The state of the building materials and what you intend to do with them establish this. Asbestos-containing roof tiles, in general, pose no serious health hazards if they are in excellent condition and are unlikely to be disturbed. When asbestos fibres are discharged into the atmosphere and breathed into the lungs, they are dangerous. Asbestos fibres in the environment can be harmful to the body and health. You may not experience any symptoms.