Measurement of the durability of man-made vitreous fibres

The persistence of fibres within lung tissue is believed to be an important influence on their potential to cause disease and the reliable prediction of persistence could be useful in hazard classification. Traditionally “”biopersistence”” has been assessed from animal experiments but in vitro testing could offer a less expensive and rapid alternative. We have developed an in vitro dissolution assay that uses a continuous flow through (CFT) test rig and a protocol that is similar to that recently proposed by European Insulation Manufacturer’s Association. Weighed samples of test fibre are put into test cells and exposed to simulated extracellular lung fluid over a six week period. The dissolution rate of each sample is assessed from the concentrations of silicon in test fluid that has passed through each cell. Our estimated dissolution rates for a range of fibre types are generally within the wide range of published values. The main cause of variation between laboratories may be the use of different methodologies to calculate initial specific surface area. The results of CFT experiments are also sensitive to the effects of test fluid composition and flow rate. We found that CFT tests conducted at fluid flow to surface area (F/a) ratios of around 0.03�m-1 discriminated between very rapidly dissolving fibres, rapidly dissolving fibres and fibres that dissolve relatively slowly. In general, fibres that dissolved rapidly in vitro also disappear relatively rapidly from animal lungs, whereas those that dissolved more slowly disappear relatively slowly in vivo. The precision associated with individual determination of Kdis is poorer than for many standard laboratory analysis and at least 10 determinations would be required to give a precision close to 10%. An interlaboratory comparison with the Health and Safety Laboratory, however, found a high level of correlation between estimates of dissolution rate made in the two laboratories, although actual values were slightly different. “”