Officials say a malfunctioning heater caused a smoke condition and forced the evacuation of the Union County College science building Thursday.

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College spokesman Stephen Nacco tells The Courier News of Bridgewater students returned to the building about 20 minutes later.

The incident comes two days after the college in Cranford received a third bomb threat this month. No explosive devices have been found.

The FBI is investigating those threats.

(Copyright 2012 by The Associated Press. All Rights Reserved.)

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