Exposure estimates from personal lapel monitors

Abstract

Full-shift personal monitors commonly are placed at the lapel or on the chest because these are convenient sampling locations. The effects of the position of the monitors on the exposure estimates have been investigated with three test aerosols. Comparative measurements were made for personnel exposed to a submicrometer ambient aerosol in a chamber in which an elevated radon atmosphere was maintained. Radioactive short lived radon daughters provided a convenient tag for the ambient aerosol particles, whose activity median aerodynamic diameter was 0.15 µm. Similar measurements were made on a mannekin exposed to uniform dust concentrations in a specially designed dust room. The dust room studies were conducted with magnetite (mass median aerodynamic diameter=1.6 µm) and standardized road dust (mass median diameter=8.0 µm). The average mean ratio of concentration measured at the lapel to that at the nose for all three aerosols was 0.98±0.01 and the forehead to nose ratio was 1.01±0.02. Clearly, for aerosols dispersed uniformly within the breathing zone under controlled conditions, no bias results from either location when estimating inhalation exposure. In cases where different exposure estimates have been noted for different sampler positions, factors such as resuspended dust, spatial concentration variability and electrostatic charges may be involved. During the course of this investigation, it was noted that errors may result from the electrostatic charge accumulated by the plastic filter cassette holders during normal handling. The median electrostatic field at 1 cm from the face of the cassettes was −220 volts/cm. In the experiments reported here the field was neutralized before sampling.