Several Charleston tourism pamphlets were found inside an envelope with white powder that prompted authorities to close off a section of a busy downtown street on Monday, according to police.

The envelope, marked “return to sender,” was mailed to Historical Charleston Foundation at 40 East Bay St., according to an incident report. It appeared to have been initially labeled to be sent to a Jami Helmi in Helsinki, Finland, the report stated.

A foundation employee opened the envelope, which contained the tourist attraction materials along with a folded stack of copier paper, the report stated.

The employee told police she unfolded the paper and found a plastic bag containing a white powdery substance. The employee called police and authorities cordoned off the area as a precautionary measure.

The powder was tested to determine if it was an illegal narcotic, but it tested negative. Officials later determined it was baking soda.

The employee told police that this envelope was the third she’d received in the past year with a return address like this one, the report stated. She said she had always thrown them away without sorting through them, according to her report to police.

The incident blocked East Bay Street near The Battery for about three hours starting at around 8 a.m. on Monday as the explosives and hazardous-materials experts tried to figure out what they were dealing with.