In this episode of the Dust Safety Science Podcast, we review the US Chemical Safety Board (CSB) report on the Imperial Sugar Refinery Explosion in Wentworth, Georgia on February 7, 2008.
The explosion and following fire resulted in 14 fatalities and 38 injuries.
In the podcast episode we cover the regulatory landscape in 2008, the events that lead up to the incident, deficiencies reported by the US Chemical Safety Board and the main findings from their investigation.
The episode concludes with key take-aways from the investigation and comparing to what we have seen with the Combustible Dust Incident Database to date.
Regulatory Landscape
The Imperial Sugar Refinery explosion occurred at a time when dust explosions where just beginning to come under the microscope in the United States.
Two years prior in 2006, the US Chemical Safety Board released its Combustible Dust Hazard Study which summarized 281 major combustible dust incidents between 1980 and 2005. In this report, the CSB recommended that the Occupational Safety and Health Administration (OSHA) issue a comprehensive combustible dust standard for general powder handling industries.
Just months after the Imperial Sugar Refinery explosion, OSHA announced that it intended to initiate rule making towards a comprehensive combustible dust standard. In its investigation into the Imperial Sugar Explosion released in September 2009, the CSB strongly reiterated its recommendation to OSHA.
Unfortunately, at the time of writing (November, 2018), little progress has been made towards a comprehensive combustible dust standard in the United States.
Imperial Sugar Refinery Explosion Incident
The Imperial Sugar Refinery consisted of a large processing facility which refined raw cane sugar. The processing facility was connected to three storage silos and the packaging and specialty products area by a large system of bucket elevators, screw conveyors an horizontal conveying systems.
Major Deficiencies
The Chemical Safety Board report highlights several deficiencies that contributed to the explosion incident. Two of these had a very large impact on the severity of the explosion. The first was that the conveying systems, dust collectors, and bagging systems continuously spilled sugar throughout the facility. Up to two months prior to the incident, internal documentation indicated that tons of sugar dust were routinely removed from the facility.
The second major deficiency was clogging in the conveying system below the storrage silos which caused sugar dust to spill off of the conveyor in the tunnel. Making this situation even more dangerous, a few months prior to the incident this conveyor was enclosed allowing the dust concentration to increase above the minimum explosible concentration.
Primary Explosion Ignition Sources
The US Chemical Safety Board investigation reviewed four potential ignition sources for the Imperial Sugar Refinery Explosion.
- Open Flame: Ignition by open flame was ruled out as no workers were present inside the tunnel system
- Faulty Switches: Switches inside the enclosed conveyor were ruled out as the two remaining after the explosion appeared to be rated as explosion proof
- Friction Sparks: Sparks from a jammed conveyor could not be ruled out, but additional testing by the CSB demonstrated that these sparks were unlikely to ignite the sugar dust
- Hot Surface Ignition: The CSB report indicates that ignition from an overheated bearing may be the most likely ignition scenario. The conveyor was designed such that the bearings were inside the enclosure and in direct contact with the potential sugar dust which had a Minimum Ignition Temperature ranging from 306-420 degrees Celsius.
Secondary Explosions and Fires
Reports from workers and the company CEO who was walking the floor at the time of the incident, state that the initial explosion heaved the three inch concrete floors and shook the building.
This caused the fugitive dust to be dislodged and dispersed allowing for subsequent explosions and fires.
Video from an adjacent business shows explosions occurring up to 15 minutes after the primary incident and fires starting up to 100 feet away from the silos.
The US Chemical Safety Board concluded that the secondary explosions and fires played an important role in the overall severity of the incident. In addition to injuring employees, these acted to knock out the power system and majority of the sprinkler systems. Knocked down walls and destroyed stairwells also played an important role in making it difficult for employees to escape the secondary fires.
Findings from the Chemical Safety Board Report
In their report, the US Chemical Safety board summarizes nine key findings. This information is summarized here to help push these lessons forward and keep them top of mind. Please review the full incident report for the reasoning behind these findings and recommendations from their work.
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.
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 insurance companies in May 2007 and the report submitted to Imperial Sugar management did not adequately address combustible dust hazards.
Key Take-Aways
Comparing the data we have gathered from the Combustible Dust Incident Database to the incident report from the Imperial Sugar Refinery explosion, several key take-aways were outlined in concluding the podcast episode.
#1 – Risk Perception
The first take-away is the inherent difficulty in risk perception of workers and management in so-called “low-frequency” but “high-severity” catastrophic safety incidents like dust explosions. Although both management and workers were aware of the hazards of combustible dust and the facility had had several near-miss fires and explosions, efforts were not made to reduce the accumulation of fugitive dust in the facility which ultimately lead to the large loss of life during this incident.
#2 – Importance of Training
The second key take-away is the importance of training in preventing and responding to a process safety incidents. Lack of site specific combustible dust training, review and understanding of evacuation procedures, and lack of an effective management of change program all acted to increase the severity of the Imperial Sugar Refinery explosion.
#3 – Role of External Groups During Audits
The third and final take-away outlined at the end of the podcast demonstrates a potential way forward to help reduce these types of incidents in the future. Both insurance companies and industry trade association groups are reported to have audited the Imperial Sugar Refinery, prior to the explosion. Although inspectors from these groups had training in recognizing combustible dust hazards, this information was not passed on to management at the facility during these audits.
Education and encouragement of communication between these groups provides a potential avenue for stopping these type of explosions before they happen in the future.
Resources Mentioned
The resources mentioned in this episode are listed below.
Imperial Sugar Refinery Explosion Investigation:
Imperial Sugar Company Dust Explosion and Fire
US Chemical Safety Board Investigation Report:
Investigation Report – Sugar Dust Explosion and Fire
US Chemical Safety Board Video:
Inferno: Dust Explosion and Fire at Imperial Sugar
OHSA Combustible Dust National Emphasis Program:
Combustible Dust National Emphasis Program (Reissued) CPL 03-00-008
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