The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released a major update on its investigation into the deadly tank failure at Nippon Dynawave Packaging in Longview, saying the tank that failed had been identified as a serious safety concern 10 months before the May 26th disaster.
The CSB says an exterior inspection of the 1.2-million-gallon tank in July 2025 found significant portions of its carbon-steel shell had thinned below the minimum thickness considered safe for continued operation.
The inspection contractor recommended that the tank be internally inspected and that the damaged areas be repaired. The report specifically said the tank was “not fit for continued service” unless repairs were made and warned of a “high likelihood/consequence of failure.” Despite those findings, for reasons that remain unclear, the tank remained in service.
According to the CSB, additional external inspections in October 2025 and February of this year also found substantial portions of the tank shell remained thinner than the minimum safe thickness. The tank was not internally inspected or repaired, taken out of service, or placed under reduced operating conditions before the failure.
On May 26th, a process problem at the mill stopped white liquor from being sent from the tank to the digester, where it would normally be used in the papermaking process. However, white liquor continued entering the tank from another part of the mill.
By about 6:22 a.m. that morning, the tank was approximately 90 percent full. At about 7:09 a.m., the tank catastrophically failed, releasing about 900,000 gallons of extremely hot, highly caustic white liquor. 11 Nippon Dynawave employees were killed and many others were injured, including 3 who were severely injured.
The investigation is now focusing in part on why the tank remained in service despite the inspection findings. CSB Chairperson Steve Owens said, “Although the CSB’s investigation is still ongoing, we are greatly concerned that the tank was not promptly removed from service or properly repaired after the clear findings in the inspection report.”
The agency has not yet determined the specific cause or mechanism of the tank’s failure, and its investigation remains ongoing.
The Association of Western Pulp and Paper Workers, or AWPPW, which represents the mill’s employees, called the findings “deeply troubling.” AWPPW spokesperson Joshua Estes said the families of the 11 workers killed deserve a complete accounting of how the inspection findings were communicated and why the tank remained in operation. However, he also cautioned against drawing conclusions about responsibility before the full investigation is complete.
The CSB says its full investigation will ultimately seek to determine what led to the tank remaining in service and what can be done to prevent a similar tragedy from happening again.
