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PES Explosion Released Highly Toxic Chemical Into Atmosphere, Investigators Say

The U.S. Chemical Safety Board just released the first update of its investigation into the June accident, which, in addition to releasing a potentially deadly chemical compound, flung 38,000 pounds of scrap across the Schuylkill River.


This story has been updated.

The massive explosions that occurred at a South Philly oil refinery complex this past June released more than 5,000 pounds of hydrofluoric acid, a potentially deadly chemical, according to federal investigators with the U.S. Chemical Safety Board.

On Wednesday, the agency released its first update into an investigation of the high-profile incident at Philadelphia Energy Solutions, which rocked the city and ultimately forced the closure of the facility, the largest and oldest oil refinery complex on the East Coast.

The CSB update provides what is might be the closest look yet at what occurred at the refinery complex in the early morning of June 21st. Here’s a preliminary video summarizing the incident.

And here’s a timeline of what happened, according to investigators:

  • 4:00:16 a.m.: A flammable process fluid containing hydrofluoric acid is released from PES’s unit for alkylation (a refining process used to create gasoline), forming a low-lying flammable vapor cloud
  • 4:02:06 a.m.: The vapor cloud ignites, starting a fire in the alkylation unit
  • 4:02:37 a.m.: A control room operator quickly moves the vast majority of the hydrofluoric acid and relocates it to a separate drum, a measure meant to help prevent mass disaster
  • 4:15 a.m.: The first explosion occurs in the alkylation unit
  • 4:19 a.m.: A second explosion occur in the unit
  • 4:22 a.m.: The third and largest explosion occurs when a drum containing primarily butylene, isobutane and butane “violently” ruptures. As a result, drum fragments weighing about 38,000 pounds, 23,000 pounds and 15,500 pounds fly across the Schuylkill river and the refinery complex. Investigators say this explosion “appears to be a secondary event caused by the fire.”

According to the investigation, PES estimates that about 676,000 pounds of hydrocarbons were released during the fire and explosions, of which 608,000 were combusted, as well as 5,239 pounds of hydrofluoric acid.

Hydrofluoric acid, which is used as a catalyst in the alkylation unit, is a highly toxic chemical compound that can penetrate and damage skin and tissue cells in the body. If inhaled, the chemical compound can harm lung tissue and cause swelling and fluid accumulation in the lungs. Skin contact can cause severe burns and skin ulcers. Even small splashes of the product on the skin — or swallowing a small amount — can be fatal. Breathing in hydrogen fluoride at high levels in combination with skin contact can lead to death from an irregular heartbeat or fluid buildup in the lungs, according to the Centers for Disease Control and Prevention.

Of the 5,239 pounds of hydrofluoric acid released during the incident, the CSB estimates that about 1,968 pounds were contained by water spray within the unit, while 3,271 pounds were not contained and were instead released to the atmosphere.

Five PES employees were treated for minor injuries at the time of the explosion. Neither the city nor the CSB have said they are aware of any offsite or onsite health impacts from the hydrofluoric acid release.

The organization has investigated three major incidents at refineries that use hydrogen fluoride for alkylation, a controversial practice, since 2015. The two others, which occurred in Wisconsin and California, did not result in a hydrogen fluoride release.

“That was not the case here in Philadelphia,” CSB interim executive director Kristen Kulinowski said. “Though the main tank holding HF was not breached, HF was a component of the process fluid released from the alkylation unit. We are lucky there were no serious injuries or fatalities.”

The Philadelphia Health Department had measured an “elevated” level of hydrogen fluoride outside the refinery during the incident, but the reading was labeled a “false positive,” according to a July state legislative committee testimony by Peter DeCarlo, a Drexel environmental engineering professor.

City spokesperson Deana Gamble said on Wednesday that the city’s air quality meter had not been properly calibrated at the time of the measurement, and that inspectors with the city’s Air Management Services had asked the Environmental Protection Agency and PES to confirm “zero readings” for hydrogen fluoride.

“Both confirmed that there was no HF present in the community, and the AMS inspectors took the improperly calibrated meter out of service,” Gamble said. “AMS subsequently confirmed with the manufacturer that the handheld device was in fact in need of recalibration and was thus unreliable when used immediately after the fire.”

“Ultimately, the city believes that the public was in no immediate danger from HF during the fire and response,” she added.

The pipe elbow that ruptured and effectively caused the explosions in June had been corroded to about half the thickness of a credit card, according to the CSB. The hydrofluoric acid (hydrogen fluoride that’s been mixed with water) in the process fluid had made the pipe susceptible to corrosion, which had not been monitored, investigators said.

PES filed for bankruptcy on July 22nd, roughly a month after the incident occurred. The CSB investigation is ongoing and will likely play a role in the future of the site. Kulinowski said the agency will examine the need for “more robust reviews of corrosion mechanisms,” as well as the use of hydrogen fluoride in the refining process, according to the organization.