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Explosion investigation
Published:  25 April, 2018

The 2017 explosion in Packaging Corporation of America’s paper mill could have been prevented, says CSB final report. SEE ANIMATION

A combination of process hazard analysis, effective safeguards, safer design and a clearly defined responsible person could have prevented the non-condensable gas system explosion that killed three and injured seven workers.

The explosion occurred on 8 February last year at the pulp and paper mill in DeRidder, Louisiana, around 400km southeast of Dallas.

The contract workers had been performing hot work above a tank that contained flammable materials at the time of the explosion, which occurred during the facility’s annual shutdown.

At the time of the incident, the workers had been welding on water piping above, and disconnected from, a 38,000-litre storage tank.

The tank contained around 3m of foul condensate liquid composed mostly of water. It also contained a floating layer of flammable hydrocarbons, in the form of residual turpentine and other sulphur-containing compounds. Under normal operations the atmosphere inside the foul condensate tank is not explosive.

The US Chemical Safety and Hazard Investigation Board found 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. However, 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. Although the presence of some air in the vapour space of the foul condensate tank is considered 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.

Prior to the explosion, a combustible gas detector had been used to test the flammable atmosphere outside of the foul condensate tank where the repairs would occur. However, as the operators were unaware of the dangerous mixture of air and turpentine that had accumulated inside the foul condensate tank, this area was not tested.

The CSB investigation has 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 114m away.

The CSB noted that process safety management regulations issued by the Occupational Safety and Health Administration did not apply to the mill’s non-condensable gas system, which is the process at the facility that included the foul condensate tank. It has pointed out that nevertheless good-practice guidance recommendations existed to voluntarily apply those kinds of rigorous safety management systems to the process, which were not followed by PCA.

The CSB has stated that the use of 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. 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 has issued safety guidance to the pulp and paper industry. It has also issued a recommendation to PCA to apply process safety management principles to non-condensable gas systems, even if not required by regulations.

The CSB has 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.

An animation showing the sequence of events is available to view here:

To download the final report click here.