The disastrous fire at the Glasgow School of Art, which destroyed its famous Mackintosh library, was started when flammable gases from a canister of expanding foam were set alight by a film projector, the official fire report has found.

The official fire service report also confirms that a sprinkler system was not fully installed at the building and was not operational on the day of the blaze in May.

The report found that the fire's rapid progress through the Charles Rennie Mackintosh designed-building was aided by timber lined walls and voids, and original ventilation ducts running both vertically and horizontally throughout the building.

The Investigation Report, the result of six months investigation by the Scottish Fire and Rescure Service (SFRS) looks into how the fire of 23 May began and how it spread through the world famous building.

It says "a fire suppression system, designed to enhance existing fire protection measures, was being installed and was in the latter stages of completion; at the time of the fire the system it was not fully commissioned and was not operational."

Professor Tom Inns, director of the GSA, maintained that the fire was an accident and no one is being held to blame - he said a "series of events" were responsible for the blaze.

He said he is sure exhibitions will be held in the Mackintosh Building again, but would not commit fully to holding the full Degree Show in the building again.

The fire itself started in Studio 19, in the north basement of the west wing of the building as students were assembling their degree shows.

One student, unnamed, was assembling work made from foam panels, fastened to three walls of a space made from chipboard and wooden studs, with one wall left blank to receive projected images from the project mounted on the opposite wall.

The student was filling in gaps between the foam panels by applying foam directly from a canister when the flammable gases in the tin - isobutane, propane and dimethyl ether - were sprayed close to the projector and drawn into its cooling fan.

Professor Inns said that students had been told not to use such sprayable expanding foam and that an error was made.

The projector, purchased in 2008 by the GSA and not defective, according to the report, ignited the gases with its electrical components, burning through the plastic of the projector and then igniting the foam walls placed directly behind it.

The flames spread through Studio 19, igniting timber panelling, and travelling through voids in the walls into Studio 31 on the ground floor, directly above.

The fire, aided by voids in the walls, spreading unchecked to Studio 32 and through voids to the Mackintosh Library above.

The report says: "The construction, layout, and high fire loading (timber furniture, panelling and books) meant that the room and its contents became totally involved in the fire."

The fire spread through various studios in the west end of the building and the report adds: "A major contributory factor for the fire spreading throughout the building was the number of timber lined walls and voids, and original ventilation ducts running both vertically and horizontally throughout the building."

In addition to ventilation ducts, a vertical service void ran "the entire height of the building to roof level and acted like a chimney. It allowed flames, hot gases and smoke to travel vertically."

The Glasgow School of Art has commissioned an external review of its management of the critical incident.

A statement from the school last night said: "Now that the SFRS has concluded its investigation into the cause of the fire, The Glasgow School of Art will be reviewing the specific lessons to be learnt from the incident.

"Information from the SFRS Fire Report will also be used to inform the Mackintosh Building restoration and GSA's broader approach to health and safety management going forward."

With the addition of a temporary roof, the building is now wind and water tight and specialists from Kirkdale Archaeology are forensically excavating the remains of the Mackintosh Library.

A special Board Committee has been established under the leadership of Eleanor McAlister OBE to oversee the restoration project.

The statement added: "We aim that the building will be fully restored and operational as a working art school, exhibition space and visitor attraction between 2018 and 2019."