Flames licked the sky near the intersection of Interstate 295 and Route 130 in Westville, Gloucester County, for more than 3 1/2 hours before the fire was extinguished about 8 p.m., after emergency crews had smothered it with firefighting foam.
Officials had originally planned to let the material burn itself out, but decided to attack the blaze with foam.
At no point did the blaze appear to threaten other structures within the plant or the neighboring community, said John McCann, a Sunoco spokesman. No injuries were reported, and no evacuations were ordered.
McCann described the fire as an "extremely rare occurrence" for Sunoco. "I cannot tell you the last time we had a tank fire," he said.
The storage tank held more than 1 1/2 million gallons of xylene, a chemical found in crude oil and used as a gasoline supplement. The substance also is used to manufacture paints, adhesives and plastics.
McCann said he didn't know how much of the chemical had been consumed by the fire.
The burning chemical posed no threat to nearby residents, McCann said.
The sooty plume of smoke, which rose in the flight path of aircraft approaching Philadelphia International Airport, did not affect any incoming flights, an airport spokeswoman said.
The state Department of Environmental Protection said officials were headed to the scene to study the situation, according to spokeswoman Darlene Yuhas.
Exposure to xylene can cause headaches, lack of muscle coordination, dizziness and confusion. High doses can lead to unconsciousness and death, according to the Agency for Toxic Substances and Disease Registry.
The storms that produced the dangerous lightning strikes also drenched parts of the Philadelphia suburbs, causing some rush-hour flooding. In Radnor Township, more than 2.5 inches of rain fell in 90 minutes. Parts of South Jersey received heavy rain and hail, the National Weather Service reported.
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