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Safe handling of organic peroxides.

Organic peroxides are organic compounds having a double oxygen or peroxy (-O-O-) group in their chemical structure. There are many types of organic peroxides and peroxide formulations which are used by industries. It is important to note that organic peroxides differ widely in their relative hazard level depending on their composition. In some cases, diluents such as clay are added to the peroxide to lower the risk. Some organic peroxide products are manufactured to be used in elastomer curing operations. These materials thermally decompose and promote crosslinking in rubber and plastic compounds. They are predictively reactive and are very safe to use as long as they are stored and handled properly. They can represent a hazard, however, if they are stored or used improperly.

Shipping and storage regulations

There are shipping and storage regulations which apply to organic peroxides. In the United States, the Department of Transportation (DOT) has specific regulations concerning the size and type of package in which peroxides can be shipped. In general, these materials are considered hazardous and fall into classification 5.2 "organic peroxides" (not the "oxidizers" classification which is 5.1). The DOT has now adopted the United Nations (UN) system and shipment. The resulting requirements stipulate the container size, type and labeling which must be used for shipping organic peroxide products. Failure to follow the DOT requirements could result in accidents or very substantial fines.

In reviewing storage considerations for organic peroxides, it is best to refer to the National Fire Protection Association (NFPA) Code 43B entitled, "Code for the Storage of Organic Peroxide Formulations." This code was last revised in 1993 and serves as a standard for establishing and maintaining safe storage facilities for commercially available organic peroxides. A key provision of NFPA 43B is the classification system for peroxides. Remember the hazards of peroxide formulations vary widely. The NFPA 43B system establishes a class system which indicates the relative risk of each peroxide product. Peroxides are classified according to characteristics such as:

* Burning rate or flammability;

* Sensitivity to contamination or impact;

* Self-accelerating decomposition temperature;

* Rate and violence of decomposition or burning.

The classes of peroxides are defined as follows:

* Class I peroxides are these formulations that are capable of deflagration but not detonation. These materials can exhibit easily initiated, rapid explosive decomposition.

* Class II peroxides are formulations that bum very rapidly and present a severe reactivity hazard. These materials present severe fire hazards but decomposition is not as rapid or violent as Class I materials. * Class III peroxides are formulations which burn rapidly and present a moderate reactivity hazard. These materials will bum rapidly and liberate a lot of heat due to decomposition.

* Class IV peroxides are formulations that burn in the same manner as ordinary combustibles and that present a minimal reactivity hazard. These materials are less reactive than the Class I - III peroxides and present a fire hazard that is easily controlled.

* Class V peroxides are formulations that bum with less intensity than ordinary combustibles or do not sustain combustion and that present no reactivity hazard. NFPA 43B contains tables indicating the class of different peroxide formulations. It is important to know the hazard class of the peroxide so you can determine the relative risk.

Many of you use a 40% peroxide which is dispersed on clay or calcium carbonate (for example, Di-Cup or Vul-Cup 40 KE). These are Class V peroxides meaning they represent the lowest hazard class. As a matter of fact, their cardboard shipping containers bum faster than these peroxide/clay formulations. These materials are also considered as non-hazardous for DOT shipping purposes. Pure dicumyl peroxide (Di-Cup R) is a Class IV peroxide but again represents a relatively low hazard compared to other peroxides on the market.

NFPA 43B also contains the following information concerning peroxide storage:

* Basic peroxide storage requirements;

* Fire protection requirements;

* Storage quantity limitations for various classes of peroxides;

* Separation distance requirements between buildings and property lines and peroxide storage areas;

* Allowable storage heights and clearances for peroxides in storage;

* Storage area building design requirements.

If you are using organic peroxides. my recommendation is to refer to NFPA 43B and make sure you're in compliance with the storage requirements. This code is used by local fire departments and OSHA.

Fundamental safety considerations

There are a few fundamental things which must be controlled if organic peroxides are to be stored and handled safely. The primary concerns can be easily summarized:

* Avoid overheating the peroxide;

* Avoid peroxide contact with incompatible materials.

What we are trying to do by following these precautions is to avoid a decomposition of the peroxide which can self-accelerate and generate flammable gases or overpressure containers. Let's look at these two fundamental peroxide safety concerns individually.

Keep peroxides at a safe temperature

One thing that can quickly cause a serious safety problem with peroxides is to overheat the material. Peroxides will start to decompose at a rate which is dangerous when they are exposed to certain temperatures. These temperatures vary with each type of peroxide formulation. The self-accelerating decomposition temperature (SADT) is a value which can be referred to provide guidance in this area. This is the lowest temperature at which self-accelerating decomposition occurs when the peroxide is held at that temperature for seven days (in the shipping container). Obviously the peroxide formulations should be stored in your plant well below this temperature. Some of the very reactive peroxides require refrigerated storage. Peroxides used in the rubber industry are not this reactive. In some cases, peroxides should not be subjected to low/temperatures. The best thing to do is to follow the instructions outlined in the suppliers material safety data sheet and keep the peroxides at the required temperatures.

Avoid incompatible materials

The next area we want to talk about is avoiding peroxide contact with incompatible materials. Some incompatible materials can react with the peroxide and cause a decomposition hazard. This can occur for example, when the peroxide is mixed with the wrong material such as acids, catalysts, oxidizing or reducing agents. It can also occur if the peroxide is placed in the wrong type of container or stored in a tank made out of the wrong materials of construction. Every precaution should be made to separate peroxides from incompatible materials (both in storage and process areas). In addition, the supplier should be asked about the correct materials of construction for storage containers, tanks, pumps, piping and other devices which may contact the peroxide. Again, when the peroxides are dispersed on clay, the compatibility hazard is reduced.

In addition to avoiding high temperature and incompatible materials, peroxides should be stored in a manner that lowers the risk of overpressuring containers in the event of decomposition. This can include providing emergency venting on tanks and other containers.

Employee exposure/health concerns

Awareness and concern about the effects of employee exposure to chemicals is growing all the time. As with the burning and decomposition hazards, the toxicity of the various peroxide formulations on the market varies widely. In general, we recommend that employees limit their exposure to chemicals as much as possible. Since using some of the peroxide products may result in possible inhalation or skin and eye contact hazards, local controls or special personal protective equipment may be required.

OSHA hazard communication regulations require that all employees be thoroughly trained about the hazards of any materials they are working with. In the case of peroxides, this should include not only employee exposure concerns but also decomposition and fire hazards.

Fire hazards

We mentioned earlier that peroxides vary widely in their flammability and burning rate. Fire is a very dangerous enemy since the heat from a fire can cause decomposition of the peroxides. This can cause the fire to spread or could result in ignition of flammable gases which are formed in the decomposition reaction. Protecting peroxides from fire should be a prime concern. Remember that NFPA 43B spells out storage requirements that will prevent or control the effects of a fire. These requirements include use of sprinkler systems, separation of peroxides and quantity/distance restrictions.

In general, water is recommended to be used to control peroxide fires. An adequate water supply should be made available to allow for fighting fires involving peroxides. Water is the preferred extinguishing medium (as opposed to dry chemical, [CO.sub.2] or Halon) because the water will extinguish the fire and will provide cooling which decreases the rate of peroxide decomposition. Of course, the design of your peroxide storage and process areas should allow for retention of fire water runoff. This runoff should not be permitted to flow off-site into sewers or streams.

Environmental concerns

Peroxide spills or other releases into the environment can cause serious concerns. Spills of peroxides can create immediate fire or decomposition hazards (for example, if the peroxide accidentally contacts a hot surface). In addition, many of the peroxide formulations are considered hazardous wastes so proper cleanup of a spill is essential. Even disposal of empty containers must be done in accordance with federal and local environmental regulations. You should check with the supplier to see if the peroxide is considered a RCRA hazardous waste or is on any hazardous substance lists.

In general, spills of peroxides should be cleaned up based on the manufacturers recommendations. I would like to point out three things to watch out for, however.

* Always use clean, uncontaminated containers to place the spilled peroxide into.

* Don't put the spilled peroxide back into the original container.

* Avoid using "oil dry" or other absorbents that are acidic since the acidic component can sometimes cause the peroxide to decompose. Clean, dry sand or calcium carbonate are preferred adsorbents for liquid peroxide spills.

All of these general precautions are designed to eliminate the chance of a contaminant causing a peroxide decomposition. Again, it's important to have employees properly trained to respond to a spill. Proper protective equipment should be available and cleanup procedures should be established to deal with a spill of peroxide.

Summary

Organic peroxides have been used safely in rubber and plastic compounding operations for many years. Incidents have occurred, however, when peroxides were stored or handled improperly. Following a few fundamental rules of peroxide safety is all that's needed to use these materials safely.
COPYRIGHT 1995 Lippincott & Peto, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1995, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:Tech Service
Author:Berkey, Brian D.
Publication:Rubber World
Date:Sep 1, 1995
Words:1704
Previous Article:Huge growth potential for recycled rubber.
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