OSHA Excavation & Trenching Quiz — 29 CFR 1926.650-652 Practice Questions — Page 4 of 4
Free OSHA 30-Hour Construction excavation and trenching practice test with 40 realistic scenarios. Soil classification, protective systems, spoil piles, access/egress, competent person duties, hazardous atmospheres with 29 CFR 1926 Subpart P references. (Page 4 of 4)
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Q31/ 40
A competent person uses a pocket penetrometer reading 1.2 tsf on cohesive clay and classifies it as Type A. No other tests were done. Is this classification defensible?
✅ Correct Answer: B
1926 Subpart P Appendix A(c)(1)(ii): Type A requires unconfined compressive strength of 1.5 tsf or greater. At 1.2 tsf, the soil is Type B (0.5-1.5 tsf). Appendix A(d) requires at least one visual AND one manual test — a single penetrometer reading is insufficient.
Q32/ 40
After a 3-inch rainstorm, a 12-foot trench in Type B soil with hydraulic shoring has 2 feet of water. The competent person plans to pump it out and resume work 1 hour later without adjusting the shoring. Is this sufficient?
✅ Correct Answer: B
1926.651(h)(1): employees shall not work in excavations with water unless precautions are taken. Water exerts hydrostatic pressure on walls, can shift shoring, saturates soil (Type C), and reduces floor bearing capacity. A thorough re-inspection of the entire protective system is required before workers re-enter.
Q33/ 40
A trench in Type B soil is open for 3 weeks. After 1 week of hot dry weather, tension cracks appear 3 feet from the edge. Hydraulic shoring pressure has dropped 20%. Workers continue. What must happen?
✅ Correct Answer: B
1926.651(k)(1): inspections required after any condition change. Tension cracks are a serious precursor to block failure (toppling or sliding) — this failure mode is sudden with no warning. 1926.652(d)(2): hydraulic shoring shall be maintained to specified pressure. A 20% drop means the wall is under-supported.
Q34/ 40
How many cubic yards of soil must collapse to cause a fatal cave-in?
✅ Correct Answer: B
A cubic yard of soil weighs 2,700-3,000 lbs. Even 2-3 feet of wall collapsing along a section can release 1-2 cubic yards. Soil weight on a worker's chest prevents breathing (traumatic asphyxia), and soil in the mouth/nose causes suffocation. Unlike water, soil does not 'swim' — the worker is immobilized instantly. Rescue is extremely difficult; prolonged burial even 5-10 minutes is often fatal.
Q35/ 40
A benching system for a 16-foot excavation in Type A soil uses Appendix B Figure B-1. After 4 days, vertical bench faces are spalling (peeling). The soil appears drier. What is happening?
✅ Correct Answer: B
1926.651(k)(1): inspection required after condition changes. Soil exposed to atmosphere weathers — clay shrinks and cracks as it dries (desiccation), creating fissures that reduce mass strength. Bench faces spalling are a visible sign of this degradation. The competent person must reclassify the soil and potentially modify the protective system to meet Type B requirements.
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Q36/ 40
A worker is in a 6-foot trench kneeling to make a pipe connection. Their hard hat falls and rolls outside the trench box. They crawl out of the box for a moment to retrieve it. Is this 10-second exposure outside the box acceptable?
✅ Correct Answer: B
1926.652(g)(2): employees must be within the protection of the shield at all times. There is no 'short exposure' exception. Soil failure is often instantaneous. Proper procedure: exit the trench entirely using the ladder, retrieve the hard hat from the surface, re-enter using the ladder.
Q37/ 40
A contractor digging a 5-foot trench for a water line decides no protective system is needed because it's 'only 5 feet deep.' Is this correct?
✅ Correct Answer: B
1926.652(a)(1)(i): protective systems are required for excavations 5 feet or more in depth, except those made entirely in stable rock or those less than 5 feet where a competent person finds no indication of potential cave-in. The standard's plain language covers exactly 5 feet — the exception is for 'less than 5 feet.' Many contractors misinterpret this.
Q38/ 40
A crew is digging a 12-foot-deep trench in Type B soil. The trench runs parallel to a busy highway, and vibrations from traffic are noticeable. The competent person classified the soil as Type B based on one manual test. What additional protective measure is required?
✅ Correct Answer: B
1926.651(c) requires that surface encumbrances and surcharge loads (including nearby vehicle traffic, spoil piles, and equipment) be considered in the design of protective systems. Traffic-induced vibration can destabilize trench walls and invalidate a Type B classification. 1926.652 requires protective systems designed by a registered professional engineer when surcharge loads are present beyond what the standard tabulated data covers. OSHA Standard Interpretation letters consistently reaffirm that highway vibration constitutes a surcharge hazard.
Q39/ 40
An excavation is 5 feet deep in stable rock. The competent person inspects it at the start of the shift and finds no issues. A rainstorm passes through at 10 AM but the trench appears dry. When must the next inspection occur?
✅ Correct Answer: B
1926.651(k)(1) requires daily inspections by a competent person, AND after every rainstorm or other hazard-increasing occurrence. 'Stable rock' is the exception to protective system requirements under 1926.652(b)(1)(i), but the inspection requirement of 1926.651(k)(1) applies to ALL excavations regardless of soil type. Rain can seep into rock fissures, create hydrostatic pressure, and cause rockfall — making immediate re-inspection mandatory.
Q40/ 40
A 6-foot deep trench in Type C soil is being excavated near an existing underground fiber optic line. The one-call center marked the line, but the exact depth is uncertain. The operator begins digging within 2 feet of the marking using a backhoe. Is this compliant?
✅ Correct Answer: B
1926.651(b)(2) requires that while the excavation is open, underground installations be protected, supported, or removed as necessary to safeguard employees. Additionally, 1926.651(b)(1) requires the exact location of underground installations to be determined prior to excavation. Most state one-call laws define a tolerance zone (typically 18-24 inches on either side of the marking), within which ONLY hand digging or non-invasive methods (vacuum excavation) are permitted. Using a backhoe within 2 feet of a marked utility line violates both OSHA requirements and industry practice (CGA Best Practices).