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Organic peroxides & polymerization...

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Support and Safety Measures...

Introduction   |   Explosion & Fire Hazards   |   Contamination   |   Health Hazards   |   Precautions

Storage   |   Handling   |   Supervision & Maintenance   |   Fire Protection  |  Working of OP  |  FAQ


  1. Organic peroxides should be brought into the manufacturing area in the original shipping containers. Opened containers should not be returned to primary storage. Material that has not been used should not be returned to the original container. Containers of organic peroxides should be securely closed to prevent contamination when not in use. Opened containers of Dibenzoyl Peroxide containing water as a phlegmatizer such as hydrous Dibenzoyl Peroxide or many pastes and slurries must be promptly closed to prevent drying of the material which will result in a large increase in hazard.
  2. No secondary or loose storage of organic peroxides should be permitted in the manufacturing area. The material brought into this area should be limited to the requirements for immediate use. Organic peroxides should be removed from the manufacturing area and placed in the weighing and dispensing room each day at the close of business.
  3. Areas where organic peroxides are handled should be well ventilated and sprinklered. Appropriate protective clothing, such as rubber gloves, safety glasses, goggles or face shields should always be worn to avoid bodily contact from inadvertent splashing or spills.
  4. When organic peroxides are poured into mixing dispensing containers, care should be taken to provide clean and properly designed equipment. Copper, brass, mild steel or lead equipment is dangerous in contact with organic peroxides. Zinc and galvanized equipment can also cause accelerated decomposition of organic peroxides. The use of compatible type equipment with each organic peroxide is essential. (Consult the manufacturer or supplier of organic peroxides for recommended materials to be used.)
  5. Where it is necessary to slurry, mix, or dissolve organic peroxide in very small quantities of monomer (such as styrene) prior to incorporating the material into the resin mix, the peroxide should be added to the monomer and used promptly. These "small quantity" mixtures are polymerizable and they may develop considerable heat. This could be sufficient to boil the solvent monomer and cause it to ignite.
  6. Dilution of organic peroxides by users is not recommended. Notwithstanding the recommended practices, it is known that some composite producers do dilute MEK peroxide. In this instance, the following instructions should be followed: Be sure to consult with the peroxide manufacturer for compatible solvents. Use only high purity solvents. Never use contaminated solvents. Never use reclaimed solvents unless they have been specifically tested by the organic peroxide manufacturer. The use of an incompatible or contaminated solvent may cause a violent decomposition of the organic peroxide.
  7. The fire hazard of an organic peroxide can be drastically changed by the diluent employed. The fire hazard can be increased by using a low flash point solvent, such as ethyl acetate, or decreased by using a high flash point plasticizer such as dimethyl phthalate.
  8. Organic peroxides should not be used in pressurized vessels or confined unless adequate provisions have been made to relieve the sudden pressure that may develop if the peroxide is decomposed by heat or contamination. Organic peroxide may be released during venting and provisions should be made for the protection of personnel and the possibility of fire.
  9. Mechanical processing, e.g. "Spray Up" Equipment, should be given special consideration. Keep this equipment very clean and scrupulously avoid contaminating the organic peroxide when filling the dispensing containers. Protect dispensing containers from fire and all sources of heat. Pressurized dispensing containers should comply with item 8. Strictly observe dilution instructions (item 6). When testing, spray organic peroxide solutions into a container of water. Do not spray into the air, on resin overspray, etc. Wear protective eye equipment at all times.
  10. Organic peroxides should never be mixed directly with any accelerators or promoters, as violent decomposition or explosion may result. The accelerator should be thoroughly dispersed in the resin mixture before adding the peroxide catalyst.
  11. Organic peroxides should be kept away from all sources of ignition, such as open flames, electrical devices and heating equipment.
  12. All processing equipment should be properly grounded and inter-bonded. Non-sparking tools should be used for weighing the peroxides.
  13. Solid organic peroxides should not be subjected to any frictional or grinding operation.
  14. Organic peroxides should not be added to materials at temperatures exceeding safe tolerances for the particular peroxide.
  15. "No smoking" regulations should be strictly enforced in the organic peroxide storage and processing area . No matches, open lights or flame should be permitted in this area.


Additional Information:

Handling of organic peroxides

Organic peroxides must always be handled by skilled personal, wearing appropriate equipment: goggles, gloves, a face mask and a helmet should be worn whenever handling peroxides.
Peroxides are formulated to reduce risks. However, these safety formulations remain sensitive and must be handled with care.

Classification and labeling depend on product properties and are described in the safety data sheet according to the Directive 67/548/EEC and its amendments. The relevant symbols and Risk and Safety phrases are on the label.
In addition to this labeling (according to the European Directive), each package is also identified by the yellow N5.2 "Organic Peroxide" warning symbol.

Handling procedures should be set up to ensure that peroxides are protected from sources of heat such as hot ambient air, radiators, pipes, direct sunlight, sparks and flames. The recommended storage temperature should be observed at all times. Smoking must be strictly forbidden.

At the work place, only the minimum quantity of peroxide required for one operation should be stored. Return of unused organic peroxide to the original container is not allowed due to risk of contamination. The material must be disposed of.

Dispensing and weighing should be done in a specially designated area and should not be permitted in the storage area.

Spilled materials should be soaked up immediately on an inert absorbent such as Vermiculite or Perlite. The contaminated Vermiculite should be taken up by non sparking equipment and disposed of according to local regulations.
The place where the spillage occurred should then be cleaned with water containing a surfactant to guarantee that no traces of peroxide to be left.

Packaging is chosen in accordance with the characteristics of the organic peroxide. For transportation, only approved packaging material may be used; moreover, the maximum quantity of peroxide per packaging unit is given by transportation regulations.
When peroxides are transported or when they are stored during a long period, pressure can build up within the container due to a small amount of decomposition or volatility of a component in the peroxide formulation. Polyethylene is therefore the preferred packing material since it is relatively inert, is flexible enough to withstand normal pressure build-up.
Peroxides should not be kept in glass or metal vessels where a built up of pressure by decomposition cannot be noticed.
Organic peroxides must be kept in their original containers, as every contact with rust, ashes, dirt, accelerators, promotors and many chemicals can lead to a violent decomposition.

Storage regulations vary from one country to another and it is essential to check with local
authorities and insurance companies on specific regulations.
In most cases, the regulation (if one regulation exists) defines:

  • A classification group depending on the hazard involved (flammability, decomposition, burning, or explosive properties)
  • The requirements for the storage construction. These specific classifications are available on request (our peroxides are classified according to all existing European regulations).
    However, the following requirements must be applied in all cases. More specific information is given in your local regulation.

Basic Requirements
A peroxide storage facility should be:

  • Located away from the manufacturing area: the hazards linked to the storage of peroxides involve effects outside of the storage building and required safety distances. The minimum safety distances required by local regulations vary according to the countries.
  • Used exclusively for organic peroxides to avoid contamination.
  • Built with construction material according to local -regulations.
  • Equipped with specific electrical installations (explosion proof), heating and cooling systems.
  • Kept under controlled temperature conditions: the maximum storage temperature must not be exceeded and temperature alarms must be installed
  • Provided with vent relief system, fire protection equipment (water sprays, sprinklers, deluges).
  • Equipped with retaining basins to prevent accidental discharge to the environment.
  • Clearly identified as "peroxide storage" and marked outside "No smoking".


Recommendations to avoid accidents

What to do before delivery of a peroxide?

  • Check if the safety data sheet is available.
  • Read it carefully.
  • Check the required storage temperature.
  • Read the storage requirements.

What to do on arrival?

  • Check if the storage building is at the required temperature.
  • Mark each container with delivery date.
  • Check if the delivered product is at temperature below the required one. If not, the transportation was incorrect. If temperature of the product is above SADT, don't put in storage with other products.
  • Check carefully the packages to avoid leakage and spillage.

How to store the product safely?

  • Respect an air cooling circulation of ~ 5 cm between each package and ~ 30 cms with the walls.
  • Always verify that the door of the storage is closed.
  • Avoid leaving the door open during long periods.
  • Respect the amount allowed in storage.

If the refrigeration system fails
The failure is easy to detect in a well built storage (temperature alarm...) and the time before an accident is long enough to implement preventive measures: refrigeration back up, transfer in another storage.

How to dispose of the product?
Disposal must be accomplished in accordance with local regulations.
Small quantities of organic peroxides that are spilled or became contaminated, or any samples
no longer needed should be destroyed.
Spilled solid peroxides should be carefully swept together, collected into suitable labeled container, and destroyed.
Large quantities of organic peroxides must be handled and disposed of differently.
Peroxide formulation should be diluted in mineral oil or fuel oil to an active oxygen content of less than 1% and then be burnt in an incinerator. This must be done in accordance with the local legislation.

What can we do with the empty containers?
They have to be emptied completely and must also be transported as dangerous goods. Following local regulations, some answers may be given by your supplier.

Safe use and Handling of Organic peroxide initiator
1. Know the storage temperature and do not exceed it.
2. Know the SADT "Danger Temperature" and respect it.
3. Equip storage area properly.
4. Have fire extinguishers available.
5. Rotate inventory: "First In, First Out".
6. Take only the amount that will be used.
7. Do NOT return unused initiator to storage buildings.
8. Rinse and slash containers prior to disposal.
9. Immediately clean up spills and dispose of them properly.
10. Protect your eyes and skin.
11. Use appropriate Personal Protective Equipment (PPE).
12. Initiator in large vessels should be diluted.
13. Know your plant's emergency procedures.

Above all, when it comes to storing, handling and using organic peroxide initiators,
"Don't Lose Your Cool!"
For additional information consult the Material Safety Data

Toxicological and ecotoxilogical

Organic peroxides can generally be considered as having a moderate toxicity.

The main effects associated with contact with organic peroxides are local irritations, burns of the skin, and mucous membranes: of the eyes and of the respiratory tract.

Inhalation of the vapor of volatile peroxides also leads to irritation or burns of the mucous membranes of the eyes and the respiratory

Why use organic peroxides in Unsaturated polyester?

Unsaturated polyester is a family of thermosets with many uses such as in engine parts, covers, electrical terminal boxes, swimming pools, boats, tanks and so on.

Polyester resins are generally associated with fillers (Silica, CaCO3), glass fibers, glass fibers mats or fabrics acting mainly as a binder.

There are two main processes:

  • Cold process
  • Hot process (Sheet molding compound (SMC), Bulk molding compound (BMC))



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