NEBOSH CC Excavation & Ground Work Hazards 1 — Questions and Answers
Question 1: What is the primary hazard that must be controlled when carrying out excavation work on a construction site?
- Collapse of the excavation sides (Correct answer)
- Excessive noise from plant
- Dust generation
- Surface water drainage
Correct answer: Collapse of the excavation sides
The collapse of excavation sides is the primary and most dangerous hazard associated with excavation work. It can bury workers instantly and the sudden nature of collapse means there is often no time to escape.
Question 2: Before commencing any excavation work, which essential check must be carried out?
- Survey for underground services (Correct answer)
- Assess the colour of the soil
- Check the weather forecast
- Measure the noise levels
Correct answer: Survey for underground services
Before any excavation begins, a survey for underground services (gas, electricity, water, telecommunications, sewers) must be carried out. Striking an underground service can cause death or serious injury.
Question 3: What is the recommended distance from the edge of an excavation that heavy plant and spoil should be kept?
- At least 1 metre from the edge (Correct answer)
- At least 0.5 metres from the edge
- At least 2 metres from the edge
- At least 3 metres from the edge
Correct answer: At least 1 metre from the edge
Heavy plant and excavated spoil should be kept at least 1 metre from the edge of the excavation. Placing these too close can overload the ground and cause the sides to collapse, endangering workers below.
Question 4: Which type of support system uses horizontal boards (poling boards) held in place by adjustable struts?
- Timbering (traditional shoring) (Correct answer)
- Sheet piling
- Hydraulic shoring
- Trench boxes
Correct answer: Timbering (traditional shoring)
Traditional timber shoring (timbering) uses vertical poling boards held in position by horizontal walings and adjustable struts to prevent the sides of an excavation from collapsing.
Question 5: What must be provided at all excavations to allow workers to exit safely in the event of a collapse or emergency?
- Safe means of access and egress such as a ladder (Correct answer)
- A warning siren
- An emergency first aid kit within the excavation
- A CCTV system
Correct answer: Safe means of access and egress such as a ladder
Safe means of access and egress, such as a properly secured ladder, must be provided at all excavations. Workers must be able to exit quickly, especially in an emergency.
Question 6: At what depth does an excavation typically require a formal support system to prevent collapse?
- When the sides cannot be safely battered back, typically from 1.2 metres (Correct answer)
- Always at depths exceeding 3 metres
- Only at depths exceeding 5 metres
- At any depth in sandy soil
Correct answer: When the sides cannot be safely battered back, typically from 1.2 metres
While there is no absolute depth rule, excavations where the sides cannot be safely battered back — commonly from 1.2 metres — require a formal support system. Sandy or loose soils may require support at shallower depths.
NEBOSH CC Excavation & Ground Work Hazards 1
What is the primary hazard that must be controlled when carrying out excavation work on a construction site?