Concerns for safety are growing after fire crews dealt with a fourth blaze in four days at the old Kirklees College site in Huddersfield.
Firefighters were called out again shortly before 5.30am on Monday to reports of a fire on the first floor.
Firefighters used breathing apparatus, a large jet and a hose reel to extinguish the flames with crews from Huddersfield and Rastrick attending.
One firefighter said worries were increasing for people’s safety due to the size of the building.
Watch commander Shane Byrne said: “The building is huge and can’t be policed.
“It’s like a rabbit warren inside and when it’s filled with smoke it’s very dangerous and difficult to find your way around.
“Whoever starts a fire in there is putting themselves at risk of being hurt due to the disorientating nature of the building.
“The main issue is that there is still lots of furniture left. There is a lot of stuff in there to burn.”
Measures have been taken to board up the site, although there are still concerns people are getting in.
Calls are now being made to increase police presence around the building.