Fire safety experts say plans to install a sprinkler system at the Glasgow School of Art had not been completed before the blaze broke out on Friday.
Firefighters remain at the scene for a second day and are using thermal imaging cameras to identify remaining hotspots at the world-renowned building.
The blaze was the second in four years to hit the Mackintosh Building, which was undergoing a multi-million pound restoration project to return it to its former glory.
Repairing the latest damage could cost at least £100m, according to initial estimates.
The neighbouring O2 ABC nightclub was also badly damaged in the fire.
Keith MacGillivray, of the British Automatic Fire Sprinkler Association, said plans to install a mist system has not been finished.
He told STV News: “Obviously we’re devastated at the loss of another heritage building in Scotland.
“There were plans to have a mist system installed in the building, unfortunately that wasn’t completed at the time of the fire so obviously the system couldn’t actuate, it wasn’t fully operational.
“We had recommended before that sprinkler systems and mist systems be installed in heritage buildings, and we lose a huge amount of heritage buildings every year.”
Earlier, Scotland’s chief fire officer Alasdair Hay said the blaze was one of the most significant he had seen in 35 years.
He said: “I’ve been in the fire service for 35 years, and let me tell you this is one of the most significant fires I have actually experienced.
“I just want to again put out that message, what an incredible job the firefighters have faced.
“All fires are inherently dangerous, this was a really significant fire and they have done an incredible job to extinguish it and to contain it.”
Around 50 firefighters remain at the scene on Sunday, with most of the blaze thought to be contained.