Work involving trenching and excavating activities tends to be the most hazardous in the industry. Yet, we see trenching and excavating work going on all around us. Excavations are needed for the installation and repair of utility lines, replacement of water and sewer lines, swimming pool construction, even grave digging. Excavation projects vary considerably, each with its own set of unique problems.
An unsupported, improperly shored or sloped trench or excavation wall can collapse killing or injuring workers with little or no warning. However, most of these accidents can be anticipated and prevented with the proper training and education.
What conditions influence the kind and amount of shoring needed?
- Depth of trench – If a trench is five feet deep or more, it must be shored or sloped. If there’s a possibility of soil movement, even in shallower trenches, it must be shored. If there’s any doubt, shore or slope it!
- Soil Classification – The more liquid the soil, the more you need to protect against cave-ins. Try to prevent water from collecting in existing trenches.
- Changing weather conditions - Trenches safely sloped or shored in dry weather can become deathtraps when wet. Even hard-packed soil can become unstable after a rain.
- Heavy loads in the area – Understand that nearby structures such as buildings, curbs, trees, and utility poles put stress on trench shoring. Never operate or park heavy equipment next to a trench.
- Vibration – If digging a trench near a roadway or where other operations create vibration make sure the shoring/sloping design reflects those conditions.
Make sure to acquire permits and call 811 (Underground Service Alert) to locate hidden obstructions like underground pipes or utilities that may affect the trench prior to any excavation. If any obstructions are located, remove or protect them from damage. Precautions are needed when excavating near backfilled or disturbed soil, they may require additional sheeting and bracing, as will hard compact ground if there is filled ground nearby. Warning signs should be posted around trenches, provide adequate lighting for nighttime work. Also, when there is any doubt of the atmosphere in the trench, test and ventilate.
A “competent person” must make daily inspections of the trench and protective systems and anytime there is a change in the conditions that could weaken the trench (such as a rainstorm). A “competent person” as defined by Cal/OSHA is a person who is capable of identifying existing and predictable hazards in the surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees. The competent person has the authority to impose prompt corrective measures to eliminate these hazards.
In this case it would apply to someone who is familiar with Cal/OSHA provisions relating to trenches, excavations, and earthwork with its related protective systems and is knowledgeable in soil analysis. They must also be able to recognize and test for hazardous atmospheres and also have the authority to take prompt corrective action.
Make sure workers can get in and out of the trench quickly. If hazardous conditions are detected, all work must be stopped and not resumed until the hazard(s) has been corrected. When the work is completed, all excavations must be backfilled.
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from the State Compensation Insurance Fund Safety Newsletter, April 2011