COS/Specific Substances/TBT-COS-010

Chlorine and Water Treatment Chemicals

COSHH & Hazardous Substances › Specific Substances › Chlorine and Water Treatment Chemicals

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Chlorine-based chemicals including sodium hypochlorite and calcium hypochlorite are used in water treatment.
Sodium hypochlorite is a corrosive liquid that causes severe burns to skin and eyes on contact.
Calcium hypochlorite is a strong oxidiser in granular form that reacts violently with organic materials.
Chlorine gas released from concentrated solutions or reactions is toxic — it attacks the lungs and airways.
Mixing chlorine products with acids, ammonia, or other chemicals causes dangerous gas release.
COSHH 2002 requires a specific assessment for every chlorine product used on the construction site.
Emergency eyewash and shower stations must be within 10 seconds travel of any chlorine handling area.
Storage must keep chlorine products separate from acids, organic materials, and combustible substances.
The workplace exposure limit for chlorine gas is 0.5 ppm over an 8-hour time-weighted average.
Spill kits specific to chlorine products must be available at all storage and use locations.

Chemical burns	Sodium hypochlorite causes severe corrosive burns to skin and permanent eye damage.
Toxic gas release	Chlorine gas from spills or incorrect mixing attacks lungs and can be fatal.
Reactive hazard	Chlorine products react violently with acids and organics, causing fires and gas release.
Legal compliance	COSHH requires specific assessment, controls, and emergency provisions for chlorine chemicals.

Don't

Read the safety data sheet for every chlorine product before handling it.
Wear chemical-resistant gloves, goggles, and apron when handling chlorine solutions.
Ensure emergency eyewash and showers are within 10 seconds of the handling area.
Store chlorine products separately from acids, organics, and combustible materials.
Use dedicated measuring and transfer equipment — do not share with other chemicals.
Ventilate areas where chlorine solutions are handled to prevent gas accumulation.
Keep spill kits specific to chlorine products available at storage and dosing areas.
Flush any skin or eye contact with clean water for at least 20 minutes immediately.
Follow the COSHH assessment controls for the specific chlorine product in use.
Label all containers clearly and never decant into unmarked vessels.

DON'T mix chlorine products with acids, ammonia, or any other chemical.
DON'T handle chlorine solutions without chemical-resistant PPE including goggles.
DON'T store chlorine products next to acids, fuels, or organic materials.
DON'T use chlorine in enclosed areas without ventilation — toxic gas accumulates.
DON'T decant chlorine solutions into unmarked or food-type containers.
DON'T eat, drink, or smoke while handling chlorine products.
DON'T inhale fumes from chlorine solutions — work upwind and use ventilation.
DON'T delay flushing skin or eyes after chlorine contact — every second matters.
DON'T store calcium hypochlorite in damp conditions — moisture causes decomposition.
DON'T dispose of chlorine products down drains without neutralisation and approval.

See also: COSHH Awareness | Chemical Spill Response

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