MCARTHUR, Ohio — For weeks before the explosion of toxic gas that forced a Vinton County community to evacuate, the warning signs were there. The temperature inside a storage tank full of explosive-laden acid was climbing. Alarms were going off. And someone kept turning them off.
On the morning of June 11, 2025, nearly two tons of toxic nitrogen oxide gas poured out of Austin Powder Company’s Red Diamond facility in McArthur. The cloud sent the residents of Zaleski running from their homes. The FAA shut down the airspace for 30 miles in every direction. More than a dozen fire departments, HAZMAT teams, and state agencies flooded into Vinton County. The evacuation lasted more than eight hours.
Nobody was physically hurt. But the December results of a federal investigation revealed that what happened that morning wasn’t an accident. It was the end of a weeks-long chain of decisions — and non-decisions — that federal regulators say turned a manageable situation into a near catastrophe.
The slow-motion disaster
It started April 29, when a critical piece of equipment in the plant’s acid recovery system broke down. The column used to destroy explosive material from the facility’s waste acid stream suffered catastrophic internal damage. Replacement parts were weeks away.
The entire system shut down. But the tank that stored the explosive-containing waste acid — a vessel called TA-520 — kept running. With no way to process what was inside it, the contents just sat there. Stagnant. And accumulating.
Federal regulations require that when something like this happens — a major change to how a process operates — a formal safety review has to be completed before work continues. It’s called a Management of Change procedure. At Austin Powder, nobody did one.
Management knew the acid recovery system was down. They knew what it meant for the tank. And they kept going.
They ran production anyway
A month later, with explosive-grade material already loaded in the manufacturing line, facility management made a call: run a brief production campaign to use up the stockpile rather than dispose of it.
There was still no working acid recovery system. There were still no temporary safety procedures for the tank. No safety review was completed. They ran the production anyway — on May 29 and 30 — pumping more explosive-containing waste acid into a tank that already couldn’t be processed.
After the run was finished, the tank sat. The explosive material settled toward the bottom. And the temperature started to climb.
The alarms nobody listened to
The tank has a cooling system and a temperature alarm. Normal operating temperature is below 50 degrees Fahrenheit. By June 4, the cooling system was off and the temperature was rising. By June 10 — just 24 hours before the release — the tank had already exceeded 80 degrees. On the morning of June 11 it surpassed 150 degrees, the maximum the gauge could read. The actual temperature was likely higher.
The alarms were going off. Investigators found they had been silenced — acknowledged and switched off — while the underlying problem continued to build.
And on the morning of June 11, the control room where operators monitored the tank was closed. The floor was being resurfaced. Workers had been moved to a nearby room where they couldn’t see the tank’s camera feeds or continuously monitor its readings.
At 5:00 a.m., workers smelled something acidic. At 6:00 a.m. they found a leaking plug and replaced it. But by 6:40 a.m., toxic gas was already venting visibly from the facility — and nobody noticed.
By 7:54 a.m. an emergency pressure relief valve was cycling open and shut every 30 seconds. By 8:19 a.m. it was open and staying open. The plant alarm didn’t sound until 8:24 a.m. Emergency services weren’t called until 8:30 a.m.
The visible release didn’t stop until 11:25 a.m. By then, Zaleski had been evacuated. The airspace had been locked down. And an estimated 3,945 pounds of nitrogen oxide had been released into the sky above Vinton County.
What the government found
OSHA’s Columbus Area Office cited Austin Powder for seven serious violations totaling more than $101,000. The citations painted a picture of a facility that had the safety rules written down — and simply didn’t follow them.
The company’s own shutdown procedures required the tank to be emptied during a prolonged shutdown. It wasn’t. Federal regulations required the plant to update its process hazard analysis every five years. The last one covering that tank was done in 2017, and never updated. The company was required to formally document the chemistry of what was inside the tank. It wasn’t documented. The cooling water safeguards were never analyzed. And when the control room was closed for floor work on a day the tank was running hot, nobody filed a safety review for that either.
OSHA called the release “catastrophic” in its inspection narrative — language that triggers the agency’s most serious enforcement track.
After negotiations, Austin Powder settled the case in December 2025. The penalty was cut in half to $50,835, to be paid in installments through October 2027. The company agreed to bring in an outside consultant to audit the entire facility and provide mandatory safety training for plant staff. The settlement agreement includes standard language stating Austin Powder does not admit wrongdoing.
The U.S. Chemical Safety and Hazard Investigation Board’s investigation remains open. Investigators are still testing materials from inside the tank, analyzing how far the toxic cloud spread, and evaluating whether the facility’s safety systems were ever adequate for what was being stored inside them.