Before any ground is broken on a construction site, buried services must be located to prevent cable strikes and pipe damage. The Cable Avoidance Tool (CAT) and Signal Generator (Genny) are the primary detection equipment used on UK sites. Incorrect use or over-reliance on these tools has led to serious injuries and fatalities from striking live electricity cables and gas mains. Competent operation requires proper training and understanding of the equipment limitations.
Key Hazards
Electric shock or electrocution from striking live underground cables
Gas explosions from damage to buried gas mains during excavation
Water main bursts causing flooding and trench collapse risk
False confidence from incorrect CAT readings missing buried services
Control Measures
Ensure all CAT and Genny operators have completed an approved training course and hold valid certification.
Obtain and review utility service plans and drawings before starting any detection survey.
Carry out a CAT survey in all three modes — power, radio, and Genny — across the full work area.
Calibrate the equipment at the start of each shift and perform the self-test function before use.
Mark the location of all detected services clearly on the ground using spray paint and markers.
Use hand digging or vacuum excavation within 500mm of any detected or suspected service.
Never assume an area is clear of services based solely on CAT readings without trial holes.
Keep the CAT away from vehicles, plant, and metal structures that can distort signal readings.
Record all survey results and communicate findings to the excavation team before digging begins.
Emergency / Rescue
If a cable is struck, move everyone away and call the utility company and 999 immediately. Do not touch exposed cables. If a gas main is damaged, evacuate the area upwind and prohibit ignition sources.
Remember
A CAT and Genny will not detect every buried service — always use plans as well.
All three detection modes must be used on every survey to maximise detection reliability.
Hand dig within 500mm of any known or suspected service to confirm its exact position.
Training and certification are required — untrained operators must not use this equipment.
Striking a live cable can kill instantly, and a gas strike can cause a fatal explosion.
Always complete trial holes to visually confirm service positions before machine excavation.
Applicable Legislation: Health and Safety at Work etc. Act 1974 · CDM Regulations 2015 · HSG47 (Avoiding Danger from Underground Services) · PAS 128 (Underground Utility Detection)