This test is designed to determine the lowest temperature at which a substance shows an exothermic reaction under defined oxygen-lean conditions. It is applied to products which are subjected to an elevated temperature over long periods, closed off from fresh air (e.g. in vacuum ovens, fluid-bed drier etc.). With this test, the maximum permissible temperature of the heating medium can be derived. The substance to be tested and graphite powder as reference are heated up at a linear rate of 2.5°C/min(dynamic test).

The temperatures of the samples are recorded. An exothermic reaction is considered to have occurred if the temperature curve of the test sample rises above the reference sample temperature. Alternatively, a series of isothermal tests is performed at temperature intervals of 10°C. As the test result, the highest temperature is reported at which no overheating of the sample is observed for 8 hours.

Exothermic Decomposition

Elevated temperatures may subject a product to chemical transformation which will not require oxygen. The reaction may be endothermic or exothermic. An exothermic reaction is classified as an exothermic decomposition. It is, from a safety point of view, of great importance, contrary to endothermic decompositions.

Such reactions may liberate gases of decomposition (smolder gases), which will result in a pressure rise in a closed vessel, which may subsequently tear or burst.

In addition, the gases of decomposition may be flammable and present an explosion risk.

In case of an exothermic change, the heat may be trapped, resulting in self-heating, with a thermal explosion as the consequence. As with auto ignition, the exothermic decomposition depend upon the volume and size of the sample. With increasing volume, the danger of a heat accumulation increases.

The decomposition temperature measured is a relative value. It is dependent on the test method, and a conversion to actual conditions is problematic. In any case, the test method has to be stated together with the temperatures.

Test Procedure: dynamic test

Determination under temperature-programmed conditions. Approximately 2 grams of the test sample and 2 grams of graphite as a reference substance are heated each in a test tube at 2.5°C/min up to 350°C oven temperature. The sample temperature is recorded. An exothermic reaction is indicated when the temperature curve of the product is above the one for the reference substance

Test Procedure: Isoperibolic test

If the temperature-programmed test results in an exothermic reaction, then the sample is subjected to an isoperibolic test (at constant oven temperature). Again 2 g product are used, and the starting temperature will be the one where the product recording in the programmed test crosses the reference curve. The isoperibolic test is repeated with fresh samples in decreasing 10°C steps until the substance does not show an exothermic reaction for 8 h (in certain cases even longer).

Test Procedure: Influence of materials of construction on the exothermic decomposition

Proceed as above. 100 mg of the material of construction are added to the sample. For instance, iron powder or stainless steel turnings. Compare the results obtained with and without the additional material.

Test Procedure: Flammability of the gases of decomposition

While heating up, check the flammability of the gases or vapors produced at a certain temperature interval (e.g., 50°C) with an ignition source (glowing platinum wire)

Test Procedure: Determination of the amount of decomposition gases

A longer test tube (160 mm) containing 1 g product is sealed with a rubber stopper equipped with a glass pipe with latex tube. The test tube is put into a heating block at 350°C. The gases are passed through an empty wash bottle to a gas meter. In general, gas production stops after a few minutes. The gas quantity is stated as l/kg. In special cases, the gas evaluation is also measured under different parameters such as isothermally at 250°C over 8 h.

The test set consists of:

- Lütolf oven: Electrically heated aluminum

block, with 6 holes to receive test tubes

for 1 reference and 5 test samples.

- Temperature controller and data acquisition

system: Sipcon

- Metal-sheathed iron-constantan

thermocouples, inserted in thin glass tubes

to protect against corrosion

- Gas meter with paraffin oil as sealing liquid

- Electrically heated platinum wire: MP-1

Swiss Institute for the Promotion of Safety and Security

Adrien Bisel, Phone +41 (0)61 696 55 99, Fax +41 (0)61 696 70 72

Petra Meier, Phone +41 (0)61 696 57 24, Fax +41 (0)61 696 70 72