Sewers and drains carry wastewater, surface water, and sometimes combined flows beneath construction sites. Excavating near live sewers risks collapse, flooding, biological contamination, and exposure to toxic gases. Damaging a sewer can also cause environmental pollution and incur significant repair costs. This talk covers the precautions needed when working near underground sewers and drains.
Key Hazards
Sewer collapse flooding the excavation with contaminated wastewater
Hydrogen sulphide gas accumulating in excavations near damaged sewers
Biological infection from contact with raw sewage during accidental breakage
Environmental prosecution from sewage polluting watercourses or groundwater
Control Measures
Obtain up-to-date sewer records from the water company before excavating in the area.
Verify sewer positions using CCTV survey and ground-level tracing before breaking ground.
Hand dig within 500mm of the indicated sewer position to expose the pipe safely.
Support exposed sewer pipes to prevent settlement, displacement, or joint failure.
Monitor the atmosphere in excavations near sewers for H2S and methane using portable gas detectors.
Wear biological hazard PPE if there is any risk of contact with sewage during the work.
Notify the water company immediately if a sewer is damaged during excavation.
Ensure hand washing facilities are available near all work areas adjacent to live sewers.
Brief the excavation team on the sewer location, depth, and the emergency response for a burst.
Emergency / Rescue
If a sewer bursts during excavation, evacuate the trench immediately. Move upwind to avoid H2S exposure. Call the water company emergency number. Do not re-enter the excavation until gas levels are confirmed safe. Decontaminate any workers who contacted sewage.
Remember
Obtain sewer records and verify positions before excavating anywhere near underground drains
Hand dig within 500mm of indicated sewer positions to avoid machine damage to the pipe
Monitor the atmosphere for H2S and methane in all excavations near live sewers
Notify the water company immediately if a sewer is accidentally damaged during work
Wear biological hazard PPE and use hand washing facilities when working near sewage
Applicable Legislation: CDM 2015 · Water Industry Act 1991 · HSG47 (Avoiding Danger from Underground Services) · COSHH 2002