CSB Releases Final Report on 2020 Fatal Propylene Release and Explosion at the Watson Grinding facility in Houston, Texas

U.S. Chemical Safety and Hazard Investigation Board (CSB), June 30, 2023

The U.S. Chemical Safety and Hazard Investigation Board (CSB) released its final investigation report on the 2020 propylene release and explosion at the Watson Grinding facility in Houston, Texas, that fatally injured two workers and a nearby resident and damaged hundreds of neighboring homes. The CSB’s final report highlights two key safety issues: the lack of a comprehensive process safety management program at the Watson Grinding facility to manage the risks of its thermal spray coating operations and an ineffective emergency response plan.

CSB Chairperson Steve Owens said, “Our investigation found that Watson Grinding did not have an effective program in place to assess potential hazards in its propylene process and did not have a mechanical integrity program or written operating procedures. This tragic incident was made even worse due to the lack of emergency response training for employees at the facility. Three lives were lost, and the surrounding community was put at risk as a result.

The incident occurred shortly after 4:30 am on January 23, 2020, when an accidental release of propylene accumulated and exploded inside the building at Watson Grinding. The CSB found that prior to the incident, a hose disconnected from its fitting inside a coating booth and released propylene, a flammable hydrocarbon vapor, which accumulated inside the coating building at Watson Grinding. By the time that employees arrived at the facility early on the morning of January 23, an explosive concentration of propylene had formed inside the building. When one of the employees entered the building and turned on the lights, the flammable vapor ignited, triggering the explosion.

The CSB determined that the cause of the accidental release of propylene was a degraded and poorly crimped rubber welding hose that disconnected from its fitting inside a coating booth, combined with two other circumstances: (1) not closing the manual shutoff valve at the propylene storage tank at the conclusion of production operations the previous workday; and (2) the inoperative automated gas detection alarm, exhaust fan startup, and gas shutoff system.

Investigator-in-Charge Benjamin Schrader said, “As highlighted in our safety issues, Watson Grinding did not effectively train its workers on the hazards of propylene, and on the morning of the incident these workers were not warned to evacuate, instructed to prevent others from entering the area, or informed to contact emergency responders when the propylene release was suspected.

As a result of its findings, the CSB is issuing recommendations to encourage both companies and standard-setting bodies to share information from the CSB’s report, as well as existing industry guidelines that emphasize the need for an effective process safety management system.

About the CSB

The CSB is an independent, non-regulatory federal agency whose mission is to drive chemical safety change through independent investigations to protect people and the environment. The agency’s board members are appointed by the President and confirmed by the Senate. CSB investigations look into all aspects of chemical incidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards, and safety management systems. The CSB does not issue citations or fines but makes safety recommendations to companies, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. For more information, please visit

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