A company’s failure to realize that welding work was being done near flammable materials was behind a fatal explosion, according to the U.S. Chemical Safety Board (CSB), which has released its final investigation report into the February 8, 2017, blast at the Packaging Corporation of America’s (PCA’s) DeRidder, Louisiana, pulp and paper mill. The incident killed three contract workers who were performing welding and grinding, referred to as “hot work,” above a tank that contained flammable materials. Seven others were injured.

The explosion at PCA occurred during the facility’s annual shutdown. On the day of the incident, contract workers were welding on water piping above and disconnected from a 100,000-gallon-capacity storage tank. The tank contained about ten feet of liquid, called “foul condensate.” The foul condensate was composed of mostly water, but 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 is not explosive.

More turpentine than usual

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 who at the mill was responsible for foul condensate tank operations led to turpentine accumulating in the tank. And although some air in the vapor space of the foul condensate tank is normal, because of the non-routine conditions present during the annual shutdown, more air than usual found its way into the tank, resulting in an explosive atmosphere.

Workers tested outside the tank

Prior to initiation of the hot work, workers used a combustible gas detector to test for a flammable atmosphere outside of the foul condensate tank where the repairs would occur. But workers were unaware of the dangerous mixture of air and turpentine that had accumulated inside the foul condensate tank, and did not know the tank presented a serious hazard to the contractors who were about to conduct the necessary repairs.

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 feet away. It killed three people and injured seven others. All were contractors working around the foul condensate tank.

CSB Chairperson Vanessa Allen Sutherland said, “As seen in this incident, hot work conducted around tanks containing flammable materials can be catastrophic. That is why it is so important for companies to effectively identify, evaluate, and control potential hazards prior to initiation of hot work.”

An animation showing the sequence of events is available to view on the CSB website, www.CSB.gov, as well as its YouTube channel.

PSM not a factor

Process safety management (PSM) regulations issued by the Occupational Safety and Health Administration (OSHA) do not apply to the mill’s “non-condensable gas system,” which is the process at the facility that included the foul condensate tank. There are, however, good-practice guidance recommendations to voluntarily apply those kinds of rigorous safety management systems to the process. The CSB found that PCA did not do this. Using a more robust safety system approach could have helped PCA to identify, evaluate, and control the hazards present in the process, and likely could have prevented the explosion.

How it could have been prevented

In particular, the CSB found that the explosion could have been prevented if PCA had:

• Conducted a process hazard analysis for the non-condensable gas system.

• Applied effective safeguards to prevent a non-condesable 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.

In its final report, the CSB issued safety guidance to the pulp and paper industry and a recommendation to PCA to apply process safety management principles to non-condensable gas systems, even if not required by regulations. The CSB also reiterated a 2002 recommendation issued to OSHA to cover under their Process Safety Management standard atmospheric storage tanks that are interconnected to a covered process, such as the foul condensate tank.

CSB Chairperson Vanessa Allen Sutherland said, “Hot work incidents occur across all industries and cause far too many serious injuries and deaths. These events, like the explosion at PCA, often reveal weaknesses in a facility’s process safety management system. Companies must effectively identify, evaluate, and control hazards at their facilities so that future hot work incidents can be prevented.”

The CSB is an independent, non-regulatory federal agency whose mission is to drive chemical safety change through independent investigations to protect people and the environment. The agency’s board members are appointed by the President and confirmed by the Senate. CSB investigations look into all aspects of chemical incidents, including physical causes such as equipment failure as well as inadequacies in regulations, industry standards, and safety management systems. For more information, contact public@csb.gov.