
• Never smoke near explosives or in demolition areas
• Never mix incompatible explosives or materials
• Always use the minimum explosive necessary for the mission

Storage Safety:

• Store explosives in approved magazines or containers
• Separate blasting caps from main explosive charges
• Maintain inventory records — account for every item
• Post warning signs and secure storage areas
• Limit access to authorized personnel only

Handling Safety:

• Handle explosives gently — avoid dropping or striking
• Keep explosives dry — moisture affects performance
• Inspect before use — damaged explosives may be unstable
• Wear appropriate PPE: gloves, eye protection, helmet
• Wash hands after handling explosives before eating or smoking

Blasting Cap Safety:

• Blasting caps are the most sensitive component — handle with extreme care
• Never remove blasting cap from charge once inserted
• Keep blasting caps away from all radio transmitters (30-meter minimum)
• Inspect caps before use — damaged caps are unsafe
• Short electrical cap leads until ready to connect

Firing Safety:

• Clear minimum safe distance before firing (varies by charge size)
• Sound warning signals: 5-minute warning, 1-minute warning, fire signal
• Account for all personnel before firing
• Never fire during electrical storms
• Have EOD or qualified personnel available for misfires

Misfire Procedures:

1. Wait minimum 30 minutes (electrical) or 60 minutes (time fuse)
2. Do not approach misfire until wait time elapsed
3. Report misfire to qualified personnel or EOD
4. Do not attempt to disarm or recover misfire charge
5. Mark location and secure area
6. Document misfire on after-action report

Minimum Safe Distances:

• 1 lb charge: 300 meters
• 10 lb charge: 600 meters
• 100 lb charge: 1,500 meters
• In structures or confined spaces: increase distances by 50%

Knowledge must be applied. These exercises develop the hands-on skills required for demolitions operations.

Exercise 1: Calculation Drills

Drill calculations until automatic. Create flashcards with problem on front, solution on back. Time yourself — you should solve standard breaching problems in under 60 seconds.

• 50 breaching problems with varying materials and conditions
• 25 timber cutting problems
• 25 steel cutting problems
• Practice converting between TNT and C4

Exercise 2: Charge Construction Simulation

Practice constructing charges using inert materials (Play-Doh, modeling clay, or inert training C4 if available):

1. Practice forming charges of specific weights
2. Construct mock M112 block arrangements
3. Practice priming with dummy blasting caps
4. Work on speed — you have limited time in the field

Exercise 3: Priming Practice

With inert training materials:

1. Practice creating cavities in C4 for blasting caps
2. Simulate inserting caps and securing them
3. Practice working with detonating cord — cutting, tying knots
4. Time yourself from start to primed charge

Exercise 4: Knot Tying for Demolitions

Practice knots used in demolitions:

• Square knot — joining ropes
• Bowline — fixed loop
• Round turn and two half hitches — securing under tension
• Uli knot — joining det cord

Exercise 5: Mental Map of Formulas

Write out all formulas from memory daily:

• P = R x K x C (breaching)
• P = (D² / 40) x K (timber)
• P = 3/8 x A (steel)
• C4 = P / 1.34 (conversion)

Exercise 6: Full Mission Profile

Combine all skills in a timed scenario:

1. Receive target description and parameters
2. Calculate required explosive
3. Determine charge type and construction
4. Plan priming and firing method
5. Write out safety and firing procedures
6. Time limit: 15 minutes for complete plan

Standards Reference:

For complete demolitions standards and testing requirements, see the Standards page.