Ambiguity about responsibility for foul condensate tank operations and a failure to conduct a proper process hazard analysis of the noncondensable gas system contributed to a pulp mill incident that killed three workers, says the U.S. Chemical Safety Board (CSB).
On Tuesday, CSB issued its final investigation report into the February 8, 2017, explosion at the DeRidder, La., pulp-and-paper mill owned by Packaging Corp. of America (PCA). In addition to the deaths of three contract workers were performing welding and grinding above a tank that contained flammable materials at the time of the incident, and seven others were injured.
On the day of the incident during the facility’s annual shutdown, contract workers were welding a water piping above and disconnected from a 100,000-gallon-capacity storage tank. The tank contained about 10’ of liquid foul condensate. The foul condensate was composed of mostly water, but it also contained a floating layer of flammable hydrocarbons in the form of residual turpentine and other sulfur-containing compounds. Under normal operations, the atmosphere inside the foul condensate tank would not be explosive.
The CSB found, however, that on the day of the incident, there was more flammable turpentine present on top of the water than expected. The foul condensate tank was designed so that residual turpentine would be skimmed off the top of the water and sent downstream to a turpentine-recovery system at regular intervals. But in the months leading up to the incident, confusion as to whom at the mill was responsible for foul condensate tank operations led to turpentine accumulating in the tank.
The CSB determined that hot-work activities likely ignited the contents of the foul condensate tank, which exploded and separated from its base, launching up and over a six-story structure before landing on process equipment approximately 375’ away.
According to the CSB, the explosion could have been prevented if PCA had:
- Conducted a process hazard analysis for the noncondensable gas system.
- Applied effective safeguards to prevent a noncondensable gas system explosion.
- Evaluated safer design options that could have eliminated the possibility of additional air entering the foul condensate tank.
- And established who at the mill was responsible for operation of the foul condensate tank.