Peroxide forming chemicals are compounds that have the ability to form shock-sensitive explosive peroxide crystals.

To reduce this risk, EH&S has dating requirements and other guidelines. While peroxide formation rate varies dependent of the chemical, if it has inhibitors, and exposure to oxygen, light, and time, the EH&S guidelines apply to all peroxide formers equally.

Peroxide formers can be split into 3 classes:

• Class A peroxide formers can autoxidize and form explosive levels even in unopened containers and can form explosive levels of peroxides without concentration.
• Class B peroxide formers can form explosive levels of peroxides, but typically require concentration of some variety.  Most of these are volatile enough that repeated opening of their container can allow for evaporation thus forming enough concentration to form peroxides.
• Class C peroxide formers are not particularly hazardous, but decomposition can initiate explosive polymerization of the bulk monomer.

All three classes must be disposed of after 12 months from receipt, or 3 (Category A) or 6 (Category B/C) months after opening, whichever occurs first.

For the full list of peroxide formers, please refer to the Safety Fact Sheet.