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Excavation and Trenching Basics

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Working in and around excavations or trenches can be hazardous. In 2017, the U.S. Bureau of Labor Statistics reported 23 workers were killed in excavation cave-ins alone. Falls, falling loads, hazardous atmospheres and mobile excavating equipment can also create hazards for workers in trenches and excavations. Any personnel sent to perform this job needs excavating training over the hazards they may face, and every workplace should have controls in place to help protect workers from cave-ins, hazardous atmospheres and other hazards.

OSHA Excavation Requirements

Excavator digging trench

The Occupational Safety and Health Administration (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 deeper than it is wide and is less than 15 feet (4.5 meters) wide. Any trench that is five feet or deeper requires a protective system unless the trench is dug entirely into stable rock. If the trench is 20 feet or deeper, a professional engineer must design its protective system, or prepare or approve data to design the system.

OSHA requires all excavations that are four feet or deeper to have safe means of access and egress for employees to safely enter and exit, such as ladders, steps or ramps. Entrances and exits must be installed so workers never have to travel more than 25 feet to exit the excavation.

Competent Person Requirements

Before personnel can enter and work in an excavation, a competent person must ensure all hazards are identified and removed or controlled. The competent person also has the authority and responsibility to stop work if conditions become unsafe and either eliminate or control these hazards. OSHA also requires that a competent person perform a daily inspection for hazards. Inspections must also be done when conditions change, such as after a rainstorm.

Some excavations can include confined spaces. If a competent person determines that work in an excavation also includes confined space work, workers will require additional training and precautions, including a confined space permit in some situations.

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Excavation Hazards and Controls

Workers in excavations can face a wide variety of hazards, including:

  • Hazardous atmospheres
  • Cave-ins
  • Water accumulation
  • Falling loads
  • Underground utility lines
  • Vehicles and surface structures

Your workplace’s competent person will need to be trained to identify and remove or control these hazards. The controls they implement will depend on the identified hazards, but here are some of the controls they may use.

  • If a hazardous atmosphere could exist, precautions such as ventilation or respiratory protection may be needed. After control measures are put into place, atmospheric monitoring must be done to keep the excavation safe.
  • If an excavation has water in it or is taking on water, no workers can enter until appropriate precautions are taken, such as water diversion, special shield systems, water removal equipment or safety harnesses.
  • When vehicles or other heavy equipment are present near an excavation, workers need to wear reflective warning vests or other high-visibility clothing.
  • Workers must never stand or walk underneath lifted loads and should stay away from vehicles while they load or unload materials.
  • No excavations can be done below a foundation or retaining wall until there is a support system in place, unless the excavation is in entirely stable rock or a registered professional engineer says the work is far enough away that it will not be a hazard.
  • Before excavation begins, site personnel should call 811, the “Call Before You Dig” number, a few days before digging so utility companies can locate their underground lines. Some states require more time before starting work.

Protective Systems

Excavator working on protective sytem

There are many different protective systems that can be used in excavations. A competent person or engineer must design protective systems for your excavations based on several factors, such as the type of soil, the soil’s water content, the weather and climate, and if there are other operations being performed in the area.

In general, protective systems include any of the following:

  • Benching – cutting into the sides of an excavation in stable soil to create horizontal levels with vertical or almost-vertical faces between the levels
  • Sloping – creating a gradual incline in the excavation’s walls away from the bottom of the excavation
  • Shielding – using a trench box or other similar support system to prevent cave-ins
  • Shoring – installing supports to prevent unstable soil from moving in the excavation

Conclusion

Excavations are important construction activities, but they can be potentially hazardous to both the workers doing the excavating and the structures or utilities nearby. Having a competent person available to identify and remove hazards and properly training your personnel will help complete excavations safely and properly.

SafetySkills offers an Excavation and Trenching course intended for general-industry and construction employees who are required to work in or around trenching or excavation operations.

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