A drift is a tunnel driven horizontally into a hillside along an outcropping coal seam. It is only defensible when it is shallow, timbered with props no more than 1.5 m apart, drained outward, given a second opening for through-ventilation, and worked by at least two people with one always at the entrance.
Part of Coal Surface Mining
Driving a tunnel into a hillside along a coal seam: layout, timbering, drainage, ventilation and the limits that decide when to stop.
A Drift Fails In Four Ways
The parent article gives the basic recipe: enter horizontally where the seam meets the surface, cut a tunnel at least 1.5 m × 1.5 m, timber as you advance, and follow the coal. It also gives a depth of 30-50 m “without ventilation engineering”. Treat that as an upper limit on how far to go, not as a promise of safety at that depth: a dead-end tunnel with one opening has no through-flow, and the failure modes below do not depend on distance. They are roof fall, water, bad air and fire.
Layout Decisions
- Drainage. Water runs downhill, so drive the drift on a slight upward grade inward, so water drains out of the mouth. A drift that dips inward collects water at the working face. If the seam dips into the hill, a drift that follows it will go down; this is a sign to choose open-cut, or to stop.
- Two openings. A second, small opening at a different height lets air move through by stack effect. That flow is driven by temperature difference and can reverse with the seasons (Ventilation Shafts and Chimneys explains the same effect in a buried room). Do not rely on it as a gas safeguard.
- The mouth. The portal is the weakest ground. Timber it first, and clear loose soil and rock from the slope above it.
- Size. The parent gives 1.5 m × 1.5 m as the minimum working section. A roof that is only high enough to crawl under cannot be timbered safely.
Method
Step 1: Open the portal. Cut the face back until you reach solid rock or coal, then set two legs and a cap (a “set”) against it.
Step 2: Advance one set at a time. Break out a short length of coal, then timber it before going further. Space sets at no more than 1.5 m (parent figure), closer where the roof is shale that flakes.
Step 3: Sound the roof. Tap the roof with a bar after each advance: sound rock rings, loose rock sounds dull or drummy. Pull back at the first dull sound.
Step 4: Keep one person at the mouth. That person keeps a count of who is inside, watches the entrance for dust or haze, and goes for help, never in.
Step 5: Stop at the limit. Stop at the parent’s depth, or at the first sign of gas, water inflow or roof trouble, whichever comes first.
Common Mistakes
- Advancing past the last timber “just to get the coal”. Falls occur where there is no support.
- Working a seam with a thin or flaky roof. Shale that slakes in damp air will come down without warning.
- Letting water pool at the face. Wet coal heaps and wet roof both weaken.
Safety
A drift concentrates every coal-mining hazard in one place
Roof fall is the largest killer, followed by methane and carbon monoxide that collect with no through-air. Never enter alone, never with a naked flame in a seam that may hold methane, and never run toward a collapse or an unconscious worker without air: the rule from shaft work applies, rescuers die in the same bad air (Safety Protocol). Roof, gas and dust are covered in their own articles; read them before a drift is opened.
What’s Next
- Learn next: Roof Collapse Prevention — timbering and ground control in detail
- Combine with: Gas Hazards — why through-air and no flame matter