Fire investigators are at Millais School in Horsham this morning (Friday March 21) in a bid to determine the cause of the blaze that destroyed part of the top floor.
The inferno swept through two art classrooms, a hallway and storage areas at around 3pm yesterday (Thursday March 20).
Crews responded to initial reports of a blaze in the girls’ toilets.
Around 26 firefighters wearing breathing apparatus were sent in to battle the flames.
Police officers were on scene guarding the school all night.
Station commander Steve Clack, who helped lead yesterday’s incident, said two crews from Horsham were sent - but the number of engines was quickly increased upon arrival.
He said: “It was a significant fire on the top floor that has spread rapidly.
“Fortunately all the students were out and nobody from the school or fire were hurt which is an achievement in itself.”
Mr Clack explained that fire investigators are on the scene today alongside police - but just because they are working together it does not mean there is any indication of foul play.
He praised the school’s quick response.
“The school’s evacuation process was really good. It’s a big school in the Horsham area and the staff did a great job.”
The station commander added it is likely the cause of the fire will be revealed later today, and the site could be re-opened for students to be reunited with their possessions.