EN 15188:2007 – Determination of the spontaneous ignition behaviour of dust accumulations

3 Test apparatus
3.1 Sample baskets
The samples have to be loosely filled into mesh wire baskets of different volumes. The baskets have to be open at the top and closed at the bottom. They consist of a narrow-meshed wire net, made of e.g. stainless steel. The width of the mesh has to be chosen in such a way that the dust cannot fall through the mesh, but the diffusion of oxygen from the oven air into the dust sample is not hindered. Recommended shapes of the mesh wire baskets are that of a cylinder with a height to diameter ratio of 1 or that of a cube. To allow an assessment of the self-ignition behaviour of dust accumulations of larger sizes than the laboratory-scale at least three mesh wire baskets of different volumes have to be used for the tests.
NOTE 1 A higher level of certainty is achieved with four different sample volumes. The smallest volume should normally be in the order of 10 cm 3 and the largest should normally not be smaller than approximately 1 l.
If only a limited amount of sample material is available, even smaller baskets may be used. However it has to be assured that the volume of the basket following in a series exceeds that of the previous one by a factor of 2 at a minimum. NOTE 2 For the sake of comparing products with respect to their self-ignition behaviour in devices or apparatus, where the sizes of the dust accumulations are limited for the reason of a specific design, often the determination of the selfignition temperature for a basket of 400 cm 3 or 1 000 cm 3 is sufficient. 3.2 Oven Commercially available ovens can be used.
They shall have an air inlet opening in the lower section and an air outlet opening in the upper section (see schematic drawing in Figure 1). They should have a useful volume of about 120 l (enabling the installation of an inner chamber into the oven, surrounding the dust samples and the thermocouples, being equipped with an upstream heat exchanger consisting of copper tube coils) and be controllable in a temperature range from 35 °C to 300 °C. This construction enables a prescribed air flow through this chamber.
The oven temperature shall be stable within a range of ± 1 % of the respective oven temperature. Alternative test arrangements can be used to provide the specified test conditions. For example, the test basket can be shielded by placing it inside an additional mesh wire basket. Mechanically ventilated ovens can also be used provided the test basket is shielded (e.g. by using an inner chamber or an additional mesh wire basket).
3.3 Thermocouples Both for measuring the sample temperature as well as for measuring the oven temperature, sheathed thermocouples with an external diameter of e.g. 1 mm are recommended.
3.4 Temperature recording equipment Appropriate data acquisition may be used for measuring and recording signals of the thermocouples.
4 Preparation of dust samples To investigate situations occurring in practice a representative sample should be used (produced by the operating conditions of the process). The sample characteristics shall be recorded in the test report. The bulk density of the dust for each experiment is determined by weighing the baskets as well as the moisture content of the dust before and after filling.
EN 15188:2007 – Determination of the spontaneous ignition behaviour of dust accumulations