Excavation work kills in two distinct ways: something buried is struck, or the sides come in. A cubic metre of soil weighs well over a tonne, and a partial collapse onto a kneeling worker is enough to cause fatal crush injuries or asphyxiation before anyone can dig them out.
An excavation RAMS is therefore read against two questions before anything else. How do you know what is down there? And what stops the sides coming in?
Buried services
HSG47, HSE's guidance on avoiding danger from underground services, sets the expected approach: plans, locators, safe digging practice. Your RAMS should describe all three as a sequence, not as a list.
- Obtain and reference current service drawings from every utility and from the client's own records, and state their date. Drawings are indicative, never definitive.
- Survey the area with a cable avoidance tool and signal generator, and where appropriate ground-penetrating radar, by a trained operator, with the results marked on the surface.
- Hand-dig or use vacuum excavation trial holes to confirm the position and depth of anything located, before mechanical excavation starts.
- Maintain an exclusion distance around known services — commonly 500mm either side by hand only, with greater distances for high-pressure gas and high-voltage cables as the asset owner requires.
- Treat any unidentified service as live until proven otherwise, and stop and reassess when something unexpected is found.
Name the person responsible for the survey and their competence, state the permit-to-dig arrangement if the site operates one — what a permit to work is covers the structure — and say what happens on a strike: stop, evacuate, do not touch, notify the asset owner and the emergency services, and report it. Electricity strikes cause severe burns from arcing even without contact; a gas strike creates an explosive atmosphere immediately.
Preventing collapse
CDM 2015 regulation 22 requires all practicable steps to prevent danger from collapse of an excavation or anything falling into it, and requires support or battering to be put in place where necessary before anyone works in it. Your document must state which method you are using and why.
The options
- Battering or benching the sides to a safe angle, which needs space and a stated angle derived from the ground conditions.
- Trench boxes or drag boxes, which protect the worker inside them but do not support the ground — so entry and egress must stay within the box.
- Trench sheets, proprietary hydraulic props or a full shoring system, installed and removed in a stated sequence by competent operatives.
- Piling or a designed retaining solution for deeper or more complex excavations.
Do not write "excavation to be battered or supported as required". Say which, based on what: the ground investigation report, the soil type, groundwater, the depth, the duration and the surcharge loading nearby. The old rule of thumb that anything under 1.2 metres is safe has no basis in the regulations — people have been killed in trenches shallower than that.
Surcharge and adjacent structures
Spoil heaps set back from the edge with a stated distance, plant and vehicle routes kept away from the edge or protected by stop blocks, and materials not stacked alongside. Where the excavation is near a foundation, a wall or a highway, say what assessment has been done of the effect on it, and whether a temporary works design is required. Anything beyond a simple, standard excavation should be signed off by a temporary works designer and coordinator, and your RAMS should name them.
Falls into the excavation
Edge protection or barriers around the perimeter, secure and unclimbable where the public can reach it, with lighting where visibility is poor and covers on any opening left overnight. Falls into excavations are work at height under the Work at Height Regulations 2005 — the definition includes falling below ground level — so the same hierarchy applies, and the work at height RAMS requirements are worth reading alongside this.
Safe access and egress
A secured ladder extending at least a metre above the top, positioned so that nobody in the excavation is ever more than a short distance from a means of escape — commonly taken as 7.5 metres for a trench, but state the figure you are working to. Access must be inside any trench box, and must be usable in a hurry.
Atmosphere and confined space
Deep or narrow excavations, and any excavation near a sewer, a landfill, contaminated ground or a fuel storage area, can accumulate hazardous atmospheres: carbon dioxide and hydrogen sulphide displacing oxygen at the bottom, methane migrating in, petrol vapour from contaminated ground, or exhaust from a pump or generator running at the edge.
Where the excavation meets the definition in the Confined Spaces Regulations 1997 — a substantially enclosed space with a reasonably foreseeable specified risk — the full confined space regime applies, including a safe system of work and suitable emergency arrangements before entry. State whether you have assessed it as a confined space and on what basis. Where gas monitoring is required, say which gases, what the alarm levels are, who is trained to use the monitor and when readings are taken.
Water
Groundwater ingress, surface run-off and the effect of rain on stability. State the dewatering method, where the discharge goes and under what consent, and the trigger to evacuate — a rapidly filling excavation is a drowning and a collapse risk at the same time.
Plant and people together
Excavators and workers in the same space is the other recurring fatality pattern. Segregate them: an exclusion zone around the slew radius, a banksman with an agreed signalling method and high-visibility clothing that distinguishes them, quick-hitch checks, 360-degree cameras or proximity systems where the machine has them, and a rule that nobody enters the working radius without the operator's acknowledgement. Name the operator competency — CPCS or NPORS with the relevant category — and the plant inspection regime under PUWER.
Inspection
Regulation 24 of CDM 2015 requires an excavation that has been supported to be inspected by a competent person at the start of every shift before work begins, after any event likely to have affected its strength or stability, and after any accidental fall of material — with a written report for the shift-start inspection. Name the competent person, state where the reports are kept, and state that work does not start until the inspection is recorded.
Emergency and rescue
A collapse rescue plan that does not put rescuers into an unsupported excavation, a means of raising the alarm from inside the excavation, casualty extraction arrangements, and the location of the nearest A&E. For a confined space, rescue arrangements must be in place before entry and must not rely solely on the fire and rescue service. State who is trained, what equipment is on site and where it is.
Also cover
- Contaminated ground: what the site investigation found, decontamination, welfare and hygiene arrangements, and Weil's disease awareness where rats or standing water are likely.
- Noise and vibration: breaker use, hand-arm vibration exposure limits and trigger times.
- Manual handling of trench sheets, props and pipes, and the mechanical aids used instead.
- Reinstatement and backfilling sequence, including removal of support in the correct order.
- Public interface: pedestrian routes, signage and traffic management under Chapter 8 where the work affects a highway.
Excavation documents are long, and the length is legitimate — there is a lot to say. What is not legitimate is a long document that never states the support method, never names the competent person for inspections, or never explains how somebody gets out. Those three are the ones a reviewer checks first, and they are the ones an automated pass will flag hardest. Which documents Valify reviews covers what can be submitted alongside the RAMS, including the permit and the inspection schedule.
This article is general guidance on UK construction documentation practice. It is not legal advice, a compliance certification or a substitute for review by your own qualified health and safety personnel, who remain responsible for deciding whether any particular document is adequate. See our disclaimer.