Striking a buried service can cause fatal electric shock, burns, a gas explosion, flooding and loss of supply to the public. The Construction (Design and Management) Regulations 2015 say that construction work liable to create a risk from an underground service must not be carried out unless suitable and sufficient steps have been taken to prevent the risk, so far as is reasonably practicable. The Electricity at Work Regulations 1989 add that nobody may work on or near a live conductor where danger may arise unless it is unreasonable for it to be dead, it is reasonable to work on it live and suitable precautions are taken.
HSE's guidance HSG47 sets out how to do this, and following it will normally be enough to comply. It applies to any excavation where services may be present: trenching, foundations, drainage, landscaping and highway works. Its method has three parts. You plan the work, locate and identify the services, then dig safely. Write what you will do into your construction phase plan before any digging starts.
Get plans from every owner
Before you plan the dig, find out who owns services in the work area and ask each owner for their plans. There may be more than one owner for a single type of service. A one-call service such as LSBUD is a quick way to identify owners and request plans. It is free to use, but it covers its members' networks, so check who is missing and ask them directly.
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Ask every owner of electricity, gas, water, telecoms and private services
Request plans for the whole work area, and allow time for the replies before the start date.
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Look for signs on the ground
Look for lamp posts, pit covers, pipeline marker posts, gas pipes entering buildings and reinstated trenches. The absence of signs does not mean there are no services.
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Assume gas service pipes exist
Plans do not normally show gas service connections. Work out the probable line from the meter position or the point where the pipe enters the building.
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Give the plans to the people doing the work
Give those digging a written plan showing where services are and what they are, with enough time and the right protective equipment.
Plans alone are not enough. They are not always drawn accurately to scale, so do not take distances or depths from them. Services may have been moved without the owner knowing, and cables marked as straight lines can snake or loop.
Survey with a cable avoidance tool and signal generator
Use a detecting device to locate the services shown on the plans and any the plans miss. A cable avoidance tool (CAT) picks up the field from live power cables and radio signals re-radiated by metal pipes and cables. A signal generator (Genny) puts a signal onto a known cable or pipe so that the CAT can trace it, and it greatly improves accuracy.
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Make sure the operator is trained
Anyone using a locator needs thorough training in its use and limits. Use it as the maker directs, and check and calibrate it regularly.
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Scan the whole work area
Trace each service through the full area, because cables loop and pipes bend. Scan again as the cover is removed, because readings get more accurate closer to the service.
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Mark what you find
Mark the line of each service on the ground with chalk, crayon or paint on paved surfaces, or with wooden pegs on grass, preferably to one side of the service. Do not use steel pins or spikes.
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Record the results on the working drawings
Share the survey results with the designer and show them on drawings the site team can use.
A locator has limits. It may not separate services that run close together or one above the other. It does not detect plastic pipes without a metallic tracer wire, and many telecoms and railway signalling cables cannot be detected. A cable ended in the ground (pot-ended) may carry power even though it looks disused. Treat every service as live until the owner confirms in writing that it has been disconnected and is safe.
Dig trial holes and expose services by hand
Dig trial holes to confirm the position, depth and identity of each service before you start the main excavation. Everyone who exposes services, and everyone who supervises them, must be competent and understand the value of hand digging and the risks of power tools and mechanical excavators.
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Dig trial holes by hand
Use suitable hand tools or vacuum excavation to confirm each service where the locator has shown it. Take special care above or close to the assumed line.
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Dig alongside the service, not on top of it
Use spades and shovels eased in with gentle foot pressure rather than thrown or spiked into the ground. Use picks only with care to free stones or hard layers, and never in soft clay or soft soil near a service.
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Use insulated tools near electricity cables
Expose the final stretch with horizontal digging, because you can control the force better.
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Keep power tools and machines back
Where practicable, use hand-held power tools to break a hard surface only 500mm or more from the indicated line of a service. Do not use a mechanical excavator within 500mm of a gas pipe. Reduce the margin only where congestion or obstructions leave no choice, the line is already confirmed by plans and a locator, and extra precautions are in place.
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Put a banksman by the excavator
Have another person watch from a safe position outside the machine's reach, where they can see into the excavation and warn the driver.
Support and protect what you expose
Once a service is exposed it may need support, and it must never be used as a handhold or foothold. Cable joints need proper support and should not be moved without the owner's agreement. If an excavation could affect the support for a gas pipe, ask the owner first, because it may need to be diverted before work begins.
Backfill carefully so that you do not damage the service. Put warning tiles or tape back above it, and do not use large pieces of rock or hard core. Do not encase a service in concrete, and keep concrete at least 300mm from a gas pipe. If plans proved wrong, tell the owner so they can correct their records, and show how any new service was laid rather than how it was planned.
If you damage a service, tell its owner and keep everyone well clear until the owner has made it safe.
Legal basis
Primary legislation and key regulations
Official guidance
Excavation safety - HSE construction guidance (opens in a new tab)
HSE · Great Britain
HSE: Avoiding danger from underground services (HSG47) (opens in a new tab)
HSE
Street works qualifications in England: guidance for operatives and supervisors (opens in a new tab)
Publication · DfT · England
Report serious construction incidents (opens in a new tab)
Great Britain
LSBUD (LinesearchbeforeUdig) - utility asset search (opens in a new tab)
www.lsbud.co.uk