Excavation and Trenching Safety: OSHA Subpart P Requirements for 2026 | SafetyRegulatory.com — Workplace Safety Certifications, Training & Careers

Soil weighs over 100 pounds per cubic foot. A cubic yard of saturated clay can weigh close to 3,000 pounds. When a trench wall fails, that weight hits a worker in less than a second. There’s no time to react, no time to run, and often no way to survive. OSHA estimates that cave-ins kill about 23 workers per year in the United States, and most of those deaths happen in trenches that were never protected in the first place.

Excavation safety isn’t complicated. The standard is clear, the controls are well-established, and the competent person requirement puts a trained set of eyes on site every day. The violations that kill workers are almost always failures of basics: no protective system, no competent person, no hazard assessment before digging started.

OSHA Subpart P: What It Covers

OSHA’s excavation standard lives at 29 CFR 1926 Subpart P, starting at 1926.650. It applies to all open excavations made in the surface of the earth, including trenches. The scope is broad. A trench dug for a residential utility line falls under this standard. So does a large cut for a commercial foundation.

An excavation is any man-made cut, cavity, trench, or depression in the earth. A trench is a narrow excavation made below the surface of the ground where the depth is greater than the width, and the width is no more than 15 feet. Most field work involves trenches, and the terms are often used interchangeably on job sites.

The standard applies regardless of whether heavy equipment was used, regardless of soil conditions, and regardless of project size. A two-person crew digging a gas line is covered the same as a large commercial excavation contractor.

Protective systems are required in any trench five feet or deeper where workers will enter. For trenches deeper than 20 feet, a registered professional engineer must design the protective system. Between five and 20 feet, your competent person selects the system.

Why Cave-Ins Happen Fast

Understanding the physics matters here, because it explains why speed of response is irrelevant once a wall starts moving.

Undisturbed soil is in a state of equilibrium. When you cut into it, you remove the lateral support that was holding everything in balance. The soil on the cut face now has nothing pushing back against it. Depending on soil type, moisture content, and surcharge loads (spoil pile, equipment, nearby structures), that wall can fail in seconds. There’s no visual warning. No cracking sound. It just moves.

Saturated soil, frozen and thawed soil, and previously disturbed soil fail faster and with less warning than dry undisturbed clay. This is why soil classification isn’t just a paperwork exercise. The classification determines how fast a wall can move and what kind of protection you need.

A worker caught in a trench collapse doesn’t usually suffocate from dirt filling the space above them. The weight of the soil compresses the chest and prevents breathing. Even partial burial of the torso can be fatal. Rescue operations are measured in minutes, and in most cases, rescuers can’t reach a buried worker fast enough.

The Competent Person Requirement

Every excavation operation must have a designated competent person. This is one of OSHA’s most specific requirements in Subpart P, and it’s one of the most commonly cited violations when it isn’t met.

The competent person must be capable of identifying existing and predictable hazards in excavation work, including soil conditions, surcharge loads, water accumulation, and atmospheric hazards. They must have the authority to take prompt corrective action. That last part matters. A designation that doesn’t come with actual authority to stop work is not a valid competent person designation.

Competent person status is job-specific. Someone who is a general industry competent person for lockout/tagout is not automatically a competent person for excavation work. Excavation requires specific training in soil mechanics, protective system selection, and inspection procedures.

Document the designation. Put the competent person’s name in the project file. Update it when the person changes. OSHA inspectors ask for this documentation. Not having it is a separate citation from any underlying hazard violation.

The competent person must inspect the excavation before each shift, after any rainstorm or other event that could have affected conditions, and when conditions change during the shift. They must also be on site when workers are in the excavation, or immediately available.

Soil Classification

Soil classification is the foundation of everything that follows. The class you assign to the soil determines which protective systems are allowed and what slope angles are safe. Get it wrong and you’ve built the rest of your program on a false premise.

Subpart P recognizes three soil classes plus rock.

Type A soil is the most stable. It’s cohesive, with an unconfined compressive strength of 1.5 tons per square foot or more. Undisturbed hard clay is a common Type A example. But Type A has disqualifiers. Soil fissured by previous excavation or subject to vibration from traffic or equipment cannot be classified Type A, even if it otherwise meets the strength criteria. The classification reflects current conditions, not what the soil would be if conditions were different.

Type B soil is intermediate. It includes angular gravel, silt, silty loam, and previously disturbed soils that don’t fall to Type C. It also includes Type A soil that’s been fissured or affected by vibration.

Type C is the least stable and requires the most conservative protective system. It includes granular soil with no cohesion, submerged soil, and soil from which water is actively seeping. Sand is Type C. Gravel is Type C. Anything that flows or crumbles when you cut it is Type C.

To classify soil in the field, the competent person uses one or more of four accepted methods: thumb penetration test (can you push your thumb into the soil wall), pocket penetrometer, manual or mechanical analysis of a freshly cut sample, and visual inspection. The most conservative test result governs. If visual inspection suggests Type A but the pocket penetrometer reads Type B, classify it Type B.

Protective System Options

Subpart P allows four protective system approaches. Each fits different conditions, depths, and job site constraints.

Sloping cuts the trench walls back at an angle that puts the face of the soil beyond the failure plane. No workers are at risk in the collapse zone because there isn’t one. Sloping requires more space and more excavation, which adds cost, but it’s the cleanest solution and the only option that actually eliminates the cave-in hazard rather than managing it.

Required slope angles by soil class: Type A soils may be sloped at a maximum ratio of 3/4 horizontal to 1 vertical (53 degrees from horizontal). Type B soils require at least 1:1 (45 degrees). Type C soils require at least 1.5:1 (34 degrees). These are maximums, not targets. If you’re unsure of the classification, use the more conservative angle.

Benching is a variation on sloping, cutting the walls in stair-step fashion rather than a continuous slope. It’s only allowed in Type A and Type B soils. Type C soils don’t allow benching because the soil lacks the cohesion to hold the bench faces.

Shoring uses timber, hydraulic, or pneumatic systems to brace the trench walls. It’s common in urban environments where sloping would require excavating across existing infrastructure. Shoring systems must be designed in compliance with Appendix C of Subpart P or by a registered professional engineer.

Trench boxes (trench shields) are pre-fabricated steel structures placed inside the trench. Unlike shoring, a trench box doesn’t prevent the walls from moving. It protects workers inside the box if the walls do move. The box must extend from the bottom of the trench to at least 18 inches above the surrounding ground surface, and workers must stay inside the protected zone. Trench boxes are commonly used for utility work because they’re fast to deploy and easy to move.

Daily Inspection Procedures

The competent person must inspect the excavation before each shift, after rain or other weather events that could affect stability, and whenever conditions change during the shift.

The inspection covers the trench walls for signs of cracking, bulging, or sloughing. It covers the bottom for water accumulation. It covers the area adjacent to the trench for surcharge loads, cracks in the surface, and equipment vibration. And it covers the protective system itself for any signs of movement, damage, or inadequacy.

If the inspection reveals hazardous conditions, the competent person must take corrective action before allowing workers to enter. If the hazard can’t be corrected immediately, workers stay out until it is.

Inspections must be documented. Date, time, conditions observed, any corrective actions taken. That record is your evidence of compliance and your first line of defense in any OSHA investigation after an incident.

Atmospheric Hazards

Trenches deeper than four feet in certain conditions can accumulate hazardous atmospheres. OSHA requires testing before workers enter if the trench is near a landfill, near an area where organic material is decomposing, near fuel or chemical pipelines, in a former industrial area, or anywhere hazardous gases might be present.

Oxygen deficiency (below 19.5%) and flammable gas accumulation are the primary concerns. Carbon monoxide from nearby equipment is a real hazard in deep excavations.

Testing requires calibrated direct-reading instruments. Sniff-testing by a worker’s nose is not acceptable. The competent person must be trained to interpret the results and know what actions to take when a reading exceeds action levels.

Never enter an excavation that has been identified as having a hazardous atmosphere until it has been ventilated and re-tested. The confined space rules in 1910.146 and 1926.1200 may also apply depending on conditions.

Access, Egress, and the Spoil Pile

Every trench four feet deep or greater that workers enter must have a means of access and egress. Ladders are the most common solution. The standard requires that no worker be more than 25 feet of lateral travel from a ladder or ramp.

Ladders must extend at least three feet above the top of the trench. They must be secured to prevent movement. And they must be positioned within the protected zone, not outside the trench box.

The spoil pile must be kept at least two feet back from the edge of the trench. Closer than that and you’re adding surcharge load directly to the most vulnerable part of the trench wall. This is one of the most frequently cited Subpart P violations, and it’s one of the easiest to fix. Mark the two-foot line with stakes or paint before digging starts.

Heavy equipment must stay back from the trench edge at a distance determined by soil type and equipment weight. Your competent person must assess this as part of the pre-shift inspection.

Utility Notification

Call 811 before every excavation. Every state has a one-call utility notification system, and calling before you dig is a legal requirement in all 50 states, not just an OSHA best practice.

The 811 notification process triggers member utilities to mark their buried lines within a set timeframe, typically two to three business days depending on the state. Those marks are your starting point. They’re not your endpoint.

After utilities mark their lines, physically verify by hand digging near the marked locations before moving mechanical equipment in. Utility marks can be off by several feet. And not all utilities are members of the notification system. Older private utilities, some irrigation systems, and some fiber runs may not appear in the 811 response.

Document your 811 ticket number, the date you called, and the date marking was completed. Keep this in your job file.

Common Subpart P Violations

OSHA’s excavation standard is consistently among the most frequently cited standards in construction. The violations that show up most often are: no protective system in a trench requiring one, no competent person designation, the spoil pile on the trench edge, no ladders or access in trenches requiring them, and failure to conduct required inspections.

Every one of these is a paper and training problem before it becomes a fatality problem. The standard has existed since 1989. Employers who still get cited for these violations either didn’t train their competent person properly, didn’t give them actual authority to stop work, or treated the designation as a checkbox.

The inspections also matter because conditions change. A trench that was safely sloped on Monday morning can be a Type C nightmare on Tuesday afternoon after overnight rain. The competent person who checked the trench before each shift and documented it is the employer who doesn’t end up in OSHA enforcement proceedings after a collapse.

Start with Soil Classification

Everything in excavation safety flows from the soil classification. The slope angle you’re allowed to use, the shoring design you need, whether a trench box is an appropriate solution for your depth and width, the stability of your bench faces. All of it depends on the soil type.

Classify soil conservatively. When you’re between Type A and Type B, call it Type B. When conditions change during the day, the competent person reassesses. Train your competent person to do this with actual soil samples and field tests, not intuition.

Get the soil class right and the rest of the program follows logically. Skip it or guess wrong and even a well-documented program with proper equipment can fail.

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