STSC Excavation and Trenching Safety 4 — Questions and Answers
Question 1: When must a competent person inspect an excavation?
- Only at the start of each week
- Daily and after any hazard-increasing event such as rain (Correct answer)
- Once before work begins on the project
- Only when workers report a concern
Correct answer: Daily and after any hazard-increasing event such as rain
OSHA requires a competent person to inspect excavations daily and after any event that could increase hazards, such as rainfall or vibration.
Question 2: What is the maximum depth of an excavation before a ladder or other safe means of egress is required?
- 2 feet
- 3 feet
- 4 feet (Correct answer)
- 5 feet
Correct answer: 4 feet
OSHA mandates that a ladder, stairway, or ramp be provided in excavations deeper than 4 feet.
Question 3: Which soil type is classified as the most stable under OSHA's soil classification system?
- Type C
- Type B
- Type A (Correct answer)
- Unclassified fill
Correct answer: Type A
Type A soil is the most stable, exhibiting high cohesiveness and requiring the least-aggressive protective system.
Question 4: A trench is 6 feet deep and 3 feet wide. Workers must not be in the trench unless:
- A competent person is on the site
- Adequate cave-in protection is in place (Correct answer)
- A supervisor approves the entry verbally
- The trench is less than 100 feet long
Correct answer: Adequate cave-in protection is in place
OSHA requires that cave-in protection (sloping, shoring, or trench box) be installed before workers enter any trench 5 feet or deeper.
Question 5: What minimum distance must spoil piles be kept from the edge of an excavation?
- 1 foot
- 2 feet (Correct answer)
- 3 feet
- 5 feet
Correct answer: 2 feet
OSHA requires excavated material (spoil) to be kept at least 2 feet from the edge to prevent it from falling back into the excavation.
Question 6: Which condition would cause a competent person to classify soil as Type C instead of Type B?
- Soil is dry and granular
- Cracks are visible running parallel to the trench wall
- Soil was previously disturbed by construction
- Water is seeping into the excavation (Correct answer)
Correct answer: Water is seeping into the excavation
Water seeping into an excavation indicates unstable conditions consistent with Type C, the least stable soil classification.
Question 7: Before beginning excavation work, what underground utility notification requirement must be met in most US states?
- Post a written notice at the job-site entrance
- Contact 811 (Call Before You Dig) at least 2–3 business days in advance (Correct answer)
- Submit a permit to the local municipality 30 days ahead
- Notify only the electrical utility provider
Correct answer: Contact 811 (Call Before You Dig) at least 2–3 business days in advance
Federal and state laws require contractors to notify the 811 one-call system before digging so utilities can be located and marked.
STSC Excavation and Trenching Safety 4
When must a competent person inspect an excavation?