SHELTON - Shelton and state fire officials are investigating a fire at Shelton High School that officials believe started in a storage room around noon Tuesday.

The Shelton Police Department has set up a command post outside the school, expecting a "long and extensive investigation,? according to officials.

Smoke was reported emanating from the second floor of the school. Firefighters from Shelton, Ansonia, Derby and Trumbull responded to the scene and found flames in a storage room on that floor.

Though students were out of class for winter break, the police department says about 75 people were in the building at the time. They included maintenance workers, faculty, staff and some students participating in athletics.

Health and environmental officials were also on the scene as police say several light bulbs in the school exploded, causing mercury to be released.