CSB Releases Final Report into Fatal Chemical Release at Wacker Polysilicon Facility in Tennessee

U.S. Chemical Safety Board, June 15, 2023

The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released its final report into the November 2020 hydrogen chloride (HCl) release that occurred during maintenance activities at the Wacker Polysilicon North American facility in Charleston, Tennessee.  A worker was fatally injured in the incident.

In its final report, the CSB found that at the time of the incident there were multiple contract workers present on the fifth-floor of an equipment access platform at the facility. The contract workers were from two different firms, conducting different work, and were wearing different levels of Personal Protective Equipment (PPE). One of the workers applied excessive torque to flange bolts on a heat exchanger outlet pipe containing HCl, causing the pipe to crack and release the hazardous chemical in the vicinity of the workers.

There was only one way to exit the platform – via a staircase. As the white cloud of HCl expanded, the workers on the platform were not able to see their surroundings or access the staircase. Three of the workers who were not wearing full-body chemical resistant suits began climbing down the side of the structure to escape the HCl cloud. All three workers fell approximately 70 feet during their attempt to escape. One of the workers died from the fall, and the other two sustained serious injuries.

CSB Chairperson Steve Owens said, “What should have been fairly straightforward activity by two separate groups of workers turned deadly because of several tragic circumstances. Our report identifies several critical issues that must be addressed to ensure safe operations whenever there are different groups of workers performing equipment maintenance and other work simultaneously in an area.  This incident was completely preventable.

The CSB identified Four Key Safety Lessons:

  • Written Procedures: Wacker tasked contract pipefitters with torquing flange bolts on a pipe segment, which contained hazardous HCl and was equipped with multiple bolts with different torque requirements. Wacker did not have written procedures for the contractors to follow and relied on the piping manufacturers’ equipment manual which did not include torque specifics for all bolts on the piping segment, and on verbal instructions for which bolts to torque.
  • Control of Hazardous Energy: Wacker did not treat torquing operations on equipment containing hazardous chemicals as an activity that required isolation of that equipment since it did not involve the intentional opening of a line. Wacker did not perform a risk analysis and did not implement precautions to mitigate risk.
  • Simultaneous Operations: When the incident occurred, four workers from a separate contract company were performing an unrelated pipe insulation task on the same structure where the pipefitter crew was working. Wacker did not have a procedure or policy for evaluating simultaneous operations, referred to as SIMOPs, and no evaluation of risk to the other contractors was conducted.
  • Means of Egress: During the incident, a total of seven workers were present on the fifth-floor open-air platform, which was equipped with just a single point of egress. The structure was based on current building code requirements which the CSB determined do not provide for sufficient means of egress. Additionally, three months before the incident, Wacker employees identified a need for a second point of egress, but Wacker did not take any action to address this recommendation prior to the 2020 incident.

Deputy Investigator-in-Charge Tyler Nelson said, “The CSB determined that the cause of the incident was the accidental over-torquing of bolts on equipment containing hazardous HCl. Both the lack of written procedures and ineffective control of hazardous energy contributed the occurrence of the event. Uncontrolled simultaneous operations and a limited means of egress, significantly contributed to the severity of this event.

The CSB’s investigation resulted in several key recommendations, including a recommendation to the U.S. Occupational Safety and Health Administration (OSHA) to require the coordination of simultaneous operations involving multiple work groups, including contractors. The CSB is also calling on OSHA and the Center for Chemical Process Safety (CCPS) to create safety products to provide guidance on simultaneous operations. At the company level, the CSB is calling on Wacker to improve its company policies and procedures which would specifically address torquing, control of hazardous energy, and simultaneous operations.

The CSB is also recommending that Wacker install an additional means of egress for tower platforms. Additionally, the CSB is issuing recommendations to the International Code Council (ICC) and the National Fire Protection Association (NFPA) to address requirements for multiple means of egress from elevated structures.

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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