Crystalline silica in heated man-made vitreous fibres: A review

•Describes the chemico-physical processes involved and the morphological consequences.•Reveals some gaps in knowledge of the process and of the toxicity of devitrified MMVF.•Indicates the toxicity of devitrified MMVFs is not related to cristobalite content.•Shows there is limited information on the exposure of MMVF workers to cristobalite. Refractory ceramic fibres (RCF) and alkaline earth silicate (AES) wools are types of man-made vitreous fibre (MMVF) that are used in demanding high-temperature industrial applications, generally above 900°C and up to 1400°C. When exposed to prolonged high temperatures, MMVF can devitrify with the formation of cristobalite and other crystalline silica species, which is of potential concern because crystalline silica (CS) is classified as carcinogenic. This article reviews the chemico-physical processes and morphological consequences of fibre devitrification, the forms and micro-location of CS produced, and the toxicity of devitrified fibres and the CS species formed in this way. It also examines scenarios for worker exposure to the products of fibre devitrification in industries using RCF and/or AES wools. We identify gaps in knowledge and make recommendations for future research.