Spatial variability of airborne and settled dust in a piggery

Abstract

An experiment was conducted to assess the spatial variability of dust within theairspace of an occupied piggery. Measurements of airborne and settled dust were made for 16 days at 16 locations within a 180 place, partially slatted-floor, grower-finisher piggery. Eight locations were in a vertical cross-section covering half the width of the building. Two of these locations were used in conjunction with eight further locations over the remaining pen barriers to establish a horizontal sampling plane. Aerial dust samples were collected every 24h and settled dust samples every 4 days. Particle size analysis was carried out on all of the settled dust and half of the aerial dust samples. Measurements were made of airspace temperature and air velocity at each sampling location, and of pen cleanliness throughout the building. The mean aerial dust concentration was 2·2 mg/m 3, ranging from a minimum of1·6 mg/m 3 to a maximum of 2·74 mg/m 3. The mean dust sedimentation rate was 137 mg m −2 h −1 and varied from 70 mg m −2 h −1 to 295 mg m −2 h −1. The lowest values for both measures of dust occurred at pen barrier height over the slatted portion of a centrally located pen and the highest values occurred at floor level within the solid-floor portion of the pen. The average mass mean diameter of the particles in the airborne samples was 14 μm compared with 18 ,um for the settled dust samples. In general, there was a greater percentage of larger particles in both the airborne and settled dust at the front of the pens. The spatial variability of dust from end to end of the building was smaller than the variability within a building cross-section. These results were consistent with what was expected given an intuitive knowledge of where the dust was produced and the direction of air currents. In this building with sidewall extraction fans and centre air inlets, sampling at a location near the front of the pen, just above the pen barrier top, gave data representative of the dust levels to which the operator would be subjected. The spatial distribution of dust did not change appreciably from day to day; however, the day to day variability was large, such that health risks should not be assessed on data taken on one or two days only.