Demolition Near Live Services: Gas, Electric, Water and Telecoms — Disconnection Before Work Starts

Summary

Striking a live service during demolition is one of the most serious risks on any site. The consequences range from personal injury to multiple fatalities — a struck live gas main can cause an explosion affecting the entire street; striking a high-voltage cable can kill instantly. The legal framework is clear: before any demolition or excavation commences, all services must be identified, traced, and — where possible — disconnected at source. Working near live services that cannot be disconnected requires a specific risk assessment, permit-to-dig, and trained operatives using CAT and Genny equipment.

The most common failure mode is assuming that because a building has been vacated, the services have been disconnected. They have not — building operators routinely cut off gas and electricity internally (turning off at the meter or isolator) without arranging formal statutory disconnection at the network level. Meters are not enough. A gas meter can be off at the inlet valve but the supply main at the street remains live. If the building is subsequently demolished and a machine strikes that supply pipe, the result can be catastrophic. The only safe assumption is that all services are live until formally disconnected by the network operator and confirmed on site.

A secondary risk is that as-built drawings and utility records are frequently inaccurate. Services deviate from records, undocumented alterations exist, and old services are abandoned in place without being capped or recorded. CAT and Genny surveys, ground-penetrating radar, and trial trenching are the on-site methods for verifying actual service locations before bulk demolition begins. The UK One Call (formerly called LSBUD — Lines Search Before You Dig) service is the first step, but it is a records service — it tells you what should be there, not what is.

Key Facts

• HSG47: Avoiding danger from underground services is the primary HSE guidance document — must be read and followed for all near-services work
• UK One Call (previously LSBUD) is the national "dial before you dig" service — submit a plan search request for all utility owners in the area before any excavation or demolition
• Gas disconnection: must be arranged with the Gas Distribution Network (GDN) — in England this is one of the four regional gas distributors (Cadent, SGN, WWU, Northern Gas Networks) — typical lead time 4–8 weeks
• Electricity disconnection: arranged with the Distribution Network Operator (DNO) — the 14 regional DNOs in England cover different areas — lead time 4–8 weeks, but complex wayleave or easement issues can extend this to 3–6 months
• Water disconnection: arranged with the regional water company (Anglian, Thames, Severn Trent, etc.) — typical lead time 2–4 weeks; sewers are managed by the water company or Ofwat regulated undertakers
• Telecoms disconnection: arranged directly with Openreach (BT infrastructure) or Virgin Media — lead times 2–6 weeks; failure to disconnect fibre/copper services before demolition can cause widespread network outage beyond the site
• CAT and Genny (cable avoidance tool and signal generator): mandatory on-site tools for locating buried services before any excavation or breaking in the vicinity of known services
• Ground-penetrating radar (GPR): increasingly used where services records are absent or unreliable — provides a scan of buried objects without excavation
• GN2: National Grid's guidance document "Avoiding danger from buried gas pipes" — should be read by all contractors working near gas mains
• Safe dig zones: HSG47 defines reduced-risk zones around located services — within 0.5m of a located service, no powered mechanical plant; hand digging only
• Permit to Dig: formal written permit system required on many sites — authorises specific excavation work after services have been located and marked
• New Roads and Street Works Act 1991: governs works in the public highway — notifiable works require coordination with the highway authority
• Gas Safety (Installation and Use) Regulations 1998: governs safe isolation of gas supplies — disconnection must be by a Gas Safe registered engineer
• Electricity at Work Regulations 1989: electrical work during disconnection must be carried out by a competent person — in practice, DNO operatives
• Statutory undertakers have powers to enter land to repair or disconnect services — understand that the network may extend through your demolition site

Quick Reference Table

Detailed Guidance

UK One Call: The Starting Point for All Service Searches

UK One Call (formerly LSBUD — Lines Search Before You Dig) is the national single-point enquiry service that notifies all registered utility owners of your planned work area. Submit a plan search as soon as a project is confirmed — the service is free and available online at ukonecall.com.

When you submit a search, utility owners with records of services in your search area will respond — typically within 5 working days — with drawings or information about their assets. The search results tell you which utilities have records of services in the area, but not necessarily where every pipe and cable runs — service records can be incomplete, especially for older infrastructure.

Treat the UK One Call response as the starting point for further investigation, not the final answer. If a utility owner indicates they have no assets in the area, keep that response on file. If they indicate assets are present, request detailed drawings and contact the local network operations team to discuss disconnection or protection requirements.

CAT and Genny: On-Site Service Location

The CAT (Cable Avoidance Tool) and Genny (Signal Generator) are the standard on-site equipment for locating buried services. The Genny clamps to a known service access point (such as a stop tap or gas valve cover) and injects an electrical signal into the service. The CAT then detects the signal along the route of the service, allowing the operative to trace its path and mark it on the ground.

The CAT also has a passive mode that detects naturally occurring signals from live electricity cables. Use passive mode to scan the whole area first; use active mode with the Genny to trace specific services.

Every operative using CAT equipment on a demolition or excavation site must be trained. The HSE guidance HSG47 strongly recommends formal training — certification schemes are available through NCQF and industry bodies. An untrained operative with a CAT can give false confidence — the equipment has limitations including ground conditions, depth of burial, and proximity of other services that can interfere with readings.

Mark located services clearly on the ground surface with paint or flags. Update the site plan with located service positions. Hand over marked locations at each shift change so no operative starts work without knowing where services are.

Gas Disconnection: Process and Safety

Gas disconnection at the site boundary is the only safe approach to demolition near gas mains. Turning off at the meter is insufficient — the service pipe from the main to the building remains pressurised. Full disconnection means the GDN disconnects and caps the service pipe at the distribution main in the street, removing the connection entirely.

Contact the GDN (identified from your UK One Call search) as early as possible. They will require a written request, site plans, and an agreed access date. The GDN carries out the disconnection work themselves — it cannot be done by a Gas Safe registered contractor alone. The Gas Safe contractor's role is to isolate and purge internal pipework; the GDN's role is to disconnect the service at the main.

Allow 4–8 weeks minimum for gas disconnection. In complex cases (multiple services, shared supplies to neighbouring properties, high-pressure mains) the timescale can extend to 3–6 months. Do not proceed with demolition until written confirmation of disconnection has been received from the GDN and the disconnection has been physically verified on site.

If you strike a live gas main during demolition: stop all work immediately, evacuate the area, do not use any ignition source (including mobile phones within 25 metres), call the National Gas Emergency number (0800 111 999), and keep people back until the GDN arrives and makes the service safe.

Electricity Disconnection: DNO and Wayleaves

HV (high voltage) cables on demolition sites present an extreme hazard — the exclusion zone around 11kV cables is typically 3 metres, and an arc from an HV cable can kill at distances well beyond direct contact. Always identify whether any HV cables are present from UK One Call results before any work commences.

LV (low voltage) disconnection is arranged through the DNO and involves removal of the service fuse at the cut-out (normally at the meter position), followed by disconnection at the street substation or overhead line. The DNO carries out this work. Allow 4–8 weeks for LV disconnection.

HV disconnection (11kV and above) is more complex and involves formal application to the DNO's connections team. Where a cable provides supply to neighbouring properties as well as the demolition building, a temporary service diversion may be needed before disconnection of the local section. This can add months to the programme and significant cost — identify HV routes at the earliest opportunity.

Wayleaves: if an electricity cable runs through or under your demolition site en route to another property (not serving your building), the DNO holds a wayleave (right of access) for that cable. You cannot demolish over or through a live wayleaved cable without agreement from the DNO. Discuss wayleave status with the DNO's land team early — options include cable diversion (at your cost unless the cable is being diverted for your benefit) or a temporary protection scheme agreed with the DNO.

Water and Sewer Services

Water supply disconnection is arranged with the regional water company. The connection is cut at the communication pipe in the street (the water company's responsibility up to this point). Sewer connections are sealed by the water company or their approved contractor at the inspection chamber outside the building.

Before disconnecting, check whether the building's drainage system receives flows from neighbouring properties (common in terrace and urban situations). Drainage from neighbouring properties must continue to flow — if your demolition affects shared drainage, a temporary system or diversion must be agreed before work starts.

Water companies also have rights to inspect and protect their assets during nearby demolition under the Water Industry Act 1991. Discuss demolition plans with the water company where supply mains or sewers run within or adjacent to the demolition footprint — they may require a build-over/near agreement and additional protection measures.

Telecoms Disconnection and Ducting

BT Openreach and Virgin Media infrastructure is frequently embedded in or close to demolition buildings — fibre to the premises (FTTP) connections, copper distribution cables in ducts, and multi-operator ducting chambers. Striking a major duct route during demolition can cause network outages for hundreds or thousands of customers and results in significant claims against the contractor.

Submit a UK One Call search for Openreach and Virgin Media assets. Request asset drawings through the relevant network operator portals. Arrange disconnection of all connections to the building well in advance — disconnection of multiple premises can trigger a requirement for temporary alternative provision that extends timescales.

Existing duct infrastructure (Openreach D-series ducts, multi-operator infrastructure) may be retained and reused in the new development — discuss with Openreach's duct management team whether ducts should be protected rather than demolished.

What to Do If You Strike a Live Service

Despite all precautions, service strikes do occur. Your response in the first 60 seconds matters enormously:

Gas strike: Stop all work. Evacuate the area to at least 100 metres. Do not use mobile phones, light cigarettes, or operate any electrical equipment within the exclusion zone. Call 0800 111 999 (National Gas Emergency). Do not attempt to cap or plug the pipe yourself. Keep people back until the GDN emergency team arrives.

Electricity strike: Do not touch the cable or anyone in contact with it. Call 999 and then the DNO emergency line. Keep everyone at least 15 metres from the cable and prohibit re-entry until the DNO confirms the cable is made dead.

Water strike: This is lower immediate risk but can cause flooding, structural damage, and traffic disruption. Stop work in the area, call the water company emergency line, and isolate the supply at any accessible valve.

All service strikes must be reported to the HSE under RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 2013) if they result in an injury, and should be reported to the relevant network operator regardless of whether anyone is injured.

Frequently Asked Questions

The building has been empty for 5 years — are the services definitely disconnected?

No. A building being empty does not mean services are disconnected. The most common situation on long-empty buildings is that the meter was isolated (gas turned off at the emergency control valve, electricity isolated at the cut-out fuse) but the service pipe and cable were left in place and remain live up to the meter. Always treat all services as live until you have written confirmation of disconnection from the network operator and you have physically verified it on site with CAT or pressure testing.

Who pays for disconnection and reconnection?

Disconnection costs are generally borne by the client or developer. The DNO, GDN, and water company charge for disconnection work — costs vary but budget £500–£3,000 for LV electricity and water disconnections; HV disconnections and service diversions can run to tens of thousands of pounds. These costs should be identified and agreed in the pre-contract stage, not left to emerge during construction. A service search and disconnection programme should form part of the pre-demolition audit (see pre demolition audit).

Can I work around a live service rather than disconnecting it?

Only in exceptional circumstances and with a specific risk assessment, method statement, and written agreement from the network operator. For gas mains and HV electricity, there is no practical "work around" option for demolition — they must be disconnected or diverted before demolition proceeds. For LV electricity and water pipes, it may occasionally be possible to work around a service with adequate protection in place (concrete encasement, bridging, exclusion zones enforced by barriers), but this requires DNO or water company approval and a specific permit to work.

What is a permit to dig and do I need one?

A permit to dig is a formal written control document that authorises specific excavation or breaking work in an area where services are present. It records: what services are present, where they are, what controls are in place, what equipment can be used, and who has authorised the work. Many principal contractors make permits to dig mandatory on all sites. Even where not required by the principal contractor, a permit to dig system is best practice for demolition near services — it provides a formal check before any machine or tool breaks ground and creates a record that controls were in place if an incident occurs.

Regulations & Standards

• HSG47: Avoiding danger from underground services (HSE) — the primary guidance document

• GN2: Avoiding danger from buried gas pipes (National Grid) — gas-specific guidance

• Health and Safety at Work etc. Act 1974 — general duty to manage risks from services

• Electricity at Work Regulations 1989 — competency requirements for electrical work

• Gas Safety (Installation and Use) Regulations 1998 — gas isolation and disconnection

• New Roads and Street Works Act 1991 — notifiable works in the highway

• Water Industry Act 1991 — water company powers and network protection

• RIDDOR 2013 (SI 2013/1471) — reporting of injuries from service strikes

• Construction (Design and Management) Regulations 2015 — pre-construction information to include known service locations

• HSE: Safe isolation of electrical supplies (guidance note GS38)

• PAS 128:2022 — specification for underground utility detection, verification, and location

• HSE — HSG47: Avoiding danger from underground services

• UK One Call — Lines Search Before You Dig

• National Gas Emergency — GN2 guidance

• Energy Networks Association — Find my DNO

• Openreach — Digging near our network

• HSE — RIDDOR reporting

• pre demolition audit — Services identification and disconnection programme as part of pre-demolition audit

• cdm regs demolition projects — CDM pre-construction information including utility records

• structural demolition sequence — Sequencing demolition work safely around services that remain live during phased work

• demolition dust control — Ground-level dust controls during breaking operations near live services