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CSB to investigate storage tank explosion at Wisconsin cardboard mill that killed three

22 August 2008

The US Chemical Safety Board (CSB) will investigate the storage tank explosion that killed three workers and injured a fourth at the Packaging Corporation of America corrugated cardboard mill in Tomahawk, Wisconsin, on July 29.

Tank explosion at Wisconsin cardboard manufacturer
Tank explosion at Wisconsin cardboard manufacturer

The accident occurred as workers were performing welding to repair a flange fitting on top of an 80-foot-tall storage tank, which contained recycled water and paper fibre. The three workers were standing on a catwalk above the domed, cylindrical tank performing welding when an internal explosion ripped open the tank lid. All three workers died of traumatic injuries. A fourth, survived with minor injuries.

Large storage tanks at paper mills - especially those that are stagnant, poorly mixed, or have long material retention times - are at an elevated risk for the growth of anaerobic bacteria. Recycled process water, known as 'white water,' contains nutrients that promote growth of the organisms, producing hydrogen or other flammable gases that can be ignited by hot work or other sources of ignition.

The cause of the explosion remains to be determined; the CSB plans to conduct microbiological and chemical testing to understand what fuelled the blast.

“The CSB has noted that there have been previous tank explosions at paper mills during hot work and we will be closely examining the tragedy in Wisconsin to determine if there are similarities,'” said CSB Chairman John Bresland, who announced the investigation.

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