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US Chemical Safety Board releases final report into 2019 Philadelphia Energy Solutions refinery explosion

12 October 2022

On October 11, the US Chemical Safety and Hazard Investigation Board (CSB) released its final investigative report into the significant fire and explosions at the Philadelphia Energy Solutions (PES) refinery in Philadelphia, Pennsylvania that occurred in June 2019.

Image: CSB
Image: CSB

The incident occurred when a corroded pipe elbow ruptured, releasing process fluid into the refinery’s hydrofluoric acid (HF) alkylation unit. During the incident, over 5,000 pounds of highly toxic hydrofluoric acid (HF) were released, a 38,000-pound vessel fragment launched off-site and landed on the other side of the Schuylkill River, and an estimated property damage loss of $750 million resulted.

CSB Interim Executive Authority Steve Owens said: “This is one of the largest refinery disasters worldwide in decades in terms of cost.  the local community in Philadelphia fortunately was not seriously harmed, but given the refinery’s location, it could have been much worse. This incident should be a wake-up call to industry to prevent a similar event from occurring in the future.”

The CSB’s investigation determined that over 117,000 people reside within a mile of the PES Refinery, according to US Census data.

The CSB’s investigation identified several safety issues which contributed to the incident.

- Mechanical integrity: The CSB determined that the pipe elbow that failed had corroded faster than other piping in the HF alkylation unit. That is because the steel pipe elbow contained a higher content of nickel and copper than other piping in the unit.

- Verifying safety of equipment after changes to good practice guidance: When the pipe elbow was initially installed in 1973, the standard set by American Society for Testing and Materials (ASTM) for carbon steel piping did not specify limits on nickel or copper content. Over the next decades that standard changed, and by 1995, the ASTM standard had been revised enough that the pipe elbow no longer met ASTM’s requirements due to the elbow’s high levels of nickel and copper.

CSB Supervisory Investigator Lauren Grim said: “A comprehensive evaluation of unit piping never occurred despite regulations from both the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) requiring companies to determine that their equipment is safe to operate after industry standards are updated. To prevent catastrophic incidents companies and industry trade groups must ensure process safety when new knowledge on hazards is published.”

Remotely operated emergency isolation valves

The CSB found that there were no remotely operated emergency isolation valves installed in the HF alkylation unit to isolate nearby hydrocarbon sources that could then flow through the failed elbow. Although these valves are not explicitly required by the current American Petroleum Institute (API) standard on Safe Operation of Hydrofluoric Acid Alkylation Units, if PES had installed such valves, the release from the pipe elbow could have been minimised and the subsequent explosions could have been prevented. As a result, the CSB is recommending to API to update its standard on Safe Operation of Hydrofluoric Acid Alkylation Units to require installation of remotely operated emergency isolation valves on the inlets and outlets of all hydrofluoric acid containing vessels, and any hydrocarbon containing vessels meeting defined threshold quantities.

Image: CSB
Image: CSB

Safeguard reliability in HF alkylation units

On the day of the incident, pumps designed to spray large volumes of water to suppress an HF release failed to activate early in the incident as the elements to remotely operate the pumps were damaged by the fire and explosions. Forty minutes elapsed from the time the release began before a worker was able to manually turn on a water pump. In the meantime, highly toxic HF escaped from equipment and vapourised into the air. As a result, the CSB is recommending to API to update its standard on Safe Operation of Hydrofluoric Acid Alkylation Units to require that critical safeguards and associated control system components be protected from fire and explosion hazards, including radiant heat and flying projectiles.

Inherently safer design

Of the 155 US petroleum refineries currently in operation, 46 operate HF alkylation units. Hydrofluoric acid is highly toxic and is one of the eight most hazardous chemicals regulated by EPA’s Risk Management Program (RMP). Alternative alkylation technologies have been developed, such as a solid acid catalyst and new ionic liquid acid catalyst alkylation technology. Replacing highly toxic chemicals with less hazardous chemicals is an “inherently safer design” approach. Additionally, some refinery alkylation units use sulfuric acid as a catalyst instead of HF. Although sulfuric acid is highly corrosive and can cause skin burns upon contact, it remains a liquid upon release and does not present the same risk to surrounding communities as HF, which vapourises upon release and has the potential to travel offsite.

The CSB’s investigation found that there is no federal regulatory requirement for refineries to analyse inherently safer design strategies to reduce the risk of serious accidental releases. Technologies are being developed that could be safer alternatives to HF alkylation, and refiners should periodically evaluate these available alkylation technologies. Therefore, the CSB is recommending that EPA:

- Require petroleum refineries to conduct a safer technology and alternatives analysis (STAA) as part of their Process Hazard Analysis under EPA’s RMP rule, and evaluate the practicability of any inherently safer technology; and

- Initiate prioritisation under the Toxic Substances Control Act (TSCA) to evaluate whether hydrofluoric acid is a high priority substance for risk evaluation, and if it is, conduct a TSCA risk evaluation of HF and implement any identified risk mitigation requirements.

Board Member Sylvia Johnson said: “The CSB wants to make sure that regulators are requiring companies to explore, determine and utilise the safest technology available. Understanding and mitigating the risk of using highly toxic chemicals such as HF is good for communities, workers, and industry.”

Read the CSB’s final investigation report here:

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