SafetyNet #23 - Peroxide Formation in Chemicals

There is a great deal of uncertainty regarding the hazards and safe handling of peroxidizable organic chemicals. No definitive data are available about the concentration at which these peroxides pose a hazard. Some common chemicals (e.g., isopropyl alcohol¹) are known to form potentially explosive concentrations of peroxides, but are rarely included as part of peroxide safety programs. Several common peroxide detection methods may not detect all types of unstable peroxides. Similarly, some common deperoxidation procedures may not remove all types of unstable peroxides. Recommended administrative controls (e.g., shelf life restrictions) vary widely. There are no specific Federal OSHA regulations that pertain to the handling of perxodizable organic chemicals, the various classes of peroxide formers, hazardous levels of peroxides, or methods for control, detection and removal of peroxides.

A wide variety of organic compounds spontaneously form peroxides by a free-radical reaction with molecular oxygen in a process of auto-peroxidation. Although ethers are the most notorious in this regard, many other moieties are susceptible to the same process. Table 1 lists these moieties, numbered 1 to 14 from most likely to least likely to form peroxides. 

Peroxides may explode when concentrated by evaporation or distillation, combined with compounds that create a detonable mixture, or when disturbed by heat, shock or friction.

To minimize the hazard of peroxide formation, meticulously observe the following safety guidelines:

• Any peroxidizable chemical with visible discoloration, crystallization, multiple layers, or liquid stratification should be treated as potentially explosive. Call EH&S at 530-752-1493 for immediate assistance.
  

• Label all containers of peroxide-forming chemicals with the date the chemical was received and the date the container was opened. The label shown below may be used for this purpose.
  
  

  WARNING-PEROXIDE FORMER This material will form explosive peroxides during storage and must not be kept for more than _____months after opening. Date Received_____________ Date Opened______________ Discard unopened container 12 months after receipt. Call EH&S at (530) 752-1493 for disposal. DO NOT USE IF OPENED MORE THAN ________MONTHS.

• Always store flammable materials that require reduced temperature storage in a refrigerator approved for flammable storage ("Lab-Safe"). However, refrigeration does not inhibit peroxide formation and may actually increase peroxide formation.
  
• Use or discard containers by the manufacturer's expiration date, if the expiration date is available. If there is no expiration date stamped on the container, discard according to the schedule in Tables 2, 3, and 4.
  
• Keep an inventory of peroxide-forming chemicals in the laboratory. NEVER purchase large containers of peroxide-forming chemicals if the quantity exceeds your actual need within the three- or twelve-month expiration period.
  
• Never distill potential peroxide-forming chemicals to dryness. Always leave a minimum of 20% still bottoms. When possible, adding a non-volatile organic compound (such as mineral oil) can dilute the peroxides remaining after distillation. When preparing to distill or evaporate compounds listed in the tables, always test for peroxides first, as described in reference 2.
  
• Never attempt to force open a rusted or stuck cap on a container of a peroxide-forming chemical.
  
• Never scrape or scrub glassware or containers that have been used with peroxide-forming compounds if you see an oily or crusty residue.

Listed in Table 2 are chemicals that form potentially explosive peroxides without concentration. These materials may spontaneously form peroxides that will make the materials shock- or heat-sensitive "on the shelf," that is, without any further concentration through evaporation or distillation. Table 2 chemicals have a 3-month storage limit. Store under nitrogen, if practical.

Table 2: Chemicals that form potentially explosive peroxides without concentration ^a

Listed in Table 3 are chemicals that form potentially explosive peroxides on concentration. These materials form peroxide levels that make the parent container shock sensitive only when the parent liquid is evaporated, which effectively concentrates the peroxides. This group of peroxidizable chemicals has a propensity for exploding when used experimentally in operations such as distillations. Very volatile materials in Table 3, such as diethyl ether, may evaporate if stored wthout a cap, and the resulting concentrated, peroxidized material may be shock sensitive. Test chemicals in Groups 1 through 7 on Table 1 within 12 months of receipt, and discard or deperoxidize, if necessary. Test chemicals in Groups 8 through 14 on Table 1 within 12 months of opening, and discard or deperoxidize if necessary. Alcohol/water solutions do not form high concentrations of peroxides.

Table 3: Chemicals that form potentially explosive peroxides on concentration ^a,d

Listed in Table 4 are chemicals that autopolymerize. These chemicals may autopolymerize (and thus explode) when relatively small quantities of peroxides are formed. Uninhibited chemicals to be stored for < 5 days. If inhibited, chemicals may be stored for 12 months. Avoid storing inhibited materials under inert gas as some inhibitors require a small amount of oxygen to work.

Table 4: Chemicals that autopolymerize ^a

Information is based on information contained in References 1 and 2.

References:

1. Hess, R.K. Brookhaven National Laboratory Chemical Safety Hazard Alert - Isopropanol Peroxides Result in Explosion & Injury, June 9, 19997.
   
2. Kelly, R. J. Journal of Chemical Health and Safety 1996, Sep/Oct, pp 28-36, "Review of Safety Guidelines for Peroxidizable Organic Chemicals"
   

For additional information, contact EH&S at 530-752-1493 or researchsafety@ucdavis.edu.

Reviewed/Revised. 05/2011
DMD