Microbial Gas May Have Led To Accident At Paper Mill

Anaerobic microbes may have been responsible for generating explosive gas that led to an accident that killed three welders and injured a fourth worker at the Packaging Corporation of America plant in Tomahawk, Wisc. That is a preliminary observation of the Chemical Safety & Hazard Investigation Board (CSB) as it began its investigation of the July 29 accident at the corrugated cardboard mill.

The tragedy occurred as welders repaired a flange fitting at the top of an 80-foot-tall storage tank that held recycled water and paper fiber. Three workers who were standing on a catwalk above the domed, cylindrical tank were killed when an internal explosion ripped open the tank lid. CSB investigators are examining whether the tank’s contents—stagnant water and organic material—could have promoted the growth of anaerobic bacteria within the tank. The bacteria could have produced hydrogen or other flammable gases that may have been ignited by the welders as they repaired the tank’s top flange.

The investigation is just beginning, CSB stresses, but CSB Chairman John Bresland notes similar accidents have occurred at other paper mills during “hot work.” The investigation will take about a year, he adds.