Several floors and sections of the Pentagon were evacuated Tuesday following an alarm triggered by a hazardous substance. Authorities have not yet disclosed the nature of the substance or the source of the alert, but emergency responders were dispatched to the scene. The evacuation impacted multiple areas within the sprawling defense headquarters. Initial reports indicate a precautionary measure was taken to ensure personnel safety while the situation was assessed. As of now, there are no reports of injuries. Investigations are ongoing to determine the cause of the alarm and to clear the affected areas for re-entry.