COS/Specific Substances/TBT-COS-030

Water Treatment Chemical Safety (Chlorine)

COSHH & Hazardous SubstancesSpecific SubstancesWater Treatment Chemical Safety (Chlorine)

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Water Treatment Chemical Safety (Chlorine)

TBT-COS-030

Chlorine is used extensively in water treatment to disinfect drinking water supplies. It is delivered to treatment works as sodium hypochlorite solution, calcium hypochlorite granules, or chlorine gas. All forms are hazardous — chlorine gas is toxic at very low concentrations and sodium hypochlorite causes severe chemical burns. This talk covers the controls for working safely with chlorine-based chemicals on water treatment sites.

Key Hazards
Toxic chlorine gas inhalation causing severe respiratory damage or death
Chemical burns to skin and eyes from sodium hypochlorite or calcium hypochlorite
Explosion risk from mixing incompatible chemicals in the dosing area
Corrosion of storage tanks and pipework causing uncontrolled chemical release
Control Measures
  • Read the safety data sheet and COSHH assessment for the specific chlorine product before handling.
  • Wear chemical-resistant gloves, splash goggles, and a chemical-resistant apron during all handling.
  • Ensure chlorine dosing areas have fixed gas detection systems with audible alarms.
  • Never mix chlorine-based chemicals with acids or other incompatible substances.
  • Store sodium hypochlorite in bunded, shaded areas away from direct sunlight and heat sources.
  • Use RPE with a chlorine-rated gas filter when entering areas with elevated chlorine concentrations.
  • Ensure emergency eyewash stations and safety showers are available and tested within the dosing area.
  • Ventilate chlorine storage and dosing rooms to prevent gas accumulation in enclosed spaces.
  • Report any chemical spill, leak, or strong chlorine smell to the site manager immediately.
Emergency / Rescue

If chlorine gas is detected, evacuate the area upwind immediately. Do not re-enter without breathing apparatus. Call 999 if anyone has inhaled chlorine gas. Flush any chemical burns with clean water for at least 20 minutes.

Remember
  • Read the safety data sheet for the specific chlorine product before any handling begins
  • Never mix chlorine chemicals with acids or other incompatible substances under any circumstances
  • Wear chemical-resistant gloves, splash goggles, and an apron when handling any chlorine products
  • Chlorine dosing areas must have fixed gas detection systems with audible alarm activation
  • Emergency eyewash stations and safety showers must be available and tested in all dosing areas
Applicable Legislation: COSHH Regulations 2002 · DSEAR 2002 · EH40 Workplace Exposure Limits · Health and Safety at Work etc. Act 1974
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