Field and wind tunnel comparison of four aerosol samplers using agricultural dusts.

Occupational lung disease is a significant problem among agricultural workers exposed to organic dusts. Measurements of exposure in agricultural environments in the USA have traditionally been conducted using 37-mm closed-face cassettes (CFCs) and respirable Cyclones. Inhalable aerosol samplers offer significant improvement for dose estimation studies to reduce respiratory disease. The goals of this study were to determine correction factors between the inhalable samplers (IOM and Button) and the CFC and Cyclone for dusts sampled in livestock buildings and to determine whether these factors vary among livestock types. Determination of these correction factors will allow comparison between inhalable measurements and historical measurements. Ten sets of samples were collected in swine, chicken, turkey, and dairy facilities in both Colorado and Iowa. Pairs of each sampling device were attached to the front and back of a rotating mannequin. Laboratory studies using a still-air chamber and a wind tunnel provided information regarding the effect of wind speed on sampler performance. Overall, the IOM had the lowest coefficient of variation (best precision) and was least affected by changes in wind speed. The performance of the Button was negatively impacted in poultry environments where larger (feather) particulates clogged the holes in the initial screen. The CFC/IOM ratios are important for comparisons between newer and older studies. Wind speed and dust type were both important factors affecting ratios. Based on the field studies (Table 6), a ratio of 0.56 is suggested as a conversion factor for the CFC/IOM (average for all environments because of no statistical difference). Suggested conversion factors for the Button/IOM are swine (0.57), chicken (0.80), turkey (0.53), and dairy (0.67). Any attempt to apply a conversion factor between the Cyclone and inhalable samplers is not recommended.

Correction of sampler-to-sampler comparisons based on aerosol size distribution.

This article explains a simple method for correcting a sampler-to-sampler ratio for changes in size distribution by computing a bias factor that relates the measured ratio with a ratio determined from equations that describe the collection efficiency curves of the samplers while taking size distribution into account. Laboratory trials were conducted to determine whether the resulting bias factor is independent of aerosol size distribution. During these studies, a 3-piece cassette and respirable cyclone were compared with an inhalable sampler in both a still-air chamber and a moving-air chamber operated at 0.2 m/sec and 1.0 m/sec. An ISO test dust of various size fractions was generated to produce an aerosol with mass median aerodynamic diameter ranging from 1.4 microm to 10.1 microm. An organic dust consisting of ground grain material was also applied to the still-air chamber to demonstrate differences between dust types. Results showed that the bias value was significantly different between dust types for both the cyclone/ inhalable (p=0.001) and cassette/inhalable (p=0.033) comparisons but was not different between wind conditions for either comparison. All but one comparison had insignificant slopes when comparing the bias value with median diameter, indicating that the bias value could be used to correct for size distributions in most conditions. However, bias values determined when comparing the cyclone with the inhalable sampler in the still-air condition produced a positive slope for median diameters less than 4 microm (p=0.008). Further research is needed to determine why the actual cyclone/inhalable ratio decreases relative to the expected ratio as the proportion of respirable particles increases. These results suggest that, for most conditions, the size-distribution compensation can be applied to sampler-to-sampler correlations provided that the original comparison was performed with the same dust type.