CSB Publishes Didion Milling Investigation Report
Yesterday, the Chemical Safety Board (CSB) published their final report on the Didion Milling explosion and fire that occurred on May 31st, 2023. This combustible dust incident resulted in five employee deaths and an additional 14 employees injured (100% of 19 employees working at the facility at the time of the incident). The incident resulted in $15 million in damages, with no off-site damage or injuries reported.
Safety Concerns
The CSB report identified safety concerns that contributed to the incident. These include:
Process Hazard Recognition,
Dust Hazard Analysis,
Engineering Controls for Combustible Dust Hazards,
Structural Design for Combustible Dust Hazards,
Fugitive Dust Management,
Management of Change,
Incident Investigations,
Process Safety Information,
Management of Audits and Inspections,
Emergency Preparedness,
Personal Protective Equipment,
Process Safety Leadership, and
Regulatory Coverage of Combustible Dust.
While these safety issues are discussed in detail throughout the report. CSB provides a summary of these issues on pages 173 - 183.
Incident Overview
The CSB reports that a ‘smoldering nest’ apparently occurred in one of the bran processing units. This led to the initial explosion in that unit which then propagated through interconnected process units. These process equipment explosions lifted dust from surfaces within the facility which contributed to multiple dust explosions, leading to the collapse of multiple structures within the facility.
The report notes (pg 183):
“The CSB determined the cause of the dust explosions and collapsed buildings was the ignition of combustible corn dust inside process equipment which transitioned to multiple explosions. Contributing to the severity of the explosions was Didion’s lack of engineering controls, which allowed the fire and explosions to propagate through the facility uncontrolled. The uncontrolled propagation of fire and explosions subsequently caused secondary explosions due to the inadequate fugitive dust management.”
Combustible Dust Incidents
The CSB has conducted seven other investigations over the years dealing with combustible dust incidents.
While each of these incidents had unique characteristics and failure modes, the CSB has identified a number of overarching concerns with the prevention of combustible dust incidents. Thes concerns have resulted in the publication of two special reports:
A common thread through all of these reports has been the recommendation that the DOL’s Occupational Safety and Health Administration (OSHA) provide a comprehensive standard for the control of combustible dust in manufacturing environments. In this report, the CSB is taking four of their previously issued recommendations for OSHA action and superseding them with a single recommendation based upon this latest incident. The four previous recommendations are:
2006-1-H-1, Combustible Dust Hazard Investigation,
2008-05-I-GA-11, Imperial Sugar Investigation,
2011-4-I-TN-1, Hoeganaes Corporation Investigation, and
2011-4-I-TN-2, Hoeganaes Corporation Investigation
Safety Recommendations
This report concludes with thirteen recommendations that could prevent the reoccurrence of an incident such as this:
2017-07-I-WI-R1 – Didion Milling - Contract a competent third party to develop a comprehensive combustible dust process safety management system,
2017-07-I-WI-R2 – Didion Milling - Contract a competent third party to develop and implement modifications to the pneumatic conveying and dust collector ductwork systems,
2017-07-I-WI-R3 – Didion Milling - Contract a competent third party to perform dust hazard analyses (DHAs) on all buildings and units that process combustible dust,
2017-07-I-WI-R4 – Didion Milling - Contract a competent third party to assess and implement engineering controls for the structural design and venting requirements of the reconstructed facility,
2017-07-I-WI-R5 – Didion Milling - Incorporate recording any paper-based process safety information into Didion’s existing electronic records management system so that the information can be reliably retained, retrieved, and analyzed in the event of a catastrophic incident,
2017-07-I-WI-R6 – Didion Milling - Contract a competent third party to perform personal protective equipment hazard analyses,
2017-07-I-WI-R7 – Didion Milling - Contract a competent third party to update the facility emergency response plan and train all employees on updated emergency response plan,
2017-07-I-WI-R8 – Didion Milling - Contract a competent third party to assess and update the pre-deflagration detection and suppression engineering controls,
2017-07-I-WI-R9 – Didion Milling - Contract a competent third party to develop and implement a process safety leadership and culture program,
2017-07-I-WI-R10 – OSHA - Promulgate a standard for all industries that handle combustible dust, which should be based on the requirements of current NFPA combustible dust standards,
2017-07-I-WI-R11 – OSHA - Following implementation of CSB Recommendation No. 2017-07-I-WI-R10, update the Grain Handling Facilities Standard to clarify grain handling facilities with combustible dust are covered by the new Combustible Dust Standard,
2017-07-I-WI-R12 – OSHA - Develop a program to trigger follow-up inspections when hazard alert letters are issued for combustible dust hazards and there is insufficient evidence to demonstrate that those hazards have been abated, and
2017-07-I-WI-R13 – NFPA - Update NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities, or a successor standard.
NOTE: CSB has not yet updated their Recommendations page to reflect the addition of the above recommendations, so I cannot currently provide a link to each. They are listed on pages 183 – 186 of the Report.
The fact that the CSB prefaces each of the Didion Milling recommendations with the phrase: “Contract a competent third party to” is not necessarily a commentary on the competency of the management at Didion, but it is certainly a commentary on the complexity of issues related to combustible dust recognition and mitigation.
I am surprised at the absence of a recommendation about developing a combustible dust training program for employees. It is clear from the discussions during the incident description that the employees were not aware of the problems associated with combustible dust, so they were not able to take appropriate actions to protect themselves. Additionally, such awareness training would help ensure that adequate housekeeping standards could be more readily maintained.
Commentary
This is another of a long line of comprehensive reports from the CSB. It provides a detailed review of the processes involved and an in-depth discussion of the process safety management shortcoming that inevitably led to the incident. Interestingly, it does not, however, mention the criminal investigations and convictions of Didion management employees for falsification of records related to the facility’s cleaning logs that I reported on in October. Safety oversights and misunderstandings are a large enough problem to overcome to prevent serious chemical incidents, but adding criminal malfeasance to situation is sure to exacerbate safety problems.