Excavation safety requires preplanning. There are some other areas where anticipation of possible hazards can help avoid accidents and injuries. OSHA standard 29CFR, 1926-652 contains requirements for the protection of employees from cave-ins through the use of protective systems. OSHA requires that each employee in an excavation be protected from cave-ins by a protective system except when excavations are made entirely in stable rock or excavations are less than five feet in depth and determined by a competent person to show no indication of potential cave-in.
OSHA divides protective systems into two categories: sloping and benching systems and support systems, shield systems, and other protective systems. The use of either of these categories of protective systems requires the choice of one of four design options.
There are a few allowable options when choosing sloping and benching systems. The options include allowable configurations and slopes, the use of appendices A and B, designs using other tabulated data, and designed by a registered professional engineer.
The first option specifies allowable configurations and slopes. Any excavation less than 20 feet in depth may be sloped at an angle not steeper than one and one half horizontal to one vertical- 34 degrees, measured from the horizontal. Such slopes meet OSHA's requirements for worst-case soils, Type C, as defined in 29 CFR 1926, Subpart P of Appendix A.
The second option involves the use of Appendices A and B. Maximum allowable slopes and allowable configurations for sloping and benching systems are set forth in Appendices A and B.
The third option, when choosing sloping and benching systems, involves the use of tabulated data, such as tables and charts. The tabulated data must be in written form and include selection criteria, limits on data usage to include the magnitude and configuration of slopes determined to be safe, explanatory information necessary to aid the user to make correct selection of protective systems, and the identity of the registered PE who approved the data. At least one copy of this data must be kept at the job site during construction of the protective system.
The fourth option involves the design by a registered professional engineer. Designs must be in written form and must include the magnitudes and configurations of slopes and benches determined to be safe for the project as well as the identity of the approving PE.