(Reuters) - Most of a highly toxic chemical stored at a fire-damaged Philadelphia oil refinery has been rendered inert, clearing the way for closer inspections of the site following a June blaze that led to the plant’s closure, officials said on Friday.

FILE PHOTO: The Philadelphia Energy Solutions oil refinery is shown following a recent fire that caused significant damage to the complex, in Philadelphia, Pennsylvania, U.S., June 26, 2019. REUTERS/Laila Kearney

About 340,000 pounds of hydrofluoric acid (HF) stored at Philadelphia Energy Solutions’ refinery was chemically neutralized, Philadelphia Fire Commissioner Adam Thiel said in a briefing. HF can burn the skin and form a potentially deadly fog at room temperature.

The process “substantially reduces the risk to the community,” Thiel said, noting some HF acid still remained at the site. Initial phases of the fire probes, including data gathering, have largely been completed, Thiel said.

HF is used by more than one-third of U.S. refineries in the alkylation process to make high-octane gasoline. Labor unions and environmentalists have urged that it be replaced, particularly in densely populated areas.

PES’s alkylation unit was destroyed in a fire and series of blasts on June 21 just minutes after the chemical was dumped into a safety vessel. The HF in that vessel has been neutralized, Thiel said.

Removing the HF will allow investigators, including the U.S. Chemical Safety and Hazard Investigation Board, to physically examine damaged areas of the refinery.

Since the fire, PES has closed the refinery complex, which was the largest and oldest on the East Coast, and filed for Chapter 11 bankruptcy protection.

Most of the roughly 1,100 PES workers have been laid off without health benefits, including 640 union employees.

PES on Thursday asked the bankruptcy judge to hire investigations and crisis management attorneys to advise the company on the seven federal, state and local investigations into the cause of the June blasts, court documents show.

The refiner has agreed to retain about 80 union employees as a caretaker group until the last of the HF is neutralized. Afterward, the number of workers will be reduced, according to an agreement reached last week, which is subject to bankruptcy court approval.

The last step in clearing the remaining HF from the plant is expected to begin in mid-November, said Eric Eckenrode of HF alkylation decontamination experts EnvTech, which has been working on the PES project alongside union employees.

“They are all helping us to move this along knowing that once this is complete, and we finish with the unit, then they’re going to be let go themselves,” Eckenrode said.