Wastewater treatment works present a unique combination of hazards not found on typical construction sites. Toxic gases including hydrogen sulphide and methane, open water, confined spaces, biological pathogens, chemical dosing systems, and rotating machinery are all present. Construction workers on these sites must understand these specific risks and follow additional precautions beyond standard site safety procedures.
Key Hazards
Hydrogen sulphide gas causing rapid loss of consciousness and death
Drowning in open process tanks, channels, and settlement tanks
Biological infection from contact with raw or partially treated sewage
Methane and biogas creating explosion risk in enclosed process areas
Control Measures
Carry a personal H2S gas monitor at all times when working on a wastewater treatment site.
Install edge protection around all open tanks, channels, and waterways before starting work.
Wear waterproof gloves and wash hands thoroughly before eating, drinking, or smoking.
Ensure hepatitis A and tetanus vaccinations are up to date before starting work on any WwTW.
Treat all below-ground chambers, tanks, and channels as confined spaces requiring a permit.
Identify and avoid chemical dosing areas unless specifically trained and authorised to work there.
Ensure all rotating equipment is isolated and locked off before carrying out any maintenance.
Brief all workers on the specific WwTW hazards during the site induction before work begins.
Keep a safe distance from activated sludge lanes and aeration tanks where drowning risk is highest.
Emergency / Rescue
If your H2S monitor alarms, move upwind immediately and raise the alarm. If someone falls into a process tank, throw a lifebuoy and call 999. Do not enter the water. For chemical exposure, use the emergency shower and seek medical attention.
Remember
Hydrogen sulphide is the number one killer on wastewater treatment works and smells of rotten eggs.
You cannot smell H2S above certain concentrations because it paralyses your sense of smell.
Open process tanks are drowning hazards — edge protection and lifebuoys are essential at all times.
Sewage contains dangerous pathogens so always maintain strict personal hygiene on WwTW sites.
All below-ground areas on a WwTW must be treated as confined spaces requiring formal entry procedures.
Chemical dosing areas contain concentrated acids, alkalis, and chlorine requiring specialist training.
Applicable Legislation: Confined Spaces Regulations 1997 · COSHH Regulations 2002 · CDM Regulations 2015 · Health and Safety at Work etc. Act 1974