Handling explosive dust — Part I
Handling flammable dust requires special measures to prevent dust fm and dust explosions. Although experience shows that absolutely safe operation is not possible when handling explosive dust-and-air mixtures, it is necessary to reduce the probability of an accident and the subsequent risk to personnel and equipment. Processing lines can now be designed to ensure maximum safety. This article, the first of two, will provide background information for understanding how dust explosions develop and will discuss methods for determining the explosion hazard related to processing a given product. Ignition sources, methods for testing dust explosiveness, and preventive safety measures will be covered. In February, the second part of the article will focus on situations where explosions cannot be pre- vented. It will present the background information needed to select explosion- protected equipment-equipment that protects personnel and other machinery by restricting the effects of an explosion to the interior of the system.
In operations where dust-and-air mixtures are common, flame propagation is most likely to develop in two types of equipment, cubic vessels and ducts. In cubic vessels, explosions of dust-and-air mixtures are turbulent; the flame speed is small in comparison to the sonic velocity. No local pressure differences occur, the maximum explosion pressure reaches an average of 8 to 10 times the initial pressure.