Nearly 10 months before its catastrophic failure, a storage tank at Nippon Dynawave Packaging’s pulp and paper mill in Longview, Washington, was deemed unfit for continued service unless repaired, according to a federal investigation update.
The May 26, 2026, failure of the 1.2-million-gallon atmospheric storage tank, known as G Tank, released approximately 900,000 gallons of extremely hot, highly caustic white liquor. Eleven employees were killed and three others were seriously injured.
Paper Advance initially reported the incident after one fatality had been confirmed and 10 employees remained missing. The death toll was later confirmed at 11 after recovery crews located the remaining victims.
In its investigation update, the U.S. Chemical Safety and Hazard Investigation Board (CSB) said an external inspection conducted in July 2025 found that significant portions of the tank’s carbon-steel shell had thinned below the calculated minimum safe thickness.
The inspection contractor recommended an internal examination and repairs to the affected areas. Its report also warned of a high likelihood and consequence of failure and concluded that the tank was not fit for continued service unless repairs were completed.
Nippon Dynawave conducted additional external inspections in October 2025 and February 2026. Both again found substantial areas of the tank shell below the calculated minimum safe thickness.
According to the CSB’s investigation update, the tank remained in service without an internal inspection, repairs, reduced operating conditions or removal from service.
The minimum safe thickness represents the amount of material required for an atmospheric storage tank to safely contain its contents under normal operating conditions. Investigators are examining why G Tank continued operating despite the inspection findings.
On the morning of the incident, a process upset stopped white liquor from being transferred from G Tank to the mill’s digester, where it would have been used to produce pulp from wood chips. White liquor continued entering the tank from the recausticizing process, however, raising its level to approximately 90% by 6:22 a.m.
At approximately 7:09 a.m., G Tank catastrophically failed, releasing white liquor at roughly 200°F, or 93°C, into a courtyard and nearby buildings where employees had gathered for morning meetings. Five additional employees and one firefighter sustained injuries but did not require inpatient hospitalization.
Nippon Dynawave disputed the completeness of the update, saying it was “deeply disappointed” that the document omitted what it described as important facts and context about the company’s actions and the timeline preceding the incident.
The company stressed that the update was an initial step and did not constitute a final determination of the facts or cause. Its statement did not specify which facts or actions it believed had been omitted.
The CSB’s investigation remains ongoing. The agency is reviewing the mill’s mechanical integrity, inspection and maintenance practices; decisions concerning G Tank and other atmospheric storage tanks; operating conditions before the failure; emergency-response procedures; and applicable regulations and industry guidance.
The findings were released as Nippon Dynawave continued recovery work at the Longview mill following the disaster.
The CSB is an independent, nonregulatory federal agency. It does not issue citations or fines but develops safety recommendations for companies, industry organizations, labour groups and regulators.
