More modern single-sheet, compound dome alternatives provide greater stability, longevity and reliability of dust explosion venting, according to experts at BS&B
COMBUSTIBLE DUST PROCESSORS MUST REMAIN
COMPLIANT WITH THE LATEST VENT REGULATIONS TO mitigate explosion hazards. Many industrial powders are combustible; from resins to metals and organic materials such as grain and wood. Bulk solids such as sugar, coal and chemicals can be similarly combustible. Dusty powdered materials have high surface
areas relative to their mass which provides excellent atmospheric
oxygen engagement, particularly in
confined and turbulent process conditions, so that once they are ignited, the combustion process proceeds with explosive force. So, implementing proper venting for explosion protection is essential. In response, in 1945 the US National Fire Protection
Association initiated a tentative standard, NFPA 68, titled ‘Standard on Explosion Protection by Deflagration Venting’. It is currently in its 2018 revision. In Europe, commencing with the ATEX Directive 94/9/EC, legal requirements for prevention and protection strategies were published which are today supplemented by EN Standards for explosion protection technology. Specifically, EN14491 establishes requirements for vent area sizing. Today explosion venting is the most commonly used method of mitigating the effects of a dust explosion. Designed to open rapidly at a predetermined burst pressure, explosion vents allow the combustion process to escape, while limiting the pressure generated inside to safe limits. This type of vent is installed on equipment that feeds, conveys, stores and processes dusty materials in applications that suspend the dust in air, such as in dust collectors, conveyors, bucket elevators, dryers/ovens and silos. For more than 50 years, traditional composite vents comprising a sandwich of perforated stainless steel
RECONSIDERED VENTING
sheets with a plastic film seal between them have been utilised. The perforated arrangement of the stainless steel allowed robust material to be modified to provide a pressure relief opening at a typical pressure of 0.1 bar. This design approach has fallen out of favour in all but a few niche applications, partly due to the risk that powders, bulk solids, dust and process debris can accumulate between the vent layers such that it affects the speed and reliability of the vent opening. “Over time,
there can be an evolving risk with composite vents that leakage will occur, or that dust or process materials will accumulate within the layers and the vent will become very heavy and won’t function as it should,” says Geof Brazier, chairman of BS&B Pressure Safety Management. There are more advanced single sheet vent alternatives that weigh less and include design features that make them more durable, even in the presence of cyclic vacuum conditions or vibration. These modern options reduce installation costs and increase service longevity. Vent Inspection: NFPA 68 Standard on Explosion
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