Construction compliance guide
Excavation Safety: HSG47, Trench Support and Inspections
TL;DR
Before you dig, locate underground services, plan the support and decide how people will get in and out. Check ground conditions, nearby structures, water and loads at the edge. Brief the team and inspect the excavation before work starts.
This guide covers Great Britain under CDM 2015. Northern Ireland has separate CDM 2016 arrangements; see HSENI's CDM 2016 guidance if that is where the work takes place.
Use the controls below as a starting point for planning your job. Ground conditions and temporary works are site-specific. A competent person must decide what support, battering, benching, access and inspection arrangements are suitable for the actual excavation. Do not use this guide as a substitute for that judgement.
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Before the dig: make the plan usable
Record the task, sequence and controls in the RAMS. Put the wider site arrangements in the construction phase plan (CPP). Note the excavation's location, length, width and intended depth, the ground information available, nearby structures, roads and boundaries, and who will control the work.
Consider what can change while the excavation is open:
- soil or made-up ground that may not behave as expected;
- groundwater, rain, frost, vibration or nearby water services;
- surcharge from spoil, materials, vehicles, plant or a neighbouring structure;
- people, children, traffic or members of the public approaching the edge; and
- the order in which support, work and backfilling will happen.
Choose the method before the machine arrives. If the design needs temporary works, specialist advice or a trench support system, make that requirement clear and identify who checks it. A generic method statement copied from another job is not enough if the ground, depth or surroundings differ.
Underground services: follow the HSG47 sequence
HSE guidance HSG47 describes three basic elements of safe excavation: plan the work; locate and identify buried services; and excavate safely. Use all three.
Start with current utility plans and information from the asset owners. Treat plans as evidence to investigate, not as a precise view of every service. Walk the area, look for signs of service routes and use suitable locating and identification equipment operated by a competent person. Mark the findings clearly and brief the people doing the dig.
Your RAMS or permit-to-dig record should show what information was checked, what was found, how services will be isolated or protected where possible, and what happens if the physical evidence does not match the plan. HSG47 does not create one universal hand-dig distance for every site. Follow the asset owner's requirements and the site's safe system of work, using locating equipment and controlled excavation as required.
Stop work if an unidentified service is found, the locating information is uncertain, or the planned method cannot be followed. Keep people clear, prevent further disturbance and obtain competent advice or the asset owner's emergency instructions. A strike can cause electric shock, fire, explosion, flooding or loss of essential services.
Trench support and collapse prevention
Never assume a shallow-looking trench is safe because it is short or has stood open for a while. The competent person should select the control method for the actual ground and work area. Options may include a suitable trench box or shoring system, battered or benched sides, a designed temporary works solution, or a change in sequence that avoids people entering the excavation.
Set out the exclusion zone and keep spoil, materials and plant far enough from the edge for the ground and loading conditions. There is no safe distance that can be copied into every job. Follow the support design, manufacturer's instructions and competent person's assessment. Do not undermine an adjacent wall, road or service.
Provide safe access and egress for the task, keep ladders or other access points secure, and do not climb on unsupported sides. Control water rather than allowing it to build up. If conditions alter, or support is damaged or moved, stop and reassess before anyone enters.
Controls while the excavation is open
Protect the edge where a person could fall. Use barriers, guardrails or another suitable arrangement, and prevent vehicles reversing or slewing into the exclusion zone. Keep the public out and cover or secure an excavation that is left unattended.
Brief the team on the permit or RAMS before work starts. The briefing should cover the service markings, support method, access route, plant limits, spoil position, PPE, communication, stop-work triggers and emergency contacts. Rebrief after a change in depth, method, weather, workforce or surrounding activity.
Inspections and emergencies
Name a competent person who understands the excavation and its precautions. Under CDM regulation 22, where supports or battering are provided, inspect the excavation, work equipment and materials that may affect safety at the start of the shift, after any event likely to affect strength or stability, and after any material unintentionally falls or is dislodged. No construction work should take place until the person who inspected it is satisfied that it is safe. Correct faults before work resumes.
Keep an inspection record. Under regulation 24, an inspector who is not satisfied must tell the person they inspected for before the shift ends. They must provide a report within 24 hours. Include that person's name and address, the location, time, findings, actions and inspector details. Keep it available at the site until construction finishes, then retain it for three months. HSE guidance says one written report can cover start-of-shift inspections in a seven-day period. Repeat the inspection after an event affecting stability or an accidental fall, and allow work only when the inspector is satisfied it is safe. HSE recommends reports after most inspections; complete any Regulation 24 report within the required 24 hours. Follow the regulation and HSE inspection guidance rather than relying on a generic tick-box.
Use the excavation inspection checklist to record the trigger, findings, actions and re-check.
If a collapse or service strike occurs, stop work, raise the alarm and keep people out of the danger area. Do not enter an unstable excavation to attempt a rescue. Call the emergency services and the relevant utility or asset owner, follow the site emergency plan, and only allow re-entry after a competent person has made the area safe.
What to put in your RAMS or CPP
For a small job, the record should answer these questions:
- What is being excavated, where, to what profile and in what sequence?
- What ground, water, structure, traffic and public risks were considered?
- What service plans, surveys, locating checks and markings were completed?
- Who selects and checks the support, access, edge and water controls?
- Where are spoil, materials and plant kept, and how is the exclusion zone enforced?
- Who can stop the work, inspect the excavation and authorise entry?
- What are the service-strike, collapse, flooding and first-aid arrangements?
The Site Book generates RAMS, construction phase plans and site inductions. Its generated RAMS include pre-filled site-specific hazards and control measures for you to review and adjust. Use the documents to record the actual ground, service information, support plan and work sequence. The software does not select temporary works or replace a competent person's assessment.
For related planning, see construction risk assessments, method statements and COSHH for builders.
Common questions
Is there one depth at which a trench must be supported?
No single number makes every excavation safe. Ground, loading, water, adjacent structures, access and the work method determine the control. Get competent temporary-works advice where needed.
Is a permit to dig always a legal requirement?
There is no universal permit form for every excavation. A permit-to-dig system is a useful site control where the risk and project arrangements call for it. It must support the HSG47 process and the actual RAMS, rather than become a tick-box exercise.
Can a machine operator decide the excavation is safe?
The operator’s observations matter, but the person responsible for the excavation and support must have suitable competence and authority. Stop and escalate if the conditions differ from the plan.
What a usable excavation plan does — and cannot do
Pros
- Records the ground, service, support, access and loading information considered before work starts.
- Names the competent people who select controls, inspect the excavation and authorise work.
- Gives the team clear stop-work triggers and emergency contacts.
Cons
- A written plan cannot select temporary works or prove that changing ground remains stable.
- Utility plans and locating equipment do not remove the need for controlled excavation.
- An inspection record does not make an unsafe excavation safe.
| Stage | Record | Stop or reassess when |
|---|---|---|
| Before digging | Ground, services, support, access, loads and sequence. | Information is missing or the method cannot be followed. |
| Start of shift | Competent person, time, condition, findings and actions. | The inspector is not satisfied it is safe. |
| After a change | Weather, vibration, water, support damage or material fall. | Strength or stability may have been affected. |
| Before restart | Fault corrected, re-inspection and authorisation. | The defect remains or conditions differ from the plan. |
“All practicable steps must be taken to prevent danger to any person, including, where necessary, the provision of supports or battering, to ensure that— (a) no excavation or part of an excavation collapses; (b) no material forming the walls or roof of, or adjacent to, any excavation is dislodged or falls; and (c) no person is buried or trapped in an excavation by material which is dislodged or falls.”
Need site-specific RAMS for the dig?
Draft the hazards, controls and work sequence from your actual job details. Then review them against the ground, services and support plan before work starts.
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Sources
- HSG47: Avoiding danger from underground services — HSE · Accessed 12 September 2026
- Excavations — HSE · Accessed 12 September 2026
- CDM 2015, Regulation 22 — legislation.gov.uk · Accessed 12 September 2026
- CDM 2015, Regulation 24 — legislation.gov.uk · Accessed 12 September 2026
- Health and safety in construction (HSG150) — HSE · Accessed 12 September 2026
- Managing health and safety in construction (L153) — HSE · Accessed 12 September 2026