Trenching and Excavation Safety

It is important crews are trained to prevent cave-in accidents on the jobsite.

By Alexandra Walsh

Trenching and excavation work presents serious hazards to all workers involved.

Cave-ins pose the greatest risk and are more likely than some other excavation-related incidents to result in worker fatalities. One cubic yard of soil can weigh as much as a car, and an unprotected trench can be an early grave.

Employers must ensure that workers enter trenches only after adequate protections are put in place to address cave-in hazards.

Before workers enter a trench, a soil analysis should generally be conducted to determine what appropriate employee protection methods are needed such as sloping, benching, shoring, or shielding.

Employers should also consider potential hazards associated with workers being struck by heavy equipment, falling loads, and exposure to public vehicular traffic near excavation operations.

Cave-ins pose the greatest risk and are more likely than some other excavation-related incidents to result in worker fatalities.

Also consider potential hazards resulting from sidewalks and buildings being undermined by an excavation. Other unsafe conditions that may be encountered include hazardous atmospheres and electrical hazards from overhead and underground power lines.

Safe Entry, Safe Exit

To prevent injuries, employers must provide safe means of entering and exiting a trench or excavation at a jobsite.

In some circumstances when conditions in a trench or excavation become hazardous, survival may depend on how quickly workers can climb out.

To manage the hazards:

• Provide ladders, stairways, ramps, or other safe means of exiting all trenches that are dug 5 feet deep or more.
• Position the means of exiting within 25 lateral feet of workers.
• Structural ramps for entry and exit from excavations must be designed by a competent source.
• When two or more components form a ramp or runway, they must be connected to prevent displacement and be of uniform thickness.
• Cleats or other means of connecting runway components must be attached in a way that will not cause tripping.
• Structural ramps used in place of steps must have a nonslip surface.
• Use earthen ramps as a means of exiting only if a worker can walk on them in an upright position, and only if they have been evaluated by a person trained in jobsite safety.

Cave-In Protection

All excavations are hazardous because soil can be unstable. If workers are not using protective systems or equipment while working in trenches or excavations 5 feet deep or more, they face the danger of being crushed by a cave-in.

Planning before the job starts is vital to incident-free excavation work; safety cannot be put off until once the work begins. The following concerns must be addressed:

• Evaluate soil conditions and select appropriate protective systems.
• Construct protective systems in accord with standard requirements.
• Contact utilities (gas, electric, water, and sewage) to locate underground lines; plan for traffic control; be prepared to support utilities (pipes/ducts) passing through excavations; and determine closeness to structures that could affect which protective system to choose.
• Test for low oxygen, hazardous fumes, and toxic gases, especially when gasoline engine-driven equipment is running or when the soil has been contaminated by leaking lines or storage tanks. Make sure there is adequate ventilation or respiratory protection.
• Supply appropriate protections if water accumulating presents a problem; remove water or divert the flow of water.
• Keep excavations open only for the minimum amount of time needed to complete operations.

Inspect the excavation, any areas that are close to it, and the protective systems being used—daily at the start of the shift, after a rainstorm, or after any other hazardous condition. The inspection should be conducted by someone trained in safety who is looking for a situation that could lead to a possible cave-in, a sign of failure in the protective system, hazardous atmospheres, or water in the excavation.

Hazardous Air and Water

Excavations may present risks of hazardous atmospheres and water accumulation. Be on the lookout for standing water and test for atmospheric hazards.

Water forming in an excavation can undermine the sides of the trench and make it more difficult for workers to escape out of an excavation or even drown. OSHA standards prohibit employers from allowing workers to enter an excavation where water has accumulated or is rising unless adequate precautions are taken to protect workers. A trench with any accumulation of water must be inspected by a safety professional before entering.

If conditions of hazardous atmosphere exist, workers could be exposed to the possibility of suffocating, inhaling toxic materials, being burned or engulfed by fire.

Keep Away from the Edge

Excavated materials at a dug site are hazardous if they are piled too close to the edge of a trench or excavation. The heavy weight of the materials can cause a cave-in, or the materials and equipment can roll back on top of workers, causing serious injury or death.

Provide protection by one or more of the following:

• Set excavated materials and equipment at least 2 feet back and away from an adequately protected excavation.
• Use retaining devices, such as a trench box that will extend above the top of the trench, to prevent equipment and materials from rolling or falling back into the excavation.
• Where the site does not permit a 2-foot setback, excavation materials may need to be temporarily hauled to another location.

Competent and Regular Inspection

The conditions of an excavation can change during the course of work. Even a properly protected excavation or trench can become compromised.

Employers can help ensure that excavations are safe to work by inspecting the property. Inspections must be conducted by a competent person, as defined by OSHA:

“Competent person means one who can identify existing and predictable hazards in the surroundings, or working conditions that are unsanitary, hazardous, or dangerous to employees, and who has authorization to take prompt corrective measures to eliminate them. [29 CFR 1926.32(f)]

A competent person:

• Has training in the use of protective systems
• Is knowledgeable about OSHA’s requirements
• Has the authority to immediately evacuate workers from the excavation to ensure their safety.

Once again, and it cannot be emphasized enough, employers and those who work for them need to take the time to assure that excavations are safe to work in by inspecting excavations:

• Before construction begins
• Daily before each shift
• As needed throughout the shift
• Following a rainstorm
• To avoid vehicles or equipment approaching the edge of an excavation.

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Even if and when all inspections are conducted, workers may still be in danger from time to time due to changing conditions. Workers must be alert and trained to spot and report these changes to their supervisor.

Alexandra Walsh is the vice president of Association Vision, a Washington, D.C.–area communications company. She has extensive experience in management positions with a range of organizations.