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Chemical collection and stock control for UK schools, universities and hospitals

Potassium chlorate (CAS 3811-04-9): storage and disposal

Legacy potassium chlorate still turns up in school, college and university prep rooms, bought years ago for demonstrations and rarely touched since. It is classified as a strong oxidiser that may cause fire or explosion, toxic if swallowed, harmful if inhaled and toxic to aquatic life with long lasting effects. Contamination of old stock is what makes it dangerous.

CAS number
3811-04-9
Form
Solid
Storage class
Oxidiser
Signal word
Danger
Usual EWC code
16 05 06*
  • Oxidising pictogramOxidising
  • Acute toxicity pictogramAcute toxicity
  • Hazardous to the environment pictogramHazardous to the environment

What to do this week

  1. Check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as oxidiser stock and apart from the items listed under "Do not store with".
  3. If you no longer need it, add it to your disposal list so it goes on the next collection.

Safe storage in a school or lab

One practical check a technician can make is to look at the cap, threads and shelf without opening anything: clean and dry means the stock has been left alone, while powder in the threads or on the label means there is something to report. Chlorate forms friction and shock sensitive mixtures with sulfur, phosphorus, charcoal and organic material, so legacy stock that has met any of them is dangerous. Keep it in the oxidiser space on non-combustible shelving, apart from flammable, acid, alkali and corrosive stock and from toxic stock, and never beside ammonium salts, activated charcoal or aluminium powder.

How to tell it has deteriorated

Start with the condition of the container and label. A brittle plastic tub, a cracked glass jar, a lifted or illegible label and crystals around the neck all show years of neglect. Stained or damp paper, wood or card around the base is a warning, because organic material that has touched a chlorate is a hazard. Residue in the threads of a cap is the concern, since turning the lid would grind it. Rust on shelf fittings and dust inside the container are further signs. If the stock is undated, contaminated or has been mixed with anything, do not open or move it, and ask for an assessment.

How it must be disposed of

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a oxidising laboratory pack with compatible chemicals.

Under 16 05 06* this goes as hazardous waste, or 16 05 07* where it is a discarded inorganic chemical and not part of a laboratory pack, and UN 1485 is its transport number. Because contamination decides the risk, a good record matters: what the jar sits next to, any spilt crystals, any residue on the cap and the age if known. It is packed with oxidisers only, never with sulfur, phosphorus, charcoal or organic stock. It never goes to a sink, a drain, a general waste bin or a skip, and staff should not try to treat it or tidy residue away.

Waste codes and transport details for Potassium chlorate
EWC code, laboratory chemicals16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
Hazardous wasteYes

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Do not store with

  • FlammableOxidisers can ignite flammable materials or make a fire far more intense.
  • AcidMany oxidisers release toxic gas or become unstable in contact with acid.
  • AlkaliSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
  • ToxicToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
  • CorrosiveCorrosive stock can react with oxidisers, releasing heat or fumes.

Named chemicals to keep apart

  • 1,2-DimethoxyethanePeroxide forming ethers can ignite or explode with strong oxidisers.
  • 1,4-DioxanePeroxide forming ethers can ignite or explode with strong oxidisers.
  • Activated charcoalStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Aluminium powderStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Ammonium acetateChlorates and ammonium salts can form unstable ammonium chlorate.
  • Ammonium carbonateChlorates and ammonium salts can form unstable ammonium chlorate.
  • Ammonium chlorideChlorates and ammonium salts can form unstable ammonium chlorate.
  • Ammonium nitrateChlorates and ammonium salts can form unstable ammonium chlorate.
Show 15 more
  • Ammonium oxalateChlorates and ammonium salts can form unstable ammonium chlorate.
  • Ammonium sulfateChlorates and ammonium salts can form unstable ammonium chlorate.
  • Ammonium thiocyanateChlorates and ammonium salts can form unstable ammonium chlorate.
  • Diethyl etherPeroxide forming ethers can ignite or explode with strong oxidisers.
  • Diisopropyl etherPeroxide forming ethers can ignite or explode with strong oxidisers.
  • GlucoseStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Hydrobromic acidChlorates and strong acids can form explosive chlorine dioxide.
  • Hydrochloric acidChlorates and strong acids can form explosive chlorine dioxide.
  • Hydroiodic acidChlorates and strong acids can form explosive chlorine dioxide.
  • Magnesium ribbonStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Nitric acidChlorates and strong acids can form explosive chlorine dioxide.
  • Perchloric acidChlorates and strong acids can form explosive chlorine dioxide.
  • Phosphoric acidChlorates and strong acids can form explosive chlorine dioxide.
  • Potassium cyanideCyanides react violently with strong oxidisers.
  • Red phosphorusStrong oxidisers can form mixtures with these materials that burn fiercely or explode.

Common quantities we collect

Usually held as: legacy stock.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.

Where it is commonly held

Hazard statements

  • H271 May cause fire or explosion; strong oxidiser.
  • H301 Toxic if swallowed.
  • H332 Harmful if inhaled.
  • H411 Toxic to aquatic life with long lasting effects.
Precautionary statements
  • P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
  • P220 Keep away from clothing and other combustible materials.
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P270 Do not eat, drink or smoke when using this product.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P283 Wear fire resistant or flame retardant clothing.
  • P301+P316 IF SWALLOWED: Get emergency medical help immediately.
  • P306+P360 IF ON CLOTHING: Rinse immediately contaminated clothing and skin with plenty of water before removing clothes.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P330 Rinse mouth.
  • P370+P378 In case of fire: Use suitable extinguishing media to extinguish.
  • P371+P380+P375 In case of major fire and large quantities: Evacuate area. Fight fire remotely due to the risk of explosion.
  • P405 Store locked up.
  • P420 Store separately.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
  • P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P271 Use only outdoors or in a well-ventilated area.
  • P273 Avoid release to the environment.
  • P301+P317 IF SWALLOWED: Get medical help.
  • P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
  • P317 Get medical help.
  • P391 Collect spillage.

Substance as classified, dilutions may differ.

Questions

Why is old potassium chlorate considered dangerous?

It forms friction and shock sensitive mixtures with sulfur, phosphorus, charcoal and organic material, and legacy stock with contamination is dangerous. It is also classified as able to cause fire or explosion.

What should we check on an old jar?

Look, without opening it, at the label, cap threads and shelf for residue, stains or damp, and at what sits beside it. If anything is undated, contaminated or mixed, leave it where it is and report it.

Can it be stored with sulfur and charcoal from the same demonstration?

No. Chlorate with sulfur, phosphorus, charcoal or organics forms friction and shock sensitive mixtures. Each belongs on a separate shelf, ideally in separate cabinets, with the chlorate in the oxidiser space.

Does it count as hazardous waste?

Yes. It is classified as a strong oxidiser, toxic if swallowed, harmful if inhaled and harmful to aquatic life. It goes by specialist collection and is never put in general waste, a sink or a drain.

Guidance only. Check your own risk assessment and your supplier's safety data sheet.

Hazard data source: PubChem GHS Classification, retrieved 31 Oct 2026. Formula ClKO3. EC number 223-289-7.

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