Mineral fibers in restoration work. Looking for avoiding health problems.

The World Health Organization defines asbestos as fibers with a length (L) ≥ 5 μm, a diameter (D) < 3 μm and L/D ratio > 3. When talking about hazards related to mineral fibers and asbestos, the general concern focuses on workers at quarries, extracting the material. However, there are historic buildings and monuments built on rocks containing these fibers (e.g. serpentinite, soapstone) that due to their artistic interest or links to the architectonic heritage may need to be cleaned at some point for restoration reasons. In this sense, laser cleaning is being more and more widely used in restoration. Although, in general, it is a very selective and controllable technique that allows the removal of fine layers of material (different types of crusts or patinas) with hardly any effect on the rock substrate, laser cleaning activities on this kind of fibrous materials can generate a potentially hazardous dust that, if not protective actions are taken, may affect the heath of workers, that can be from technicians to artists to scientists developing cleaning tools. Regarding the latter, we have arranged an experiment to test how much of this powder can be retained in a “homemade” filter, coupled to a laser equipment. The idea is to work with a laser in the same way a worker on restoration would do to clean a building made of, for example, serpentinite, and observe the fibers that are retained by the filter. Combination with other tools like petrographic and electronic microscopy can be used for the sake of human health.