On November 12, 2024, the batch reactor vessel at the Givaudan Sense Colour caramel
coloring manufacturing facility in Louisville, Kentucky exploded. The 2,500-gallon reactor(reactor 6) was producing the caramel coloring Product 484 when the sugar ingredient
experienced thermal runaway. The explosion resulted in two employee deaths and three serious injuries.
During the incident, the vent valve failed in the closed position, causing temperatures and
pressures to rise above the maximum operating conditions. The emergency relief system opened and temporarily reduced temperatures and pressures before the reaction again became runaway, reaching a maximum pressure of 237 psig. The failed vent valve was the initiating event, but understanding why the incident became catastrophic requires looking beyond the valve itself.
A strong process safety management system is based on four pillars: commit to process
safety, understand hazards and risk, manage risk, and learn from experience.
The incident demonstrates how severe deficiencies in a process safety management system can progress into a major process safety incident.
Understanding Hazards and Risk
In 2012, the previous site owner D.D. Williamson contracted a third-party to perform
adiabatic reactivity testing for a similar product, Product 034. The results of this test found
significant exothermic activity and pressure generation from non-condensable gas. D.D.
Williamson believed that the recipe for Product 484 was less reactive and therefore additional testing was not conducted to determine whether sugar decomposition was the source of pressure generation or whether other sugar-containing recipes could behave similarly. This demonstrates the importance of the second pillar of a process safety management system: understanding hazards and risk. Unexpected heat or pressure generation should be treated as evidence that the process is not yet fully understood.
The runaway reaction mixture was a medium invert syrup feed mixed with phosphoric acid,
sodium hydroxide, water, and an antifoam additive. At the intended process conditions, these sugars form intermediate compounds including HMF which then further react to produce caramel colors. When process conditions are exceeded at elevated temperatures, HMF and other sugar intermediates undergo exothermic decomposition, resulting in the formation of dangerous non-condensable gas and temperature generation. This behavior is not limited to the complete reactor 6 mixture. Testing of the sugar ingredient revealed that the sugar ingredient by itself was capable of undergoing thermal runaway and significant gas generation.
Post-incident calorimetry data identified that at temperatures within the reactor’s typical
operating temperature, the feed mixture was capable of decomposing exothermically. The chart shown below is calorimetry data of the reactor 6 mixture. The largest exotherm was detected at 243℉, well below the reactor’s set temperature of 300℉ and resulted in a temperature rise of 284℉ and a maximum pressure of 1,509 psig.
Understanding hazards and risk extends beyond those associated with typical operating
conditions. A complete understanding requires knowledge of runaway conditions as well as investigating unexpected temperature and pressure generation and whether that hazard applies to other products and processes.
Manage Risk
The design of the relief system demonstrates another deficiency in the process safety
management system: management of change. Management of change requires that all proposed changes be reviewed and authorized. Furthermore, documentation should be preserved and kept up to date. Following the results of the 2012 reactivity testing, the pressure relief valves for reactors 3 and 4 were resized, however the information provided on the management of change form was limited for reactor 3, and missing for reactor 4. As a result, the design team for reactor 6’s pressure relief system was unaware of the 2012 reactivity testing and the resizing of reactors 3 and 4. While the pressure relief device for reactor 6 was properly maintained, opened at the correct pressure and operated as designed, the relief system needed to be sized over four times larger to have been able to mitigate the accident,
Commitment to Process Safety
One of the most severe deficiencies in the process safety management system was their
commitment to process safety. The EPA RMP rule requires that hazard reviews are conducted at least once every five years. In 2007, D.D. Williamson reduced their ammonia levels below the EPA’s threshold quantity and conducted their final hazard review in 2008. As a result, the design changes for reactors 3 and 4 and the results of Product 034’s reactivity test were not documented in the hazard review. Maintaining process safety competency is a core element of commitment to process safety. Process safety competency requires that knowledge is continuously improving, available to those who need it, and applied where needed. The decomposition hazard on the safety data sheet (SDS) for the reactor 6 feed was not included, although other similar SDSs obtained by the CSB did include decomposition temperature. This contributed to a lack of knowledge or awareness of the hazard.
Learn from Experience
The final pillar of process safety management is to learn from experience. One way that
this can be done is by self-auditing processes. The Center for Chemical Process Safety (CCPS) published guidelines for evaluating and auditing facility siting in 2018, which state “Evaluate the control buildings for safe haven or blast-resistant construction or locate the control buildings with conventional construction in an area where safe haven or blast resistant construction is not needed. If the building is located in the hazardous area, toxic release and explosion impact analyses should be performed with consequence impact studies or quantitative risk assessments." D.D. Williamson did not evaluate their facility siting process at any point in time. Both employees with fatal injuries were occupying a control room that was not reinforced for an explosion near the reactor. As a result, when the reactor ruptured, the control room collapsed and the occupants were killed.
Summary
Process safety management underscores everything that is done at a chemical plant. The
lessons learned from this incident are summarized below.
- Unexplained reactivity should be investigated to determine whether that hazard is
applicable in other areas. - Management of change must be thoroughly documented and preserved for future use.
- Process safety reviews should be conducted at least every five years or when changes are made.
- Facility siting should be evaluated for potential hazards.
References
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American Institute of Chemical Engineers. (2007). Guidelines for Risk Based Process Safety.
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U.S. Chemical Safety and Hazard Investigation Board. (2026). Fatal Runaway Reaction and Explosion at.
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United States Environmental Protection Agency. (2026, April 20). When must RMPs be submitted, updated, and corrected? Retrieved from epa.gov: https://www.epa.gov/rmp/when-must-rmps-be-submitted-updated-and-corrected