Emergency officials banned access to the Wade Hampton office building at the State House complex for several hours Tuesday after a letter containing a powdered substance was delivered to the building.
No one was injured, and operations returned to normal shortly before 4 p.m.
State Law Enforcement Division spokeswoman Jennifer Timmons said late Tuesday afternoon analysts had determined the powder is harmless.
According to S.C. Department of Public Safety spokesman Sid Gaulden, at about 10:20 a.m., government workers in the Wade Hampton office building who were opening mail found a white powdery substance on an envelope.
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They immediately notified a nearby SLED agent, and the state Bureau of Protective Services, whose officers were also nearby, Gaulden said. Those two agencies began notifying other agencies.
The central air-ventilation system of the building was shut off, he said. People were stopped from going in, said officials at the scene. But the building was not evacuated.
A one-block area of downtown - Sumter Street, from Senate to Pendleton streets - was closed to traffic.
About 25 to 30 people gathered outside the building, mostly emergency officials, including two in blue haz-mat suits with air tanks. Also outside were staffers for Gov. Mark Sanford, who has an office in the building.