Striking buried services still shuts down UK sites every week. It causes injuries, sparks enforcement interest, and wrecks programmes and relationships. The basics remain the same: plan with decent utility information, control access with a permit, and use your CAT and Genny properly—then dig cautiously and verify. The challenge is doing those basics consistently under time pressure, in poor light, with overlapping trades and changing scope.
TL;DR
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– Get up-to-date utility plans, walk the area, and mark likely corridors before anyone fetches a bucket.
– Use a calibrated CAT and Genny in active and passive modes, scan at different angles, and treat depth readings as guidance only.
– Issue a permit to dig with clear hold points: hand-dig/trial holes to prove, then dig and detect in small bites.
– Keep services visible, protected and supported; stop work immediately if marks or readings don’t add up.
– Close out with as-built mark-ups and feed learning into the next brief.
The playbook to prevent service strikes
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Stage 1: Plan the ground investigation and obtain reliable utilities data
Start with a desktop search and recent plans from the relevant utilities. Use local knowledge: speak to the principal contractor, client team and anyone who’s worked that patch before. Overlay plans onto your setting-out to identify pinch points and high-density corridors. Decide the method: hand-dig, vacuum excavation, or carefully controlled machine digging, and whether temporary works are needed for support. Write a simple, specific safe system of work and line up competent people to brief and drive it.
# Stage 2: Mark the surface and set the site up to succeed
/> Translate drawings to the deck. Mark expected service routes with spray paint, flags or pegs, agree a colour key, and photograph the layout. Establish plant/pedestrian segregation and an exclusion zone big enough to keep non-essential people and materials out. Sort lighting if visibility is poor and tidy the area so trip hazards and spoil won’t distract the lookout. Put a banksman on the dig to manage plant movement and communication.
# Stage 3: Detect and verify with CAT and Genny before any dig
/> Use a CAT and Genny that’s in date for checks and functioning properly; do a daily function test and make sure batteries are good. Scan in passive mode to pick up background signals, then in active mode with the Genny connected, clamped, or using induction where you can’t get a connection. Work in a grid, scanning at different angles and heights; don’t rely on a single pass. Treat depth readouts as indicative only—never as permission to swing a bucket. Mark findings on the ground and on a sketch, and agree hold points for proving by hand.
# Stage 4: Control the dig with a live permit and real supervision
/> Issue a permit to dig for a defined area, timeframe and depth, describing controls, hold points, and emergency arrangements. Brief it to the crew and plant operators, and keep it visible at the workface. Use trial holes to expose and positively identify services before expanding the excavation. Maintain separation from service marks with hand-digging and insulated tools where risk demands it. Keep the banksman engaged, stop and re-brief if the scope or conditions shift, and escalate uncertainty rather than guessing.
# Stage 5: Dig, detect, and protect—repeat in small increments
/> Excavate in short sections, re-scanning faces and bases as you go. Keep exposed services supported and visible; never undermine or leave them spanning voids. Manage spoil placement to protect edges and maintain access routes; apply edge protection where there’s a fall hazard. Revisit the permit conditions through the shift—fatigue and pressure creep in as the day wears on. If you find unexpected services, cordon off, make safe, and update your mark-up and brief before restarting.
# Stage 6: Close out and capture what changed
/> Backfill carefully around services, reinstate markers, and update as-builts. Photograph any deviations from plans and log unknowns for the next phase. Close or reissue the permit if the work area, depth or method changes. Fold learning into toolbox talks so the next dig starts smarter than the last.
Streetworks near-miss: the small decision that made the difference
/> On a housing site in the North West, a subcontract gang were opening a 600 mm trench along a new estate road to tie in drainage. Utility drawings suggested electricity and water on the opposite verge, but fibre installations had gone in late in the programme. The supervisor marked up from plans and did a quick passive scan; nothing obvious showed, and the digger was itching to start. A banksman asked for one more active sweep with the Genny—this time using induction from a nearby cabinet. The CAT lit up across the proposed line, weak but consistent. The team swapped to hand-digging and found a shallow plastic duct with fibre blowing rope, unrecorded on the pack. They extended the exclusion, rang the PC, and re-routed the trench by 400 mm, losing an hour and saving a shut site.
Site-ready checks before any bucket breaks ground
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– Utility plans in date, key pinch points highlighted, and mark-up photographed.
– CAT and Genny function test completed; competent user identified for the shift.
– Permit to dig issued for a defined footprint and depth, with hold points and trial hole locations listed.
– Exclusion zone set and signed; plant routes and banksman agreed; lighting and housekeeping sorted.
– Method statement covers hand-dig/vacuum near services, insulated tools, and service support.
– Emergency arrangements briefed: who to call, stop-work triggers, and first response to gas, water or power incidents.
# Depth on the CAT means safe distance
/> Treating an indicative depth as a green light is a frequent error. It varies with conditions and technique and is never a substitute for proving by hand.
# Issuing permits from the office
/> A permit that’s written away from the workface, without walking the ground, misses details like changes in kerb lines, new cabinets, or poor access. Permits must be site-specific and briefed where the shovel will hit.
# Rushing scans in bad weather or low light
/> Wind, rain and dusk make people speed up. Slowing down to scan properly and setting up lighting is cheaper than a strike.
# Failing to re-brief when the trench line moves
/> Small layout changes accumulate. Any shift in line, level or method needs a refreshed scan, updated mark-up and a quick re-brief.
Bottom line for supervisors
/> Permits, CAT and Genny, and a tidy exclusion zone do the heavy lifting, but they only work when crews pause to verify and escalate uncertainty. If the plan, the marks and the instrument don’t agree, the safest action is to stop and prove before proceeding.
# Five moves to lock in before the first scoop
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– Walk the trench line end-to-end with the CAT and Genny, agree hold points, and paint them on the ground.
– Nominate a single competent scanner for the shift and a deputy; make sure both know the permit conditions.
– Stage the dig: trial holes first, then short excavation sections with a re-scan at each new face.
– Keep services visible and supported; tie on signage to exposed pipes/ducts indicating type and direction of travel.
– Capture as-builts and photos as you go so you can brief the next gang without relying on memory.
Service avoidance is an expectation that won’t soften; it’s squarely in the sights of clients and regulators whenever shovels are out. Ask in your next briefing: do our permits reflect the ground we’re digging today, who is actually competent to scan, and what will make us stop if the picture changes?
FAQ
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Who should operate the CAT and Genny on site?
A competent person who understands the equipment’s modes, limitations and how to interpret signals should operate it. Many crews have one or two trained users who take the lead, with others supporting by marking up and controlling the dig. Don’t assume every plant op is confident with scanning just because they’ve seen it done. Confirm competence in the briefing and keep a backup identified.
# How often should we scan during the excavation?
/> Scan before you start, then again as you open up new ground or expose fresh faces. The signal picture often changes once surfaces are broken and shielding removed. Treat scanning as part of the excavation cycle, not a one-off pre-start task. If the route or depth changes, rescan and re-brief.
# What goes into a good permit to dig?
/> It should define the exact area, scope, depth, validity period and hold points such as trial holes. List the required controls: hand-dig zones, exclusion arrangements, supervision, emergency contacts and when to stop work. Keep it at the workface and update it if the method or footprint changes. Close it properly with as-built notes and photos.
# Are CAT depth readings reliable enough to allow machine digging?
/> Depth readings are only guidance and can be affected by ground conditions, signal strength and user technique. They should never be used on their own to justify mechanical excavation close to suspected services. Proving by hand or vacuum and keeping services visible is safer practice. Use depth to inform caution, not to replace control.
# What should we do if we uncover an uncharted service?
/> Stop work, make the area safe with barriers, and keep people and plant clear. Inform the site supervisor and principal contractor, and contact the likely undertaker for advice. Mark, photograph and protect the service, then update the permit and brief the crew before restarting. Expect to adjust the method or reroute to maintain safe separation.
