Characterizing worker exposure to bitumen during hot mix paving and asphalt mixing operations

A survey of bitumen exposure was carried out during hot mix paving and asphalt mixing. Four methods of characterizing and quantifying bitumen fume in inhalable particles were used: gravimetric, infrared spectroscopy, gas chromatography, and total absorbance (of the particle filter surface). Dermal deposition of bitumen was assessed by determination of cyclohexanesoluble matter in the material collected by paper or cotton pads worn on the inside of a person's wrists. The researchers studied the correlation patterns between results of these methods using pairwise correlation coefficients and principal component analysis (for air concentrations only). For hot mix paving, within- and between-worker variance components were evaluated, adjusting for area paved. Collected fume was dark in color and mainly consisted of aliphatic hydrocarbons of less than 20 carbon atoms. Inconsistent correlation patterns between dermal deposition and air levels were observed. Quantification of organic matter using either infrared spectroscopy or gas chromatography appeared to be good methods for monitoring inhalable bitumen fume. Cotton pads seem to be more promising than paper pads for measuring dermal exposure during paving. Paving workers were uniformly exposed to bitumen fume. Assessment of the uniformity of dermal exposure depended on the type of pad used. Day-to-day variability and intensity of inhalable and dermal bitumen exposures depended on area paved. The small size of the study limits the potential application of the results to the asphalt industry in general. More research is needed to develop a valid and inexpensive method of assessing total bitumen exposure.