Excavation is one of the most hazardous activities in construction and civil works. Service strikes involving buried gas, electricity, water, and telecoms cables kill and seriously injure workers every year. Trench collapses can be fatal with no warning. Flooding can trap workers in seconds.
A well-written excavation permit to work is not a bureaucratic formality — it is the primary document that forces every person involved to confirm, before the first spade goes in the ground, that the risks have been identified, located, and controlled.
This guide covers the legal framework, the key hazards, what an excavation permit must include, and how to avoid the mistakes that lead to incidents.
The legal framework for excavation permits
Several pieces of UK legislation are directly relevant to excavation and ground works:
| Legislation | Relevance to excavation |
|---|---|
| CDM Regulations 2015 | Principal contractors must ensure suitable arrangements are in place for managing health and safety during excavation, including pre-start planning and competent supervision |
| HSG47 — Avoiding Danger from Underground Services | The HSE's core guidance on service strike prevention — sets out the standard for survey, detection, and safe digging practice |
| HS(G)185 — Health and Safety in Excavations | HSE guidance on trench support, competent person inspections, and safe access and egress |
| BS 6031:2009 — Earthworks | Code of practice for earthworks including excavation stability and shoring |
| Health and Safety at Work Act 1974 | Overarching duty to ensure the health and safety of all persons affected by the work |
CDM 2015 and the permit to work: Under CDM 2015, a permit to work is not always explicitly named, but the requirement to implement and maintain suitable safe systems of work for high-risk activities — including excavation — is a legal obligation for principal contractors and contractors alike. A permit is the recognised mechanism for satisfying this obligation.
The primary hazards in excavation
1. Service strikes
Striking a buried gas main, electricity cable, water main, or telecoms duct is one of the most common serious accidents on UK construction sites. Gas strikes cause fires and explosions. Electricity cable strikes cause electrocution. Water main strikes cause flooding and loss of structural support to the surrounding ground.
HSG47 sets out a clear hierarchy: survey for services before work, use a cable avoidance tool (CAT) and signal generator (Genny) to locate buried services, mark the routes on the ground surface, and hand-dig (or vacuum excavate) within 500 mm of any marked service. This hierarchy must be followed and confirmed on the permit before any intrusive work begins.
⚠ Utility service drawings are not sufficient on their own. Drawings may be out of date, inaccurate, or incomplete. HSG47 requires physical detection using a CAT/Genny even where drawings are available. A permit that relies only on drawings — without a physical sweep — is not compliant.
2. Trench collapse
Ground can collapse without warning, and a collapse in a trench only 1.2 metres deep can produce enough force to be fatal. The risk is highest in loose, recently disturbed, waterlogged, or frozen-thawed ground, but no ground type can be assumed safe without assessment.
HS(G)185 sets out the options for trench support: trench boxes (drag boxes), shoring, battering (cutting back the sides to a safe angle), or a combination. The choice depends on ground conditions, depth, duration, and the proximity of other loads. A competent person must assess and confirm the support is adequate before any person enters the trench.
3. Flooding and groundwater
Groundwater ingress and surface water run-off can flood a trench rapidly. The permit must record whether a risk of flooding has been assessed and whether pumping equipment is on standby. Work must be suspended if flooding is observed and the trench must not be re-entered until pumped out and inspected.
4. Contaminated ground
Ground contamination — from hazardous gases (including hydrogen sulphide and methane), asbestos, heavy metals, or chemical waste — presents risks through inhalation, skin contact, or ignition. Where contamination is suspected from a site history or Phase 1/Phase 2 survey, a COSHH assessment must accompany the permit and appropriate RPE must be specified.
5. Falls and plant overrun
Personnel falling into open excavations, and plant or vehicles toppling into them, are regular causes of serious injury. Edge protection — barriers set at least 1 metre from the excavation edge — and spoil kept back at least 1 metre from the edge are minimum requirements. Barriers must prevent both people and vehicles from approaching the edge uncontrolled.
What an excavation permit must include
Service identification and detection
The permit must confirm that service drawings have been obtained and reviewed (recording the drawing reference and revision number), that a physical CAT/Genny sweep has been completed, and that all detected services have been marked on the ground surface before any intrusive work begins.
Hand-dig zone declaration
The permit must explicitly state that the area within 500 mm of any marked service will be hand-dug or vacuum-excavated only. This is a specific, named commitment — not a general reference to "following HSG47."
Competent person inspection
HS(G)185 requires a competent person to inspect the excavation at the start of each working day, after any event that may have affected the ground stability (such as heavy rain), and after any rock blasting nearby. The permit must name the competent person and record that the inspection has been carried out before workers enter.
Standard Excavation Pre-Authorisation Checks
- Service drawings reviewed — current revision confirmed and referenced
- CAT & Genny sweep complete — all services marked on ground surface
- Hand-dig zone clearly identified within 500 mm of all marked services
- Competent person inspection complete and recorded in writing
- Trench support / battered sides confirmed adequate before any entry
- Access ladder(s) in position, secured, and extending 1 m above ground level
Trench support confirmation
The type of support installed (or the method used if battering) must be recorded, and the competent person must confirm it is adequate for the ground conditions and the anticipated loads before any worker enters.
Access and egress
HS(G)185 requires a safe means of access and egress from every excavation in which persons work. In practice this means a ladder extending at least 1 metre above the ground surface, secured against displacement, and positioned no more than 9 metres from any worker in the trench. This must be confirmed on the permit.
Groundwater and flooding controls
The permit must confirm whether pumping equipment is on standby and state the trigger condition at which work will be suspended (typically any visible ingress of water at a rate that cannot immediately be controlled).
Emergency procedure
Excavation emergencies require specific responses. A service strike (particularly gas) requires immediate evacuation and isolation — not improvised attempts to plug the leak. A collapse requires calling 999 immediately and not entering to attempt a rescue. Both scenarios must be covered explicitly.
The 500 mm hand-dig rule — what it means in practice
HSG47's requirement to hand-dig within 500 mm of a detected service is widely known. In practice, it is frequently violated — either because the hand-dig zone is never clearly marked on the permit, or because excavator operators are given the instruction verbally rather than as a documented, agreed condition of the permit.
On a compliant permit, the 500 mm hand-dig zone should be:
- Identified in the permit conditions before work starts
- Marked on a sketch plan or described by reference to a specific service marking on the ground
- Signed off by the permit holder (the person in charge of the work party) as understood and accepted
- Verified by the permit issuer — not assumed
Common mistakes to avoid
- Relying on drawings alone. Service drawings may be decades old or simply wrong. Physical detection is mandatory, not optional.
- No competent person named. The permit must name a specific individual as competent to inspect the excavation — not "the site supervisor" in generic terms.
- Issuing a single permit for prolonged excavation work. Each day of excavation should begin with a fresh inspection and confirmation. A permit issued on Monday does not cover Tuesday without re-inspection and re-confirmation.
- Overlooking contamination. If site history shows industrial use, previous burial of waste, or proximity to fuel storage, a contamination assessment must be part of the permit process — not an afterthought.
- No edge protection plan. "Barriers in place" is not enough. The permit should record the type of edge protection, its distance from the excavation edge, and who installed it.
Download a free excavation permit template
We've produced a free Excavation & Ground Works Permit to Work template in Word (.docx) format, available in both a pre-filled version (standard hazards and controls already populated) and a blank version.
Excavation & Ground Works Permit to Work — Free Template
Covers CDM 2015, HSG47, and HS(G)185 requirements. Pre-filled with standard hazards, controls, and pre-authorisation checks. Editable Word (.docx) format.
For all permit types, visit the templates page.
Beyond paper: managing excavation permits digitally
Excavation sites change daily. The ground conditions on Tuesday may be very different from Monday after overnight rain. A paper permit issued at the start of a job and left in a site cabin does not capture daily re-inspections, changed conditions, or on-the-ground decisions made during the work.
PermitDesk generates excavation permits and all other PTW types digitally — with daily re-confirmation workflows, digital sign-off by the competent person, and a full timestamped audit trail. When the HSE or an insurer asks for records, you can produce the complete inspection history in seconds.
Issue your first excavation permit in under 2 minutes
PermitDesk handles the drafting. You stay in control of authorisation and daily re-confirmation.
Start your free 14-day trialRelated reading
→ What is a permit to work? A plain-English guide
→ Lifting Operations Permits: LOLER 1998 guide