After several hours of waiting and careful procedures Monday, the Andover Fire Department and District 6 HazMat team declared the building to be safe.
Around 10:30 a.m. on Monday a mail room worker found and was immediately suspicious, dropping the material as soon as he saw what it may have been.
Emergency officials then locked down the mail room and the 30 people in the room.
"We just isolated those people," said Andover Fire Chief Michael Mansfield. "It gave us a little bit of time to determine what type of risk level we were dealing with."
The HazMat team eventually determined that the white powder was just crushed up prescription drugs that had been presumably crushed during the mailing process and spread over a few parcels.
"We did not find any additional substance," said Mansfield. "We have nothing to indicate that this was an act of malice."
Emergency officials were moving out of the IRS by 3 pm. Roughly 1,000 employees work at the Route 133 IRS headquarters, most of whom were not affected by Monday's incident.