Washington Paper Mill Chemical Tank Was Deemed Unfit Before Deadly Failure, Federal Investigators Say

A chemical storage tank at a Washington state paper mill had been identified as “not fit for continued service” 10 months before it failed in May, killing 11 people, according to an update from the U.S. Chemical Safety Board.

The federal agency said its investigation into the May 26 failure at Nippon Dynawave Packaging Company's Longview facility remains ongoing and that it has not yet determined the cause of the incident.

An inspection conducted in July 2025 found significant thinning in the lower regions of the tank, including areas below the calculated minimum safe wall thickness, according to the board's report. The inspection contractor recommended an internal inspection and repairs, noting that the tank was not fit for continued service unless corrected and that replacement of an entire shell section was likely needed.

Further external inspections in October 2025 and February 2026 found that large portions of the tank remained below the minimum safe thickness, the board said. Nippon Dynawave did not carry out internal inspections or shell repairs between the July 2025 inspection and the May 2026 failure, according to the report, nor was the tank removed from operation or derated for reduced service.

The failure released about 900,000 gallons of white liquor, a caustic liquid used in paper manufacturing that can cause severe burns. Several other people, including a firefighter, were injured.

According to the investigation update, the tank stopped sending white liquor to a digestor that had been removed from service for repairs shortly before 2 a.m. More liquid continued flowing into the tank, which approached full capacity at about 6:20 a.m. and failed less than an hour later as employees were arriving for work.

U.S. Chemical Safety Board Chairperson Steve Owens said the agency was concerned that the tank had not been promptly removed from service or properly repaired following the inspection findings.

Nippon Dynawave said it would continue cooperating with the investigation and that its focus remained on supporting affected families and employees and reopening the Longview facility.

The board said its complete findings will be included in a final investigation report. Earlier in the week, the Washington Department of Ecology issued notice of 35 environmental violations to the company.