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How are organic peroxides hazardous?
The main hazard related to organic peroxides are their fire and explosion hazards. Organic peroxides may also be toxic or corrosive. Depending on the material, route of exposure (inhalation, eye or skin contact, or swallowing) and dose or amount of exposure, they could harm the body. Corrosive organic peroxides can also attack and destroy metals.
It is the double oxygen of the "peroxy" group that makes organic peroxides both useful and hazardous. The peroxy group is chemically unstable. It can easily decompose, giving off heat at a rate that increases as the temperature rises. Many organic peroxides give off flammable vapours when they decompose. These vapours can easily catch fire.
Most undiluted organic peroxides can catch fire easily and burn very rapidly and intensely. This is because they combine both fuel (carbon) and oxygen in the same compound. Some organic peroxides are dangerously reactive. They can decompose very rapidly or explosively if they are exposed to only slight heat, friction, mechanical shock or contamination with incompatible materials.
Organic peroxides can also be strong oxidizing agents. Combustible materials contaminated with most organic peroxides can catch fire very easily and burn very intensely (i.e., deflagrate). This means that the burn rate is very fast: it can vary from 1 m/sec to hundreds of metres per second. Also the combustion rate increases as the pressure increases and the combustion (or reaction) zone can travel through air or a gaseous medium faster than the speed of sound. However, the speed of combustion in a solid medium does not exceed the speed of sound.
This is one characteristic that distinguishes deflagration from detonation. We mention these two terms because they are used in classifying organic peroxide formulations (see next question). Deflagrations and detonations are similar chemical reactions except that in detonations the burn rate in a solid medium is faster than the speed of sound. This supersonic speed results in a shock wave being produced. They can transmit the shock wave at speeds of about 2,000 to 9,000 m/sec and is not dependent on the surrounding pressure. This is another difference between detonation and deflagration: deflagration rates increase as the pressure becomes greater.
Explosive decomposition is a rapid chemical reaction resulting in almost instantaneous release of energy. This term includes both deflagration and detonation.
Organic peroxides may also have a self accelerating decomposition temperature (SADT). SADT represents the lowest temperature in which that particular organic peroxide formulation in its commercial packaging will undergo self-accelerating decomposition (begin the chemical process that leads to explosion). The SADT value will vary with each organic peroxide formulation and the size and shape of its packaging. Storage requirements will generally be 10 to 20 degrees below the SADT.
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What is an example of an organic peroxide?
An example of an organic peroxide is methyl ethyl ketone peroxide (also known as 2-butanone peroxide, ethyl methyl ketone peroxide, or MEKP). It is used as a polymerization catalyst in the manufacture of polyester and acrylic resins and as a hardening agent for fiberglass reinforced plastics. It is a colourless liquid with a characteristic odour. It is considered a combustible liquid and vapour. There is an extreme risk of an explosion from exposure to shock, friction, flame, or other sources of ignition. It is dangerously reactive and may decompose violently. Contact with water or moist air liberates irritating gases. Contents may develop pressure if exposed to water. It is also very toxic. It may be fatal if inhaled, absorbed through the skin or swallowed and it is corrosive to the eyes, skin and respiratory tract. It may cause lung injury although the effects may be delayed.
