A report from NFPA looks at recent oven, furnace and dryer explosions — in particular, explosions in curing ovens, electric arc furnaces and grain dryers. Prepared by Fire Protection Research Foundation and the National Fire Protection Association, the report will be used by the NFPA 86 technical committee as it begins work on the next revision cycle of the industrial ovens and furnaces standard. Part of the work the committee will undertake is to revise the standard’s requirements as they relate to explosion relief. Though the standard has required explosion relief on industrial ovens and furnaces for more than 90 years, according to the report, the current requirements were deemed “founded on anecdotal information, and inconsistent with NFPA 68 Standard on Explosion Protection by Deflagration Venting.”
I found it interesting that most of the operations that experienced oven, furnace and dryer explosions — 32 completed surveys, in all — occurred in the low operating temperature range (below 500°F). The predominant industries and operations were automotive assembly, paint finishing, curing coatings and food processing, primarily baking. Is it possible that these low temperature, seemingly simple thermal processes are perceived to be safe because they are relatively simple?
By and large, these were not new systems. Most had been operating at least a few years before the reported incident. In one case, the furnace had operated for more than 30 years. In two cases, the Class A ovens (those designed to process flammable volatiles or combustibles) had operated for less than six years, but for the other reported incidents, the equipment had been in use for a decade or more.
And speaking of Class A ovens, perhaps not surprisingly, nearly two-thirds of the incidents that occurred in ovens and furnaces occurred in systems designed to operate in the presence of flammable solvents or combustible particulate. And yet, even in installations processing volatile materials, slightly less than half of the ovens, dryers or furnaces that experienced an explosion were equipped with explosion relief. It is likely that failure to incorporate explosion relief contributed to the severity of some of the explosion incidents.
For those facilities that experienced an explosion and had installed explosion relief, the report noted that hinged doors, open ends, roof panels or hatches, windows and panel enclosures were all used as relief vents. The survey then looked those incidents in which a vent operated in the explosion event and asked how successful it was. “A successful vent operation can prevent any damage to the system, or it can reduce the impact of the explosion damage to system,” say the report authors Sreenivasan Ranganathan and Sean Gillis. “Out of the 14 responses received, only two responses indicate a very successful operation of vents which resulted in no oven/furnace/dryer repair. There were four other incidents in which the vents operated, but the system needed either repair or replacement. This is an indication of the vents being only partially successful by reducing the impact of explosion.”
Human error was cited as the major cause of more than half of the explosions investigated. Combine that with the failure to include adequate — or any — explosion relief and perhaps catastrophic events are a nearly inevitable result. Nonetheless, the hard work that the NFPA committee is undertaking is welcome news.
Download the full report at http://bit.ly/1TRScJr.
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