Multiple floors of the Pentagon were locked down for several hours on Thursday and hazmat crews were deployed due to what was apparently a false alarm. 

Pentagon spokesman Sean Parnell issued a statement that Pentagon occupants were "notified of a potential air quality issue, prompting immediate precautionary safety measures and evaluation." He added that subsequent testing confirmed no hazard existed, resulting in resuming normal operations.

The Arlington County Fire Department said Thursday morning in a social media post that emergency units, including its hazardous materials team, were "operating at the Pentagon in support of PFPA's Hazmat Team during a hazardous materials incident."

Initial reports later indicated that a false alarm triggered the hazmat response, according to multiple sources familiar with the situation.  

Employees had been waiting for an all-clear as hazmat teams worked to confirm the cause.  

Parnell had said a shelter-in-place was in place for affected areas. The Pentagon's sophisticated systems had "detected an air quality issue necessitating precautionary measures until we determine its significance," he said.

Two sources confirmed that some floors were evacuated while others were told to shelter in place. 

The Pentagon Force Protection Agency put out an email to Pentagon personnel shortly before 11 a.m. ET to shelter in place, specifically in corridors 4,5,6 and 7 from floors 2-5. All staff were told to comply with the directive. Staff were told to move in person meetings to virtual meetings.