Effect of Moisture on Ignition Energy

Powders can be charged by contact and separation between particles, or between particles and other surfaces such as bags or pipe walls. Upon contact, an electronic rearrangement occurs at the surfaces to minimize the free 

The charging process is affected by atmospheric moisture only to the extent that the moisture comes to equilibrium with the contacting surfaces. 

The maximum charge density on a flat, nonconductive surface is limited by the geometry with respect to conductive surfaces (C-2.5.3 through C-2.5.5) 

For particles, the maximum field intensity occurs at the particle surface and decays inversely with distance. This highly nonuniform field allows greater surface charge densities before breakdown takes place, depending on the curvature of the particle surface. Empirical studies reviewed in [18]  

As in the case of liquids (5-2.5), the tendency of powders to lose charge can be simplified by classifying them into the three groups (1) conductive, (2) semiconductive, and (3) nonconductive. The situation with powders is somewhat different from liquids because powders exist as heterogeneous 

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