Sodium hypochlorite (NaOCl), the active ingredient in bleach, is one of the most widely used disinfectants in water treatment, food processing and industrial cleaning. It is also one of the least stable chemicals most plants store: it loses strength over time, and if it is handled badly it can release toxic gas. This guide covers how to store and handle bulk sodium hypochlorite safely and keep it at full strength for longer.
Why sodium hypochlorite loses strength
Hypochlorite solutions slowly break down into salt, oxygen and sodium chlorate. You cannot stop this, but you can slow it down a lot. The main factors are:
- Temperature: the biggest factor. As a rule of thumb, every 10 °C rise makes it decompose roughly three to four times faster.
- Concentration: stronger solutions (for example 12–15%) lose strength faster than weaker ones.
- Sunlight: UV light speeds up decomposition, so tanks and containers should be opaque and shaded.
- Metal contamination: traces of iron, copper, nickel or cobalt act as catalysts and greatly speed up breakdown.
- pH: hypochlorite is most stable at high pH (around 11–13). Commercial grades contain a little excess caustic soda for this reason.
Storage best practice
- Keep it cool: store indoors or in a shaded area, ideally below 25 °C and away from heat sources.
- Use compatible tanks: HDPE, cross-linked polyethylene, FRP or PVC/CPVC. Avoid ordinary steel, stainless steel, copper and brass, which corrode and contaminate the solution.
- Vent the tank: decomposition releases oxygen, so tanks and drums need venting to prevent pressure build-up.
- Buy what you can use: order quantities you will use within a few weeks, and rotate stock first-in, first-out. Old hypochlorite is weaker and contains more chlorate.
- Bund the storage area: use secondary containment large enough to hold the contents of the largest tank.
Never mix with these chemicals
This is the most important safety rule. Keep sodium hypochlorite physically separate, including in spill bunds and drainage, from:
- Acids such as sulfuric acid, hydrochloric acid or acidic cleaners. Mixing releases chlorine gas.
- Ammonia and ammonium compounds. Mixing forms toxic chloramines.
- Organic materials, fuels and reducing agents. These can react violently.
- Other oxidisers such as hydrogen peroxide. Mixing releases oxygen rapidly and causes the solution to break down.
Label every tank, line and transfer hose clearly, and use dedicated pumps and hoses so hypochlorite is never pumped into an acid tank by mistake.
Personal protective equipment
- Chemical splash goggles and a face shield
- Rubber or PVC gloves and an apron or chemical suit
- Rubber boots when handling bulk quantities
- An eyewash station and safety shower close to the storage and dosing area
Handling spills
- Keep people away and ventilate the area.
- Stop the leak if it is safe to do so, and contain the spill with sand or an inert absorbent. Do not use sawdust or other organic absorbents.
- Small spills can be diluted with plenty of water or neutralised with a reducing agent such as sodium thiosulfate, following your SDS and local regulations.
- Keep the spill away from drains and from any acids.
Transport and documentation
Hypochlorite solutions ship as UN 1791, Class 8 (Corrosive). Every delivery should come with a Safety Data Sheet and a Certificate of Analysis showing the available chlorine content, so you can confirm the strength you are paying for.
Buy bulk sodium hypochlorite
Saeby Chemical supplies bulk sodium hypochlorite for water treatment and industrial use, with a CoA and SDS for every batch. For complete treatment programmes, see also aluminum chlorohydrate (ACH) for coagulation. Contact us with your concentration, volume and delivery location for a quotation.
Related guides: ACH vs Alum for Water Treatment · Caustic Soda Flakes vs Pearls vs Liquid
