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Working in trenches and excavations can be one of the most dangerous construction operations. Soil cave-ins pose the greatest risk, but there are other potential hazards including fall into the trench, loads falling striking workers, hazardous atmospheres present, and being stuck by mobile equipment. The Occupational Safety and Health Administration’s (OSHA) Excavation and Trenching Standard is designed to protect workers from these hazards.

Trenching and Excavation Resources

• OSHA Trenching and Excavation Safety Guide
• NAHB Trenching and Excavation Daily Checklist (English and Spanish)
• NAHB Soil Classification and Testing Methods (English and Spanish)
• (English and Spanish)

Requirements for Foundations and Basements

In 1995, Federal OSHA granted the home building industry some from the excavation requirements during residential basement foundation excavation work. The requirements DO NOT apply to house foundation/basement excavations when all the following conditions are present:

• The house foundation/basement excavation is less than seven and one-half feet in depth or is benched for at least two (2) feet horizontally for every five (5) feet or less of vertical height.
• The minimum horizontal width (excavation face to formwork/wall) at the bottom of the excavation is as wide as practicable but not less than two (2) feet.
• There is no water, surface tension cracks, nor other environmental conditions present that reduce the stability of the excavation.
• All soil, equipment, and material surcharge loads are no closer in distance to the top edge of the excavation than the excavation is deep; however, when front end loaders are used to dig the excavations, the soil surcharge load shall be placed as far back from the excavation as possible, but never closer than two (2) feet.
• Work crews in the excavation are the minimum number needed to perform the work.
• The work has been planned and is carried out in a manner to minimize the time employees are in the excavation.

Trenching and Excavation Requirements

• Determine the soil classification and requirements for the soil type (A, B, or C).
• Request utility companies or owners to determine the location of underground utility installations before excavating.
• Dig a minimum of 5 ft. away from marked utilities.
• If the trench is 5 ft. in depth or greater, then ensure proper sloping, benching, or shoring is in place.
• If the trench is 20 ft. in depth or greater, then ensure engineering protective systems are in place.
• Ensure that underground installations are protected, supported, or removed while the excavation is open.
• Keep heavy equipment away from trench edges and identify other sources that might affect trench stability.
• Keep all spoils piles and equipment at least 2 ft. away from the edge of the excavation.
• Use stairs, ladders, and ramps every 25 ft. to exit the excavation.
• Do not stand beneath loads handled by lifting or digging equipment.
• Do not work in excavations where water is standing or accumulating unless special supports are used to prevent cave-ins.
• Inspect excavations, adjacent areas, and protective systems for evidence of possible cave-ins, indications of failure of protective systems, hazardous atmospheres, other hazardous conditions at the beginning of each workday or if the stability of the excavation could change.
• Test for atmospheric hazards such as low oxygen, hazardous fumes and toxic gases when greater than 4 ft. deep.
• Wear warning vests or other high visibility materials when working near moving equipment or vehicles.

Trenching Basics

What is an excavation or a trench?

OSHA defines an excavation as any man-made cut, cavity, trench, or depression in the earth’s surface formed by earth removal. A trench is defined as a narrow underground excavation that is deeper than it is wide, and is no wider than 15 feet (4.5 meters).

Which OSHA standards address trenching and excavation hazards in construction work?

Employers are required to comply with the trenching and excavation requirements 29 CFR Part 1926, Subpart P.

What are the Competent Person responsibilities?

OSHA’s trenching and excavation standard requires that a competent person inspect jobsite trenches daily, as the conditions change such as a rainstorm occurring, and before a worker enters the trench, to ensure elimination of excavation hazards. A competent person is knowledgeable about excavation hazards and has the authority to fix those hazards.

How to do you protect workers in an excavation or trench?

All workers who enter a trench or excavation more than 5 ft. deep must be protected by benching or sloping of the earth, shoring, or shielding (i.e., trench boxes) to the direction of the competent person.

Protective Systems:

• Benching means 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. NOTE: Benching cannot be done in Type C soil, which is the least stable soil type.
• 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.

DO NOT enter an unprotected trench that is 5 feet (1.5 meters) deep or greater unless a protective system is in place.