Ammonia Exposure on Wastewater Treatment Works

Ammonia (NH3) is generated naturally during the biological breakdown of sewage at treatment works.
Concentrated ammonia gas is toxic — the workplace exposure limit (WEL) is 25 ppm (8-hour TWA).
At 50 ppm and above, ammonia causes severe irritation to the eyes, throat, and respiratory system.
Exposure above 300 ppm can be immediately dangerous to life and health (IDLH).
Ammonia is also used as a reagent in some treatment processes, stored in bulk tanks on site.
Heavier-than-air in cold conditions, ammonia can accumulate in pits, channels, and enclosed spaces.
The COSHH Regulations 2002 require exposure assessment and control for ammonia on treatment works.
Sludge handling areas, digester buildings, and return liquor streams have the highest ammonia levels.
Ammonia reacts dangerously with chlorine-based chemicals, producing toxic chloramine gas.
Personal gas monitors with NH3 sensors should be worn in areas with known ammonia exposure risk.

Protect your health	Ammonia causes chemical burns to the lungs, eyes, and skin — high concentrations can be fatal.
Legal duty	COSHH 2002 requires employers to assess ammonia exposure and implement controls at treatment works.
Prevent chemical reactions	Mixing ammonia with chlorine compounds creates toxic chloramine gas that is immediately dangerous.

Do

Don't

Wear a personal gas monitor with an NH3 sensor in all areas with ammonia risk
Check ammonia levels before entering enclosed areas near sludge or digester processes
Ensure mechanical ventilation is running in buildings where ammonia may accumulate
Know the location of emergency eyewash stations and safety showers on the works
Evacuate immediately upwind if your gas monitor alarms at the set action level
Store ammonia chemicals away from chlorine-based products to prevent toxic reactions
Wear appropriate RPE with ammonia-specific cartridges when levels may exceed the WEL
Report any strong ammonia smell immediately to the site supervisor and process team
Flush eyes and skin with clean water for at least fifteen minutes after contact
Review the COSHH assessment before starting any task in high-ammonia risk areas

DON'T enter enclosed spaces near sludge or digesters without checking ammonia levels
DON'T ignore ammonia odour — if you can smell it, exposure may already be significant
DON'T store or use chlorine products near ammonia sources or ammonia storage tanks
DON'T work in ammonia-rich areas without a correctly fitted and in-date RPE cartridge
DON'T disable or silence personal gas monitor alarms while working on site
DON'T attempt to deal with a bulk ammonia leak without specialist training and equipment
DON'T rely on smell alone to detect ammonia — at high levels the sense of smell fails
DON'T eat, drink, or smoke in areas where ammonia exposure is possible
DON'T remove ventilation covers or block air intakes in ammonia risk areas
DON'T re-enter an evacuated area until atmospheric monitoring confirms it is safe

See also: Hydrogen Sulphide (H2S) on WwTW | Chemical Dosing Area Safety

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