Key points to cover
- No one should enter an excavation until a competent person has checked it is safe — no ground can be relied on to stand unsupported, whatever the depth
- Excavations must be inspected at the start of every shift and after any event that may affect stability (rain, vibration, nearby loading)
- Support systems — trench sheets, hydraulic frames, battering — must be designed and installed by competent persons
- Underground services (gas, electricity, water, telecoms) must be located and marked before digging starts
- Steps must be taken to stop people, vehicles and materials falling in — such as barriers or edge protection, with signs to warn people
- Spoil, materials, and plant must be kept well back from the excavation edge to prevent collapse
Do's and don'ts
Do
- Use CAT and Genny scans and check utility plans before digging
- Dig trial holes by hand near known services
- Put substantial barriers or edge protection around the excavation wherever people, plant or materials could fall in
- Check the excavation at the start of every shift and after heavy rain
- Ensure a safe means of entry and exit (e.g. a secured ladder close to where people are working in the trench)
Don't
- Never enter an excavation that a competent person hasn't checked, however shallow it is
- Never undermine an excavation face — work from top to bottom
- Never stack materials or park vehicles close to the edge of an excavation
- Never work alone in a trench
- Never ignore water seeping into an excavation — it can rapidly destabilise the sides
Questions to check understanding
Q1: How often must excavations be inspected?
Show the answer
At the start of every shift, after any event that may affect stability (e.g. heavy rain, vibration from nearby work, adjacent vehicle loading), and before anyone enters after a period when the excavation has been unattended.
Q2: What is the approximate weight of one cubic metre of soil?
Show the answer
Over one tonne (typically 1.5 to 2 tonnes depending on soil type and moisture content). This is why a trench collapse can be instantly fatal — there is no time to escape and the weight makes self-rescue impossible.
Q3: What should you do before digging to avoid striking underground services?
Show the answer
Obtain up-to-date utility plans (from the asset owners), scan the area with a CAT and Genny, mark the positions of services on the ground, and hand dig trial holes near known or suspected services.
Q4: Why must spoil be kept back from the excavation edge?
Show the answer
Spoil placed too close to the edge adds weight to the ground above the excavation face, dramatically increasing the risk of collapse. It can also fall into the trench, striking anyone working below. Keep spoil at least 1 metre from the edge.
This is general guidance for UK construction sites. Check it against your own risk assessment, method statement and the site before you deliver it.