For me it began with a disquieting tweet from a Glasgow contact, around lunchtime on Friday, May 23. “Is the Art School on fire?” she asked. Yes, she confirmed when I urgently asked for information, it seemed to be gushing smoke. Then the photos and newsreel footage started to appear. It was looking worse and worse, especially when flames burst out of the top floor of the building. The horror from the world’s architecture community was real and immediate. Many, including me, were in tears. There is only one Art School in Glasgow: the one that is celebrated worldwide as Charles Rennie Mackintosh’s masterpiece. An extraordinary synthesis of Scottish Baronial, Arts and Crafts, Art Nouveau, and Japanese styles with industrial-modern construction methods, built in two phases from 1897 and 1909. Its interiors, especially its extraordinarily rich, timber-lined library with its purpose-designed furniture and fittings, also show the guiding hand of Mackintosh’s artist-designer wife Margaret MacDonald. This much-loved building was still in use exactly as designed.

All it took was an electrical explosion in a projector in the basement as the student degree shows were being prepared. Reports suggest that an installation using spray foam was nearby: highly flammable, it caught on fire, which then spread with terrifying rapidity through the voids of the building, from the bottom to the top. Attempts to quench it failed; staff and students had to evacuate and all did so safely. Well-drilled fire crews were on the scene in minutes, to find a growing inferno. They knew the importance of the building and its contents. Their task was to save as much as possible.

A week later, students and staff of the School of Art formed a guard of honour to salute those same fire crews as they finally left the building, led by a piper. What was still a cultural disaster of international proportions had also turned into something else: cautious optimism that the masterpiece could be restored. Yes, the jewel-like heart of the building—the library, only recently restored—had been destroyed. So had much else, including the extraordinary top-story ‘hen run,’ a glazed loggia that Mackintosh built to link the two halves of the building. But the worst fears of May 23—that the building would be completely gutted, might even have to be demolished—were allayed. The first phase of the building remains largely intact, thanks to the firefighters forming a 100-strong human chain on the main stair, successfully containing the blaze. Scotland’s fire service reported that 90 per cent of the building’s structure and 70 per cent of its contents had been saved, including its archive. But those reassuring statistics belied the devastation to the interiors simultaneously being shown in official photos. And the structural damage to the steel frame of the building has yet to be assessed.

The exterior of the newer western end of the building is now smoke blackened, especially poignant where the flames had burst through the multi-level metal-framed bay windows of the library. These were the inspiration for Steven Holl’s “driven voids of light” in his recently-opened extension across the street. That new building proved its worth in the aftermath when the school reopened and salvaged artifacts were laid out there for assessment and cataloguing. Holl and his partner Chris McVoy issued a statement describing the fire as “unbelievably tragic for architecture and the history of architecture. This is an unimaginably sad and deeply spiritual loss.”

A similar sentiment was expressed by Stephen Hodder, president of the Royal Institute of British Architects. “Damage to a building of such immense significance and uniqueness is an international tragedy. It is irreplaceable,” he said. Nobody disagrees, and it is significant that both British and Scottish governments immediately pledged funds to help with the restoration. And with very few exceptions, full restoration is what architects of all persuasions are agreed on. As leading architect and academic Nigel Coates tweeted in the immediate aftermath, to widespread approval: “One of the most perfect interiors on the planet: the exquisite library at the Glasgow School of Art must be restored as was.”

It hurts, of course, to discover that an advanced water-mist fire suppression system was in the process of being installed in the building. Work on this had reportedly commenced in 2013, and was due for completion this summer, but had been delayed by—supreme irony—the discovery of an older fire-protection material, asbestos, in the building’s foyer, which requires specialist removal techniques. Older-style fire-activated drenchersystems were not popular in historic buildings in the UK because of their visual intrusiveness and the water damage they caused to contents, especially if set off accidentally. And this, of course, was a building full of students.

Work is well under way to sift through the debris. Part of the damaged stone western gable of the building is being dismantled for conservation and rebuilding in collaboration with conservation agency Historic Scotland. And the school has launched a “fire fund” appeal to help with the reconstruction work. Terrible though it was, the fire at Mackintosh’s Glasgow School of Art has served to unite the world of architecture in a determination to save it.

Hugh Pearman is architecture critic of The Sunday Times, London, and editor of the RIBA Journal.