The treasured building designed by Charles Rennie Mackintosh went up in flames on Friday afternoon, destroying the library and valuable artworks.
The school has hailed the efforts of firefighters who succeeded in salvaging the vast majority of the building and contents.
As work continues to make the site safe and fully assess the scale of the damage, Scottish Fire and Rescue Service Assistant Chief Officer David Goodhew described how crews were sent to each floor to create a barrier and prevent the fire from spreading.
He said: "When we arrived we made a very quick decision that we were going to try put in what we call a fire break right through the middle of the building so that the 50% of the building that wasn't on fire didn't become involved in the fire.
"We made that break using breathing apparatus crews with jets of water. We sent crews to every single floor, and in the roof space they physically cut into spaces that were hidden in order to make a complete break.
"While we were doing that we sent other crews towards the fire internally and externally, and effectively fought the fire from inside and from outside to stop it getting any larger.
"The professionalism of the crews was absolutely outstanding.
"We worked as a complete team. Everybody working on that incident, from the person operating the pumps to the person who was running out water from the hydrants to the people wearing breathing apparatus inside the building, we were all working to achieve one goal - to save that building and stop that fire getting any bigger."
The fire service has yet to confirm the cause of the blaze, which some students have suggested could have started when a spark from a projector caught a piece of foam.
It was reported today that a new "fire suppression" system was due to be fitted in the summer.
Mr Goodhew said the building's age, the construction materials and the complexity of the structure all made it an extremely challenging fire to tackle.
He said: "The fire started in the basement and very soon it spread to the roof because of the voids.
"It's a very old building, built just after 1900, so we always knew it was going to be a particularly difficult fire to fight.
"Fire regulations were different when it was built, they used different materials. They used wood to line walls for example, and that creates hidden voids where fire can travel unseen by the human eye.
"It took about six or seven hours to get it truly under control.
"It was a very, very difficult fire - one of the most difficult fires that I've been to, certainly to try and stop it. We wanted to stop the fire and everybody was working to achieve that goal."
More than 400 fire service personnel were involved in tackling Friday's fire.
Today crews remained at the scene to dampen any hot spots and attempt to excavate any artworks that may have been buried by collapsed internal walls.
School chairwoman Muriel Gray has paid fulsome tribute to the firefighters. She said yesterday: "After ensuring no lives were in peril they displayed an impressive understanding of the precious nature of the building, and due to their careful and meticulous handling of each developing situation the damage is considerably less than we dreaded. We have run out of words with which to thank them, but the school has most certainly gained a new gallery of heroes."
Community Safety Minister Roseanna Cunningham, responsible for the delivery of the fire service in Scotland, added her praise on a visit to Cowcaddens fire station today.
She said: "They have done an absolutely astonishingly remarkable job in very, very difficult circumstances.
"This is a very complex building so they had to make snap decisions and they had to make those decisions in such a way to protect as much of the building as possible, as well as putting out the fire and attempting to salvage what they could.
"I think everybody has recognised the extraordinarily professional job that has been done and I have been joking a little with them that they perhaps never expected to find themselves the toast of the art world, but they are."
Both the Scottish and UK Governments have pledged funding to support restoration work on the Mackintosh building.