The Pentagon was placed on lockdown Tuesday following reports of a potential hazardous materials incident. Firefighters, equipped with gas masks and protective gear, responded to the headquarters of the U.S. Department of Defense to investigate. Authorities later determined the initial reports were a false alarm. The lockdown caused a temporary disruption of activity within the Pentagon complex. No injuries were reported, and normal operations have since resumed. The cause of the false alarm is currently under investigation by officials. CNN was among the first to report on the incident and subsequent all-clear.