Federal Report: Washington Tank Was Unfit Months Before Collapse
A chemical storage tank that collapsed at a Washington pulp and paper mill, killing 11 workers, had been deemed unfit for continued service about 10 months earlier, according to a federal investigative update released Friday, August 28.
The U.S. Chemical Safety and Hazard Investigation Board said a July 2025 inspection found significant thinning in the carbon-steel shell of G Tank at Nippon Dynawave Packaging’s mill in Longview, Washington. The inspection contractor recommended an internal inspection and repairs and warned of a high likelihood and consequence of failure.
The tank remained in service until it failed on May 26, 2026. The CSB said its investigation is ongoing and has not assigned final responsibility.
What the July inspection found
G Tank was an atmospheric storage tank holding approximately 1.2 million gallons. The July 2025 external-shell inspection found portions of the carbon-steel shell below the calculated minimum safe thickness — the amount of material the tank needed to safely contain its contents under its typical operating conditions.
The contractor recommended that Nippon Dynawave inspect the tank internally and repair the thinned areas. The report described G Tank as “not fit for continued service” unless it was repaired and cited a “high likelihood/consequence of failure,” the CSB said. Those statements were the contractor’s inspection conclusions, not a final federal finding of legal liability.
What happened after the warning
Nippon Dynawave conducted additional external inspections in October 2025 and February 2026. Both found that substantial portions of the shell remained below the calculated minimum safe thickness.
According to the CSB’s investigative update, the tank was not internally inspected or repaired, removed from service, or operated under reduced conditions before the collapse. The agency is examining why the tank remained in service after the initial warning and the two later inspection findings.
How the collapse unfolded
On the morning of May 26, a process upset required the mill to stop sending white liquor from G Tank to its digestor, where the chemical is used in pulp production. White liquor continued entering the tank from the mill’s recausticizing process, however, causing the level to rise to approximately 90% full by 6:22 a.m.
At approximately 7:09 a.m., G Tank catastrophically failed. The CSB said the collapse released approximately 900,000 gallons of extremely hot, highly caustic white liquor, reported at about 200 degrees Fahrenheit, into the surrounding courtyard and nearby buildings, where employees were gathered for morning meetings.
Eleven Nippon Dynawave employees were killed, and three others were seriously injured. Five additional employees and one firefighter suffered injuries that did not require inpatient hospitalization.
Several investigations remain separate
The CSB is examining the company’s mechanical-integrity, inspection and maintenance practices; decisions involving the inspection, repair or replacement of G Tank and other atmospheric storage tanks; operating conditions before the failure; emergency-response procedures; and applicable regulations and industry guidance. The CSB is an independent, nonregulatory federal agency. It does not issue citations or fines, but it can issue safety recommendations.
OSHA’s accident inspection opened on May 26 and remains listed as open. Washington’s Department of Labor & Industries is conducting a separate workplace-safety investigation that includes document reviews, witness interviews and a physical inspection of the site. L&I says it has 180 days by law to complete the investigation, although complex inspections can take the full period. After final findings are issued, the employer has 15 working days to appeal any violations.
Washington’s Department of Ecology is handling a separate environmental process. The agency issued a notice of violation containing an initial determination of 35 environmental violations connected to the release. Ecology said the white liquor reached storm drains, the mill’s wastewater treatment system and the Columbia River, with impacts continuing for up to eight days.
Nippon Dynawave has 30 days to respond or provide additional information before Ecology decides whether to issue a penalty or take other enforcement action. The notice is not itself a final penalty or completed enforcement action. Ecology said it may also seek recovery of state emergency-response costs and assess environmental damage.
What remains unresolved
The new federal update adds a major issue to the investigation: not only how the tank failed, but why it remained in service after an inspection contractor documented wall thinning below the calculated minimum safe thickness and recommended repairs and an internal inspection.
That record does not yet establish criminal, civil or regulatory liability. The CSB has not issued a final root-cause report, and OSHA and Washington Labor & Industries have not completed their workplace-safety investigations. Ecology’s 35 violations remain initial determinations pending the company’s response and the agency’s next action.
Nippon Dynawave has said it is cooperating with the investigations and will not speculate about the root cause before the facts are complete. The next milestones to watch are the final CSB report, OSHA and L&I findings, and Ecology’s response after the company’s 30-day window.
Sources
- U.S. Chemical Safety Board investigation update
- Associated Press report
- OSHA accident inspection record
- Washington Department of Ecology notice
Look for updates to this story
Discover more from Interactive News
Subscribe to get the latest posts sent to your email.