PHILADELPHIA (CBS) – Philadelphia Energy Solutions announced Wednesday they will be shutting down its South Philadelphia refinery within the next month after last week’s massive explosion and fire. PES says the fire at the refinery complex has made it impossible for them to continue operations.

“We are grateful that the fire resulted in only a few minor injuries,” PES CEO Mark Smith said in a statement Wednesday. “I want to thank our employees for their hard work and dedication and to thank the Philadelphia community for their support. We are committed to an orderly process to safely wind down our operations.”

Smith went on to say the company will position the refinery for a sale and restart.

Mayor Jim Kenney was the first to confirm the refinery’s intent to permanently close. The closure will impact more than 1,000 workers, Kenney said.

“I’m extremely disappointed for the more than one thousand workers who will be immediately impacted by this closure, as well as other businesses that are dependent on the refinery operations,” Kenney said in a statement Wednesday. “The City is committed to supporting them during this difficult time in any way possible. We will immediately convene a group of City and quasi-governmental organizations to discuss the economic and employment impacts, and what the City is able to do in response. We are also retooling the plans of the working group led by the City’s Managing Director and Fire Commissioner to focus efforts on determining the future of the refinery, assisting PES to transition the site safely, communicating with local residents, and supporting the employees impacted PES’ decision.”

Sen. Pat Toomey, R-Pa., said in a statement he hopes a viable option comes forward to save the refinery.

“This morning, my office received confirmation from Philadelphia Energy Solutions that it intends to cease operations. My thoughts and sympathies are with the hardworking employees who are losing their jobs,” Toomey said. “In the coming weeks, I hope a viable option will come to the forefront to stave off this closure. My office intends to remain engaged with PES workers and management.”

PES, which stood on the banks of the Schuylkill River for generations, is the largest and oldest refinery on the East Coast. Shutting it down would not only cost hundreds of jobs but could send gas prices soaring.

“I was stunned, the way I found out, I can’t really talk about it but I was stunned,” employee Wayne Flood said.

The news of PES’ closure comes on the heels of an investigation launched Monday. The city’s fire marshal’s office joined federal investigators from OSHA, the ATF and the U.S. Chemical Safety Board to look into the cause of Friday’s fire and explosions.

Officials say the investigation into the explosion and fire could take months or even years given the instability of the structures that need to be examined.

“We still have a pretty large, operational footprint down there in the fire department, our hazmat task force is 24-7, 365,” Philadelphia Fire Department Commissioner Adam Thiel said.

Around 4 a.m. Friday, cellphone video captured a huge fireball exploding into the sky above the refinery. PES later confirmed the fire started in a unit used to create a component for high octane gas. It was finally extinguished Saturday afternoon after raging for more than 24 hours.

In a news conference Tuesday, Kenney addressed air quality concerns in the aftermath of the fire.

“Philadelphia Fire Department hazmat unit and the city’s Department of Public Health continues to monitor the air quality around the refinery. There are no findings that would suggest a threat to public health as a result of the fire,” Kenney said.

Despite repeated assurances of the air quality from city and company officials, protesters showed up outside the PES refinery Tuesday, demanding accountability after two fires there in the past few weeks. They also called for the refinery to be shut down for health and safety reasons.

CBS3 is awaiting a response from the union representative of the workers that lost their job.

CBS3’s Trang Do and Joe Holden contributed to this report.