Below ground drainage installation involves excavating trenches, laying pipes to precise gradients, constructing manholes and inspection chambers, and backfilling around completed runs. The work combines excavation hazards, manual handling of heavy pipes and precast components, and working in close proximity to plant. Connections to existing live sewers introduce additional risks from hydrogen sulphide gas and biological contamination. Careful planning and strict adherence to the method statement are essential.
Key Hazards
Trench collapse during pipe laying in unsupported or poorly supported excavations
Manual handling injuries from heavy pipes, manhole rings, and cover slabs
Hydrogen sulphide gas exposure when connecting to existing live sewer systems
Workers struck by excavators operating in close proximity to trench operatives
Control Measures
Support all trenches with shoring or trench boxes before anyone enters for pipe installation.
Use mechanical lifting for heavy precast manhole rings, cover slabs, and pipe sections.
Carry a personal H2S gas monitor when working near or connecting to live sewer systems.
Maintain safe separation between excavator operations and workers inside the trench.
Ensure pipe bedding and surround materials are placed and compacted as specified in the design.
Provide safe access and egress with ladders at intervals not exceeding 25 metres.
Brief all operatives on the drainage design, trench support plan, and connection procedures.
Wear waterproof gloves and maintain strict hygiene when handling materials near live sewers.
Inspect the trench conditions at the start of each shift and after any rainfall or disturbance.
Emergency / Rescue
If an H2S alarm sounds while connecting to a live sewer, evacuate the trench immediately via the nearest ladder. Move upwind and raise the alarm. Call 999 if anyone shows symptoms of gas exposure.
Remember
Trench support is required for all drainage trenches before anyone enters for pipe laying.
Heavy precast drainage components must be lifted mechanically and never manhandled into position.
Hydrogen sulphide from live sewers is immediately dangerous to life at very low concentrations.
Maintain strict personal hygiene when working near live sewers due to biological contamination risks.
Pipe bedding and surround must be placed correctly because poor installation leads to premature failure.
Keep plant away from trench edges and maintain clear communication between operators and trench workers.
Applicable Legislation: CDM Regulations 2015 · Confined Spaces Regulations 1997 · Manual Handling Operations Regulations 1992 · Health and Safety at Work etc. Act 1974