An overview is presented on the comparison between asbestos and nanofiber from the viewpoint of risk perception. After reviewing various fundamental concepts related to fibers, it is pointed out that asbestos and nanofiber have significant differences in size and structure, although both fall into the category of respirable fiber. The results of hazard evaluation for asbestos and related fibers show significant variability among materials, thus making a simple extrapolation of previous knowledge to nanofiber impossible. Therefore, the risk analysis of various nanofibers, such as carbon nanotubes, needs to be carried out for individual classes with specific size, shape, and other structural characteristics. Towards this end, an increasing number of toxicological studies are indeed under way, especially for carbon nanotubes.
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