As part of its ongoing investigation, the U.S. Chemical Safety and Hazard Investigation Board (CSB) has issued an update and identified several potential process safety deficiencies following an April 22, 2026, hydrogen sulfide release that killed two workers and seriously injured four others at Catalyst Refiners Inc. in Institute, West Virginia.

The incident occurred while Catalyst Refiners was decommissioning its silver and ethylene oxide catalyst refining operations. The facility’s wastewater pretreatment system remained in operation, and employees were disposing of chemicals left onsite. The CSB opened its investigation shortly after the incident. According to the agency, the facility had no written procedure for disposing of the chemicals through the wastewater system.

On April 22, employees pumped two chemicals used in the former silver-reclamation process into a wastewater receiving tank before adding diluted nitric acid. A chemical reaction produced a fog over the tank, and several employees were overcome after entering the area. Two workers later died and four others were seriously injured.

Emergency responders detected hydrogen sulfide at the facility, prompting a shelter-in-place order within a one-mile area, said the CSB. Twenty-two people, including four responders, were decontaminated onsite and 18 were transported to medical facilities for evaluation. Hydrogen sulfide is highly toxic and is considered immediately dangerous to life or health at concentrations of 100 ppm.

The CSB is now focused on examining chemical incompatibilities, decommissioning hazard analysis, chemical disposal procedures, PPE and atmospheric monitoring, as well as corporate oversight. Investigators found four full-face respirators at the facility, but none had filters designed to protect against gases such as hydrogen sulfide.

Workers told the CSB that respirator use was no longer required after the facility transitioned to decommissioning. Catalyst Refiners also did not provide or require employees or contractors to use personal gas monitors.

The findings underscore the need to reassess hazards and safety procedures as facilities transition from production to shutdown or decommissioning, when chemical inventories, operating conditions and work activities can change. The CSB will continue its investigation and address these issues in its final report and any recommendations.

The Catalyst Refiners update follows several recent CSB reports and investigation updates involving process safety and hazard management.

Earlier this week, the agency released its final report on the August 2025 explosion at U.S. Steel’s Clairton Coke Works in Pennsylvania. The CSB found that an informal valve-cleaning practice, inadequate facility siting and process safety management deficiencies contributed to the incident, which killed two workers and injured 11. 

The CSB also recently concluded that Didion Milling had implemented all nine recommendations issued following its investigation of the 2017 combustible-dust explosion at the company’s Wisconsin facility. The recommendations included improvements to dust hazard management, engineered safeguards, emergency response and personal protective equipment.

In July, the CSB's final report on the 2024 Bio-Lab warehouse fire and toxic gas release in Georgia identified inadequate safeguards for reactive chemical storage, along with deficiencies in hazard identification and risk management.

The recent investigations point to several recurring process safety considerations for chemical facilities: written procedures need to reflect actual work practices, hazard assessments must account for changes in operating conditions, and workers need effective methods to identify and protect against hazardous releases.