Trench and Excavation Safety
Trenching and Excavation is dangerous work that construction workers face daily. Depending on the task at hand, there are different risks involved. Let's dig into the differences between trenching and excavation, the hazards involved, and how to mitigate risks while working.
Excavation vs. Trenching
An excavation is defined as any man-made cut, cavity, trench, or depression in the Earth’s surface formed by earth removal. A trench is defined as a narrow excavation (in relation to its length) made below the surface of the ground. In general, the depth of a trench is greater than its width, but the width of a trench (measured at the bottom) is not greater than 15 feet (4.6 m).
Hazards of Trench and Excavation Work
Workers who dig or excavate trenches are at risk of death if they enter an unprotected trench and the walls collapse. According to the Bureau of Labor Statistics, 271 workers died in trenching or excavation cave-ins from 2000 through 2006. A review of multiple national databases by NIOSH researchers found that trenching and excavation hazards during construction activities resulted in 488 deaths between 1992 and 2000. That is an average of 54 fatalities each year. Have a small business? 68% of those fatalities occurred in companies with fewer than 50 employees, and 46% of the deaths occurred in small companies with ten or fewer workers. The lack of a protective system was the leading cause of the trench-related fatalities.
Hazards associated with trench work and excavation are recognized and preventable, yet injuries and fatalities associated with these hazards continue to occur. Both OSHA and NIOSH have great resources to help employers understand how to prevent injury or death to their employees. They recommend engineering controls, protective equipment, and safe work practices to minimize worker’s hazards during trench work and excavations. The OSHA Standards outline the specific requirements for excavations (1926.651) and requirements for protective systems (1926.652).
Competent Person Responsibilities
Every trench and excavation job needs a designated and trained competent person on site. A competent person is an individual who is capable of identifying existing and predictable hazards or working conditions that are dangerous to workers. They can identify soil types and the protective systems required and are authorized to take prompt corrective measures to eliminate these hazards and conditions. The competent person should evaluate the soil to identify its stability. After identifying soil stability, they should determine what type of protective system is to be used. Before a worker enters a trench, the protective system must be in place and completed before work starts. The competent person must remove workers from the excavation area upon any evidence of a situation that could cause a cave-in, such as accumulation of water in the trench or protective system problems. The competent person must also take action for other hazardous situations such as falling loads or hazardous atmospheres.
Employers must have a competent person inspect trenches before work begins and as conditions change before any worker enters a trench. The competent person inspects the trench for excavation hazards and must eliminate them if they are identified. Trenches should also be inspected following a rainstorm or other water intrusion or after any other occurrence that could have changed the trench conditions.
Requirements for Protective Systems
Trenches 5 feet deep or greater require a protective system unless the excavation is made entirely in stable rock. If less than 5 feet deep, a competent person may determine that a protective system is not required. Trenches 20 feet deep or greater require that the protective system be designed by a registered professional engineer or be based on data approved by a registered professional engineer.
Types of Protective Systems
The following are types of protective systems that are used to prevent cave-ins. Designing a protective system can be complex. Considerations include soil classification, depth of cut, the soil's water content, changes caused by weather, surcharge loads (e.g., spoil, other materials to be used in the trench), and other operations in the area.
Benching means a method of protecting workers from cave-ins by excavating the sides of an excavation to form one or a series of horizontal levels or steps, usually with vertical or near-vertical surfaces between levels. Benching cannot be done in Type C soil. Type C soil is classified as the least stable type of soil, and examples include gravel and sand.
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.
Safe Work Practices for Trench Safety
The best practices outlined below are critical elements to keeping your workers safe when performing trench and excavation duties.
- Plan the job before starting by laying out safe locations away from the trench for spoil piles and heavy equipment routes
- Keep heavy equipment away from trench edges. Heavy equipment can cause stability problems of the trench
- Keep excavated soil (also known as spoils) and other materials at least 2 feet from the trench's edge
- Know where underground utilities are located before digging. Always call 811 so that utility lines can be marked
- Test for atmospheric hazards such as low oxygen, hazardous fumes, and toxic gases when greater than 4 feet deep
- Do not work under suspended loads
- Ensure that personnel wear high visibility vests
- Ladders should never be more than 25 feet from any worker in the trench
- To prevent falls into an open trench, ensure the trench is covered. A simple solution could be a piece of plywood, or an expandable trellis mat, to ensure the hole is properly secured. It allows for easy inspection of the trench, is a physical barrier between the workers and the fall hazard, and can be secured to the ground.
Trenching and excavation tasks can be deadly if they are not performed using the controls outlined in this blog. Always take trenching and excavation hazards seriously, as even a 6-foot cave-in can cause a worker fatality.