Abstract
This chapter provides an overview of some vent sizing methods used in Europe and the United States.. The vent ratio is defined as vent area per unit of enclosure volume. Originally, a fixed vent ratio, determined by the maximum rate of pressure rise in the 1.2 liter Hartmann bomb, was specified for a specific dust. However, as the enclosure volume gets larger, the required vent area increases. The nomograph method was originally designed by Verein deutscher Ingenieure (1979), but later it was also adopted by the National Fire Protection Association in the United States. The relevance of this method is tied to the nature of the large-scale experiments on which it rests. These experiments were conducted with dust clouds generated by blowing dust into the experimental enclosures from pressurized reservoirs through narrow nozzles to ensure uniform, well-dispersed, and highly turbulent dust clouds. . The Norwegian method and the Randandt scaling law are also discussed in this chapter. It is necessary, in each specific case, to analyze carefully what kind of ignition sources are likely to occur and what locations within the silo volume ignition have a significant probability. The theories by Maisey, Heinrich and Kowall, Rust, Nomura and Tanaka, Nagy and Verakis, Gruber et al, Swift, and Ural are explained in the chapter. The venting philosophy outlined in the chapter implies that even a modestly sized vent may add significantly to the safety standard of the plant by being capable of providing adequate relief for the majority of the expected explosions.
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