The “OSHA 6-foot rule” is shorthand for the depth-based safety requirements in OSHA’s trenching and excavation standard, 29 CFR 1926 Subpart P. In practice there isn’t a single 6-foot rule: OSHA sets different requirements at 4 feet, 5 feet, 6 feet, and 20 feet of depth. Here’s what applies at each threshold.
4 feet: safe access and atmospheric testing. In trenches 4 feet (1.22 meters) or deeper, OSHA requires a safe means of entry and exit, such as a ladder, stairway, or ramp, located so that no worker has to travel more than 25 feet laterally to reach it (29 CFR 1926.651(c)(2)). At the same depth, if a hazardous atmosphere exists or could reasonably be expected (for example, in excavations near landfills or where hazardous substances are stored), the air must be tested before workers enter (29 CFR 1926.651(g)(1)).
5 feet: cave-in protection. Any excavation 5 feet (1.52 meters) or deeper must have a protective system in place, unless it is made entirely in stable rock (29 CFR 1926.652(a)(1)). Excavations shallower than 5 feet still need protection if a competent person finds any indication of a potential cave-in. This is the most important threshold in the standard, because cave-ins are the leading cause of excavation fatalities.
6 feet: fall protection. OSHA’s fall protection rules apply at the edge of an excavation 6 feet (1.83 meters) or deeper. Guardrails, fences, or barricades are required where the excavation is not readily visible because of plant growth or another visual barrier, and wells, pits, shafts, and similar excavations 6 feet or deeper must be guarded by guardrails, fences, barricades, or covers (29 CFR 1926.501(b)(7)). Walkways that cross an excavation must have guardrails when they are 6 feet or more above the lower level (29 CFR 1926.651(l)(2)).
20 feet: engineered protection. For excavations deeper than 20 feet, sloping, benching, shoring, or shielding systems must be designed by a registered professional engineer rather than taken from the standard’s tables (29 CFR 1926.652(b) and (c)).
Protective system options. The standard outlines several protective systems that can be used, including sloping, benching, shoring, and shielding (trench boxes), depending on the soil classification and the conditions at the site.
The competent person requirement. Employers are responsible for ensuring that a competent person who has completed competent person safety training inspects the excavation daily, before each shift, and as conditions change to determine the protective measures required. This competent person must have the knowledge to identify existing and predictable hazards and the authority to take prompt corrective action to eliminate them.
