by Dennis Dalman
Oil vapor from an overheated air compressor is what caused the May 28 explosion at the Verso paper mill in Sartell, according to an investigator with the State Fire Marshal Division of the Department of Public Safety.
The long-awaited 27-page report was released Monday.
One man died in the catastrophe, which caused an estimated $50 million in damage.
Investigator John Steinbach, author of the report, concluded a severely limited flow of cooling water contributed to the overheating of the air compressor. Flammable oil vapors then built up in a connected air-receiver tank, which then exploded at 11:17 a.m. that day. Steinbach said the air compressor should have shut itself down, but it didn’t either because of a faulty automatic shut-down mechanism and/or because of in-house maintenance issues.
Steinbach’s report attributes no blame to anyone for the disaster, which killed one employee and injured four others. According to the report, several witnesses said Jon Maus, the employee who died, was standing at the entrance of the air-compressor room by another employee. Maus was carrying a fire extinguisher. Another employee in the warehouse yelled to Maus not to use the extinguisher because of the uncertainty of chemicals. Maus and the other employee had just turned to walk back into the warehouse when the explosion occurred. When the air-receiver tank exploded, the tank was ruptured, and the force blasted down the concrete walls of the compressor room and then ignited many giant paper rolls in the southwest part of the warehouse.
Steinbach’s report is the result of many meticulous on-site inspections, as well as many interviews with plant employees and others involved with the post-explosion clean-up.
All of the paper-mill processes were recorded via computer records. An analysis of those records by Steinbach clearly showed a water-flow problem that became increasingly worse an hour or so before the explosion.
Early on the morning of May 28, at about 5 a.m., employees noticed a steam-pipe leak under one of the paper-making machines. The water flow was shut down while employees fixed the leak problem, which took about 11 minutes.
Verso’s water supply was provided mainly through treated water from the river, but it also had its own well and was connected to city water. During the repair, operations in the plant ceased, and there was a switch from the river-water supply to the well-city water supply.
At about that same time, 5:20 a.m., some loud banging sounds could be heard in the plant — so loud a nearby resident called 911 to report the sounds. A security guard also heard the sounds and investigated. A police officer arrived at the scene. A power-plant operator told the officer and the security guard there had been a problem with a leaking steam valve, which had caused the noises, but there was no danger.
Throughout the morning, water pressure to cool the plant’s five air compressors continued to drop — from 215 gallons early in the morning to 78 gallons by 7 a.m. After 10:05 a.m., the water pressure dropped to 19 gallons per minute to as low as three gallons per minute, Steinbach noted.
During that time, two of the plant’s five air compressors shut down automatically, as they were supposed to do, because of overheating. Workers then started up two stand-by compressors. Compressor number 3 (the one that blew up later) continued to operate.
The normal operating temperature of the air-compressor oil is 150 degrees. That oil reached a temperature of as high as 484 degrees just before the explosion, according to the computer-monitored data.
Due to the repair of the steam-water leak, the plant had been shut down most of the morning. As workers began to start up the plant to resume production, at about 11 a.m., the problems began. Cooling-water pressure fell, air compressor number 3 began to overheat, oil fumes caught on fire and then exploded in the air-receiver tank.
Just minutes before the disaster, at least four employees, including Maus, noticed smoke and an orange glow coming from the compressor room. An in-house fire brigade hurried to the scene, but it was too late to do anything about the problem.
The report does not explain what might have caused the water pressure to fall so low in the hour before the explosion.
At the time, there were 100 people working in the plant, less than half of the plant’s full contingent of 259 employees. The Memorial Day holiday, May 28, was the reason for a reduced work force.
Another report about the disaster is being prepared by the Occupational Health and Safety Administration.