Types of asbestos:
The term asbestos refers to a group of six natural hydrated magnesium silicates. They share remarkable properties of heat, chemical and mechanical resistance (flexibility, tensile strength and friction) and a high surface area. These properties have contributed to the industrial use of asbestos in more than 3,000 different applications and products. It was used massively especially in the construction sector and building renovation for decades. This usage continued in the 80s and 90s, while the dangers of asbestos were now well known.
Asbestos fibres belong to two distinct mineralogical families, serpentine and amphibole. Only the three following types are usually present in building materials: chrysotile, amosite and crocidolite.
Over time, asbestos containing materials (ACM) are deteriorating for many reasons (dilapidation, vibrations, air flow, technical interventions, etc.) and they release into the atmosphere of fibres with significant health risks.
The harmful effects of asbestos exposure are principally a result of inhalation, deposition and retention in the airways of fibres suspended in the air. The dimensions of the fibres have a certain influence on their toxicity. By convention a fibre is an elongated particle, having parallel edges, and its length-diameter ratio is greater than 3. The main requirement of breathable asbestos fibres and other silicate is to have a diameter less than 3 µm. Furthermore, these dimensional characteristics are very important in carcinogenesis. Experimental studies have shown that the loins and fine fibres (longer than 5 or 8 µm according to the authors and diameter less than 0.25 µm) are the most carcinogenic.
Clinical signs associated with pathologies of asbestos do not directly appear but usually occur after a long latency, usually several decades after the start of the exhibition. This helps to explain the fears of those exposed, since the risk of disease persists throughout life. Asbestos is responsible for lung and pleural diseases. The asbestosis, pleural plaques and mesothelioma are specific while the lung cancer or benign exudative effusions are multifactorial, and the causal link with asbestos is based on statistical associations.