CSP/Equipment/TBT-CSP-032

WwTW Process Tank and Channel Entry

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WwTW Process Tank and Channel Entry

TBT-CSP-032

Process tanks and channels at wastewater treatment works are confined spaces containing toxic gases, biological pathogens, and the risk of drowning in residual liquids. Entry is required for construction, maintenance, and inspection but must be treated as high-risk confined space work. This talk explains the specific entry procedures for WwTW tanks and channels and the controls that protect every entrant.

Key Hazards
Hydrogen sulphide gas causing rapid loss of consciousness and death in enclosed tanks
Drowning in residual liquids or sludge remaining in partially drained process tanks
Biological infection from direct contact with sewage in tanks and channels
Oxygen depletion in enclosed channels due to decomposing organic matter
Control Measures
  • Obtain a confined space entry permit specific to the tank or channel before any person enters.
  • Drain the tank to the lowest practicable level and confirm residual liquid depth before entry.
  • Carry out continuous atmospheric monitoring for H2S, methane, and oxygen throughout the entry.
  • Isolate all inlet and outlet valves, penstocks, and return flows using lock out tag out procedures.
  • Provide forced ventilation to establish and maintain a safe atmosphere inside the tank or channel.
  • Station a trained top man at the entry point with rescue equipment and continuous communication.
  • Wear full waterproof PPE, RPE, and a personal flotation device if residual liquid remains in the tank.
  • Cover all cuts and wounds with waterproof dressings and ensure hepatitis A vaccination is current.
  • Limit entry duration and the number of entrants to the minimum necessary for the task.
Emergency / Rescue

If an entrant becomes unresponsive or the gas alarm activates, do not enter the tank. Raise the alarm, deploy the rescue winch, and call 999. Begin first aid once the casualty is extracted to a safe area.

Remember
  • A confined space entry permit is required before anyone enters a WwTW tank or channel
  • Drain the tank to the lowest level and confirm residual liquid depth before permitting entry
  • Continuous atmospheric monitoring for H2S, methane, and oxygen must run throughout the entry
  • All inlet and outlet flows must be isolated using lock out tag out before anyone enters
  • A trained top man with rescue equipment must remain at the entry point at all times
Applicable Legislation: Confined Spaces Regulations 1997 · COSHH Regulations 2002 · Health and Safety at Work etc. Act 1974 · Management of Health and Safety at Work Regulations 1999
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