UK trade-and-hazard guidance by the Riskora Editorial Team
A cubic metre of soil weighs around 1.5 to 2 tonnes — a worker buried to chest level cannot self-extricate, and asphyxia or crush injury can be fatal within minutes. The CDM Regulations 2015 explicitly require excavation support for any trench where collapse could endanger persons, and HSG185 Health and Safety in Excavations is the operational reference. RAMS that rely on 'support as required' or 'battering will be assessed on site' will not pass any competent review — the support method must be specified and the soil class must drive the choice.
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CDM Regulations 2015
Regulation 22(1)(a)
All practicable steps to prevent danger to any person from collapse of an excavation or any part of the surrounding ground.
HSG185 Health and Safety in Excavations
Sections 3-5
Soil classification, support method selection (battering, benching, trench box, sheet piling), inspection regime, and rescue planning.
Every UK RAMS reviewer applies the hierarchy of controls in the order below. Defaulting straight to PPE is the single most common reason a RAMS fails review.
1. Eliminate
Trenchless installation (directional drilling, mole, pipe-bursting) where the service permits — removes the open trench entirely.
2. Substitute
Open-cut and lay rather than open-trench-and-leave — minimise trench duration and length open at any one time.
3. Engineering controls
Trench box (drag box or hydraulic shore) sized for the soil class and depth. Battering at the soil-class angle. Sheet piling for waterlogged or running ground.
4. Administrative controls
Daily Reg 12 inspection by competent person. Permit-to-enter for any trench over 1.2m. Buddy system — never lone working in an open trench. Edge protection or 1m exclusion zone from trench edge.
5. PPE (last line)
Hi-vis, helmet, safety boots. Harness with rescue line for entry over 1.5m if trench box not full-depth.
Generic statements like 'trench will be supported' or 'trench box used as required' without naming the soil class, support method and depth threshold. Reviewers want to see the support equipment named and rated for the conditions.
An illustrative extract structured for principal-contractor review. Site-specific facts must be substituted and checked by a competent person.
Soil classification (Class B, firm cohesive clay) confirmed by site investigation report SI-2026-014. Trench depth 1.8m. Trenches will be supported using a Mabey Hire Lite Box (drag box, certified to 4.5m depth, current cert ref MH-44021). Trench box will be installed before any operative enters the trench and will remain in place until backfill is complete. Battering option not selected due to space constraint at site boundary. Daily Reg 12 inspection by Site Supervisor (CSCS Gold, MEWP-trained, NVQ Level 3). Excavator quick-hitch checked at sign-on each shift.
Reg 12 inspection at start of every shift and after any event that could affect stability. Trench box position and integrity photographed daily. Spoil heaps positioned minimum 1m from trench edge. Operative awareness check at sign-on.
At what depth must a trench be supported?
There is no statutory depth threshold — CDM 2015 requires support whenever collapse could endanger persons. In practice, most groundworks contractors treat 1.2m as the trigger because that is the depth at which an operative could be buried to chest level. Cohesive ground may be self-supporting at greater depths; running sand may need support at a fraction of that.
Can battering replace a trench box?
Yes, where space permits and the angle matches the soil class. For Class A (stable) ground around 1:1 may be acceptable; for Class C (loose, granular) closer to 1:1.5 with a benched profile. The angle must be specified, not implied.
How quickly can a trench collapse kill someone?
Asphyxia from chest compression can be fatal within 3-5 minutes once an operative is buried to chest level. Even partial burial can cause crush syndrome, where toxins released after rescue can prove fatal hours later. Speed of rescue is critical and a documented rescue plan is mandatory.
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