If the “ignition sensitivity” is greater than 0.2 and/or the “explosion
severity” is greater than 0.5, the dust is defined as Class II. If the
“ignition sensitivity” is less than 0.2 and the “explosion severity” is
less than 0.5, the dust explosion hazard is not “significant”.
OSHA will only characterize a sample sufficiently to prove (or
disprove) that the sample meets the definition for Class II dusts
based on the “ignition sensitivity” or the “explosion severity” test
results.
It should be noted that the dust sample preparation and test
methods/apparatus suggested by OSHA may not comply with the
current ASTM test methods and suggestions for sample preparations
as described in Section 4 of this paper. For example, ASTM
E1226 (test method for the determination of the Maximum
Explosion Pressure and Maximum Rate of Pressure Rise (Kst))