When done safely, trenching and excavation operations can reduce worker exposure to risks like falls, cave-ins, falling loads, hazardous atmospheres, and incidents involving mobile equipment.
An excavation is any man-made cut, cavity, trench, or depression in the ground that is created by earth removal.
A trench is a type of narrow excavation where the depth is typically greater than the width, but the width is not greater than 15 feet.
Potential hazards during excavation work include:
- soil collapse or cave-ins
- slips, trips, and falls
- falling objects, loads, tools, materials, or soil
- mobile equipment struck-by, caught-in, or back over risks
- hazardous atmospheres caused by toxic gases, fumes, or vapors
- damaged utilities causing risk of explosion, electrocution, or drowning
Trench collapses, or cave-ins, pose the greatest risk to workers’ lives and are much more likely than other excavation-related accidents to result in death.
Before any worker enters a trench or any excavation, a competent person must inspect it every day and also as conditions change to ensure elimination of excavation hazards.
Inspect trenches:
- at the start of each shift and as needed throughout the workday
- following a rainstorm or other water intrusion
- after any occurrence that could have changed conditions in the trench like vibrations or excessive surcharge loads
A competent person is an individual who is capable of:
- classifying soil types
- identifying existing and predictable hazards or working conditions that are hazardous, unsanitary, or dangerous to workers
- understanding the protective systems required
- monitoring water removal equipment
- conducting site inspections
A competent person is authorized to take prompt corrective measures to eliminate hazards and dangerous conditions. If there are unsafe conditions discovered, workers should be cleared from the hazardous area until the necessary safety precautions have been taken.
Safe entry and exit is required in all excavations 4 feet or deeper which may be a ladder, steps, a ramp, or some other safe way that workers can get in and out. The entry/exit point must be located within 25 feet of all workers in the trench or excavation.
There should be a warning system when mobile equipment is operated near the excavation when the operator does not have a clear and direct view of the edge. Warning systems may include barricades, hand or mechanical signals, or stop logs.
Workers must be protected from loose rock or soil that could fall or roll from the face of an excavation. Protection may include:
- scaling to remove loose material
- installing protective barricades at appropriate intervals
- using other equivalent forms of protection
OSHA Standard 1926.501(b)(7)(i) Each employee at the edge of an excavation 6 feet or more in depth shall be protected from falling by guardrail systems, fences, or barricades when the excavations are not readily seen because of plant growth or other visual barrier.
Working should not be allowed on the faces of sloped or benched excavations at levels above other workers unless those at the lower levels are adequately protected from the hazards of falling, rolling, or sliding material or equipment.
Trenches 5 feet deep or greater require a protective system unless the excavation is made entirely in stable rock. If a trench is less than 5 feet deep, a competent person may determine that a protective system is not required.
OSHA Standard 1926.652(a)(2) Protective systems shall have the capacity to resist without failure all loads that are intended or could reasonably be expected to be applied or transmitted to the system.
There are different types of protective systems for trenches and excavations including benching, sloping, shoring, and shielding.
Benching is 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.
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.
Designing a protective system can be complex because many factors must be considered including soil type, the size of the excavation, how much water is in the soil, the climate, surcharge loads, and other operations near the worksite.
It is critically important that underground utilities be located before the excavation work begins. And then while the excavation is open, ensure the underground utilities are protected, supported, or removed as necessary to safeguard workers.
OSHA Standard 1926.651(b)(1) The estimated location of utility installations, such as sewer, telephone, fuel, electric, water lines, or any other underground installations that reasonably may be expected to be encountered during excavation work, shall be determined prior to opening an excavation.
During the safety meeting on excavation safety, review these safety tips with the crew:
- Identify sources that might affect trench stability.
- Test for atmospheric hazards such as low oxygen, hazardous fumes, and toxic gases when the excavation is deeper than four feet.
- Do not enter an unprotected trench. Remember – it only takes seconds to become buried in thousands of pounds of soil.
- Keep excavated dirt (spoils), materials, and heavy equipment at least 2 feet from trench edges.
- Do not stand or work under suspended or raised loads and materials.
- Stand away from vehicles being loaded or unloaded to avoid being struck by any spillage or falling materials.
- Keep a safe distance (at least 10 feet) when working near overhead power lines.
- All personnel should be wearing high-visibility clothing when exposed to vehicular traffic or moving equipment.
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