Police investigation reveals auxiliary power remained on during NIRS data center fire
Published: 10 Oct. 2025, 18:59
![A firefighter cools down burnt batteries at the National Information Resources Service (NIRS) in Daejeon on Sept. 27. [YONHAP]](https://koreajoongangdaily.joins.com/data/photo/2025/10/10/5400df02-452b-4fdd-ab94-f666cdddb4a1.jpg)
A firefighter cools down burnt batteries at the National Information Resources Service (NIRS) in Daejeon on Sept. 27. [YONHAP]
Police have obtained testimony suggesting that auxiliary power was not shut off during last month’s fire at the National Information Resources Service (NIRS) data center in Daejeon, which paralyzed hundreds of government systems. Investigators also found that the battery’s charge level at the time of the fire was about 80 percent.
The Daejeon Metropolitan Police Agency, which is investigating the fire at the NIRS Daejeon headquarters, said Friday that it has questioned 26 people so far and booked five on charges of negligent arson. The suspects include one NIRS employee and four contractors.
According to police, witnesses said that while the main power switch was turned off during maintenance work, the auxiliary power connected to the battery system was not. Investigators have requested a forensic analysis from the National Forensic Service to verify whether the auxiliary power was left on.
The fire broke out at 8:16 p.m. on Sept. 26 on the fifth floor of the NIRS building, where lithium-ion batteries were stored, burning 384 battery cells and multiple servers. The blaze caused major disruptions to 709 government information systems, including administrative databases. As of noon Friday, 217 systems amounting up to 30.6 percent had been restored, including 75 percent of the highest-priority, Level 1 systems.
Investigators said the data center’s power system supplied electricity to servers through two routes: one directly from the external power grid, and the other via an uninterruptible power supply (UPS) system using stored battery power in case of outage. However, the rack switch connecting the batteries to the UPS appears to have been left on during the fire.
![Officials move a burnt battery at the National Information Resources Service (NIRS) in Daejeon on Sept. 27. [YONHAP]](https://koreajoongangdaily.joins.com/data/photo/2025/10/10/8b35b20e-9161-4a38-9d8a-4a89c62dcac7.jpg)
Officials move a burnt battery at the National Information Resources Service (NIRS) in Daejeon on Sept. 27. [YONHAP]
Multiple on-site workers reportedly told police that the auxiliary power had not been cut. Logs recovered from the scene show the battery that first caught fire had a charge level of about 90 percent, which experts estimate to be around 80 percent after calibration.
According to major battery manufacturers’ safety manuals, lithium-ion batteries should be discharged to below 30 percent before being transported. “Experts say that the higher the battery charge, the greater the potential damage in the event of a fire,” a police official said.
The fire occurred during work to relocate lithium-ion UPS batteries from the fifth-floor data room to the basement by disconnecting power cables. Workers reportedly shut off the main power at 7:09 p.m., about an hour before the fire started.
![Officials work to restore the damaged system at the National Information Resources Service (NIRS) headquarters in Daejeon on Oct. 4, 12 days after a fire took down the major servers on Sept. 26. [JOONGANG ILBO]](https://koreajoongangdaily.joins.com/data/photo/2025/10/10/8291a135-f54e-4d31-a091-22733d6a9676.jpg)
Officials work to restore the damaged system at the National Information Resources Service (NIRS) headquarters in Daejeon on Oct. 4, 12 days after a fire took down the major servers on Sept. 26. [JOONGANG ILBO]
Police previously conducted search and seizure operations on Oct. 2 at four locations, including the NIRS and three partner companies, securing around nine boxes of materials, including project plans and battery log data. Investigators are analyzing the seized evidence, viewing the power shutdown procedure as a key factor in determining the cause of the fire.
“Given testimony that the auxiliary power was not turned off, we will use forensic analysis to verify the sequence of events,” a police official said. “Recovered batteries are undergoing disassembly testing, and identical models will be used in re-creation experiments to determine the cause of ignition.”
This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.
BY KIM BANG-HYUN [[email protected]]
with the Korea JoongAng Daily
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