CSCS Excavation Safety 1 — Questions and Answers
Question 1: What is the primary purpose of installing trench boxes during excavation work on a construction site?
- To store tools and materials underground
- To prevent the collapse of trench sides and protect operatives working within the excavation (Correct answer)
- To channel rainwater away from the trench
- To mark the boundaries of the excavation for surveying
Correct answer: To prevent the collapse of trench sides and protect operatives working within the excavation
Trench boxes (also called trench shields) are structural supports placed inside excavations to prevent the sides from collapsing onto workers. Under the CDM Regulations 2015 and the Work at Height Regulations 2005 (which also cover work below ground), adequate support must be provided to prevent collapse in any excavation where there is a risk.
Question 2: What must be done before any excavation work begins on a construction site under CDM Regulations 2015?
- Nothing — excavation can begin as soon as the digger arrives
- A permit to dig must be obtained, underground services located using CAT and Genny, and a risk assessment completed (Correct answer)
- Only a verbal agreement from the site manager is needed
- Excavation can proceed once the weather forecast has been checked
Correct answer: A permit to dig must be obtained, underground services located using CAT and Genny, and a risk assessment completed
CDM Regulations 2015 require that before excavation, all underground services must be identified using utility plans, CAT (Cable Avoidance Tool) and Genny scans, and trial holes where necessary. A permit to dig must be issued, a site-specific risk assessment completed, and a method statement prepared covering support systems, access/egress, and emergency procedures.
Question 3: At what depth must an excavation generally be provided with edge protection barriers under UK health and safety law?
- 5 metres
- Any depth where there is a risk of persons or materials falling in (Correct answer)
- 3 metres
- Edge protection is only required on roads
Correct answer: Any depth where there is a risk of persons or materials falling in
There is no specific depth threshold for edge protection. Under the CDM Regulations 2015 and the Work at Height Regulations 2005, edge protection such as guardrails, barriers, or stop blocks must be provided at any excavation where there is a risk of persons falling in or materials falling onto workers below, regardless of depth.
Question 4: How often must excavations be inspected under the CDM Regulations 2015?
- Monthly
- At the start of each shift, after any event likely to have affected stability, and after any accidental fall of material (Correct answer)
- Only when the client visits the site
- Weekly inspections are sufficient
Correct answer: At the start of each shift, after any event likely to have affected stability, and after any accidental fall of material
Regulation 22 of the CDM Regulations 2015 requires excavations to be inspected by a competent person at the start of every shift, after any event likely to have affected the strength or stability of the excavation (such as heavy rain or vibration), and after any accidental fall of rock, earth, or other material. Written reports must be kept.
Question 5: What is the purpose of 'battering back' the sides of an excavation?
- To create storage shelves in the trench walls
- To slope the sides to a safe angle to prevent collapse, reducing the risk without using shoring (Correct answer)
- To compact the soil for stronger foundations
- To create steps for access and egress
Correct answer: To slope the sides to a safe angle to prevent collapse, reducing the risk without using shoring
Battering back involves cutting the excavation sides at an angle (typically 45 degrees or less depending on soil type) rather than leaving them vertical. This reduces the risk of collapse by using the natural angle of repose of the soil. It is an alternative to shoring or trench boxes where space permits, as recognised in HSE guidance.
Question 6: What type of access and egress must be provided for excavations deeper than 1.2 metres?
- Operatives can climb the shoring framework
- A secured ladder or other safe means of access/egress must be provided within the excavation, positioned so no operative has to travel more than 25 metres to reach it (Correct answer)
- Ropes are sufficient for access and egress
- No specific access provisions are required if the excavation is less than 2 metres deep
Correct answer: A secured ladder or other safe means of access/egress must be provided within the excavation, positioned so no operative has to travel more than 25 metres to reach it
HSE guidance requires that for excavations deeper than 1.2 metres, suitable and sufficient means of access and egress must be provided, typically secured ladders extending at least 1 metre above the excavation edge. Ladders should be positioned so that no worker has to travel more than 25 metres along the trench to reach one. Under CDM 2015, these provisions must be planned.
CSCS Excavation Safety 1
What is the primary purpose of installing trench boxes during excavation work on a construction site?