Abstract
Occupational exposure to dusts containing crystalline silica have long been associated with the induction of silicosis, a focal fibrosis of the pulmonary parenchyma. Since only the dust that could penetrate to the gas exchange region of the lung, defined as respirable dust, could produce a pneumoconiosis such as silicosis, size-selective respirable dust inlets were developed for air samplers to restrict the dust analyses to the respirable fraction of the airborne dust. Analyses of respirable dust are reported in terms of mass concentration, although a case can be made for associating the hazard more closely with the surface area of the dust. The hazards associated with inhaling crystalline silica within dust mixtures also depend on the properties of the coconstituents of the mixed aerosol, as documented in epidemiological studies on miners. Other considerations affecting exposure assessment strategies are concerns about diseases other than silicosis that may be caused by exposure to dusts containing crystalline silica. These include bronchitis and lung and stomach cancer, which may be related to the thoracic fraction of the airborne dust. Technical issues affecting the selection of size-selective samplers, their siting, sampling periods, flow rates, and sampling schedules can all be important in evaluating the effectiveness of an exposure assessment strategy. Changes in the work environment also need to be considered to the extent that they may affect airborne exposure and dose to target tissues in the lungs. Automation and production rate changes can alter both dust concentrations and size distributions, as well as respiratory patterns of the workers and their proximity to dust sources. These factors can also influence optimal placement of dust samplers and/or monitors. These and other factors are critically reviewed in terms of current and future exposure assessment strategies. Lippmann, M.: Exposure Assessment Strategies for Crystalline Silica Health Effects. Appl. Occup. Environ. Hyg. 10(12):981–990;1995.