4:00 a.m.: Flammable process fluid containing hydrofluoric acid leaks from the refinery’s alkylation unit, forming a ground-hugging vapor cloud.

4:02:06: The vapor cloud ignites, causing a large fire.

4:02:37: A control room operator empties most of the hydrofluoric acid in the alkylation unit into a safety storage drum.

4:15: An explosion occurs in the alkylation unit, followed by a second explosion four minutes later.

4:22: A third explosion occurs when a drum containing butylene, isobutane, and butane ruptures. The force of the explosion sends a 38,000-pound drum fragment across the Schuylkill, 2,100 feet away. Two other large fragments land 1,800 and 800 feet away, within the refinery grounds.

Philadelphia Energy Solutions refinery estimated that 3,271 pounds of hydrofluoric acid was released to the atmosphere. If contacted, hydrofluoric acid can cause destruction to deep tissue layers and bone. If inhaled, it can cause severe lung injury resulting in death.

Five workers experienced minor injuries during the incident, requiring first aid treatment. The U.S. Chemical Safety and Hazard Investigation Board says it is unaware of any health impacts from the hydrofluoric acid release either within or outside of the refinery.

4:00 a.m.: Flammable process fluid containing hydrofluoric acid leaks from the refinery’s alkylation unit, forming a ground-hugging vapor cloud.

4:02:06: The vapor cloud ignites, causing a large fire.

4:02:37: A control room operator empties most of the hydrofluoric acid in the alkylation unit into a safety storage drum.

4:15: An explosion occurs in the alkylation unit, followed by a second explosion four minutes later.

4:22: A third explosion occurs when a drum containing butylene, isobutane, and butane ruptures. The force of the explosion sends a 38,000-pound drum fragment across the Schuylkill, 2,100 feet away. Two other large fragments land 1,800 and 800 feet away, within the refinery grounds.

Philadelphia Energy Solutions refinery estimated that 3,271 pounds of hydrofluoric acid was released to the atmosphere. If contacted, hydrofluoric acid can cause destruction to deep tissue layers and bone. If inhaled, it can cause severe lung injury resulting in death.

Five workers experienced minor injuries during the incident, requiring first aid treatment. The U.S. Chemical Safety and Hazard Investigation Board says it is unaware of any health impacts from the hydrofluoric acid release either within or outside of the refinery.