A false alarm at the Pentagon following an air quality warning briefly triggered a partial shelter-in-place order at the US military's headquarters, as first responders worked to rule out exposure to hazardous materials, officials say.

The lockdown applied to several corridors of the five-sided building in Arlington, Virginia.

Employees were told to stay put while tests were carried out to determine whether a faulty sensor was to blame.

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

Many employees outside the areas of concern were told to leave the building as a precaution, officials said.

"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," chief Pentagon spokesman Sean Parnell said.

"We express our sincere appreciation to the first responders for their swift actions to ensure the safety of all personnel."

The Pentagon is one of the world's largest office buildings.