Optical aerosol spectrometers are used to assess the extent to which employees are exposed to respirable dust in their workplaces. Such measurements are also being carried out increasingly in indoor spaces in response to the COVID-19 pandemic.
These instruments measure the light scattered by particles, from which they determine the numbers of particles and/or their mass concentration. When calibrating the devices, certain assumptions have to be made concerning the particles’ properties, which can vary from workplace to workplace.
The aim of this project, which was conducted by the Institute of Energy and Environmental Technology (Institut für Energie- und Umwelttechnik, lUTA) in Duisburg and the Institute for Research on Hazardous Substances (Institut für Gefahrstoffforschung, IGF) in Dortmund, was to compare different optical measurement techniques and instruments, both under reproducible laboratory conditions and in a range of workplaces. In addition to conventional optical measurement instruments, low-cost dust sensors were also used. The various measurements taken were compared with the particulate levels found using the MPG II gravimetric reference method originally developed by the Silicosis Research Institute (Silikose Forschungsinstitut) so that the devices’ general suitability for exposure monitoring could be assessed.
The results from the project show that the instruments looked at are suitable for the performance of exposure measurements, but in almost all cases the data need to be corrected to take account of the specific conditions in each workplace. In order to do this, it is necessary for the respirable dust concentration to be determined gravimetrically at least once. Accuracies of ±30% or better can be achieved if the data are corrected in this way. Low-cost sensors are less accurate. However, it is perfectly acceptable to deploy them for measurements that do not require a high degree of absolute accuracy. This might be done, for example, in a continuous monitoring system intended to detect relative changes in the respirable dust concentration.
All the instruments were also capable of detecting the airborne droplets that play a role in the transmission of SARS-CoV-2 infections. However, these droplets are only relevant in the immediate area where the air is being breathed, because their water content evaporates very rapidly under normal ambient conditions, leaving solid particles behind. Optical aerosol spectrometers are also good at detecting these solid particles, provided they fall within the instrument’s size range.
Unit 4.5 "Particulate Hazardous Substances, Advanced Materials"