Philadelphia Fire Department says it doesn't know source of gas-like odor that forced evacuations in Center City

UPDATED: 5:56 p.m.

PHILADELPHIA (KYW Newsradio) — The Philadelphia Fire Department is still mystified as to the source of natural gas-like odors that forced the evacuations of several buildings in Center City Monday morning.  

Numerous buildings were evacuated as a precaution shortly before noon, from The Bellevue and Rittenhouse Square to 1500 Market St.

A police officer told KYW Newsradio that the odor came from workers cleaning out tanks at the former site of the Philadelphia Energy Solutions refinery. That odor made its way to Center City on this windy day, and ended up in buildings' ventilation systems.

The Office of Emergency Management said in a tweet that the cause of the smell was "a release of mercaptan, a non-hazardous substance, during equipment cleaning." Since natural gas is odorless, mercaptan if often added to make the gas easier to detect.

However, the Philadelphia Fire Department said after an investigation, it could not confirm the release of mercaptan, and the source of the odor remains undetermined.

After an investigation at PES, the PFD Hazmat Task Force cannot confirm the initial report of a mercaptan release at the refinery. PES did clean equipment today, but the actual source of the smell remains undetermined.

— Philadelphia Fire (@PhillyFireDept) March 2, 2020

"Despite some initial reports that perhaps some cleaning work they were doing on a tank down there was the source of the odors, we actually went in and checked that vessel, our hazmat task force did, and did not find that to be the source of the odors," said Fire Commissioner Adam Thiel.

Thiel says as Center City buildings, including the Municipal Services Building, were evacuated because of the odor, PGW got 500 calls from Lawncrest to Southwest Philadelphia about the smell. 

He says the PES sensors did pick up some product in the air that seemed to cross the refinery property in the morning. But Thiel says a check with New Jersey DEP and other area agencies failed to solve the mystery.