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

Potassium nitrate (CAS 7757-79-1): storage and disposal

Potassium nitrate is the white crystalline oxidiser kept in school, college and university stores, often for salt bridges and combustion demonstrations. It is classified as an oxidiser that may intensify fire, and it irritates skin, eyes and the respiratory tract. A spill onto paper or wood is the real problem on a prep room shelf.

CAS number
7757-79-1
Form
Solid
Storage class
Oxidiser
Signal word
Danger
Usual EWC code
16 05 06*
  • Oxidising pictogramOxidising
  • Harmful or irritant pictogramHarmful or irritant

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

White crystals or small prills in a plastic or glass tub are the usual form, and in a school prep room the tub often sits near the carbon, sulfur and charcoal used for demonstrations. Keep it away from those: activated charcoal, aluminium powder and peroxide forming ethers such as diethyl ether and dioxane should not share its shelf. Place it in the oxidiser space on non-combustible shelving, apart from flammable, acid, alkali and corrosive stock and from toxic stock. Use a resistant tray, not wood or card, and screw the lid down so damp air stays out. Date the tub on arrival.

How to tell it has deteriorated

Look at the tub and label before the crystals. A cracked lid, a stained or lifted label and crystals crusted around the neck show that the seal has gone. Damp air makes the crystals cake into a hard lump, which is the commonest change on older stock. The bigger concern is spilt crystals soaked into paper labels, card boxes, wooden shelves or cloth, because organic material that has absorbed a nitrate burns far more fiercely once dry. This substance gives few other visible signs. Rust on shelf fittings and dust or paper inside the container are further warnings.

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.

The waste code for this item is 16 05 06*, and the asterisk marks it as hazardous waste, with 16 05 07* where it is a discarded inorganic chemical and not part of a laboratory pack. UN 1486 is the transport number. As an oxidiser it is packed apart from flammable, acid and organic stock and from any charcoal or powdered metal, and it does not go into a sink, a drain, a general waste bin or a skip. Staff should not try to treat it first. Record the container size, any caking and whether crystals have spilt onto paper or wood.

Waste codes and transport details for Potassium nitrate
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.
  • Acetic acidMany oxidisers release toxic gas or become unstable in contact with acid.
  • AcetoneOxidisers can ignite flammable materials or make a fire far more intense.
  • 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.
  • Ammonia solutionSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
  • Diethyl etherPeroxide forming ethers can ignite or explode with strong oxidisers.
Show 14 more
  • Diisopropyl etherPeroxide forming ethers can ignite or explode with strong oxidisers.
  • EthanolOxidisers can ignite flammable materials or make a fire far more intense.
  • FormalinToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
  • GlucoseStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • HexaneOxidisers can ignite flammable materials or make a fire far more intense.
  • Hydrochloric acidMany oxidisers release toxic gas or become unstable in contact with acid.
  • Magnesium ribbonStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Potassium cyanideCyanides react violently with strong oxidisers.
  • Red phosphorusStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Sodium cyanideCyanides react violently with strong oxidisers.
  • SucroseStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • SulfurStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • TetrahydrofuranPeroxide forming ethers can ignite or explode with strong oxidisers.
  • White phosphorusPhosphorus can ignite or explode with oxidisers.

Common quantities we collect

Usually held as: solid.

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

  • H272 May intensify fire; oxidiser.
  • H315 Causes skin irritation.
  • H319 Causes serious eye irritation.
  • H335 May cause respiratory irritation.
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.
  • P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P271 Use only outdoors or in a well-ventilated area.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
  • P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
  • P319 Get medical help if you feel unwell.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P332+P317 If skin irritation occurs: Get medical help.
  • P337+P317 If eye irritation persists: Get medical help.
  • P362+P364 Take off contaminated clothing. And wash it before reuse.
  • P370+P378 In case of fire: Use suitable extinguishing media to extinguish.
  • P403+P233 Store in a well-ventilated place. Keep container tightly closed.
  • P405 Store locked up.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Why is potassium nitrate kept away from charcoal?

Strong oxidisers can form mixtures with materials such as activated charcoal that burn fiercely or explode. Keep the nitrate on its own shelf in the oxidiser space, and keep carbon, sulfur and powdered metal stock elsewhere.

What if crystals spill on a wooden shelf?

Organic material that has soaked up a nitrate burns far more fiercely when dry. Report it, keep ignition sources away and describe the spill when you ask for collection. Do not wipe it up with paper.

Our tub has set solid. Is it still usable?

Damp has caked the crystals. Do not break the lump up. Record the tub as caked stock, make sure the lid is tight and list it for collection, describing the condition as you found it.

Which hazards apply to it?

It may intensify fire as an oxidiser, and it irritates skin, eyes and the respiratory tract. Wear eye protection and gloves, and keep it away from flammable and organic stock.

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 KNO3. EC number 231-818-8.

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