A chemical storage tank that exploded in May at a paper mill in Longview, Washington, was identified as unsafe nearly a year before the fatal incident, according to a federal investigation report released on August 28. The blast at the Nippon Dynawave Packaging Company killed 11 workers and injured several others, including one firefighter.

The U.S. Chemical Safety and Hazard Investigation Board (CSB) updated its findings on the failure of the 1.2 million-gallon atmospheric tank, revealing that a July 2025 inspection had flagged significant thinning of the tank’s carbon-steel exterior shell. Investigators noted the shell had degraded below the minimum safe thickness, stating there was a “high likelihood/consequence of failure” if the tank was not repaired or taken out of service. Despite these warnings, the tank remained operational until it ruptured on May 26.

The explosion occurred at 7:09 a.m. while 17 employees were present on the ground level of the mill, with others working in nearby maintenance shops and an operator stationed in the courtyard. When the tank failed, approximately 900,000 gallons of extremely hot, highly caustic white liquor—a chemical used in the paper pulping process—was released. The rapidly moving liquid flooded the courtyard, crushing vehicles and damaging parts of adjacent buildings, including a roll-up door and a wall.

The hazardous chemicals penetrated the lower floors of the buildings through door seals at a time when morning meetings were underway, contributing to the severity of injuries. In total, three workers sustained serious injuries, five suffered minor injuries, and one firefighter was treated for chemical burns. Scott Goldstein, chief of Cowlitz 2 Fire & Rescue, described the injuries as ranging from critical to minor.

The CSB report is part of an ongoing investigation, with officials continuing to determine the precise cause of the explosion. A spokesperson for Nippon Dynawave Packaging Company, Sam Jefferies, expressed the company’s cooperation with the investigation and emphasized their commitment to supporting affected families and employees. Jefferies also highlighted the company’s intent to thoroughly review the report’s findings while continuing to work with authorities before drawing conclusions.

“We believe the responsible course is to allow the full investigative process to proceed and establish a complete and accurate record before conclusions are reached,” Jefferies said. Meanwhile, efforts are underway to fully reopen the Longview mill.