CSB Finds Nippon Dynawave Left Unsafe Tank in Service
The May 26 failure released about 900,000 gallons of hot, caustic white liquor, killing 11 employees.
- By Danielle Naidu
- Sep 11, 2026
Workers had gathered for morning meetings at Nippon Dynawave Packaging Co.’s mill in Longview, Washington, when a storage tank failed after three external inspections found its shell was thinner than the calculated minimum for safe operation, federal investigators reported.
A July 2025 inspection determined that substantial portions of the tank’s carbon-steel shell were below the calculated minimum safe thickness. The contractor recommended an internal inspection and repairs. Its report found the tank was not fit for continued service unless repaired and warned of a high likelihood and consequence of failure.
Additional inspections in October 2025 and February 2026 found that substantial portions of the shell remained below the calculated minimum safe thickness. Nippon Dynawave did not internally inspect or repair the shell, remove the tank from service or reduce its operating conditions before the failure, according to the U.S. Chemical Safety and Hazard Investigation Board (CSB).
A process upset on May 26, 2026, stopped white liquor from leaving the tank while additional liquid continued to enter. The tank was approximately 90% full by 6:22 a.m. and failed at about 7:09 a.m. The release flooded a courtyard and nearby buildings.
Eleven Nippon Dynawave employees were fatally injured, and three sustained serious injuries. Five other employees and a firefighter were injured but did not require inpatient hospitalization.
The CSB is examining the company’s mechanical integrity, inspection and maintenance practices, operating conditions and emergency response procedures. Investigators are also reviewing regulatory requirements and industry guidance. The board has not issued its final findings on the causes and contributing factors.
The Washington State Department of Labor and Industries is conducting a separate workplace safety investigation. The agency will determine whether safety violations occurred and whether citations or penalties are warranted.
About the Author
Danielle Naidu is assistant editor for Security Today, Campus Security Today, Occupational Health & Safety and Environmental Protection Online.