What Does OSHA Require for Trench Safety?
By Wyatt Cooper · Published · 8 min read
Key takeaways
- Every worker in an excavation needs a protective system against cave-ins unless it is entirely in stable rock, or less than 5 feet deep and a competent person's examination shows no sign of a cave-in.
- The protective system is sloping or benching, shoring, or a shield (trench box), each designed by one of the options in 29 CFR 1926.652; Appendix B's slopes cover excavations 20 feet deep or less.
- A competent person classifies the soil and inspects the excavation daily before work, as needed during the shift, and after every rainstorm.
- Trenches 4 feet or deeper need a ladder, stairway or ramp within 25 feet of lateral travel, and spoil stays at least 2 feet from the edge.
OSHA requires a protective system for every worker in a trench or excavation (29 CFR 1926.652(a)(1)), except where it is made entirely in stable rock, or is less than 5 feet deep and a competent person finds no sign of a potential cave-in. The system is sloping or benching, shoring, or a shield, chosen by soil type and depth. A competent person inspects daily, and trenches 4 feet deep need a way out within 25 feet.
The 5-foot rule and its two exceptions
29 CFR 1926.652(a)(1): "Each employee in an excavation shall be protected from cave-ins by an adequate protective system designed in accordance with paragraph (b) or (c) of this section except when: (i) Excavations are made entirely in stable rock; or (ii) Excavations are less than 5 feet (1.52m) in depth and examination of the ground by a competent person provides no indication of a potential cave-in."
Read the second exception closely: it needs both a depth under 5 feet and a competent person's examination. A 4-foot trench in ground showing cracks still needs protection. A trench is "a narrow excavation (in relation to its length) made below the surface of the ground", generally deeper than it is wide, and not more than 15 feet wide at the bottom (1926.650). OSHA's own summary: "SLOPE or bench trench walls", "SHORE trench walls with supports", or "SHIELD trench walls with trench boxes" (OSHA, Trenching and Excavation).
Soil types decide the slope
Appendix A to Subpart P has a competent person classify each deposit as Stable Rock, Type A, Type B or Type C, "based on the results of at least one visual and at least one manual analysis", and classify a layered system by its weakest layer (Subpart P, Appendix A). Appendix B then sets the maximum slope for excavations 20 feet deep or less.
| Type | What it is (Appendix A) | Maximum slope (horizontal : vertical) |
|---|---|---|
| Stable rock | Natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed | Vertical (90°); no protective system required if the excavation is entirely in stable rock (1926.652(a)(1)(i)) |
| Type A | Cohesive soil with an unconfined compressive strength of 1.5 tons per square foot or more, such as clay; never Type A if fissured, subject to vibration from heavy traffic or pile driving, or previously disturbed | 3/4 : 1 (1/2 : 1 for a short-term excavation 12 feet deep or less, open 24 hours or less) |
| Type B | Cohesive soil between 0.5 and 1.5 tsf; angular gravel, silt, silt loam, sandy loam; previously disturbed soil not Type C; fissured or vibrated Type A | 1 : 1 |
| Type C | Cohesive soil of 0.5 tsf or less; gravel, sand and loamy sand; submerged soil or soil with water freely seeping | 1 1/2 : 1 |
Without classifying the soil, an employer can use Option 1 in 1926.652(b)(1): slopes no steeper than one and one-half horizontal to one vertical (34 degrees from horizontal), cut to the Type C configurations. When there are signs of distress, the slope must be cut back at least 1/2 horizontal to 1 vertical less steep than the maximum, and surcharge loads from spoil, equipment or traffic call for a flatter slope set by the competent person.
Shoring, shields and engineered designs
- Sloping and benching can be designed four ways (1926.652(b)): Option 1's 1 1/2 : 1; Appendices A and B; other tabulated data approved by a registered professional engineer; or a design by a registered professional engineer. Configurations deeper than Appendix B covers go to the last two.
- Support and shield systems also have four routes (1926.652(c)): timber shoring per Appendices A and C (aluminum hydraulic shoring follows the manufacturer's data, or Appendix D if that data can't be used); the manufacturer's tabulated data; other tabulated data approved by an engineer; or an engineer's design.
- Manufacturer's data for a trench box, and any written approval to deviate from it, must be in writing at the jobsite while the system is being built. Engineer-approved tabulated data and designs must also be kept at the jobsite during construction.
- Digging up to 2 feet below the bottom of a shield or a support system is allowed only if the system is designed for the full depth and there's no sign of soil loss from behind or below it.
- No one may be inside a shield while it is being installed, removed or moved vertically.
The rest of Subpart P every trench needs
| Requirement | Paragraph | What it says |
|---|---|---|
| Utilities located first | (b) | Estimated locations determined and utility owners asked to mark them before excavation starts |
| A way out | (c)(2) | A stairway, ladder, ramp or other safe means of egress in trenches 4 feet or deeper, so no more than 25 feet of lateral travel |
| Air testing | (g) | Test before entry into excavations deeper than 4 feet where oxygen deficiency or a hazardous atmosphere exists or could be expected |
| Spoil and equipment | (j)(2) | At least 2 feet from the edge, or held back by retaining devices |
| Daily inspections | (k)(1) | By a competent person before work starts, as needed during the shift, and after every rainstorm or other hazard-increasing event |
| Removal from danger | (k)(2) | Workers removed when the competent person finds signs of a possible cave-in or other hazard, until it is made safe |
| Edge protection | 1926.501(b)(7) | Guardrails, fences or barricades at excavations 6 feet or deeper that are hard to see |
A worked example: an 8-foot sewer trench
Sanitary sewer trench — 8 feet deep, 4 feet wide at the bottom, 100 feet long, previously disturbed backfill
- Protective system needed?
- Yes: 8 feet is not less than 5 feet, and the ground isn't stable rock
- Soil type
- Previously disturbed soil can't be Type A; the competent person classifies it Type B
- Option A: slope at 1 : 1
- Each side lays back 8 feet; top width = 4 + 8 + 8 = 20 feet
- Option B: unclassified, 1 1/2 : 1
- Each side lays back 12 feet; top width = 4 + 12 + 12 = 28 feet
- Option C: trench box
- A box rated for 8 feet in Type B soil, used to the manufacturer's tabulated data kept on site; the trench stays about 4 feet wide
- Egress
- Trench is 4 feet or deeper: ladders at 25 and 75 feet along the run, so no one is more than 25 feet from a ladder
- Spoil
- Piled at least 2 feet back from the edge
- Inspections
- Before each shift, as needed, and after rain, by the competent person; anyone out if they see distress
Sloping at 1 : 1 needs 20 feet of open width at the top and at 1 1/2 : 1 needs 28, which a street or a building next to the trench often rules out; that's why a box is common on utility work. The rules for the edge itself are in fall protection, and 1926.501(b)(7) applies at 6 feet. How earthwork subs carry this in the price is in how earthwork subs bid and bill. Make the setup the morning's toolbox talk, and see the subcontractor's guide for the rest of the job. Full text of § 1926.651 is on eCFR.
The bottom line
At 5 feet, a trench needs a protective system unless it is entirely stable rock; under 5 feet, only a competent person's examination showing no sign of a cave-in excuses it. Choose sloping, shoring or a box by soil type and depth, keep the design data on site, and inspect every day and after rain.
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Sources
- 29 CFR 1926.652, Requirements for protective systems — eCFR (Office of the Federal Register). Read October 22, 2026.
- 29 CFR 1926.651, Specific excavation requirements — eCFR (Office of the Federal Register). Read October 22, 2026.
- 29 CFR 1926.650, Scope, application, and definitions — eCFR (Office of the Federal Register). Read October 22, 2026.
- 29 CFR 1926 Subpart P, Excavations, with Appendices A (soil classification) and B (sloping and benching) — eCFR (Office of the Federal Register). Read October 22, 2026.
- 29 CFR 1926.501, Duty to have fall protection — eCFR (Office of the Federal Register). Read October 22, 2026.
- Trenching and Excavation — Occupational Safety and Health Administration. Read October 22, 2026.
Questions
How deep can a trench be without protection?
Less than 5 feet, and only if a competent person examines the ground and finds no indication of a potential cave-in. A trench made entirely in stable rock is the other exception. At 5 feet or deeper in soil, a protective system is required.
When does a trench need a ladder?
At 4 feet deep or more, a stairway, ladder, ramp or other safe means of egress must be within 25 feet of lateral travel for every worker in the trench.
When does a trench need an engineer?
When the sloping or support isn't taken from the standard's options or the appendices, or from manufacturer's tabulated data. Appendix B's slopes cover excavations 20 feet deep or less; other configurations need tabulated data approved by a registered professional engineer or an engineer's design.
How far back must spoil be from a trench?
At least 2 feet from the edge, or held back by retaining devices that stop it falling or rolling in, or both.
Who is the competent person for a trench?
Someone able to identify existing and predictable hazards and authorized to take prompt corrective action. For trenches, they classify the soil, inspect before each shift and after rain, and pull workers out when they see danger.
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