U.S. CHEMICAL SAFETY AND HAZARD INVESTIGATION BOARD

INVESTIGATION REPORT

Report No. 2008-05-I-GA

September 2009

SUGAR DUST EXPLOSION AND FIRE 

(14 Killed, 36 Injured)

 IMPERIAL SUGAR COMPANY

PORT WENTWORTH, GEORGIA

FEBRUARY 7, 2008

KEY ISSUES:

• COMBUSTIBLE DUST HAZARD RECOGNITION 

• MINIMIZING COMBUSTIBLE DUST ACCUMULATION IN THE WORKPLACE

• EQUIPMENT DESIGN AND MAINTENANCE 
i 

Contents

EXECUTIVE SUMMARY .......................................................................................................................... 1

1.0 INTRODUCTION ........................................................................................................................... 3

1.1 Background ......................................................................................................................... 3

1.2 Investigative Process ........................................................................................................... 5

1.3 Imperial Sugar Company .................................................................................................... 6

1.3.1 Corporate Governance ............................................................................................ 6

1.3.2 Corporate and Facility Management ...................................................................... 7

1.4 Facility Description ............................................................................................................. 8

1.4.1 Granulated Sugar Storage Silos ............................................................................ 10

1.4.2 Silos 1 and 2 Steel Conveyor Belt ........................................................................ 14

1.4.3 Bosch Packing Building ....................................................................................... 15

1.4.4 South Packing Building ........................................................................................ 16

1.4.5 Sugar Spillage and Dust Control .......................................................................... 17

2.0 INCIDENT DESCRIPTION .......................................................................................................... 19

2.1 Explosions and fires .......................................................................................................... 19

2.2 Emergency Response ........................................................................................................ 21

3.0 INCIDENT ANALYSIS ................................................................................................................ 22

3.1 Combustible Dust Characteristics ..................................................................................... 22

3.2 Combustible Dust Explosions ........................................................................................... 26

3.3 The Port Wentworth Incident............................................................................................ 27

3.3.1 Pre-explosion Sugar Dust Incident History .......................................................... 28

3.3.2 Steel Belt Conveyor Modifications ...................................................................... 29

3.3.3 Primary Event Location ........................................................................................ 29

3.3.4 Primary Event Combustible Dust Source ............................................................. 32

3.3.5 Secondary Dust Explosions .................................................................................. 34

3.4 Ignition Sources ................................................................................................................ 35

3.4.1 Open Flames and Hot Surfaces ............................................................................ 35

3.4.2 Ignition Sources Inside the Steel Belt Enclosure .................................................. 36

3.5 Worker Training ............................................................................................................... 37

3.6 Hazards Management ....................................................................................................... 39
ii

3.6.1 Evacuation, Fire Alarms, and Fire Suppression ................................................... 39

3.6.2 Electrical Systems Design .................................................................................... 40

3.6.3 Sugar Dust Handling Equipment .......................................................................... 44

3.6.4 Housekeeping and Dust Control ........................................................................... 45

3.7 Dust Explosion Hazard Awareness ................................................................................... 47

3.7.1 Imperial Sugar Management and Workers ........................................................... 47

3.7.2 Property Risk Insurers .......................................................................................... 51

4.0 REGULATORY ANALYSIS ........................................................................................................ 53

4.1 Georgia Fire Codes ........................................................................................................... 53

4.2 Occupational Safety and Health Administration (OSHA) ................................................ 54

5.0 MODEL FIRE CODES.................................................................................................................. 56

5.1 National Fire Protection Association ................................................................................ 56

5.2 International Code Council ............................................................................................... 57

6.0 TRADE ASSOCIATIONS ............................................................................................................ 58

6.1 AIB International .............................................................................................................. 58

6.2 American Bakers Association ........................................................................................... 59

6.3 The Sugar Association ...................................................................................................... 59

6.4 Sugar Industry Technologists ........................................................................................... 60

7.0 PREVIOUS CSB DUST EXPLOSION INVESTIGATIONS ....................................................... 61

8.0 KEY FINDINGS: .......................................................................................................................... 63

9.0 INCIDENT CAUSES .................................................................................................................... 65

10.0 RECOMMENDATIONS ............................................................................................................... 66

10.1 Imperial Sugar Company .................................................................................................. 66

10.2 AIB International .............................................................................................................. 67

10.3 American Bakers Association ........................................................................................... 68

10.4 Risk Insurance Management Society, Inc ......................................................................... 68

10.5 Zurich Services Corporation ............................................................................................. 68

11.0 REFERENCES .............................................................................................................................. 70

APPENDIX A – INCIDENT EVENT SEQUENCE .................................................................................. 72

APPENDIX B – EXPLOSION PROGRESSION IN PACKING BUILDINGS ........................................ 81
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Figures 

Figure 1. West bucket elevator tower; silos 3, 2, and 1; and south packing building ............................... 4

Figure 2. Imperial Sugar Company organization prior to the incident ..................................................... 7

Figure 3. Port Wentworth, Georgia, organization prior to the incident ................................................... 8

Figure 4. Imperial Sugar facility before the explosion. ............................................................................ 9

Figure 5. Packing buildings’ first floor plan ........................................................................................... 11

Figure 6. Silo tunnel and conveyor plan ................................................................................................. 12

Figure 7. Granulated sugar supply and discharge through the silos ....................................................... 13

Figure 8. Granulated sugar steel conveyor belts above the silos ............................................................ 14

Figure 9. Silo tunnel steel conveyor belt ................................................................................................ 14

Figure 10. Violent fireball erupting from the facility ............................................................................... 19

Figure 11. Large fireball erupts from the packing buildings 15 minutes after first explosion ................. 20

Figure 12. Screw conveyors and ruptured steel bulk granulated sugar bins ............................................. 27

Figure 13. Steel belt covers crumpled from an initial dust explosion inside the steel belt enclosure ....... 30

Figure 14. Steel belt cover panels blown out of the tunnel into the packing building .............................. 31

Figure 15. South stairwell brick walls blown into the packing building .................................................. 31

Figure 16. Access port and steel rod inside the pantleg room used to break sugar lumps ........................ 33

Figure 17. Limited clearance between discharge chute and the steel belt ................................................ 33

Figure 18. Three-inch thick concrete floor slabs lifted off the steel supports .......................................... 34

Figure 19. Motor cooling fins and fan guard covered with sugar dust ..................................................... 36

Figure 20. Packaging equipment hindered evacuation in the darkened building ..................................... 40

Figure 21. Sugar dust and cornstarch accumulations ................................................................................ 42

Figure 22. Non-dust rated and rated electrical devices in the silo tunnel ................................................. 42

Figure 23. Sugar and dust accumulation on a screw conveyor in the south packing building ................. 43

Figure 24. Deep piles of sugar accumulated on floors and equipment.. ................................................... 47

Tables 

Table 1. Measured properties of combustible dusts .............................................................................. 23

Table 2. Particle size of some common combustible and non-combustible materials ......................... 24

Table 3. Combustible dust hazard classes ............................................................................................. 25

Table 4. Test results of samples collected from the Port Wentworth facility ........................................ 25
iv

Acronyms and Abbreviations

AIB AIB International

ABA American Bakers Association

ATF U.S. Bureau of Alcohol, Tobacco, Firearms, and Explosives 

CFR Code of Federal Regulations 

CSB U.S. Chemical Safety and Hazard Investigation Board

EPA U.S. Environmental Protection Agency 

gm grams 

GMP Good Manufacturing Practice (GMP)

IC Incident Commander 

IBC International Building Code 

ICC International Code Council 

IFC International Fire Code 

L Liter

m meters

m3 cubic meter

MEC minimum explosible concentration 

MIE minimum ignition energy

MIT minimum ignition temperature

mJ millijoules

MSDS Material Safety Data Sheet(s)

NEP National Emphasis Program

NFPA National Fire Protection Association 

OSHA Occupational Safety and Health Administration 

μm microns (10-6 meters)
1 

Executive Summary 

On February 7, 2008, at about 7:15 p.m., a series of sugar dust explosions at the Imperial Sugar 

manufacturing facility in Port Wentworth, Georgia, resulted in 14 worker fatalities. Eight workers 

died at the scene and six others eventually succumbed to their injuries at the Joseph M. Still Burn 

Center in Augusta, Georgia. Thirty six workers were treated for serious burns and injuries—some 

caused permanent, life altering conditions. The explosions and subsequent fires destroyed the sugar 

packing buildings, palletizer room, and silos, and severely damaged the bulk train car loading area 

and parts of the sugar refining process areas. 

The Imperial Sugar manufacturing facility housed a refinery that converts raw cane sugar into 

granulated sugar. A system of screw and belt conveyors, and bucket elevators transported granulated 

sugar from the refinery to three 105-foot tall sugar storage silos. It was then transported through 

conveyors and bucket elevators to specialty sugar processing areas and granulated sugar packaging 

machines. Sugar products were packaged in four-story packing buildings that surrounded the silos, or 

loaded into railcars and tanker trucks in the bulk sugar loading area. 

The U.S. Chemical Safety and Hazard Investigation Board (CSB) determined that the first dust 

explosion initiated in the enclosed steel belt conveyor located below the sugar silos. The recently 

installed steel cover panels on the belt conveyor allowed explosive concentrations of sugar dust to 

accumulate inside the enclosure. An unknown source ignited the sugar dust, causing a violent 

explosion. The explosion lofted sugar dust that had accumulated on the floors and elevated horizontal 

surfaces, propagating more dust explosions through the buildings. Secondary dust explosions 

occurred throughout the packing buildings, parts of the refinery, and the bulk sugar loading buildings. 

The pressure waves from the explosions heaved thick concrete floors and collapsed brick walls, 

blocking stairwell and other exit routes. The resulting fires destroyed the packing buildings, silos, 

palletizer building and heavily damaged parts of the refinery and bulk sugar loading area. 
2 

The CSB investigation identified the following incident causes:

1. Sugar and cornstarch conveying equipment was not designed or maintained to minimize the 

release of sugar and sugar dust into the work area.

2. Inadequate housekeeping practices resulted in significant accumulations of combustible 

granulated and powdered sugar and combustible sugar dust on the floors and elevated 

surfaces throughout the packing buildings. 

3. Airborne combustible sugar dust accumulated above the minimum explosible concentration 

inside the newly enclosed steel belt assembly under silos 1 and 2. 

4. An overheated bearing in the steel belt conveyor most likely ignited a primary dust explosion. 

5. The primary dust explosion inside the enclosed steel conveyor belt under silos 1 and 2 

triggered massive secondary dust explosions and fires throughout the packing buildings. 

6. The 14 fatalities were most likely the result of the secondary explosions and fires.

7. Imperial Sugar emergency evacuation plans were inadequate. Emergency notifications inside 

the refinery and packaging buildings were announced only to personnel using 2-way radios 

and cell phones. Many workers had to rely on face-to-face verbal alerts in the event of an 

emergency. Also, the company did not conduct emergency evacuation drills. 

Subsequent to the Imperial Sugar incident, the Occupational Safety and Health Administration 

(OSHA) announced it intends to initiate rulemaking on a combustible dust standard. This was among 

several recommendations that the CSBs 2006 Combustible Dust Study made to address combustible 

dust workplace hazards in general industry. 

Based on this incident, the CSB makes recommendations to The Imperial Sugar Company; AIB 

International; The American Bakers Association; The Risk Management Society, Inc.; Zurich 

Services Corporation; and The Occupational Safety and Health Administration. 
3 

1.0 Introduction

1.1 Background

At about 7:15 p.m. on February 7, 2008, a sugar dust explosion occurred in the enclosed steel 

conveyor belt under the granulated sugar storage silos at the Imperial Sugar Company sugar 

manufacturing facility in Port Wentworth, Georgia. Seconds later, massive secondary dust explosions 

propagated throughout the entire granulated and powdered sugar packing buildings, bulk sugar 

loading buildings, and parts of the raw sugar refinery. Three-inch thick concrete floors heaved and 

buckled from the explosive force of the secondary dust explosions as they moved through the fourstory building on the south and east sides of the silos. The wooden plank roof on the palletizer 

building was shattered and blown into the bulk sugar railcar loading area. Security cameras located at 

businesses to the north, south, and west of the facility captured the sudden, violent fireball eruptions 

out of the penthouse1

When Garden City and Port Wentworth fire department personnel arrived minutes later they were 

confronted with dense smoke, intense heat, ruptured fire water mains, and large amounts of debris 

strewn around the fully involved burning buildings. Workers at the facility had already started search 

and rescue efforts and injured workers were being triaged at the main gate guardhouse. 

 on top of the silos, the west bucket elevator structure, and surrounding 

buildings. 

Eight workers died at the scene, including four who were trapped by falling debris and collapsing 

floors. Two of these fatally injured workers had reportedly reentered the building to attempt to rescue 

their co-workers, but failed to safely escape. Nineteen of the 36 workers transported to Savannah 

Memorial Hospital who were severely burned were transported to the Joseph M. Still Burn Center in 

 

1 The silo penthouse was a weather-tight structure on top of the three silos that housed granulated sugar belt 

conveyors. 
4 

Augusta, Georgia where six eventually succumbed to injuries, bringing the total fatalities to 14 

workers—the last burn victim died at the burn center six months after the incident. 

Thirty six injured workers ultimately survived including some with permanent, life altering 

conditions. Approximately 85 other workers at the facility at the time of the incident were uninjured. 

The major fires in the buildings were extinguished the next day, but small fires continued burning for 

many days. The granulated sugar fires in the 105-foot tall silos continued to smolder for more than 7 

days before being extinguished by a commercial industrial firefighting company. The packing 

buildings, granulated sugar silos, and palletizer room were destroyed. The bulk sugar loading area 

and parts of the refinery were severely damaged by the explosion and fires (Figure 1).

Figure 1. West bucket elevator tower; silos 3, 2, and 1; and south packing building destroyed 

by the February 7, 2008, sugar dust explosions and fires
5 

This report makes recommendations to Imperial Sugar Company; AIB International; the American 

Bakers Association; the Risk Insurance Management Society, Inc.; Zurich Services Corporation; and 

The Occupational Safety and Health Administration. 

1.2 Investigative Process

The CSB investigation team arrived at the Imperial Sugar facility the morning of February 8, 2008. 

The Bureau of Alcohol, Tobacco, Firearms, and Explosives (ATF), the Georgia State Fire Marshal’s 

office, and the responding fire departments were conducting victim recovery operations, fire 

suppression inside the silos and other hot-spots inside the buildings, and the cause and origin 

investigation. 

The CSB team met with the Port Wentworth fire chief,2

During the next 4 months, the CSB investigators examined and photographed the interior of the 

heavily damaged buildings and equipment and interviewed eyewitnesses who were working at the 

refinery the night of the incident, other company and contractor employees, and injured workers. The 

team examined engineering documents, worker training records, and equipment operation and 

maintenance records; witnessed the building demolition work; and examined equipment recovered 

from the wreckage before releasing the equipment to the company. Finally, the CSB commissioned 

 the ATF lead investigator, the State Fire 

Marshal, Occupational Safety and Health Administration (OSHA) investigators, and Imperial Sugar 

management personnel to explain the CSBs purpose and authority for conducting an investigation 

independently of the other agencies and organizations. The CSB and OSHA investigation supervisors 

coordinated witness interviews, evidence collection, and other investigation activities with the ATF 

lead investigator and the incident commander. 

 

2 Incident management conformed to the National Incident Management System (NIMS) structure throughout 

the fire suppression, search, rescue, and recovery activities. The Port Wentworth Fire Department headed the 

incident command.
6 

testing to determine the combustibility characteristics of the granulated and powdered sugar, raw 

sugar, and cornstarch samples collected at the site. 

1.3 Imperial Sugar Company

Imperial Sugar Company, headquartered in Sugar Land, Texas, was incorporated in 1924. The 

company purchased the Port Wentworth facility from Savannah Foods and Industries, Inc. in 

December 1997. At the time of the incident, Imperial Sugar operated the Port Wentworth facility and 

a sugar manufacturing and packaging facility in Gramercy, Louisiana, and a warehousing operation in 

Ludlow, KY. The sugar manufacturing facilities received raw sugar3 and refined it into granulated 

sugar. Some granulated sugar was used to make powdered sugar, specialty sugars, and liquid sugar 

products. They packaged sugar products in capacities ranging from bulk tank and hopper railcar, to 

100-pound bags, to small boxes and bags. Customers included industrial bakeries, and large chain 

and small grocers.4

1.3.1 Corporate Governance 

 In 2007, the company produced more than 1.3 million tons of sugar, making it 

one of the largest sugar refiners in the U.S. More than 350 employees and contractors worked at the 

Port Wentworth facility, where annual sugar production exceeded 700 thousand tons.

Imperial Sugar Company is a public company, listed on the NASDAQ. The Imperial Sugar Company 

Board of Directors comprises eight members plus the board chairman. Board member backgrounds 

include investment banking, international diversified manufacturing, food and chemical 

manufacturing industries, and wholesale food distribution. The president and chief executive officer 

(CEO) is also a board member. 

 

3 Imperial Sugar material suppliers process sugar cane into “raw sugar,” a crystalline product that resembles 

light- to medium-brown granulated sugar. Raw sugar has low combustibility characteristics and is unlikely to 

generate combustible sugar dust. 

4 As of the date of this report, the Gramercy, LA facility continued operations and the Port Wentworth, GA 

facility was being rebuilt. 
7 

1.3.2 Corporate and Facility Management

Nine company officers in Sugar Land, Texas, manage the day-to-day business of Imperial Sugar. 

Management positions include finance, commodities management, general counsel, administration, 

engineering, technology, and sales (Figure 2). Prior to the incident, the company did not have a 

dedicated officer level position responsible for workplace safety. Instead, the corporate safety director 

reported to the director of human resources in the administration department. The director of human 

resources had minimal occupational safety management experience and training.

Figure 2. Imperial Sugar Company organization prior to the incident

The corporate safety director was responsible for overseeing workplace safety and facility security 

programs. The Port Wentworth management team had a safety and environmental manager who 

reported directly to the plant manager (Figure 3). Safety and product quality personnel at the 
8 

refineries reported to the corporate technical services manager in Port Wentworth. The Port 

Wentworth safety coordinator reported to the safety and environmental manager. 

Figure 3. Port Wentworth, Georgia, organization prior to the incident

1.4 Facility Description

Savannah Foods and Industries, Inc. began constructing the Port Wentworth facility in the early 

1900s; granulated sugar production started in 1917.5

Figure 4

 Over the years the facility added refining and 

packaging capacity, raw sugar and product warehouses, and upgraded the steam/electric powerplant 

( ). 

Refined sugar was stored in three silos, and then transferred to the bulk sugar truck and train loading 

area, to the packing buildings, and to the powdered sugar production equipment, which was located in 

 

5 The product name “Dixie Crystals”® was created when the Savannah Foods refinery began production in the 

early 1900s.
9 

the south packing building. Packaged products were palletized, and transferred to a warehouse for 

distribution to customers.

Figure 4. Imperial Sugar facility before the explosion. Granulated sugar 

storage silos and packing buildings are circled. Raw sugar 

warehouses in lower right (Chatham County, GA GIS photo)

Dozens of screw conveyors,6 bucket elevators,7

Figure 5

 and horizontal conveyor belts transported granulated 

sugar throughout the packing buildings ( ). Although bucket elevators were enclosed and 

screw conveyors were covered, they were not adequately sealed to prevent releasing sugar dust and 

sugar into the work areas. Because the large open work areas were not equipped with airborne dust 

removal equipment, sugar dust accumulated on overhead conduit, piping, ceiling beams, lights, and 

equipment. The closed granulated sugar screw conveyors located throughout the facility were not 

 

6 A screw conveyor is a dry bulk material conveyor consisting of a rotating helical screw inside a closed trough. 

Granulated or powdered sugar enters the top feed opening at one end. The rotating helical screw pushes the 

sugar along the trough to the opposite end of the conveyor where it exits through a bottom discharge chute at 

the opposite end.

7 A bucket elevator is a dry bulk material conveyor consisting of plastic or metal buckets attached to an endless 

fiber belt inside a closed vertical rectangular housing. Granulated sugar is scooped from a pit, or directly 

flows into the buckets at the base of the bucket elevator and pours out of the bucket into a discharge chute at 

the top of the housing. 
10 

equipped with dust removal equipment and were not designed to safely vent overpressure outside the 

building if combustible dust inside the enclosure ignited. 

1.4.1 Granulated Sugar Storage Silos

Three 40-foot diameter, 105-foot tall concrete silos conditioned and stored the granulated sugar 

produced in the refinery. Each 5-million pound capacity silo sat on a raised circular concrete 

foundation above the packing building floor. Two belt conveyors were located under the silo floors in 

a 130-foot long tunnel, which was 7 1⁄2 feet tall and 12 feet wide (Figure 6). 

Granulated sugar from the refinery entered silo 3 and then was transferred into silo 1 and 2. The 

sugar was transferred from silos 1 and 2 to the bulk sugar building, powdered sugar mills, specialty 

sugar production equipment, and granulated sugar packing machines. 

Sugar exited silo 3 into an Aerobelt® 8

Figure 7

 conveyor in the silo tunnel, which discharged the sugar into 

the west bucket elevator pit. The bucket elevator lifted the sugar to the penthouse and onto another 

series of conveyor belts, into silos 1 and 2 ( and Figure 8). Granulated sugar exited two 18-

inch diameter penetrations in the floors of silo 1 and 2 onto a steel conveyor belt in the silo tunnel. 

Separate 18-inch diameter floor openings fed sugar to the screw conveyors under the north and south 

quadrants of each silo. Various conveyors and bucket elevators distributed the sugar to the powdered 

sugar mills, the packaging equipment, and the bulk sugar building.9

 

 

8 An Aerobelt is a dust-tight conveyor belt assembly with a fiber belt that travels on an air cushion. It is 

equipped with dust collector attachment ports for removing airborne dust inside the enclosure, which were 

connected to the wet dust collectors.

9 Granulated sugar was loaded into semi-trailers and railcars in the bulk sugar building. 
11 

Figure 5. Packing buildings first floor plan
12 

Figure 6. Silo tunnel and conveyor plan
13 

Figure 7. Granulated sugar supply and discharge through the silos 

Pantleg rooms 

(typical)
14 

Figure 8. Granulated sugar steel conveyor belts above the silos, circa 

1990. Heavy dust accumulation on conduit and spilled sugar on 

the floor (Imperial Sugar photo)

1.4.2 Silos 1 and 2 Steel Conveyor Belt

A 32-inch wide, 80-foot long steel conveyor belt (Figure 9) in the silo tunnel transported granulated 

sugar from silos 1 and 2 into the packaging production bucket elevator pit at the east side of silo 1. 

Similar steel belt conveyors were located in the penthouse above the silos.

Figure 9. Silo tunnel steel conveyor belt (removed after incident)

For many years, granulated sugar on these conveyors was exposed to possible contamination from 

debris that could fall onto the sugar. In 2007, Imperial Sugar installed a stainless steel frame with top 
15 

and side panels to fully enclose each belt assembly to protect the granulated sugar from falling debris 

and reduce the possibility of intentional contamination. The top and side panels were removable to 

provide access for cleaning and conveyor maintenance. Although sugar dust was generated as the 

sugar flowed onto the belt and when flow blockages caused sugar to spill off the belt, these new 

enclosures were not equipped with a dust removal system and were not equipped with explosion 

vents. 

During more than 80 years of operation, sugar dust released inside the large open volume of the silo 

tunnel most likely never accumulated to concentrations above the minimum explosible concentration 

(MEC). However, after the steel belt was enclosed, sugar dust was contained and remained suspended 

inside the unventilated enclosed space. Because the enclosure was one-tenth the volume of the 

tunnel,10

1.4.3 Bosch Packing Building 

sugar dust could easily accumulate to concentrations above the MEC. Furthermore, multiple 

potential dust ignition sources were identified inside the enclosure. 

The four-story Bosch packing building located on the north side of the silos was a steel frame, 

corrugated steel-sided structure with poured concrete floors. Large doorways at the south-east corner 

on each floor gave forklift and personnel access to the south packing building. A steel-framed 

stairway enclosed in a concrete masonry block wall was located between silos 1 and 2 to provide 

access to each floor and the roof (see Figure 5).

Granulated sugar was transported by screw conveyors and a bucket elevator to the screens inside the 

“hummer room”11

 

10 The volume inside the tunnel was approximately 8,700 cubic feet. The volume inside the enclosed steel belt 

assembly was approximately 850 cubic feet. 

 located on the roof of the building. Screw conveyors transported the screened 

sugar to feed hoppers on the third floor above each packaging machine. The second floor contained 

11 The hummer room contained granulated sugar sieves, which removed lumps and separated the sugar into 

standard grain sizes.
16 

granulated sugar packaging machines and paper and plastic packaging supplies. Conveyors

transported the packaged sugar west to the palletizer room. Packaging supplies, including paper and 

plastic rolls, and pre-formed paper bags and boxes were stored on the first, third, and fourth floors. 

1.4.4 South Packing Building

The south packing building was a four-story, steel-frame structure with 3-inch thick poured concrete 

floors and brick exterior walls. The three silos formed the north wall. A steel-frame, brick wall 

enclosed stairway was located between silos 1 and 2 to provide access to the floors above. The east 

end of the packing building opened into the refinery areas. Heavy, semi-transparent plastic strip 

curtains were typically installed on the large passageways to contain airborne dust. 

The second and third floors housed granulated, powdered, and soft (brown) sugar packaging 

equipment. Screw conveyors and bucket elevators transported the granulated sugar to hoppers above 

the packaging equipment throughout the packing building. Belt and roller conveyors transported the 

packaged sugar products to the palletizer room, some passing through large openings in the floors and 

west wall.12

Container packaging supplies including paper, plastic, and cardboard were stored near the packaging 

equipment. Packaging machines filled paper and plastic bags and cardboard containers. The machines 

were equipped with Plexiglas® panels to protect workers from moving machine parts, hot surfaces, 

and other hazards. The enclosures also contained some of the sugar dust that was generated during 

container filling. Vacuum ductwork attached to the packaging machines removed some sugar dust 

from the packaging machines. Dust collectors located on the packing building roof removed sugar 

dust from air transferred from the packaging machines.

 

 

12 Floor and wall openings provided conduits for the explosive overpressures and fires.
17 

The powdered sugar production equipment was located on the fourth floor. Cornstarch was 

transported from an outdoor storage silo into hoppers above the grinding mills through a pressurized 

air transfer line. A small amount of cornstarch13

1.4.5 Sugar Spillage and Dust Control

 was added to the granulated sugar; then the mixture 

was fed into the grinding mills. The mills pulverized the granulated sugar/cornstarch mixture to the 

specified grain size, and then discharged the powdered sugar into hoppers above the packaging 

machines. The grinding mills were connected to the dry dust collectors system to remove airborne 

sugar and cornstarch dust.

The CSBs investigation determined that sugar conveying and processing equipment were not 

adequately sealed; so significant quantities of sugar spilled onto the floors. Injury incident reports, 

internal correspondence, and other records identified significant accumulations of spilled sugar. Less 

than 2 months before the incident, an internal inspection performed by company supervisors and 

quality assurance personnel indicated that many tons of spilled sugar had to be routinely removed 

from the floors and returned to the refinery for reprocessing. Packaging operators and other 

employees also reported significant sugar dust escaping the packaging equipment into the work areas. 

The cornstarch transport system, grinding mills, and powdered sugar packaging machines generated 

significant sugar dust in the work area. Workers reported that airborne sugar dust and spilled sugar in 

the powdered sugar processing and packaging work areas were a constant problem and that 

significant accumulations were typically seen on equipment and the floor. One worker told the CSB 

that he used a squeegee to clear a path on the floor through spilled powdered sugar to get to 

equipment he operated during his shift. 

 

13 Powdered sugar contains about 3% cornstarch to prevent the sugar from clumping. 
18 

Dust collection systems were attached to the packaging machines to remove sugar dust generated 

during container filling. Sugar screening equipment and the powdered sugar mills were also equipped 

with dust removal systems. 

The dust transport ducts attached to the powdered sugar and cornstarch systems were connected to 

dry dust collectors. Dust transport ducts attached to granulated sugar equipment were connected to 

wet dust collectors. However, as reported in a January 2008 review of the dust handling system,14

 

14 Imperial Sugar hired an outside consultant to evaluate air flow velocities, pressure drops, and other operating 

parameters on the dry and wet dust collection systems. The report identified numerous dust collection 

system design and maintenance deficiencies. Because the report was delivered only a few days before the 

February incident, Imperial Sugar management had not had the opportunity to review or act on the report 

findings.

 the 

dust collection equipment was in disrepair, and some equipment was significantly undersized or 

incorrectly installed. Some dust duct pipes were found to be partially, and in some locations, 

completely filled with sugar dust. 
19 

2.0 Incident Description 

2.1 Explosions and fires

Shortly before 7:15 p.m. on February 7, 2008, the new Imperial Sugar Company CEO15

Figure 10

 was touring 

the facility with three employees. Walking through the refinery toward the south packing building 

they were startled by what sounded and felt like a heavy roll of packing material dropped from a 

forklift somewhere in the packing building. Three to five seconds later a loud explosion knocked 

them backward, and debris was thrown through the large packing building doorway. The security 

guard at the gatehouse, and other workers in nearby buildings, also heard a loud explosive report. 

Outside, massive flames and debris erupted above the packing buildings and silos. A security camera 

at the Georgia Ports Authority located south of the facility recorded the first of many fireballs 

erupting from the Imperial Sugar facility ( ). 

Figure 10. Violent fireball erupting from the facility (elapsed time - 16 seconds) 

(Georgia Ports Authority security video).

Three-inch thick concrete floors in the south packing building heaved and buckled from the explosive 

force of the sugar dust-fueled explosions as they progressed through the packing buildings and into 

 

15 Imperial Sugar Company hired a new Chief Operating Officer in February, 2007. He was promoted to the 

position of Chief Executive Officer on January 29, 2008, nine days before the Port Wentworth explosion.
20 

adjacent buildings. The wooden roof on the palletizer room was shattered and blown into the bulk 

sugar rail loading area.

Workers in the packing buildings had little or no warning as walls, equipment, and furniture were 

thrown about. Superheated air burned exposed flesh. Workers attempting to escape struggled to find 

their way out of the smoke-filled, darkened work areas. Debris littered the passageways. Some exits 

were blocked by collapsed brick walls and other debris. The fire sprinkler system failed because the 

explosions ruptured the water pipes. 

Intense fireballs advanced through the entire north and south packing and palletizer buildings as sugar 

dust, shaken loose from overhead surfaces, ignited. Heaving and buckling floors opened large 

crevasses. The piles of granulated and powdered sugar that had accumulated around equipment rained 

down and intensified the fires burning below. Fireballs advanced through enclosed screw conveyors 

and ignited fires in the refinery and bulk sugar building hundreds of feet from the packing buildings 

where the incident had begun. Violent fireballs erupted from the facility for more than 15 minutes as 

spilled sugar and accumulated sugar dust continued fueling the fires (Figure 11).

Figure 11. Large fireball and burning debris erupt from the packing buildings 15 minutes after first 

explosion (elapsed time - 10 seconds) (PCS Phosphate security video).
21 

2.2 Emergency Response

Garden City and Port Wentworth fire department personnel were on the scene in less than 10 minutes 

after the first explosion. They were confronted with dense smoke, intense heat, ruptured water mains, 

and large debris strewn around the fully involved burning buildings. The emergency responders 

immediately started search and rescue operation, which continued for many hours. Workers at the 

facility had already started search and rescue efforts, and seriously burned victims were being triaged 

at the main guardhouse north of the packing building and at the truck scale located west of the 

warehouse. Other agencies responded and assisted the Port Wentworth fire department with the 

emergency response, including

• Pooler, Bloomingdale, Thunderbolt, Savannah, and Effingham County Fire Departments

• Savannah Chatham Metropolitan Police 

• Georgia State Fire Marshal

• Georgia Emergency Management Agency

• Chatham County Emergency Management Agency

• Georgia Search and Rescue 

• Salvation Army

• American Red Cross

The major fires in the buildings were extinguished the next day; however, the silo fires continued to 

smolder for 7 days before they were finally extinguished on February 15. 

Twelve Imperial Sugar employees and two contractors were fatally injured; four workers were fatally 

burned when falling debris and collapsing floors trapped them in the burning buildings. Four other 

workers could not escape the fires and died at the scene, including two who had reentered the burning 

structure to attempt to rescue their coworkers. Six seriously burned victims died at the Joseph M. Still 

Burn Center in Augusta, Georgia; the last died six months after the incident. Thirty-six injured 

workers, some seriously burned, ultimately survived. Approximately 70 other workers at the facility 

the night of the incident were uninjured. 
22 

3.0 Incident Analysis 

3.1 Combustible Dust Characteristics

Combustible dust hazard studies, including sugar dust, date back more than 80 years. In 1924, R.V. 

Wheeler (Wheeler, 1924) divided combustible dusts into three classes based on ignitability and 

relative burn rates: 

• Class I – Dusts that ignite and propagate flame readily, the source of heat required for 

ignition being comparatively small. 

• Class II – Dusts that are readily ignited, and which, for the propagation of flame, require a 

heat source of large size or high temperature.

• Class III – Dusts that do not appear to be capable of propagating flame.

The 1925 publication The Dust Hazard in Industry (Gibbs) concludes that

[S]ugar, dextrin, starch and cocoa are the most dangerous, sugar exceptionally so. 

Sugar ignites when projected as a cloud against a surface heated to below red heat, 

and when ignition has taken place, the flame travels throughout the dust-cloud with 

great rapidity.

The National Fire Protection Association (NFPA) defines a combustible dust as any “finely divided 

solid material regardless of particle size and [that] presents a fire or explosion hazard when dispersed 

and ignited in air” (NFPA, 2006). Standardized test procedures used to experimentally determine 

important properties of a combustible dust are listed in Table 1. 
23 

Table 1. Measured properties of combustible dusts (Dastidar, 2005)

Property Definition Test Method Application

Kst

Dust deflagration 

index ASTM E 1226 Measures the relative explosion 

severity compared to other dusts

Pmax

Maximum explosion 

overpressure 

generated in the test 

chamber

ASTM E 1226

Used to design enclosures and 

predict the severity of the 

consequence

(dP/dt)max Maximum rate of 

pressure rise ASTM E 1226 Predicts the violence of an 

explosion; used to calculate KSt

MIE Minimum ignition 

energy

ASTM E 2019 Predicts the ease and likelihood of 

ignition of a dispersed dust cloud

MEC Minimum explosible 

concentration ASTM E 1515

Measures the minimum amount of 

dust, dispersed in air, required to 

spread an explosion. 

Analogous to the lower 

flammability limit (LFL) for gas/air 

mixtures

Table 2 lists particle sizes of common materials, and the sugar and cornstarch samples collected at the 

Port Wentworth facility.
24 

Table 2. Particle size of some common combustible and 

non-combustible materials16

Material

 

Size (microns)

Talcum powder, red blood cells 

fine silt, cocoa 5 to 10

Pollen, milled flour, coarse silt 44 to 74

Table salt 105 to 149

Cornstarch from the Port Wentworth 

facility storage silo 10

Powdered sugar product from the 

Port Wentworth facility 23

Granulated sugar product from the 

Port Wentworth facility1

 286

Note 1. Sample first passed through 500 μm sieve

The deflagration index, Kst, is used to estimate the relative explosion severity of the dust being 

examined. To determine Kst, dust samples of known particle size, moisture content, and concentration 

are ignited in a standard 20-liter test apparatus. The test chamber pressure as a function of time is 

recorded for successively increasing sample concentrations. The value of Kst is calculated using the 

equation: 

Kst = (dP/dt)max x [Test chamber volume]1/3

The higher the value of Kst, the more energetic a dust explosion can be. Combustible dust is assigned 

one of three hazard classes, ST1, ST2, or ST3, based on the deflagration index determined from the 

test results (Table 3).

 

16 Source unless noted in table: http://www.wateruse.com/micron_equivalents.htm (June, 2009).
25 

Table 3. Combustible dust hazard classes

Hazard Class Kst (bar m/s) Characteristic

ST 1 1 - 200 Weak explosion

ST 2 201 - 300 Strong explosion

ST 3 > 300 Very strong explosion

Table 4 shows the test results on the sugar and cornstarch samples collected at the Port Wentworth 

facility. The near-total destruction of the packing building prevented collection of actual sugar dust 

samples; however, the mean particle size of the powdered sugar is representative of dust that would 

result from processing granulated sugar. Furthermore, the samples of granulated and powdered sugar 

were typical of the spilled sugar that had accumulated around equipment in the work areas. In the test 

chamber, these samples generated significant overpressures of 5.2 bar (76.4 psig) and 7.5 bar (110.2 

psig), respectively. A primary event fueled by airborne sugar dust would most likely loft and ignite 

sugar that had accumulated on the floor or equipment, causing secondary and tertiary dust explosions. 

Table 4. Test results of samples collected from the Port Wentworth facility

Material

Moisture

Content

(wt.%)

Mean 

Particle Size

(μm)

Pmax

[bar]

KST

[bar m/s]

MEC

[g/m3]

MIE

[mJ]

Cornstarch 11.5 10 8.5 189 105 10 < MIE < 30

Powdered Sugar 0.5 23 7.5 139 95 10 < MIE < 30

Granulated Sugar

(as received) 0.1 Not 

determined 5.2 35 115 MIE >1000

Granulated Sugar 

(sieved to < 500μm) 0.1 286 6.0 56 115 MIE >1000
26 

3.2 Combustible Dust Explosions 

Airborne sugar dust or other combustible dust around dust-generating equipment and in the work 

areas poses an immediate fire or explosion hazard only under specific conditions.17

A fireball will likely result when airborne combustible dust concentrates above the MEC and comes 

in contact with an ignition source. The likelihood of explosive ignition increases if the airborne 

combustible dust is concentrated in a semi-confined or confined workspace. When confined, 

concentrated, and ignited, airborne sugar dust can generate overpressure sufficient to cause explosive 

destruction, as indicated by the maximum pressure recorded in a test cell, Pmax (

 Accumulations of 

combustible dust on horizontal surfaces in the work area are a serious fire hazard because they can 

ignite and burn. However, dust on horizontal surfaces will not explosively ignite, even when it has 

accumulated to a depth of an inch or more. Combustible dusts must become airborne and achieve a 

concentration above the MEC in the air to ignite explosively. In fact, industrial hygiene-based dust 

concentration limits (concentrations in air that can pose a health hazard) are four to five orders of 

magnitude lower than the minimum dust concentrations necessary to propagate a dust explosion 

(Eckhoff, 2003). 

Table 4). 

Immediate explosive ignition is not the only means of causing overpressure damage. If sufficient dust 

has accumulated inside ducts or other equipment and airborne dust inside the equipment ignites, the 

pressure wave advancing ahead of the rapidly burning dust cloud will loft additional dust into the air 

and provide additional fuel to the advancing fireball, further increasing the pressure inside the 

equipment. This so-called “pressure piling” can cause the equipment to explosively rupture. If the 

equipment does not rupture, it can provide a conduit for the fireball to travel long distances and ignite 

fires or rupture equipment far from the ignition source. Some dust collection ducts and screw 

 

17 The approximate concentration of a typical combustible dust in an airborne dust cloud needed to sustain 

combustion would reduce visibility to 5 to 10 feet. Actual cloud density depends on the dust particle size and 

minimum concentration needed to sustain combustion. 
27 

conveyors in the Port Wentworth facility acted as conduits and ignited fires and ruptured equipment 

hundreds of feet from the packing building where the incident originated (Figure 12). 

 

Figure 12. Pressure waves traveled through screw conveyors and ruptured steel bulk granulated 

sugar bins (arrows) hundreds of feet from the sources of the dust explosions

Similarly, if a burning dust cloud is confined inside a building or small structure, combustible dust 

that has accumulated on overhead horizontal surfaces and the floor can be lofted by the initial 

overpressure and further fuel the advancing fireball. Pressure piling also results when the fireball and 

pressure wave advance through a structure filled with manufacturing equipment and other large items. 

The resulting overpressure can heave floors and roofs upward and blow out windows and 

unreinforced walls, as occurred throughout the Port Wentworth facility sugar packing buildings.18

3.3 The Port Wentworth Incident 

 

The CSB concluded that the Port Wentworth manufacturing facility incident was a combination of a 

primary and multiple secondary dust explosions. The CSB further concluded that the secondary dust 

explosions would have been highly unlikely had Imperial Sugar performed routine maintenance on 

sugar conveying and packaging equipment to minimize dust releases and sugar spillage, and promptly 

 

18 Some steel-framed windows on the south wall of the packing building were blown more than 200 feet.
28 

removed accumulated dust and spilled sugar. When sugar dust and sugar escaped the equipment in 

the packing buildings, timely housekeeping activities should have been performed to remove 

accumulations from elevated horizontal surfaces and spilled granulated and powdered sugar on the 

floors before the sugar accumulated to hazardous levels.19

3.3.1 Pre-explosion Sugar Dust Incident History 

 

The Port Wentworth facility operated for more than 80 years without experiencing a devastating dust 

explosion,20

Workers told the CSB investigators that small fires sometimes occurred in the buildings but were 

quickly extinguished without escalating to a major incident. Less than two weeks before the February 

incident, a small explosion in a dry dust collector on the roof of the packing building damaged the 

dust collector, but was safely vented through the deflagration vent panels. The dust collector had not 

yet been returned to service at the time of the incident.

 even though photographs dating from the 1970s through 2007 and internal 

correspondence dating to the early 1960s confirmed that significant sugar dust and spilled sugar in the 

packing buildings and silo penthouse were long-standing problems. In the year preceding the 

February 2008 explosion, quality audits and worker injury reports documented spilled sugar at “knee 

deep” levels in some areas. 

Operators reported that the buckets inside bucket elevators throughout the facility sometimes broke 

loose and fell to the bottom of the elevator. However, they could recall only one incident, some 10 

years earlier, where a falling bucket was thought to be the ignition source of a fire involving a bucket 

elevator in the raw sugar warehouse. That event did not escalate to a major facility fire or explosion. 

 

19 For combustible dust with bulk density above 75 pounds per cubic foot, accumulation on elevated horizontal 

surfaces in rooms with average ceiling height of about ten to twelve feet should not exceed 1/32 inch (NFPA 

654, 2006). Elevated surfaces in a typical factory are equal to about 5-10% of the floor area.

20 Workers recalled explosions in the fourth floor mill room in the 1960s, which did not cause widespread 

damage.
29 

3.3.2 Steel Belt Conveyor Modifications 

The CSB investigators learned through worker interviews that conveying granulated sugar on the 

steel belt conveyor in the tunnel under silos 1 and 2 generated some sugar dust. When sugar lumps 

lodged in a silo outlet pipe and blocked the movement of the sugar on the belt, as operators reported 

sometimes occurred, sugar spilling off the belt would release airborne dust. Before the company 

enclosed the steel belt conveyor, the dust was released into the large volume of the tunnel. Airflow 

through the tunnel would also keep the airborne dust concentration low; thus, airborne sugar dust 

likely never accumulated to an ignitable concentration. 

In 2007, Imperial Sugar enclosed the granulated sugar belt conveyors in the penthouse and the tunnel 

under the silos to address sugar contamination concerns. However, the company did not evaluate the

hazards associated with generating and accumulating combustible dust inside the new enclosure. 

They did not install a dust removal system to ensure that sugar dust did not reach the MEC inside the 

enclosure.

21 Furthermore, the enclosures were not equipped with deflagration vents to direct 

overpressure safely out of the building22, 23

3.3.3 Primary Event Location

 if airborne sugar dust ignited. 

For more than 80 years, the facility operated the open steel belt conveyor in the silo tunnel without 

incident. Less than a year after the enclosure was completed, however, the silos and packing buildings 

were destroyed by devastating explosions and fires. The CSB examined the blast patterns and damage 

inside the tunnel, at the east and west tunnel openings, and rooms inside the base of the silos directly 

 

21 The volume in the new steel belt enclosure was ten times smaller than the silo tunnel volume. Airborne sugar 

dust could easily accumulate above the MEC in the unventilated enclosure.

22 Enclosed equipment, such as bucket elevators and closed conveyors, should be designed in accordance with 

NFPA 654.

23 Although the enclosure on the belt conveyors in the penthouse could have been designed to safely vent an 

explosive overpressure outside the building, designing a deflagration vent system for the belt conveyor in the 

silo tunnel was impractical. That conveyor was located on the ground floor in the center of the building 

(Figure 5) far from any building exterior wall or roof.
30 

above the silo tunnel (pantleg rooms, see Figure 7) and concluded that the primary dust explosion 

most likely occurred in the silo tunnel, approximately midway along the length of the steel belt. 

Examination of the equipment in the silo tunnel found that every panel used to enclose the 80-foot 

long steel belt conveyor had been violently blown off the support frame (Figure 13). Panels east of 

the approximate midpoint of the conveyor (directly under the silo 1–silo 2 abutment) were deflected 

eastward, and panels west of the midpoint were deflected westward. Pressure damage inside the 

pantleg rooms above the tunnel was greatest inside the silo 2 pantleg room and least inside silo 3 

pantleg room. Major equipment damage was observed at the east entrance of the silo tunnel with all 

equipment deflections eastward, away from the tunnel. The equipment under silo 3 and outside the 

west end of the tunnel had damage patterns clearly indicating that a pressure wave traveled west out 

of the tunnel.24

Figure 13. Steel belt covers (arrows) crumpled from an initial dust explosion inside the steel belt 

enclosure (steel frame structure, right photo)

Pressure waves blew the wood walls and doors off the west and east tunnel entrances. Mangled steel 

belt cover panels were blown out of the east end of the tunnel (Figure 14). The pressure wave also 

 

24 The east face of the Aerobelt under silo 3 was distorted to the west as the explosive overpressure moved 

through the tunnel.
31 

traveled up between silos 1 and 2 and blew the brick walls that enclosed the south stairwell into the 

work areas on each floor of the south packing building (Figure 15). 

Figure 14. Stainless steel cover panels (arrows) blown off the steel belt enclosure and out of the 

tunnel into the packing building

Figure 15. South stairwell brick walls blown into the packing building
32 

3.3.4 Primary Event Combustible Dust Source

The CSB learned that, during the 3 to 4 days preceding the incident, workers were clearing sugar 

lumps lodged in the silo 1 sugar discharge holes above the steel belt. Through access ports in the 

pantleg room (Figure 16), they used steel rods to break and dislodge sugar lumps found above and 

inside the sugar discharge holes. Workers also used access ports located on the discharge chutes to 

break lumps that lodged on the steel belt, blocking sugar flow from the upstream discharge chutes 

(Figure 17). 

During the silo 1 “rodding” activities, sugar continued to flow from silo 2 onto the steel belt upstream 

of the silo 1 discharge chutes. Based on the statements from the workers who were clearing the sugar 

lumps from the silo outlets, it is highly likely that sugar lumps lodged between the moving steel belt 

and one or both silo 1 discharge chutes. Sugar lumps small enough to enter the discharge chute, but 

too large to pass between the end of the chute and the steel belt would create a “dam” that would 

cause sugar traveling from silo 2 to spill off the steel belt upstream of the silo 1 discharge chute. 

Spilled sugar would then accumulate inside the covered conveyor, likely covering parts of the steel 

belt.25

 

25 The steel belt return loop was fewer than 10 inches above the tunnel floor. Workers reported that spilled 

granulated sugar sometimes covered the belt return loop and support bearings. 

 Sugar dust released into the air from the sugar spilling off the conveyor, and sugar dust 

generated as the steel belt traveled through the sugar pile, below, could accumulate in the unventilated 

enclosure. 
33 

Figure 16. Access port inside the pantleg room and steel rod used to 

break sugar lumps in the sugar outlet on silo floor

Figure 17. Limited clearance between sugar discharge chute and the 

steel belt would sometimes be blocked by large sugar 

lumps; lump-clearing access port (arrow) is on top of the 

chute 

The CSB concluded that as granulated sugar spilled off the moving steel conveyor at the blocked 

outlet, sugar dust accumulated above the MEC inside the enclosed conveyor, and then ignited. The 

explosion triggered a series of secondary explosions that rapidly progressed through the packing 

buildings, palletizer room, and into the bulk sugar station. 
34 

3.3.5 Secondary Dust Explosions

The primary dust explosion in the silo tunnel sent overpressure waves into the three silo pantleg 

rooms,26

The fireballs continued to be fueled by sugar dust dislodged from overhead equipment. Powdered and 

granulated sugar added fuel as sugar was thrown into the air by the advancing pressure waves. The 

pressure waves also violently heaved concrete floors upward throughout the south packing building 

(

 and then out into the first floor of the Bosch building. Explosion pressure waves traveled 

between silos 1 and 2 and exited into the south stairwell, blowing the brick walls out into the packing 

building. Sugar dust accumulations on elevated surfaces and spilled sugar on the floors around the 

packaging equipment contributed to the explosion energy. 

Figure 18). Spilled sugar that had accumulated on the floors around conveyors and packaging 

equipment rained into the rooms below adding more fuel to the advancing fireballs. 

Appendix A describes the explosions’ and fires’ progression and resulting facility damage. Appendix 

B displays the blast patterns and worker locations in the buildings at the time of the incident.

Figure 18. Three-inch thick concrete floor slabs lifted off the steel supports by the explosion pressure 

waves

 

26 Each pantleg room had up to four 12-inch diameter holes through the floor into the tunnel below.
35 

3.4 Ignition Sources

Combustible dust can be ignited by electrical sparks or static discharge, hot surfaces, open flames, or 

friction-induced hot surfaces or sparks. Controlling possible ignition sources wherever combustible 

dust is present helps minimize the chance of a fire or explosion. 

3.4.1 Open Flames and Hot Surfaces

Imperial Sugar had policies and procedures to control open flames. Workers were permitted to smoke 

only in designated areas, which were away from the production or packaging equipment. The hot 

work permit procedure required the workers to control combustible materials and post a fire watch 

whenever they performed welding or other hot work activities. 

The CSB obtained photographs taken in the fall of 2006 that showed large electric motors covered 

with sugar dust (Figure 19), a condition that could cause the motors to overheat and possibly ignite 

the spilled sugar or airborne sugar dust. These poor housekeeping practices likely contributed to, or 

directly resulted in, some of the small sugar fires that sometimes occurred.

Workers told the CSB investigators that occasionally, small incipient stage fires27

 

27 "Incipient stage fire" is a fire that is in the initial or beginning stage and that can be controlled or extinguished 

by portable fire extinguishers, a Class II standpipe, or small hose systems without the need for protective 

clothing or breathing apparatus [29 CFR 1910.155(c)(26)].

occurred in the 

packing buildings when sugar or packaging materials was ignited by a hot electrical device or a hot 

bearing. However, none of these earlier incidents ever resulted in a large fire or involved airborne 

dust. The CSB ruled out open flame as a possible ignition source for the February 2008 incident. 
36 

Figure 19. Motor cooling fins and fan guard covered with sugar dust; 

large piles of sugar cover the floor (Imperial Sugar photo)

3.4.2 Ignition Sources Inside the Steel Belt Enclosure 

The CSB concluded that the initiating event was most likely the ignition of an explosive 

concentration of sugar dust within the steel belt enclosure under silos 1 and 2. Multiple possible 

ignition sources were identified during examination of the damaged steel belt and discussions with 

operations and maintenance personnel. However, the extent of the destruction from the explosions 

and long-burning fires prevented identifying a likely ignition source for the primary explosion. 

3.4.2.1 Electric Spark Ignition

Because the four limit switches on the steel belt conveyor were located inside the newly installed 

enclosure, they were exposed to airborne sugar dust. Examination of two of the four switches that 

survived the fires showed that they were rated explosion proof. Therefore, the CSB concluded the 

switches most likely were not the ignition source of the primary dust explosion. 

3.4.2.2 Hot Surface Ignition

Experiments have been conducted on various combustible dusts to measure the minimum ignition 

temperatures (MIT) of a dust cloud. Sugar MITs range from 360°C to 420°C (680°F to 788°F), 

depending on the test apparatus used. Similar experiments involving combustible dusts have been 

conducted to examine the influence of the time a combustible dust cloud remains in the test apparatus 
37 

(i.e., residence time, from 0.1-0.4 seconds). Those experiments found that the MIT decreases as the 

residence time of the dust in the test furnace increases (Eckhoff, 2003). Airborne combustible dust 

was likely always present when sugar was being transported inside the enclosed steel belt conveyor, 

especially when blockages caused the granulated sugar to spill off the steel belt.

Operators told the CSB investigators that bearings on the steel belt roller supports sometimes 

malfunctioned and “got very hot.” A hot bearing inside the enclosed steel belt conveyor could ignite 

airborne sugar dust, especially if the dust remained in contact with the hot surface for many seconds, 

as it likely did in the unventilated enclosure. Also, if sugar in contact with a hot surface begins to 

smolder, combustion gases that are released will mix with the airborne sugar dust and decrease the 

ignition temperature below the ignition temperature of pure sugar dust (Eckhoff, 2003). 

3.4.2.3 Friction Sparks

Although not ruled out, the least likely ignition source could have been from metal-to-metal sliding 

between the steel belt and a jammed support wheel or the steel enclosure frame. Testing has 

demonstrated that sparks from carbon steel sliding contact are unlikely to ignite combustible dust 

unless the contact speed exceeds 30.1 feet per second (9.2 meters per second) (Dahn, 1986). The steel 

conveyor belt operating speed was estimated to be less than 5 feet per second (1.5 meters per second). 

3.5 Worker Training 

Imperial Sugar conducted routine subject-specific worker training for employees and contractors. The 

company’s “Specific Safety Rules” policy stated that new workers receive comprehensive safety rule 

training on the first day of employment. The policy also required workers to attend annual refresher 

safety training. A day-long, annual training session was conducted once each month. Workers 

typically attended the training during the month of their birthday, a scheduling practice that led to the 

safety training being called “Birthday Safety Training.” Interviews showed that most, but not all, 

personnel received their safety training in a timely fashion in accordance with the “Specific Safety 

Rules” policy requirements.
38 

“Birthday Safety Training” subjects in 2006 and 2007 included personal protective equipment, 

lockout/tagout procedures, confined space entry, fall protection, manlift operation, forklift operation, 

fire extinguisher operation, compressed air nozzle use, safe and at-risk behaviors, employee self 

(safety) audits, Material Safety Data Sheets, emergency communication, workers compensation, and 

maritime security. Interviews revealed minimal retention of the topics covered: while some 

employees said that the hazard of dust accumulation was included at some time in the training 

sessions, a review of more than 10,000 pages of “Birthday Safety Training” and “Plant Rules and 

Guidelines” tests revealed no such coverage since 2005. Furthermore, the training materials did not 

contain information about combustible dust, and no other documents were provided to verify that 

training on the hazard of dust accumulation occurred prior to 2005. Although “Birthday Safety 

Training” extensively covered site safety issues, the hazard of dust accumulation was not among them 

and was not included in the site’s “Specific Safety Rules.”

Imperial Sugar quality assurance and safety personnel were made aware of the OSHA combustible 

dust national emphasis program28 in early December 2007. Yet a January 30, 2008, “Safety Focus of 

the Month” email from the safety manager and the Written Program-- Housekeeping & Material 

Storage Program that was attached made no mention of combustible dust.29

 

28 The OSHA Combustible Dust National Emphasis Program, CPL 03-00-006, was issued in October 2007. 

 Failure to understand the 

hazard and control sugar dust accumulations in the work areas by properly maintaining equipment 

and performing routine housekeeping led to the massive secondary explosions and fires that claimed 

the lives of the 14 workers and injured dozens.

29 The memo said “We will continue to focus on housekeeping, material storage and handling walking/working 

surfaces, and leaks.” However, the memo and the written program did not mention hazardous dust or the 

OSHA NEP.
39 

Had the company trained the workers on the hazards of combustible sugar dust and adopted an 

effective dust control program, the secondary dust explosions that devastated the facility would likely 

not have occurred. 

3.6 Hazards Management 

3.6.1 Evacuation, Fire Alarms, and Fire Suppression 

The written emergency response procedure directed workers to use an intercom system to report an 

emergency. However, workers told the CSB investigators that the intercom system was not used 

inside the refinery or packing buildings. Rather, they had to rely on radios and cell phones carried by 

some personnel to announce or be alerted to an emergency. Having no audible or visual alarm 

devices in the work areas, some workers had no means of prompt notification in the event of an 

emergency.

The company had posted emergency evacuation routes, but did not provide work location specific 

evacuation training to all employees and contractors30

Emergency evacuation lights and illuminated exit signs were provided throughout the facility. 

However, many workers reported that the explosions and fires caused the normal lighting and many 

emergency lights to fail. The emergency lights that worked did not provide adequate illumination—

some workers had extreme difficulty finding their way out of the darkened buildings. Large, complex 

mechanical equipment and long package conveyors 3 to 4 feet above the floors (

 and did not conduct evacuation drills. 

Figure 20) impeded 

rapid and safe emergency egress in the darkened work areas. 

A fire suppression sprinkler system was intended to protect each floor of the packing buildings and 

the palletizer room. The city water main and an onsite firewater tank and emergency diesel-driven 

pump provided water to the heat-activated sprinkler heads. However, typical of incidents involving 

 

30 As part of the new employee/contractor training process, newly hired workers were told to familiarize 

themselves with evacuation routes when they reported to their work location. 
40 

explosive energy releases, the fire suppression piping system was heavily damaged in the initial 

explosions and rendered ineffective. Lack of water flow from the fire hydrants around the perimeter 

of the buildings caused by the ruptured sprinkler systems severely hampered firefighting efforts.

Figure 20. Packaging equipment hindered evacuation in the darkened building

Portable fire extinguishers were located throughout the work areas. Wheeled carts containing as many 

as 16 portable fire extinguishers were located in sugar packaging areas, such as the south packing 

building third floor. Workers reported using fire extinguishers to extinguish small fires that 

sometimes occurred. However, the fire extinguishers were useless against the rapidly progressing 

fires that quickly engulfed the packing building. 

3.6.2 Electrical Systems Design 

The NFPA publishes NFPA 499, Recommended Practice for the Classification of Combustible Dusts 

and Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, which 

is used to classify hazardous work locations, including locations where combustible dust is or might 

be present. Electrical devices installed in these “classified” locations should comply with applicable 

NFPA design standards to minimize ignition sources such as NFPA 654 - Standard for the Prevention 

of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible 
41 

Particulate Solids. The National Electric Code (NEC) and International Fire Code (IFC) incorporate 

these and other NFPA standards and guidelines. Local, state, and federal government agencies 

sometimes incorporate the NEC or IFC into building regulations or worker safety standards. 

OSHA standard 1910 Subpart S contains the electrical equipment safety requirements to protect 

employees in their workplaces. The standard addresses work practices and electrical device 

maintenance requirements for hazardous locations including electrical devices and wiring installed in 

locations where combustible dusts or fibers may be present. 

Imperial Sugar had no written policy or procedure to require classifying hazardous areas or require 

electrical devices rated for such locations at the Port Wentworth facility. Some locations at the facility 

contained significant accumulations of combustible sugar or cornstarch dust (Figure 21). The CSB 

investigators noted that some electrical devices were rated for use in hazardous work locations, but 

non-rated devices were also installed in the same location, frequently near the rated devices (Figure 

22). The CSB investigators also observed many non-hazard classified electrical devices installed in 

dusty work areas and equipment enclosures. Furthermore, some electrical devices in dusty areas were 

poorly maintained, such as having missing covers or open doors on many breaker panels and other 

electrical enclosures. 
42 

Figure 21. Left: Sugar dust accumulation on steel belt drive motor in silo tunnel (Imperial 

Sugar Co. photo, Oct. 2006). Right: Cornstarch spilled under cornstarch silo 

(March 2008).

Figure 22. Non-dust rated and rated electrical devices in the silo tunnel

The powdered sugar grinding mills motor control room located on the fourth floor of the south 

packing building was the only area that contained hazardous dust control features to protect the nonrated electrical switchgear. The room was equipped with a positive pressure air conditioning system 

and sealed doors to prevent sugar dust from entering the room and accumulating on or near the 

electrical control equipment. 
43 

The south packing building sustained extensive blast damage (report cover photo). The ceilings in 

areas where sugar dust was present were not protected with a suspended ceiling31

Figure 23

to minimize dust 

accumulation on rafters, conduit, conveyors, piping, and other equipment. Elevated areas were 

infrequently cleaned so sugar dust accumulated to dangerous levels. The secondary explosions were 

most likely fueled by significant accumulations of sugar dust on elevated surfaces. When the floors 

heaved from the first series of explosive overpressures, large piles of sugar on the floors ( ) 

would have been released into the areas below and ignited. Overpressure waves advancing 

horizontally through the packing buildings would also loft sugar piles into flaming fireballs. 

Figure 23. Sugar and dust accumulation on a screw conveyor in the 

south packing building fourth floor near silo 1 

(Imperial Sugar photo) 

 

31 Suspended ceilings can be designed, installed, and maintained above dusty work areas to prevent airborne 

dust accumulation on overhead piping, electrical devices, and building structural components. 
44 

3.6.3 Sugar Dust Handling Equipment 

Transporting granulated and powdered sugar in mechanical conveying devices, and filling bags and 

boxes in the packaging machines generated sugar dust. To control dust, a duct system connected to 

wet dust collectors was designed to remove sugar dust from granulated sugar process equipment 

including some conveyors, bucket elevators, and packaging machines. Dust removal ducts were also 

located in the silos’ penthouse and the tunnel under the silos. The dust collectors used water spray to 

remove the sugar dust from the air. The water from the collectors was returned to the refinery to 

recover the dissolved sugar. The roof mounted collectors exhausted the cleaned air outside the 

building. 

The powdered sugar and cornstarch process equipment dust collection system used dry dust 

collectors. Filter bags inside six dust collectors located on the roof of the south packing building 

captured the sugar and cornstarch dust. Traveling “blow rings” used compressed-air to dislodge the 

accumulated sugar from the filter bags. The dislodged sugar fell to the bottom of the filter chamber. It 

then passed through a rotary valve to containers below the dust collectors. 

Explosion vent panels protected the dry dust collectors from excessive overpressure if sugar dust 

ignited inside a collector. In fact, 10 days before the February incident, a malfunction inside a 

powdered sugar atomizer resulted in a sugar dust fire and explosion inside one of the dry dust 

collectors. The explosion panels operated as intended and the dust fire safely vented to the 

atmosphere. 

Although much of the granulated and powdered sugar processing equipment was connected to the 

dust collection system, it was inadequately maintained and did not effectively remove dust from the 

equipment. A report submitted to Imperial Sugar management by an independent contractor less than 
45 

a week before the incident identified the following major problems with the two dust collection 

systems:32

• Air flow in ducts significantly below the minimum dust conveying velocity

• Undersized fans--static pressure too low to transport sugar dust 

• Fans operating well below the required performance curve

• Incorrectly installed duct piping 

• Duct piping plugged with sugar 

In that the dust collection systems were ineffective, the only solution for minimizing sugar dust 

accumulation to prevent a dust explosion would be timely and effective housekeeping practices to 

remove the sugar dust from the work areas.

3.6.4 Housekeeping and Dust Control

Workers told CSB investigators that sugar spillage and dust generation were constant problems in the 

packing buildings. They reported that sugar leaked from worn seals, loose or missing covers, and 

other breaches in the aging screw conveyors, bucket elevators, hoppers, and other bulk sugar transport 

devices.

Leaks in the pressurized air ducts used to transport cornstarch, and the occasional powdered sugar 

packaging machine malfunction, released dust into the work areas. In addition, sugar-filled paper or 

plastic containers sometimes tore open and spilled their contents as they traveled along the 

conveyors,33

 

32 Imperial Sugar management had not had the opportunity to act on the report findings before the February dust 

explosion occurred.

generating more sugar dust. However, because the large work areas were typically not 

equipped with dust removal systems, the dust released from these sources would float in the air and 

settle on overhead piping, equipment, lights, ceiling support beams, and any other horizontal surface. 

33 Packaging machine operators reported spilled sugar frequently was as deep as 2-3 feet. 
46 

Packaging machines required frequent cleaning to operate properly. Workers routinely used water or 

steam, and sometimes industrial vacuum cleaners to remove sugar and sugar dust from equipment and 

work areas. But they also routinely used compressed air34

Because Imperial Sugar manufactured and packaged food-grade sugar products, general area 

cleanliness (removal of trash and other debris) was necessary to prevent product contamination and 

control rodents. Spilled sugar also presented a slip or trip hazard, especially when wet, as workers 

reported was often the case throughout the facility. 

to remove accumulated granulated sugar or 

sugar dust from packaging equipment. Compressed air cleaning only lofted dust into the air where it 

would later accumulate on horizontal surfaces in the area. More frequent cleaning was needed to 

remove dust in the work areas, especially on elevated surfaces, before it accumulated to hazardous 

levels, but was not routinely performed. 

Written housekeeping policies included planned daily, weekly, and monthly packaging area cleaning 

schedules, but workers reported that these policies were not effectively implemented. Pre-incident 

photographs of equipment and packaging areas, worker injury reports in 2006 and 2007, and a 

December 2007 quality assurance survey provided evidence that the housekeeping practices were 

inadequate—deep piles of spilled granulated and powdered sugar accumulated around and on 

equipment, and sugar dust accumulated on floors, equipment, and other elevated horizontal surfaces 

(Figure 24). Workers interviewed by the CSB investigators reported cleaning activities were seldom 

performed on hard-to-reach elevated surfaces and some powdered sugar packaging areas frequently 

had dense sugar dust in the air.35

 

34 Compressed air cleaning might be needed to remove combustible dust from inaccessible areas inside 

equipment. Where compressed air is used, care must be taken to minimize lofting combustible dust into the 

air. Overhead equipment and structures cleaning frequencies must be sufficient to prevent the displaced dust 

from accumulating above unsafe levels.

 

35 A combustible dust explosion hazard is unlikely unless the dust in the air reduces visibility to a few feet. 

Employee descriptions indicated that airborne sugar dust minimally impacted visibility. However, the 

airborne dust accumulated on elevated surfaces throughout the work areas. 
47 

Figure 24. Deep piles of sugar accumulated on floors and equipment. Note shield installed above 

screw conveyor drive motor to deflect sugar dust (Imperial Sugar photos).

3.7 Dust Explosion Hazard Awareness

3.7.1 Imperial Sugar Management and Workers

Correspondence dating to as early as 196136

This dust problem has become so serious and dangerous in modern refineries...at 

present, we have so much to correct that is knowingly wrong, there is no need for 

outside help. We make a lot of dust in the plant and have had a very inefficient 

dust collecting system[;] consequently, it has been hopeless to try to keep the dry

end of our plant clean. We have heavy accumulations of dust in several areas... 

we hope to improve the house keeping around the silos... 

indicates that management and refinery personnel were 

aware of the explosive nature of sugar dust and the importance of minimizing dust accumulation. An 

August 1961 internal memo describes a dust explosion in the powdered sugar room. A September 

1967 internal memo from a refinery engineer to the executive vice president and treasurer reported 

that

 

36 The refinery was then owned and operated by Savannah Sugar Refining Corporation. 
48 

By removing these heavy accumulations of dust on beams, sills, and walls, the 

fuel for a continuous explosion will be eliminated. This is the reason an 

explosion will travel from one area to another, wrecking large sections of a plant.

One year later, a September 1968 dust explosion occurred inside the mill room. Refinery 

workers successfully extinguished the fire but not before significant fire and smoke 

damage occurred.

The CSB reviewed Imperial Sugar-published MSDSs for granulated and powdered sugar 

products, both of which warn: 

Explosion: NFPA Class 2 Group G Airborne sugar dust accumulation 

ignition temperature is 370°C. At airborne concentrations of 0.045 gm/L 

or higher, sugar dust accumulations are explosive.

Another MSDS on file at Imperial Sugar issued by a cornstarch supplier identified the 

explosion hazard associated with cornstarch dust and warned: “Avoid procedures which 

could cause a dust cloud to be formed.” 

Over the years, combustible dust incidents at sugar refineries worldwide,37, 38

In 1998, an employee was severely burned by a sugar dust explosion in the powdered 

sugar mill room at the Imperial Sugar refinery in Sugar Land, Texas. Yet, more than eight 

years after that incident the corporate safety manager wrote in a memo to senior 

 and small 

combustible dust incidents at the Port Wentworth facility and other Imperial Sugar 

facilities were known to company management and employees. However, management 

action to control dust generation and accumulation was ineffective; thus, combustible 

dust remained a major workplace hazard. 

 

37 On September 25, 1963, an explosion and fire at the sugar beet factory of the Utah-Idaho Company resulted

in seven deaths. Damage was estimated at $2.9 million at the time of the incident. 

38 On February 15, 1965, a sugar dust explosion and fire in the American Sugar Company Chalmette Refinery 

near New Orleans killed three and injured many more. Damage was estimated at $17 million at the time of 

the incident. 
49 

management: “Based on conversations with the quality team at each location, we did not 

have a formal policy for sanitation/housekeeping at any of our sites,” Still, the draft 

sanitation/housekeeping policy attached to the memo did not discuss sugar dust. 

Management did not take adequate action to correct the long-standing hazardous 

combustible dust conditions in their facilities. 

Workers told the CSB investigators that occasionally, small fires occurred in the packing 

buildings when sugar or packaging material was ignited by a hot electrical device or 

overheated bearing. As recently as January 2008, one worker observed flames “3 feet 

high” before he and other workers in the area extinguished the fire with portable fire 

extinguishers. As noted in Section 3.6.3, the explosion panels on a dust collector were 

blown open when the dust inside the collector was ignited. None of these events resulted 

in a widespread fire or secondary dust explosion. Fires and even dust explosions occurred 

at the Imperial Sugar facilities and other sugar refineries39

The CSB concluded that the small events and near-misses caused company management, 

and the managers and workers at both the Port Wentworth, Georgia, and Gramercy, 

Louisiana, facilities to lose sight of the ongoing and significant hazards posed by 

accumulated sugar dust in the packing buildings. Imperial Sugar management and staff 

accepted a riskier condition and failed to correct the ongoing hazardous conditions, 

despite the well-known and broadly published hazards associated with combustible sugar 

dust accumulation in the workplace. 

without ever propagating into 

a secondary dust explosion or large fire. The unsafe work practices continued and the 

combustible dust hazards were not abated.

 

39 In November 2007, an equipment malfunction at the Domino Sugar facility in Baltimore, Maryland, resulted 

in a dust explosion in the powdered sugar mill room. There were no injuries, but the equipment in the mill 

room sustained major damage. 
50 

The process wherein successful operations continue despite existing rejectable conditions 

or unsafe behaviors results in relaxing the minimum performance standard without basis 

is called “normalization of deviance.” That is, an organization relaxes the criteria rather 

than identifying and correcting the underlying causes, so the deviations become the new 

normal operating condition. Normalization of deviance was a principal organizational 

flaw that led to the space shuttle Columbia disaster in February 2003. The Columbia 

Accident Investigation Board (NASA, 2003) concluded that 

[B]oth accidents were ‘failures of foresight’ in which history played a prominent 

role. First, the history of engineering decisions on foam and O-ring incidents had 

identical trajectories that ‘normalized’ these anomalies, so that flying with these 

flaws became routine and acceptable. 

The concept of normalization of deviance is applicable to any operating system. The Columbia 

accident involved known hazards in highly complex systems and deviation from clearly defined and 

predetermined safety limits based on operating history. Similarly, the Imperial Sugar incident 

involved known hazards and acceptance of a lesser performance standard based on operating history.

Imperial Sugar management was aware of the hazards associated with combustible sugar dust, but in 

the absence of any major catastrophic incident during many years of facility operation, the hazardous 

conditions went uncorrected. Management did not enforce adequate equipment design and 

maintenance practices to control sugar dust and spilled sugar. Furthermore, management did not 

ensure housekeeping activities were adequate to prevent sugar dust and spilled sugar from 

accumulating to unsafe levels in the workplace. Then, on February 7, 2008 conditions necessary to 

propagate a dust explosion aligned to cause the catastrophic explosions and fires that swept through 

the Port Wentworth facility. 
51 

3.7.2 Property Risk Insurers 

Property insurance carriers conduct facility audits to determine a client’s relative insurance risk. 

Zurich Services Corporation (Zurich) conducted such an audit of the Port Wentworth facility in April 

2007 and submitted a “Property Policyholder Risk Improvement Report” to company management in 

May 2007, which said 

This entire facility was toured during this visit, to evaluate the physical aspects of 

property loss prevention ... The evaluation consisted of a review of building 

construction; existing occupancies operations; storage arrangements; general

housekeeping; management loss prevention and self-inspections programs... 

The CSB investigators reviewed Imperial Sugar documents including photographic records, incident 

reports, quality assurance self-audits, and employee statements about sugar spillage and dust 

accumulation dated before and after the Zurich audit. The CSB concluded that typical sugar 

accumulations shown in the photos contained in this report most likely existed at the time of the audit, 

and in the months after the auditor visited the site. However, the Zurich audit report did not mention 

spilled sugar and sugar dust accumulation in the areas visited by the auditor. 40

Zurich told the CSB that they conduct combustible dust hazard awareness training for their facility 

auditors. They provided the CSB with copies of two comprehensive combustible dust hazard 

awareness training slide presentations titled “Dust Explosion Prevention and Control” and “Science 

of a Dust Explosion.” This training was developed by Senior Risk Engineers and contained about 79 

pages of combined dust awareness training. In September 2007, both sessions were delivered to their 

personnel who conduct risk assessments. However, Zurich acknowledged that they did not share 

these training materials with Imperial Sugar Company or other clients who handle combustible dust. 

 

 

40 The Zurich auditor told the CSB that the company is notified ten days in advance of a planned insurance 

audit. Furthermore, the audit focused on property loss risk in anticipation of the upcoming hurricane season.
52 

 

In the three dust explosion incidents investigated by the CSB in 2003 (CTA Acoustics, Inc.; West 

Pharmaceutical Services, Inc.; and Hayes Lemmerz International), risk insurer facility audits failed to 

identify combustible dust hazards. The CSB made a formal recommendation to the Risk Insurance 

Management Society, Inc.41

 

41 The Risk Insurance Management Society, Inc. is a not-for-profit organization dedicated to advancing the 

practice of risk management

to “communicate the findings and recommendations of [the Hayes 

Lemmerz] report to your members” (CSB, 2005). In response to the recommendation the organization 

posted a link to the CSB investigation on its website in December 2005, a link that was later removed. 

Additionally, its website contains no information about risks associated with combustible dust in the 

workplace. 

www.rims.org, 2009.
53 

4.0 Regulatory Analysis

4.1 Georgia Fire Codes

Prior to the Imperial Sugar incident, the state of Georgia did not have specific rules or regulations 

addressing combustible dust in industrial facilities. However, one month after the refinery explosion, 

the Georgia Office of Insurance and Safety Fire Commissioner promulgated a new, emergency 

regulation covering combustible dust: Regulations of the Safety Fire Commissioner Chapter 120-3-

24-0.12 Rules and Regulations for Loss Prevention Due to Combustible Dust Explosions and Fire. 

The regulation establishes minimum fire safety standards and requirements in all facilities that handle 

combustible particulate solids. Effective January 1, 2010 covered facilities will be required to file an 

annual registration to the Georgia Safety Fire Commissioner. Other key provisions of the new 

regulation include

• compliance with applicable International Fire Code and National Fire Protection Association 

standards addressing combustible dust;

• maintaining a current “Certificate of Registration” issued by the office of the Safety Fire 

Commissioner; 

• written safety procedures;

• employee training and periodic refresher training; 

• written evacuation plans and periodic drills; 

• annual reports on training and evacuation; 

• fire alarm systems and other emergency egress design features as provided in NFPA 101, Life 

Safety Code and the International Fire Code. 
54 

4.2 Occupational Safety and Health Administration (OSHA) 

In 1983, in response to major industrial accidents involving combustible dust in grain handling 

industries, OSHA promulgated regulations specifically addressing grain dust hazards. The CSB noted 

in testimony to the Subcommittee on Employment and Workplace Safety, Senate Health, Education, 

Labor and Pensions Committee in July 2008 that

According to OSHAs own review in 2003, this standard has cut deaths and 

injuries from grain dust explosions and fires by 60%. And as noted in the CSB 

study, the grain industry itself now credits the standard with helping to make the 

design of grain handling facilities safer. 

The grain handling facilities standard (§1910.272) contains specific requirements for minimizing 

grain dust hazards, periodic worker training, emergency action plans, and written housekeeping 

procedures to control hazardous dust. OSHA has not promulgated similar combustible dust 

workplace safety standards for industries outside the grain handling industry. 

Between 2003 and 2008, three major combustible dust explosions and the Imperial Sugar Port 

Wentworth incident killed 28, seriously injured 119, and resulted in many millions in property 

damage. In 2005, OSHA issued a Safety and Health Information Bulletin (SHIB), Combustible Dust 

in Industry: Preventing and Mitigating the Effects of Fire and Explosions. The bulletin provided 

general guidance to industry on controlling combustible dust hazards. 

In October 2007, approximately five months before the Imperial Sugar incident, OSHA initiated a 

National Emphasis Program (NEP) targeting industries where combustible dust could be present in 

the workplace. The NEP was based on a regional combustible dust Special Emphasis Program OSHA 

implemented in 2004. The NEP focuses on workplaces where combustible dust hazards are likely to 

be found, including granulated sugar manufacturing and packaging facilities. 

Although the NEP is not a worker safety standard, it provides guidance to OSHA inspectors for 

applying the General Duty Clause and existing standards, such as the Walking-Working Surfaces 
55 

standard, to conditions and practices that impact or are related to combustible dust hazards. It does 

not establish new enforceable combustible dust hazard standards. 

In July 2008, OSHA announced that it intends to amend the housekeeping standard (§1910.22) to 

“more explicitly state what had always been true: that the standard applies to accumulations of 

dust that contribute to an explosion hazard.” 42

In April 2009, 14 months after the Imperial Sugar incident, OSHA announced it intends to initiate 

rulemaking on a general industry combustible dust standard. This is the first step in addressing the 

CSB 2006 Combustible Dust Study recommendation that OSHA issue a combustible dust standard to 

address combustible dust workplace hazards in general industry. Until a new standard is in place, 

OSHA will continue to apply the Combustible Dust NEP to address combustible dust workplace 

hazards.

 

42 Written statement from the Assistant Secretary, OSHA, before the subcommittee on Employment and 

Workplace Safety; Committee on Health, Education, Labor and Pensions; U.S. Senate; July 29, 2008.
56 

5.0 Model Fire Codes 

Industry best practices addressing process equipment design and fire detection and suppression 

systems design for manufacturing facilities that generate combustible dust are contained in many 

standards. These standards, frequently codified into federal, state, or local regulations, typically apply 

to new construction or expansions and modifications inside existing facilities. The principle standards 

that address combustible dust are summarized below. 

5.1 National Fire Protection Association 

The National Fire Protection Association NFPA 654: Standard for the Prevention of Fire and Dust 

Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids

dates to 1945. It is a consensus standard applied to the safe handling, storage, and processing of 

combustible materials, including sugar dust. Subjects include facility and process design, fugitive dust 

control and housekeeping, ignition sources, and other prevention topics. 

NFPA 61: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food 

Processing Facilities contains standards applicable to facilities that process, mill, package, store, or 

ship dry agricultural bulk materials including sugar and starch and dusts generated from these 

processes. This standard provides information on facility construction, ventilation, dust control, fire 

prevention, and other topics. 

NFPA 499: Recommended Practice for the Classification of Combustible Dusts and of Hazardous 

(Classified) Locations for Electrical Installations in Chemical Process Areas contains standards 

applicable to facilities where combustible dusts are produced, processed, or handled. It also applies to 

facilities, like sugar refining and packaging, where combustible dust is released into the atmosphere 

and might accumulate on surfaces. The recommended practice contains guidelines for classifying 

areas based on the presence of combustible dust for the purpose of selecting suitable electrical devices 

to minimize the possibility of ignition. 
57 

NFPA 101: Life Safety Code contains criteria for construction, fire protection, and occupancy 

features as well as egress features including fire alarms and evacuation routes. 

5.2 International Code Council 

The International Code Council (ICC) is a membership association “dedicated to building safety and 

fire prevention, and developing codes used in residential and commercial buildings.” The ICC 

publishes the International Building Code (IBC) and International Fire Code (IFC). 

As noted in Section 4.1, Georgia enacted an emergency rule shortly after the Port Wentworth 

explosion that adopts much of the IBC addressing combustible dust hazards management. The IBC 

incorporates the NFPA standards and recommended practices addressing combustible dust as listed 

above. 

Chapter 13 of the IFC covers combustible dust hazards. This one-page chapter provides brief 

performance requirements addressing the prohibition of ignition sources where combustible dust is 

generated, stored, manufactured, processed, or handled, and advises that combustible dust 

accumulations be minimized and not collected by any means that will put combustible dust into the 

air. 

The IFC briefly discusses application of NFPA 654 and NFPA 484, but does not require industry to 

use them. The IFC “authorizes” the “code official” (the government authority having jurisdiction) to 

require and enforce “applicable provisions” of the NFPA and other standards included by reference in 

Chapter 13. Requirements for specific compliance to IFC or other standards are established only 

through laws and regulations promulgated by local, state, or federal government bodies. 
58 

6.0 Trade Associations

6.1 AIB International

Founded in 1919, AIB International (AIB), formerly the American Institute of Baking, provides 

independent inspections, audits, and training to food processing, distribution, and retail industries 

worldwide. Although its services focus primarily on food safety and quality, its website states that its

staff includes experts in occupational safety and maintenance practices. It reports that the 

organization provides training on OSHA compliance programs including confined spaces, hot work, 

lockout/tagout, and other OSHA standards to member companies. AIB also offers a Safety and Health 

Management Systems three-day training course to member companies.

Being a member company in AIB, Imperial Sugar receives annual AIB Good Manufacturing Practice 

(GMP) audits.43

AIB audited the Port Wentworth facility in May 2007 and awarded a “superior” rating. However, the 

audit considered only sugar dust accumulation that might impact food quality and not workplace 

hazards associated with combustible sugar dust accumulation.

The audit assesses company policies, operations, and condition of buildings, 

production, and storage, among other GMP elements. A “participation certificate” is issued to the 

company if it passes the audit. A full inspection report is also issued to the company. 

AIB is well-positioned to help member companies become better informed about the hazards 

associated with combustible dust in food manufacturing facilities. Although the AIB annual audits are 

intended to address food safety issues, the audit criteria could be amended to include basic reviews of 

workplace dust hazard awareness and control. Trained auditors could observe conditions in 

manufacturing facilities and examine hazard communication policies and procedures as part of the 

 

43 Membership in AIB and annual AIB audits are contractually required by many Imperial Sugar Co. customers.
59 

annual facility inspection. Furthermore, AIB could revise the Safety and Health Management Systems

training course to address combustible dust. 

6.2 American Bakers Association 

Established in 1897, the American Bakers Association (ABA) represents the interests of the 

wholesale baking industry before the U.S. Congress, federal agencies, state legislatures and agencies, 

and international regulatory authorities. 

[The]ABA is dedicated to the principles of free enterprise, competition and the 

economic health of the entire food industry. To that end, ABA’s organization 

functions primarily in the areas of government relations (federal and state), 

industry relations, communications, conventions and meetings.44

The ABA Safety Committee 

is comprised of safety and loss control professionals of the wholesale baking 

industry....Committee members share strategies to help protect the industry’s 

skilled workforce and reduce workers compensation costs and exposures. 

Like the AIB, the ABA can promote improvements in combustible dust hazard awareness and control 

throughout their membership. It could develop and publish bulletins, or safety guidance similar to its 

Confined Space Entry webinar presentation material, that address combustible dust characteristics 

including ignition energy, minimum explosible concentration, best practices for proper design and 

operation to minimizing dust accumulation on elevated surfaces, and safe housekeeping practices. 

6.3 The Sugar Association

The Sugar Association, founded by members of the U.S. sugar industry began as the Sugar Research 

Foundation in 1943. The organization’s focus is on the scientific study of sugar’s role in food and 

communication of that role to the public. The Sugar Association's member companies are producers 

 

44 http://www.americanbakers.org/about/MissionStmt.htm (February 2008).
60 

and growers of sugar in the United States. The organizations’ Board of Directors is comprised of 

decision-making representatives from each of those companies or groups. Additionally, three 

advisory committees are made up of member company staff, which assists in guiding the direction of 

Public Policy, Public Education, and Scientific Affairs for the association. Imperial Sugar Company 

is a member of the Sugar Association.

6.4 Sugar Industry Technologists

Sugar Industry Technologists, Inc. was established in the United States in 1941 by several North 

American sugar refiners. It has developed into an international association with a membership of 

about 50 corporate sugar refining companies including Imperial Sugar, about 50 corporate allied 

companies, and has more than 500 individual members from around the world. 

The organization holds an annual convention, typically in May, where technical sessions are held. At 

these sessions, members present technical papers based on research or development in cane sugar 

processing technology, quality control, environmental issues, and other topics of interest to the cane 

sugar refining industry. 
61 

7.0 Previous CSB Dust Explosion Investigations

On January 29, 2003, a massive dust explosion at the West Pharmaceutical Services facility in 

Kinston, North Carolina, killed six workers and destroyed the facility. Polyethylene powder 

accumulated on surfaces above the suspended ceiling, providing fuel for a devastating secondary 

explosion (CSB, 2004). 

On February 20, 2003, a series of dust explosions at the CTA Acoustics facility in Corbin, Kentucky, 

killed seven workers, injured 37, and destroyed the facility. Although management was aware of dust 

explosion hazards associated with the phenolic resin used in the manufacturing process, inadequate 

housekeeping and equipment maintenance resulted in dust accumulation to dangerous amounts 

throughout the production areas, in vent ducting, and in dust collector housings. An overheated open 

oven ignited airborne resin dust during an area cleaning activity. The concussion from that event 

caused a massive secondary dust explosion fueled by dust that had accumulated on horizontal 

surfaces throughout the work areas (CSB, 2004). 

On October 29, 2003, an aluminum dust fueled explosion killed one worker and injured several others 

at Hayes Lemmerz International in Huntington, Indiana. The explosion likely originated in the dust 

collector, which had not been adequately maintained. The initial explosion spread through dust 

collector ducting, causing a large fireball to emerge inside the building and fatally burn the worker. 

The concussion from the primary event lofted aluminum dust that had accumulated on the rafters and 

other horizontal surfaces inside the building. The secondary explosion injured the other workers and 

heavily damaged the facility (CSB, 2004). 

In 2006, the CSB issued the Combustible Dust Hazard Study (CSB, 2006), which identified 281 

combustible dust incidents between 1980 and 2005 that killed 119 workers and injured 718 and 
62 

caused extensive property damage.45

The study found that OSHA typically applied the General Duty Clause (Section 5(a)(1)) or a variety 

of OSHA standards only tangentially related to dust explosion hazards to cite employers only after 

devastating dust explosions. In contrast, the OSHA Grain Handling Facilities Standard, issued almost 

20 years ago, effectively reduced the number and severity of combustible grain dust explosions in the 

grain handling industry and sets an example of OSHA addressing a similar problem through 

regulation. 

 The CSB study found that the NFPA publishes comprehensive 

standards on combustible dust hazard minimization that “are widely recognized by experts as 

effective and authoritative.” 

The continuing catastrophic dust incidents presented in the dust study prompted the CSB to issue a 

recommendation to OSHA in 2006 to issue a comprehensive combustible dust standard for general 

industry. As discussed in Section 4.2, in April 2009 OSHA took the first step toward implementing 

the CSB recommendation by announcing that an advanced notice of proposed rulemaking was in 

development. 

 

45 As of July 31, 2008, the number of dust incidents had increased to 363.
63 

8.0 Key Findings:

1. Imperial Sugar and the granulated sugar refining and packaging industry have been aware of 

sugar dust explosion hazards as far back as 1925.

2. Port Wentworth facility management personnel were aware of sugar dust explosion hazards 

and emphasized the importance of properly designed dust handling equipment and good 

housekeeping practices to minimize dust accumulation as long ago as 1958, but did not take 

action to minimize and control sugar dust hazards. 

3. Over the years, the facility experienced granulated sugar and powdered sugar fires caused by 

overheated bearings or electrical devices in the packing building. However, none of these 

incidents resulted in a devastating sugar dust explosion or major fire before the February 

2008 incident. 

4. Company management and the managers and workers at both the Port Wentworth, Georgia, 

and Gramercy, Louisiana, refineries did not recognize the significant hazard posed by sugar 

dust, despite the continuing history of near-misses. 

5. The enclosure installed on the steel conveyor belt under silos 1 and 2 created a confined, 

unventilated space where sugar dust could easily accumulate above the minimum explosible 

concentration. 

6. The enclosed steel conveyor belt was not equipped with explosion vents to safely vent a 

combustible dust explosion outside the building.

7. Company management and supervisory personnel had reviewed and distributed the OSHA 

Combustible Dust National Emphasis Program shortly after it was issued in October 2007, 

but did not promptly act to remove all significant accumulations of sugar and sugar dust 

throughout the packing buildings and in the silo penthouse. 
64 

8. The secondary dust explosions, rapid spreading of the fires throughout the facility, and 

resulting fatalities would likely not have occurred if Imperial Sugar had enforced routine 

housekeeping policies and procedures to remove sugar dust from overhead and elevated work 

surfaces and remove the large accumulations of spilled sugar throughout the packing 

buildings. 

9. The Port Wentworth facility risk assessment performed by Zurich Services Corporation in 

May 2007 and the report submitted to Imperial Sugar management did not adequately address 

combustible dust hazards.
65 

9.0 Incident Causes

1. Sugar and cornstarch conveying equipment was not designed or maintained to minimize the 

release of sugar and sugar dust into the work area.

2. Inadequate housekeeping practices resulted in significant accumulations of combustible sugar 

and sugar dust on the floors and elevated surfaces throughout the packing buildings. 

3. Airborne combustible sugar dust accumulated above the minimum explosible concentration 

inside the newly enclosed steel belt assembly under silos 1 and 2. 

4. An overheated bearing in the steel belt conveyor most likely ignited a primary dust explosion. 

5. The primary dust explosion inside the enclosed steel conveyor belt under silos 1 and 2 led to 

massive secondary dust explosions and fires throughout the packing buildings. 

6. The 14 fatalities were most likely the result of the secondary explosions and fires.

7. Imperial Sugar emergency evacuation plans were inadequate. Emergency evacuation drills 

were not conducted, and prompt worker notification to evacuate in the event of an emergency 

was inadequate. 
66 

10.0 Recommendations

The CSB makes recommendations based on the findings and conclusions of its investigations. 

Recommendations are made to parties that can effect change to prevent future incidents, which may 

include the companies involved, industry organizations responsible for developing good practice 

guidelines, regulatory bodies, and/or organizations that have the ability to broadly communicate 

lessons learned from the incident, such as trade associations and labor unions. 

10.1 Imperial Sugar Company

2008-05-I-GA-R1 Apply the following standards to the design and operation of the new Port 

Wentworth facility:

• NFPA 61: Standard for the Prevention of Fires and Dust Explosions in 

Agricultural and Food Processing Facilities 

• NFPA 499-Recommended Practice for the Classification of Combustible 

Dusts and Hazardous (Classified) Locations for Electrical Installations 

in Chemical Process Areas. 

• NFPA 654-Standard for the Prevention of Fire and Dust Explosions 

from the Manufacturing, Processing, and Handling of Combustible 

Particulate Solids. 

• NFPA Handbook, Electrical Installations in Hazardous Locations. 

• NFPA 70, Article 500 - Hazardous (Classified) Locations. 

2008-05-I-GA-R2 Conduct a comprehensive review of all existing Imperial Sugar Company 

sugar manufacturing facilities against the standards listed in recommendation 

R1 and implement identified corrective actions. 
67 

2008-05-I-GA-R3 Implement a corporate-wide comprehensive housekeeping program to 

control combustible dust accumulation that will ensure sugar dust, cornstarch 

dust, or other combustible dust does not accumulate to hazardous quantities 

on overhead horizontal surfaces, packing equipment, and floors. 

2008-05-I-GA-R4 Develop training materials that address combustible dust hazards and train all 

employees and contractors at all Imperial Sugar Company facilities. Require 

periodic (e.g., annual) refresher training for all employees and contractors. 

2008-05-I-GA-R5 Improve the emergency evacuation policies and procedures at the Port 

Wentworth facility; specifically,

• Install an emergency alert (alarm) system in the facility, and 

• Require routine emergency evacuation drills and critiques

10.2 AIB International

2008-05-I-GA-R6 Incorporate combustible dust hazard awareness into employee and member 

companies’ training programs, such as the Safety and Health Management 

Systems training course. Include combustible dust characteristics, especially 

ignition energy and minimum explosible concentration; best practices for 

minimizing dust accumulation, especially on elevated surfaces; and safe 

housekeeping practices. 

2008-05-I-GA-R7 Add specific combustible dust inspection requirements and metrics to the 

Food Contact Packaging Facility audit procedures.
68 

10.3 American Bakers Association

2008-05-I-GA-R8 Actively promote improvements in combustible dust hazard awareness and 

control throughout the wholesale baking industry by publishing bulletins or 

safety guidance that address combustible dust characteristics including 

ignition energy, minimum explosible concentration, best practices for 

minimizing dust accumulation, and safe housekeeping practices. 

10.4 Risk Insurance Management Society, Inc

2008-05-I-GA-R9 Require member companies to

• Develop and implement combustible dust hazard awareness training for 

all facility audit personnel, and 

• Incorporate combustible dust hazard identification in the audit protocols. 

10.5 Zurich Services Corporation

2008-05-I-GA-R10 Ensure that all risk engineers are trained in the hazards of combustible dust, 

and that refresher training occurs at regular intervals. Provide a copy of your 

combustible dust hazard awareness training materials to your clients who 

deal with combustible dust. 

 
69 

10.6 Occupational Safety and Health Administration

2008-05-I-GA-R11 Proceed expeditiously, consistent with the Chemical Safety Board’s 

November, 2006 recommendation and OSHA’s announced intention to 

conduct rulemaking, to promulgate a comprehensive standard to reduce or 

eliminate hazards from fire and explosion from combustible powders and 

dust.
70 

11.0 REFERENCES 

Babrauskas, V. Ignition Handbook, Fire Science and Technology, Inc., Issaquah, WA.2003.

Center for Chemical Process Safety (CCPS). Guidelines for Safe Handling of Powders and Bulk 

Solids, AIChE/CCPS, New York, NY, 2005. 

Chou, C.C. Handbook of Sugar Refining, Sugar Processing Research Institute, Inc., John Wiley & 

Sons, Inc. New York, 2000. 

Crowl, D.A. Understanding Explosions, American Institute of Chemical Engineers (AIChE), New 

York, NY, 2003. 

Dahn, J.C.; Reyes, B.N., Determination of Metal Sparking Characteristics and the Effects on 

Explosive Dust Clouds,” Industrial Dust Explosions, ASTM Special Technical Publication 958, 

Philadelphia, PA, 1986. 

Dastidar, A.G. et. al., “Evaluation of Dust and Hybrid Mixture Explosion Potential in Process Plants,” 

Process Safety Progress. Vol. 24, No. 4, December 2005. 

Eckhoff, R. Dust Explosions in the Process Industries, 3rd ed. Gulf Professional Publishing, Houston, 

TX, 2003. 

Gibbs, W.E. The Dust Hazard in Industry. Richard Clay & Sons, Ltd., Bungay, Suffolk, U.K, 1925. 

International Code Council, International Fire Code, Falls Church, VA, 2006 ed. 

National Fire Protection Association (NFPA) NFPA 61. Standard for the Prevention of Fires and 

Dust Explosions in Agricultural and Food Processing Facilities, Quincy, MA, 2008. 

NFPA 70, National Electric Code, Article 500 - Hazardous (Classified) Locations, 2008 ed. 

NFPA 101, Life Safety Code, 2009 ed.

NFPA 499, Recommended Practice for the Classification of Combustible Dusts and Hazardous 

(Classified) Locations for Electrical Installations in Chemical Process Areas, 2008 ed. 

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, 

Processing, and Handling of Combustible Particulate Solids, 2006 ed. 

U.S. Chemical Safety Board (CSB). Investigation Report, Dust Explosion, West Pharmaceutical 

Services, Inc., U.S. Chemical Safety and Hazard Investigation Board (CSB), September 2004. 
71 

CSB. Investigation Report. Combustible Dust Fire and Explosions, CTA Acoustics, Inc., U.S. 

Chemical Safety and Hazard Investigation Board, February 2005. 

CSB. Investigation Report. Aluminum Dust Explosion, Hayes Lemmerz International-Huntington, 

Inc., U.S. Chemical Safety and Hazard Investigation Board, September 2005. 

CSB. Investigation Report, Combustible Dust Hazard Study, Investigation Number 2006-H-1, U.S. 

Chemical Safety and Hazard Investigation Board, November 2006. 

U.S. National Aeronautics and Space Administration (NASA). Columbia Accident Investigation 

Board Final Report, Government Printing Office, Washington, DC, 2003. 

U.S. Occupational Safety and Health Administration (OSHA). Combustible Dust in Industry: 

Preventing and Mitigating the Effects of Fire and Explosions, Safety and Health Information Bulletin 

SHIB, July 31, 2005. 

OSHA. Combustible Dust National Emphasis Program, CPL 03-00-006, October 18, 2007, reissued 

as CPL 03-00-008, March 11, 2008. 

Wheeler, R.V. Coal Dust Explosions, Eskmeals, H.M. Stationery Office, U.K., 1924. 
Appendix A. Incident Event Sequence

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Appendix A – Incident Event Sequence
Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix A. Incident Event Sequence

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Appendix B. Explosion Progression in the Packing Buildings

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Appendix B – Explosion Progression in Packing Buildings
Appendix B. Explosion Progression in the Packing Buildings

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Appendix B. Explosion Progression in the Packing Buildings

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Appendix B. Explosion Progression in the Packing Buildings

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Appendix B. Explosion Progression in the Packing Buildings

85