Receiver tank exploded at Verso paper mill after water leak fix - KMSP-TV

The state fire marshal announced Monday it has concluded its investigation into the Verso Paper Mill fire in Sartell, saying smoke and flames broke out above an air compressor before a receiver tank in the compressor room exploded.

According to the 27-page report, employees saw the fire at the east end of the plant after hearing a hissing sound. They notified the on-site fire brigade and were in the process of evacuating the staff of about 100 when a receiver tank on the north side of the compressor room exploded, killing one and injuring five others.

The investigation found a severe drop in cooling water flowing to the operating compressors led the compressor to overheat, ultimately leading to the explosion and fire on Memorial Day after oil vapor in the receiver tank ignited.

Multiple fire departments and aerial firefighting vehicles battled the resulting fire for days. The sprinkler system was compromised during the explosion, and the extensive structural damage is estimated at a $50 million loss.

New details in the fire marshal's paint a clearer picture of how the day began. A resident near the mill called 911 at 5:20 a.m. to report loud banging noises coming from the area. A security officer at the plant confirmed that he also heard loud popping sounds coming from the North Power Plant on the mill grounds.

The operator told the security officer that a water leak had sprung in a steam valve that morning, but there was no danger. Soon afterward, an officer with the Sartell Police Department arrived to investigate the 911 call. The security officer relayed the message from the operator and said the public was not at risk.

Investigators say a leaking water valve was also found beneath paper machine No. 3 that morning, and mill water was shut off in the pump house to allow for repair.

The plant was scheduled to shut down at 10:40 a.m. for repairs. The explosion happened at about 11 a.m. as employees were bringing the plant back online.

About two years ago, Verso received a grant to convert its compressors from air-cooling to water-cooling. Officials say several outside vendors were involved in the installation process. Within the past six months, the fourth compressor was swapped with a rebuilt air compressor, but it had documented issues with leaking oil, oil consumption, and vibration. There are no vibration alarms for the compressors.

Verso had attempted to fix the compressor by moving it place of the first compressor and changing the filter. The compressor that had been moved was taken out and used as a spare after that switch. Both compressors had been installed in 1981.

The mill was built in 1905 and has several additions, varying in height from one to six stories.

Earlier this month, Verso announced that the damage to mill is too extensive to warrant repair in light of a languishing paper market. State lawmakers have vowed to try to bring a new business to the site.