A cubic yard of soil weighs about as much as a car
Cave-ins are the reason Subpart P exists: a trench wall gives way in seconds and there is no outrunning it. OSHA’s answer is a protective system — sloping, benching, shoring, or shielding — and 29 CFR 1926.652(a)(1) requires one for every employee in an excavation, except where the dig is entirely in stable rock, or is under 5 ft deep and a competent person examines the ground and finds no indication of a potential cave-in. Shallow is not automatically safe; it is a judgment someone has to make and own.
Table B-1: the maximum allowable slopes
| Soil or rock type | Max slope (H:V) | Angle from horizontal |
|---|---|---|
| Stable rock | Vertical | 90° |
| Type A soil | 3/4:1 | 53° |
| Type B soil | 1:1 | 45° |
| Type C soil | 1½:1 | 34° |
| Type A — short term 12 ft or less, open 24 hours or less | 1/2:1 | 63° |
Sloping or benching for an excavation deeper than 20 ft must be designed by a registered professional engineer. Table B-1 stops being a sufficient answer at that depth.
Why sloping often loses to a trench box
The cut-back is the depth times the ratio, on each side. A 6 ft trench in Type C soil (1½:1) needs 9 ft of cut-back per side — a 3 ft trench bottom becomes 21 ft wide at the top. In a street, between utilities, or inside a property line, that space usually does not exist, which is why shoring or a manufactured trench shield is the common answer. Shields and shoring are governed by the manufacturer’s tabulated data, which must be on site.
The duties that come with the hole
- Egress — a ladder, stairway or ramp within 25 ft of lateral travel in any trench 4 ft or deeper 29 CFR 1926.651(c)(2)
- Spoil set-back — materials and equipment kept at least 2 ft from the edge 29 CFR 1926.651(j)(2)
- Atmosphere — tested before entry in excavations over 4 ft where a hazardous atmosphere could reasonably exist 29 CFR 1926.651(g)(1)(i)
- Daily inspection — of the excavation, adjacent areas and protective systems, by a competent person, before work starts and as conditions change 29 CFR 1926.651(k)(1)
Frequently asked questions
When does OSHA require a trench protective system?
29 CFR 1926.652(a)(1) requires each employee in an excavation to be protected from cave-ins by an adequate protective system, except when the excavation is made entirely in stable rock, or is less than 5 feet deep and examination of the ground by a competent person provides no indication of a potential cave-in. Note what that means: under 5 feet is not automatically exempt — it takes a competent person's examination.
What are OSHA's maximum allowable slopes?
Table B-1 of Appendix B to Subpart P sets them by soil type: stable rock may be vertical (90°); Type A is 3/4:1, or 53° from horizontal; Type B is 1:1, or 45°; and Type C is 1½:1, or 34°. A short-term option lets Type A excavations 12 feet or less that stay open 24 hours or less be sloped at 1/2:1 (63°). Sloping or benching for any excavation deeper than 20 feet must be designed by a registered professional engineer.
How far back do I have to cut the slope?
Multiply the depth by the soil's horizontal-to-vertical ratio. Type C soil at 1½:1 in a 6-foot trench means cutting back 9 feet on each side, so a 3-foot-wide trench bottom becomes 21 feet wide at the top. Type A at 3/4:1 in the same trench cuts back 4.5 feet per side. That arithmetic is why shoring or a trench shield is often chosen instead of sloping — there simply isn't room in a street or between utilities.
Does a trench need a ladder?
Yes, at 4 feet. 29 CFR 1926.651(c)(2) requires a stairway, ladder, ramp or other safe means of egress in trench excavations that are 4 feet or more in depth, positioned so no worker travels more than 25 feet laterally to reach it. In practice that means moving the ladder as the trench advances, not leaving one at the end.
Who classifies the soil?
A competent person, using the visual and manual tests in Appendix A to Subpart P. The classification is a judgment about the actual material on site — Type A requires cohesive soil at 1.5 tsf or greater and is ruled out where the soil is fissured, subject to vibration from traffic or pile driving, previously disturbed, or part of a layered system dipping into the excavation at 4H:1V or steeper. Type C covers submerged soil or soil from which water is freely seeping. This tool applies the classification you enter; it cannot verify it.
Sources & verification
- 29 CFR 1926.652 — requirements for protective systems
- 29 CFR 1926.651 — specific excavation requirements
- Subpart P Appendix B — sloping and benching (Table B-1)
Slopes, depths and duties verified against osha.gov on 2026-10-05. Soil classification is a competent-person determination made with the tests in Appendix A; this tool applies the classification you enter and does not verify it. General guidance, not legal advice. State-Plan states may impose additional requirements.
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