Excavation and trenching cave-ins result in more than 100 fatalities annually in the United States. Too often an improperly protected trench or excavated wall will collapse, trapping workers These accidents can be eliminated if we follow proper excavation and trenching procedures.
Several months ago, a plumbing contractor’s employee was working in a residential neighborhood between two homes in an improperly shored trench. The worker was down about 7 feet when the trench collapsed and the worker was buried. When the rescue services arrived, it no longer was a rescue, but a recovery and the worker did not go home, but became a fatal statistic.
Soil weights a lot. A cubic foot of soil can weight up to 150 pounds and a cubic yard of soil weighs at least 3000 pounds. Soil moves suddenly, and it moves faster than a person can run.
So, what is an excavation? An excavation is any man-made cavity or depression in the earth's surface, a trench is a narrow excavation usually longer than it is wide.
What are soil types - soil types are Class A, B, or class C soil. Soil in the Pacific Northwest is typically classified as type C, but occasionally it can be classified type B.
Protective systems for an excavation are benching, sloping, shielding, shoring or engineering. Once the soil is classified then soil conditions, weather, climate and other factors will determine how the protective system can be used.
How can we protect ourselves against an accident in an excavation/trench?
There are several different ways;
Sloping - Sloping is accomplished by cutting the banks of the excavation back to a safe angle.
Benching - benching creates steps in the excavation from the bottom of the excavation to the top of the excavation. Benching can only be done in class A or B soil types.
Shielding - 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.
Shoring - Shoring is a hydraulic mechanical bracing system that supports the sides of an excavation. A shoring system may include specially engineered sheeting, bracing or jacks.
Engineering - Engineered systems, is a recognized protective system so long as the engineering is done by a Registered Professional Engineer (RPE) that knows soil types and familiar with excavations.
Any surface encumbrances which may create a hazard to workers in a trench need to be removed or supported, as necessary, to protect workers, such as roadways, sidewalks, light poles, or mailboxes.
Before an excavation begins, underground locates are required.
The presence of all installations such as sewer, telephone, fuel, electric, or water lines must be located and marked prior to starting an excavation.
A competent person must inspect the excavation and adjacent areas daily for possible cave-ins, failure of protective systems, hazardous atmospheres, or any other condition which may present a danger.
The competent person must understand the excavation standards and must know how to test soil types. The competent person must take these factors into consideration and reevaluate the jobsite periodically. An important role of the competent person is having the authority to stop work.
Access - access for trenches 4 feet in depth or more, must have sufficient means of exit such as a ladder and these must be located within 25 feet of lateral travel.
Finally, if you see someone in an un-shored trench, ask them to get out immediately.
Please, don’t take chances, your life and your family are not worth getting into an unprotected excavation/trench.