Underground service strikes remain one of the fastest ways to turn a routine dig into a life-altering incident. Buried electric, gas, water, fibre and drainage are routinely mis-recorded or shallow, and HSG47 is clear on the principle: assume services are present until you have proved where they are and controlled the dig accordingly. The reality on UK sites is that programme pressure, plant availability and patchy records combine to erode discipline. A practical, staged approach keeps responsibility clear and the controls visible.
TL;DR
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– Plan the dig around what might be underground, not what you hope is there; treat old drawings as hints, not truths.
– Detect and mark up with competent people and the right kit; refresh markings as the workface moves.
– Use a permit-to-dig with real hold points, daily briefings and clear stop rules when things don’t match.
– Hand-dig or vacuum around suspected lines; only bring in machinery when the tolerance zone is proven clear.
– Support, protect and record any services you find; reinstate with care and capture as-builts for the next team.
Service avoidance: a staged controls playbook
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Start with information you can trust
Begin by pulling utility records from all relevant undertakers and anything the client or designer can supply. Treat them as indicative, not definitive. Walk the route: look for tell-tales like covers, cabinets, street lighting, patch trenching and marker posts. Note third-party interfaces like railway, highways and private supplies from adjacent buildings. Build a simple plan showing the intended excavation, likely service corridors and hold points where you will switch from machine to trial holes. If the design changes, your service plan changes with it.
# Detect, confirm and mark the ground
/> Use competent operatives to scan with a locator and transmitter, and consider radar where depth or congested corridors are suspected. Agree a marking convention and paint lines, widths and knowns/unknowns clearly; date and initial each mark-up. Photograph the markings and pin them to the permit file; this helps if weather, traffic or plant track over the area. Establish a tolerance zone around each detected line and manage that space as live until proved otherwise. If scanning is hampered by rebar, water or noise, say so in the brief and adjust the method.
# Control entry: permit-to-dig and briefings
/> No bucket goes in without an authorised permit that is specific to the location, depth and method. Build in hold points: after scan, after mark-up, after trial holes, and whenever the scope shifts. Confirm competence for everyone involved: locator, banksman, machine operator and ganger. Deliver a concise briefing on the dig sequence, stop rules, isolation arrangements (if any) and emergency actions. Set plant/pedestrian segregation with clear barriers, and maintain housekeeping so markings stay visible. PPE is the last line, not the plan.
# Expose services safely
/> Around suspected lines, change pace. Hand-dig with insulated tools and controlled technique, or bring in vacuum excavation where the risk justifies it. Keep spoil heaps away from edges, markings and service runs; do not bury what you have just proved. Probe carefully in soft ground and be wary of changes in soil colour or texture. In wet conditions, slow down and improve lighting to read the ground. If you meet warning tape, stop and verify what it protects before proceeding.
# Excavate with discipline
/> Once the tolerance zone is proven and opened, mechanical digging can proceed with set rules. Approach crossings at right angles and skim in thin layers; no ramming or ripping. Use a bucket without teeth near exposed services and agree slewing limits so the machine cannot swing over people or fragile plant. Keep a dedicated banksman eyes-on at the workface and empower them to halt the dig without debate. Re-brief if the trench steps out, deepens or encounters new features; yesterday’s permit rarely fits today’s change.
# Manage discovered or live services
/> When services are found, identify them properly; if in doubt, assume live and dangerous. Support and protect with timber, foam, matting or suitably rated hangers; avoid kinks, sharp bends and loading. Do not attempt isolation or alteration unless you are the authorised person with the right approvals; engage the utility owner early if diversions or shutdowns are required. Maintain temporary barriers and signs to keep others out of harm’s way, especially on busy civils corridors. Log what you have discovered and communicate it to all shifts and adjacent workfaces.
# Record, reinstate and learn
/> Before backfilling, capture clear photos and measurements, then update the as-built/service register. Reinstate with suitable bedding and marker tape; don’t crush or damage insulation or ducts during compaction. Remove redundant markings to avoid confusing the next team. Close out the permit properly and hold a quick debrief: what matched, what didn’t, and what you’ll change next time. Feed improvements back into the method statement and future permits so lessons stick.
Where service strikes creep in: common mistakes
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Treating trial holes as optional
Skipping or skimping trial holes because “we’ve scanned it” removes the last layer of certainty. Trial holes verify depth, route and unexpected crossings.
# One-off scan, then straight to dig
/> Doing a locator pass on Monday and digging on Thursday, after deliveries and rain have changed the surface, is asking for drift. Refresh scans and markings as the workface advances.
# Blanket permits that cover half a site
/> Permits that are too broad get ignored. Keep them location-specific with real boundaries and expiry, and reissue when scope moves.
# No stop rule when the ground disagrees
/> Pressing on when markings don’t match what you find is a common precursor to hits. Build in a clear “down tools and escalate” trigger that everyone understands.
On a real UK site: a near-miss scenario
/> A small civils team is cutting a trench for a new water connection on a housing estate, tight to an adopted footway with street lighting and a telecoms cabinet nearby. The utility plans are a mixed bag and the client’s drawing shows “assumed” positions. The gang scans, marks up and starts trial holes, but a visiting delivery lorry muddies the markings and the permit isn’t refreshed. Under programme pressure, the machine edges in to speed things up. The banksman notices a thin orange duct emerging off-line from the cabinet and shouts stop; the bucket halts with a thin sliver of backfill left over the duct. A quick rethink brings in vacuum excavation to expose the area safely, and the telecoms owner later confirms an unrecorded spur. The team updates the as-built, refreshes the permit and tightens their stop rules for the remaining connections.
Pre-dig checklist for supervisors and gangs
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Actions before the bucket hits the ground
Use this to set a disciplined tone at the workface.
– Latest utility plans from all undertakers obtained, reviewed and on hand; site walk completed noting visible indicators.
– Competent scanning completed for the exact dig line; markings dated, photographed and visible after housekeeping.
– Permit-to-dig authorised for the specific location, depth and method; hold points agreed and contact details posted.
– Trial hole method agreed (hand or vacuum) with insulated tools, spoil placement and lighting sorted.
– Segregation in place for plant and pedestrians; banksman named, with clear line of sight and control of the workface.
– Stop rules briefed for mismatches, unexpected finds and poor visibility; escalation route and utility contacts available.
– Temporary works, edge protection and spoil stability checks confirmed where trenches and pits will be open.
Bottom line for site leaders
/> Service avoidance is not a paperwork exercise; it’s a visible, supervised routine that treats ground as unknown until proven otherwise. HSG47 gives the principles; your job is to make them live in the method, the permit and the behaviour at the bucket. Expect sharper scrutiny of how you know what’s underground and who is competent to find and expose it. If the plan leans on luck or a single keen labourer with a CAT, the risk hasn’t been controlled.
FAQ
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Do I always need a permit-to-dig for small hand excavations?
Where there’s any chance of buried services, a permit-to-dig is sensible, even for shallow hand work. It formalises checks, confirms who’s competent, and sets stop rules. If your organisation has a blanket rule, follow it; if not, adopt a proportionate permit for any excavation near likely services.
# How often should I rescan and remark the ground?
/> Rescan whenever the workface moves, the scope changes, or conditions make markings unreliable. Rain, traffic and housekeeping can erase lines or shift your reference points. Build rescans into the sequence rather than treating them as a delay.
# Is vacuum excavation overkill on small jobs?
/> Not if the consequence of a strike is high or congestion is suspected. Vacuum excavation reduces the chance of contact and is especially useful around unknowns, shallow corridors and brittle services. Use it to complement, not replace, scanning and trial holes.
# What’s a sensible approach when drawings and the ground don’t match?
/> Stop, make the area safe, and escalate to your supervisor or H&S adviser. Refresh the scan, adjust the permit, and consider bringing in the utility owner if necessary. Don’t force the dig to fit the drawing; let the evidence drive the method.
# How do I manage other trades working near my excavation?
/> Set and maintain exclusion zones, with clear barriers and a single point of control at the workface. Coordinate through daily briefings and short-term permits so no one re-routes a trench or opens a pit without review. Keep housekeeping tight so markings remain visible and routes stay defined. If interfaces get messy, pause and reset with the affected supervisors.
