Environmental Health & Safety
Peroxide Forming Chemicals
Safe Handling of Peroxidizable Chemicals
A wide variety of organic compounds spontaneously form peroxides by a free radical reaction of the hydrocarbon with molecular oxygen. Under normal storage conditions peroxides can accumulate in the chemical container and may explode when subjected to heat, friction or mechanical shock. The danger is increased when a peroxide forming chemical is concentrated by distillation or evaporation. Peroxides tend to explode violently and are capable of causing serious injury or death to researchers in the laboratory. It is imperative that all researchers learn to recognize and safely handle peroxidizable chemicals. Use of any peroxide forming chemical requires a SOP, reviewed by EH&S and approved by your PI. If the lab does not have an existing SOP that covers your process please contact EH&S, prior to use, for assistance in developing a process-specific SOP.
Recognition of Chemicals Prone to Peroxide Formation
The first step in learning how to handle peroxidizable chemicals safely is to learn how to recognize materials which are prone to hazardous peroxide formation. Although ethers are the most notorious
peroxide formers, other peroxidizable organic materials include acetals, certain allyic alkenes (olefins), chloro- and fluoroalkenes, dienes, aldehydes, amides, lactams, ureas, some alkylarenes, ketones, vinyl monomers, and some alcohols. A more extensive list of peroxidizable chemicals is available here.
Classes of Peroxide Formers
Different peroxidizable chemicals tend to form dangerous levels of peroxides at varying rates and under different conditions. For some materials the concentration of peroxide reaches dangerous, shock sensitive levels, without concentration. Other compounds do not usually accumulate potentially explosive concentrations of peroxides unless the volatile organic material is reduced in volume--i.e. through incidental evaporation or distillation.
Peroxide forming compounds fall under one of four classes.
Class A - Chemicals that form explosive levels of peroxides without concentration. These are the most hazardous and can form explosive peroxide levels even if not opened.
Discard after 3 months of receiving the chemicals. Do not test if suspected (e.g., from visual evidence) or known to contain peroxides.
Class B - Chemicals that form explosive levels of peroxides after concentration.
Test for peroxide formation monthly after opening and reduce peroxides if present after 12 months. Test prior to discarding.
Class C - Chemicals that may autopolymerize as a result of peroxide formation. These materials are typically stored with polymerization inhibitors to prevent the polymerization reactions.
For inhibited chemicals: Test for peroxide formation after opening and reduce peroxides if present after 12 months. Test peroxide levels prior to discarding. Uninhibited chemicals should be disposed after 24 hours. Do not store inhibited chemicals under inert atmosphere.
Class D - Chemicals that may form peroxides but cannot be clearly placed in Class A-C. Test peroxide levels quarterly.
Testing for Peroxides
There is a great deal of uncertainty regarding the concentration at which peroxides pose a hazard to researchers. It is important to note that peroxide concentrations greater than 20 ppm is considered explosive and poses issues with Hazardous waste vendors will not pick up containers with 20 ppm peroxide concentration.
There are several methods that are commonly used to detect peroxides in the laboratory. Peroxide test strips provide a simple and convenient mechanism for detection, they are available from several suppliers. For volatile organic chemicals the test strip is immersed in the chemical for 1 second, then the tester breathes slowly on the strip for 15-30 seconds or until the color stabilizes. Test strip color is compared with a colormetric scale provided on the test kit bottle. Strips that offer a 1-100 PPM peroxide range are useful for determining if the material is below the control point of 100 PPM. Other testing methods are available, see manufacturer, SOP, or contact EH&S (479-5742) for more information.
Before the end of the storage date for a particular peroxide forming chemical the person using the chemical should either test and dispose of it or test it monthly for peroxide content. Any container found to have a peroxide concentration greater than or equal to 100 PPM should be disposed of (contact EH&S, 479-5742, for assistance). Materials which are older than the suggested shelf life but have been tested and have no detectable peroxides or peroxide concentrations less than 100 PPM may be retained. However, these materials should be tested at frequent (monthly or quarterly) intervals and peroxides reduced (neutralized) prior to any distillation or heating.
All chemicals which are to be distilled must be tested prior to distillation regardless of age. Important note - researchers should never test containers of unknown age or origin. Older containers are far more likely to have concentrated peroxides or peroxide crystallization in the cap threads and therefore can present a serious hazard when opened for testing. Please read section below on managing older containers.
Minimizing the Hazards of Peroxidizable Compounds
Researchers who handle peroxidizable compounds must learn to handle these materials safely. Safe handling practices and procedures involve making effective purchasing decisions, implementing a storage control program, periodic testing for peroxides, and proper disposal of hazardous containers. The elements of safe practices and procedures are described below.
Storage and Shelf Life
Peroxides tend to form in materials as a function of age and exposure to oxygen. Therefore, it is imperative that researchers are keenly aware of the age and handling of their peroxidizable chemicals. Researchers must date each container of peroxidizable chemical upon arrival in the laboratory; containers must be dated again when opened for the first time. Testing dates should be noted on the label or other documentation sheet easily communicating the hazards of the chemical to the researchers that may be using it. Special labels make dating of the containers convenient, and are available from EH&S, 479-5742.
Peroxide forming chemicals should be stored in the original manufacturer container whenever possible. Peroxidizable chemicals should be stored in sealed, air-impermeable, containers and should be kept away from light (light can initiate peroxide formation). A dark amber glass bottle with a tight fitting cap is generally appropriate.
The following table lists the suggested time table for testing of peroxides and different classes of peroxidizable compounds. Suggested time limits are given for testing of these compounds, However, it must be noted that these shelf life durations are minimum criteria, and we recommend more frequent testing for peroxides.
Peroxidizable Chemical Classification | |
|---|---|
Unopened chemicals from the manufacturer | |
Class A | |
Class B | |
Class C | (Uninhibited) 24 hours |
Class C | (Inhibited) 12 months |
Class D | |