Two things kill people in excavations: the sides come in, and the digger hits a service. The law answers each with a different document. The inspection record deals with the ground after the hole is open; the permit to dig deals with what is under the ground before the bucket goes in. A site needs both, and a main contractor will ask for both.
Before you dig: the permit
Regulation 25 of CDM 2015 requires steps to be taken to prevent danger from underground services, and HSG47, HSE's guidance on avoiding danger from underground services, sets out the method everyone follows: obtain the plans, look for the signs on the surface, scan with a locator, and dig trial holes by hand to prove the position before machinery goes near it.
A permit to dig is how a site makes that sequence happen every time. It is issued for a defined area and a defined period, and it records:
- The service plans obtained and their date, because plans are wrong often enough that nobody digs on them alone
- The scan — who did it, with what, and what it found, marked on the ground
- The trial holes — where hand-dug pits proved the services
- The exclusion — where mechanical digging is prohibited
- Who issued it, who accepted it, and when it expires
The permit is not a formality on a greenfield site either. Redundant services are still live services until somebody proves otherwise.
After the hole is open: the inspection
Regulation 22 of CDM 2015 requires an excavation to be supported or battered so it cannot collapse, and regulation 24 requires it to be inspected by a competent person:
- at the start of every shift in which someone will work in it
- after any event likely to have affected its strength or stability
- after any accidental fall of rock, earth or other material
The inspector is looking at the sides and the support, the edges and what is stored on them, water in the base, the services exposed, the access in and out, and whether anyone should be in there at all. A trench that was fine on Monday is not fine after a night of rain.
Regulation 24 also sets what the report must contain and how quickly it must be prepared. A register with one sheet per excavation per week, inspected at the start of each shift, is the practical form of that duty.
The mistakes that come up
- "It is only a metre deep." Ground pressure does not know that. People have died in excavations shallower than they were tall.
- Materials and plant on the edge, loading the sides the support was not designed for.
- The support is there but the inspection is not, so nobody noticed the trench sheets moving.
- The scan was done last week, and the area of the permit has crept since.
What a template does not do
The permit and the record give the sequence and the fields. They do not know your ground or your services. A competent person judges the excavation, and no document makes anyone compliant. Why we will never call a document "compliant".
Documents for this work
- Excavation and Permit to Dig — plans, scan, trial holes, exclusion, sign-off
- Excavation Inspection Record — the start-of-shift inspection, one sheet per excavation per week
- Toolbox Talk — Excavations and Buried Services
- Everything for groundworks and civils