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How To Prevent Trench Collapses

The Occupational Safety and Health Administration (OSHA) warns that excavations and trenches are among the most hazardous of construction operations. In 2018, a spike in trenching and excavation-related deaths led OSHA to redouble its enforcement efforts. OSHA created a revised National Emphasis Program (NEP) to target contractors who disregarded its safety standards.

The Bureau of Labor Statistics reported trenching and excavation deaths nearly tripled between 2011 and 2016, for a total of 130 worker deaths. As a result, OSHA’s NEP requires inspectors to review all trenches they see, regardless of the circumstances.

Despite this renewed emphasis on compliance, trench fatalities remain a serious but preventable problem in construction. Cave-ins cause about three out of four of these types of fatalities, with the remaining quarter due to electrocution or workers being struck by equipment or falling loads.

During a cave-in, the walls of a trench can collapse suddenly and without warning. Just one cubic yard of dirt can weigh more than 3,000 pounds, the weight of a compact car. A collapse in a four- or five-foot trench can exert more than 20,000 pounds of force, compressing a worker’s chest so tightly they can’t breathe.

In addition to dozens of fatalities, OSHA reports trench-related accidents cause hundreds of injuries every year. These include falls into trenches, hazardous atmospheres in trenches, dirt or material falling on workers, and accidents involving mobile equipment.

Excavation and trench safety

OSHA, the National Institute for Occupational Safety and Health (NIOSH) and various trade groups have all urged contractors to take steps to avoid collapses. If you’re a contractor, familiarize yourself with safety procedures and regulations. A good start is OSHA’s Trenching and Excavation Safety publication.

The OSHA rules are clear: Don’t let your employees enter a trench that isn’t protected. As OSHA puts it in its guidance to employers, “An unprotected trench can be an early grave.” Trenches 5 feet deep or greater require a protective system unless the excavation is made entirely from stable rock. Trenches 20 feet deep or greater require the protective system to be designed by a registered professional engineer or be based on tabulated data prepared and/or approved by a registered professional engineer.

“Competent person”

OSHA standards require that a “competent person” inspect trenches daily and as conditions change. The inspection must be performed before workers enter the excavation area. A competent person is an individual designated by the employer “who is capable of identifying existing and predictable hazards or working conditions that are hazardous, unsanitary or dangerous to employees, and who is authorized to take prompt corrective measures to eliminate them.”

Excavation standards require the competent person to also classify soil, inspect protective systems, design structural ramps, monitor water removal equipment and conduct site inspections.

Make sure your company has someone at the job site who can meet OSHA’s “competent person” standard. Many construction companies have safety officers and other designated employees who can serve in this capacity.

Before you dig

Planning is essential for construction safety, and it’s especially important in excavation. Before you dig:

  • Determine the type of soil and the depth of the water table

  • Identify overhead and underground utilities

  • Consider traffic and the proximity of nearby structures

  • Take weather into accountCheck for surface and ground water

  • Check for surface and ground water

  • Determine your equipment and protection needs

You may need to conduct test borings of the soil to determine conditions. You may also need to consult with engineers, local building officials and utility companies.

Always locate utility lines, including sewer, electric, gas, cable, telephone and water, before excavating. In most areas, you can call the 811, or “call before you dig,” line to identify underground lines. For the safety of your workers, make sure these utility lines are protected, supported or removed before you dig.

Protective systems

OSHA requires different types of protective systems, depending on the slope and depth of the trench and type of 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.

In designing a protective system, you must consider several factors, including the soil classification, the depth of the cut, the water content of the soil, changes due to weather or climate, surcharge loads (spoil or other materials to be used in the trench) and other operations in the vicinity.

You may also need to establish support systems such as shoring, bracing or underpinning whenever your excavation is near existing walls, sidewalks, pavement or buildings.

Water accumulation

The accumulation of water in a trench from heavy rain or runoff can be dangerous. Water can undermine the sides of the trench and make it more difficult for workers to exit. OSHA standards prohibit employers from allowing workers to enter an excavation where water has accumulated or is accumulating, unless adequate precautions have been taken to protect workers. Such precautions include special support or shield systems to prevent cave-ins, water removal to control the water level, and safety harnesses or lifelines.

Commercial general liability and workers’ compensation

Make sure you are adequately insured before you begin any excavation project. Most owners and general contractors will require you to have commercial general liability (CGL) and workers’ compensation insurance as part of your contract.

Excavation contractors insurance is a form of CGL coverage designed to address risks involved in moving earth, including:

  • Meeting proper grades for water runoff

  • Soil movement, landslides, mudslides, soil runoff and other environmental concerns

  • Property damage due to your equipment

  • Equipment operator error

  • Hitting underground utilities

  • Worker injuries

You’ll also need to carry workers’ compensation insurance for your employees. Workers’ compensation premiums can be quite high for excavation and trenching work. Depending on your experience modifier (ex-mod), you may need to purchase workers’ compensation through your state’s assigned risk plan.

Talk to an insurance professional who specializes in construction to see what types of coverage you need and how to save on premiums. For example, some insurers provide training resources to help educate workers and reduce the likelihood of accidents and claims.

Excavation is dangerous work. Make protecting your workers your No. 1 priority. You might just save someone’s life.