Investigation of the chrysotile fibres in an asbestos cement sample

To investigate whether claims of a physical and chemical change to chrysotile fibres in a cement matrix (A/C), are valid and merit further investigation.

Claims have been made in correspondence to HSE and in various media outlets (Bridle and Stone, 2006), that the chrysotile asbestos in asbestos cement products is altered, by an unexplained process, into a non-asbestos fibrous material. The claims being made suggest that this process is 100% efficient and no chrysotile asbestos remains in the matrix and also no “actionable release” of airborne asbestos fibres can occur. The outcome of these claims would be to show that, “ if white asbestos cement products are seen as no longer containing the chemical which has been banned, this should eventually exempt such products from many regulations”. There is also the underlying assumption that the, “ fibres have been rendered safe by the attendant chemical process”.

These observation are reported to be based partly on changes to the appearance of some of the fibres recovered from the matrix of the cement when viewed at high magnifications in a transmission electron microscope (TEM) and changes to the fibre chemistry as detected using energy dispersive x-ray analysis (EDXA) attached to the TEM (unpublished report by Pooley, F.D., 2004). More specifically the claim made was; “The conclusions which emerged from Professor Pooley’s report were unequivocal. They confirmed that mixing with cement induces chemical and structural change to the chrysotile fibres. Increased levels of calcium and silicon and an increased tendency to aggregate leaves the fibre definitively altered.”

The aim of the work in this report was to investigate whether the claims that have been made are readily and uniformly observed and merit further investigation. Alternatively, if they occur only partially or are artefacts of the sampling and analytical procedures used, can they be discounted as a significant effect. The examination was carried out using similar methods to those that were been used to claim that changes to the chrysotile asbestos had occurred. Some additional electron diffraction analysis has also been carried out.

The issue appears to be similar to previous claims (e.g. Deruyterre et al., 1980) that asbestos cement converted the chrysotile to a less hazardous material, which behaves more like a cement dust than an asbestos dust because small individual particles of cement were attached to the surface of the fibres.

Download: HSE-Asbestos-Cement