What to Know There have been two fires in two weeks at the Philadelphia Energy Services refinery in South Philadelphia.

Neighbors around the refinery and some experts are expressing concerns about air quality and cancer risks.

After the latest fire, which happened early Friday, the refinery owner said they had not detected any unsafe inhalants in the air.

The South Philadelphia refinery that caught fire in a series of dramatic explosions Friday morning is the region's largest single air pollutant even when it's not burning, according to local environmental experts.

Those experts and nearby neighbors worry that smoke from the fire at Philadelphia Energy Solutions refinery could pose a threat, especially to people with respiratory disease.

"If it were me, what I would do is leave the area for as much of the day as possible," Peter DeCarlo, a professor at Drexel University and an air quality expert, said.

DeCarlo suggested that neighbors air out their homes once the fire was completely out.

Two air samples taken by the Philadelphia Health Department later Friday morning found that none of 61 chemical compounds tested were at unsafe levels, an official with the Philadelphia Office of Emergency Management said.

"In both samples, no chemical compounds were found to be above or even near the level set by the American Conference of Governmental and Industrial Hygienists as safe for workers who are exposed every day for a lifetime. Only two compounds were found to be above five parts per billion, acetone and ethanol,” said OEM deputy director Noëlle Foizen.

Still, Mayor Jim Kenney said that he is aware of community concerns regarding air quality, adding that there is "room for improvement both in the operation of the refinery ... and communication to residents."

He asked Managing Director Brian Abernathy and Fire Commissioner Adam Thiel to convene a group with PES leaderhip and its Community Advisory Panel to explore these issues.

Smoke continued to billow from the fire for hours after it erupted just after 4 a.m. Friday. It was heavy at times, and blew over much of South Philadelphia and Center City, as well as communities surrounding Philadelphia.

Part of a South Philadelphia refinery caught fire Friday morning, sending thick smoke into the air. Recent incidents at the refinery have sparked concerns about air quality.

Residents were asked to shelter inside about two hours into the fire response, but that shelter-in-place was lifted just after 7 a.m.

Philadelphia Energy Solutions, which processes approximately 335,000 barrels of crude oil per day, did not detect anything in the air that could be inhaled, according to city officials. PES said it will continue to monitor air quality.

"PES is following protocol to protect the environment, its employees, and the surrounding community to bring the incident to a safe conclusion, and minimize any impacts from the event," PES said in a statement.

The cause of the fire remains under investigation, according to a PES.

Despite the company's reassurances, DeCarlo said exposure to the smoke could exacerbate asthma or other respiratory issues and have long-term effects. DeCarlo said the smoke could contain PHAs, which have been linked to cancer.

The refinery, the largest on the East Coast, has been the focus of protesters who worry about its environmental impacts.

Just last week there was another fire at the refinery, and neighbors gathered outside to demand answers from the company. The protesters refer to the area surrounding the plant as "cancer alley."

"What chemicals were on fire? Which way was the wind blowing? Why was nobody notified?" South Philadelphia resident Shamar Pitts asked.

Among the concerns is how much carbon dioxide is pumped into the air through refineries.

A greenhouse gas, carbon dioxide absorbs heat and re-emits it into the atmosphere. This contributes to an overall warming effect when levels are higher than organic matter, such as plants and algae, is able to absorb, according to NASA.

Part of this carbon dioxide will be soaked up by the ocean, which causes its PH balance to change, according to the National Oceanic and Atmospheric Administration. As oceans become more acidic over time, marine life will be negatively affected.

David Masur, the executive director for environmental advocacy group PennEnvironment, said he hoped Friday's explosion would bring more attention to the role that fossil fuels play in the health of residents and the environment, as whole.

Masur lives in South Philly and was among those woken up by the blasts.

"This explosion embodied what we all know: fossil fuels as a source of energy are dirty and dangerous, and don't deliver for our communities," he said in a statement.