The Myth: One very common misconception among contractors is that any protective system is required to extend at least 18 inches above the top of the trench. Although many of them will tell you that they can’t pinpoint the exact place or cite the exact wording of “the 18 inch rule” from the Federal Regulation, they will still insist that the OSHA rules require the protective system to extend 18 inches above grade.
The Fact: The Code of Federal Regulations actually cites the following situation:
Standard for Excavation Subpart P; General Reqs: When a protective system has been installed in an excavation but that system does not reach ground level, then if sloping is selected as the option to protect workers, the protective system must extend above the vertical side of the trench a minimum of 18 inches.
The intent of this rule is to provide a barrier on slopes that will protect workers from any loose debris which might roll down the face of the slope into the trench. If the contractor determines that the roll-off protection is required under any other set of circumstances, OSHA simply states that protection must be “adequate and it must be specifically tailored to control the hazard”.
Standard for Excavation Subpart P; General Reqs (j)(2): Protection shall be provided by placing the materials or equipment at least 2 feet from the edge of excavations or by the use of retaining devices that are sufficient to prevent materials or equipment from falling or rolling into excavations, or by a combination of both if necessary.