What happened

A corroded pipe elbow ruptured just after 4am in the hydrofluoric-acid alkylation unit, releasing hydrocarbons mixed with HF that formed a ground-hugging vapor cloud and ignited in three explosions minutes apart. Over 5,000 pounds of toxic hydrofluoric acid were released and a 38,000-pound vessel fragment landed across the Schuylkill River; property damage was estimated at $750 million. The refinery closed permanently soon after. This was an accidental industrial incident, not an attack.

When cited sources give different casualty, damage or spill figures for this event, they’re reported side by side above rather than merged into one number. See how confidence levels work.