Avoiding Underground Services — Safe Digging Rules for Trades (2026)

The Danger: What's Buried Beneath You

The Health & Safety Executive's guidance document HSG47, "Avoiding danger from underground services", exists because people are killed and maimed by buried services every year in the UK. Each service type carries a distinct hazard:

• Electricity cables: Striking a live cable can cause an explosive arc flash, severe burns, electrocution and death. Even contact through a tool handle can be fatal, and the flash can ignite clothing or cause life-changing facial and hand injuries.
• Gas mains: A ruptured gas main can ignite and explode, levelling structures and killing anyone nearby. Escaping gas also creates an asphyxiation and fire risk that can travel into buildings and drains.
• Water mains: A burst high-pressure water main can flood excavations in seconds, undermine foundations and wash out trench supports, risking collapse and drowning.
• Fibre and telecoms: While not lethal, cutting fibre or copper telecoms can knock out 999 access, businesses and broadband for thousands, with repair bills and claims running into tens of thousands of pounds.
• Sewers and drains: Breaching a foul sewer creates a biohazard, contaminates the dig and can trigger expensive water-company remediation.

The Safe-Digging Hierarchy: Plan, Locate, Dig

HSG47 sets out a simple, three-stage discipline that every excavation must follow. Skip a stage and you are working blind. The three stages are Plan, Locate and Dig — in that order, every time.

Stage 1 — Plan (Get the Records Before You Break Ground)

Planning starts long before the spade comes out. Obtain utility records and plans for the site. The single most efficient route in the UK is LinesearchbeforeUdig (LSBUD), a free online portal that searches the assets of hundreds of registered network operators in one enquiry and tells you which companies have plant in the area. It does not cover every operator — water companies and some local networks are notable gaps — so you may still need to contact utility companies directly, including the local Distribution Network Operator (DNO) for electricity and the relevant water and gas networks.

Read every plan carefully, note depths and positions, and treat the drawings as a guide rather than gospel: services move, get re-routed and are sometimes laid shallower than recorded. Allow time for responses — utility plans are not instant, so build the search into your job programme rather than the morning you start.

Stage 2 — Locate (Find and Mark Before You Dig)

Plans tell you roughly where services run; locating tells you precisely. Use a Cable Avoidance Tool (CAT) and signal generator (Genny) to sweep the area before any excavation. Scan systematically across the whole working area in each available mode — power, radio and genny/signal modes — and physically mark up the positions of detected services on the ground with spray paint or pegs so the gang can see them throughout the job.

Locating is a survey, not a one-off check. Re-scan as the dig progresses, and never assume a clear scan means clear ground — plastic and non-metallic services give little or no signal without a trace applied.

Stage 3 — Dig (Excavate as if Everything Is Live)

Once planned and located, dig carefully. Hand-dig trial holes and inspection pits to expose services near their marked positions before bringing in any machine. Use insulated hand tools, dig alongside a service rather than directly over it, and excavate down to it gently rather than driving a tool straight onto its line. Above all, treat every service as live and dangerous until it has been positively identified and, where relevant, confirmed isolated.

The CAT & Genny: How It Works and Its Limits

The CAT and Genny are the workhorses of service location, but they only protect you if you understand how they work and where they fall short.

• Power mode: The CAT detects the electromagnetic field given off by live, loaded power cables. It is excellent for finding energised mains but can miss cables carrying little or no current.
• Radio mode: Detects radio signals re-radiated by long metallic services such as pipes and cables, useful for picking up conductors that are not actively powered.
• Genny / signal mode: The Genny applies a specific signal to a known service — by direct connection or by induction — which the CAT then traces precisely. This is the most accurate method for following a particular line.

Operators must be competent. CAT and Genny use should be backed by recognised training — for example EUSR-registered or utility-detection courses — not just handed to whoever is nearest. The equipment needs calibration to a regular schedule and a daily function check before use; a CAT that has not been checked may read falsely clear. And the critical limitation: a CAT will not detect plastic water or gas pipes, or non-metallic ducts, unless a trace is applied. That is precisely why plans and hand-dug trial holes remain essential — the kit is one layer of defence, not the whole strategy.

Safe Digging Near Electricity Cables

Electricity cables deserve their own discipline because the consequences of striking one are so severe. UK cables are usually laid to recognised colours and depths, often protected by cable covers, tiles or coloured marker tape laid above them as a warning. Knowing these conventions helps, but never rely on depth alone — cables are frequently found shallower than the standard.

Once a cable is located, do not use a mechanical excavator within the location tolerance — typically the marked position plus a generous buffer on either side. Inside that zone, work is hand-dig only, using insulated tools, until the cable is exposed and its position confirmed. On managed sites and live utility works, a formal permit-to-dig system controls who may excavate, where, and only after locating has been signed off. If your site operates a permit-to-dig regime, no ground is broken without an authorised permit in hand.

Driving Posts, Stakes and Ground Spikes

Fencers, landscapers and anyone driving posts face a particular trap: a post or ground spike concentrates force into a single point and can be driven straight through a cable or pipe in one blow, with no chance to feel resistance and stop. Ground-penetrating spikes for marquees, signage and temporary works carry the same risk.

Apply the full plan-locate-dig discipline before every post — not just at the start of the run. Scan each individual post position with the CAT, and where there is any doubt, hand-dig a trial hole at the spot before driving. The few minutes this takes are nothing compared with hitting an 11kV cable with a steel post.

If You Strike a Service: Emergency Procedure

Despite best practice, strikes happen. Knowing the immediate response can save lives — yours and the public's.

• Gas main: Stop work immediately. Evacuate the area and keep everyone upwind. Eliminate all ignition sources — no smoking, no phones or vehicles started near the leak, no electrical switches operated. Do not attempt to stop the escape yourself. Call the National Gas Emergency line on 0800 111 999 from a safe distance.
• Electricity cable: Keep yourself and everyone else well clear — do not touch the cable, the tool or the machine in contact with it. Treat it as live. Call the DNO's emergency number, or dial 105, the national power-cut and electricity emergency number, and follow their instructions. Do not return to the excavation until the network confirms it is safe.
• Water main: Stop work, get people out of the excavation in case of flooding or collapse, and call the water company's emergency line.

In all cases, anyone injured needs medical attention without delay — electrical burns and internal injuries can be far worse than they first appear.

Quick Reference: Services and How to Detect Them

Practical Tips From the Trench

• Run your LSBUD and utility searches early — make them part of the quoting and programming stage, not a panic the night before.
• Do a daily function check on your CAT and keep it within calibration date; log it so you can prove the kit was working.
• Spray-mark detected services on the ground and brief the whole gang at the start of each shift.
• Always assume plastic services exist where your plans show metallic ones — and dig trial holes accordingly.
• Keep emergency numbers — 105 for power, 0800 111 999 for gas — on the site board where everyone can see them.
• Re-scan and re-mark whenever the dig moves to new ground or a new post position.

The Legal Duty — and What Happens If You Get It Wrong

Safe digging is not optional best practice; it is a legal duty. Under the Provision and Use of Work Equipment Regulations (PUWER) you must provide suitable, maintained equipment such as a calibrated CAT and Genny and ensure operators are trained. The Construction (Design and Management) Regulations (CDM) place duties on clients, principal contractors and contractors to plan and manage excavation work, including identifying and protecting underground services. The Health and Safety at Work etc. Act sits over all of it.

Get it wrong and the consequences are severe in every direction. A worker can suffer life-changing burns, amputations or death. The business can face HSE prosecution, unlimited fines, and in the worst cases corporate manslaughter charges, alongside the civil claims and reputational damage that follow a serious incident. The cost of doing it properly — a utility search, an hour with the CAT, a few trial holes — is trivial next to that. Plan, locate, dig, every time, and treat every service as live until proven otherwise.