A competent person under OSHA 29 CFR 1926 Subpart P must be capable of identifying existing and predictable excavation hazards and be authorized to take prompt corrective measures to eliminate them. Preparation should center on three applied skills: classifying soil using visual and manual tests, selecting a protective system appropriate to that soil and depth, and performing inspections at the required times, including after conditions change such as following a rainstorm.
What the term 'competent person' actually obligates you to do
Under Subpart P, a competent person is one who can identify existing and predictable hazards in excavation surroundings or working conditions that are unsanitary, hazardous, or dangerous to employees, and who has employer authorization to take prompt corrective measures.
Compare this definition with the informal way the title is used on job sites. Two elements must both be present: capability, meaning genuine hazard-identification knowledge of the excavation itself, and authorization, meaning the employer has empowered the individual to act immediately. A foreman with deep experience but no authority to remove workers is not filling the role. Neither is a safety officer who can identify problems but can only file a report and wait. When a scenario describes a technically knowledgeable person whose corrective action is limited to notifying a supervisor, trace whether the described authority satisfies the definition before treating that person as the competent person.
The definition connects directly to a specific duty: conducting inspections of excavations, adjacent areas, and protective systems. Under 1926.651, these inspections must occur every day at the start of work and whenever conditions change, with the example OSHA gives being after a rainstorm. The inspection also applies to adjacent areas and protective systems, not just the trench walls. When an inspection reveals evidence of a hazard such as a cave-in potential or a hazardous atmosphere, exposed employees must be removed from the hazardous area until the problem is corrected. In scenario work, trace the two elements together: the inspection duty and the removal authority operate as a pair, so identifying a hazard triggers removal of exposed employees until the condition is corrected.
Separating Type A, B, and C soil using visual and manual tests
Subpart P Appendix A classifies soil into Stable Rock, Type A, Type B, and Type C by unconfined compressive strength. Competent persons classify using visual analysis of site conditions plus manual analysis tests such as dry strength, thumb penetration, and plasticity.
Trace the classification as an ordered decision, not a label lookup. Start with the visual test: look for previously disturbed ground, layered rock systems, cracks or fissures in open faces, surface water pooling, and nearby sources of vibration. Several of these observations cap the classification regardless of what manual tests show, so a wet, sandy site can be ruled out of Type A on visual grounds alone. Then run manual tests on a fresh sample: dry strength (does it crumble easily, or clump firmly when dry), thumb penetration (can your thumbnail or thumb indent it), and plasticity (does it roll into a thread without crumbling).
The strength bands are the anchor points: Type A soils have unconfined compressive strength of 1.5 tons per square foot or greater, Type B ranges from greater than 0.5 up to 1.5 tsf, and Type C is 0.5 tsf or less. In plain terms, a cohesive clay that takes firm thumb pressure to indent trends toward A or B, while a granular sand you cannot hold together trends toward C. Remember the caps: previously disturbed soil is classified no higher than Type B, and soil that is fissured, subject to vibration from traffic or equipment, or submerged cannot be classified as Type A. To see why the caps matter, consider a gravelly backfill area that looks cohesive in one sample; the visual evidence of prior disturbance controls, and the better decision is to classify no higher than Type B and verify with manual tests on fresh material.
| Classification | Unconfined compressive strength | Typical examples | Reference slope for a simple slope, excavation 20 feet or less deep (Appendix B) |
|---|---|---|---|
| Stable Rock | Solid, intact mineral matter | Unfractured granite, limestone in place | Vertical |
| Type A | 1.5 tsf or greater | Cohesive clays, cemented soils like caliche | 3/4 : 1 |
| Type B | Greater than 0.5 tsf and less than 1.5 tsf | Angular gravel, silt, previously disturbed soil | 1 : 1 |
| Type C | 0.5 tsf or less | Granular sand, gravel, submerged or very soft soil | 1.5 : 1 |
Choosing between sloping, benching, shoring, and shielding
OSHA frames the choice as slope it, shore it, or shield it. Sloping or benching uses the soil classification to set angles; shoring resists soil pressure with supports; shielding uses a trench box to protect workers even if soil moves. Stable rock is the only condition needing no system.
Compare the three families by what they assume. Sloping and benching (Appendix B) assume the exposed soil can stand at the chosen angle, so the angle is a direct function of the classification: for example, a simple slope in Type B soil is cut at 1 : 1, while Type C requires a flatter 1.5 : 1. Shoring, such as timber (Appendix C) or aluminum hydraulic shoring (Appendix D), actively resists soil pressure and is sized from the classification and depth. Shielding, such as a trench box, does not hold the walls in place; it protects the space between its walls, so soil movement outside the box remains possible. This difference drives two rules worth tracing: workers must stay inside the shield while it is in the trench, and shields must extend appropriately above the bottom of the excavation when conditions warrant.
Selection also depends on depth limits and design authority. Protective systems are generally required where the excavation is five feet or deeper unless the material is stable rock; for excavations less than five feet deep, entry without a system is permitted only after the competent person examines the ground and finds no indication of a potential cave-in. Systems deeper than 20 feet generally require a design by a registered professional engineer rather than tabulated appendix data. Recognize the design options in 1926.652(c): appendix methods, manufacturer tabulated data, or an engineered design, each tied to specific soil types. To practice this, trace what happens when a shoring system is matched to the wrong classification, for example using data based on Type B assumptions in soil later reclassified as Type C; the better decision is to reclassify first and verify the system's tabulated data covers the actual condition.
Worked scenario 1: reclassifying a trench after overnight rain
After a rainstorm, the competent person must re-inspect before employees re-enter. Saturated soil may drop from Type B to Type C behavior, so a slope cut for Type B may no longer be acceptable and must be corrected before work resumes.
Scenario: a crew digs a six-foot trench in what was classified as Type B soil and cuts the walls at a 1 : 1 simple slope. Overnight it rains heavily. At 7 a.m. an operator wants to resume digging and says the slope was fine yesterday, so it is fine today. The plausible mistake is accepting that reasoning and re-entering on the existing slope. Why it matters: rain adds water, and water saturation reduces soil strength and is one of the conditions that pushes soil toward Type C behavior, for which Appendix B requires a flatter 1.5 : 1 simple slope.
The better decision sequence: stop entry, conduct the inspection required after the rainstorm, and reclassify. Visual tests now show standing water and soft, slumping walls; thumb penetration shows the soil is easily indented, indicating strength below the Type B range. The competent person reclassifies the affected soil as Type C, and the team either re-cuts the slope to 1.5 : 1, benches appropriately, or installs shoring or a shield rated for the depth, before anyone re-enters. The rule that matters is not just 'slopes depend on soil type' but 'inspections and reclassification are triggered by condition changes.' Trace the trigger, then the test, then the corrected system, and note that water also raises 1926.651 concerns such as removal of accumulated water before entry.
Inspection duties beyond the walls: spoils, access, utilities, and atmosphere
A competent-person inspection covers the whole excavation environment: spoil placement kept back from edges, safe access and egress, underground utilities located and supported, surface encumbrances, exposure to falling loads, water, and possible hazardous atmospheres before entry.
Compare 'checking the trench' with 'inspecting the excavation, adjacent areas, and protective systems.' Subpart P's specific requirements in 1926.651 extend the daily inspection into a checklist of site conditions. Spoil piles and equipment must be kept a safe distance back from excavation edges, with two feet as the commonly cited minimum, to prevent roll-in and surcharge loading. Where a trench is four feet or deeper, a ladder, ramp, or other means of egress must be positioned so lateral travel is no more than 25 feet for any worker inside. Underground utilities must be located and supported or removed before digging near them, and surface encumbrances that could slide or fall in must be removed or stabilized.
The remaining triggers are the ones that change an answer mid-scenario. Falling loads: no one may stand under loads handled by lifting or digging equipment, and employees must be kept away from vehicles being loaded. Atmospheric hazards: where oxygen deficiency or toxic gases could reasonably be expected, for example in landfill-adjacent ground or near sewers, testing must be done before entry, with ventilation or respiratory protection as indicated. Water and vibration: accumulated water must be controlled or removed, and operations that could compromise adjacent structures need supports or underpinning. When reading a site scenario, notice which of these the narrator has already addressed and which condition the description quietly omits, such as a spoil pile parked directly at the edge of an otherwise shielded trench; the omitted condition is the one that still needs a control.
Worked scenario 2: a trench shield that protects the box but not the trench
A shield protects only the space between its walls. Workers inside must remain within the shield, the system must be used within its rated depth for the actual soil, and external hazards like edge spoil still require 1926.651 controls.
Scenario: an eight-foot trench in Type C soil is equipped with a trench shield. The crew has set a spoil pile about a foot from the excavation edge, the shield's label shows tabulated data for a maximum eight feet in Type C soil, and a worker climbs in while the machine passes the spoil bucket overhead. The plausible mistake is treating the shield as a complete answer: 'we have a box, so we are safe.' Why it matters: the shield does not stop the spoil pile from rolling in at the edge, does not permit exposure to loads passing overhead, and is only valid if the ground and depth match its tabulated data.
The better decision: verify each element separately. Confirm the shield's tabulated data covers eight feet in the actual reclassified soil and that it is installed as designed. Keep the spoil pile at least two feet back from the edge. Ensure no one works under the raised bucket. Check egress: at eight feet deep, a ladder must be within 25 feet lateral travel of the worker, inside the shield's protected zone. Finally, remind the crew to stay within the shield walls while it is in the trench. This scenario teaches the partition of responsibilities: 1926.652 answers 'is there a protective system, correctly selected and used,' while 1926.651 answers 'is the surrounding site condition controlled.' Both halves must pass independently before entry is appropriate.
Practice exercise: classify, select, inspect, and self-check
Build three mock site cards describing soil feel, visual evidence, and depth. For each, run the visual-then-manual test sequence, classify the soil, choose a protective system with its limits, list inspection triggers, and score yourself against a rubric.
Exercise: write three short site descriptions, for example (1) a damp, previously excavated fill area with angular gravel fragments, six feet deep; (2) a stiff clay bank, eight feet deep, showing no fissures and no vibration sources, where a fresh sample rolls into a thread and resists thumb indentation; (3) a sandy trench bottom with water seeping, five and a half feet deep. For each card, trace: visual findings, manual test findings, classification with reasoning, chosen system (slope angle from Appendix B, or a shoring or shield system with stated depth and soil limits), and the specific 1926.651 items your site description makes relevant, such as water removal or spoil distance. Write the answers before checking them against Subpart P Appendices A, B, and F.
Self-check rubric, scored per card: (1 point) named the correct classification; (1 point) cited at least one visual and one manual test that support it; (1 point) stated a protective system matched to that classification and depth, including any 20-foot engineering limit; (1 point) listed the inspection schedule including condition-change triggers such as rain; (1 point) identified the omitted 1926.651 hazard the card implies. A useful learning milestone is scoring at least 4 of 5 on every card before moving on; this is a study checkpoint, not a prediction of exam performance. Adaptable preparation sequence: week one, learn the competent-person definition and inspection duties; week two, drill soil classification with real or described samples; week three, work the protective-system selection table and each scenario's depth limits; week four, cycle full mock scenarios and re-score old cards cold.
References and further reading
Use these references to explore the concepts and check the latest information from the relevant organizations.