During the discharge of fine powders from silos, quite often temporary ratholes occur, By collapsing of this rat holes dust clouds occurs which can form a danger for dust explosion, The dust concentration we can not control, it changes with time because the dust settles on the surface. That means that the critical dust concentration exists for certain time by each rathole collapse. The only possibility is to prevent dust development: where is no dust, the dust explosion can not occur. The Siletta discharge equipment allow to discharge the silo in so called "IDEAL FLOW" whereby the whole silo content sinks like a piston in a cylinder and thus there is no dust development and no danger for dust explosion, The second danger arising from collapsing ratholes is that when the rathole collapse, the collapsed powder mixes with air and fluidizes, This leads to hydrostatic pressure on the silo walls. This hydrostatic pressure results in high wall pressure - much more than normal silo pressure. From this point of view ratholing should be prevented, too.
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