SUBJECT: Peroxide Formation Potential

Peroxides: Potentially explosive crystals formed due to chemical changes in volatile organic materials over time caused by, but not limited to evaporation, storage conditions, or breakdown of inhibitors. The crystals can be detonated by shock, heat or spontaneously if the right conditions exist.

Could a suspect compound be a peroxide former? Review the list of questions below to determine if a suspect compound could be a peroxide former.

1) Determine if suspect compound can form peroxides. Review the following list of materials that are the most common  peroxide formers.


The most hazardous compounds - those that form peroxides that may explode even without being concentrated - are in List A. Compounds forming peroxides that are hazardous only on concentration, such as distillation or evaporation, are in List B. List C is made up of vinyl monomers that may form peroxides that can initiate explosive polymerization of the bulk monomers. Each list contains the recommended storage period in parenthesis.

List A - (Three Months) - Peroxide Hazard on Storage

  • Divinyl acetylene
  • Isopropyl ether
  • Potassium metal
  • Sodium amide
  • Vinylidene chloride

List B - (Twelve Months) - Peroxide Hazard on Concentration

  • Acetal
  • Cumene
  • Cyclohexene
  • Diacetylene
  • Dicyclopentadiene t-butylalcohol
  • Dioxane
  • Ethylene glycol dimethyl ether (glyme)
  • Ethyl ether
  • Methyl acetylene
  • Methylcyclopentane
  • Methyl i-butyl ketone
  • Tetrahydrofuran
  • Tetrahydronophthalene
  • Vinyl ethers

List C - (Twelve Months) - Hazard Due to Peroxide Initiation of Polymerization*

  • Acrylonitrile
  • Butadiene
  • Chlorobutadiene (Chloroprene)
  • Chlorotrifluoroethylene
  • Dibenzocyclopentadiene
  • 9,10 Dihydroanthracene
  • Indene
  • Styrene
  • Tetrafluoroethylene
  • Vinyl acetate
  • Vinyl acetylene
  • Vinyl chloride
  • Vinyl pyridine

*When stored as a liquid, the peroxide-forming potential increases and certain of these monomers (especially butadiene ) chloroprene and tetrafluoroethylene) should then be considered as List A compounds.


  • Bis (2-chloroisopropyl) ether
  • Bis (2-ethoxyethyl) ether
  • Butyl-lithium
  • Cyclopentadiene
  • Ethylene Glycol Dimethyl Ether
  • Methyl Isobutyl Ketone
  • Methyl Lithium
  • Phenyl Lithium
  • Tetrafluoroethylene

2) How old is suspect materials?
  • Try to determine when material was purchased. The longer a chemical is stored, the better chance it has to form peroxides.

3) Check storage conditions.

  • Stored in sunlight - good promoter of peroxidation.
  • Stored in heated area (e.g. above room temperature) - good promoter of peroxidation.
  • Shape of container - Are they dented, in bad shape? - Could lead to peroxidation.
  • Are containers free from contamination? - Contamination by metals or metal oxides can help promote peroxidation.
  • Have containers been opened? - Containers that have been opened are more of a threat to form peroxide.
  • Is cap on container secure? - Unsecured cap can cause air to be let into container, could lead to peroxide formation. If compound is suspect, do not open, friction can cause enough shock to detonate the material.

4) Visual inspection of containers.

  • Increased or unusual viscosity.
  • Color changes.
  • Pale or brown crystal formation around rims or caps.
  • Do not shake bottles or cans upon inspection.

If any of the above problems are identified upon inspection, do not touch material, contact the Environmental Health and Safety Office for assistance.


1) Store in cool area.

2) Store away from direct sunlight.

3) Purchase materials only as needed.

4) Protect containers from physical damage.

5) Monitor with the use of log.

  • Purchase date
  • Opening date
  • Open only when needed, eliminate unnecessary opening. Do not expose to air unnecessarily.

6) Keep container tightly closed or stoppered.