CSB Discovers that Nippon Dynawave Packaging Company Was Told in July 2025 that the Tank Was Not Fit for Continued Service and Could Fail
Washington, D.C., August 28, 2026 — The U.S. Chemical Safety and Hazard Investigation Board (CSB) today released an update on its investigation into the deadly May 26, 2026, catastrophic failure of a 1.2-million-gallon atmospheric storage tank at the Nippon Dynawave Packaging Company, LLC (NDP) pulp and paper mill in Longview, Washington. The tank (identified as G Tank) released approximately 900,000 gallons of extremely hot highly caustic white liquor, fatally injuring 11 NDP employees and seriously injuring three others.
The CSB’s investigation found that an inspection of the exterior shell of G Tank conducted in July 2025 -- approximately 10 months before the fatal incident -- identified that significant portions of the tank’s carbon-steel shell had thinned below the calculated minimum safe thickness.
The inspection contractor’s report recommended that NDP internally inspect and repair the identified thinned areas of G Tank’s shell. The inspection report also stated that G Tank was “[n]ot fit for continued service” unless it was repaired and that there was a “[h]igh likelihood/consequence of failure”. Despite the inspection’s findings, G Tank remained in service until it catastrophically failed on May 26, 2026.
NDP conducted additional external inspections of G Tank in October 2025 and February 2026. Both inspections also determined that substantial portions of G Tank’s shell remained thinner than the calculated minimum safe thickness. Even after these additional inspections, NDP still did not internally inspect or repair the tank shell, remove it from service, or reduce its operating conditions before it failed.
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.”
CSB Investigator-in-Charge Drew Sahli explained, “The minimum safe thickness is the amount of material necessary for an atmospheric storage tank to safely contain its contents. G Tank’s shell had areas thinner than the minimum thickness required for continued service at its typical operating conditions.”
CSB Supervisory Investigator Mark Wingard said, “The inspection identified significant tank-wall thinning below the minimum safe thickness months before the failure. Our investigation is examining why the tank remained in service without either being repaired, or operated under reduced conditions.”
On the day of the incident, May 26, 2026, a process upset required NDP to stop sending white liquor from G Tank to the digestor at the mill where it would have been used to produce pulp from wood chips. However, even though no white liquor was leaving G Tank, white liquor continued to enter the tank from the recausticizing process at the mill, causing the tank level to rise to approximately 90 percent full by 6:22 a.m.
As shown in recently released surveillance footage, at approximately 7:09 a.m., G Tank catastrophically failed, rapidly releasing approximately 900,000 gallons of the scalding hot (200° F) highly corrosive liquid, flooding the surrounding courtyard and nearby buildings where employees were gathered for morning meetings. Eleven NDP employees were fatally injured, and three were seriously injured by the release. Five additional NDP employees and one firefighter sustained injuries but did not require inpatient hospitalization.
CSB Board Member Sylvia Johnson said, “The CSB’s investigation will determine the events that led to the tank remaining in service and our investigation will seek to determine how future incidents can be prevented.”
The CSB continues to investigate the causes and contributing factors associated with the failure, including NDP’s mechanical integrity, inspection and maintenance practices; NDP’s actions to inspect, repair, and/or replace G Tank and other atmospheric storage tanks in light of G Tank’s deteriorated condition; operating conditions preceding the failure; NDP’s emergency response policies and procedures; and regulatory requirements and industry guidance.
The CSB is an independent, nonregulatory federal agency charged with investigating incidents and hazards that result, or may result, in the catastrophic release of extremely hazardous substances. The agency’s core mission activities include conducting incident investigations to identify root cause of releases; formulating preventive or mitigative recommendations based on investigation findings and advocating for their implementation; issuing reports containing the findings, conclusions, and recommendations arising from incident investigations; and conducting studies on chemical hazards.
The agency's board members are appointed by the President subject to Senate confirmation. The Board does not issue citations or fines but makes safety recommendations to companies, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA.
Please visit our website, www.csb.gov. For more information, contact Director of External Affairs Hillary Cohen at [email protected].