Philadelphia refinery blast released 5,000 pounds of hydrogen fluoride, federal investigators say

Fears of a hydrogen fluoride release during the April 2018 Husky Energy refinery explosion and fire prompted evacuations.

A view of the oil refinery where a fire was reported in Philadelphia on Friday, June 21, 2019. (Jessica Griffin / Philadelphia Inquirer)

PHILADELPHIA — Philadelphia dodged several potential catastrophes during a dramatic June 21 refinery blast, which released about 5,239 pounds of a deadly chemical and launched pieces of shrapnel as large as a truck hurtling across the 1,300-acre refinery complex, according to federal findings released Wednesday.

The disaster at the Philadelphia Energy Solutions complex began with the early morning failure of an elbow section of pipe that had corroded to half the thickness of a credit card, according to investigators for the U.S. Chemical Safety and Hazard Investigation Board (CSB). In a matter of minutes, the fire triggered three successive explosions, the largest of which blew a fuel tank into massive projectiles, including one weighing 19 tons that traveled 2,100 feet and landed on the opposite bank of the Schuylkill.

The failure of a section of pipe was similar to a 2012 accident at a Chevron refinery in Richmond, Calif., after which the CSB recommended that refinery operators inspect all components of the piping systems. That was not done at PES, said Kristen Kulinowski, the CSB’s interim executive.

The agency’s report is the first to confirm the release of toxic hydrogen fluoride, a material used as a catalyst in the alkylation unit that was destroyed in the blast.

“The board remains concerned that the next time there is a major explosion at a refinery that uses (hydrogen fluoride) for alkylation, workers and those living nearby will not be so lucky,” Kulinowski said. “By their nature, refineries are high hazard operations and it is imperative that they are run and managed with the most robust of safety management systems.”


The acid can destroy tissue and bone, and has caused fatalities with skin exposures to as little as 2.5% of body surface area, the CSB said. “If inhaled, (hydrogen fluoride) can cause severe lung injury and pulmonary edema — fluid in the lungs — which can result in death,” the report said.

Despite the release of hydrogen fluoride, called hydrofluoric acid in its liquid form, and a fireball that flung large chunks of steel through a complex where millions of barrels of crude oil and fuel were stored, there were no deaths. Only five refinery workers experienced minor injuries that required first aid treatment, CSB said.

“The CSB is unaware of any offsite or onsite health impacts from the hydrofluoric acid release,” the agency said.

Local officials in Superior last year ordered an evacuation of much of the city of 27,000 when an explosion and raging fire at a Husky Energy refinery threatened a storage tank containing 15,000 pounds of hydrogen fluoride. Nearly four hours into the evacuation, the News Tribune was first to question Husky and government officials about hydrogen fluoride. A Superior Fire Department official confirmed to the News Tribune that evacuations were based on the "worst-case scenario" — a rupture of the hydrogen fluoride tank that could have caused a toxic cloud of gas for miles downwind.

While no hydrogen fluoride was released during the Superior incident and the fire never reached the hydrogen fluoride — which was 150 feet away from the location of the explosion — shrapnel was flung 200 feet, the CSB said.

Thirty-six people sought medical attention, including 11 refinery and contract workers. Superior Mayor Jim Paine and Duluth Mayor Emily Larson called on Husky to switch away from hydrogen fluoride. But Husky Energy announced in April it plans to rebuild the refinery and continue to use hydrogen fluoride when it resumes operations in late 2020.

In a 2015 accident at a Torrance, Calif., refinery, the CSB discovered that a large piece of debris from an explosion narrowly missed hitting a tank containing tens of thousands of pounds of modified hydrofluoric acid, or MHF.

In the wake of the Torrance, Superior and Philadelphia incidents, the CSB and several U.S. Senators have called on the Environmental Protection Agency to review its hydrogen fluoride regulations.


The Chemical Safety Board has investigated about a dozen refinery incidents in the last 20 years, including those resulting in fatalities, serious injury, and property damage. The agency has no enforcement powers and can only make recommendations. Other agencies, including the Occupational Safety and Health Administration, are also investigating

The CSB’s 10-page “factual update” does not attempt to affix blame or fully explain the circumstances leading to the fire, which shut down the largest oil refinery on the East Coast. The report does not suggest whether the refinery’s long-standing financial problems or its maintenance practices contributed to the accident.

The refining company and its workforce appear to be the biggest casualty of the accident. Its owners announced the plant’s closure on June 26, throwing most of the 1,100 workers out of jobs, and filed for Chapter 11 bankruptcy protection in July. The refinery remains shut down as the U.S. Bankruptcy Court in Delaware determines if its creditors will take ownership, or the complex will be sold.

PES estimated that about 676,000 pounds of hydrocarbons — mostly propane, butane and butylene used in the alkylation processing unit — were released during the event, of which 608,000 pounds were combusted or burned up.

Thirty seconds after the fire started, a control room operator emptied most of the hydrogen fluoride in the alkylation unit into a “rapid deinventory drum,” a system the refinery’s previous owner, Sunoco Inc., had installed more than 10 years ago to reduce the chances of a catastrophic release of hydrogen fluoride in such an accident.

But a “low concentration” of hydrogen fluoride remained in some of the equipment that failed during the event, and PES estimated that 5,239 pounds was released. About 1,968 pounds of the released hydrogen fluoride was contained by water spray within the unit and was processed in the refinery wastewater treatment plant. But about 3,271 pounds was released to the atmosphere.

At the time of the fire, a shelter-in-place order was put in place for residents near the refinery, but no evacuation ordered. The Philadelphia Health Department measured an “elevated” level of hydrogen fluoride gas outside the South Philadelphia refinery during the accident, but the reading was dismissed as a “false positive.”

The disaster unfolded in a matter of minutes. CSB said the alkylation unit was operating normally, and then at 4:00:16 a.m., a sudden loss of containment in the piping system in the unit caused a combustible mixture of process fluid and hydrogen fluoride to release, forming a “ground-hugging vapor cloud.”


Less than two minutes later, the cloud ignited. About 30 seconds later, the control room operator emptied the hydrogen fluoride from the unit into the safety storage drum.

At 4:15 a.m., 13 minutes after the fire began, the first explosion occurred, followed by a second at 4:19 a.m. At 4:22, the third explosion occurred when a large drum containing butylene, isobutane and butane ruptured.

That explosion, captured by remote television cameras, sent three large fragments of the drum flying in different directions. A 38,000-pound piece traveled four-tenths of a mile and landed on opposite bank of the Schuylkill, near the refinery’s tank farm. Two other pieces, one weighing 23,000 pounds and another weighing 15,500 pounds, landed in the refinery.

The reason for the pipe failure remains a metallurgical mystery. One of the CSB’s remaining challenges appears to be trying to resolve why one elbow section of pipe in the doomed alkylation unit failed while others that had been inspected recently showed no sign of excessive corrosion.

The piping circuit in the PES alkylation unit that contained the ruptured elbow was installed in about 1973, and CSB said it appears to be original piping. The pipes are subject to regular ultrasonic thickness measurements at designated “condition monitoring locations” as part of a PES inspection program to monitor metal losses due to corrosion.

A pipe wall thinner than 0.18 inch is subject to replacement. But the most recent measurements did not indicate a thin pipe — PES recorded wall thicknesses ranging from .229 to .345 inch in previous tests.

The elbow joint that failed, however, was among several that were not subject to the measurements. CSB measured the pipe after the incident and said that at its thinnest point, it measured a mere 0.012 inch thick, or 7% of the minimum, or about half the thickness of a credit card.

The ruptured steel pipe elbow contained a much higher percentage of nickel and copper alloys than the adjacent joint, which measured well above the standard thickness. CSB noted that industry experts had singled out nickel, copper and chromium alloys as contributing to a higher corrosion rate in pipes that contain hydrogen fluoride.


CSB said the failure was reminiscent of a 2009 refinery explosion in Woods Cross, Utah, and a 2012 accident at the Chevron Richmond Refinery near San Francisco, both of which involved pipes that had corroded and burst.

The News Tribune contributed to this report.

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