CHST CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers 4 — Questions and Answers
Question 1: Which atmospheric condition in an excavation requires air monitoring BEFORE workers enter?
- Excavation is in urban soil only
- Excavation is more than 4 feet deep AND oxygen-deficient or hazardous atmospheres may be present (Correct answer)
- Excavation depth exceeds 10 feet
- Any excavation with standing water
Correct answer: Excavation is more than 4 feet deep AND oxygen-deficient or hazardous atmospheres may be present
OSHA 29 CFR 1926.651(g) requires testing for hazardous atmospheres in excavations deeper than 4 feet where such conditions may reasonably be expected.
Question 2: A utility strike occurs during excavation. Which action should be taken FIRST?
- Continue excavating carefully by hand
- Call 811 (one-call center) immediately
- Stop work, remove workers, and notify the utility owner (Correct answer)
- Install additional shoring around the strike location
Correct answer: Stop work, remove workers, and notify the utility owner
Worker safety is paramount — immediately stop work, evacuate all personnel, and then notify the utility company to assess and control the hazard.
Question 3: Under OSHA standards, how often must a competent person inspect an excavation?
- Once per week
- Before each work shift and after any event that could affect its integrity (Correct answer)
- Monthly
- Only when soil conditions change
Correct answer: Before each work shift and after any event that could affect its integrity
OSHA 29 CFR 1926.651(k) requires inspection by a competent person before each shift and after any rain, freeze/thaw, or other potentially hazardous event.
Question 4: What is the required minimum oxygen concentration level for workers to safely enter a trench or excavation?
- 16.0%
- 17.5%
- 19.5% (Correct answer)
- 21.0%
Correct answer: 19.5%
OSHA defines an oxygen-deficient atmosphere as below 19.5% oxygen by volume; workers may not enter without respiratory protection below this level.
Question 5: When is a registered professional engineer (PE) required to design a protective system for an excavation?
- Any excavation deeper than 4 feet
- Tabulated data or manufacturer data is not available for the site conditions (Correct answer)
- When more than 5 workers are in the trench
- Any trench in Type B soil
Correct answer: Tabulated data or manufacturer data is not available for the site conditions
A PE-designed system is required when site conditions fall outside the scope of OSHA Appendix tables or manufacturer-supplied tabulated data under 29 CFR 1926.652(b)(4).
Question 6: What is the OSHA requirement for means of egress from a trench that is 4 feet or more in depth?
- A rope must be provided
- A ladder, stairway, or ramp must be present within 25 feet of lateral travel (Correct answer)
- A ladder must be at each end of the trench
- Workers may use the trench wall for climbing if footholds are cut
Correct answer: A ladder, stairway, or ramp must be present within 25 feet of lateral travel
OSHA 29 CFR 1926.651(c)(2) requires a means of egress (ladder, ramp, or stairway) within 25 lateral feet of any worker in a trench 4 or more feet deep.
Question 7: Which soil test uses a penetrometer pushed into freshly cut soil to estimate unconfined compressive strength?
- Ribbon test
- Plasticity test
- Manual penetrometer test (Correct answer)
- Sieve analysis
Correct answer: Manual penetrometer test
A pocket penetrometer measures the resistance of soil in tons per square foot (tsf) to help classify soil type for excavation safety decisions.
CHST CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers 4
Which atmospheric condition in an excavation requires air monitoring BEFORE workers enter?