Charge Placement

Part of Gunpowder and Explosives

Placing explosive charges safely and effectively for blasting rock, quarrying stone, and clearing obstacles.

Why This Matters

Gunpowder is only useful if you can direct its force where you need it. A charge placed on the surface of a rock wastes most of its energy blasting outward into the air. The same amount of powder placed correctly inside the rock can split a boulder that would take days to break with hammer and chisel. Charge placement is the difference between efficient engineering and wasted resources.

In a rebuilding society, every grain of gunpowder represents significant labor — months of niter bed cultivation, careful charcoal preparation, sulfur procurement. Wasting powder through poor placement is not just inefficient; it may mean the difference between completing a mine shaft or road cut and running out of explosives halfway through.

Beyond efficiency, incorrect charge placement is extremely dangerous. Poorly loaded charges can blow out sideways, shower the blast zone with rock fragments at lethal velocities, or fail to detonate entirely — leaving a live charge buried in the rock that can explode during later work.

Understanding How Charges Work

Black powder is a low explosive — it deflagrates (burns very rapidly) rather than detonating like modern high explosives. This means it produces a sustained push of expanding gases rather than a shattering shock wave. This characteristic determines how charges must be placed.

The Confinement Principle

Black powder requires confinement to do useful work. Unconfined powder simply burns with a flash and a puff of smoke. The more tightly the powder is confined, the more pressure builds before the containing material fails, and the more forcefully the charge breaks rock.

This is why bore holes are essential. A charge placed deep inside a drill hole, with the remaining space firmly tamped (plugged), is confined on all sides by rock except the tamped end. When the powder ignites, pressure builds until the rock fractures along its natural weaknesses.

Burden and Spacing

Burden is the distance from the charge to the nearest free face (exposed rock surface). This is the most critical measurement in blasting:

• Too little burden: The charge blows out through the free face, throwing rock violently but not breaking deep into the formation. Dangerous flying debris.
• Too much burden: The charge cannot overcome the weight of rock above it. The result is a muffled thump, cracked but unmoved rock, and wasted powder.
• Optimal burden: For black powder, the burden should be approximately 0.7 to 1.0 times the depth of the bore hole.

Spacing is the distance between adjacent charges when multiple bore holes are used. Typical spacing is 1.0 to 1.5 times the burden distance.

Bore Hole Preparation

Drilling

Bore holes for black powder charges are drilled by hand using a star drill (a steel chisel with a cross-shaped tip) and a hammer:

1. Mark the hole location on the rock face
2. Hold the star drill against the rock
3. Strike the drill with a sledgehammer
4. Rotate the drill 1/8 turn between each strike
5. Periodically remove dust by inserting a thin stick or blowing (use a tube, never your mouth directly over the hole)

Hole Dimensions

Application	Hole Diameter	Hole Depth	Typical Charge
Boulder splitting	2-3 cm	15-30 cm	50-100 g
Quarry bench	3-5 cm	30-60 cm	200-500 g
Mine shaft advance	3-4 cm	30-50 cm	100-300 g
Road cut	3-5 cm	40-80 cm	300-800 g

Hole Angle

• For quarry benches, drill holes vertically or angled slightly toward the free face (10-15 degrees from vertical)
• For tunnel work, drill holes angled slightly upward (5-10 degrees) so loose rock falls away from the face
• Never drill into existing cracks — the charge may vent through the crack instead of breaking new rock

Loading the Charge

Critical Safety Rules

• Never use metal tools inside a bore hole that contains powder. Use only wooden or copper implements.
• Never force or pound powder into a hole. Pour it gently.
• Never load a bore hole if lightning is possible within the area.
• Have only one person loading at a time. All others must be at safe distance.

Step-by-Step Loading Procedure

1. Clean the hole. Use a wooden scraper or compressed air (bellows) to remove all drill dust. Dust absorbs moisture and can prevent the charge from igniting.

2. Check for water. If the hole contains water, the charge must be waterproofed. Wrap the powder in greased leather or place it in a waxed paper cartridge. Small amounts of water can be absorbed with dry rags on a stick.

3. Insert the cartridge or pour the powder. Lower the powder charge to the bottom of the hole. If using loose powder, pour it slowly and steadily. If using a cartridge (powder wrapped in paper), lower it on a string or slide it down gently.

4. Insert the fuse. Place the fuse so that one end reaches into the powder charge and the other extends well beyond the mouth of the bore hole. For safety fuse, ensure at least 30 cm extends beyond the hole. The fuse must be in contact with the powder or it will not ignite the charge.

5. Tamp the stemming. This is the most critical and dangerous step. Stemming material (dry sand, clay, or drill cuttings) is placed on top of the charge and packed firmly to confine the explosion. Use a wooden tamping rod — never metal.

Tamping Procedure

• Add stemming material in small increments (2-3 cm at a time)
• Press each increment firmly with the wooden tamping rod using steady pressure — never strike or pound
• The total stemming length should be at least one-third of the hole depth, and ideally one-half
• Leave the fuse running through the stemming without kinking or crushing it
• The final tamp should be firm enough that the stemming does not fall out when the drill hole is horizontal

Tamping Danger

Tamping is historically the most dangerous step in blasting. Excessive force, metal tools, or sparks from grit can ignite the charge while you are standing directly over it. Use only steady hand pressure on a wooden rod. If you feel resistance, stop — the stemming may be binding on an irregularity in the hole wall.

Pattern Blasting

When multiple charges are needed (quarrying a bench, advancing a tunnel), the pattern and sequence of detonation matter greatly.

Quarry Bench Pattern

For breaking a section of rock from a quarry face:

1. Drill a row of holes parallel to the free face, spaced 0.5-1.0 m apart
2. Set the burden (distance to free face) at 0.7-1.0 times hole depth
3. Fire all charges simultaneously, or fire the center hole first and work outward
4. The first charge creates a new free face; subsequent charges break toward it

Tunnel Advance Pattern

For advancing a mine shaft or tunnel:

1. Drill a central “cut” hole aimed slightly off-axis to create initial breakage
2. Surround the cut with “relief” holes drilled parallel to the tunnel axis
3. Drill “trim” holes around the perimeter for final shaping
4. Fire in sequence: cut first, then relief, then trim
5. Each round typically advances the tunnel face by 60-80% of the hole depth

V-Cut Pattern

The simplest tunnel-blasting pattern:

1. Drill two holes angled toward each other, meeting at a point near the bottom
2. These form a V shape when viewed from above
3. When fired, the converging charges break out a wedge of rock, creating a free face
4. Subsequent charges break toward this V-shaped void

Post-Blast Safety

After firing charges:

1. Wait. Do not approach the blast area for at least 15 minutes after the last shot fires. Delayed detonations are possible.
2. Count shots. Compare the number of detonations heard to the number of charges placed. If any charge did not fire, treat it as a misfire.
3. Inspect. Approach the blast area cautiously. Look for unexploded powder, damaged fuse remnants, or suspicious cavities.
4. Handle misfires. Never attempt to dig out or re-drill a misfired charge. Drill a new hole at least 30 cm away from the misfire, load and fire it. The concussion will usually detonate the misfired charge.
5. Ventilate. In underground work, do not re-enter until fumes have cleared. Black powder produces carbon monoxide, carbon dioxide, and sulfur dioxide — all dangerous in confined spaces. Wait at least 30 minutes and verify air quality with a candle (if it dims or goes out, the air is not safe).