Light micrograph in dark field illumination of asbestos fibres. Asbestos has been used in the building industry for many years as a result of its heat resistance. When mixed with cement and moulded under high pressure, asbestos board is formed, able to resist temperatures of up to 540 Celcius. In its fibrous form, it is used both as a thermal and an electrical insulator. Disposal of asbestos is highly hazardous, as exposure to asbestos dust and fine fibres can cause a respiratory ailment called asbestosis. The disposal of asbestos waste is now carefully regulated by law. Magnification x200 at 4x5" size, x116 at 6x7mm size."