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Staff File Photo by Doug Strickland A plume billows from the Wacker polysilicon chemical plant after an explosion released a hydrogen chemical gas on Sept. 7., 2017, in Charleston, Tenn. The explosion and leaks are under investigation and officials now say the plant will be closed for "several months."

The final state investigation into a Sept. 7 explosion at the Wacker Polysilicon plant in Charleston, Tenn. recommended no enforcement action be taken against the company. The incident resulted in a plant worker, a firefighter, four deputies and seven local residents being treated by local hospitals. The explosion also closed some area roads and led Bradley County Emergency Management Agency to urge residents to shelter in place and turn off HVAC units.

The Tennessee Department of Environment and Conservation investigation released today ruled the blast sent 1,784 pounds of hydrochloric acid into the air and was caused by a "sudden and unavoidable failure of process equipment."  The investigation also determined there were no hydrochloric acid readings that exceeded exposure guidance levels. The threshold for reportable quantity is 5,000 pounds, according to the report.

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"Because the event meets the definition of a malfunction, and it is unlikely that public health or the environment were impacted due to the excess [hydrochloric acid] and [Trichlorosilane] emissions, it is recommended that no enforcement action be taken for the excess emissions resulting from the event," according to the report.

Investigators determined the explosion was caused by a mechanical failure in the company's hydrogen recovery building. The failure occurred when a new piston part of an upgraded compressor design broke, resulting in the explosion.

A Tennessee Occupational Safety and Health Administration investigation into the same incident determined there were five serious violations and two "other-than-serious" violations that resulted in more than $25,000 in fines. A separate TOSHA investigation into an unrelated chemical spill that sent five workers to area hospitals a week prior to the explosion found two serious violations resulting in more than $20,000 in fines. 

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However, the two agencies were conducting entirely independent investigations.  

"These are independent investigations that are looking at different requirements," TDEC communications director Eric Ward said. "[TOSHA is] looking at workplace safety for the workers. We're looking at public health and the environment. They're very independent." 

Wacker officials suspended chemical production for nearly eight months following the explosion as they looked into the incident, hired a third-party investigator, cleared the area of dangerous debris and chemicals, and made safety improvements to the facility. The company went back to the original compressor design and adopted other preventive measures, according to a statement from site manager Mary Beth Hudson. 

"TDEC's findings support the conclusions of WACKER's outside independent expert that the September 7 incident resulted from a mechanical failure with equipment in our hydrogen recovery building," according to the statement. ""At WACKER, we are continually working to ensure the safety of our site, our team members, our community, and our environment. We are committed to providing safe and secure jobs in our community."

Contact staff writer Mark Pace at mpace@timesfreepress.com or 423-757-6659. Follow him on Twitter @themarkpace and on Facebook at ChattanoogaOutdoorsTFP.

Updated July 6 at 11:25 a.m. with a statement from Wacker-Charleston site manager Mary Beth Hudson.

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