CSB Report: Longview Tank Was Flagged "Not Fit for Service" 10 Months Before Fatal Failure
The U.S. Chemical Safety and Hazard Investigation Board released an update this week on its investigation into the May 26, 2026, failure of a 1.2-million-gallon storage tank at the Nippon Dynawave Packaging Company mill in Longview, Washington, ISHN reports.
The tank, known as G Tank, released roughly 900,000 gallons of caustic white liquor heated to 200°F, fatally injuring 11 employees and seriously injuring three others.
What the Inspection Report Said
An exterior shell inspection conducted in July 2025, about 10 months before the failure, found that significant portions of G Tank’s carbon-steel shell had thinned below the calculated minimum safe thickness. The inspection contractor’s report explicitly stated the tank was “not fit for continued service” unless repaired, and flagged a “high likelihood/consequence of failure.”
NDP did not act on that warning. The company conducted two more external inspections, in October 2025 and February 2026, and both confirmed the shell remained thinner than the minimum safe thickness. Despite three separate inspections documenting the problem, NDP never internally inspected or repaired the tank, never pulled it from service, and never reduced its operating conditions.
The failure itself was triggered by a process upset on the morning of May 26. White liquor stopped flowing out of G Tank to the mill’s digestor, but liquid kept flowing in from the recausticizing process, pushing the tank to about 90% full by 6:22 a.m. At 7:09 a.m., the tank catastrophically failed, according to surveillance footage cited by the CSB.
“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,” said CSB Chairperson Steve Owens. CSB Supervisory Investigator Mark Wingard added that the agency is examining “why the tank remained in service without either being repaired, or operated under reduced conditions.”
What It Means for Subcontractors
- If your inspection report says “not fit for continued service,” get that finding in writing to the asset owner and keep a copy. NDP’s contractor issued that exact language in July 2025, and it sat unaddressed for 10 months before the tank killed 11 people.
- Mechanical integrity and API 653 tank inspection subs should treat repeat findings as escalation triggers. NDP received the same thinning-below-minimum-thickness result three times (July 2025, October 2025, February 2026) without internal inspection or repair, a pattern worth flagging contractually if you’re the inspection vendor of record.
- Expect the CSB’s final report to address mechanical integrity and inspection/maintenance practices directly, which could shape future OSHA Process Safety Management enforcement and industry guidance for atmospheric storage tank operators in pulp, paper, and chemical processing.
- Firms doing tank inspection, repair, or turnaround work at similar facilities should document any recommendation to remove equipment from service or reduce operating conditions, since the CSB is specifically examining why those steps weren’t taken at NDP.
