The heading of Class 5.2 covers organic peroxides and formulations of organic peroxides.

The substances of Class 5.2 are subdivided as follows:

P1 Organic peroxides, not requiring temperature control;

P2 Organic peroxides, requiring temperature control.


Organic peroxidesare organic substances which contain the bivalent -O-O- structure and may be considered derivatives of hydrogen peroxide, where one or both of the hydrogen atoms have been replaced by organic radicals.


Organic peroxides are liable to exothermic decomposition at normal or elevated temperatures. The decomposition can be initiated by heat, contact with impurities (e.g. acids, heavy-metal compounds, amines), friction or impact. The rate of decomposition increases with temperature and varies with the organic peroxide formulation. Decomposition may resultin the evolution of harmful, or flammable, gases or vapours. For certain organic peroxides the temperature shall be controlled during carriage. Some organic peroxides may decompose explosively, particularly if confined. This characteristic may be modifiedby the addition of diluents or by the use of appropriate packagings. Many organic peroxides burn vigorously. Contact of organic peroxides with the eyes is to be avoided. Some organic peroxides will cause serious injury to the cornea, even after brief contact, or will be corrosive to the skin.

NOTE:Test methods for determining the flammability of organic peroxides are set out in the Manual of Tests and Criteria, Part III, sub-section 32.4. Because organic peroxides may react vigorously when heated, it is recommended to determine their flash-point using small sample sizes such as described in ISO 3679:1983.


Any organic peroxide shall be considered for classification in Class 5.2 unless the organic peroxide formulation contains:

(a) Not more than 1.0% available oxygen from the organic peroxides when containing not morethan 1.0% hydrogen peroxide;

(b) Not more than 0.5% available oxygen from the organic peroxides when containing more than1.0% but not more than 7.0% hydrogen peroxide.

NOTE:The available oxygen content (%) of an organic peroxide formulation is given by the formula

16 × Σ(ni× ci/mi)


ni = number of peroxygen groups per molecule of organic peroxide i;

ci=concentration (mass %) of organic peroxide i; and

mi=molecular mass of organic peroxide i.

Organic peroxides are classified into seven types according to the degree of danger they present. The types of organic peroxide range from typeA, which is not accepted for carriage in the packaging in which it is tested, to typeG, which is not subject to the provisions of Class5.2. The classification of types B to F is directly related to the maximum quantity allowed in one package. The principles to be applied to the classification of substances not listed in are set out in the Manual of Tests and Criteria, Part II.

Organic peroxides which have already been classified and are already permitted for carriage in packagings are listed in, those already permitted for carriage in IBCs are listed in4.1.4.2, packing instruction IBC520 and those already permitted for carriage in tanks in accordance with Chapters 4.2 and 4.3 are listed in4.2.5.2, portable tank instruction T23. Each permitted substance listed is assigned to a generic entry of Table A of Chapter 3.2 (UN Nos. 3101 to 3120) and appropriate subsidiary hazardsand remarks providing relevant transport information are given.

These generic entries specify:

- the type (B to F) of organic peroxide (see above);

- physical state (liquid/solid); and

- temperature control (when required), see and

Mixtures of these formulations may be classified as the same type of organic peroxide as that of the most dangerous component and be carried under the  conditions of carriage given for this type. However, as two stable components can form a thermally less stable mixture, the self-accelerating
decomposition temperature (SADT) of the mixture shall be determined and, if necessary, the control and emergency temperatures derived from the SADT in accordance with 

Classification of organic peroxides not listed in, packing instruction IBC520 or, portable tank instruction T23, and assignment to a collective entry shall be made by the competent authority of the country of origin. The statement of approval shall contain the classification and the relevant conditions of carriage. If the country of origin is not a Contracting Party to ADR, the classification and conditions of carriage shall be recognized by the competent authority of the first country Contracting Party to ADR reached by the consignment.

Samples of organic peroxides or formulations of organic peroxides not listed in, for which a complete set of test results is not available and which are to be carried for further testing or evaluation, shall be assigned to one of the appropriate entries for organic peroxides type C provided the following conditions are met:

- the available data indicate that the sample would be no more dangerous than organic peroxides type B;

- the sample is packaged in accordance with packing method OP2 and the quantity per transport unit is limited to 10 kg;

- the available data indicate that the control temperature, if any, is sufficiently low to prevent any dangerous decomposition and sufficiently high to prevent any dangerous phase separation.

Desensitization of organic peroxides

In order to ensure safety during carriage, organic peroxides are in many cases desensitized by organic liquids or solids, inorganic solids or water. Where a percentage of a substance is stipulated, this refers to the percentage by mass, rounded to the nearest whole number. In general, desensitization shall be such that, in case of spillage, the organic peroxide will not concentrate to a dangerous extent.

Unless otherwise stated for the individual organic peroxide formulation, the following definition(s) shall apply to diluents used for desensitization:
- diluents type A are organic liquids which are compatible with the organic peroxide and which have a boiling point of not less than 150 °C. Type A diluents may be used for desensitizing all organic peroxides;

- diluents type B are organic liquids which are compatible with the organic peroxide and which have a boiling point of less than 150 °C but not less than 60 °C and a flash-point of not less than 5 °C. 

Type B diluents may be used for desensitization of all organic peroxides provided that the boiling point of the liquid is at least 60 °C higher than the SADT in a 50 kg package.

Diluents, other than type A or type B, may be added to organic peroxide formulations as listed in provided that they are compatible. However, replacement of all or part of a type A or type B diluent by another diluent with differing properties requires that the organic peroxide formulation be re-assessed in accordance with the normal acceptance procedure for Class 5.2.

Water may only be used for the desensitization of organic peroxides which are listed in or in the competent authority decision according to as being "with water" or "as a stable dispersion in water". Samples of organic peroxides or formulations of organic peroxides not listed in may also be desensitized with water provided the requirements of are met.

Organic and inorganic solids may be used for desensitization of organic peroxides provided that they are compatible. Compatible liquids and solids are those which have no detrimental influence on the thermal stability and hazard type of theorganic peroxide formulation.

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