RISE Fire Research installs equipment for testing explosive properties in dust.
A dust explosion occurs when an ignitable concentration of fine dust particles forms in the air and comes into contact with an ignition source, which can be a hot surface, static electricity, self-heating material or a naked flame. An explosion can be caused by both organic and inorganic dust, including some metal dust. In general terms, smaller particles of dust result in a more powerful reaction, as smaller particle size creates a bigger specific area (i.e. area per mass), but it also depends on other particle characteristics.
Different parameters are investigated when characterising explosion properties in dust, and a total of six new pieces of equipment have been installed for analysis at Fire Research. The principle when testing is that an initial screening test is conducted to investigate whether the dust has any explosive properties at all. If this is the case, tests are conducted on the minimum ignition temperature of the dust, the minimum electrical ignition energy, resistivity, as well as the pressure development of combustion at a constant volume.
Testing and the future
It is estimated that there is at least one dust explosion a week in Sweden. According to the user directive (1999/92/EC) linked to ATEX and incorporated into Swedish legislation in 2003, the employer is obliged to prevent explosions in its activities by classifying zones in which an explosive atmosphere can arise, and by preventing ignition sources. Most products have table values that can be used to offer guidance, but far from all materials have been documented. These then need to be tested to make it possible to perform a correct risk analysis. In the past there have been very limited opportunities to test dust in Sweden, but thanks to our new equipment we can now offer help with this.
In parallel with the creation of a test installation in the fire lab, research projects are being started, including studies of metal dust. There are also plans for a seminar/workshop this autumn on dust explosions, which we will return to later.