ARLINGTON, Va. — The Pentagon went into a shelter-in-place on Thursday after reports of a potential air hazard situation, officials told CNN.

The incident locked down multiple floors and hallways in the Department of Defense headquarters. A spokesperson told CNN that building monitoring systems detected an air-quality issue, prompting precautionary measures while officials worked to determine its source.

The evacuation was triggered when a Pentagon sensor system detected the possible presence of anthrax, officials told CNN. But the sensor system was malfunctioning, sources added, causing the false alarm.

At 12:31 p.m., Pentagon spokesman Sean Parnell said that the Pentagon resumed normal operations.