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 peroxides are 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considered derivatives of hydrogen peroxide, where one or both of the hydrogen atoms have been
replaced by organic radicals.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 result in 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 modified by 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
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
(a) Not more than 1.0% available oxygen from the organic peroxides when containing not more
than 1.0% hydrogen peroxide;
(b) Not more than 0.5% available oxygen from the organic peroxides when containing more than
1.0% but not more than 7.0% hydrogen peroxide.
NOTE: The available oxygen content (%) of an organic peroxide formulation is given by the formula
Organic peroxides are classified into seven types according to the degree of danger they present. The
types of organic peroxide range from type A, which is not accepted for carriage in the packaging in
which it is tested, to type G, which is not subject to the provisions of Class 5.2. 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 188.8.131.52 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 184.108.40.206, those already permitted for carriage in IBCs are listed in 220.127.116.11,
packing instruction IBC520 and those already permitted for carriage in tanks in accordance with
Chapters 4.2 and 4.3 are listed in 18.104.22.168, 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 risks and remarks providing relevant transport information are given.
These generic entries specify:
- the type (B to F) of organic peroxide (see 22.214.171.124.6 above);
- physical state (liquid/solid); and
- temperature control (when required), see 126.96.36.199.15 to 188.8.131.52.18.
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 184.108.40.206.16.
Classification of organic peroxides not listed in 220.127.116.11, 18.104.22.168 packing instruction IBC520 or
22.214.171.124, 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 126.96.36.199, 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
- 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
- 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
188.8.131.52 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 184.108.40.206 or in
the competent authority decision according to 220.127.116.11.8 as being "with water" or "as a stable
dispersion in water". Samples of organic peroxides or formulations of organic peroxides not listed in
18.104.22.168 may also be desensitized with water provided the requirements of 22.214.171.124.9 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 the organic peroxide formulation.