Constructing manholes and chambers involves deep excavation, working in confined spaces, heavy precast unit handling, and connecting into live drainage or sewer systems. Workers face risks from trench collapse, toxic gases in sewer connections, and crushing from precast rings and covers. This talk covers the hazards specific to manhole and chamber construction and the controls every operative must follow.
Key Hazards
Trench collapse around the manhole excavation burying workers at depth
Toxic gases from live sewer connections entering the chamber during construction
Crushing injuries from precast rings and covers during lifting and placement
Falls into the open chamber from unprotected edges during construction
Control Measures
Support the excavation walls using shoring, sheeting, or battered slopes before entering the dig.
Treat any manhole connecting to a live sewer as a confined space requiring atmospheric monitoring.
Use a crane or excavator with certified lifting accessories to lower all precast rings into position.
Install edge protection around the top of the chamber and the excavation perimeter throughout.
Use tag lines to guide precast units during lowering and never stand beneath a suspended load.
Monitor the atmosphere inside the chamber for H2S, methane, and oxygen before and during work.
Provide a safe means of access into the chamber using a fixed ladder or secured step irons.
Brief the team on the connection sequence and the isolation status of any live sewer or drainage.
Backfill around the chamber in layers as specified, compacting each layer before adding the next.
Emergency / Rescue
If a worker collapses inside a manhole or chamber, suspect gas poisoning. Do not enter without breathing apparatus. Raise the alarm, call 999, and attempt to recover the casualty using a rescue line from above.
Remember
Support the excavation before entering and treat sewer connections as confined space work
Monitor the atmosphere inside the chamber for H2S, methane, and oxygen before entry
Use a crane with certified lifting accessories for all precast ring placement operations
Edge protection must be maintained around the chamber top and excavation perimeter throughout
Never stand beneath a suspended precast ring or cover during lifting and placement
Applicable Legislation: CDM Regulations 2015 · Confined Spaces Regulations 1997 · LOLER 1998 · Health and Safety at Work etc. Act 1974