The University of Iowa

Peroxide Formers

Purpose and Applicability

Peroxide forming chemicals are a class of compounds that have the ability to form shock-sensitive explosive peroxide crystals. To reduce this risk, EHS developed dating requirements, special handling information, and prudent safety practices for use of this chemical in research labs. While peroxide formers break down at different rates and some may have inhibitors, this guidance applies to all peroxide formers equally. The principal investigator (PI) or the lab manager is responsible for developing and implementing standard operating procedures (SOPs) for the purchase, storage, and safe handling of peroxide forming chemicals specific to the PI’s research.

The peroxide formation rate is dependent on the chemical and its exposure to oxygen, light, and time. Note: On a safety data sheet (SDS), peroxide formation falls under “Hazard not otherwise classified” (HNOC) as it is not a hazard defined by GHS guidelines; however, not all manufacturers will include this information on the SDS.

Peroxide formers can be split into 3 classes:

  • Class A peroxide formers can autoxidize, forming peroxides that can spontaneously decompose during storage or may explode even without being concentrated (e.g., concentration through evaporation or distillation). Take extra care to manage these materials because they may become hazardous even if never opened.
  • Class B peroxide formers can form explosive levels of peroxides, but typically require a means of concentration. Most of these are volatile enough that repeated opening of their container can allow for concentration of peroxides through evaporation.
  • Class C peroxide formers have the potential to form peroxide polymers. These chemicals may polymerize violently due to initiation by peroxide accumulation in solution and are extremely heat- and shock-sensitive. They are typically stored with polymerization inhibitors to prevent this from occurring.

Requirements for testing peroxide formation:

  • Unopened chemicals from manufacturer: 12 months after purchase or upon expiration date, whichever is sooner. Then as outlined for open containers below.
  • Opened chemicals:
    • Class A Chemicals: every 3 months
    • Class B Chemicals: every 6 months
    • Class C Chemicals: every 6 months

Examples for each class are listed below.

Class A

Butadiene Isopropyl ether Sodium amide
Chloroprene Potassium metal Vinylidene chloride
Divinyl ether Potassium amide  


Class B

Acetal Dicyclopentadiene Methyl acetylene
t-Butyl alcohol Diethylene glycol dimethyl ether Methyl cyclopentane
Cumene 1,4-dioxane Methyl isobutyl ketone
Cyclohexene Ethyl ether (diethyl ether) Tetrahydrofuran
Cyclooctene Ethylene glycol dimethyl ether Tetrahydronaphthalene
Diacetylene Furan Vinyl ethers


Class C

Acrylic acid Styrene Vinyl chloride
Acrylonitrile Tetrafluoroethylene Vinyl pyridine
Chlorotrifluoroethylene Vinyl acetate  
Methyl methacrylate Vinyl acetylene  


All labs should actively manage peroxide forming chemicals. Utilize the following practices:

  • Purchase chemicals in small quantities.
  • Date containers upon receipt.
  • Date containers when first opened.
  • Obtain peroxide test strips such as KI/starch, Aquafast, EM Quant, or Quantofix. They are available from most large chemical distributors, such as VWR, Fisher and Aldrich.
  • Test contents for peroxides as stated above.
  • Record test date and results on container.
  • Dispose of containers once chemicals start showing peroxide formation.
  • Containers must be disposed of before reaching 25 ppm peroxide. For containers above 25 ppm see Disposal Procedure for Improperly Managed Peroxide Forming Chemicals. 
  • Contact EHS for disposal.
  •  Do not open any container with evidence of peroxide formation such as obvious crystal formation around the lid or in the liquid, or visible discoloration.
  • Keep peroxide forming chemicals in their original containers to minimize conditions that accelerate peroxide formation.
  • Other precautions are similar to those used for flammables.

The PI or lab manger is responsible for the site specific and hands-on training for this chemical in their lab. Training should be directly documented in the researcher’s lab notebook. On each day of training, both trainer and trainee should sign the lab notebook.

Initially, researchers should perform the reactions with the PI or senior researcher present to observe the safe handling of this chemical. Review the chemical-specific safety data sheets (SDSs). Evaluate the hazards associated with the chemical reaction and experimental setup.