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ASP Construction Exam: Excavations and confined spaces

Locating utilities, shoring, spoil and vehicle setbacks, ladders and watchers in trenches, and the air-testing, ventilation and entry rules for confined spaces.

  • 14 questions
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Excavations and confined spaces · Question 1Score 0/0

A truck wants to park 2 m from the edge of a trench with normal shoring. What does the Code say?

Study reference: Québec Construction Safety Code (CSTC), OHS Act (LSST) and ASP Construction (Oct 2026), Ch. 12 Excavations and confined spaces — CSTC ss. 3.15, 3.21

All 14 questions in this test

Every question and its answer choices. The correct answers and explanations appear when you take the test above.

  1. A truck wants to park 2 m from the edge of a trench with normal shoring. What does the Code say?

    1. It is banned within 3 m unless reinforced shoring is provided for it
    2. It is allowed if it parks for under 30 minutes with the engine turned off
    3. It is allowed if the truck is empty
    4. It is allowed if the driver stays in the cab

  2. As a rule, how must the walls of a trench that workers enter be protected?

    1. By having an experienced worker stand at the bottom of the trench
    2. By solid shoring that follows an engineer's plans and specifications
    3. By a plastic tarp stretched over the walls to hold back soil and rain
    4. By watering often to keep the soil damp and packed

  3. A water main crosses the planned trench. Under what conditions may it stay in place during digging?

    1. If the pipe is metal rather than plastic, since it is stronger
    2. If the city is told by phone after the digging is done
    3. If the excavator operator promises to dig slowly and carefully all around the pipe
    4. If the utility approved the method, with a safe work method and temporary supports

  4. How often must air readings be taken in a confined space, without a continuous monitor with alarm?

    1. Once, before the first entry
    2. Every 2 hours, by a trained person
    3. Once a day, at the start of the shift
    4. Every 8 hours, by the inspector

  5. May a 17-year-old apprentice work at the bottom of a trench?

    1. Yes, if the trench is under 3 m
    2. Yes, if a journeyman is with them
    3. Yes, if they passed the 30-hour course
    4. No, this work is banned for anyone under 18

  6. Which of these cases exempts a trench from shoring?

    1. The workers who go down all wear a hard hat and a harness clipped to an anchor
    2. The trench will be open less than 24 hours and the soil looks dry
    3. The trench is under 2 m wide, whatever its depth
    4. The walls are stable and slope at less than 45° starting less than 1.2 m from the bottom

  7. A reading shows 18% oxygen in a tank. May a worker with a respirator enter for normal work?

    1. Yes, since he is wearing a compliant respirator that meets current standards
    2. No, entry is banned below 19.5% oxygen, even with a respirator
    3. Yes, if he stays inside for less than fifteen minutes
    4. Yes, if a co-worker watches him from the tank opening

  8. When workers are in a trench, who or what must be at the surface?

    1. A running excavator, ready to dig an emergency exit
    2. An experienced person watching for cracks and cave-ins
    3. A red flag at each end of the trench
    4. A sign showing the general contractor's name and the city permit number

  9. What is the minimum distance from the top of the walls for placing spoil and materials?

    1. 0.3 m
    2. 6 m
    3. 3 m
    4. 1.2 m

  10. Which of these is an example of a confined space under the Code?

    1. A tank or access shaft not designed to be occupied by people
    2. A closed stairwell in a building under construction
    3. A site office on the ground floor of a building
    4. A heated site trailer with a door and windows

  11. What concentration of flammable gas or vapour bars entry into a confined space?

    1. More than 100% of the lower explosive limit
    2. More than 5% of the lower explosive limit
    3. More than 50% of the upper explosive limit
    4. More than 25% of the lower explosive limit

  12. Before starting to dig, what must the employer check?

    1. Whether there are underground utilities and their exact location
    2. The colour of the soil, to see if it contains clay
    3. The weather forecast for the week after the planned end of the work
    4. How many shovels are in the site trailer

  13. How far must shoring extend above the excavation?

    1. 1 m
    2. It must be flush with the ground
    3. 50 mm
    4. 300 mm

  14. A trench is 40 m long. How many ladders are needed at minimum under the 15 m rule?

    1. 1 ladder
    2. 4 ladders
    3. 2 ladders
    4. 3 ladders

Excavations and confined spaces: key rules to remember

Our summary of what the official handbook says on this topic, in our own words. Read it before or after the practice questions above, then check the original chapter. Read the official chapter ↗

Before digging

  • Before digging, the employer checks for underground utilities and locates them exactly on the ground.
  • A utility line may stay in place or be moved only if the service concerned approved the method, with a method that prevents damage and temporary supports.
  • If digging threatens a neighbouring structure, underpinning or shoring is done.

Shoring

  • The walls of an excavation or trench are shored to an engineer's plans.
  • Exceptions: sound rock (which can only be dug with explosives) or no worker goes down; stable walls sloped at less than 45° from less than 1.2 m above the bottom; or an engineer certifies in writing that shoring is not needed.
  • Shoring extends 300 mm above the excavation and is installed as the work progresses.
  • Banned: placing materials within 1.2 m of the top of the walls; driving or parking vehicles within 3 m (without reinforced shoring).
  • Shores are removed from the bottom up, by or under an experienced person, where workers no longer have access.

Access, watching and age

  • A ladder every 15 m of trench (or part of 15 m), moving with the work, resting on the bottom and rising at least 1 m above ground.
  • When workers are in a trench, an experienced person watches from the surface for cracks and cave-ins.
  • Barriers at least 0.7 m high or a warning line are installed at the top of any excavation deeper than 3 m or otherwise dangerous.
  • The excavation is kept reasonably dry.
  • All work in excavations and trenches is banned for workers under 18.

Confined space: definition and preparation

  • The Code defines a confined space as a space not designed to be occupied by a person, such as a tank, silo, vat, caisson, foundation pile, chimney or access shaft.
  • Before work, the principal contractor and the employer identify in writing the tools, equipment, pipes and lines, risks, possible contaminants and rescue and emergency means.

Air, ventilation and entry

  • No worker, even with a respirator, enters if oxygen is below 19.5% or above 23%.
  • Nor if a flammable gas or vapour exceeds 25% of the lower explosive limit, or if a contaminant exceeds its exposure limit.
  • Readings are taken every 2 hours, at the riskiest spots, by a trained person, and recorded in a register (unless continuous-reading instruments with alarms are used).
  • The employer installs adequate ventilation and keeps out workers not assigned to the job.
  • In an emergency, only a worker with special training who is informed of the risk may enter despite the conditions.

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