The pipe fitting gave way around 4:00 a.m. ET (0800 GMT) on June 21, releasing more than 3,200 pounds of highly toxic chemical hydrofluoric acid (HF) into the atmosphere, the CSB said.
That led to three separate explosions that hurled pieces of the refinery across the nearby Schuylkill River and onto highways, causing a blaze that was visible for miles, and destroyed an alkylation unit that treats HF.
No one was killed in the explosion, and only five minor injuries were reported. However, Philadelphia Energy Solutions filed for bankruptcy a month later and shut down the 335,000 barrel-per day refinery, the largest on the U.S. East Coast.
