CHST Excavation and Trenching Safety 4 — Questions and Answers
Question 1: Under OSHA 29 CFR 1926 Subpart P, who is qualified to classify soil at an excavation site?
- Any experienced laborer on the crew
- A competent person with soil classification training (Correct answer)
- The project engineer only
- A licensed geotechnical engineer only
Correct answer: A competent person with soil classification training
OSHA requires a competent person — one who can identify hazards and has authority to correct them — to classify soil using visual and manual tests.
Question 2: Which soil test involves rolling a moist soil sample into a thread and observing if it crumbles?
- Pocket penetrometer test
- Ribbon test
- Thumb penetration test
- Thread test (Correct answer)
Correct answer: Thread test
The thread test (dry strength test) checks cohesion by rolling soil into a 1/8-inch thread; if it holds, the soil has higher cohesion.
Question 3: A trench 6 feet deep is being excavated in Type B soil. What is the maximum allowable slope ratio?
- 1H:1V (Correct answer)
- 3/4H:1V
- 1.5H:1V
- 1/2H:1V
Correct answer: 1H:1V
Type B soil requires a 1H:1V (45°) slope per OSHA 29 CFR 1926 Appendix B.
Question 4: What is the minimum distance spoil piles must be kept from the edge of an excavation?
- 1 foot
- 2 feet (Correct answer)
- 3 feet
- 5 feet
Correct answer: 2 feet
OSHA 1926.651(j)(2) requires spoil piles and equipment to be kept at least 2 feet from excavation edges to prevent cave-in from surcharge loads.
Question 5: When is a stairway, ladder, or ramp required in an excavation?
- Only when the excavation is deeper than 10 feet
- When workers must enter an excavation 4 feet or more in depth (Correct answer)
- Whenever heavy equipment is present
- Only in Type C soil excavations
Correct answer: When workers must enter an excavation 4 feet or more in depth
OSHA 1926.651(c)(2) requires a means of egress (ladder, stairway, or ramp) for any excavation 4 feet or deeper.
Question 6: Which condition would cause an excavation previously classified as Type A soil to be reclassified?
- Air temperature drops below 40°F
- Previously disturbed soil is discovered beneath the surface (Correct answer)
- A water pump is brought on site
- The excavation depth exceeds 10 feet
Correct answer: Previously disturbed soil is discovered beneath the surface
Previously disturbed soil cannot be classified as Type A; its prior disturbance reduces cohesion and stability.
Question 7: A rescue retrieval system for permit-required confined spaces adjacent to a trench must be capable of retrieving workers without requiring rescuers to:
- Use fall arrest equipment
- Enter the confined space (Correct answer)
- Wear respiratory protection
- Carry radio communications
Correct answer: Enter the confined space
OSHA 1910.146(k)(3) requires non-entry rescue systems so rescuers can retrieve workers without entering the hazardous space themselves.
CHST Excavation and Trenching Safety 4
Under OSHA 29 CFR 1926 Subpart P, who is qualified to classify soil at an excavation site?