The cause and origin of the fire of Friday's blast will be investigated by the Occupational Safety and Health Administration, the Bureau of Alcohol, Tobacco, Firearms and Explosives, the U.S. Chemical Safety and Hazard Investigation Board and the fire marshal's office, officials said.
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The blaze at the Philadelphia Energy Solutions Refining Complex, the East Coast's largest oil refinery, was extinguished Saturday afternoon, fire department and city officials said in a statement Sunday.
The gas valve that had been fueling the blaze had been shut off and the tank involved in the explosion had been isolated, officials said.
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The fire department's hazmat unit and the public health department are still monitoring air quality, which they said earlier they have been doing every two or three hours without finding any threat to public health.
The blasts and fire at the plant at about 4 a.m. Friday, which shook homes and sent a fireball aloft, occurred at a tank containing a mixture of butane and propane, authorities said.
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Daryl Lee was on his paper delivery route when he saw it.
"All of a sudden - boom - the ground shook. The flame went up. Parts were falling out of the sky," Lee said. "Like the sun landed on the ground, that's how bright it was. Then as it fell back down, you saw what looked like metal coming down. Like glitter, sparkles, raining down. That's when I realized this thing blew up."
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Five workers were treated for minor injuries.
Concerned residents can call the PES Community Information Hotline at 215-339-7300 for updates and the status of the refining complex. PES also set up a number for residents to report damage from the incident: 800-899-1844.
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The Associated Press contributed to this report.