By Kelly Bubolz, Compliance Assistance Specialist, Appleton Area OSHA Office
The fatality rate for excavation work is 112 percent higher than the rate for general construction. Excavations are inherently unstable, whether dug deep or shallow, which makes pre-planning, protective systems and evaluation by a competent person critical to keeping workers safe. Between 50 and 100 workers die in trench collapses each year, according to NIOSH. Most injuries – 75-95% – occur in trenches lacking protective systems or found a protective system was used incorrectly in about one-quarter of trench deaths and, in 12%, a protective system was on site but not used in the trench.
Why Does a Trench Collapse Occur? Soil is normally kept in place by the pressure generated from the horizontal and vertical forces of the surrounding soil. During a conventional excavation operation, when the soil is being removed or dug-out in bulk form, the surrounding support is removed; the remaining soil becomes a vertical wall without lateral support. Because of that lack of surrounding pressure, most soil types will eventually collapse into the open excavation. This often happens suddenly, and usually, without warning. Ground that previously has been disturbed may be more likely to cave in. But also, once a trench has been opened, the soil’s moisture conditions are constantly changing, and if there’s rain or seepage or anything like that it could encourage a cave-in of the walls of the trench.
OSHA regulations governing the protection of employees working in trenches state that workers must be protected from trench collapse/cave-ins by an adequately designed protective system; unless the proposed excavation depth is less than five (5) feet, and the examination of the soil by the competent person reveals no indication of a potential cave-in.
