With the current focus on combustible dust hazards in industry, an increasing number of dusts are being tested by facilities to determine their explosibility. For marginally explosible dusts (low P_(max) and K_(St)), this can be a difficult task. Most commonly, explosibility screening tests are performed in a spherical 20-L vessel using strong pyrotechnic igniters in accordance with ASTM E1226 Standard Test Method for Explosibility of Dust Clouds. The 20-L vessel was originally designed by Siwek to correlate with data in the much larger cubic meter (1,000 L) vessel while requiring less dust and time to perform testing. Previous studies have shown that some marginally explosible materials may appear to be explosible when tested in the 20-L vessel but non-explosible when tested in the cubic meter vessel. This phenomenon has been attributed to "overdriving" by the strong chemical igniters in the 20-L vessel. The cubic meter vessel is seen as a more reliable vessel to determine whether a deflagration will propagate through a cloud of marginally explosible dust because of the lower chance of overdriving in the larger vessel. It has been hypothesized that overdriving may be relevant to situations that can occur in industry involving strong ignition sources, such as an initial gas explosion which then propagates through a combustible dust cloud.
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