Federal Probe Finds Washington Mill Ignored Warnings Before Fatal Tank Blast
A federal investigation found that Nippon Dynawave's Longview, Washington, chemical tank was declared unfit for service before it catastrophically failed on May 26, 2026, killing 11 workers.[1]
An inspection contractor flagged the tank in July 2025 as "not fit for continued service unless corrected" because wall thickness had thinned below safe limits.[1] Follow-up exterior inspections in October 2025 and February 2026 again found large areas thinner than the calculated minimum safe thickness, but the company did not repair, derate, or remove the tank from service.[1] The vessel ruptured May 26, 2026, around 7 a.m., releasing about 900,000 gallons of caustic white liquor, blowing out building walls and killing 11 workers.[1] The U.S. Chemical Safety Board says process conditions shifted hours before the blast when a digestor was taken offline, allowing the tank to fill toward capacity before it failed.[1]
Nippon Dynawave bought the Longview pulp mill from Weyerhaeuser in 2016. State inspection records show a vapor leak on the facility's G-Tank was identified in December 2023 and persisted into early 2024. A related pressure-vacuum-breaker leak on the same tank was documented from December 2023 through at least September 2024 and was not fixed during a May-June 2024 outage. Records show the mill accumulated environmental violations and faced separate state safety inspections for valve failures and other equipment problems. Since the 2016 acquisition the facility received about 54 clean air or water violations between 2016 and 2026.
Washington's Department of Ecology has cited the company with 35 environmental violations related to the incident, and the Chemical Safety Board's full investigation remains ongoing.[1] CSB and lawmakers posted updates on social media and said more information will follow as the board continues its work.
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📊 Relevant Data
The Nippon Dynawave Packaging liquid packaging facility in Longview employs approximately 450-500 workers and produces 260,000-300,000 metric tons of paperboard annually, enough for roughly 6 billion one-liter milk cartons.
Nippon Dynawave Packaging Longview WA — Packaging Dive; Zippia; Seattle Times
Since the 2016 acquisition, the facility has received around 54 clean air or water violations from state regulators, including prior white liquor leaks from the same tank in 2023-2024.
Longview pulp mill had reported other leaks at tank that killed 11 workers, records show — The Seattle Times
📌 Key Facts
- On July 2025, an inspection contractor found the Longview, Washington mill’s chemical tank 'not fit for continued service unless corrected' due to significant wall thinning below minimum safe thickness.
- Follow-up exterior inspections in October 2025 and February 2026 again found large portions of the tank thinner than the calculated minimum safe wall thickness, but Nippon Dynawave did not repair, derate, or remove it from operation.
- The tank catastrophically failed on May 26, 2026, around 7 a.m., releasing about 900,000 gallons of caustic white liquor, blowing out building walls, and killing 11 workers.
- CSB’s update details that process conditions changed hours before the failure when a digestor was taken offline, causing the tank to fill toward capacity before it ruptured.
- Washington’s Department of Ecology has issued 35 environmental violations related to the incident, and CSB’s full investigation is ongoing.
📰 Source Timeline (1)
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