Excavation & Trench Safety: slope it, shore it, or shield it
A trench wall does not sag before it fails — it goes all at once, and a cubic yard of soil weighs more than a small car. That is why OSHA does not treat cave-in protection as a judgment call: at five feet an excavation needs a protective system unless it is cut entirely in stable rock, and the shallower exception still requires a competent person to examine the ground and find no indication of a cave-in. This hub turns 29 CFR 1926 Subpart P into the numbers you need on site — the slope your soil allows, the duties your depth triggers, and the inspection that has to happen every single day.
Verified against osha.gov · July 24, 2026
At a glance
Protective system
Required in every excavation, except one made entirely in stable rock, or under 5 ft where a competent person finds no cave-in indication
1926.652(a)(1)Maximum slopes
Stable rock vertical; Type A 3/4:1 (53°); Type B 1:1 (45°); Type C 1½:1 (34°)
Subpart P App. B, Table B-1Deeper than 20 ft
Sloping and benching must be designed by a registered professional engineer
Subpart P App. BEgress
A ladder, stairway or ramp in any trench 4 ft or deeper, within 25 ft of lateral travel
1926.651(c)(2)Atmosphere
Tested before entry in excavations over 4 ft deep where a hazardous atmosphere could reasonably exist
1926.651(g)(1)(i)Daily inspection
Of the excavation, adjacent areas and protective systems, by a competent person, before each shift and as conditions change
1926.651(k)(1)Every figure is a 29 CFR 1926 Subpart P threshold, verified against osha.gov on July 24, 2026. OSHA runs a National Emphasis Program on trenching and excavation; we do not publish a fatality count here because OSHA’s trenching page does not.
What does OSHA allow for this excavation?
Pick the soil classification and the depth to see the maximum allowable slope, the cut-back per side, and every Subpart P duty that kicks in — each with its CFR paragraph. Runs on the same verified engine as our full Trench Protective System Selector.
Classification is a competent-person call using the visual and manual tests in Appendix A. When the material is in doubt, the safer class governs.
Pick the soil class and depth to see the maximum allowable slope, the cut-back, and every Subpart P duty that applies — with the CFR paragraph.
Four ways to protect a trench
Subpart P gives you options, not one answer. The competent person picks the system that fits the soil, the depth, and the space available.
Sloping
Cut the walls back to the maximum allowable angle for the soil. Simple and needs no hardware, but it eats space fast: Type C at 1½:1 turns a 3 ft trench bottom 8 ft deep into a 27 ft opening at the surface.
1926.652(b)Benching
Step the walls instead of cutting one continuous slope. Benching is not permitted in Type C soil, and the step geometry comes from the same appendix as the slopes.
Subpart P App. BShoring
Support the walls with hydraulic, pneumatic, timber or aluminum shoring so the soil cannot move. Governed by the manufacturer's tabulated data, which has to be on site.
1926.652(c)Shielding
A trench box does not stop the wall failing — it protects the workers inside it when the wall does. It must be rated for the depth and soil, and workers stay inside it, including during entry and exit.
1926.652(c),(g)Soil classification decides everything
The slope, and often the system, follow from the classification a competent person makes with the visual and manual tests in Appendix A. Get this wrong and every number after it is wrong.
| Class | Max slope | Angle | What it is |
|---|---|---|---|
| Stable rock | Vertical | 90° | Natural solid mineral matter that can be excavated with vertical sides and stay intact while exposed. An excavation entirely in stable rock does not require a protective system. |
| Type A soil | 3/4:1 | 53° | Cohesive soil with an unconfined compressive strength of 1.5 tsf or greater. It is NOT Type A if 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 B soil | 1:1 | 45° | Cohesive soil above 0.5 tsf but below 1.5 tsf, plus granular cohesionless soils, previously disturbed soils, fissured material, and dry unstable rock. |
| Type C soil | 1½:1 | 34° | The least stable class: cohesive soil at 0.5 tsf or less, granular soils such as gravel and sand, submerged soil or soil from which water is freely seeping, and submerged rock that is not stable. |
Slopes are Table B-1 (Subpart P Appendix B); classifications are Appendix A. A short-term option allows Type A excavations 12 ft or less, open 24 hours or less, at 1/2:1 (63°).
What each depth triggers
- 4 ft
Egress + atmosphere
A ladder, stairway or ramp in any trench 4 ft or deeper, within 25 ft of lateral travel (1926.651(c)(2)). Above 4 ft, the atmosphere is tested before entry wherever a hazardous atmosphere could reasonably exist (1926.651(g)(1)(i)).
- 5 ft
Protective system
Slope, bench, shore or shield — unless the excavation is entirely in stable rock (1926.652(a)(1)).
- 20 ft
Engineer design
Above 20 ft, sloping and benching must be designed by a registered professional engineer (Subpart P Appendix B).
- Any depth
Daily inspection & 2 ft set-back
A competent person inspects daily and as conditions change (1926.651(k)(1)); spoil, materials and equipment stay at least 2 ft from the edge (1926.651(j)(2)).
Subpart P is a daily-inspection standard
Most standards ask for a plan. This one asks for a competent person, every day — before work starts, whenever conditions change, and after every rainstorm. The paperwork question after a collapse is never “did you have a system?” It is “who inspected it that morning, and what did they write down?”
This is what HazComFast keeps together
The daily competent-person inspection, the atmospheric tests, the competent-person designation itself, and the JHA behind the dig — timestamped in one place and exportable on demand, instead of a notebook in a truck.
Key facts
- A protective system is required in every excavation except one made entirely in stable rock, or one less than 5 ft deep where examination of the ground by a competent person provides no indication of a potential cave-in (29 CFR 1926.652(a)(1)) — shallow is a judgment someone has to make and own, not an automatic exemption.
- Table B-1 caps the slope by soil type: stable rock vertical (90°), Type A 3/4:1 (53°), Type B 1:1 (45°), Type C 1½:1 (34°). A short-term option allows Type A excavations 12 ft or less, open 24 hours or less, at 1/2:1 (63°).
- Sloping or benching for any excavation deeper than 20 ft must be designed by a registered professional engineer — Table B-1 stops being a sufficient answer at that depth.
- A stairway, ladder, ramp or other safe means of egress is required in trench excavations 4 ft or deeper, positioned so no worker travels more than 25 ft laterally to reach it (29 CFR 1926.651(c)(2)) — which means moving the ladder as the trench advances.
- Spoil, materials and equipment stay at least 2 ft back from the edge (29 CFR 1926.651(j)(2)); the atmosphere is tested before entry in excavations over 4 ft where a hazardous atmosphere could reasonably exist (1926.651(g)(1)(i)).
- A competent person inspects the excavation, the adjacent areas and the protective systems daily before work starts and as conditions change — and after every rainstorm (29 CFR 1926.651(k)(1)). OSHA also runs a National Emphasis Program on trenching and excavation.
Tools, guides and the standards
Free tools
- Competent Person Designation Letter
The signed designation, basis of competency, and stop-work authority — before the daily inspections start.
- Trench Protective System Selector
Slope, cut-back, top width, and every duty at your depth — with a cross-section diagram.
- Job Hazard Analysis Builder
Break the dig into steps, hazards and controls.
- Daily Pre-Task / STA Card
Brief the crew before the shift.
- Confined Space Entry Permit
When the excavation is also a permit space.
- Weekly Site Inspection
The whole-site self-inspection around the dig.
In-depth guides
- Does OSHA certify competent persons? The 4 documents that prove a designation
- The trench geometry problem: OSHA's slope table, computed
- Trenching & excavation safety: the OSHA requirements
- Is a trench a confined space? Subpart AA vs 1910.146
- The OSHA inspection process: what to expect
- Equipment lifecycle & inspection tracking
Excavation safety FAQ
At what depth does OSHA require trench protection?
Five feet, with a nuance most people miss. 29 CFR 1926.652(a)(1) requires every 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. So under 5 feet is not automatically exempt — the exemption depends on a competent person actually examining the ground and concluding there is no cave-in potential.
What are the maximum allowable slopes for each soil type?
From Table B-1 of Appendix B to Subpart P: stable rock may be cut vertical (90°); Type A soil is 3/4:1, or 53° from horizontal; Type B is 1:1, or 45°; and Type C is 1½:1, or 34°. There is also a short-term option: a Type A excavation 12 feet or less deep that will be open 24 hours or less may be sloped at 1/2:1 (63°). Any sloping or benching deeper than 20 feet must be designed by a registered professional engineer.
How do you classify trench soil?
A competent person classifies it using the visual and manual tests in Appendix A to Subpart P. Type A is cohesive soil with an unconfined compressive strength of 1.5 tsf or greater, but it cannot be classified Type A if it 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 B sits between 0.5 and 1.5 tsf and includes previously disturbed soils and dry unstable rock. Type C covers 0.5 tsf or less, granular soils, and submerged soil or soil from which water is freely seeping.
Does a trench box mean I can skip the slope?
Yes — shielding is an alternative to sloping, not an addition to it. A trench shield does not prevent the wall from collapsing; it protects the workers inside it when the wall moves. The shield must be rated for the depth and soil, installed per the manufacturer's tabulated data (which must be on site), and workers must stay within the protected zone, including while entering and leaving the trench.
Does a trench need a ladder every 25 feet?
Effectively, yes. 29 CFR 1926.651(c)(2) requires a stairway, ladder, ramp or other safe means of egress in trench excavations 4 feet or more deep, located so that no employee has to travel more than 25 feet laterally to reach it. In a long trench that means multiple access points, or moving the ladder forward as the excavation advances — an inspector will check the distance from the farthest worker.
Who has to inspect an excavation, and how often?
A competent person — someone able to identify the hazards and authorized to take prompt corrective action (29 CFR 1926.32(f)) — must inspect the excavation, the adjacent areas and the protective systems daily before work starts, as conditions change, and after every rainstorm or other hazard-increasing event (1926.651(k)(1)). If the inspection reveals a hazard, workers are removed from the excavation until the necessary precautions are taken.
Sources
- osha.gov/trenching-excavation
- osha.gov/laws-regs/regulations/standardnumber/1926/1926.651
- osha.gov/laws-regs/regulations/standardnumber/1926/1926.652
- osha.gov/laws-regs/regulations/standardnumber/1926/1926SubpartPAppA
- osha.gov/laws-regs/regulations/standardnumber/1926/1926SubpartPAppB
Protective-system trigger (1926.652(a)(1)), Table B-1 slopes, egress (1926.651(c)(2)), atmospheric testing (1926.651(g)(1)(i)), spoil set-back (1926.651(j)(2)) and daily inspection (1926.651(k)(1)) verified verbatim against osha.gov on July 24, 2026. Soil classification is a competent-person determination made with the tests in Appendix A. General guidance, not legal advice; OSHA-approved State Plans may impose additional requirements.
Get the Binder in Order Before the Inspector Arrives. Are You Ready?
OSHA does not give advance notice of inspections (29 CFR 1903.6). Get the binder in order before the opening conference, not during it.
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