This test is designed to determine the lowest temperature at which a substance or reaction mixture shows an exothermic reaction under defined isochoric conditions, while the pressure is measured.

The test is applied to products or reaction mixtures with low boiling points in order to suppress evaporation effects in the temperature range of interest.

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.

Test Procedure:

Weigh 2 g of the test substance into a test tube (15,5 mm dia, 45 mm long). Place test tube into the mini-autoclave. Slide glass sheath over thermocouple. Screw cover on, check whether rupture disk is inserted. Connect capillary tube. In an other test tube 2 g of fine graphite powder are inserted in a autoclave as a reference sample for comparative temperature measurement. This reference-autoclave is not closed tightly, i.e. it will always be under atmospheric pressure.

Dynamic test:

Raise the temperature of the heating block continuously at a rate of 2.5°C/min up to at least 50°C above the desired operating temperature in the plant. Maximum test temperature 400°C.

An exothermic reaction is considered to have occurred if the temperature curve of the test sample on the recorder rises above that of the reference sample. The test report gives the starting temperature of the first exothermic reaction found by the dynamic test described above.

Isoperibolic test:

If required an isoperibolic test is carried out. To this end, a fresh sample is placed into the heating block at a temperature chosen by the operator (e.g. temperature of first exothermic reaction determined as above) and held at this temperature for 8 hours. If an exothermic reaction occurs during heating up or holding the temperature, a fresh sample is tested at a temperature 10°C lower. This is repeated, the test temperature being reduced by 10°C each time, until a temperature is reached at which a fresh sample shows no exothermic reaction during a period of 8 hours. The highest temperature at which no exothermic reaction occurs, is reported.

A pressure increase is considered to have occurred if the pressure curve on the recorder shows a slope. The test report describes the course of pressure in relation to temperature (dynamic test) or time (isoperibolic test). The pressures measured are not necessarily representative for those to be expected in production equipment (different volumes of apparatus).

The test set consists of:

- Electrically heated aluminum

block with two heating zones

- 2 pcs stainless steel mini

autoclaves

- 1 pc stainless steel reference

autoclave

- Pressure measuring system

(pressure transmission through

capillary tube)

- Temperature controller and data

acquisition system: Sipcon

- Metal-sheathed iron-constantan

thermocouples.

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