One person was taken to Hackensack University Medical Center and was released after being evaluated, responders said.
A county Hazardous Materials Unit tested the substance and determined it wasn't harmful, Bergen County Director of Communications Derek Sands said.
It turned out to be powder from a fire extinguisher, Bergen County Sheriff Anthony Cureton said, adding that there wasn't any "criminal nexus" that required investigating.
The dried sodium and potassium bicarbonate apparently had come from a fire at the point of origin, the sheriff said.
The area was cleaned and the building at 1 Bergen County Plaza was reopened for business after about an hour, Sands said.
Staff members had remained in the building, he said.
City firefighters decontaminated the unit members, Hackensack Fire Capt. Justin Derevyanik said.
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