Danger Asbestos sign on a construction / demolition site on 30th March 2021 in Birmingham, United Kingdom. Asbestos is a naturally occurring fibrous mineral which is composed of long crystals, each fibre being composed of many microscopic fibrils that can be released into the atmosphere by abrasion and other processes. Asbestos is an excellent electrical insulator and is highly heat-resistant, so for many years it was used as a building material. However, it is now a well-known health and safety hazard and the use of asbestos as a building material is illegal in many countries. Inhalation of asbestos fibres can lead to various serious lung conditions, including asbestosis and cancer.