An organic peroxide is any organic (carbon-containing) compound having two oxygen atoms joined together (-O-O-). This chemical group is called a “peroxy” group. Organic peroxides can be severe fire and explosion hazards. Containers need to be protected from impact or other physical damage, when storing, transferring or using them.
Never use combustible pallets, such as wood, for storing organic peroxide containers. Some liquid organic peroxides, such as methyl ethyl ketone peroxide, gradually decompose resulting in off gassing.
These peroxides should always be shipped in containers with specially vented caps. These caps relieve the normal buildup of gas pressure that could shatter an unvented container. Therefore it is important that these vent caps are checked regularly to ensure that they are working properly. Also, vented containers need to be maintained (stored) in an upright position and should NEVER have another container (box, bottle, etc.) stacked on top of it (as this could interfere with the caps’ venting ability).
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.
In general, organic peroxides should be stored:
· In well ventilated areas.
· Out of direct sunlight and away from steam pipes, boilers or other heat sources.
· At temperature as recommended by manufacturer/supplier. Always keep the storage area within the recommended temperature range.
· Supplied with adequate firefighting equipment, including sprinklers.
· Supplied with suitable spill clean-up equipment and materials.
· Free of ignition sources such as open flames, hot surfaces, burning tobacco and spark-producing tools and devices.
· Accessible at all times.
· Labelled with suitable warning signs. Because peroxides are corrosive, appropriate (impervious) gloves should always be worn. This includes proper outer clothing (coveralls or aprons) and goggles or a full face shield. Because of their ability to splash, regular safety glasses (even with side shields) are generally not appropriate for handling peroxides. The specific material for gloves and coveralls needs to be prescribed by a S&H professional as peroxides are a complex group where not every type of glove (i.e nitrile, neoprene, etc) would be appropriate.
If the occupational exposure limits for airborne/inhalation exposures, such as OSHA/OH&S PELs and ACGIH TLVs, are assessed to be approached or exceeded, and engineering controls are not feasible, respiratory protection needs to be considered. Once again, it is important that a S&H professional assess the specific scenario where peroxides may be encountered so that the most appropriate respiratory protection can be selected. It is typical to use a self-contained breathing apparatus with a full face-piece operated in the pressure demand (or other positive pressure mode) or a supplied air respirator. Many times, a typical air purifying respirator would not ensure workers are properly protected.
Be aware of lower limits of safe storage as well. Some peroxides have temperature below which storage can be hazardous. For example, acetyl peroxide, which is very shock-sensitive, is usually sold as a 25 percent solution in dimethyl phthalate to make it less sensitive. At temperatures below about -8°C (17°F), pure crystals of shock-sensitive acetyl peroxide form in the solution. Do not store organic peroxides which are diluted with water at temperatures below 0°C (32°F) to avoid separating out the pure organic peroxide.
Organic peroxides can also be strong oxidizing agents. Combustible materials contaminated with most organic peroxides can catch fire very easily, even spontaneously, and burn very intensely. Extinguishing organic peroxide-fed fires is extremely difficult since the chemical provides the necessary oxygen to support combustion.
Organic peroxide decomposition can also be initiated by chemical contaminants, particularly oxidizing and reducing agents, metal salts, and strong mineral acids. Heavy metals and alloys are another contaminant of concern. While the main hazards related to organic peroxides are their fire and explosion hazards, they 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 can harm the body. Corrosive organic peroxides can also attack and destroy metals.
Organic peroxides are available as solids (usually fine powders), liquids, or pastes. Some materials, such as water, odorless mineral spirits, and some phthalate esters are stable when mixed with organic peroxides and are often used to dilute them. Diluted mixtures or formulations are less likely to explode when exposed to heat or physical shock than undiluted organic peroxide formulations.