Standard Test Method for Minimum Explosible Concentration of Combustible Dusts

Importancia y uso:

5.1 This test method provides a procedure for performing laboratory tests to evaluate relative deflagration parameters of dusts.

5.2 The MEC as measured by this test method provides a relative measure of the concentration of a dust cloud necessary for an explosion.

5.3 Since the MEC as measured by this test method may vary with the uniformity of the dust dispersion, energy of the ignitor, and propagation criteria, the MEC should be considered a relative rather than absolute measurement.

5.4 If too weak an ignition source is used, the measured MEC would be higher than the “true” value. This is an ignitability limit rather than a flammability limit, and the test could be described as “underdriven.” Ideally, the ignition energy is increased until the measured MEC is independent of ignition energy. However, at some point the ignition energy may become too strong for the size of the test chamber, and the system becomes “overdriven.” When the ignitor flame becomes too large relative to the chamber volume, a test could appear to result in an explosion, while it is actually just dust burning in the ignitor flame with no real propagation beyond the ignitor.

5.5 The recommended ignition source for measuring the MEC of dusts in 20-L chambers is a 2500 or 5000 J pyrotechnic ignitor.4 Measuring the MEC at both ignition energies will provide information on the possible overdriving of the system.5 To evaluate the effect of possible overdriving in a 20-L chamber, comparison tests may also be made in a larger chamber, such as a 1 m³-chamber.

5.6 If a dust ignites with a 5000 J ignitor but not with a 2500 J ignitor in a 20-L chamber, this may be an overdriven system.5 In this case, it is recommended that the dust be tested with a 10 000 J ignitor in a larger chamber, such as a 1 m³-chamber, to determine if it is actually explosible.

5.7 The values obtained by this test method are specific to the sample tested (particularly the particle size distribution) and the method used and are not to be considered intrinsic material constants.

Subcomité:

E27.05

Referida por:

F3187-16R23, E2931-13R19, E0681-09R23, E1226-19, E1445-08R23

Volúmen:

14.01

Número ICS:

13.230 (Explosion protection)

Palabras clave:

dust explosion; minimum explosible concentration;