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April 12, 2021

Trenching and excavation safety

Make a plan to protect workers and prevent accidents

John Bestman

Trenching and Excavation Safety

An excavation is any man-made cut, cavity, trench or depression in an earth surface formed by earth removal. “Trench” means a narrow excavation, in relation to its length, made below the surface of the ground. In general, the depth is greater than the width, but the width of a trench, measured at the bottom, is not greater than 15 feet.

Dangers of Trenching and Excavation

According to the most recent data available from the Bureau of Labor Statistics, from 2013 to 2017 there were 97 trenching fatalities in the construction industry – an average of 19 per year.  This results in a fatality rate for excavation work that is 112 percent higher than the rate for general construction.  This is one of the reasons why OSHA has made Trenching and Excavations part of a National Emphasis Program, subject to additional enforcement and training.

Cave-ins pose the greatest risk and are much more likely to result in worker fatalities than other excavation-related accidents. One cubic yard of soil can weigh as much as a car. Never enter an unprotected trench. Protective systems include proper sloping or benching based on the soil type, the use of a shoring system and/or the use of a shielding system such as a trench box.

Competent Person

OSHA standards require that trenches be inspected daily and as conditions change by a competent person prior to worker entry to ensure elimination of excavation hazards.

In addition, the competent person is responsible for the following:

  • Classification of the soil as Type A, B or C using more than one of the approved methods: Penetrometer, shear vane, thumb penetration, or plasticity test.

  • Conducting site inspections to identify potential hazards such as:

  • Vibration, nearby equipment

  • Previously disturbed soil

  • Water seepage, wet soils or accumulated water

  • Fissures/cracks

  • Inspect protective systems: sloping, benching, shoring, shielding

  • Design structural ramps

  • Monitor water removal equipment

Remember the Numbers

Feet Tip to Remember
2' Keep heavy equipment and spoil piles at least two feet back from the edge of a trench or excavation.
4' Once an trench or excavation reaches four feet deep, a safe means of egress must be provided such as ladders, steps, ramps or other safe means.  
5' Once a trench or excavation reaches five feet deep, a protective system must be used unless the excavation is made entirely in stable rock.  Protective systems include proper sloping or benching based on the soil type, the use of a shoring system and/or the use of a shielding system such as a trench box.
20' Once an excavation reaches a depth of twenty feet or greater, the protective system must be designed by a registered professional engineer or be based upon tabulated data prepared and/or approved by a registered professional engineer.
25’ Once an excavation reaches four feet deep, a means of egress must be provided within twenty five feet of employees.

General Trenching and Excavation Rules

  • Keep heavy equipment away from trench edges.

  • Identify other sources that might affect trench stability.

  • Know where underground utilities are located 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.

Use MMA’s Excavation Safety Checklist to help you and your employees make sure you’ve done everything necessary to prevent excavation accidents.

If you find yourself short on time or in need of assistance evaluating your health and safety programs, please contact your local Marsh McLennan representative.