CSB Clarifies Events Leading to Fatal Hydrogen Sulfide Release
According to an update (PDF) issued Aug. 13, investigators for the Chemical Safety and Hazard Investigation Board have determined the sequence of events leading up to the hydrogen sulfide release that caused the deaths of two workers on April 22, 2026. The incident occurred during the decommissioning of the Catalyst Refiners Inc. facility, which conducted silver and ethylene oxide catalyst refining operations in Kanawha County, West Virginia.
CSB found that Catalyst Refiners no longer conducted silver reclamation operations by the time of the incident, but the facility’s wastewater treatment system was still functional. The decommissioning process involved the disposal of chemicals used in the silver reclamation process, including nitric acid and two proprietary chemicals. CSB identifies these as A-50, “a proprietary calcium chloride solution used as a coagulant,” and M-2000A, “a proprietary sodium trithiocarbonate solution used as a metal precipitant.”
On the day of the incident, workers pumped approximately 80 gallons of A-50 and 275 gallons of M-2000A into a wastewater receiving tank, then began to pump diluted nitric acid into the same tank. The employees observed a fog forming over the tank. The worker operating the pump stopped the flow of nitric acid, left the area, and briefly lost consciousness. A supervisor notified of the issue entered the tank area and also lost consciousness.
Two other workers not involved with the chemical transfer then entered the tank area. One of them rescued the unconscious supervisor, who subsequently recovered, as did the employee tasked with pump operation. But both of the workers who subsequently entered the tank area were overcome by the released vapors and later died from their injuries.
CSB’s update notes that Catalyst Refiners did not have a written procedure for disposing of A-50, M-2000A, and nitric acid through the wastewater treatment system. The facility had four full-face respirators on site, but not all were equipped with filters that would protect wearers from hydrogen sulfide. Workers told CSB that respirators were no longer required at the facility while it was being decommissioned, and Catalyst Refiners did not provide employees or contractors with personal gas monitors or require their use.
In addition to the two workers killed, 22 workers and first responders were decontaminated on site, and 18 were transported to medical facilities. State and national news outlets reported that local officials temporarily closed nearby roads and issued shelter-in-place orders, while agents of EPA and the West Virginia Department of Environmental Protection conducted monitoring and oversaw cleanup. CSB’s investigation will continue to assess chemical hazards and incompatibilities, decommissioning hazards, chemical disposal procedures, personal protective equipment, atmospheric monitoring, and corporate governance and oversight.
More information can be found in CSB’s Aug. 13 news release. The agency’s complete findings, analyses, and recommendations will be published in its final investigation report.