Fears that residue found in classrooms at WA's biggest high school was asbestos dust have been confirmed.
The Education Department revealed yesterday that 10 rooms were contaminated.
The department took the precaution of closing Willetton Senior High School last week after teachers became concerned that dust left behind by contractors in some classrooms resembled residue that had already been identified as asbestos in four rooms scheduled for demolition.
Infrastructure executive director John Fischer confirmed that independent consultants had found asbestos residue in another six classrooms.
He blamed contractors who failed to follow protocols for dealing with asbestos when they drilled holes in classroom ceiling tiles in the school holidays.
"It appears some contractors had not followed correct procedures for working with asbestos, which includes checking the school's asbestos register and properly recording any work done," Mr Fischer said.
"We didn't want to take any chances with safety, so we decided to clean and air-test the whole school so we could be certain all classrooms were safe for students and staff to return to."
He said the school had since been provided with a certificate from qualified experts stating that all 200-plus classrooms had been thoroughly cleaned and tested.
"We are now working with the Department of Finance's Building Management and Works and all schools to ensure contractors are reminded of their responsibilities when working with asbestos," Mr Fischer said.
The department's policy for asbestos management says power tools should not be used on asbestos cement products.
Parents of Willetton's 1800 students were told last Friday that the school would reopen this week after testing, repairs and cleaning.
Lawyer Laine McDonald, from asbestos compensation law firm Slater and Gordon, said if a teacher or student was negligently exposed to asbestos at a public school and later diagnosed with an asbestos-related disease, they might be able to bring a claim against Education Minister Peter Collier.
"Damaged asbestos products can release a dangerous and toxic dust which, once breathed in, can cause mesothelioma, lung cancer and other serious lung diseases," she said.