Permit to Dig: When to Use One and What It Covers

Use a permit to dig before any excavation where buried services may be present. In practice that means almost every dig on a civil engineering site in the UK.

HSG47 — Avoiding danger from underground services — is HSE's guidance on safe digging.

When is a permit to dig required?

There's no law that names a permit to dig. HSG47 says a safe system of work is essential when working near underground services, and that a permit system "may be appropriate for particularly hazardous work". On most construction sites a permit to dig is how that's done (CITB's Construction Site Safety handbook includes a model permit to dig form), and principal contractors and clients commonly make one a site rule. Use one before any excavation where services may be present.

When to use one

Use a permit to dig whenever:

• Excavation is taking place where services may exist

• Ground is being broken within 500mm of a known service

• Hand digging is required to expose an existing service

• Trial holes are being excavated to locate services

HSG47 is HSE guidance, not law, and its 500 mm figures are worded with care. For hand-held power tools breaking hard surfaces it says: "Where practicable, only use such power tools 500 mm or more away from the indicated line of a service buried in or below a hard surface." For gas pipes: "do not use mechanical excavators within 500 mm of a gas pipe. The gas transporter may advise greater safety distances, depending on the pipeline pressure". For major hazard pipelines: "do not use mechanical excavators within 500 mm of a pipeline." On site, the safe approach is that within 500 mm of a located service you dig by hand, or by another safe method such as vacuum excavation, not with a mechanical excavator. That is the hand-dig zone our Permit to Dig template uses, and the permit records which method is allowed.

What the permit should cover

Before excavation starts:

Statutory records should be obtained from all relevant utility companies. A CAT and Genny scan should be carried out by a trained operative. The results should be recorded — equipment serial number, calibration date, operative name, and findings. Services identified should be marked on the ground before any ground is broken.

The precaution checklist:

The precaution checklist has 11 items, each answered before the permit is issued:

1. Service drawings and statutory undertaker records reviewed

2. CAT and Genny scan completed, with the locator's serial number and calibration date recorded

3. Every service found marked on the ground along the route

4. Area or activity flagged if high risk (for example an HV cable or gas main)

5. Each service type at the location recorded, with drawing numbers and trial hole findings

6. Cable locating equipment available throughout the excavation

7. Trial holes hand dug with insulated tools to confirm where services are

8. Services exposed along their full length in the works area

9. Plated pins or marker pegs used where needed

10. Hand digging within 500 mm of a known service, unless the permit allows another safe method such as vacuum excavation

11. Emergency contact number and assembly point on the permit

Who signs the permit:

Our template takes the permit through five signed stages. The engineer issues it once the precautions are identified and any isolations are complete. The client authorises it. The activity supervisor signs to receive it, and the gang is briefed and signs the briefing record. Until the site manager signs that every service on the permit has been located and marked, only hand-dug trial holes are allowed; that signature authorises full excavation. When the work is finished, the permit coordinator confirms the area is clear and safe, and cancels the permit.

Duration and review:

A permit to dig should not run indefinitely. Set a review interval and a maximum duration on the permit, and reissue it if the excavation runs longer.

What happens if you skip it

A struck electricity cable can kill. A struck gas main can cause an explosion. A struck water main can undermine adjacent structures. All of these have happened on UK construction sites.

Beyond the human cost, a struck service without a permit to dig in place can lead to HSE enforcement action.

The permit to dig is the document that proves you did what you were supposed to do. Without it there is no proof.