[Evaluation of occupational exposure to dusts of mixed free crystalline silica and natural respirable mineral fibers].

An appropriate evaluation of exposure to dust containing both crystalline silica and asbestos (e.g., some mines of rock materials, installation and disassembly of thermal insulation and frictional products etc.) requires that the presence of these two potentially carcinogenic dust components should be taken into account. In Poland, the present legal regulations provide for rather extensive freedom in both defining the scope of studies performed and interpreting their results. In consequences, the evaluation of dust exposure at similar workposts in different plant is based on different criteria, which means that in some cases the presence of free crystalline silica (MAC value for dust containing from 2 to 50% of SiO2--is 4 mg/m3 for total dust and 1 mg/m3 for respirable dust) is taken into account, and in others the presence of mineral fibers such as chrysotile and other fibrous mineral except for crocidolite (MAC value--1 mg/m3 and 0.2 f/cm3, respectively). The evaluation of exposure usually involves only one factor, i.e. free silica crystalline (more favorable for the administration of a given plant). The present study reveals that depending on the criterion adopted for evaluating the exposure at a given workpost (e.g. exchange of thermal insulation), the working conditions may be classified as safe (criterion for the presence of SiO2) or as harmful to workers' health if a complete composition of mineral dust (chrysotile, amosite, quartz) is considered. In order to clarify the present situation, the authors present in this paper the proposals on the scope of required studies (measurements of total and respirable dust, as well as respirable mineral fibers concentrations, determination of SiO2 contents, identification of dust crystalline phases) and the principles on which the interpretation of results should be based.