CHST Excavation and Trenching Safety 5 — Questions and Answers
Question 1: What action must be taken before an excavation is entered each day or after a rainstorm?
- Complete a new permit application
- Have a competent person inspect for hazardous conditions (Correct answer)
- Test air quality for all four atmospheric hazards
- Erect additional barrier fencing around the perimeter
Correct answer: Have a competent person inspect for hazardous conditions
OSHA 1926.651(k) requires a competent person to inspect excavations daily and after any event that could increase hazard potential, such as rain.
Question 2: Which shoring system uses vertical members (uprights) driven or placed against trench walls, held by walers and cross braces?
- Slide rail system
- Timber shoring (Correct answer)
- Hydraulic shoring
- Trench box (shield)
Correct answer: Timber shoring
Timber shoring uses vertical uprights, horizontal walers, and cross braces to support trench walls against collapse.
Question 3: Under what circumstance may workers enter an unprotected excavation less than 5 feet deep?
- When the soil is visually assessed as stable by the crew foreman
- Never — all excavations require protection regardless of depth
- Only when a competent person determines there is no cave-in hazard (Correct answer)
- When the work will be completed in under 30 minutes
Correct answer: Only when a competent person determines there is no cave-in hazard
OSHA 1926.652(a) allows excavations under 5 feet to go unprotected only if a competent person examines the ground and finds no cave-in potential.
Question 4: Fissured soil discovered during excavation typically indicates what type of soil classification?
- Type A
- Type B
- Type C
- Type B or C depending on other factors (Correct answer)
Correct answer: Type B or C depending on other factors
Fissured soil is excluded from Type A classification and may be Type B or Type C depending on its other properties and conditions.
Question 5: Which utility locating service must be contacted before excavation begins in the United States?
- State labor department
- 811 (Call Before You Dig) (Correct answer)
- Local fire authority
- OSHA area office
Correct answer: 811 (Call Before You Dig)
Federal law requires contractors to contact 811 (the national call-before-you-dig number) to have underground utilities marked before any excavation.
Question 6: A trench box (shield) used in an excavation must be:
- Approved by OSHA before each use
- Designed or approved by a registered professional engineer (Correct answer)
- Constructed entirely of timber materials
- Installed only in Type C soils
Correct answer: Designed or approved by a registered professional engineer
OSHA 1926.652(c)(3) requires trench shields to be designed by a registered PE or to meet OSHA tabulated data to ensure they can withstand expected loads.
Question 7: What is the maximum spacing allowed between cross braces in a timber shoring system for a trench in Type C soil, per OSHA Appendix C tables?
- 4 feet
- 6 feet
- 8 feet
- Tables vary by depth and soil type — no single maximum applies universally (Correct answer)
Correct answer: Tables vary by depth and soil type — no single maximum applies universally
OSHA Appendix C timber shoring tables specify brace spacing based on the combination of trench depth and soil type, so a universal single maximum does not apply.
CHST Excavation and Trenching Safety 5
What action must be taken before an excavation is entered each day or after a rainstorm?