It’s critical workers know the requirements for working in trenches.
By Alexandra Walsh
Trenching and excavation jobs present serious hazards to all workers involved. Cave-ins pose the greatest risk and are more likely than other excavation-related incidents to result in worker fatalities.
Not long ago, the Occupational Safety and Health Administration released a graphic showing the amount of trench injuries and deaths over a five-year period. In 2016, there were more deaths than in 2014 and 2015 combined—23 deaths in 2016 vs. 11 deaths in 2015 and 11 deaths in 2014.
Trench collapses happen fast and often have devastating results, as 1 cubic yard of soil can weigh up to 3000 pounds—as much as a car!
The good news, though, is trench collapse deaths are easily preventable. They continue to happen because of ignorance of safety rules, lack of supervision, and pressures of time and money.
Employers must ensure workers enter trenches only after adequate protections are in place to address the hazards of a cave-in. Other potential hazards associated with trenching work include falling loads, hazards from mobile equipment, and hazardous atmospheres.
29 Code of Federal Regulations, Part 1926, Subpart P: Excavations contain OSHA’s standard requirements for excavation and trenching operations.
The standards apply to all open excavations made in the earth’s surface—this includes trenches. Following the standards’ requirements will prevent or greatly reduce the risk of cave-ins and other excavation-related incidents.
Some of the compliance methods permitted under the OSHA excavation standards require a competent person to classify soil and rock deposits.
Looked at more closely, a competent person is an individual designated by the employer who is capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to workers. Acting as such, this person is authorized to take prompt corrective measures to eliminate such hazards.
Under the excavation standards, the tasks performed by the competent person include:
- Classifying soil
- Inspecting protective systems
- Designing structural ramps
- Monitoring water removal equipment
- Conducting site inspections.
No matter how many well drilling, trenching, shoring, and backfilling jobs an employer has done in the past, it is important to approach each new job with care and preparation.
Many on-the-job incidents result from inadequate initial planning. Waiting until after the work starts to correct mistakes in shoring or sloping slows down the operation, adds to the cost of the project, and makes a cave-in or other excavation failure more likely.
Before beginning a job, employers should know as much as possible about the jobsite and the materials they will need to have on hand to perform the work safely and in compliance with OSHA standards. A safety checklist may prove helpful when employers are considering new projects. Factors to consider may include:
- Traffic patterns
- Proximity and physical condition of nearby structures
- Soil classification
- Surface water and groundwater
- Location of the water table
- Overhead and underground utilities
- Weather conditions
- Quantity of shoring or protective systems that may be required
- Fall protection needs
- Number of ladders that may be needed
- Other equipment needs.
Employers can gather the information they need through jobsite studies, observations, test borings for soil type or conditions, and consultations with local officials and utility companies. This information will help employers determine the amount, kind, and cost of safety equipment they will need to perform the work safely.
OSHA generally requires employers to protect workers from cave-ins by:
- Sloping and benching the sides of the excavation
- Supporting the sides of the excavation
- Placing a shield between the side of the excavation and the work area.
In many cases the type of protective system needed is one well known and simple to use. At other times employers will undertake the more complex process of designing a protective system.
Designing a protective system requires consideration of many factors—soil classification, depth of the cut, water content of soil, weather and climate, other operations in the vicinity. Employers are free to choose the most practical design that will provide the necessary protections. Any system used must meet the required performance criteria.
OSHA’s excavation standards also require employers to provide support systems such as shoring, bracing, or underpinning when necessary to make sure adjacent structures (adjoining buildings, walls, sidewalks, pavements) remain stable for the protection of workers. The standards also prohibit excavation below the base or footing of any foundation or retaining wall that could reasonably be expected to pose a hazard to workers. That is, unless:
- The employer provides a support system, such as underpinning
- The excavation is in stable rock
- A registered professional engineer determines the structure is far enough away from the excavation that it would not be affected by the excavation activity or the excavation work will not pose a hazard to workers.
Excavations that would undermine sidewalks, pavements, and related structures are prohibited unless the employer provides an appropriately designed support system or another effective method of protecting workers from the possible collapse of any of those.
Falling Loads and Mobile Equipment Standards
In addition to cave-ins and related hazards, workers involved in excavation work are exposed to hazards involving falling loads and mobile equipment. To protect workers from these hazards, OSHA requires employers to take certain precautions. For example, employers must:
- Protect workers from excavated or other materials or equipment that could pose a hazard by falling or rolling inside the excavation by placing and keeping such materials or equipment at least 2 feet from the edge or by using a retaining device to keep the materials or equipment from falling or rolling into the excavation.
- Provide a warning system (barricades, hand or mechanical signals, stop logs) when mobile equipment is operated near an excavation, or when such equipment must approach the edge of an excavation and the operator doesn’t have a clear and direct view of the edge.
- Protect workers from loose rock or soil that could fall or roll from an excavation face by scaling or scraping to remove loose material or installing protective barricades at appropriate intervals.
- Prohibit workers from working on faces of sloped or benched excavations at levels above other workers unless the workers at the lower levels are adequately protected from the hazards of falling, rolling, or sliding material or equipment.
Additional Hazards and Protections
Employers also need to emphasize specific practices that will help reduce the risk of on-the-job injuries at excavation and trenching sites. Such practices can include the following:
- Know where underground utilities are located before digging.
- Keep heavy equipment away from trench edges.
- Identify any equipment or activities that could affect trench stability.
- Test for atmospheric hazards such as low oxygen, hazardous fumes, and toxic gases when workers are more than 4 feet deep.
- Inspect trenches at the start of each shift.
- Inspect trenches following a rainstorm or other water flooding.
- Inspect trenches after any occurrence that could change conditions in the trench.
- Do not work under suspended or raised loads and materials.
- Require personnel wear high-visibility or other suitable clothing when exposed to vehicular traffic.
With excavation, trenching, and water well drilling, employers should already have safety systems in place providing policies, procedures, and practices for protecting workers from job-related hazards. Employers need to share the details of their safety program with workers and emphasize the critical role workers play in keeping the jobsite safe.