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September 24, 2009

CSB reports its conclusions on the causes of massive sugar explosions

Dorothy Lozowski

In a final draft report released today, U.S. Chemical Safety Board (CSB; www.csb.gov) investigators said the February 7, 2008, explosion at the Imperial Sugar refinery in Port Wentworth, Ga., resulted from ongoing releases of sugar from inadequately designed and maintained dust-collection equipment, conveyors, and sugar-handling equipment. Inadequate housekeeping practices allowed highly combustible sugar dust and granulated sugar to build up throughout the refinery’s packing buildings, CSB investigators concluded. Earlier this year, the CSB released a safety video depicting how accumulations of combustible dust at worksites can provide the fuel for devastating explosions  (click here for more on this).
 
The first explosion — known as a “primary event” — likely occurred inside a sugar conveyor located beneath two large, sugar storage silos. The conveyor had recently been enclosed with steel panels creating a confined, unventilated space where sugar dust could accumulate to an explosive concentration. Sugar dust inside the enclosed conveyor was likely ignited by an overheated bearing, causing an explosion that traveled into the adjacent packing buildings, dislodging sugar-dust accumulations and spilled sugar located on equipment, floors, and other horizontal surfaces. The result was a powerful cascade of secondary dust explosions that fatally injured 14 workers and injured 36 others, many with life-threatening burns. The refinery’s packing buildings were largely destroyed by the blasts and ensuing fires.
 
CSB investigation supervisor John Vorderbrueggen, P.E., who led the 19-month investigation, said, “Imperial’s management as well as the managers at the Port Wentworth refinery did not take effective actions over many years to control dust explosion hazards — even as smaller fires and explosions continued to occur at their plants and other sugar facilities around the country.”
 
The CSB report said that the sugar industry was familiar with dust explosion hazards at least as far back as 1925. Internal correspondence dating from 1967 showed that Port Wentworth refinery managers were seriously concerned about the possibility of a sugar dust explosion that could “travel from one area to another, wrecking large sections of a plant.” Precursor events included a 1998 explosion at Imperial’s plant in Sugar Land, Tex.; an explosion at the Domino Sugar plant in Baltimore in November 2007; and two sugar-dust explosions in the 1960s that killed a total of ten workers.
 
CSB chairman John Bresland said, “Dust explosions can be among the deadliest of industrial hazards, particularly inside heavily occupied buildings. But these explosions are readily prevented through appropriate equipment design and maintenance and rigorous dust-cleaning programs. I call upon the sugar industry and other industries to be alert to this serious danger.”
 
The final report proposed a series of safety recommendations for Board consideration. Imperial Sugar was urged to comply with National Fire Protection Association (NFPA) recommended practices for preventing dust fires and explosions, develop dust training and housekeeping programs, and improve its evacuation procedures. The report also called on industry groups to develop combustible dust training and auditing materials. Imperial’s insurer, Zurich Services, and an insurance industry trade association should improve their insurance audit procedures for dust hazards and share their dust hazard training materials with clients, investigators concluded.
 
A 2006 CSB study identified 281 combustible-dust fires and explosions between 1980 and 2005 that killed 119 workers and injured 718, and extensively damaged industrial facilities. The CSB recommended in November 2006 to the U.S. Occupational Safety and Health Administration (OSHA) to develop a comprehensive regulatory standard for combustible dust, based on existing NFPA consensus standards, and improve requirements for dust hazard communication to workers. In April 2009, OSHA announced it would commence the development of a standard.

 



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