COS/Specific Substances/TBT-COS-019

Sodium Hypochlorite Handling

COSHH & Hazardous Substances › Specific Substances › Sodium Hypochlorite Handling

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Sodium hypochlorite (NaOCl) is a strong oxidising disinfectant used in water treatment and swimming pools.
It is corrosive to skin, eyes, and the respiratory system — even dilute solutions cause irritation.
Concentrated solutions (10–15% available chlorine) can cause severe chemical burns on contact.
Mixing sodium hypochlorite with acids produces toxic chlorine gas that can be fatal in enclosed spaces.
The workplace exposure limit for chlorine gas is 0.5 ppm short-term — an extremely low threshold.
Deliveries arrive by tanker or in IBCs — transfer to bulk storage creates splash and spill hazards.
Storage tanks must be bunded to 110% capacity and made from compatible materials such as GRP or HDPE.
UV degradation reduces the strength of sodium hypochlorite — storage should be in shaded cool locations.
Emergency eyewash stations must be within 10 seconds travel of any handling location.
COSHH 2002 requires a specific assessment for sodium hypochlorite covering all handling and dosing activities.

Chemical burns	Concentrated sodium hypochlorite causes severe burns to skin and eyes on contact — speed of decontamination is critical.
Chlorine gas	Mixing with acid releases chlorine gas that causes respiratory failure and death in enclosed spaces.
Environmental harm	Hypochlorite spilled into watercourses kills aquatic life — bunding and spill containment are essential.

Don't

Complete a COSHH assessment for sodium hypochlorite before any handling or dosing activity
Wear chemical splash goggles, face shield, chemical gloves, and apron during handling
Ensure emergency eyewash stations are accessible within 10 seconds of the handling area
Store in bunded areas made from compatible materials away from heat and direct sunlight
Check that the storage bund holds at least 110% of the largest container volume
Flush any skin or eye contact immediately with copious clean water for at least 20 minutes
Ventilate enclosed areas where sodium hypochlorite is stored or dosed to prevent gas build-up
Supervise tanker deliveries and IBC transfers to contain any splashes or spills
Label all storage tanks, IBCs, and dosing lines clearly with the chemical identity
Train all handlers on the specific hazards and emergency procedures for hypochlorite

DON'T mix sodium hypochlorite with acid or acid-based cleaners under any circumstances
DON'T handle concentrated hypochlorite without chemical goggles and face shield
DON'T store hypochlorite in direct sunlight or near heat sources — it degrades rapidly
DON'T allow spillage to enter surface water drains, rivers, or groundwater
DON'T use metal containers or fittings that are incompatible with hypochlorite
DON'T enter a space where chlorine gas may be present without atmospheric monitoring
DON'T delay washing eyes or skin after hypochlorite contact — seconds matter
DON'T leave empty IBCs or drums open where residual vapour can escape
DON'T store hypochlorite near incompatible chemicals including acids and ammonia
DON'T assume dilute solutions are harmless — they still cause irritation and burns

See also: COSHH Awareness | Chemical Spill Clean-Up Procedures

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