The Pentagon was locked down and partially evacuated on Thursday due to a false alarm by a hazardous materials sensor, two sources familiar told CNN.

Multiple floors and corridors inside the building had been locked down and others were evacuated due to a “hazardous materials incident,” three sources familiar and the local fire department said earlier on Thursday.

The evacuation was triggered when a Pentagon sensor system detected the possible presence of anthrax, according to first responder radio traffic and a source familiar with the incident. But the sensor system was malfunctioning, one of the sources familiar said, causing the false alarm.