Support systems must be installed and removed in a way which protects employees from cave-ins, structural collapses, or from being struck by system members. Installation should begin at the top and progress to the bottom of the excavation. Removal reverses this process. Installation of support systems is to be closely coordinated with the excavation of trenches.
Backfilling shall progress together with the removal of support systems. Material may be dug to a level no more than two feet below the bottom members of a support system if the system is designed to resist the forces calculated to the full depth of the trench and there is no indication of soil loss from behind or below the bottom of the support system. This allowance for two free feet also applies to trench shields.
Employees may not work on the faces of slopes or benches above other workers unless the workers at the lower level are protected from the hazard of falling, rolling, or sliding material or equipment.
Shields shall be installed in a way that will restrict lateral or other hazardous movement of the shield in the event of sudden lateral pressures. Employees are not to be in shields when they are being installed, removed, or moved vertically. Employees may remain inside shields being moved horizontally. Employees are also to be protected from the hazards of cave-ins when they are entering or leaving the areas protected the shield.
Contractors who choose to use the appendices of OSHA's Excavation Standards in Design and Construction of a protective system must thereafter treat the provisions of the selected appendices as mandatory. Appendix A describes a method of classifying soil and rock deposits based on site and environmental conditions and on the structure and composition of the earth deposits. The appendix contains definitions, sets forth requirements, and describes acceptable visual and manual tests for use in classifying soils. This appendix applies when a sloping or benching system designed in accordance with the requirements of 1926, 652-B2 is chosen, when timber shoring for excavations is designed in accordance Appendix C of Subpart P, or when aluminum hydraulic shoring is designed in accordance with Appendix D.
Appendix A also if other protective systems are designed and selected for use from data prepared in accordance with requirements set forth in 1926, 652C and the use of the data is based on use of the soil classification system presented in Appendix A.
To restate, use of Appendix B- Sloping and Benching, Appendix C- Timber Shoring for Trenches, or Appendix D- Aluminum Hydraulic Shoring for Trenches all require the use of Appendix A- Soil Classification. Indeed, any protective system based on the use of the soil classification system presented in Appendix A must meet all the requirements of that appendix.
Appendix B contains specifications for sloping and benching when used to protect employees from cave-ins. Maximum allowable slopes and benches are based on the soil types as classified in Appendix A and are found in Tables B1 through B1.4.
Appendix C contains information to be used when timber shoring is provided as a method of protection from cave-ins in trenches not more than 20 feet deep. Selection of required timber dimensions and placement may be found in Tables C1.1 through C2.3. Each table presents the minimum sizes of timber members to use in a shoring system. Tables C1.1 through C1.3 are for actual size. Tables C2.1 through C2.3 are for nominal size.
Appendix D sets forth requirements for aluminum hydraulic shoring in trenches less than 20 feet deep. This appendix must be used when manufacturer's tabulated data are not available. Required sizes and placement of hydraulic shoring are given in Tables D1.1 through D1.4.
Appendix E illustrates alternatives to timber shoring such as aluminum hydraulic shoring, pneumatic hydraulic shoring, trench jacks, and trench shields. Appendix F presents a graphic summary of the requirements and options in Subpart P for excavations 20 feet or less in depth. Deeper excavations require protective systems designed by a registered professional engineer or manufactured systems capable of the needed depth and used in accordance with manufacturer specifications.