NASHVILLE, Tenn. (WKRN) — The Nashville International Airport (BNA) was evacuated following an incident inside one of the concourses that left many with breathing problems Sunday afternoon.

The airport’s Concourse C was evacuated shortly before 2:45 p.m. because of “the presence of a noxious odor,” BNA said in a statement posted to Twitter.

At the time, the Nashville Fire Department told Nexstar’s WKRN that personnel were responding to Concourse C due to “something airborne causing breathing problems.”

In photos shared with WKRN, multiple emergency units were seen on the tarmak outside the concourse. Fire crews were quick to walk through the airport while wearing oxygen tanks and masks.

An emergency responder was also seen checking a garbage can near a wall that appeared to be covered in an orange substance. It’s not clear if that substance was related to the incident.

According to BNA, the fire department “conducted air quality testing and determined there were no air contaminants.”

Sunday night, the airport confirmed crews also took chemical samples from the area, which detected the substance butoxyethyl acetate, a solvent commonly used in lacquers, varnishes, enamels and resins. Officials haven’t said why the solvent was in the concourse.

“It was a strong odor,” Kyler Robinson, an airport employee, told WKRN, saying it seemed similar to a pepper spray.

As of 4:35 p.m., BNA said Concourse C has reopened, but officials say they will continue to monitor the situation. A ground stop was issued for the airport by the FAA but as of 4:50 p.m., that ground stop had been lifted and flights were resuming.

Roughly 150 flights in and out of Nashville International were delayed Sunday, according to flight tracking site FlightAware, but it’s unclear how many were impacted by the ground stop.

Travelers are encouraged to check with the airlines about the flight status for arrivals and departures.

There is still no word on the cause of the incident.