SEATTLE — Three years before a deadly tank rupture at a Longview pulp and paper mill, a fire lasting several days raised concerns that the owner had scaled back maintenance at the decades-old facility.

Crews battled the flames for three days as the fire burned through wood chips — pulp’s core ingredient — and spread from a conveyor belt to a barge, a dock and a maintenance building at the Nippon Dynawave Packaging plant in July 2023.

When the blaze subsided and investigators dug into the cause, employees pointed to years of “dissolved maintenance” on equipment, according to Cowlitz County fire records. Two employees told investigators upkeep of the conveyors declined “approximately 6-7 years ago and the employees have been trying to keep up on the maintenance,” the investigation report reads.

The rollers on Nippon’s conveyor belts were “from several eras in the past,” the employees said, according to the report. Nippon Dynawave relied on staff to “come and perform maintenance on their time off” for overtime pay, workers said. But the overtime work had been cut just weeks before the fire, they added.

Investigators ultimately considered it “probable” that the fire was “mechanical in nature” and that “the decrease in maintenance on the aging equipment” contributed to the blaze, according to the final report. Still, there wasn’t enough evidence to say for sure what caused the fire, which Cowlitz 2 Fire and Rescue ruled accidental.

The Nippon Dynawave Packaging mill is now at the center of multiple government investigations after a storage tank implosion last week killed 11 people, injured seven others and spilled hundreds of thousands of gallons of harmful chemicals into the surrounding area. Federal, state and local officials are still grappling with the aftermath and looking into what caused the failure.

Local media have pressed Nippon Dynawave’s top officer on the tank’s maintenance history at news conferences, but little has been made public about those practices. On Friday, after a reporter asked Nippon Dynawave Director of Support Services Brian Wood when the collapsed tank was last inspected, he replied, “I don’t have that information for you today.”

Wood said the company is cooperating with investigators and it would “be very premature to estimate” when a cause will be determined.

Nippon Dynawave did not respond to questions from The Seattle Times about the 2023 fire investigation or the report’s mentions of scaled-back maintenance.

When firefighters arrived at the plant in 2023, they spotted flames near a 40-foot-high conveyor tower. The conveyor belt, used to carry wood chips, was still running above fire crews. Fire officials twice urged employees to shut down the belt, according to the report.

The employees refused, citing company policy. Workers said at the time that shutting down the conveyor belt was prohibited “to prevent the belt from burning through,” according to records.

Officials were probably concerned about the firefighters’ safety near running equipment, said Michael Fitz, who owns a Seattle-based fire and explosion investigation firm. At the same time, it’s not uncommon for companies to run conveyors during a fire to get flammable material out of the way, added Fitz, who has 40 years of experience, including investigations into conveyor belt fires.

Fitz is not involved in the investigation into last week’s implosion, nor was he involved in the probe into the 2023 fire.

It isn’t clear from county fire records whether Nippon Dynawave eventually shut down the belt or if the running machine played a role in the fire’s spread. The investigation report noted that while the belt was running, the fire spread to two more places and across the entire conveyor.

It took crews three days to fully extinguish the flames. All told, fire officials estimated at least $1.5 million in property damage and $2 million in damage to the mill’s contents, according to records.

Investigators launched their probe while hot spots were still smoldering at the Nippon Dynawave property. As they researched the cause, a helicopter flew overhead, dropping water from a 2,500-pound bucket, according to fire records.

A 2023 fire at the Nippon Dynawave Packaging pulp and paper mill in Longview burned for days, requiring helicopter support to help extinguish the blaze. Source: Cowlitz 2 Fire & Rescue

At the time, Nippon Dynawave gave the department video of the initial sparks, photos and a timeline showing where employees were and what they did during the fire. Some of the pictures captured billowing clouds of smoke and orange flames in the sky above the plant.

Workers told the investigators that the same location had caught fire just a week earlier, but that smaller blaze was quickly contained.

In their final report, Cowlitz fire officials wrote that they couldn’t rule out an electrical failure or overheating of a structural element as possible causes. Burn patterns and video evidence suggested the blaze started at the conveyor belt.

The timing of the decline in maintenance described by employees would have coincided with Nippon Dynawave’s purchase of the mill from the previous owner, Weyerhaeuser. Neither the sale nor the ownership change is mentioned in the 2023 fire records.

Fitz said a change in ownership often comes with a change in practices.

In general, “when you talk about safety and planning, all of that starts at the top,” he said, adding that any “corporate philosophy” should prioritize the workers’ well-being and safe equipment.

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(Seattle Times staff reporter Shauna Sowersby contributed to this report.)

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