HSG47 is the Health and Safety Executive guidance titled Avoiding danger from underground services. It explains the three basic elements of a safe system of work when digging near buried services: planning the work, locating and identifying the services, and excavating safely. Following it reduces the risk of striking gas, electricity, water, telecoms or drainage during excavation, which can injure people, halt a programme and run to serious cost.
The current third edition was published in 2014, and it is aimed at everyone involved in commissioning, planning, managing and carrying out work on or near underground services, as well as the owners and operators of those services. This guide sets out what HSG47 requires, the tools it relies on, their limitations, and how a utility survey fits in.
The three essentials of HSG47
HSG47 boils safe digging down to three elements that work together. Miss any one and the system breaks down.
Plan the work. Before anyone digs, gather the available information about what is likely to be buried. That means obtaining and studying the utility owners’ plans and records, understanding the site history, and using that to plan the work and its method so that risk is designed out where possible. Planning also covers who is competent to do the work and what to do if a service is found or damaged.
Locate and identify. Plans alone are never enough, because records are often incomplete or inaccurate and services move over time. So the buried services must be located and identified on site using detection equipment, typically a cable avoidance tool and a signal generator, supported where needed by ground penetrating radar. Detected services should be marked on the ground so everyone can see where they are.
Dig safely. Even with good plans and detection, the final safeguard is careful excavation. That means digging trial holes to confirm position and depth, working carefully by hand or with safe techniques near located services, treating every unidentified service as live, and keeping the located positions in mind throughout. Safe digging assumes the detection was not perfect and builds in a margin.
The tools, and their limits
The cable avoidance tool, often called a CAT, and its companion signal generator, the genny, are the workhorses of on-site location. The CAT detects the electromagnetic fields around buried services. In power mode it picks up the field radiated by live power cables, in radio mode it detects re-radiated radio signals on long conductors, and used with the genny it can trace a specific service that the generator has been connected to or clamped around.
These tools are essential, but HSG47 is clear that they have limits. A CAT will not reliably find non-conductive services, such as plastic water or gas pipes with no tracer wire, because there is no metal to carry a signal. Detection depends heavily on operator competence, on the equipment being calibrated and in date, and on using it correctly in the right modes. Congested ground, deep services and interference all make the picture harder to read. This is exactly why HSG47 treats location as one layer among three, rather than a single answer, and why ground penetrating radar is used alongside electromagnetic tools to pick up the non-metallic services a CAT cannot.
How a utility survey supports HSG47
A professional underground utility survey is how the planning and locating elements of HSG47 are delivered to a defined standard. Carried out to PAS 128, the British standard for underground utility detection, verification and location, it combines electromagnetic location for metallic services with GPR for non-metallic ones, and classifies the result by a stated quality level so the whole team knows how far the findings can be relied upon.
That matters because it turns a utility drawing into a stated level of confidence rather than just a picture. It does not remove the need for safe digging, HSG47’s third element remains, but it gives the design and construction team a far better basis for planning excavation, and it can be taken through to physical verification where the highest certainty is needed near high-risk services.
The verification level, exposing a service physically by trial hole or vacuum excavation, is used selectively rather than everywhere. It is reserved for the highest-risk locations, such as near a high-pressure gas main, where the cost of being wrong is greatest and absolute certainty about position and depth is worth the extra work.
Common questions
What is HSG47?
HSG47 is the HSE guidance document Avoiding danger from underground services. It sets out the three basic elements of a safe system of work when working near buried services: planning the work, locating and identifying the services, and excavating safely. The current third edition was published in 2014.
What are the three key steps in HSG47?
Planning the work using available plans and records; locating and identifying the buried services on site with detection equipment such as a cable avoidance tool, signal generator and GPR, and marking them; and excavating safely, using trial holes and careful digging and treating unidentified services as live. The three work together as a system.
Does a CAT scanner find every buried service?
No. A cable avoidance tool detects electromagnetic fields, so it will not reliably find non-conductive services such as plastic pipes with no tracer wire. Its results also depend on operator competence, correct use and calibration. This is why HSG47 combines detection with careful planning and safe digging, and why GPR is used alongside a CAT to find non-metallic services.
Is HSG47 a legal requirement?
HSG47 is guidance rather than law, but it represents recognised good practice for meeting duties under health and safety legislation such as the Construction (Design and Management) Regulations. Following it is a well-established way to show that the risk from underground services has been sensibly managed.
If your programme includes digging, trenching, piling or foundation work, a PAS 128 utility survey locates and maps the buried services first, giving you the record to plan safe excavation against. For more on scoping and timing, see our guides on PAS 128 survey quality levels and whether you need a utility survey before excavation.