Permits to Work · Mandatory · Construction
Permit to Work — Excavation and Permit to Dig
The Excavation and Permit to Dig authorises ground-breaking works and requires confirmation that underground service scans (CAT and Genny) have been completed, service drawings reviewed, and trial holes dug where necessary. It covers trench support, edge protection, safe access, and daily inspections by a competent person. The permit must be issued before any mechanical or hand excavation begins.
Last reviewed: 29 March 2026 — This guide reflects UK law as of this date. MHSWR 1999 remains current with no amendments enacted as of 29 March 2026. Next scheduled review: 29 March 2027.
| Cable and pipe strikes | One of the most common causes of serious injury and fatality during groundworks — contact with live electricity cables, high-pressure gas mains, and fibre-optic telecoms |
| HSG47 hierarchy | Obtain service drawings, CAT/Genny scan, trial holes by hand, 500mm hand-dig zone either side of any identified service |
| Service drawings | Must be obtained from all utility providers (gas, electricity, water, telecoms, drainage) before any excavation is planned |
| Excavation safety | CDM 2015 Reg 22 — prevent collapse, competent person inspection at the start of each shift, edge protection, safe access/egress |
| Emergency contacts | Contact details for all relevant utility providers must be recorded on the permit and available at the point of work for immediate use in the event of a strike |
1. The Permit to Dig: Managing Underground Service Risk
The permit to dig (also referred to as the excavation permit or permit to excavate) is a specific type of permit to work designed to control the risks associated with ground disturbance, principally the risk of striking underground services. Every year in the UK, excavation work results in cable strikes, gas main ruptures, and damage to water and telecoms infrastructure — incidents that cause fatal electrocutions, gas explosions, and significant disruption to essential services.
The legal basis for the permit to dig derives from the Management of Health and Safety at Work Regulations 1999, CDM 2015 Regulation 22 (excavations), and HSG47 (Avoiding danger from underground services). HSG47 sets out the protocol that must be followed before any ground disturbance takes place and is the standard against which compliance will be judged in any investigation following a service strike.
The permit to dig confirms that the HSG47 protocol has been completed in full: service drawings have been obtained and reviewed, a CAT/Genny survey has been carried out by a trained operative, trial holes have been dug by hand to confirm service positions, services have been marked on the ground, and safe digging practices have been briefed to all operatives. Without this confirmation, no excavation should proceed.
A CAT scan alone is not sufficient to confirm the absence of underground services
A Cable Avoidance Tool (CAT) detects electromagnetic signals from live cables and metallic pipes. It will not detect de-energised cables, plastic gas or water pipes without metallic tracer wire, fibre-optic telecoms ducts, or services that are buried deeper than the instrument’s effective range. Service drawings must always be consulted alongside the CAT survey, and trial holes dug by hand to physically confirm the position and depth of any service identified on drawings or by the scan. Relying on a CAT scan alone has been the precursor to numerous fatal cable strikes.
2. Permit to Dig Required Content
The permit to dig must contain the following fields. Each must be completed and verified before excavation is authorised. The permit is location-specific — a separate permit is required for each distinct excavation area.
| Field | Required content |
|---|---|
| Excavation location and extent | Precise location of the proposed excavation referenced to site grid, drawing number, or physical landmarks; planned dimensions (length, width, depth); purpose of the excavation |
| Service drawings obtained | Confirmation that service record drawings have been obtained from all relevant utility providers (gas, electricity, water, telecoms, drainage, highway authority); drawing reference numbers recorded; date of drawings noted (stale drawings must be re-requested) |
| CAT/Genny survey completed | Name and CSCS/CSES certification number of the operative who carried out the CAT/Genny survey; date and time of the survey; instrument serial number and calibration date; results summarised (services identified, approximate positions and depths) |
| Trial holes completed | Confirmation that trial holes have been hand-dug to confirm the position and depth of all services identified by drawings and/or the CAT/Genny survey; results recorded (actual depth and position versus predicted) |
| Services marked on ground | Confirmation that all identified services have been marked on the ground surface using paint, pegs, or markers; colour coding applied in accordance with service type (red for electricity, yellow for gas, blue for water, green for telecoms) |
| Hand-dig zone defined | Confirmation that a 500mm hand-dig zone has been established either side of every identified service; no mechanical excavation permitted within this zone; hand-dig tools specified (insulated tools for work near electrical cables) |
| Safe digging method | Method of excavation specified: hand dig, machine dig, or combination; confirmation that machine bucket teeth will not be used within the hand-dig zone; vacuum excavation specified where appropriate for exposing services |
| Trench support or battering | Method of preventing trench collapse specified based on ground conditions: battering angle, trench box, sheet piling, or hydraulic props; competent person named for excavation inspections under CDM 2015 Regulation 22 |
| Edge protection and barriers | Type of edge protection specified (guard rails, barriers, stop blocks for vehicles); lighting for excavations that will be open during hours of darkness; signage to warn of open excavation |
| Emergency procedure for service strike | Step-by-step procedure in the event of a cable strike, gas escape, or water main burst; emergency contact numbers for each utility provider; evacuation distance and assembly point; instruction that no attempt should be made to repair a damaged service |
| Issue, acceptance, and close-out | Signatures of the issuer (confirming HSG47 protocol has been completed and all preconditions are in place), the permit holder (accepting responsibility for safe digging within the permitted area), and the close-out signature (confirming the excavation is either backfilled or made safe) |
3. Common Mistakes
Relying on CAT scan alone without service drawings or trial holes
A CAT scan only detects live cables and metallic pipes. It will not find de-energised cables, plastic pipes without tracer wire, or fibre-optic ducts. Service drawings identify what should be present; the CAT scan locates live metallic services; trial holes physically confirm positions and depths. All three steps of the HSG47 protocol are required — omitting any one of them creates a gap in the detection system.
No permit to dig in place before excavation begins
The permit to dig is a separate document from the excavation RAMS. It confirms that the HSG47 protocol has been completed, that services have been identified and marked, and that safe digging practices have been briefed. Excavation without a permit to dig is a significant compliance failure and is one of the most common enforcement actions taken by the HSE following a service strike.
Machine excavation within the 500mm hand-dig zone
The 500mm hand-dig zone either side of any identified service is a non-negotiable exclusion zone for mechanical excavation. Excavator buckets can sever a cable or rupture a gas main with a single tooth. Within the hand-dig zone, all excavation must be carried out by hand using appropriate tools — including insulated hand tools where electrical cables are present. No exceptions.
Using stale or incomplete service drawings
Service drawings must be current. Drawings obtained for a previous phase of work, or drawings that are several years old, may not reflect services that have been installed, diverted, or abandoned since the drawings were produced. Fresh drawing requests should be submitted before each new phase of excavation. Drawings should be checked against the CAT survey results to identify any discrepancies.
No emergency procedure briefed for a service strike
Every operative involved in the excavation must know what to do if a service is struck. The emergency procedure must cover: do not touch the damaged service; evacuate to the specified safe distance; call the utility provider emergency number (recorded on the permit); call 999 if there is a fire, explosion, or injury; do not attempt to repair the damage. This briefing must be delivered before work starts, not after an incident has occurred.
5. Frequently Asked Questions
Is a permit to dig required for every excavation?▾
Yes. Any ground disturbance that could encounter underground services requires a permit to dig. This includes not only trench and foundation excavation but also piling, ground investigation, fence post installation, tree planting, and any activity that involves breaking the ground surface. The depth of the excavation is not a reliable indicator of risk — services can be as shallow as 250mm below the surface where cover has been reduced by previous ground disturbance.
Who can carry out a CAT/Genny survey?▾
The CAT/Genny survey must be carried out by a trained and competent operative. The recognised standard in the UK is the CSCS Scan to Dig card or CSES (Cable and Service Enquiry System) certification. The operative must be trained in the use of the specific instrument, understand its limitations, and be able to interpret the results in conjunction with service drawings. An untrained person using a CAT may miss services or misinterpret signals, creating a false sense of security.
Can a single permit to dig cover multiple excavation locations?▾
No. A permit to dig is location-specific. Each distinct excavation area requires its own permit because the service profile, ground conditions, and hazards differ from one location to another. A single permit covering multiple locations provides no assurance that the HSG47 protocol has been completed for each individual area. Where multiple excavations are planned across a site, each one must have its own permit based on the specific service information for that location.
What should happen if an uncharted service is discovered during excavation?▾
Work must stop immediately. The excavation must be secured and the area made safe. The site manager and permit issuer must be notified. The service must be identified — by contacting utility providers if necessary — and its position and type confirmed before any further excavation takes place. The permit to dig must be suspended and re-issued only after the newly discovered service has been properly identified, marked, and the safe digging method adjusted to account for it. Under no circumstances should excavation continue around an unidentified service.
Generate your Permit to Work — Excavation and Permit to Dig on Construction Suite
Construction Suite walks you through every required section with a guided Q&A — built to MHSWR 1999 — and generates a professionally formatted document in minutes.
Get started freeThis guide is for general informational purposes only and does not constitute legal advice. While every effort is made to ensure accuracy, regulations change and individual project circumstances vary. Construction Suite is a trading name of Xzist Digital Ltd, registered in England and Wales.