#2 Test Your Dust
The collection and testing of dust samples is a long-established practice used by manufacturing professionals to make informed dust collection decisions. While dust testing has always been good practice, it is rapidly becoming a necessity in today’s regulatory climate.
|An engineered test is performed at an official testing facility to confirm that this dust collector can withstand an explosive event.|
There are two types of dust testing: (1) bench testing, which pinpoints physical properties of the dust, and (2) explosibility testing, which determines whether a dust is combustible.
Bench testing involves a series of tests that provide valuable data for filter selection. Particle size analysis reveals the dust’s particle size distribution down to the submicron range to determine the filtration efficiency needed to meet emissions standards. This test pinpoints both the count (the number of particles of a given size) and the volume or mass spread of the dust. Knowing both is important because many dusts are mixed.
A video microscope provides visual analysis of the dust shape and characteristics. Together with particle-size analysis, this tool is vital for proper filter selection. For example, a microscope may be needed to detect oil in the dust.
Moisture analysis equipment measures a dust’s moisture percentage by weight, providing information that can prevent moisture problems. A humidity chamber is used to see how quickly a dust will absorb moisture. This helps to identify hygroscopic (moisture-absorbent) dust which requires widely pleated filter cartridges, as these sticky dusts cause filters to plug. Additional bench tests can help to determine the optimal design of other dust collection system components. It is not necessary to bench-test dust 100 percent of the time, but if there is anything at all unusual about the process and/or the dust, it’s a good idea.
To determine whether a dust is combustible, it should undergo separate explosibility testing as stated in NFPA Standard 68. If a dust sample is not available, it is permissible to use an equivalent dust (i.e., same particle size, etc.) in an equivalent application to determine combustibility. But once the dust becomes available, it is still recommended that you go back and test the dust using either the 20-liter test method described in ASTM E1226-12a or the similar method described in ISO 6184/1.
Using your dust sample, the lab will start with a screening test to determine whether the dust is combustible. If the dust is not combustible, testing will stop there. If it is combustible, the lab will conduct further testing on dust cloud parameters to pinpoint the Kst (defined as the deflagration index of a dust cloud, or rate of pressure rise) and Pmax (the maximum pressure in a contained explosion).
Explosibility testing is performed primarily to help determine what explosion protection or prevention equipment is needed on your dust collector and related components. But it can also play a role in filter selection. For example, testing for the minimum ignition energy can help determine if conductive filters are needed.
This tip is an excerpt from the white paper "Five Tips for Selecting Cartridge Dust Collecting Filters" by Rick Kreczmer of Camfil APC. The full article can be downloaded here.