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Excavation and Trenching Safety Flashcards

7 cards from real STSC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Excavation and Trenching Safety flashcards as text

  1. What is the primary purpose of a trench shield (trench box)?

    Answer: To protect workers from cave-ins by containing soil movement

    A trench box (shield) is designed to protect workers inside it from cave-ins, though it does not prevent the surrounding soil from collapsing.

  2. Sloping as a cave-in protection method for Type C soil requires a maximum slope angle of:

    Answer: 34° from horizontal (1½:1)

    Type C soil requires the most gradual slope of 1½H:1V (approximately 34°) because it is the least stable classification.

  3. When using a hydraulic shoring system, workers should:

    Answer: Install shores from outside or from the top before worker entry

    Hydraulic shores must be installed from the top down so workers are never exposed to an unprotected trench face during installation.

  4. Which hazard is specifically associated with excavations near roadways or heavy equipment operation?

    Answer: Surcharge loading from vibration causing soil instability

    Vibration from traffic or equipment creates dynamic surcharge loads that can destabilize trench walls, increasing cave-in risk.

  5. An excavation is considered a permit-required confined space when it:

    Answer: Has limited means of entry or exit AND contains or has the potential to contain a serious hazard

    An excavation becomes a permit-required confined space when it is large enough to enter AND contains or may contain a hazardous atmosphere, engulfment hazard, or other serious safety risk.

  6. What action should a supervisor take if workers must enter an excavation where atmospheric testing shows oxygen content of 18%?

    Answer: Prohibit entry until ventilation raises oxygen to at least 19.5%

    OSHA defines an oxygen-deficient atmosphere as below 19.5%; workers must not enter until ventilation or other means restore safe oxygen levels.

  7. Which document must be completed before excavation work begins in areas with suspected hazardous contamination?

    Answer: A site-specific health and safety plan (HASP)

    OSHA 29 CFR 1910.120 requires a written Health and Safety Plan (HASP) before work at hazardous waste sites or areas with known contamination.