A chemical tank at a Washington state paper mill was identified as “not fit for continued service” by an inspection contractor 10 months before it failed in May, killing 11 workers in one of the deadliest U.S. workplace disasters in recent history, according to a federal report released Friday.
The U.S. Chemical Safety Board (CSB) stated that the ongoing investigation into the May 26 failure in Longview, which released a caustic liquid powerful enough to breach building walls, is still working to determine the exact cause.
The contractor had recommended internal inspections and shell repairs for the tank to Nippon Dynawave Packaging Company. However, the company reportedly performed no work on the tank between the July 2025 inspection and the failure in May 2026.
“Because the investigation remains ongoing, we will not comment on individual findings or documents at this time,” a Nippon spokesperson said Friday. “Our focus remains on supporting affected families and employees and taking the necessary steps toward fully reopening the Longview facility.” The spokesperson added that the company is cooperating fully with the CSB.
The Association of Western Pulp and Paper Workers called the CSB's findings “deeply troubling,” and stated that the update “raises urgent questions about how technical findings and recommendations concerning the tank were communicated, evaluated and incorporated into decisions about its continued operation.” The association added, “The families and workforce deserve a complete accounting of that process.”
Inspection Findings
According to the CSB's report, the contractor found “significant thinning” below the minimum safe thickness in the lower sections of the tank during a July 2025 external inspection. This minimum safe thickness is a measure of a tank's structural integrity and its ability to contain the liquid's pressure and support its own weight.
Subsequent external inspections in October 2025 and February 2026 also indicated that