Trenching & Excavation Basics

Trench collapses happen in seconds and often give no warning. One cubic yard of soil can weigh as much as a car, about 3,000 pounds. A worker buried even to the waist can be crushed or unable to breathe before anyone can dig them out. Almost every trench death is preventable with a protective system and a competent person who checks it.

• Construction
• Utilities
• Plumbing
• Landscaping

Trench or excavation?

• An excavation is any man-made cut, cavity, trench or depression in the earth formed by removing soil.
• A trench is a narrow excavation that is deeper than it is wide, and no more than 15 feet wide at the bottom.

Both are covered by OSHA’s excavation rules (29 CFR 1926 Subpart P).

Why trenches collapse

Soil is held in place by the soil around it. When you dig a trench, you remove that support, and the walls start trying to move into the hole. Collapse is more likely when:

• The soil is sandy, gravelly, loose, or was dug before (backfill around old utilities)
• Water is present: rain, groundwater, a broken pipe, or melting frost
• The soil dries out and cracks, or freezes and thaws
• Heavy weight sits near the edge: spoil piles, equipment, trucks, stacked pipe
• Vibration from traffic, compactors, pile driving or nearby equipment shakes the soil
• The trench stays open for a long time

A competent person classifies the soil as stable rock, Type A, Type B or Type C to decide how steep the walls can be and what protection is needed. See Soil Classification.

The depth rules

The main types of protective systems are:

• Sloping and benching: cutting the walls back at an angle so they can’t collapse. The allowed angle depends on the soil type. Type C soil requires a slope of 1½ feet back for every 1 foot down (34 degrees).
• Shoring: hydraulic, timber or screw-jack supports that hold the walls in place.
• Shielding: trench boxes or shields that protect workers inside if the walls fail. Workers must stay inside the shield.

See Protective Systems for details.

The competent person

Every excavation needs a competent person: someone trained in soil analysis, protective systems and the excavation rules, who can recognize hazards and has the authority to fix them right away. The competent person must:

• Inspect the excavation, the area around it and the protective system daily before work starts and as needed throughout the shift
• Inspect again after every rainstorm or other event that could increase the hazard, such as vibration or a water leak
• Remove workers from the excavation immediately if there’s evidence of a possible cave-in, a failing protective system, a hazardous atmosphere or other danger

See Excavation Inspections & the Competent Person.

The other trench hazards

Getting in and out

In trenches 4 feet or deeper, a ladder, stairway or ramp must be within 25 feet of every worker. Ladders must extend 3 feet above the edge and be secured. Climbing the walls or a trench box spreader is not a safe way out.

Spoil piles and falling material

Keep spoil piles, material and equipment at least 2 feet back from the edge, or use retaining devices to keep them from falling in. Scale loose rock and soil from the walls.

Water

Don’t work in an excavation where water is collecting unless precautions are taken, such as special support or shield systems, water removal, or safety harnesses and lifelines. If pumps are used, the competent person must monitor them. Water also weakens walls, so watch for seepage.

Hazardous atmospheres

Trenches can fill with low-oxygen air, carbon monoxide from equipment exhaust, sewer gases or fuel vapors that are heavier than air. Where a hazardous atmosphere could reasonably exist in an excavation deeper than 4 feet, such as near landfills, sewers, gas lines or fuel tanks, the air must be tested before workers enter and as often as needed. Keep gas-powered equipment and generators away from the trench. See Access, Egress, Spoils & Water.

Underground utilities

Before digging, call 811 and wait for utilities to be marked. Find the exact location of utilities by careful hand digging or vacuum excavation inside the tolerance zone. Once exposed, utilities must be supported or protected. See Call 811.

Falling loads and moving equipment

• No one may be under loads handled by lifting or digging equipment.
• Workers must stand away from vehicles being loaded or unloaded.
• Equipment working near the edge needs a warning system, such as barricades, hand or mechanical signals, or stop logs, when the operator doesn’t have a clear view of the edge.
• Workers exposed to traffic must wear high-visibility vests.

Falls into the trench

Provide walkways with guardrails where people cross trenches 6 feet or deeper. Barricade or cover wells, pits and shafts, and backfill temporary pits as soon as you can.

Nearby structures

Digging next to buildings, walls, sidewalks and roads can undermine them. Shoring, bracing or underpinning, designed by a qualified person, may be needed. See Excavating Near Buildings & Roads.

Warning signs of a collapse

• Cracks along the top edge, on the surface parallel to the trench, or in the walls
• Bulging, sagging or sloughing (soil falling away) from the walls
• Water seeping into the trench, or wet spots on the walls
• Soil crumbling from under the edge, or a gap behind a trench box
• Soil that’s sandy, wet, or was dug before
• Vibration from traffic or equipment nearby
• Shoring that is bent, cracked, or has moved

If you see any of these, get out of the trench immediately and tell the competent person.

Before you enter: checklist

• The competent person has inspected the trench today (and after any rain)
• A protective system is in place, and I’ll stay inside the protected area
• A ladder or ramp is within 25 feet and extends 3 feet above the edge
• Spoil and equipment are at least 2 feet from the edge
• Utilities are located, marked and supported
• No water is collecting, or it’s being controlled
• The air has been tested if needed
• I’m not under a load or in the path of equipment

If a trench collapses

1. Call 911 and ask for a trench rescue team.
2. Don’t jump in. Secondary collapses are common, and would-be rescuers are often killed.
3. Shut down equipment and traffic nearby to reduce vibration.
4. Keep people and weight away from the edge.
5. Only trained rescuers with protective systems should enter.

See Trench Cave-In Emergencies.

OSHA takes this seriously

Trenching and excavation are a national emphasis program for OSHA, so inspectors stop at open trenches they see. Employers who put workers in unprotected trenches face serious penalties, and some have been criminally charged after workers died.

Last updated: October 1, 2026