Trench collapse accidents are rarely survivable. OSHA statistics reveal fatalities caused by trench wall collapse are increasing. This trend is preventable by complying with OSHA standards that every municipal utility service employee should know. Municipal employees who dig or excavate trenches are at risk of death if they enter an unprotected trench and the walls collapse.
Hazards associated with trench work and excavation are well defined in the OSHA standard for excavation and trenching found in 29 CFR 1926.651 and 1926.652 Subpart P. It describes the precautions needed for safe excavation work. There is no reliable warning when a trench fails. The walls can collapse suddenly, and workers will not have time to move out of the way. Even though small amounts of dirt may not seem dangerous, a single cubic yard of dirt can weigh more than 3,000 pounds, which can fatally crush or suffocate workers. Even small, solid pieces of dirt can cause serious injuries.
Most incidents involve excavation work on water, sewer, pipeline, communications and power-line maintenance, repair, and/or construction. OSHA data shows that most fatalities in trenches occur at depths of 10 feet or less. Lack of a protective system was the leading cause of trench-related fatalities.
OSHA requires all trenches 5 feet deep or more use one of the following protective systems:
- Sloping the trench walls
- Benching the trench walls
- Shoring the trench with pneumatic or hydraulic jacks and trench plates
- Shielding the trench using a trench box
Workers should never enter a trench that does not have a protective system in place designed and installed by a competent person. Factors such as type of soil, water content of soil, environmental conditions, proximity to previously backfilled excavations, weight of heavy equipment or tools, and vibrations from machines and motor vehicles can greatly affect soil. Not all protective systems can be used in all types of soil. A competent person is one who understands OSHA regulations, can recognize hazards, and is authorized to correct them.
Call 811 before digging so that utility lines can be marked. Train and designate a competent person to ensure safety measures are in place. What is a competent person? A competent person is an individual who can identify existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to workers, and who is authorized to take prompt corrective measures to eliminate them.
Competent Person Responsibilities
- Classifying soil
- Inspecting protective systems
- Designing structural ramps
- Monitoring water removal equipment
- Conducting site inspections
- Planning the job layout to identify safe locations for spoil piles and heavy equipment routes
- Determining what type of protective system will be used for the job and scheduling the steps needed to have the system complete and in place before workers enter
- Ensuring that employees are trained to spot signs of imminent trench collapse, including tension cracks, bulging, and toppling
- Developing a trench emergency action plan to describe steps to be taken and to provide contact information in case of an emergency
- Ensuring that ladders and other means of exit from the trench are repositioned so that ladders are never more than 25 feet away from any worker in the trench
- Must remove workers from the excavation upon any evidence of a situation that could cause a cave-in, such as accumulation of water in the trench or protective system problems
- Take actions for other types of hazards such as falling loads or hazardous atmospheres
- Monitor other types of trench–related hazards that can occur such as falls from the edge, rigging hazards, or toxic and combustible gases
- Implement and enforce procedures to ensure that work in an unprotected trench is not allowed
- Do not enter an unprotected trench, even for a short task
- Inspect the protected trench before entering
- Exit the trench and call the competent person if you see any evidence of problems with a protective system
- Do not assume there will be a warning sign before a cave in or that you will have time to move out of the way
- Manually uncover utilities to determine the exact location and depth before mechanical digging with a backhoe or trackhoe