A pool pump overloaded, causing a haze in the ground-floor gymnasium at 1040 River Road, the spokesman said.
The haze set off a smoke alarm which prompted a brief evacuation of the building at 1040 River Road in Ewing, according to Sgt. Alejandro Goez.
No one was hurt, Goez said.
Area firefighters and a Trenton HazMat team responded shortly before 2 p.m. on Friday.
There was no serious chlorine leak and nothing hazardous lingered around, HazMat experts told State Police.
It was safe to return to the offices, they said.
Because Friday happened to be a Juneteenth state holiday, non-essential staff were not in the South Jersey building when it was evacuated.
Click here to follow Daily Voice North Hunterdon and receive free news updates.