Striking a live cable, gas main or fibre trunk doesn’t just wreck a day’s programme; it injures people, shuts down streets and drags in regulators. The controls are not complicated, but they are unforgiving: plan the dig, prove what’s in the ground, and only then put a shovel or bucket in. Two things decide whether you succeed—how you run the permit-to-dig, and whether your CAT and Genny work is competent, recorded and actually used to steer the method.
TL;DR
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– Treat the permit-to-dig as the live plan: mark-out, scan, trial holes, hand-dig, then controlled machine excavation.
– Use the CAT and Genny as a system, not a gadget: multiple modes, Genny where possible, grid scans, and records.
– Hold points matter: stop if services are not where shown, or anything changes the method or people involved.
– Keep people and plant apart and protect open edges; PPE is last line, not your control for electricity or gas.
Core risk and control concepts for buried and overhead services
/> Electric, gas, water and telecoms are everywhere, often shallower or more congested than drawings suggest. Good practice is to avoid disturbing services where possible; if not, build a layered defence: up-to-date plans, competent detection, physical verification, and controlled excavation with exclusion. Work to a tolerance zone around expected runs, not a pencil line. Assume uncharted services exist until trial holes prove otherwise. Overheads count too—brief plant operators on height limits and set clearances before slewing.
Permit-to-dig that actually controls the work
/> A permit is the supervisor’s licence to start, pause and stop. Make it specific: exact area, depth, dates/times, known services with references, who scanned and when, and what hold points trigger a stop. Tie it to the RAMS and temporary works where trench support, road plates or shoring are in play. The issuing manager should walk the area with the operative who will dig, not just the subcontractor’s manager. Set expiry (e.g. end of shift) so changes in people, plant, ground or weather force a re-brief. Close the loop: as-built mark-ups and photos go back into the file so the next dig isn’t blind.
# Seven-day push: getting digs under control
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– Walk all open permits and redraw faded mark-outs with photos and chainage notes.
– Swap any out-of-date or uncertified CATs and Gennys with maintained units and log serials.
– Re-brief crews on tolerance zones and hand-dig rules before exposing any service.
– Add stop-work cards at each dig: “Unexpected service? Stop and call [named supervisor].”
– Block plant access to non-permitted areas with barriers, not just cones and tape.
Using a CAT and Genny like a grown-up
/> A CAT (Cable Avoidance Tool) detects electromagnetic fields; a Genny (signal generator) makes buried metallic services easier to find. That means one person rarely does it all in a minute. Start with visuals and plans; then sweep in power and radio modes. Where possible, connect the Genny to known services or use induction to put a signal on them. Scan in a grid pattern at different angles, re-scan after marking, and never trust a depth reading as clearance. Record who scanned, when, modes used, and key finds; photos of paint marks and stakes help when rain or traffic lifts your chalk by lunchtime.
On-site reality: how the sequence should run
/> The clean sequence is: collate plans and client records; walk the area; mark known and suspected runs; CAT/Genny scan and record; issue the permit; brief the crew; dig trial holes by hand at key points; hand-dig inside the tolerance zone to expose; then proceed with machine under a banksman’s control. Use vacuum excavation where ground or congestion suits it. Keep plant out until proof is in the ground. As you expose services, protect them—sand blinding, timber caps, clear tags—and build temporary support to suit your excavation. Before backfilling, take photos and update drawings.
Scenario: a civils crew on a congested high street
/> A groundworks team is cutting for a new drainage connection outside a shop parade. Plans show a low-voltage cable and water main near the kerb. Morning rush compresses set-up time, and fresh parking bay lines have covered last week’s mark-out. The CAT picks up a weak power tone, but the Genny isn’t used because “we’re only going 400 mm.” The mini-excavator clips a duct; it turns out to be a street lighting cable that wasn’t on the print. Work stops, the road is coned off and an emergency jointer makes it safe. The re-start takes the proper path: full Genny sweep with induction clamp, hand-dug trial holes to find both services, and a tighter permit with a hold point before machine digs resume.
Checklist: pre-dig controls for supervisors
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– Latest utility plans on hand, site-walked and marked onto ground with photos and notes.
– Competent CAT/Genny user named, with evidence of recent familiarisation and equipment in date.
– Grid scan completed in multiple modes; Genny used where possible; results recorded and briefed.
– Permit-to-dig issued, area pegged or barriered, hold points defined, and expiry set.
– Trial holes located and method agreed (hand-dig/vac ex), with tolerance zones identified.
– Exclusion in place: plant kept out until services exposed; banksman named; emergency contacts posted.
Common mistakes on service detection and permits
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Treating the permit as paperwork rather than a control
Signing in the office without a walk-round and live mark-out makes it meaningless.
# Relying on CAT power mode alone
/> Power mode can miss dead cables, neutrals and plastic-ducted runs; use the Genny to prove lines.
# Machine digging inside the tolerance zone
/> Buckets and breakers creep in “to speed up” and that’s when strikes happen; hand tools or vac ex only inside the zone.
# Losing the mark-out between shifts
/> Rain, traffic and re-surfacing remove your only ground truth; refresh marks at the start of each shift with photos.
Interfaces to watch: trades, traffic and temporary works
/> Groundworks rarely happen in isolation. Coordinate with utilities, telecoms installers and streetworks teams so you’re not scanning over someone else’s live works. Manage deliveries and public interface—closing a footpath may be the safest way to keep plant and pedestrians apart, with clear signage and a banksman. Temporary works don’t stop at big digs; even shallow trenches can collapse or trip—guard edges, use end stops and toe boards, and brief on access/egress. Night or weekend shifts need the same controls, not a cut-down version because “it’s quieter.”
A permit that holds the line and CAT/Genny work done properly are the quickest way to avoid injury and programme pain. Watch for drift: rushed briefings, faded marks and “just this once” machine digs inside the zone are where standards slide.
FAQ
# When should a permit-to-dig be reissued?
/> Reissue it when anything material changes: people, plant, area, method, weather, or findings in the ground. If a shift ends with open questions or incomplete exposures, close the permit and start clean the next day. Short validity keeps the control live rather than filed.
# How far from a marked service should I hand-dig?
/> Operate to a tolerance zone agreed in the method and permit, not an assumed distance. Good practice is to hand-dig and prove the exact position before any machine works approach the marker line. Vacuum excavation can reduce manual effort while keeping control.
# Do I need a Genny if the CAT shows a strong signal?
/> Yes. The Genny helps trace specific services and reduces ambiguity from stray signals or parallel runs. Use it to impose a signal on known assets and confirm routes; combine with multiple CAT modes and angles.
# What records are worth keeping from a scan?
/> Keep who scanned, when, equipment serials, modes used, sketches or photos of the mark-out, and any anomalies or assumptions. Those notes support the briefing, back up the permit, and help explain decisions if conditions change or a near-miss occurs.
# How do I manage open trenches around the public?
/> Plan for segregation first: barriers rated for the environment, clear signs, lighting where needed, and a banksman at pinch points. Keep edges protected, provide safe crossings or diversions, and control plant movements. If the layout can’t be made safe, change the programme or working hours to remove the interface.
