Importance of Properly Designing Dust Explosion Protection Systems: Case Study – 2014 Georgia Pacific Corrigan Facility Fire and Explosion

摘要

When designing handling and conveying equipment for combustible dusts, it is crucial to properly implement protective measures (e.g., deflagration venting, suppression, and isolation) capable of mitigating the potential consequences in the event the dust is ignited. Generally speaking, dust processing, storage, and collection equipment, such as cyclones, mills, baghouses, dryers, and silos are typically connected via pipes, pneumatic conveyors, and dust extraction or aspiration lines. If a fire or dust explosion occurs in one vessel, or the interconnecting piping, the flame front or pressure can quickly propagate through these conduits to other parts of the plant and potentially escalate to even worse consequences than the original event. More specifically, pressure piling or flame jet ignition in connected vessels can result in a series of more catastrophic secondary events. To effectively prevent or mitigate these phenomena, deflagration suppression or venting is provided for the source vessel, and explosion isolation is used to prevent the explosions or fire from propagating to neighboring vessels. Improper design of isolation devices can be costly, as illustrated by this case study on the fire and explosion that occurred in 2014 at a plywood manufacturing facility in Corrigan, Texas. On April 26, 2014, a fire that originated at a plywood sander eventually propagated through a pneumatic dust conveying system resulting in an explosion in a baghouse (dust collector), fatally injuring two employees, and seriously injuring others who were responding to the incident. Sparks from the sander entered the extraction pipe, which was protected by an active suppression/isolation system (spark-sprinkler-abort gate) upstream of the baghouse. The sparks ignited dust piles that accumulated in the extraction pipe (prior to the first spark detection zone) due to an insufficient flow velocity through the system. When the fire in the extraction pipe was discovered, the extraction blower downstream the baghouse (negative pressure system) was turned off, which allowed smoldering and burning to continue within the pipe. When the blower was subsequently turned back on, a flame front developed that propagated into the baghouse due to an improperly designed isolation system. This incident occurred because of: (1) an insufficient flow velocity, which allowed dust to accumulate in the extraction pipe; (2) the improper design of a passive damper as an isolation device; (3) and operational errors associated with the blower being turned off and then back on prior to extinguishing the burning material in the pipe. This paper analyzes the root causes of the incident as well as key lessons learned related to: system design; performing a dust hazard analysis; required air stream flow rates; proper back blast designs; impeding deflagration vents; and exclusion zones in the path of a vented deflagration in the baghouse.