On February 27, the U.S. Chemical Safety and Hazard Investigation Board (CSB) released an update on its investigation into a fatal November 12, 2024, explosion at the Givaudan Sense Colour facility in Louisville, Kentucky.

The explosion killed two employees and seriously injured three others, and it caused significant property damage to the facility and nearby homes and businesses, according to the CSB. Debris was ejected outside the facility's fence line, flying up to 400 feet into a nearby neighborhood. Local authorities issued a shelter-in-place order for a 1-mile radius around the facility.

The CSB offered the following timeline of events leading up to the explosion:

• At 10:22 a.m., the facility's operators began a process in a batch reactor to produce caramel coloring for a food product. Operations were initially normal.
• At 2:17 p.m., the pressure setpoint for the batch reactor was adjusted to 12 pounds per square inch gauge (psig), and the temperature setpoint was set to 300 degrees Fahrenheit (°F), as specified in the batch instruction.
• By 2:39 p.m., pressure in the reactor exceeded the setpoint. Despite attempts to reduce it, the pressure continued to rise.
• After the pressure relief valve opened at 2:54 p.m., the pressure initially decreased but then continued to climb. The temperature also increased far above the setpoint, reaching 385°F, 85° above the setpoint and 30° above the reactor’s allowable limit of 355°F.  
• A few minutes later, at 2:57 p.m., the reactor catastrophically ruptured when its pressure reached 237 psig, over three times the maximum allowable pressure.

It was discovered after the incident that the reactor vessel’s automated vent valve was almost fully closed. The vent valve was supposed to automatically open to relieve pressure in the vessel to maintain the pressure at the 12-psig setpoint. The CSB will further inspect the recovered vent valve and actuator as part of its ongoing investigation.

The board is also taking the following steps:

• Testing the raw materials to identify potential reactive hazards,
• Analyzing the batch reactor relief system,
• Reviewing process data and process conditions leading to the incident,
• Further analyzing the recovered vent valve and actuator, and
• Evaluating emergency response efforts.

“This massive explosion should not have happened,” CSB Chairperson Steve Owens said in a board statement. “Two people died, homes and businesses were severely damaged, and the neighboring community was put at serious risk.”

The CSB is an independent federal government board that investigates industrial chemical incidents and makes safety recommendations to companies, industry organizations, labor unions, and regulatory agencies, including the Environmental Protection Agency (EPA) and Occupational Safety and Health Administration (OSHA). However, it doesn’t issue citations for regulatory violations or impose any fines. Board members are appointed by the president and are subject to Senate confirmation.

The board also released a new video on its YouTube channel of its investigation into the January 24, 2020, fatal propylene release and explosion at the Watson Grinding and Manufacturing Company facility in Houston, Texas, the CSB announced on February 25.

The explosion resulted in the death of two workers and a nearby resident and damaged hundreds of neighboring homes.