OSHA Trenching and Excavation Safety Fact Sheet

Trench collapses and cave-ins pose a risk to workers’ lives. When done safely, trenching operations can reduce worker exposure to other potential hazards including falls and falling loads, hazardous atmospheres, and incidents involving mobile equipment.

OSHA standards require employers provide workplaces free of recognized hazards. The employer must comply with trenching and excavation requirements of Specific Excavation Requirements (29 CFR §1926.651) and Requirements for protective systems (29 CFR §1926.652) or comparable OSHA-approved state plan requirements.

Trench Safety Measures

Trenches 5 feet deep or greater require a protective system unless the excavation is made entirely in stable rock. If less than 5 feet deep, a competent person may determine that a protective system is not required.

Trenches 20 feet deep or greater require that the protective system be designed by a registered professional engineer or be based on tabulated data prepared and/or approved by a registered professional engineer in accordance with §1926.652(b) and (c).

Competent Person

OSHA standards require, before any worker entry, that employers have a competent person inspect trenches daily and as conditions change to ensure elimination of excavation hazards.

A competent person is an individual who is capable of identifying existing and predictable hazards or working conditions that are hazardous, unsanitary, or dangerous to workers, soil types and protective systems required, and who is authorized to take prompt corrective measures to eliminate these hazards and conditions.

Access and Egress

• Keep heavy equipment away from trench edges.
• Identify other sources that might affect trench stability.
• Keep excavated soil (spoils) and other materials at least 2 feet from trench edges.
• Know where underground utilities are located before digging. Call 811 before digging.
• Test for atmospheric hazards such as low oxygen, hazardous fumes and toxic gases when greater than 4 feet deep.
• Inspect trenches at the start of each shift.
• Inspect trenches following a rainstorm or other water intrusion.
• Do not work under suspended or raised loads and materials.
• Inspect trenches after any occurrence that could have changed conditions in the trench.
• Ensure that personnel wear high visibility or other suitable clothing when exposed to vehicular traffic.

Protective Systems

There are different types of protective systems:

• Benching is a method of protecting workers from cave-ins by excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or near- vertical surfaces between levels. Benching cannot be done in Type C soil.
• Sloping involves cutting back the trench wall at an angle inclined away from the excavation.
• Shoring requires installing aluminum hydraulic or other types of supports to prevent soil movement and cave-ins.

Shielding protects workers by using trench boxes or other types of supports to prevent soil cave-ins. Designing a protective system can be complex because you must consider many factors: soil classification, depth of cut, water content of soil, changes caused by weather or climate, surcharge loads (e.g., spoil, other materials to be used in the trench) and other operations in the vicinity.