Oxidizing properties of liquids: UN Test O.2

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Oxidizing properties of liquids: UN Test O.2

Oxidizing liquids are liquid substances or mixtures which, although not necessarily combustible themselves, may generally cause or support a fire in other materials by releasing oxygen.

This test is used to determine the oxidizing properties of liquid substances and mixtures as a criterion for evaluation from a safety perspective or for classification in hazard classes and packing groups within the framework of relevant regulations, in particular pursuant to the UN Manual of Tests and Criteria, Part III, Chapter 34: Oxidizing Substances of Class 5, Division 5.1, Test O.2.

The test and reference substances are mixed at 1:1 weight ratio with a defined combustible substance (cellulose). The mixture is filled into a pressure vessel, in which a heating coil is located at the lower end. The pressure vessel is then closed with a bursting disc at the upper end. The heating coil is then activated and the time pressure profile is measured. The time taken for the pressure to rise from 690 kPa to 2 070 kPa above atmospheric is noted.

The mean pressure rise times are calculated for both the test substance and the reference substances.

The test results are assessed on the basis of:

  • whether the mixture of test substance and cellulose spontaneously ignites; and
  • the comparison of the mean time taken for the pressure to rise from 690 kPa to 2 070 kPa with that of the reference substances.

Classification of the test substance in packing groups pursuant to UN transport law and categories pursuant to GHS

Packing group I / category 1:

  • The mixture of test substance and cellulose with a mass ratio of 1:1 ignites spontaneously, or
  • The mean pressure rise time of the mixture of test substance and cellulose is less than or equal to that of a reference mixture of 50% aqueous perchloric acid and cellulose in a mass ratio of 1:1.

Packing group II / category 2:

  • The mixture of test substance and cellulose with a mass ratio of 1:1 shows a mean pressure rise time that is less than or equal to that of a reference mixture of 40% aqueous sodium chlorate solution and cellulose with a mass ratio of 1:1;
  • and the criteria for packing group I are not met.

Packing group III / category 3:

  • The mixture of test substance and cellulose with a mass ratio of 1:1 shows a mean pressure rise time that is less than or equal to that of a reference mixture of 65% aqueous nitric acid and cellulose with a mass ratio of 1:1;
  • and the criteria for packing groups I and II are not met.

Not classified pursuant to 5.1 / not oxidizing:

  • The mixture of test substance and cellulose with a mass ratio of 1:1 shows a mean pressure rise of less than 2 070 kPa;
  • or a mean pressure rise time greater than that of a reference mixture of 65 % aqueous nitric acid and cellulose in a mass ratio of 1:1.
Test method for UN Test O.2

Figure: Test method for UN Test O.2