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Peroxide Formation

Peroxide formation in common laboratory chemicals is caused by an autoxidation reaction.  The reaction can be initiated by light, heat, introduction of a contaminant, or the loss of an inhibitor.  Some chemicals have inhibitors such as BHT (2,6-di-tert-butyl-4-methyl phenol) hydroquinone and diphenylamine to slow peroxide formation. Most organic peroxide crystals are sensitive to heat, shock, or friction, and their accumulation in laboratory reagents has resulted in numerous explosions.   For this reason, it is important to identify and control chemicals that form potentially explosive peroxides. 

Peroxide-Forming Compounds

In general, the more volatile the compound, the greater its hazard, since the evaporation of the compound allows the peroxide to concentrate.  Peroxide accumulation is a balance between peroxide formation and degradation. Some common compounds that are known to form peroxides are listed in the following table.  NOTE: This is not an exhaustive list. Researchers must consult the MSDSs and other sources of information for the chemicals used in their work areas to determine their peroxide-forming potential. Group A are chemicals that spontaneously form peroxides on exposure to air without further concentration or evaporation.  These materials should be tested or disposed of within three months of opening (testing is discussed later in this section).  Group B lists chemicals that form peroxides only upon concentration by evaporation or distillation.  The materials in this list should be tested or disposed of within one year of opening their containers.  Group C is a representative list of monomers that form peroxides that may act as a catalyst, resulting in explosive polymerization.

Group A: Chemicals That Form Explosive Levels of Peroxides Without Concentration
(Safe Storage Time After Opening: 3 Months)


CAS Synonyms State Reference
Butadiene(1,3)                106-99-0 1,3-Butadiene G 4
Chloroprene (1,3) 126-99-8            2-Chloro-1,3- butadiene L 4
Divinyl acetylene 821-08-9 1,5-Hexadien- 3-yne L 5
Isopropyl ether 108-20-3 L 5
Tetrafluoroethylene 116-14-3 G 4
Vinyl ether        109-93-3 Divinyl ether L 5
Vinylidene chloride 75-35-4 1,1- Dichloroethylene L 5

Group B: Chemicals That Form Explosive Levels

of Peroxides on Concentration
(Safe Storage Time After Opening: 12 Months)


CAS Synonyms State Reference
Acetal              105-57-7 L 5
Acetaldehyde   75-07-0 L 4
Benzyl alcohol 100-51-6 L 4
2-Butanol 78-92-2 l 4
Cyclohexanol    108-93-0 l 4
Cyclohexene     110-83-8 l 5
2-Cyclohexen-1-ol 822-67-3 l 4
Cyclopentene   142-29-0 l 5
Decahydronaphthalene 91-17-8 l 4
Diacetylene 460-12-8 g 5
Dicyclopentadiene 77-73-6 l 5
Diethylene glycol dimethyl ether 111-96-6 Diglyme l 5
Dioxane 123-91-1 1,4-Dioxane l 5
Ethylene glycol dimethyl ether 110-71-4 Glyme l 5
Ethyl ether 60-29-7 Diethyl ether l 5
Furan 128-37-0 l 5
4-Heptanol 589-55-9 l 4
2-Hexanol 626-93-7 l 4
Isopropyl benzene 98-82-8 Cumene l 5
Methyl acetylene 74-99-7 Propyne g 5
3-Methyl-1-butanol 123-51-3 Isoamyl alcohol l 4
Methyl cyclopentane 96-37-7 l 5
Methyl isobutyl ketone 108-10-1 Methyl-i-butyl ketone l 5
4-Methyl-2-pentanol 108-11-2 l 4
2-Pentanol 6032-29-7 l 4
4-Penten-1-ol 821-09-0 l 4
1-Phenylethanol 98-85-1 alpha-Methyl-benzyl alcohol l 4
2-Phenylethanol 60-12-8 Phenethyl alcohol l 4
2-Propanol 67-63-0 Isopropanol l 6, 7
Tetrahydrofuran 109-99-9 l 5
Tetrahydronaphthalene 119-64-2 l 5

Group C: Chemicals That May Autopolymerize

 as a Result of Peroxide Accumulation
(Safe Storage Time After Opening:

Inhibited Chemicals, 12 Months;

Uninhibited Chemicals, 24 Hours)

Chemical CAS Synonyms State Reference
Acrylic acid(2) 79-10-7 l 5
Acrylonitrile(2)   107-13-1 l 5
Butadiene(1,3) 106-99-0 g 5
Buten-3-yne 689-97-4 Vinyl acetylene & Butenyne g 5
Chloroprene(1,3) 126-99-8 2-Chloro-1,3-butadiene l 5
Chlorotrifluoroethylene 79-38-9 g 5
Methyl methracrylate(2) 80-62-6 l 5
Styrene 100-42-5 l 5
Tetrafluoroethylene 116-14-3 g 5
Vinyl acetate 108-05-4 l 5
Vinyl chloride 75-01-4 Mono-chloroethylene g 5
Vinylidene chloride       75-35-4 1,1-Dichloroethylene l 5
2-Vinyl pyridine 100-69-6 l 5
4-Vinyl pyridine 100-43-6 l 5


    1. When stored as a liquid monomer.
    2. Although these form peroxides, no explosions involving these monomers have been reported.
    3. Also stored as a gas in gas cylinders.
    4. Kelly, R.J., Review of Safety Guidelines for Peroxidizable Organic Chemicals, Chemical Health and Safety, September/October, 1996.
    5. National Research Council, Prudent Practices in the Laboratory, Handling and Disposal of Chemicals; National Academy Press; Washington, D.C., 1999. 
    6. Clark, D.E., Peroxides and Peroxide-Forming Compounds, Chemical Health and Safety, September/October, 2001.
    7. This material is peroxidizable but not dangerous unless distilled or concentrated. Testing (see “Peroxide Testing Method”) is required only prior to distillation or concentration.

Control Measures

  • Work Leads are responsible for identifying peroxide forming compounds used in the work area.  Review sources such as MSDSs for specific compounds.  Table 1, Labels, MSDSs and other sources of hazard information (refer to the EH&S Chemical Safety Web Page) should be reviewed.  Also, use the Chemical Management System to electronically search the chemical inventory for peroxide formers in an area and/or for a specific owner. However, the Chemical Management System is based on the list in Table 1 and is not an exhaustive method of identifying peroxide-forming compounds.
  • A hazard assessment of these materials, their use and the controls in place must be conducted.  This should be done in conjunction with an EH&S Industrial Hygienist. Operations involving peroxide-forming chemicals may require an AHD.  Consult PUB-3000, Chapter 6, “Safe Work Authorizations” to make this determination.
  • The flag image Peroxide-Forming Chemical Appraisal Process flag image for Divisions is a guide for researchers to evaluate their chemicals.
  • The flag image Peroxide Former Evaluation Sheet flag image provides guidance to determine if a container is safe to open for testing. Testing is addressed later in this section.

Training and Information

  • Employees who either handle or who may be exposed to hazardous materials, including peroxide-forming chemicals, must complete Chemical Hygiene and Safety Training, EHS 348 (or 345 for Facilities personnel or 352 for summer students). 
  • All employees in the work area require training in the specific hazards and controls of the materials being handled. Area-specific training is a line management responsibility.  EH&S Industrial Hygienists are available to provide assistance.
  • flag image Consult the section entitled: Labels, for labeling requirements for primary and secondary containers. flag image  Additional labeling requirements are discussed below.
  • Entrances to work areas should be posted with a Caution Placard depicting area hazards and emergency contact information.

Substitution and Chemical Inventory Management

  • Identify and use safer chemical alternatives (e.g., chemicals that don’t form peroxide crystals).
  • Otherwise, procure chemicals that have a peroxide inhibitor added (e.g., BHT).
  • If a safer chemical can’t be used, limit what you buy or borrow what you need from a colleague in your group or contact the Chemical Management System coordinator to assist you in finding a source of the chemical at LBNL.
  • Conduct periodic cleanouts to prevent accumulating unneeded chemicals.
  • Procure and use the minimum amount of material required for the operation, or
  • Keep working quantities of chemicals to a minimum. Don’t stockpile chemicals. 
  • Enter these materials into the Chemical Management System (CMS).

Engineering Controls

  • A fume hood or other appropriate exhaust ventilation must be used when handling peroxide-forming chemicals in a manner that may produce an airborne hazard (such as fumes, gases, vapors, and mists).  This includes procedures such as transfer operations, preparation of mixtures, blending, sonification, spraying, heating, evaporation and distilling.
  • Place safety shields in front of reaction vessels, distillation columns and other apparatuses when fire, explosion or detonation may occur.
  • Leave at least 10% bottoms when distilling peroxide-forming chemicals.

Personal Protective Equipment (PPE)

Skin and eye contact shall be prevented. The following PPE should be worn when handling these materials.  Additional information may be found in the Personal Protective Equipment Section:

  • At a minimum, safety glasses with side shields, laboratory coats (coveralls are acceptable in shop settings) and closed- toe shoes will be worn when handling these materials. This is to be considered as minimum protection and must be upgraded if necessary.
  • Additional PPE such as chemical goggles, face shields, chemical aprons, disposable coveralls, chemically resistant gloves and respiratory protection must be worn if there is a greater chance of chemical exposure. An EH&S Industrial Hygienist may be contacted for assistance in selecting appropriate gloves and respiratory protection. The use of respiratory protection requires an industrial hygiene hazard evaluation and a medical clearance followed by a fit test and training by the Industrial Hygiene Group.
  • Consult “Eye and Face Protection” in the Personal Protective Equipment Section for guidance on the selection, uses, and limitations of safety glasses, chemical goggles, and face shields.
  • Since many chemicals are skin-absorbers (i.e. agents that readily pass through the skin) it is important to select gloves that are chemically resistant to the material.  Consult the PPE section.  This contains a list of skin-absorbing agents and provides detailed guidance for selecting chemically resistant gloves.
  • Gloves must be selected on the basis of their chemical resistance to the material(s) being handled, their suitability for the procedures being conducted, and their resistance to wear as well as temperature extremes. Improper selection may result in glove degradation, permeation of the chemical through the glove and ultimately personal exposure to the chemical.  This is a potentially serious situation.  Consult “Gloves” in the Personal Protective Equipment Section for guidance on the selection, uses, limitations, and disposal of chemically resistant gloves.  An EH&S Industrial Hygienist may also be contacted for assistance in selecting appropriate gloves.


flag image Consult the section entitled Storage Guidelines for hazardous materials storage requirements, recommendations and information on chemical incompatibility.  Additional requirements are provided below.

  • Follow the storage guidelines in Control Procedures for Flammable and Combustible Liquids if the material is either flammable or combustible.
  • Store peroxide-forming chemicals in sealed, air-impermeable containers.  Dark amber glass containers with tight-fitting caps are required.  Do not use containers with loose-fitting lids or glass stoppers.  These may allow the introduction of air and result in peroxide formation.
  • Label and test containers of peroxide formers in accordance with the details provided in the sections entitled: Peroxide Testing Method and Labeling.

Safe Storage Times

    • Table I provides safe storage times and peroxide- testing frequencies (see above). 
    • Peroxide-forming compounds may be safely stored for the indicated time periods.  Storage for longer periods of time is allowable provided that testing is conducted at the indicated frequencies and that the results are within acceptable limits (see Peroxide Testing Method below). 
    • Containers of unknown age or history, as well as those that have exceeded their shelf lives and that have no evidence of testing should not be opened or disturbed. Contact the Industrial Hygienist supporting your Division for guidance.

Peroxide Testing Method

flag image Testing and labeling (see below) are necessary to ensure the container can be safely handled.  Testing frequency intervals are the same length as the indicated storage times.

  • The testing method used at LBNL is the EMQuant® Peroxide Test Strip, 0-100 mg/l, or Baker Test Strips for Peroxides 0-100 mg/l.  These are available via the Lab's Procurement website. (Note: the units: "mg/l" and "ppm" are equivalent in solution concentrations). These test strips contain the enzyme peroxidase, which transfers oxygen from the peroxide to an organic redox indicator, which is then converted to a blue oxidation product.  Follow manufacturer’s instructions for testing and interpreting results.
  • The Peroxide-Forming Chemical Appraisal Process for Divisions is a guide for researchers to evaluate their chemicals.
  • The Peroxide-Former Evaluation Sheet provides guidance to determine if a container is safe to open for testing.
  • Although it has not been conclusively determined what concentration of peroxide is safe, the following rules should provide a reasonable margin of safety.
    • If the peroxide concentration is greater than 25 ppm, but less than 100 ppm, the chemical may be used, but DO NOT DISTILL OR CONCENTRATE.
    • If the peroxide concentration is greater than or equal to 100 ppm, it should be disposed of as hazardous waste (see next section).
  • Contact your Division industrial hygienist if you have any doubt about the safety of opening and testing a container. flag image


If a peroxide-forming compound has been stored either beyond its useful shelf life, or if its age or history can not be determined, it must be considered unsafe and should be disposed of as hazardous waste.  Submit a Hazardous Waste Disposal Requisition Form to the EH&S Waste Management Group.  Write “Peroxide-forming Compound” on the form to alert EH&S Waste Management Group to the potential hazard.  Contact the Industrial Hygienist supporting your Division if you have questions regarding safety.  Waste disposal questions should be addressed to the EH&S Waste Management Group.


  • All materials listed in Table 1, as well as any other suspect peroxide former, should be dated when the container is received and when the container is first opened.   A label for this purpose is available from the industrial hygienist who supports your Division.
  • The chemicals will be tested or disposed of according to the frequencies listed in Table 1.

Consult the section entitled: Labels, for labeling requirements for primary and secondary containers.

Post the area entrance with a Caution Placard depicting hazards and emergency contact information.

Emergency Procedures

  • Consult the “Emergency Procedures and Equipment” section for emergency actions regarding chemical spill and personal exposure to chemicals.
  • In addition to these requirements, the following applies to spills of peroxide-forming compounds:
    • Do not attempt to clean up peroxide former spills if there is any indication that these actions could initiate a detonation.
    • Never use combustible or reactive materials (such as paper towels) to clean up or absorb spills of peroxide formers.  Keep an adequate number of appropriate spill kits to meet anticipated needs. These are commercially available through VWR Scientific.  Typically, products containing diatomaceous earth are used for absorbing organic solvents.
    • An emergency eyewash and safety shower should be located in all areas where laser dye and solvents are used. In the event of skin or eye contact, flush the affected area for at least 15 minutes and report to Health Services for evaluation and treatment.

Last updated: 11/18/2011