The U.S. Chemical Safety Board (CSB) released a new animation detailing the events of the February 8, 2017, explosion at the Packaging Corporation of America’s DeRidder, Louisiana, Pulp and Paper Mill that killed three contract workers and injured seven others.
The explosion occurred during hot work activities during the facility’s annual shutdown.
Several months prior to the incident, water piping located above and connected to a 100,000-gallon capacity atmospheric storage tank had cracked and shifted. In preparation for repair work, the piping was isolated from the storage tank, which had about ten feet of liquid inside.
On the morning of the incident, a mill employee used a gas detector to check for a flammable atmosphere in and around the water piping and found none. But the nearby storage tank was not tested and posed a serious safety hazard.
The liquid in the tank normally consists of mainly water, but also residual amounts of sulfur compounds and turpentine. But on the day of the incident, there was more flammable turpentine present in the tank than expected due to confusion over a valve. Also, because of the non-routine conditions during the shutdown, the vapor space of the tank contained more air than usual, resulting in an explosive atmosphere.
The animation explains that the CSB was unable to determine an exact ignition source but it is likely that sparks or molten slag produced from the hot work landed on or near the tank, heating up the tank wall or otherwise igniting the contents inside. The tank exploded and separated from its base, launching up and over a six-story structure, and landing approximately 375-feet away.
The final report of the CSB investigation is currently under review by the Board members for adoption. Once it is finalized, it will be publicly released.