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

Propylene oxide (CAS 75-56-9): storage and disposal

Propylene oxide turns up in university electron microscopy suites and histology preparation areas as the transition fluid between dehydration and resin. It is an extremely flammable liquid, toxic by skin contact and inhalation, and may cause genetic defects and cancer. A very low boiling point means a sealed bottle can build pressure in a warm room. Those facts decide how it is stored, checked and handed over.

CAS number
75-56-9
Form
Liquid
Storage class
Flammable
Signal word
Danger
Usual EWC code, laboratory stock
16 05 06*
  • Flammable pictogramFlammable
  • Acute toxicity pictogramAcute toxicity
  • Serious health hazard pictogramSerious health hazard

What to do this week

  1. Without moving anything that looks damaged, check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as flammable stock, and apart from anything listed under "Do not store with" on this page. If nothing is listed, that does not prove it is safe with everything.
  3. If you no longer need it, add it to your disposal list so it can be included in a collection.

Safe storage in a school or lab

Small glass bottles with tight caps are the usual form, and the bottle should stay somewhere cool, because the low boiling point lets pressure rise inside a sealed container when the room warms. Place it in a ventilated fire-resistant cabinet with spill containment, well away from ignition sources. Only a spark-free refrigerator should hold it if cooling is needed. It is a reactive epoxide that can polymerise violently with acids, alkalis and some metal salts, so keep it away from these and from water, and from oxidisers, which could ignite it or make a fire far more intense. Corrosive stock leaking onto a flammable bottle can break the container down. Label bottles with the date opened and keep the quantity small.

How to tell it has deteriorated

Check the cap and shoulder first. A bottle with a domed or lifting cap, a bulging seal or a hissing release when touched has been building pressure, and it should be left where it stands and reported rather than handled further. Level is the next clue: a volatile liquid in a poorly closed bottle drops quickly, and a half empty bottle with no record of use suggests escape. Look for stained labels, residue around the neck and cracked glass. Propylene oxide has no reliable visual sign of its own to rely on, so any bottle that looks different from a fresh one is treated as suspect.

How it is disposed of

We arrange this by specialist collection. We do not publish a drain or general waste route for any chemical. It is normally packed in a flammable laboratory pack with compatible chemicals.

For the university or histology holder, the waste code 16 05 06* is the usual description, with 16 05 08* where it is a discarded organic chemical and not part of a laboratory pack. The matter that decides the packing is the combination of extreme flammability and cancer classification, so the collector wants the exact volume, the bottle condition and any sign of pressure. Tell them if a cap looks raised. It never goes into a sink, a drain or a skip, and nobody should try to let it evaporate in a fume cupboard or treat it first. A registered carrier moves it to a permitted facility.

Waste codes for Propylene oxide
Usual EWC code, laboratory stock16 05 06*
Discarded organic chemical, not a laboratory pack16 05 08*
Human healthcare setting18 01 06*
Usually classed as hazardous wasteYes

20 01 13* (solvents) belongs to municipal collections and is shown for reference only. It is not the normal code for a laboratory collection.

The code depends on where the waste came from and what it contains, and classifying it is the producer's duty. Use the waste code finder to see why.

Do not store with

  • OxidiserOxidisers can ignite flammable materials or make a fire far more intense.
  • AcidSome acids, especially oxidising acids, can ignite flammable materials, and acid fumes attack containers and seals.
  • CorrosiveA leak of corrosive stock can break down flammable containers and feed a fire.

Named chemicals to keep apart

  • Acetic acidOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
  • Calcium hypochloriteOxidisers can ignite flammable materials or make a fire far more intense.
  • Hydrochloric acidOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
  • Hydrogen peroxideOxidisers can ignite flammable materials or make a fire far more intense.
  • Nitric acidOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
  • Potassium nitrateOxidisers can ignite flammable materials or make a fire far more intense.
  • Potassium permanganateOxidisers can ignite flammable materials or make a fire far more intense.
  • Sulfuric acidOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
Show 2 more
  • Thionyl chlorideA leak of corrosive stock can break down flammable containers and feed a fire.
  • Zinc chlorideA leak of corrosive stock can break down flammable containers and feed a fire.

Common quantities

Usually held as: electron microscopy transition fluid.

Tell us the container size and how many you hold. An estimate is enough to start with, and some items cannot be priced until someone has looked at them.

Where it is commonly held

Hazard statements

  • H224 Extremely flammable liquid and vapour.
  • H302 Harmful if swallowed.
  • H311 Toxic in contact with skin.
  • H315 Causes skin irritation.
  • H319 Causes serious eye irritation.
  • H331 Toxic if inhaled.
  • H335 May cause respiratory irritation.
  • H340 May cause genetic defects.
  • H350 May cause cancer.
Precautionary statements
  • P203 Obtain, read and follow all safety instructions before use.
  • P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
  • P233 Keep container tightly closed.
  • P240 Ground and bond container and receiving equipment.
  • P241 Use explosion-proof electrical, ventilating and lighting equipment.
  • P242 Use non-sparking tools.
  • P243 Take action to prevent static discharges.
  • P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P262 Do not get in eyes, on skin, or on clothing.
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
  • P270 Do not eat, drink or smoke when using this product.
  • P271 Use only outdoors or in a well-ventilated area.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P301+P317 IF SWALLOWED: Get medical help.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • P303+P361+P353 IF ON SKIN (or hair): Take off immediately all contaminated clothing. Rinse skin with water or shower.
  • 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.
  • P316 Get emergency medical help immediately.
  • P318 If exposed or concerned, get medical advice.
  • P319 Get medical help if you feel unwell.
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P330 Rinse mouth.
  • P337+P317 If eye irritation persists: Get medical help.
  • P361+P364 Take off immediately all 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.
  • P403+P235 Store in a well-ventilated place. Keep cool.
  • P405 Store locked up.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
  • P317 Get medical help.
  • P332+P317 If skin irritation occurs: Get medical help.
  • P362+P364 Take off contaminated clothing. And wash it before reuse.

Substance as classified, dilutions may differ.

Questions

Why does our propylene oxide bottle feel tight when we open the cabinet?

Its low boiling point means pressure can build in a sealed bottle in a warm store. If the cap looks domed or the bottle is bulging, do not open it. Leave it in the cabinet, keep people away from it and ask for advice.

Can we keep propylene oxide in an ordinary lab fridge?

Only in a spark-free refrigerator. An ordinary domestic fridge has ignition sources inside and is unsuitable for an extremely flammable liquid. If the fire-resistant cabinet stays cool enough, that is the simpler choice.

How long can an opened bottle stay in the EM suite?

We do not set a shelf life. Date the bottle when opened, keep the quantity small, and declare it as waste once the project ends or the condition of the cap, label or level gives you doubts.

Which waste code do we give for a part used bottle?

Usually 16 05 06* when it goes in a lab pack, or 16 05 08* if it is a discarded organic chemical outside a pack. Describe the bottle accurately and the collector will confirm how it is grouped.

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 C3H6O. EC number 200-879-2.

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