The Pentagon was locked down and partially evacuated Thursday morning after a hazardous materials sensor triggered an alarm, prompting emergency response teams to sweep the building.

CNN, citing a source, said the sensor system detected the possible presence of anthrax. One source said the system was malfunctioning, resulting in a false alarm.

“Earlier this morning, Pentagon occupants were notified of a potential air quality issue, prompting immediate precautionary safety measures and evaluation,” Pentagon spokesman Sean Parnell said in a post on X. 

STATEMENT:

Earlier this morning, Pentagon occupants were notified of a potential air quality issue, prompting immediate precautionary safety measures and evaluation. Subsequent testing confirmed no hazard exists, and normal operations have resumed.

We express our sincere… https://t.co/QReD77PR4V

— Sean Parnell (@SeanParnellASW) June 11, 2026

After the alert, Parnell said the Pentagon executed standard protection protocols, including a shelter-in-place order for the affected area. “Response teams are in place and ready to support building occupants,” he added.

Fire and hazmat teams from Virginia responded to the incident, according to reports.

ACFD units, including our Hazardous Materials Team, are currently operating at the Pentagon in support of PFPA’s Hazmat Team during a hazardous materials incident. pic.twitter.com/7qzOzbwh8W

— Arlington Fire & EMS (@ArlingtonVaFD) June 11, 2026

At 1:31 p.m., Parnell said subsequent testing confirmed no hazard exists and that normal operations have resumed. 

“We express our sincere appreciation to the first responders for their swift actions to ensure the safety of all personnel,” Parnell added.