Workers tried to isolate the remaining line feeding the fire, but access is limited "due to the damage and instability of the remaining structure," Philadelphia Energy Solutions said. Officials haven't decided whether to let fire burn itself out, "but that may occur before we can safely isolate it," a spokeswoman said.
"Managing the small existing fire in this manner is safest for the environment, (company) employees, and the surrounding community to bring the incident to a safe conclusion," the company said in a statement.
The blaze at the Philadelphia Energy Solutions Refining Complex broke out around 4 a.m. Friday at a tank containing a mixture of butane and propane. Five workers were treated for minor injuries, and nearby residents were asked to stay inside. The cause remained unclear.
The Philadelphia Fire Department has been conducting air monitoring every two or three hours, focusing on the perimeter of the refinery and surrounding neighborhoods, the department said.