What caused the Port Wentworth sugar refinery explosion in 2008?
Abstract
The US Chemical Safety Board found that sugar dust in a newly enclosed conveyor under two silos most likely ignited from an overheated bearing. The blast raised dust and spilled sugar in the packing buildings and set off secondary explosions that killed 14 workers.
According to the US Chemical Safety Board (CSB), a primary sugar dust explosion inside a newly enclosed conveyor beneath two storage silos, most likely ignited by an overheated bearing, set off a chain of secondary explosions fuelled by sugar dust and spilled sugar that had built up throughout the packing buildings. The explosions on 7 February 2008 at the refinery in Port Wentworth, Georgia, killed 14 workers and injured dozens more. The CSB's root causes were inadequate equipment design, maintenance and housekeeping.
Short answer
- Date and place: 7 February 2008, sugar refinery at Port Wentworth, near Savannah, Georgia, USA.
- Casualties: 14 deaths; the CSB gives 36 injured in its 2009 report release and 38 injured, 14 of them with serious and life-threatening burns, on its investigation page.
- Primary event: a sugar conveyor under two silos. Steel panels had recently been fitted around it, creating a confined, unventilated space where sugar dust could reach an explosive concentration.
- Likely ignition: an overheated bearing in the conveyor.
- What made it a disaster: the blast raised dust and spilled sugar in the adjacent packing buildings, causing cascading secondary explosions and fires that largely destroyed them.
- Final report: released by the CSB on 24 September 2009.
The sequence of events
The CSB describes two stages, a pattern typical of serious dust explosions.
1. The primary explosion. Granulated sugar was moved on a conveyor under two large storage silos. Shortly before the accident, steel panels had been installed around this conveyor. The enclosure kept spilled sugar and dust in a closed, unventilated space, where the dust cloud could reach an explosive concentration. The CSB concluded that an overheated bearing most likely ignited it.
2. The secondary explosions. The pressure wave and flame from the primary event travelled into the neighbouring packing buildings. There, the CSB found, poor housekeeping had allowed sugar dust and granulated sugar to accumulate on floors, equipment and elevated surfaces; workers testified that spilled sugar was knee-deep in places. The blast lifted these deposits into the air and ignited them, and each explosion raised more dust for the next. The resulting explosions and fires largely destroyed the packing buildings.
A small primary event in one piece of equipment can thus become a building-wide catastrophe when settled dust is available. HSE guidance makes the same point: a layer of flour only 0.3 mm thick on the floor can, in principle, fill a room with an explosible dust cloud up to 3 m above the floor once it is raised.
What the CSB found behind the immediate cause
| Finding | Why it mattered |
|---|---|
| Inadequately designed and maintained dust handling and collection equipment | Sugar and dust escaped from conveyors and equipment into the buildings |
| Chronic poor housekeeping | Deposits of dust and spilled sugar supplied the fuel for the secondary explosions |
| Hazard known but not corrected | The sugar industry had known of dust explosion hazards since at least 1925; a 1967 internal memo from a refinery engineer warned that the dust problem had become serious and dangerous, and correspondence of the time feared an explosion could travel through the plant, yet the dust problems were not resolved |
| Earlier warnings in the industry | The CSB cited previous sugar dust explosions, including two in the 1960s that killed ten workers in total, and others in 1998 and 2007 |
| Emergency arrangements | Emergency notification relied largely on radios, phones and word of mouth, and no evacuation drills had been held; the CSB recommended an alarm system and routine drills |
The CSB recommended that the company apply the NFPA standards for agricultural and food dusts, combustible dust and electrical equipment in hazardous locations, implement a housekeeping programme and train employees and contractors. It also recommended that OSHA issue a comprehensive combustible dust standard. That recommendation was later closed as superseded by a similar recommendation from the CSB's investigation of a 2017 corn mill explosion. OSHA reissued its Combustible Dust National Emphasis Program on 11 March 2008, citing the sugar refinery explosion.
Lessons for any plant handling combustible dust
- Treat sugar, flour and other food powders as combustible dusts. A product sold as food can still produce an explosible cloud; test the dust (see Is sugar dust explosive?).
- Do not enclose dusty equipment without an assessment. An enclosure that keeps dust in creates a confined volume where a cloud can form; it may need ventilation, dust extraction, explosion protection or a change of zone.
- Control ignition sources on conveyors and elevators. Bearing temperature monitoring, alignment and speed monitoring and maintenance prevent the frictional heating that the CSB identified as the likely ignition.
- Housekeeping is explosion protection. Removing deposits takes away the fuel for secondary explosions. Rules such as the US grain handling standard's limit of 1/8 inch (about 3 mm) in priority areas show how specific such programmes can be.
- Isolate and separate. Explosion isolation, walls and good layout limit how far a primary event can travel.
Related on excodex
- Dust collectors, silos and bucket elevators: where dust explosions start
- Dust layers and housekeeping: how thick is too thick?
- Why is a secondary dust explosion usually worse than the first?
- Is sugar dust explosive?
- Why do bucket elevators cause so many dust explosions?
Standards and further reading
- US Chemical Safety Board, investigation page for the 2008 Port Wentworth sugar dust explosion and fire, with the final report and recommendations: csb.gov
- US Chemical Safety Board, final investigation report (findings and recommendations): csb.gov (PDF)
- US Chemical Safety Board, release on the final report (24 September 2009): csb.gov
- OSHA, Combustible Dust National Emphasis Program, directive CPL 03-00-008: osha.gov (PDF)
- OSHA 29 CFR 1910.272, grain handling facilities (housekeeping, bucket elevators): osha.gov
- HSE, HSG103 Safe handling of combustible dusts (secondary explosions from settled dust): hse.gov.uk (PDF)
- NFPA 660, standard for combustible dusts and particulate solids, which consolidates NFPA 61 and NFPA 654 cited by the CSB.
This article is general technical information prepared by the excodex editorial team. It does not replace the applicable standards, the equipment certificates and instructions, national regulations or the assessment of a competent person.