Excavation Hazards: What Can Hurt You In and Around a Trench

If you search for excavation safety, you will quickly run into a common quiz question: which of the following is an excavation hazard? The honest answer is "all of them." Excavations concentrate many construction hazards in one small space, and they often show up together. A rainstorm saturates the soil, a pump runs with a gas engine at the edge, and a loaded excavator swings over the trench, all at once.

This lesson walks through the ten hazards OSHA's excavation standard is built around, and the control for each one.

1. Cave-ins

The hazard most likely to kill. When a trench wall fails, soil weighing about a ton and a half per cubic yard can bury or crush a worker in seconds.

Control: OSHA 1926.652(a) requires an adequate protective system (sloping, benching, shoring or shielding) for every excavation 5 feet or deeper, unless it is entirely in stable rock. Excavations shallower than 5 feet still need a protective system if a competent person sees any indication of a potential cave-in. See sloping and benching, shoring and trench boxes.

2. Falling loads and struck-by hazards

Buckets, pipe sections, trench boxes and loads swinging overhead can drop into the trench.

Control: No employee may be under loads handled by lifting or digging equipment (1926.651(e)). Workers must stand away from vehicles being loaded or unloaded to avoid spilled or falling material.

3. Mobile equipment near the edge

Excavators, loaders and dump trucks add weight at the edge and can roll or slide in.

Control: When equipment works next to an excavation and the operator cannot clearly see the edge, a warning system such as barricades, hand or mechanical signals, or stop logs must be used (1926.651(f)). Where possible, the grade should slope away from the excavation.

4. Falling or rolling materials

Spoil, rocks, tools and stockpiled pipe can roll back in.

Control: Keep spoil, materials and equipment at least 2 feet from the edge, use retaining devices, or both (1926.651(j)(2)). Loose rock or soil on the face must be scaled off or held back with barricades (1926.651(j)(1)).

5. Underground utilities

Striking a gas line, electrical cable or water main can cause explosions, electrocution, flooding and washouts that collapse the trench.

Control: Determine the estimated location of utilities before digging, contact utility owners (through the 811 one-call system), and find the exact location by safe means as you approach the marks (1926.651(b)). See utilities and 811.

6. Hazardous atmospheres

Low oxygen, toxic gases such as hydrogen sulfide and carbon monoxide, and flammable gases can collect in excavations, especially near landfills, sewers, fuel tanks or engine exhaust.

Control: Where a hazardous atmosphere exists or could reasonably be expected, test the air before workers enter excavations deeper than 4 feet (1926.651(g)). Keep flammable gas below 20 percent of its lower flammable limit and provide rescue equipment where hazardous atmospheres may develop. See atmospheres and water.

7. Water accumulation

Water softens and saturates soil, adds pressure to walls, can carry soil in from behind a shield, and creates a drowning hazard.

Control: Workers may not work in excavations with accumulated or accumulating water unless adequate precautions are taken (1926.651(h)). Dewatering equipment must be monitored by a competent person, and surface water must be diverted.

8. Adjacent structures and surface encumbrances

Excavating near foundations, walls, sidewalks, utility poles or trees can undermine them.

Control: Remove or support surface encumbrances (1926.651(a)). Provide shoring, bracing or underpinning when adjacent structures are endangered, and do not dig below a foundation unless one of the conditions in 1926.651(i) is met, such as an engineer's approval.

9. Falls into the excavation

Workers and the public can fall into open excavations, especially at night or when the edge is hidden by vegetation.

Control: Provide walkways with guardrails where people cross excavations 6 feet or more above lower levels (1926.651(l)). Under the fall protection rule, guardrails, fences or barricades are required at the edge of excavations 6 feet or deeper when they are not readily seen, and at wells, pits and shafts (1926.501(b)(7)).

10. Traffic

Roadway work puts crews beside moving vehicles.

Control: Workers exposed to public vehicular traffic must wear high-visibility warning vests or garments (1926.651(d)). Traffic control plans and work zone devices follow the MUTCD.

How hazards combine

Real incidents rarely involve a single hazard. Consider a short-duration water main repair in a street:

This is why OSHA assigns a competent person to look at the whole picture, inspect before work and after anything that changes conditions, and remove workers when a hazard appears (1926.651(k)).

Key takeaways

• The ten major excavation hazards are cave-ins, falling loads, mobile equipment, falling materials, utilities, atmospheres, water, adjacent structures, falls and traffic.
• Each one has a specific control in 1926.651 or 1926.652.
• Hazards usually stack up, so the competent person must evaluate the whole site, not just the trench walls.

Last reviewed: October 25, 2026 · Free general education based on OSHA 29 CFR 1926 Subpart P. It does not replace the site-specific training and competent person your employer must provide, and it does not issue a certificate. Nothing you enter on this page is saved or sent.