Page 606 - Dust Explosions in the Process Industries

Electrical Apparatuses for Areas Containing Combustible Dusts 573

0.01 0.1 1 10 100 1000 10000
Minimum igniting voltage (v)

Figure 8.8 Theoretical consel-vative capacitive ignition curves tor dust clouds based on the equa-
tion 0.SCU2 = MIE. The numbers attached to the straight lines are the respective MIE values in J.

Current (A)

Figure 8.9 Theoretical conservative inductive ignition curves for dust clouds based on the equa-
tion 0.5SP = MIE, valid for L > l mH. The numbers attached to the straight lines are the respective
MIE values in J.

are obtained directly from the equation 0.5LZ2=MIE for L > 1mH. FOPsmaller L, the
ignition current is independent of L and t essentially resistive. A chart showing con-
servative ignition curves for inductive circuits, for a range of MIE values, is given in
Figure 8.9. For resistive ignition circuits, the equation I= 15,000MI[E0.45/U2provides
a first-order conservative estimate based on existing experimental ignition curves for
gases and dust clouds. A graph representing this equation for a range of ME values is
given in Figure 8.10. However, considerable uncertainty is involved in extensive extra-
polation of this equationinto the regions of higher ME. Therefore,more research is needed
to establish more-reliable resistive circuit ignition data in the range of higher MIEs.