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Peroxide Forming Chemicals

Peroxide forming chemicals (PFCs) are commonly used in research laboratories but can present a significant fire and explosion hazard if not properly managed. These chemicals react slowly with oxygen in the air to form organic peroxides, which are shock-, heat-, and friction-sensitive compounds that may detonate during routine handling, storage, distillation, or disposal. Common laboratory solvents such as tetrahydrofuran (THF), diethyl ether, and 1,4-dioxane are examples of peroxide forming chemicals.

Because peroxide formation can occur even in unopened containers and may not be immediately visible, proper labeling, storage, testing, and disposal are critical components for maintaining a safe workspace. This guidance should be used in conjunction with the chemical's Safety Data Sheet (SDS) and laboratory-specific procedures.

What is a Peroxide Forming Chemical (PFC)?


A peroxide forming chemical is a compound that can undergo slow oxidation when exposed to air, producing unstable peroxide compounds. The peroxide bond (O-O) is inherently unstable and may decompose violently when exposed to heat, friction, impact, or concentration through evaporation or distillation.

Signs of peroxide formation may include:

  • Crystals around the cap, lid threads, or inside the container
  • Visible precipitates
  • Cloudiness or discoloration
  • Viscous or oily layers
  • Bulging or deformed containers

Do not open, move, or handle any container exhibiting the above signs. Contact EHS immediately.

Classes of Peroxide Forming Chemicals

Peroxide forming chemicals (PFCs) are divided into four classes (A-D). A list of peroxide formers can be found in Appendix J.  

All peroxide forming chemicals must be routinely tested every 6 months after opening. Dispose of by the expiration date or after 12 months unless testing indicates no peroxides present. 

Class A: Severe Peroxide Hazard 

Spontaneously decompose and become explosive with exposure to air without concentration. These are the most hazardous and can form explosive peroxide levels even if not opened. 

Class B: Concentration Hazard Chemicals 

Form explosive levels of peroxides after concentration. Require external energy for spontaneous decomposition. Form explosive peroxides when distilled, evaporated or otherwise concentrated. 

Class C: Shock and Heat Sensitive 

Highly reactive and can auto-polymerize as a result of internal peroxide accumulation. The peroxides formed in these reactions are extremely shock- and heat-sensitive. These materials are typically stored with polymerization inhibitors to prevent the polymerization reactions.   

Class D: Miscellaneous Peroxide Hazard Chemicals  

May form peroxides but cannot clearly be placed in Classes A through C. 

Testing for Peroxides

All peroxide forming chemicals must be tested for peroxides at least every six (6) months after opening. Test results must be documented and retained with the container.  Peroxide test strips an be purchased through the Chemistry Stockroom or an outside vendor.  Always follow manufacturer instructions when performing peroxide tests. 

When to Test

Peroxide testing should be conducted every 6 months after opening and prior to distillation, evaporation, purification, or concentration of the chemical.  When disposing of a PFC through the EHS hazardous waste stream, a peroxide test must be performed and documented on the bottle prior to pickup. 

Do NOT Test If:

  • Crystals are present
  • A precipitate, crust, or unusual discoloration is observed
  • The container is bulging or damaged
  • The cap appears stuck or difficult to remove

In the above situations, contact EHS immediately.

Handling and Storage Guidelines

Purchasing

Purchase only the quantity needed for near-term research activities. Avoid stockpiling peroxide forming chemicals. Always purchase materials containing inhibitors or stabilizers such as butylated hydroxytoluene (BHT).  Never purchase expired peroxide formers at a discounted price. 

Labeling


All peroxide-forming chemical containers must be labeled with date received, date opened, date of most recent peroxide test, and applicable test result. Proper labeling is essential for tracking testing and disposal timelines.


Storage

Store in original containers whenever possible. Keep containers tightly closed and air-tight. Store away from heat and direct sunlight. Segregate from incompatible materials. Protect containers from physical damage. Maintain good inventory control and routinely inspect containers for signs of peroxide formation.

Use

Perform procedures involving PFCs in a chemical fume hood when appropriate. Wear appropriate personal protective equipment (PPE), including safety glasses, lab coat, and suitable gloves. Exercise extreme caution during distillation, evaporation, or concentration procedures. Never distill peroxide-forming solvents to dryness. Always leave a residual volume in the flask.

Guidelines

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