COS/Specific Substances/TBT-COS-022

Sodium Hydroxide (Caustic) Handling

COSHH & Hazardous Substances › Specific Substances › Sodium Hydroxide (Caustic) Handling

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Sodium hydroxide (caustic soda / NaOH) is a strongly alkaline chemical used in water treatment and industrial cleaning.
Concentrated solutions have a pH of 14 and cause immediate severe chemical burns to skin and eyes on contact.
Eye contact with caustic soda can cause permanent blindness within seconds without immediate irrigation.
The COSHH Regulations 2002 require a specific assessment for all sodium hydroxide handling and storage.
The workplace exposure limit for sodium hydroxide is 2 mg/m³ for the ceiling concentration (short-term).
Caustic soda reacts exothermically with water and acids, generating dangerous heat and spattering.
Bulk deliveries to storage tanks create splash risk during hose connection and disconnection operations.
Caustic soda spills are extremely slippery and cause environmental damage if they reach watercourses.
PPE for caustic handling must include chemical splash goggles, face shield, and alkali-resistant gloves.
Emergency eyewash stations and safety showers must be within 10 seconds of all handling locations.

Prevent blindness	Caustic soda destroys the cornea within seconds of eye contact — only immediate flushing can prevent permanent blindness.
Severe burns	Concentrated sodium hydroxide causes deep chemical burns that worsen rapidly without immediate water flushing.
Legal compliance	COSHH 2002 requires risk assessment, PPE provision, and emergency equipment for all caustic soda handling work.

Don't

Wear chemical splash goggles, face shield, and alkali-resistant gloves when handling caustic soda
Check that emergency eyewash stations and safety showers are functional before starting work
Flush eyes immediately with water for at least 20 minutes after any caustic soda splash
Add caustic soda to water slowly when diluting — never add water to concentrated caustic
Supervise all bulk tanker deliveries and verify the correct tank before connecting hoses
Ensure chemical bunding is intact and has capacity for a full containment spill
Store caustic soda separately from acids to prevent dangerous exothermic reactions
Clean up spills immediately using absorbent materials and neutralising agents where specified
Read the safety data sheet and complete the COSHH assessment before first handling
Wear chemical-resistant overalls and boots to prevent splashes reaching skin below the waist

DON'T handle caustic soda without chemical splash goggles and a face shield in place
DON'T add water to concentrated caustic soda — the reaction generates dangerous heat and spatter
DON'T delay eye irrigation after a splash — start flushing immediately, every second counts
DON'T store caustic soda near acids, aluminium, or zinc as dangerous reactions can occur
DON'T allow caustic soda spills to reach drains or watercourses — it kills aquatic life
DON'T use standard household gloves — only alkali-rated chemical-resistant gloves are adequate
DON'T leave bulk tank fill points unlocked or unsupervised during delivery operations
DON'T eat, drink, or smoke in areas where caustic soda is handled or stored
DON'T attempt to neutralise caustic burns on skin with acid — flush with water only
DON'T work near caustic soda without knowing the location of the nearest safety shower

See also: COSHH Awareness | Chemical Spill Response

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