PHILADELPHIA (AP) - Officials say a very small fire continues to burn at a Philadelphia refinery following explosions and a pre-dawn blaze that shook homes and caused some minor injuries.

  

Philadelphia Energy Solutions said Saturday that workers are trying to isolate the remaining line, but access is limited "due to the damage and instability of the remaining structure."

  

A company spokeswoman said officials haven't decided whether to let fire burn itself out "but that may occur before we can safely isolate it."

  

Authorities said the 4 a.m. Friday fire occurred 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. Philadelphia emergency management officials said air quality tests found no threat to public health.