According to HSG47, what is the first step before any excavation work begins?

HSG47 (Avoiding Danger from Underground Services) requires that the location of underground services is identified before any excavation begins. This involves checking utility plans, using a Cable Avoidance Tool (CAT) and signal generator (Genny) to locate buried cables and pipes, and digging trial holes by hand near identified services. Striking a live service can be fatal.

Excavating a small test pit using a mechanical digger to check the ground

Identifying the location of underground services using plans, a CAT scanner, and trial holes

Erecting edge protection around the planned excavation area

Notifying the local authority that excavation work is about to start

What is the purpose of a Cable Avoidance Tool (CAT)?

A Cable Avoidance Tool (CAT) is a hand-held device that detects electromagnetic signals emitted by or induced onto buried metallic services such as power cables, telecoms cables, and metal pipes. It is used to locate their approximate position and depth before excavation. A CAT should always be used together with a signal generator (Genny) for best results.

To measure the depth of an excavation accurately before workers enter it

To test the strength of an overhead power line before work starts nearby

To detect the presence and approximate position of underground cables and pipes

To check the load rating of lifting equipment before it is used on site

What does a signal generator (Genny) do when used alongside a CAT?

A signal generator (Genny) applies a known signal to a specific underground service, either by direct connection or induction. The CAT can then detect this distinct signal, allowing the operator to trace the route of that particular service more accurately. Using a CAT and Genny together provides much more reliable detection than using a CAT alone.

It measures the voltage carried by a buried power cable so it can be identified

It records the depth of each buried service and prints it onto a site plan

It marks the ground above a detected service with paint as the CAT passes over

It applies a detectable signal to a specific service, making it easier for the CAT to locate

Free mock exam

Specialist Knowledge & Site Safety — CSCS Card HS&E Test Practice

Free topic-focused mock exam: 30 random questions from a pool of 50 on Specialist Knowledge & Site Safety, drawn from the wider CSCS Card HS&E Test bank. 35-minute timer, 70% to pass, worked explanation on every question. Use this when you've taken the full mock once and want to drill the topics you got wrong.

Questions: 30
Time limit: 35 min
Pass mark: 70% · 21/30
Question bank: 50

Free, no sign-up. Retake as many times as you like — different questions each time.

Sample questions

01According to HSG47, what is the first step before any excavation work begins?
- AErecting edge protection around the planned excavation area
- BNotifying the local authority that excavation work is about to start
- CExcavating a small test pit using a mechanical digger to check the ground
- DIdentifying the location of underground services using plans, a CAT scanner, and trial holes
Why: HSG47 (Avoiding Danger from Underground Services) requires that the location of underground services is identified before any excavation begins. This involves checking utility plans, using a Cable Avoidance Tool (CAT) and signal generator (Genny) to locate buried cables and pipes, and digging trial holes by hand near identified services. Striking a live service can be fatal.
02What is the purpose of a Cable Avoidance Tool (CAT)?
- ATo test the strength of an overhead power line before work starts nearby
- BTo measure the depth of an excavation accurately before workers enter it
- CTo detect the presence and approximate position of underground cables and pipes
- DTo check the load rating of lifting equipment before it is used on site
Why: A Cable Avoidance Tool (CAT) is a hand-held device that detects electromagnetic signals emitted by or induced onto buried metallic services such as power cables, telecoms cables, and metal pipes. It is used to locate their approximate position and depth before excavation. A CAT should always be used together with a signal generator (Genny) for best results.
03What does a signal generator (Genny) do when used alongside a CAT?
- AIt applies a detectable signal to a specific service, making it easier for the CAT to locate
- BIt measures the voltage carried by a buried power cable so it can be identified
- CIt marks the ground above a detected service with paint as the CAT passes over
- DIt records the depth of each buried service and prints it onto a site plan
Why: A signal generator (Genny) applies a known signal to a specific underground service, either by direct connection or induction. The CAT can then detect this distinct signal, allowing the operator to trace the route of that particular service more accurately. Using a CAT and Genny together provides much more reliable detection than using a CAT alone.

Common questions

Is the Specialist Knowledge & Site Safety mock exam free?

Yes — 100% free, no sign-up needed. Questions are pulled at random from a substantial bank, with a worked explanation on every question after you submit.

Can I retake the mock exam?

Yes. Every attempt picks a different random selection and reshuffles the options, so each retake gives you genuinely new questions. No limit on retakes.

Does this count towards the real qualification?

No — this is independent practice material. To gain the actual qualification you need to sit the official assessment through an approved provider.