PHILADELPHIA (CBS) – Federal investigators will be in South Philadelphia Monday looking for the cause of Friday morning’s fire at Philadelphia Energy Solutions. A huge fireball lit up the sky around 4 a.m. Friday after a fire and explosions erupted inside one of the refinery’s butane tanks.

4 People Injured In Major Explosion, Fire At Oil Refinery In South Philadelphia, Officials Say

Four PES employees suffered minor injuries and people who live near the South Philadelphia facility were ordered to shelter in place until the air quality was determined to be safe.

The fire raged for more than 24 hours and was finally extinguished Saturday afternoon. Multiple tests conducted by the city’s Department of Public Health over the past several days determined the air quality to be normal and posed no threat to public health.

WATCH: Space Satellites Capture South Philadelphia Oil Refinery Explosion

But this fire and a smaller one at the same facility on June 10 are prompting city officials and neighbors alike to question the safety of the facility.

“It is scary, living close to something like that, knowing anybody, any one of us could have gotten hurt,” said Shaina Williams.

Philadelphia Councilwoman Calls For South Philadelphia Refinery To Be Shut Down 

Council Member At-Large Helen Gym released a statement Friday evening, which reads in part:

The PES refinery should be shut down until a full and independent investigation by city, state and federal officials have determined the cause of the explosions and the fires, assessed and improved safety protocols, and communicated clearly to residents and workers of these findings. Their health and safety must be assured, and PES should not be in charge of that determination.”

In addition to the Philadelphia Fire Marshal’s Office, investigators from OSHA, the ATF and the U.S. Chemical Safety and Hazard Investigation Board will be on site collaborating on the fire probe.

Members of the public with questions can call the PES Community Information Hotline at ‪‪215-339-7300.