Benzoyl Peroxide

Benzoyl Peroxide



BENZOYL PEROXIDE [molecular formula (C6H5CO)2O2] is an oxidizing, flammable, corrosive, toxic, irritating, white, granular crystalline solid that is tasteless and may or may not have an odor. It is an organic peroxide, and as such it is an extremely hazardous chemical, particularly in its pure, dry form. Since it is so hazardous when dry, it is usually shipped, handled and stored in a paste form with at least 33% water present.

It is a very powerful oxidizing agent, and all of its uses are because of this oxidizing power. It is used as a polymerization catalyst; a bleaching agent for fatty materials, flour, oils, and waxes; a dryer for oils; and is used in the manufacture of rubber, pharmaceuticals, and cosmetics.


Benzoyl peroxide is an organic peroxide, which means it has a self-accelerating decomposition temperature (SADT). This means that once a certain temperature is reached by the material, it begins to decompose. This decomposition, which is the breaking of covalent bonds, releases more energy, which increases the temperature of the material, which in turn accelerates the decomposition. T his cycle is very rapid, and once the SADT is reached, the resulting fire is very fierce and impossible to extinguish, since the peroxide portion of the molecule is supplying oxygen to support the combustion of the organic portion of the molecule. In essence, an organic peroxide contains all three legs of the Fire Triangle; that is, the fuel is the organic portion, the oxidizer is the peroxide portion, and the energy is the energy stored in the covalent bonds and released at the SADT. Benzoyl peroxide’s SADT is 176°F.

Benzoyl peroxide will begin to bum at 176°F or slightly higher and will burn very rapidly. It has a specific gravity of 1 33 and a molecular weight of 242. Technically, it has no melting point or boiling point because it will begin to react at temperatures far below what it would take to melt it. TTie decomposition reaction may be a fierce fire or an explosion.

It does not react with water, and is only slightly soluble in it. The pastes are made by mixing water with the product, or attaching water molecules to the peroxide molecule (a process called hydration). The presence of water greatly decreases the hazards normally associated with benzoyl peroxide.

Benzoyl peroxide is a very reactive material because of the peroxide structure. Fires are possible when the dry material comes into contact with any organic material, and explosions might occur if it is mixed with (or is in intimate contact with) ordinary combustible materials. The chemicals with which benzoyl peroxide may react is too long to list, and includes virtually everything that is easily oxidized (that is, anything that will burn).

The history’ of accidents involving benzoyl peroxide is long, and damages have been great. However, much to the credit of the manufacturers of this product and other organic peroxides, the safety record has been improved tremendously, and the safe use of the product has been extended to industries outside the polymerization industry. A rather novel use of a very dilute form of benzoyl peroxide has been as a treatment for acne. The oxidizing power of the peroxide safely oxidizes the oils and other organic material that are present w’ith acne, and in the vast majority of cases, will clear the skin. It is available in many over-the-counter preparations.


In addition to its powerful oxidizing nature, its combustibility, and its possible explosiveness, benzoyl peroxide is mildly corrosive, which makes it irritating to the eyes and skin. Prolonged or repeated contact will cause inflammation of the skin, or a skin rash. Inhalation of the dust will cause irritation of the airways, and may cause a slowing of the heartbeat and a lowering of body temperature.

Confusion and difficulty in breathing may also be a result of inhalation of the dust. At least one reference says that benzoyl peroxide is highly toxic by inhalation.

The Tl.V -TW A for benzoyl peroxide is S mg/m3 There is no reported STEL for this product.

Ingestion of small amounts has caused no reported systemic problems in humans, although laboratory animals have died after ingesting large amounts of benzoyl peroxide.

Dust that gets into the air would be extremely hazardous from an explosion and fire standpoint. Dust that contacts a hot surface or is contacted by sparks will almost certainly be raised above its SADT, producing a fire and possible explosion.

Many of the hazards of benzoyl peroxide and other organic peroxides have been lessened by the methods developed by manufacturers to compound the peroxides with water.


If the material spilled is in paste or liquid form, containment ponds may be constructed by using sand, soil, clay, or commercial sorbents. Containment pits may be dug to hold the material. Onee the product is contained, it may be removed by the consignee or a professional salvage firm, using equipment compatible with the product.

Care must be taken during salvage and any other operation at the incident site in case the paste or liquid dries out. leaving the pure product behind Contact by the dry material with any of the organic material in the soil at the bottom of the containment pond or sides of the containment pit, or with the diking material, could produce a fire.

The proper environmental authorities must be informed of any spill, and they will determine how much contaminated product and soil must be removed. They will also advise on disposal procedures. After the product has been salvaged, it may be necessary to keep any residual benzoyl peroxide wet with water to prevent a reaction from occurring. This is another reason for professional salvage/clean-up firms to handle site clean-up. They are properly educated, trained, and equipped to handle a cleanup at an incident site where the real danger does not begin until after the incident has apparently ended!



(Chemical Abstract Service)



(Registry of Toxic Effects of Chemical Substances)



(Chemical Hazard Response Information Systems)


NFPA 704 rating

(National Fire Protection Association)

1 -4-4-OXY


(Standard Transportation Commodity Code)

4919110 dry or wet with less than 30% water

4919113 technically pure or more than 52% with an inert solid

4919114 not more than 77% water

4919115 crystals, granules, or powder, wet with not less than 30% water

4919116 not more than 72% as a paste

4919117 not less than 30% but not more than 52% with inert solid

4919118 more than 77% but less than 95% with water


(International Maritime Organization)

5.2, organic peroxide

DOT placard

(U.S. Department of Transportation placard)

Yellow Organic Peroxide


(North American)



(United Nations)

I N2085 technically pure or more than 52% with inert solid

UN2086 more than 72% but less than 95% as a paste

UN2087 not more than 72% as a paste

UN2088 more than 77% but less than 95% with water

UN2089 not less than 30% but not more than 52% with an inert solid

UN2090 not more than 77% with water

UN3074 not more than 62%, with not less than 28% inert solid and not less than 10% water

If the product has been released in powder form, it will be necessary to keep the material from blowing around in the wind. This can be accomplished by covering the product with a sheet of compatible material such as polyethylene. It may be necessary to wet down the powder with water spray, being careful not to blow the powder around with the force of the spray.

Professional salvage firms are trained for when the real danger starts: after the incident has apparently ended.

Any deliberate wetting of the product could cause the spread of contamination by the product seeping into the soil, just as it could happen with the product in paste or liquid form. Foam should not be used unless recommended by the manufacturer of the benzoyl peroxide. Most foams are made by adding an organic material to water, and this organic material, if allowed to dry, could react with the peroxide.

For small amounts of paste, liquid, or whetted material, the product may be absorbed by using noncombustible absorbents such as perlite or vermiculite that have been wet with water. Absorbed material must be disposed of in accordance with federal, state, and local regulations. If the absorbed material and the materials onto which it has been absorbed are allowed to dry out, and if the dry benzoyl peroxide is allowed to contact organic material, a situation as hazardous as the original spill might develop.

Some emergency references recommend the use of neutralizing agents during the mitigation of an incident. One manufacturer of benzoyl peroxide recommends the use of hydrolysis (some may refer to it as neutralization because it reduces the product to a nonhazardous form). Both the dry and wetted forms may be safely hydrolyzed by treatment with approximately ten times its weight of a cold 5% (one reference advises using a 10%) solution of sodium hydroxide in water. The peroxide should be added gradually in small amounts with sufficient stirring to prevent settling or the formation of lumps. There will be a mild exothermic reaction if done in the correct manner, and the final product will be sodium benzoate dissolved in water. This procedure should be carried out by professionals and the final solution or slurry should be authorized for disposal by the proper environmental authorities.



benzoic acid




dibenzoyl peroxide






benzoyl superoxide



Dry and Clear



In any event, all tools or equipment that will be used in the containment, handling or salvage of benzoyl peroxide must be selected w ith compatibility in mind. Since benzoyl peroxide is so “touchy,” any friction caused by the tools could produce enough energy to reach the SADT and produce a violent fire. Also, a slower oxidation caused by the peroxide could cause severe corrosion of the tools and equipment. Make certain to avoid all chances of sparks, friction, or other sources of heat.

The material must be prevented from entering a sewer, stream, or waterway. Sewers frequently have large residues of organic material in them, and the intimate mixing of a paste or liquid form of the peroxide with the organic material, followed by a drying of the mixture, could produce explosions or underground fires all over town. It goes without saying that the spilled product should never be flushed or swept into a sewer in an effort to handle the incident quickly.

If the product does find its way into a waterway, it will sink slowly to the bottom, with some of the material dissolving. If the stream is very fast-moving, more and more of the product will dissolve. (Benzoyl peroxide may be only slightly soluble, hut with a large volume of moving water, there is more water to dissolve the product.) In any event, all downstream users must be notified immediately, especially industrial users. They will also be helpful in testing the level of contamination.

If the stream can be diverted into a holding area, there is a possibility that the undissolved product can be removed by dredging or pumping from the containment pond bottom into secure containers. The remaining water may be removed in the same fashion, or may be released back into the stream in small amounts that would be immediately diluted, and therefore safe. The soil contacted by the contaminated water may be contaminated itself to a level where it will also have to be removed and disposed of properly.

Small dams will hold back the movement of undissolved product, and should be constructed whenever possible. The best technique is to build a dam large enough to hold all contaminated water until the product is removed. However, it is highly unlikely that such a dam can be built quickly and safely.

Once the undissolved product has been removed from the water, activated charcoal may be used to adsorb the dissolved product. gently agitating and mixing the charcoal into the water. The charcoal may be removed by dredging or pumping, and it must then be disposed of properly. Adsorbents will hold the hazardous material on their surfaces, thus becoming hazardous in their own right.


If a large amount of benzoyl peroxide is exposed to flame or to the heat of a fire, evacuation of the area should be the first consideration. Evacuation distance depends upon the amount of peroxide exposed or in danger; however, safe distances should begin at 500 feet for quantities up to 500 pounds, and 2,500 feet for larger quantities.

Efforts to wet down exposed packages or containers of benzoyl peroxide and keep them cool should be done from as far away as the water can be accurately trained. If the packages are cardboard, they will soon disintegrate as they become wet and the contents will become exposed, threatening tinspread of the material. Therefore, runoff water must be contained.

If the product does begin to burn, efforts to extinguish may be fruitless because of the tremendous amounts of heat liberated and the internal supply of oxygen. Efforts should then be directed toward protecting exposures.


There are national and local codes governing the storage of all organic peroxides, established with the help of peroxide manufacturers. These codes should be consulted for local regulation. Generally, these codes call for the construction of a peroxide storage building, with the following specifications.

  • Peroxide storage buildings should be isolated from the main manufacturing location, and used only for the storage of organicperoxides.
  • Buildings should be of fireproof construction.
  • All electrical connections and fixtures should be wired with explosion-proof construction and wired in conduit. They should be located outside the building, including refrigeration equipment required to keep the interior temperatures low.
  • The proper warnings should be posted indicating peroxide storage, with no smoking or open flames allowed.
  • There must be no source of heat within the building, including solar energy through the windows, which should be painted black if they exist at all.
  • Only as much material as can be handled safely should be stored within the building, and only enough peroxide needed for immediate use should be transported to the manufacturing facility.

Some codes provide for some limited storage of peroxides within the manufacturing facility. Any storage areas inside this facility must be constructed according to code.


Protective clothing selected should keep the product from contact with the eyes, skin, and respiratory tract. This includes face shields, goggles, rubber gloves, aprons, boots, and any other articles of clothing that are impervious to benzoyl peroxide. The manufacturers of protective clothing recommend butyl rubber, neoprene, nitrile rubber, polyurethane, polyvinyl chloride (PVC), and Viton. Noncombustible clothing must be chosen, and care must be exercised to select clothing that will not generate static electricity. While walking and working around the spilled dry material, a static electricity discharge may be sufficient to cause a fire or explosion to occur.


A positive-pressure, self-contained breathing apparatus should be worn when exposed to high concentrations of benzoyl peroxide, or when fighting a fire involving the product. Wear the SCBA if the concentration of product is unknown. In lower concentrations, NIOSH-approved respirators or a high-efficiency particular filter respirator with a full facepiece may be worn, but conservatism should dictate the use of the SCBA at all times.


Victims must be moved to fresh air and kept warm and quiet. Artificial respiration should be administered if breathing stops or becomes difficult, knowing that such an action can expose the provider of first aid to the chemical in the victim’s lungs or vomit.

For skin contact, remove all contaminated clothing and wash affected areas of the body with copious amounts of soap and water. Medical attention will be required if irritation of the skin occurs.

For eye contact, the eyes must be flushed with water for a minimum of fifteen minutes, occasionally lifting the lids. Seek medical attention immediately.

For ingestion of benzoyl peroxide, large amounts of water must be administered, and the victim must be induced to vomit.


Absorbent—Any material that allows another substance to penetrate into its inner structure, thus allowing it to be “captured” and moved.

Adsorbent—Any material that has the ability to condense or hold molecules of other substances on its surface.

Catalyst—A material that speeds up or slows down a chemical reaction, but is not used up in that reaction.

Covalent bond—The sharing of two electrons between two atoms. It represents stored energy, which is released when the bond is broken.

Exothermic—A reaction in which heat is released.

Fire Triangle—A theory of fire that says whenever you have fuel, oxidizer, and sufficient energy present, a fire will occur.

Polymerization— A unique chemical reaction where a monomer (a very tiny reactive molecule) reacts with itself to form a “giant” molecule called a polymer.

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