Primary settlement tanks are large, deep structures at wastewater treatment works where heavy solids settle out of the incoming sewage flow. Construction and maintenance work on these tanks involves confined space entry, drowning risk, biological hazards, and exposure to hydrogen sulphide gas. This talk covers the specific safety requirements for working on primary settlement tanks.
Key Hazards
Drowning from falling into deep tanks containing sewage and sludge
Hydrogen sulphide gas poisoning from decomposing organic material
Biological infection from direct contact with raw sewage
Confined space atmosphere when entering drained or partially drained tanks
Control Measures
Wear a personal flotation device at all times when working above or adjacent to filled tanks.
Install edge protection around all open tank edges and access points during construction work.
Monitor the atmosphere continuously for H2S, methane, and oxygen levels near tank openings.
Treat entry into drained tanks as a confined space requiring a full entry permit and rescue plan.
Wear biological hazard PPE including waterproof coveralls, gloves, and face protection.
Ensure all workers have up-to-date hepatitis A and tetanus vaccinations.
Wash hands thoroughly with antibacterial soap before eating, drinking, or leaving the work area.
Brief all operatives on the water rescue plan and the location of rescue equipment.
Isolate rotating scraper mechanisms and lock out before anyone enters or works near the tank.
Emergency / Rescue
If someone falls into a settlement tank, throw a lifebuoy and raise the alarm. Call 999 immediately. Do not enter the water unless trained in water rescue. If H2S exposure is suspected, move upwind and call emergency services.
Remember
Wear a personal flotation device at all times when working above or adjacent to filled tanks
Monitor the atmosphere continuously for H2S and methane near all tank openings
Treat entry into any drained tank as a confined space with full permit requirements
Isolate and lock out rotating scraper mechanisms before anyone enters or works near the tank
Wash hands thoroughly before eating or drinking to prevent biological infection
Applicable Legislation: Confined Spaces Regulations 1997 · COSHH 2002 · CDM 2015 · Work at Height Regulations 2005