Teachers, janitors, cleaners and other workers were free to enter Bridge of Don Academy from July 12 because a line manager “forgot” about it for five days, according to a council investigation.
The potentially lethal substance was uncovered by a worker who was removing plasterboard above some fire doors with a hammer and chisel.
Although concerns were raised that the material might contain asbestos, it was double-bagged and left near a skip. Emergency procedures did not come into effect until July 17, according to a redacted report seen by the BBC.
The site was “not safe” as the area had “not been correctly decontaminated and isolated to prevent access by other users of the building”, the report said.
A clean-up of the area was ordered after an emergency was declared.
Two vehicles that had been used were quarantined for deep cleaning. Samples later confirmed that the material contained brown asbestos, but the report criticised the lag between the discovery and the closure of the site.
“Twenty-five persons comprising employees, sub-contractors, janitors, teachers and cleaners have been identified as being on the premises from 12 to 17 July,” the report said.
Citing several “emergency response failures”, it added: “Once the site supervisor notified his line manager about the potential disturbance of AIB (asbestos containing material) on 12 July, existing procedure was not initiated by the site manager because he was following instructions from his line manager.
“(The) line manager did not initiate procedure because he forgot about the incident until 17 July.”
The report concluded: “Throughout the project, planning has been poor.”
A spokesman for Aberdeen City Council said: “The incident at Bridge of Don Academy has been the subject of an internal investigation and the council is supporting the Health and Safety Executive as it conducts its independent investigation.”
In terms of the systematic removal of asbestos from school buildings, Scotland trails the rest of the EU, campaigners say.
In May, Clydeside Action on Asbestos (CAA) and the GMB union said there was a much stricter regime in England, as well as other EU nations.
Schools in England have a “future asbestos removal policy”, where dangerous fibres are ripped out of school buildings en masse, according to the CAA and the GMB.
However, in Scotland only periodic inspections for discrepancies take place.
The campaigners say more than 1,600 hundred primary and secondary schools in Scotland contain asbestos.
Scotland has no “future asbestos removal policy in place and is therefore lagging behind England and even further behind the rest of Europe in tackling the threat of asbestos in our schools,” Phyllis Craig of the CAA said.
“If we compare the lack of commitment in Scotland to how the issue is treated in England there are stark differences.”
About 5,000 people die in the UK each year of asbestos-related diseases, notably mesothelioma, a cancer affecting the lining of the lungs, and lung cancer itself.
Buildings built or refurbished before 2000 may have asbestos-containing material.