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NFPA 86 Exlosion Relief Requirement Exceptions

Question asked by on Jun 3, 2020
Latest reply on Aug 28, 2020 by jerome.taveau

Hello,  I am looking for information on how to take exception to NFPA 86 explosion relief requirements for Class A & B Natural Gas fired Ovens. My situation: I have an oven that cannot physically meet the 15 to 1 ratio relief area requirement because of external structure and internal components? Is there a form or process to use to take exception to the requirement.


Also, I am not sure how to calculate actual internal area on one of our standard designs.The inside of the oven has a supply duct that occupies roughly 45% of the inside of the oven, the supply duct is not fabricated from 3/16" material, but it is 16 ga steel, seam welded continuous to structural steel angle iron frame on all sides but the bottom which is open to the heater house. Both ends, one side and the roof of the duct are actually right up against the inside of the oven wall and roof panels (top and ends have a 1/2" gap to the panels for thermal expansion). The open side of the duct face is seam welded nozzles that are quite robust mechanically and are also welded continuous to the internal frame of the duct. I am questioning if I have to use the duct volume as part of the total internal oven in the calculation for explosion relief area.