Peroxide Forming Chemicals

Some common laboratory solvents oxidize to form unstable and potentially explosive organic peroxides.  The reaction can be initiated by exposure to air, heat, light, or contaminants. Most of these solvents are available with inhibitors to slow the peroxide formation. Examples of inhibitors include BHT (2,6-di-tert-butyl-4-methyl phenol) and Hydroquinone.  These chemicals are referred to as Peroxide Forming Chemicals and are categorized into classes by their ability to form peroxides:

1. Class A chemicals are those which form explosive levels of peroxides without concentration. Test these for peroxide formation before using and dispose within 3 months of opening.  Dispose of unopened containers within 12 months of purchase.  Class A chemicals form organic peroxides quickly, and are the most difficult to manage.  Alternative chemicals should be substituted whenever possible.

2. Class A (Solid) chemicals include Alkali Metal Amides such as Potassium Amide and Sodium Amide.  They are not true Peroxide Formers, but are highly reactive, combustible solids that form explosive nitrite and hyponitrite in the presence of oxygen.  Testing or inspecting these materials is not practical.  Dispose 1 year after opening or 2 years after purchase, whichever comes first.  Always store in a glove box under an inert atmosphere.

3. Class B chemicals form peroxides that are hazardous on concentration by distillation or evaporation. Test before distillation and every 6 months after opening.  Dispose of open containers if tested peroxide levels are above 10ppm.  Dispose after 18 months if unopened. Store in the dark in Amber bottles. 

3. Class C chemicals consist of monomers which form peroxides that can initiate explosive polymerization. Inhibited monomers should be tested before use and every 6 months after opening.  Dispose of open containers if tested peroxide levels are above 10ppm.  Dispose of unopened containers after 18 months. Uninhibited monomers should be disposed of 24 hours after opening.

3. Class D chemicals consist of other known or suspected Peroxide Formers.  They may form peroxides but cannot be clearly categorized in Class A, B, or C.  The speed of peroxide accumulation by these chemicals is not known.  Suggested storage periods are the same as for Class B.  The list of these chemicals is extensive, refer to the Time-Sensitive Chemicals Reference Sheet for the full list.

Labeling Peroxide Formers

Affix a Peroxide-Forming Chemical Label to each container when received and fill in the Date Received field.  Fill in the Date Opened field when the container is first used.  

Each time the container is tested for Peroxides, fill in a row on the label with:

1. Testing Date
2. Tester's Initials
3. Concentration of Peroxides Detected
4. The latest date that testing will be required again (within AT LEAST 6 months for Class B, C, or D compounds).  Test earlier if concentrating/evaporating and before any use of Class A compounds.  

Inspecting Peroxide Forming Chemical Containers

Peroxide crystals in a solvent container.

Before handling or testing a Peroxide Forming Chemical, always inspect the container first.  This is a careful visual inspection of the contents without moving or disturbing the container.  Shine a flashlight through dark or amber bottles to more easily see precipitates.  Look for any precipitation or crystal formation inside or around the cap of the container.  This could indicate that organic peroxides have accumulated to a dangerous extent.  DO NOT MOVE the container and contact OEHS immediately if you see any of the following: 

• Visible solid precipitate in the liquid
• Very fine, spun glass-wool appearance in the liquid
• Incrustation around the cap
• Layer separation (an oily viscous layer)
• Visible discoloration or Cloudiness
• Very old container (yellowed label or made by a manufacturer from many years ago)  

Testing for Peroxides

Peroxide Forming Chemicals must be tested for Peroxide levels prior to use and according to the required testing frequency listed above for their class.  Always conduct a visual inspection of the container before testing.  Record the test result on the container using a Peroxide Former Label.  

Use test strips with a range of detection of at least 0-100ppm.  OEHS recommends peroxide test strips such as MQuant Test Strips (Instructions).  Carefully read the instructions as the process is different for solvents than for aqueous solutions. 

MQuant test strips color guide.

If the tested concentration of peroxides is:

≤10ppm – Update the label with testing date and value.

>10ppm – Request pickup as waste within 2 weeks.  Include the peroxide test date and value in the request.

≥100ppm - DO NOT MOVE the container. Contact OEHS immediately.