CHST CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers 3 — Questions and Answers
Question 1: Under OSHA 29 CFR 1926.652, what is the maximum allowable slope for Type C soil when using the sloping method of protection?
- 1H:1V (45°)
- 1.5H:1V (34°) (Correct answer)
- 0.75H:1V (53°)
- 2H:1V (27°)
Correct answer: 1.5H:1V (34°)
Type C soil, the least stable classification, requires a slope of 1.5H:1V (approximately 34 degrees from horizontal).
Question 2: A competent person inspects an excavation after a rainstorm. What is the MOST important action if the walls show signs of tension cracking?
- Continue work with additional PPE
- Remove all workers and reassess protective systems (Correct answer)
- Add timber shoring immediately
- Increase dewatering pump speed
Correct answer: Remove all workers and reassess protective systems
Tension cracks are a warning sign of imminent collapse; all workers must be removed until a competent person determines the excavation is safe.
Question 3: What is the minimum distance that excavated spoil (dirt) must be kept from the edge of a trench?
- 1 foot
- 2 feet (Correct answer)
- 3 feet
- 4 feet
Correct answer: 2 feet
OSHA 29 CFR 1926.651(j)(2) requires excavated material to be kept at least 2 feet from the edge of a trench to prevent cave-in surcharge loading.
Question 4: Which condition would cause a competent person to reclassify soil from Type B to Type C?
- Soil has an unconfined compressive strength of 0.6 tsf
- Previously disturbed soil is present in the excavation
- Water seeping into the excavation from the sides (Correct answer)
- Soil is dry and granular
Correct answer: Water seeping into the excavation from the sides
Fissured soil or soil from which water is seeping must be classified as Type C under OSHA Appendix B to Subpart P.
Question 5: When using a hydraulic shoring system, what step must occur BEFORE workers enter the trench?
- Backfill the trench partially
- Install and extend all hydraulic cylinders to rated capacity (Correct answer)
- Remove all surface water
- Install a trench box over the shoring
Correct answer: Install and extend all hydraulic cylinders to rated capacity
Hydraulic cylinders must be installed and pressurized to their rated capacity before workers enter to ensure the system provides adequate lateral support.
Question 6: A trench is 7 feet deep in Type A soil with no other hazards. Which protective system option is acceptable under OSHA Appendix B?
- No protection required if workers are experienced
- Sloping at 0.75H:1V (Correct answer)
- Vertical walls with timber shoring only
- Sloping at 1.5H:1V
Correct answer: Sloping at 0.75H:1V
Type A soil allows a maximum allowable slope of 0.75H:1V (approximately 53 degrees), making it the least flat slope permissible by OSHA.
Question 7: What is the primary purpose of a trench box (shield) as a protective system?
- To prevent groundwater infiltration
- To protect workers from cave-ins by shielding them, not preventing soil movement (Correct answer)
- To classify the soil type before excavation
- To support adjacent structures above the trench
Correct answer: To protect workers from cave-ins by shielding them, not preventing soil movement
A trench shield (box) protects workers inside it from a cave-in but does not prevent soil movement — it provides a protected zone for workers to occupy.
CHST CHST - Construction Health and Safety Technician Excavation and Trenching Safety Questions and Answers 3
Under OSHA 29 CFR 1926.652, what is the maximum allowable slope for Type C soil when using the sloping method of protection?