Sodium Hypochlorite (Bleach): Strengths, Hazards and SDS Guide

Sodium hypochlorite (NaOCl, CAS 7681-52-9) is the active ingredient in household and industrial bleach. It is almost never sold as a pure solid because it is unstable, so the product traded is an aqueous solution, usually pale yellow and smelling of chlorine. It combines oxidising, corrosive and environmental properties, which makes the classification strongly dependent on strength.

Where sodium hypochlorite is used

• Water treatment: disinfecting drinking water, swimming pools and wastewater.
• Surface disinfection in hospitals, food plants, kitchens and farms.
• Laundry and textile bleaching, and pulp and paper bleaching.
• Household bleach and toilet cleaners, usually 3 to 6 percent.
• Industrial chemical processes and odour control scrubbers.

Strength and available chlorine

Concentration is expressed as available chlorine, the amount of chlorine the solution can release, not as a percentage of NaOCl. Household bleach is typically 3 to 6 percent available chlorine, pool chlorine is around 10 to 12 percent, and industrial strength is up to about 15 percent. Your specification should state available chlorine, free alkalinity (as sodium hydroxide), density and impurities such as chlorate, bromate and heavy metals, since buyers in drinking-water treatment check these closely.

Hypochlorite solutions lose strength with time, faster when warm, in sunlight, or if contaminated with metals such as iron, copper and nickel. State a shelf life and storage conditions on your documents, and consider the strength at delivery rather than at manufacture.

Hazard classification

Concentrated solutions are commonly classified as causing severe skin burns and eye damage (category 1B, H314) and as very toxic to aquatic life (H400), often with additional environmental classification for chronic effects. Many suppliers add the supplemental statement EUH031, contact with acids liberates toxic gas. The signal word is Danger and the pictograms are corrosion (GHS05) and environment (GHS09). Concentration limits in the harmonised entry mean weaker solutions are classified as irritants and then fall out of classification below roughly 1 percent available chlorine.

Because specific limits apply, use the concentration-based approach described in our mixture classification guide for each strength you sell.

The mixing hazard

The most important safety message is the reaction with acids and ammonia. Hypochlorite mixed with acid, including hydrochloric acid, vinegar-based cleaners or even some toilet cleaners, releases chlorine gas, which is toxic and can cause severe respiratory injury. Mixed with ammonia, it forms chloramines, also toxic. Your Section 10 must list these, and your label should carry the warning that it must not be mixed with other products.

Storage and handling

Store in cool, dark, vented containers made of polyethylene or other compatible plastic, never in metal containers other than suitable lined ones. Vented caps matter because the solution slowly releases oxygen, and containers can swell or burst when sealed tight in heat. Use goggles, gloves and splash protection, and ensure ventilation. Keep away from acids, ammonia, organic materials and reducing agents. See the storage compatibility guide.

Transport and further reading

Hypochlorite solutions with more than a stated available chlorine content are Class 8 corrosives, while weaker ones may be exempted from some transport rules. The environmental hazard mark may also apply. Confirm the current UN entry and packing group. Our database holds the harmonised data on the sodium hypochlorite page, and the companion guide on hydrochloric acid explains the other half of the dangerous mixture.