Excavation and trenching cave-ins result in more than 100 fatalities annually in the United States. Too often, an improperly protected trench or excavation wall will collapse, trapping workers. These accidents can be eliminated if we follow proper excavation and trenching procedures. OSHA Construction Standards for Excavation can be found in Subpart P 1926.650-.652.
An excavation is any mechanically-made cavity or depression in the earth’s surface, from cellars to highways. A shoring system, sloping of ground, or some other equivalent means must be used to protect all employees exposed to danger from moving ground in all excavations. In addition, all trenches over 3 feet deep in either hard and compact, or soft and unstable soil must be sloped, shored, sheeted, braced or otherwise supported. Trenches less than 3 feet in depth must also be effectively protected when hazardous ground movement may be expected.
Any surface encumbrances which may create a hazard to employees shall be removed or supported, as necessary, to safeguard employees. The presence of all underground installations such as sewer, telephone, fuel, electric, or water lines shall be determined prior to opening an excavation.
There are three ways to protect against accidents. Protective systems include shoring, sloping, and a trench shield or box. Shoring is a structure such as a metal hydraulic, mechanical, or timber bracing system that supports the sides of an excavation. A shoring system may include sheeting, bracing or jacks. Sloping is accomplished by cutting the banks of the excavation back to the angle of repose. At this angle the soil won’t slide. This angle varies, and depends on the soil type. A trench shield or box is a heavy metal box designed to be placed in a trench; it prevents the sides of the trench from caving in. Trench boxes are used in many types of sewer and pipeline work.
What are the major causes of cave-ins? Inadequate shoring, improper slopes on banks, poor analysis of soil conditions, defective shoring materials, nearby loads, vibrations and weather conditions.
Several precautions can and must be taken to help eliminate excavation hazards.
- The first step is to check for and locate any underground utilities or other buried items.
- Then, the soil conditions must be carefully evaluated to determine the protective system needed.
- Wear your hard hat at all times. Also wear rugged boots to protect your feet.
Material stock piled nearby can increase the pressure on trench or excavation walls. Keep heavy equipment and materials such as pipe and timbers well away from the excavation site. Maintain a minimum of two feet between any materials, including the spoils pile and the edge of the trench.
Vibrations from equipment passing by can contribute to cave-ins by loosening the soil. Any soil vibration can endanger a shoring system. Compaction operations cause vibration; therefore, check soil conditions before, during and after compaction. For your protection, OSHA’s Revised Construction Standard (Subpart P.,1926.650) clarifies the requirements for the protection of employees, both in and around excavations, and requires, that a Competent Person be present throughout the entire excavation process. A Competent Person is one who is capable of identifying existing and predictable hazards in the surroundings or working conditions which are unsanitary, hazardous, or dangerous to employees, and who has the authorization to take prompt corrective action to eliminate them.
Since quick exits are a must, ladders are to be located no more than 25 feet away from any worker if the excavation is 4 feet or more. Ladders must extend from the floor of the excavation to 3 feet above the top and must be secured at the top.
DON’T PLAY GUESSING GAMES WITH A TRENCH EXCAVATION.