Sugar dust explosion risks

US Chemical Safety Board (CSB) investigators said the 7 February 2008 explosion at the Imperial Sugar refinery in Port Wentworth, Georgia, 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.

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 travelled 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, Texas; 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 10 workers. However, Imperial's management did not correct the underlying causes of the sugar dust problem at the Port Wentworth facility, where workers testified that spilled sugar was knee deep in places on the floor, and sugar dust had coated equipment and other elevated surfaces.

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 report said the company had not conducted evacuation drills for its employees and that the explosions and fires disabled most of the emergency lighting, making it difficult for workers to escape from the labyrinth of explosion-damaged buildings as the fires continued to spread.

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 AIB International and the American Bakers Association 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 US 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.

The CSB is an independent federal agency charged with investigating industrial chemical accidents. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in safety regulations, codes, standards, management systems, training, and industry practices.
www.csb.gov.