Oxidizing agents represent a significant hazard in the laboratory due to their capacity to undergo violent reactions when they come into contact with reducing agents, causing ignition in flammable and combustible materials. Oxidizers can also increase the intensity of a small fire, making safe storage a key consideration in the lab. In addition to the risk of fire, oxidizers may release toxic gases either by reacting with other chemicals, or through decomposition caused by heating. Oxidizers on their own can also have corrosive properties.
Oxidizers may be found in both solid and liquid form. Solid oxidizing agents such as metallic chlorates, perchlorates, nitrates, chromates and permanganates may form explosive mixtures with oxidizable dusts and other suspended particles (e.g. flour, coal dust, magnesium powder, zinc dust, carbon powder).
Liquid oxidizers include nitric acid, chromic acid and sulphuric acid. In addition to being oxidizers, these are also corrosive chemicals. One of the most hazardous liquid oxidizers is perchloric acid, and should be avoided if possible. If perchloric acid must be used, workers must be trained in safe handling procedures and a perchloric acid fume hood designed and constructed for this purpose must be used.
Although inorganic peroxides can be hazardous, they are generally stable. However, they may generate peroxides in the presence of organic compounds, or can react violently in the presence of water. More hazardous are organic peroxides, which will be discussed in detail below.
Organic peroxides are carbon-based chemicals that contain the characteristic peroxide (-O-O-) bond. Many organic peroxides are shock, heat, or friction sensitive. The inadvertent production or concentration of organic peroxides have been the cause of many well-documented accidents. Safe handling and storage procedures for hazardous chemicals must be followed when dealing with organic peroxides.
Peroxide formers are compounds that may react with oxygen, even in low concentrations and temperatures often not considered as hazardous. Peroxidation is a hazard affecting primarily liquid peroxide formers, and solids that are finely divided.
The risk of peroxide formation exists when the compound is exposed to oxygen. This occurs when containers are not properly sealed. Peroxidation occurs more rapidly at elevated temperature and pressure. Blanketing peroxide formers with an inert gas reduces the opportunity for oxygen to reach the compound during storage. Become familiar with the known peroxide formers and classes in the tables below.
Follow these precautions for storing and handling peroxide formers:
Moieties that may form Peroxides
|Ethers and Acetals with alpha Hydrogen||Dienes|
|Alkenes with alyllic Hydrogen||Vinylalkynes with alpha Hydrogen|
|Fluoro or Chloroalkenes||Alkylalkyenes with alpha Hydrogen|
|Vinyl halides, esters or ethers|
|Class A||Class B||Class C|
|Chemicals that form explosive levels of peroxides without concentration||Chemicals that form explosive levels of peroxides on concentration||Chemicals that may autopolymerize as result of peroxide accumulation|
|3 months maximum storage||12 months maximum storage||Uninhibited
chemicals - 24 hours maximum storage
Inhibited chemicals - 12 months maximum storage
Diethylene glycol dimethyl ether Dioxanes
Ethylene glycol dimethyl ether 4-Heptanol
Methyl isobutyl ketone
Other secondary alcohols
stored as a liquid monomer.
b. Although these chemicals form peroxides, no explosion involving these monomers has been reported.
c. When stored in liquid form, these chemicals form explosive levels of peroxides without concentration. They may also be stored as a gas in a cylinder. When stored as a gas, these chemicals may auto polymerize as a result of peroxide accumulation.
Kelly, Richard J. . U.S. Department of Energ, Lawrence Livermore National Laboratory.
American Chemical Society. Safety in Academic Chemistry Laboratories.