According to The Associated Press, in May this year, an explosion occurred at a Japanese-owned paper factory in Washington State, USA. The explosion caused the death of 11 people and became one of the most fatal workplace accidents in the United States in recent decades. On August 28 local time, a U.S. federal report indicated that as early as 10 months before the accident, a testing contractor had determined that the storage tank was “no longer usable.”
A report released by the United States Chemical Safety and Hazard Investigation Series (CSB) indicates that in the explosion of the storage tank in Langwyu City, a large amount of corrosive liquid leaked out, causing enough force to collapse the walls of the building. The root cause of the failure of the storage tank is still under investigation.
According to an investigation by CSB, the accident occurred at the factory of Nippon Dynawave Packaging, a subsidiary of the Japanese paper-making group. As early as July 2025, a testing contractor had submitted recommendations for internal testing and repair of the tank walls to the company. However, until the accident happened, the company failed to implement any corrective measures.
The report indicates that in July 2025, external inspections by the contractor revealed “severe thinning of the tank walls” at the lower part of the tanks. The thickness has fallen below the minimum safety wall thickness standard. The report states that the minimum safety wall thickness is a critical parameter that determines how much pressure liquid can be applied to the tanks and how they can support their own weight.
The contractor indicated the risk level of the storage tank as “Priority Level 1: No longer usable without rectification” in the report, with a note that “the probability of the tank failing and the consequences would be extremely high, or there may be serious violations of key regulatory standards.” The inspection report stated: “The equipment owner should arrange for internal inspections to determine the scope of repairs required; it is highly likely that the tank’s wall panels will need to be completely replaced.”
The same contractor conducted additional inspections on the exterior of the storage tanks in October 2025 and February 2026. Both inspections confirmed that “a significant portion of the wall thickness of the storage tanks is below the calculated safety limit for tank walls.”
CSB points out that “the company neither stopped operation of the storage tank nor reduced its rated load or downgraded usage.”
This testing was conducted by Applied Technical Services LLC. The federal report does not indicate the reasons why the company carried out this testing.
Around 7 a.m. local time on May 26th, just a few minutes after employees arrived at work, the storage tank exploded, causing about 900,000 gallons (3.4 million liters) of corrosive white liquid to leak out. This white liquid is used to decompose wood materials into paper products; exposure to it can cause severe chemical burns to the human body.
According to investigations, around 2 a.m. of that day, a boiling equipment in the factory was shut down for maintenance. As a result, the storage tank no longer transferred white liquid to the boiling equipment, but white liquid continued to flow into the storage tank. At 6:20 a.m., the level of liquid in the storage tank approached full capacity. Less than an hour later, the storage tank exploded. The corrosive liquid flooded the factory courtyard, destroyed vehicles, and damaged part of a nearby building. It then flowed down to the lower floors of various workshops, where workers were holding a morning meeting at that time.
The accident resulted in the death of 11 people. Eight workers from the electrical maintenance workshop and one worker from the courtyard were killed. Two workers from the mechanical maintenance workshop died due to exposure to chemicals, and two survivors suffered severe chemical burns.
The investigation report indicates that although the factory called in the internal medical emergency response team via radio, it did not mention that a white liquid leakage accident had occurred. One of the emergency team members mistakenly believed that the water accumulation on the ground was just ordinary water. He waded into the area with accumulated white liquid in an attempt to rescue his colleague, resulting in severe chemical burns.
Earlier this week, the Washington State Department of Ecology issued 35 notices of environmental violations against Japan-based Dinawe Packaging. The state agency is responsible for regulating factory air and water emissions and overseeing companies to comply with environmental waste-related regulations.
The U.S. Chemical Safety and Hazard Investigation Staff says the investigation is still ongoing, and the complete conclusion will be included in the final investigation report.
