Carmel police headquarters had to be locked down for several hours Wednesday night when a woman brought in an envelope filled with a mysterious white powder that turned out to be benign. Officials say the woman walked into the building with an envelope inside a plastic bag. She said she experienced numbness to the face and watery eyes. The desk officer quickly sealed the bag, dropped it outside and called the Putnam hazmat unit. Investigators say the substance later proved to be folic acid, commonly known as vitamin B. The woman's identity was not released and it's unclear how she obtained the envelope.Police say that residents facing similar situations should not bring envelopes to their local police departments. Instead, they should call 911 and officers will respond.