The Sugar Dust Explosions And Fire At Imperial Sugar .
24 Loss Prevention Bulletin 266April 2019IncidentThe sugar dust explosions and fire at ImperialSugar Company, GeorgiaTony FishwickSteel Belt from RefinerySummaryKeywords: Dust explosionAerobeltAerobeltSilo 2AerobeltSteel beltSilo 1East ElevatorWest ElevatorSilo 3Pantleg room (typical)In February 2008, a series of sugar dust explosions and afire occurred at the Imperial Sugar manufacturing facilityin Port Wentworth, Georgia, USA. Fourteen workerswere killed and a further 36 injured. The facility houseda refinery that converted raw sugar cane into granulatedsugar which was then transported by screw and beltconveyors into silos from which it was further transferredto sugar processing and packaging plants. The USChemical Safety and Hazard Investigation Board (CSB)carried out an investigation into the accident, determinedthe causes of the primary and secondary explosions andidentified a range of contributory factors. The CSB thenmade recommendations to Imperial Sugar Company, andto other bodies, aimed at rectifying any shortcomings andpreventing a recurrence.Figure 1: Sugar flow into and out of the siloIntroductionThe first explosion initiated in the enclosed steel beltconveyor below the sugar silos (Figure 1) and was the resultof explosive accumulations of sugar dust inside the enclosure.Poor housekeeping was a major contributory factor, andthis is a feature that has relevance to any facility dealingwith finely divided substances that might accumulate andbe a source of explosion – due to static discharge or otherreason(s). Severe damage was caused to plant equipment andbuildings in addition to the loss of, or impairment to, life. Thecircumstances are described in detail in the CSB report into theaccident1 and summarised in this article.Background to and description of the accidentImperial Sugar Company purchased the Port Wentworth facilityin 1997 and in 2007 the company produced more than 1.3million tons of sugar, making it one of the largest sugar refinersin the USA. More than 350 employees and contractors workedat Port Wentworth where annual average sugar productionexceeded 700,000 tons.Raw sugar was received and refined, then transferred bybelt conveyor into a penthouse above the silos, then into thestorage silos themselves (3 of). From the silos, the sugar wascarried onwards to the bulk sugar truck and train loading area,the packing buildings and the powdered sugar productionequipment in the south of the building (Figure 2). Packagedproducts were palletised and transferred to a warehousefor distribution to customers. Dozens of screw conveyors,bucket elevators and horizontal conveyor belts were used tomove granulated sugar throughout the buildings. The bucketelevators were enclosed and the conveyors covered butnot adequately enough to prevent escape of sugar dust intothe open work areas. These areas were not equipped withdust extraction, so sugar settled readily on overhead piping,conduit, beams, lighting and general equipment.The granulated sugar was stored and conditioned in the 105foot (32m) tall, 40-foot (12m) diameter silos located on raisedconcrete foundations above the belt conveyors. Sugar enteredSilo 3 and was then transferred to Silos 1 and 2. An 80-foot(24m) long steel conveyor belt was used to transport sugarfrom these silos to the downstream stages and, in 2007, a steelframe with top and sides was installed round this conveyor toprevent contamination of the sugar from debris that could fallinto it. This enclosure was not equipped with dust extraction orexplosion vents. It would transpire that this was a crucial factorin the initiation and propagation of the explosions.At about 7.15 pm on 07 February 2008, a sugar dustexplosion occurred in the enclosed steel conveyor belt underthe granulated sugar silos. Seconds later, massive secondarydust explosions propagated through the entire granulated Institution of Chemical Engineers0260-9576/19/ 17.63 0.00
Loss Prevention Bulletin 266 April 2019 25Figure 2: Plan view of silos, steel conveyor belt and other itemsBosch Packing BuildingElectric PanelsBucket elevatorEquipmentroomSite OperatorOfficeAerobeltSteel beltSugar flowSugar flowSilo 3To Palletizer Buildingand WarehouseSilo 2Enclosed steelconveyor beltSilo 1Bucket elevatorSubstationRail loadingEight workers were killed at the scene and six others diedin hospital from the effects of serious burns. A further 36injured workers eventually survived, but some of them hadpermanent, life-changing conditions. Approximately 85 otherworkers on site at the time of the accident were uninjured.When local fire brigades arrived on the scene minutes afterthe first explosion, they were confronted by dense smoke,intense heat, ruptured fire water mains, buildings that wereablaze and large amounts of debris strewn about the site. Themajor fires were extinguished the next day but smaller firesburned for many days. The granulated sugar fires in the siloscontinued to smoulder for more than seven days before theywere extinguished by an industrial firefighting company.Investigation of the accidentThe primary explosionFigure 3: The damage to the south packing building andthe penthouse Institution of Chemical Engineers0260-9576/19/ 17.63 0.00The investigation carried out by the CSB determined thatthe primary dust explosion initiated in the enclosed steel beltconveyor below the sugar silos. During more than 80 yearsof operation, sugar dust spilled into the tunnel under the silosbut almost certainly never accumulated to concentrationsabove the minimum explosive concentration (MEC). This wasbecause it was a large, open, well ventilated space. However,the enclosure of the tunnel, to prevent extraneous objectsfalling into the sugar, carried out a few months before theaccident, materially changed this situation. The companydid not evaluate the hazards arising from accumulation ofcombustible dust inside the enclosure. No dust removalsystem was installed and the system was not equipped withdeflagration vents to release any overpressure arising fromignition of sugar dust.Examination of blast patterns and damage inside the tunnelenabled CSB to conclude that the primary explosion probablyoccurred at about the midway point of the conveyor belt. Everysystems andproceduresand powdered sugar packing buildings, bulk sugar loadingbuildings and the raw sugar refinery. Three-inch (75mm)thick floors buckled from the force of the explosions, theroof of the palletizer building was shattered and blown intothe railcar loading area. Violent fireballs erupted out of thepenthouse on top of the silos, the west bucket elevator andsurrounding buildings (Figure 2). The damage to the silos andadjacent buildings is shown in Figure 3, and the extent of thedevastation to the entire site is illustrated in Figure 42.The intense fireballs advanced through the entire north andsouth of the building as sugar dust ignited. Fire spread throughthe enclosed conveyors and caused more fires in the refineryand other buildings hundreds of feet from where the incidenthad begun. The fire water sprinkler system failed because theexplosions ruptured the water feed pipes.knowledge andcompetenceGranulated sugar screwconveyors
26 Loss Prevention Bulletin 266April 2019The secondary explosions and firesThe primary explosion sent overpressure waves out into thefirst floor of the Bosch Building (Figure 2). Brick walls wereblown from the silo area into the packing area. Fireballs werefuelled by sugar dust dislodged from overhead equipment andthrown into the air by the advancing pressure waves. Concretefloors were violently heaved upwards throughout the southpacking building. Workers in the packing buildings had littleor no warning as walls, equipment and furniture were throwninto the air. Escape routes were hampered by dense, darksmoke. Intense fireballs advanced through the entire north andsouth packing and palletizer buildings. Fires were ignited in therefinery and bulk sugar building hundreds of feet away from theseat of the incident. The secondary explosions and fires mostprobably caused the fourteen fatalities.HousekeepingFigure 4: The extensive damage to buildings andequipmentpanel had been blown off the tunnel support frame. Therewas major damage at the east end of the silo tunnel (Figure2) with all equipment deflections eastwards away from thetunnel. The equipment under Silo 3, and outside the west ofthe tunnel, had damage patterns indicative of a pressure wavetravelling west out of the tunnel. The wooden walls and doorswere blown off both the east and west entrances of the tunnel.Mangled steel belt cover panels were blown off and the brickwall to the south was blown into the south packing area.In the 3-4 days before the accident, sugar lump blockages inSilo 1 discharge holes were being cleared by use of steel rods.During these “rodding” operations, sugar continued to flowfrom Silo 2 onto the moving belt upstream of Silo 1 and thisprobably resulted in lumps of sugar lodging between the beltand Silo 1 discharge chutes. This would create a “dam” andcause sugar from Silo 2 to spill off the belt and this spilled sugaraccumulated inside the unventilated enclosure and reachedconcentrations above the sugar MEC. A source of ignitioncaused an explosion that triggered a series of secondaryexplosions that rapidly progressed through the packingbuildings, palletizer room and bulk sugar station.The investigation established that sugar spillage and dustgeneration were constant problems. Leakages occurred from wornseals, loose equipment covers, breaches in the screw conveyors,bucket elevators and other items. The large work areas were nottypically equipped with dust extraction systems, so sugar dustwould float into the air and settle on overhead piping, lights andother horizontal surfaces. Regular cleaning was necessary in orderto keep dust levels below dangerous (potentially flammable orexplosive) levels but this was not done despite the efforts of theworkforce with the inadequate means available to them. Writtenhousekeeping schedules were not complied with.A sugar dust extraction system was in place to remove dustfrom granulated sugar equipment and transfer it via ducts to dustcollectors. Water spray removed the sugar dust from the air. Adry dust removal system was employed for the powdered sugarand cornstarch equipment. Regrettably, these systems were notfunctioning efficiently and were inadequately maintained. A reportfrom an independent contractor less than a week before theaccident noted: air extraction flows significantly below the minimum dustconveying velocity undersized fans — some operating below the requiredperformance curve incorrectly installed duct piping duct piping blocked by sugar.Potential sources of ignitionTrainingThe actual source of ignition could not be preciselyestablished. However, CSB considered several possiblesources and came to the following conclusions. The minimumignition temperature (MIT) of sugar dust clouds ranges from360–4200C depending on the test apparatus used. Also, theMIT decreases with residence time in the environment tested.Airborne combustible sugar dust would almost always havebeen present inside the conveyor tunnel and be prone toignition if the necessary temperature was reached. There wasevidence that the steel belt roller support bearings sometimesgot very hot. CSB concluded that contact of sugar dust withthese hot bearings was the most likely cause of ignition. Apossible, but less likely, source was friction sparking, whileelectric spark ignition was considered to be very unlikely.Open flames were ruled out.The company’s “Specific Safety Rules” policy required thatnew workers should receive comprehensive safety rule trainingon the first day of employment supplemented by annualrefresher training. A range of topics, including the hazards ofdust accumulation, was covered but a review of the trainingrecords by CSB could find no evidence that this had beencovered since 2005 — between two and three years prior tothe accident. Documentary training sheets did not includeinformation on combustible dust. Some two months before theaccident (in December 2007) the US Occupational Safety andHealth Administration (OSHA) issued its Combustible DustNational Emphasis Programme3 and Imperial Sugar were awareof this. Yet, in January 2008, the company’s Written Program –Housekeeping & Material Storage Program made no mention ofcombustible dust. Institution of Chemical Engineers0260-9576/19/ 17.63 0.00
Loss Prevention Bulletin 266 April 2019 27Emergency plans and equipmentWithin the refinery and packing buildings, workers had torely on radios and cell phones to report or be alerted to anemergency. The emergency procedure directed them to useintercom but no such system was present in these areas. Therewere no visible or audible alarms.No evacuation drills were practised, though evacuationroutes were displayed. Emergency evacuation lights and exitsigns were in existence but the explosions and fires causedmany of them to fail. Thus, some workers had extremedifficulty finding their way out of the darkened buildings. Asalready stated, the emergency water sprinkler piping systemwas heavily damaged by the explosions. There were many fireextinguishers, including some on wheeled carts incorporatingas many as 16 portable ones and these were effective for smallto medium fires. However, against the major, rapidly advancingfires that ensued, they had little effect.Combustible dust characteristicsFor the best part of a century4 sugar dust has been recognisedas an extremely combustible material. Tests carried out onsamples of sugar and cornstarch from the Port Wentworthfacility indicated that a primary explosion fuelled by airbornesugar dust would be very capable of causing the degree ofdamage that resulted from this accident. Accumulations ofsugar dust on horizontal surfaces are a fire hazard. However,in order to ignite explosively, the dusts must become airborneand reach a concentration above the Minimum ExplosiveConcentration (MEC). A fireball will probably result whenairborne dust at concentrations above the MEC comes intocontact with an ignition source and the likelihood of explosionincreases if the airborne dust is confined as in the enclosedconveyors. Increasing pressure inside enclosed equipment(pressure piling) can cause rupture of equipment or, if rupturedoes not occur, result in fireballs travelling considerabledistances and igniting secondary fires far away from theinitial ignition source. All this was totally consistent with thesequence of events that actually occurred.ConclusionsStemming from their investigation, CSB came to the followingconclusions: Imperial Sugar and the granulated sugar industry generallyhad been aware of sugar dust explosion hazards since 1925but underestimated the hazard posed despite a history ofnear misses. The company had distributed the OSHA CombustibleDust National Emphasis Programme within the facility buthad not acted promptly on its advice regarding removingsignificant sugar dust accumulations. The design and maintenance of the sugar and cornstarchconveyors did not minimise the release of sugar and sugardusts into the work area. Whilst the importance of good housekeeping practiceshad been emphasised from as long ago as 1958, theywere inadequate to control and minimise significantaccumulations of sugar and combustible sugar dustthroughout the packing buildings. Institution of Chemical Engineers0260-9576/19/ 17.63 0.00 Airborne sugar dust concentrations exceeded the minimumexplosive concentration (MEC) inside the newly enclosedconveyor belts below Silos 1 and 2. Before the belts wereenclosed, it was probable that the MEC would not havebeen reached because dispersion into the wider work areawould have prevented this. The primary dust explosion was probably initiated by anoverheating bearing in the steel conveyor belt; there hadbeen previous fires caused in a similar way but all of themwere very minor. The primary explosion triggered massive secondary dustexplosions and fires throughout the packing buildings; theenclosed steel conveyor belt was not fitted with explosionvents. The secondary explosions and fires were the probablecause of the fourteen fatalities. Emergency evacuation plans were inadequate and thecompany had not carried out emergency evacuation drillsprior to the accident. The independent audit carried out in April 2007 by aproperty risk insurer did not properly address combustibledust hazards.Other dust explosionsThis accident was far from being an isolated case. The CSBreport itself instances three other accidents in the USA, all in2003, which between them resulted in a total of 14 deaths,many injuries and major plant damage. Furthermore, theCSB investigation report Combustible Dust Hazard Study(2006)5 identified 281 combustible dust incidents between1980 and 2005 that resulted in 119 fatalities and 718 injuries.This prompted CSB to recommend that OSHA should issue acomprehensive combustible dust standard for general industryand this was in progress at the time of the Port Wentworthaccident.In the UK, a major sugar dust explosion occurred in thesugar silo at the British Sugar Refinery in Cantley, Norfolk inJuly 2013. Although there were no fatalities or injuries, thedamage to plant was extensive. The plant was shut downand undergoing maintenance at the time, when weldingoperations on the outside of the silo feed bucket elevator ledto overheating of sugar coatings on the inside surface of theequipment. Molten metal penetrated through to the inside ofthe elevator casing and was a feasible cause of ignition of thesugar cloud present inside the elevator. The risk assessmentcarried out before work started was flawed in that it did notidentify the potential for an explosive atmosphere inside theelevator6.Then, in July 2015 the dreadful accident at the wood flourplant at Bosley, Cheshire occurred. Explosions and fire resultedin the deaths of four workers. Wood flour is another veryfinely divided substance prone to spontaneous ignition if notproperly controlled and contained.Against this background, the UK Health and SafetyExecutive provides guidance on the prevention of firesand explosions from dusts7 and issues an information sheetspecifically addressing Prevention of Dust Explosions in theFood Industry8. The Dangerous Substances and ExplosiveAtmospheres Regulations 2002 (DSEAR)9 underpin the
28 Loss Prevention Bulletin 266April 2019need for assessment and protection of substances that couldgive rise to explosion or fire, and methods of prevention ormitigation.RecommendationsCSB made recommendations to Imperial Sugar and to otherbodies aimed at addressing their findings. Principal amongstthese were that Imperial Sugar should: Review all of their facilities against the terms of the NationalFire Protection Association standards and other documentsand implement any corrective actions identified. Implement a company-wide comprehensive housekeepingprogramme to ensure that combustible dust does notaccumulate to hazardous quantities on horizontal surfaces,floors and equipment. Develop and implement training programmes foremployees and contractors that address combustible dusthazards. Improve the emergency evacuation policies andprocedures at the Port Wentworth facility.In addition, recommendations were made to various externalbodies to promulgate the investigation findings to a widerforum as appropriate. These included national and internationalorganisations such as The American Bakers Association, TheSugar Association, Sugar Industry Technologists and AmericanInstitute of Baking International. Risk insurance companieswere required to ensure that awareness of combustible dusthazards was fully understood.Author’s commentsThe CSB’s recommendations, although certainly valid, do notseem to go far enough to respond to such a disastrous accidentwith the hope that a recurrence could be avoided. Other issuesthat might have been addressed included: The absence of an effective “corporate memory.” Theprinciple of building up a reference bank of accident andnear miss data, and passing this on to employees, has beenestablished for many years now. However, this was notmentioned. Systems for the management of change were certainlynot strongly established unless CSB chose not to highlightthem. Enclosing the conveyor belts was a significantchange but it does not seem to have been subject to anyrisk assessment prior to implementation. OSHA were so concerned about the outcome of theaccident, and the possibility of similar ones recurring, thatthey wrote individual letters to 30,000 workers employedin dust-producing operations warning them of the hazards.The other distressing outcome of the accident, was that therefinery was closed down. Many of the damaged buildingshad to be demolished and, although Imperial Sugar intendedto rebuild the refinery and resume production, this proved tobe uneconomical and was not done. The result of this was aneconomic depression in Port Wentworth, due not only to theloss of the refinery itself, but also the knock-on effects on manylocal businesses.Relatively simple measures can sometimes yield largedividends. In this respect, a major British sugar-producingcompany eliminated, as far as was practicable, horizontalsurfaces that sugar dust could settle and accumulate on. Atriangular profile was installed on top of girders, purlins andother items thus enabling dust to slide off onto floors and othersurfaces from which it could more easily be cleaned up.References1. Investigation Report into a Sugar Dust Explosion andFire; Imperial Sugar Company, Port Wentworth, Georgia,USA, February 7, 2008. U S Chemical Safety and HazardInvestigation Board, Report No. 2008-05-1-GA, September,2009. https://www.csb.gov/assets/1/20/imperial sugarreport final updated.pdf?139022. 2008 Georgia sugar refinery explosion. https://en.wikipedia.org/wiki/2008 Georgia sugar refineryexplosion3. The OSHA Combustible Dust National Emphasis Program,CPL 03-00-006, October, 2007.4. The Dust Hazard in Industry, W E Gibbs, Richard Clay andSons Ltd, Bungay, Suffolk, UK, 1925.5. Investigation Report, Combustible Dust Hazard Study,Investigation Number 2006-H-1, US Chemical Safety andHazard Board, November 2006.6. Dust Explosion in Sugar Silo Tower; I Chem E SymposiumSeries No 154, 2008.7. Safe Handling of Combustible Dusts: Precautions AgainstExplosions, HSG 103, HSE Books, ISBN 0 7176 0725 9.8. Prevention of Dust Explosions in the Food Industry,http://www.hse.gov.uk/dustexplosion.htm9. The Dangerous Substances and Explosive AtmospheresRegulations, 2002, Statutory Instrument 2776. Institution of Chemical Engineers0260-9576/19/ 17.63 0.00
In February 2008, a series of sugar dust explosions and a fire occurred at the Imperial Sugar manufacturing facility in Port Wentworth, Georgia, USA. Fourteen workers were killed and a further 36 injured. The facility housed a refinery that converted raw sugar cane into gran
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month and year of start and end for each occupation. We also asked about occupational exposures during the past 12 months, i.e., gas, smoke or dust; smell of frying; car exhaust fumes/engine fumes; mineral dust; organic dust (flour dust, wood dust, paper dust or textile dust); inorganic dust (grinding, milling, turning, mineral wool,
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