What to Know Philadelphia firefighters identified the source of a mysterious odor that was smelled by residents throughout the city on Thursday.

The odor was released while workers at the South Philly refinery were cleaning and disassembling pipe.

The incident was placed under control. Officials said they conducted air monitoring and didn't detect any dangerous substances.

Philadelphia firefighters identified the source of a mysterious odor smelled by residents throughout the city on Thursday.

The Fire Department said the smell came from the Philadelphia Energy Solutions refinery on the 3000 block of Pennrose Avenue. Workers at the refinery were cleaning and disassembling pipe when an odor was released, a spokesperson tweeted.

"The fire department's Hazmat Task Force conducted air monitoring and did not detect hydrogen fluoride or other potentially volatile substances," the spokesperson wrote. "The release has stopped and the incident has been placed under control."

The response came after firefighters received numerous calls reporting the odor. The reports occurred during a southwest wind of 13 mph in the area.

"This wind speed and direction would be favorable for bringing in the smell to a good chunk of Philadelphia, including Center City," NBC10 meteorologist Steve Sosna said.

Around the same time crews investigated the odor in Philadelphia, emergency crews were also called to a gas leak about 40 miles away at the Texas Eastern Pipeline on Lower York Road in New Hope, Bucks County. The pipeline was shut off and the incident was placed under control.

The South Philly refinery, the largest on the East Coast, closed over the summer following a series of massive explosions that rattled parts of the region.