OSHA Excavation & Trenching Quiz — 29 CFR 1926.650-652 Practice Questions — Page 1 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.
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Q1/ 40
A crew is installing a 24-inch storm drain in a trench 8 feet deep and 3 feet wide. The competent person has classified the soil as Type C (granular, moist sand). The trench is in an open field with no vibration sources or surcharge loads. Workers must enter the trench to connect pipe. If sloping is the chosen protective method, what is the minimum required slope?
✅ Correct Answer: C
1926.652(b)(2) Table B-1: for Type C soil in an excavation less than 20 feet deep, the maximum allowable slope is 1½:1 (34° measured from horizontal). This means for every 1 foot of depth, the trench must widen 1.5 feet on each side. At 8 feet deep, the top width must be: 3 feet (bottom) + 2 × (8 × 1.5) = 27 feet MINIMUM. Type C soil CANNOT be benched (D is wrong). Vertical walls for Type C (A) would be catastrophic — Type C soil has unconfined compressive strength ≤0.5 tsf and will not stand vertically.
Q2/ 40
A competent person is performing the daily inspection of a 12-foot deep trench in Type B soil that is being used as a pipe-laying operation. The trench uses an aluminum hydraulic shoring system. The competent person notices that one of the shoring cylinders has a hydraulic fluid leak and has lost pressure. Workers are in the trench. What must happen?
✅ Correct Answer: B
1926.652(c): protective systems shall have the capacity to resist all intended loads without failure. A leaking hydraulic cylinder has already failed — it cannot maintain design pressure. 1926.651(k)(1): daily inspections of excavations and protective systems shall be conducted by a competent person. If evidence of a hazardous condition is found (which this is), exposed employees shall be removed until necessary precautions have been taken. The competent person's obligation when finding an active failure is immediate evacuation, not note-taking.
Q3/ 40
Excavated soil (spoil) from a 6-foot deep foundation excavation is being piled next to the edge. The competent person measures the spoil pile at 18 inches from the edge of the excavation. Is this compliant with 1926.651(j)(1)?
✅ Correct Answer: B
1926.651(j)(1)(i): employees shall be protected from excavated or other materials or equipment that could pose a hazard by falling or rolling into excavations by placing and keeping such materials at least 2 feet (0.61 m) from the edge of excavations. 18 inches is insufficient. The spoil pile adds surcharge weight to the trench wall, increasing the likelihood of collapse. At only 18 inches, loose material can easily roll back into the trench onto workers below.
Q4/ 40
A worker enters a 5-foot deep utility trench to make a quick repair. The competent person checked the trench and said 'it looks stable.' No protective system is used. The trench is in Type B soil. Ten minutes later, a section of the wall collapses, burying the worker to his waist. What does OSHA require for this trench?
✅ Correct Answer: B
1926.652(a)(1)(i): the only exemption for excavations under 5 feet is when examination by a competent person provides no indication of a potential cave-in. For excavations 5 feet OR MORE, 1926.652(a)(1)(ii) requires an adequate protective system UNLESS the excavation is made ENTIRELY in STABLE ROCK. Type B soil is not stable rock. The 5-foot trigger is inclusive — 5 feet requires protection. The competent person's 'visual check' does not override this standard. This soil collapse is exactly why the rule exists.
Q5/ 40
A 9-foot deep trench in Type B soil is protected by a trench box (shield). The trench box is 8 feet tall but the contractor has it sitting 2 feet above the trench bottom, leaving the bottom 3 feet of the trench walls exposed (9 feet depth - 6 feet inside the shield). Workers are laying pipe at the bottom. Is this shield placement compliant?
✅ Correct Answer: B
1926.652(g)(2): shields shall be installed in a manner to restrict lateral or other hazardous movement. Industry standards (recognized by OSHA) require the shield to extend from the bottom of the trench to a height of no less than 18 inches above the vertical face of the trench wall. Workers must stay WITHIN the protected envelope of the shield at all times. A worker at the bottom of this trench with the shield 2 feet above the bottom is outside the protective envelope — exposed to a wall collapse that could entrap or crush them.
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Q6/ 40
In a 7-foot deep excavation with vertical walls in Type A soil (clay), the competent person decides no protective system is needed because of the soil type. Is this decision correct?
✅ Correct Answer: B
1926.652(a)(1)(ii): excavations 5 feet or more in depth shall be protected from cave-ins unless the excavation is made entirely in STABLE ROCK. Stable rock means natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. Soil — even Type A clay — is NOT stable rock. Type A soil has unconfined compressive strength ≥1.5 tsf, which is strong but will still fail in time, especially after exposure to air, rain, or loading. The only legal way to have NO protective system at 5+ feet is STABLE ROCK. Everything else requires shoring, shielding, or sloping.
Q7/ 40
Workers are in a 6-foot trench laying electrical conduit. The nearest ladder is 50 feet away at the end of the trench. The trench is straight but the workers have to walk through mud to reach the ladder. What does 1926.651(c)(2) require for egress?
✅ Correct Answer: B
1926.651(c)(2): a stairway, ladder, ramp, or other safe means of egress shall be located in trench excavations that are 4 feet (1.22 m) or more in depth so as to require no more than 25 feet (7.62 m) of lateral travel for employees. At 50 feet, the workers are 25 feet beyond the maximum allowed travel distance. In a collapse, seconds matter — an extra 25 feet of travel through mud could mean the difference between escape and burial.
Q8/ 40
Surface water from a rainstorm the previous night has accumulated to 8 inches deep at the bottom of a 7-foot footing excavation. The competent person arrives in the morning and finds workers pumping the water with a trash pump while standing in the water. Is this safe practice?
✅ Correct Answer: B
1926.651(h)(1): employees shall not work in excavations in which there is accumulated water, or in excavations in which water is accumulating, unless adequate precautions have been taken. Water-saturated soil loses strength dramatically — what was Type B soil yesterday may be Type C (or worse) after a rain. Standing water also obscures the trench bottom, hiding scour holes, undermined sections, and soft spots. The competent person must reclassify the soil after the rain, implement a dewatering plan, and ensure the protective system accounts for the weakened soil conditions before workers re-enter.
Q9/ 40
A backhoe is excavating next to an existing building foundation. The excavation is 10 feet deep. There is no shoring or underpinning of the adjacent foundation. The competent person is concerned the foundation may be undermined. What does OSHA require?
✅ Correct Answer: C
1926.651(i)(1): where the stability of adjoining buildings, walls, or other structures is endangered by excavation operations, support systems such as shoring, bracing, or underpinning shall be provided to ensure the stability of such structures for the protection of employees. An adjacent foundation undermined by a 10-foot excavation can settle, crack, and collapse. A registered professional engineer may need to design the support system. The 2-foot rule in (A) applies to spoil piles, not adjacent structures.
Q10/ 40
The competent person performs a visual and manual soil test before classifying a 12-foot excavation. The soil is cohesive and can be molded into a 2-inch thread without crumbling. A pocket penetrometer reads 1.2 tsf. No fissures, vibration, or water is present. Based on 1926 Subpart P Appendix A, what is the correct soil classification?
✅ Correct Answer: A
Wait — per 1926 Subpart P Appendix A, Type A soil requires unconfined compressive strength ≥1.5 tsf. A penetrometer reading of 1.2 tsf does NOT meet this threshold. The correct classification is Type B: cohesive soil with unconfined compressive strength between 0.5 tsf and 1.5 tsf. The 2-inch thread test confirms cohesiveness but not strength. The penetrometer value of 1.2 tsf is the definitive measurement. This is Type B soil. Many accidents occur because soil is incorrectly classified as Type A based on appearance and feel alone, when quantitative testing shows it's weaker.