Hazard Class 5

Class 5 - Oxidizers and organic peroxides is separated into two divisions: a division for inorganic substances that may combust when mixed with oxygen, and a division for self-reactive organic substances.

Division 5.1 - Oxidizers are materials that are not necessarily combustible, but yield oxygen that can cause or contribute to the combustion of other material. These materials may take a solid or liquid form. Examples include ammonium nitrate fertilizer, calcium chlorate, and bleaches.

Materials are classified in Division 5.1 based on the test methods and criteria described in the UN Manual of Tests and Criteria. These tests measure the potential for the substance to increase the burning rate or the burning intensity of a combustible substance. For solids, the substance being tested is mixed with dry fibrous cellulose. The test determines whether the mixture ignites and burns and compares the mean burning time with that of a reference mixture. The burning rate determines the packing group the substance is assigned to. For liquids, the test measures the pressure rise time during combustion.

Division 5.1 materials are defined in §173.127.

Division 5.2 - Organic peroxides are organic compounds that are thermally unstable and can undergo exothermic, self-accelerating decomposition. They contain the bivalent structure -O-O- and may be considered derivatives of hydrogen peroxide. Some organic peroxides can react dangerously with others. Examples include hydrogen peroxide and calcium peroxide.

Organic peroxides are assigned to one of seven types, labeled Type A through Type G. These types are assigned based on their physical state, control temperature, and performance test procedures.

Note that previously, Division 5.2 materials were assigned to PGII. But as of July 5, 2016, the PG II designation is no longer required in the shipping description for Division 5.2 materials. Division 5.2 materials are defined in §173.128.

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