Excavation of trenches (1.5m deep x 600mm wide x 120m total length) for installation of stormwater, wastewater, and water supply pipework in a greenfield residential subdivision. Work involves machine excavation using a 5-tonne excavator, hand excavation near existing services, pipe laying and bedding, backfill, and compaction. Ground conditions are mixed clay and sandy loam with a water table at approximately 2m depth.
This SWMS does not cover road crossings (separate traffic management plan required), trenches deeper than 1.5m (requires engineered shoring design), or work within 3m of high-voltage buried cables.
| Hazard | Inherent Risk | Control Measures | Residual Risk |
|---|---|---|---|
| Trench collapse Sidewall failure burying workers in trench — clay/loam soils with potential for groundwater seepage weakening walls |
4 x 5 = 20 Extreme |
Engineering Trench walls battered back to 45 degrees in clay soils (1:1 slope) or trench shields used for vertical-sided trenches Engineering Spoil stockpiled minimum 1m from trench edge to prevent surcharge loading Administrative Competent person inspects trench conditions at start of each shift, after rain, and after any vibration event (heavy traffic, compaction) Administrative Maximum 10m open trench at any time; backfill completed sections before advancing PPE Hard hats for all personnel in or near the trench |
2 x 5 = 10 High |
| Underground service strike Excavator bucket striking buried electrical cables, gas lines, water mains, or telecommunications during machine excavation |
4 x 5 = 20 Extreme |
Elimination Ground-penetrating radar (GPR) survey and service location plans reviewed before any excavation commences Isolation All identified services potholed by hand to confirm depth and alignment before machine excavation within 2m Administrative Hand dig only within 500mm of any identified service using non-conductive, non-sparking tools Administrative Operator briefed on service locations; spotter to guide excavator when working near known services |
2 x 5 = 10 High |
| Falls into excavation Workers or public falling into open trench — 1.5m depth sufficient to cause serious injury |
4 x 4 = 16 High |
Isolation Orange mesh safety fencing around all open trenches with minimum 1m setback; hard barricading at public interfaces Engineering Steel road plates over trench at all pedestrian and vehicle crossing points Administrative Warning signage ("Open Excavation — Keep Out") at all approaches; site secured with fencing after hours PPE High-visibility vests for all workers; reflective delineators on barricades for visibility |
2 x 4 = 8 Medium |
| Mobile plant interaction Workers struck by excavator, compactor, or site trucks operating in confined trench corridor |
3 x 5 = 15 High |
Isolation Exclusion zone equal to excavator swing radius; no personnel within the swing zone during machine operation Engineering Excavator fitted with ROPS, FOPS, reversing camera, and audible reversing alarm Administrative Dedicated spotter when workers are required near operating plant; eye contact protocol between operator and ground crew PPE High-visibility Class D/N garments (AS/NZS 4602) for all ground personnel |
2 x 5 = 10 High |
| Groundwater ingress Water table at 2m depth — potential for water seepage into 1.5m trench, creating unstable conditions and drowning risk |
3 x 4 = 12 High |
Engineering Sump pump and dewatering setup on standby; pumps deployed if water ingress exceeds 50mm accumulation Engineering Discharge water managed to avoid erosion or flooding of adjacent properties (settling tank or soak pit) Administrative Monitor weather forecasts; cease excavation and dewater if heavy rain is forecast or water table rises above trench floor Administrative No personnel to enter trench with standing water above ankle height until dewatered |
2 x 3 = 6 Medium |
If a worker is buried or partially buried in a trench collapse, call 111 immediately. Do not enter the trench to attempt rescue as secondary collapse is likely. Use the excavator bucket (with extreme care) to remove large volumes of material if the operator can do so safely. Keep the casualty's airway clear. Do not pull on the person — wait for emergency services with shoring capability.
If an electrical cable is struck, do not touch the excavator or cable. Operator to remain in the cab. Clear all personnel at least 10m from the machine. Call the network operator emergency line immediately. For gas line strike, evacuate upwind, prohibit ignition sources, and call the gas emergency line.
All workers must read and understand this SWMS before commencing work. By signing below, each worker confirms they have been briefed on the hazards, controls, and emergency procedures, and agree to follow them.
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