METHODS USED BY THE IONAL-INSTITUTE-FOR-OCCUPATIONAL-SAFETY-AND-HEALTH TO MONITOR CRYSTALLINE SILICA

The National Institute for Occupational Safety and Health (NIOSH) in t he United States has four methods for monitoring the concentration of crystalline silica dust. They all employ a cyclone for size-selective sampling in the field, but differ primarily in that the laboratory mea surement is based on either infrared spectroscopy, X-ray diffraction, or colorimetry. The limits of detection for these methods are similar, but their accuracy is poor, particularly at low filter loadings near the current recommended exposure limit (50 mu g . m(-3)). Advances in analytical instrumentation have improved measurement precision. Correc tion techniques to account for X-ray absorption in samples loaded with nonsilica dust have eliminated one source of bias. Direct analysis on collection fillers is a convenient technique that should decrease sam ple manipulation errors, but it has not been shown to improve precisio n or accuracy significantly.