Chemical Safety Board: Process-safety and training failures led to 2020 Watson Grinding explosion

The U.S. Chemical Safety and Hazard Investigation Board (CSB) concluded that gaps in process safety management and emergency preparedness at Watson Grinding and Manufacturing allowed propylene to accumulate and ignite in a coating building on Jan. 24, 2020, producing an explosion that killed two workers and a nearby resident and damaged hundreds of structures.

The CSB report outlines how the company’s coating operations used high velocity oxygen fuel (HVOF) coating, which relies on propylene, an extremely flammable hydrocarbon. The board said that operators had shut down individual booths and locked the coating building the day before the incident, but there was no written company policy to isolate the remote storage tank at the end of the workday; both the manual and remote shutoff valves at the tank were left open overnight.

The CSB said a degraded rubber welding hose disconnected inside a coating booth, allowing propylene to flow from the storage tank into the booth. ‘‘This tragic incident was made even worse due to the lack of emergency response training for employees at the facility,’’ an agency official said, quoting the CSB video summary.

Watson had wall-mounted gas detectors inside each booth intended to alert operators and trigger remote shutoff valves. ‘‘Years prior to the incident, Watson Grinding disconnected the booth’s gas detectors from their computer control system,’’ the CSB report states; contractors had raised written concerns in 2013, 2016 and 2019 about the disconnected automated gas detection system, and company management discussed the issue two weeks before the blast but took no corrective action, the board found.

The CSB found that Watson did not maintain process safety information or engineering drawings for the automated detection system, did not train employees to use or maintain the system, and lacked a mechanical integrity program to ensure inspection, testing and preventive maintenance. The board also flagged an absence of a formal management-of-change review when the company replaced copper tubing with a rubber welding hose — a substitution the CSB said is not recommended for propylene service because propylene oils can cause rubber to crack and lose pliability.

The agency emphasized that regulatory thresholds did not require Watson to have a formal OSHA process safety management program or an EPA Risk Management Plan for the specific coating process, but said several elements of an effective PSM system (process hazard analysis, management of change, mechanical integrity and written operating procedures) likely would have reduced the risk of this event.

The explosion occurred in the early morning after employees smelled a strong propylene odor and heard hissing. Supervisors did not instruct employees to evacuate; shortly before 4:23 a.m., a coating booth operator entered the building, turned on the lights and the accumulated gas ignited, the CSB said. The board reported approximately 450 neighboring structures sustained damage; Watson, which employed about 130 people, later filed for bankruptcy and closed.

In addition to identifying safety-system failures, the CSB recommended that the Compressed Gas Association urge member companies that handle hazardous gases to share information about the hazards described in the Watson report and to encourage customers to adopt robust process safety management systems. The board also urged companies that handle flammable gases to maintain comprehensive written emergency response plans, train workers on those plans and conduct periodic drills.

The CSB concluded by calling for broader industry action to prevent similar tragedies. For more information and the full CSB report, the board directed viewers to csb.gov.