Choosing the number of images and image position when analyzing the UNC Passive Aerosol Sampler for occupational exposure assessment.

The University of North Carolina passive aerosol sampler (UNC sampler) could be an alternative when measuring occupational dust exposure, but the time required for microscopic imaging of the sampler needs to be reduced to make it more attractive. The aims of this study were to (1) characterize the effect on precision when reducing imaging, in order to shorten analysis time and (2) assess if the position of the images makes a difference. Eighty-eight samplers were deployed in different locations of an open pit mine. Sixty images were captured for each UNC sampler, covering 51% of its collection surface, using scanning electron microscopy. Bootstrapped samples were generated with different image combinations, to assess the within-sampler coefficient of variation (CVws) for different numbers of images. In addition, the particle concentration relative to the distance from the center of the sampler was studied. Reducing the number of images collected from the UNC sampler led to up to 8.3% CVws for 10 images when calculating respirable fraction. As the overall CV has previously been assessed to 36%, the additional contribution becomes minimal, increasing the overall CV to 37%. The mean concentrations of the images were modestly related to distance from the center of the sampler. The CVws changed from 8.26% to 8.13% for 10 images when applying rules for the image collection based on distance. Thus, the benefit of these rules on the precision is small and the images can therefore be chosen at random. In conclusion, reducing the number of images analyzed from 60 to 10, corresponding to a reduction of the imaged sampling area from 51% to 8.5%, results in a negligible loss in precision for respirable fraction dust measurements in occupational environments.

Comparison of self-assessment and expert assessment of occupational exposure to chemicals.

OBJECTIVES: Occupational assessments of chemical exposure are often inadequate because of difficulties in obtaining sufficient numbers of measurements by trained professionals (experts). The objective of this study was to determine whether workers can provide unbiased data via self-assessments of exposure facilitated by the use of simple passive monitors for personal sampling. METHODS: Untrained workers obtained personal measurements of their exposures to gaseous contaminants (terpenes in sawmills and styrene in reinforced plastics factories) with passive monitors and written instructions. To study the validity of the self-assessments, an occupational hygienist performed exposure measurements on the same occupational groups after the workers had obtained two or more measurements independently. The potential bias of the self-assessments was evaluated by comparing the self-assessments with the expert assessments in mixed-effects statistical models. RESULTS: A total of 153 terpene (97 self and 56 expert) and 216 styrene (159 self and 57 expert) measurements were obtained from four sawmills and six reinforced plastics factories, respectively. No significant differences in the geometric mean exposures were observed between the self-assessments and the expert assessments in 3 of 4 sawmills and 5 of 6 reinforced plastics factories (P > 0.10). The potential bias of the self-assessments of exposure ranged from less than 0.1% to 102% and was less than 17% in 9 of the 10 groups investigated. CONCLUSIONS: The results indicate that untrained, unsupervised workers are able to collect consistently unbiased exposure data by employing currently available passive monitors.

Self-assessment of exposure--a pilot study of assessment of exposure to benzene in tank truck drivers.

Occupational hygienists or safety engineers perform exposure assessments, mostly with very little participation by the workers. The objective of our study is to involve the workers themselves in the assessment and measurement procedure, the self-assessment method (SAE). A pilot study has been carried out involving tank truck drivers at a company transporting gasoline. The drivers were supposed to decide themselves when, and how often, they wanted to measure benzene exposure by using diffusive samplers that were then sent by mail for analysis. After every measurement they received their own results in a personal document for interpretation. The company management also received a document, which summarized all the drivers' measurements. Expert measurements, with the same type of sampler, were also accomplished to evaluate the self-assessments. The geometric mean and the 95 percent confidence intervals of the measurements made by the drivers (29 measurements) was 0.17 (0.11-0.26), and by an occupational hygienist (8 measurements) 0.12 mg/m3 (0.04-0.37). The results show that the drivers technically can perform SAE. Interviews with the workers and the management indicated that some kind of organizational support within the company is needed to implement the method into the regular internal control of the working environment.