Historically, experiments to determine the combustion characteristics of dust clouds were originally performed in a 1 cu m chamber. There are several European standards referencing vessels of this size: VDI 3673, BS 6713, and ISO 6184-1. These older standards have been superseded by the CEN/CENELEC standard EN 14034 parts 1 though 4. For years the 1 cu m has been considered the “gold standard” for combustible dust explosion testing. However, these large vessels require large quantities of sample to perform explosion severity and explosion limit testing in. They also were labor intensive.
As a result the 20-L chamber was developed as a compromise vessel. It was large enough to provide comparable explosibility data for most dusts and it was small enough to greatly reduce sample quantity and labor requirements. The 20-L chamber has become the modern workhorse of dust cloud explosibility testing. Fauske & Associates LLC (FAI) has four operating 20-L chambers with a fifth decommissioned unit that was heavily used back in the early 1980s. Explosibility testing in these chambers are performed per ASTM E1226, E1515, and E2931, as well as the EN 14034 methods. There are scores of these units around the world providing valuable data to help create dust explosion hazard mitigation strategies in various process industries ranging from agriculture, wood working, pharmaceutical, plastics and fine chemical, as well as metal working.
However, due to their small size they do have two limitations. The first is “overdriving”. Overdriving occurs when the powerful ignition source used to conduct experiments in the 20-L chamber preheats the test material and burns the dust cloud under study without really generating a propagating flame. The second limitation is “underdriving” – where the walls of the 20-L chamber abstract heat from the dust cloud explosion and thereby partially quenching the intensity of the deflagration. Both of these phenomena degrade the test data and thus impede the establishment of adequate explosion hazard mitigation. The vast majority of dusts and powders are not affected by these phenomena but there are a few that are.
The solution to both of these issues is to perform the test in a large vessel. One that is not susceptible to overdriving or underdriving. FAI has commissioned its own 1-cu-m chamber, the second unit of its kind in all of North America. This chamber brings added testing capability and will help establish dust cloud mitigation strategies.
Fauske & Associates LLC, Burr Ridge, IL 877-428-7531 www.fauske.com
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