The main post office in Saint John was closed for about four hours Monday after workers discovered an unknown white powder.
Police, fire and hazmat crews responded to the Canada Post location on Rothesay Avenue at 11:30 a.m.
Saint John Fire Platoon Chief Barry Oickle said employees found the powder in a stack of advertising flyers.
The building was evacuated.
Oickle said tested showed the substance was not hazardous, but rather what he called an “offset powder,” which develops during the production phase of the flyers.
The post office was reopened before 4 p.m.
No one was hurt.