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Sixten Dahlbom
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Wire basket tests to prevent self-heating
A common fire cause during storage of porous organic materials is autoignition. The reason is self-heating, which is triggered by microbial activity, chemical oxidation or physical processes from moisture migration. The most common small-scale method is a so-called wire basket test that evaluates self-heating from chemical oxidation.
Purpose
Wire basket tests are technically simple but time-consuming methods used to investigate self-heating and autoignition of different materials. Basket tests are available in several different versions, both analytical methods for research purposes and standardised methods for transport of dangerous goods, for example. The version needed/required depends on how and where the result will to be used. See "Method" for more information.
The tests generate data that can be used as a basis for risk analysis, research or for transport of dangerous goods (self-heating materials).
Method
In a wire basket test, the material to be examined is placed inside a wire mesh cube, which is located inside an oven at a fixed elevated temperature. The temperature is then measured in the oven and at the centre of the sample over time.
Three different temperature patterns can usually be observed:
- Subcritical. The temperature in the centre increases slowly towards the oven temperature, but never exceeds it.
- Critical. The temperature in the centre of the sample increases only a little above the oven temperature, reaches a plateau, and then decreases.
- Supercritical. The temperature in the centre increases, sometimes reaches a plateau, before rising rapidly above oven temperature. Self-heating has occurred and there is a risk for autoignition.
The procedure for testing varies somewhat depending on the version/standard of wire basket test used. If the purpose is analysis/research, repeated attempts are usually carried out with elevated oven temperatures until the supercritical temperature is found, the procedure is then repeated with different volumes on the wire basket. For example, the results can be used to calculate critical temperatures in larger scale using Frank-Kamenetskii theory. This can be used to assess critical storage size or critical storage time.
If the purpose of the test is standardised testing according to the UN N4 test, the occurrence of self-heating (temperature increase in the centre of the material > 60 °C above oven temperature) is examined at a specified oven temperature and test volume.
Deliveries
A test report, in Swedish or English, is delivered with the test results after testing. Measurement files can also be included.
