Measuring occupational dust exposure with a passive sampler 

We are exposed to dust constantly, however, not all dust is harmful. Harmful dust that we are exposed to due to work is important to measure to be able to investigate various health hazards. Active sampling is used today to measure dust in the working environment. Active sampling means that a separator draws in dust, using a pump, onto a filter that is weighed. Two examples of such separators that collect particles of interest are impactors and cyclones. An impactor operates in such a way that the dust particles that are too big collide with a surface while the rest lands on the filter. The cyclone operates almost in the same manner, but it is based on an air vortex that separates the dust particles by size. An alternative to active sampling of dust in the working environment could be passive sampling. Passive sampling does not require a power source to sample particles. A specific passive sampler, University of North Carolina passive aerosol sampler, was studied. Promising results have already been shown with the passive sampler for particles larger than 2.5 µm, but it has shown too low concentrations for the smaller particle sizes. The aim was to acquire more knowledge about this passive sampler and to investigate whether it can be used for personal sampling in the working environment.

The working environment chosen to investigate the passive sampler in was a mine (open pit mine). Since the sampler had never been used in the mine earlier, samplers that had already been evaluated were used, such as impactors and cyclones. The measurements were performed in two different ways, both at different locations in the mine and also on different persons. To evaluate the result of the passive sampler, images of the particles are taken with an advanced microscope. The information from the images is then converted to the concentration of the dust in order to compare it with the other samplers.

After the first measurements the passive sampler showed lower concentrations compared to the impactors. As previous studies have showed that measurements with the passive sampler agrees with concentrations for larger particles, more measurements were made. From the new set of measurements, the same phenomenon was exhibited. What had not been taken into account in the theory of the passive sampler was that it works differently when there is no wind. In every location at the mine where the measurements had been made there was no wind registered. After changing the model to consider the windless conditions, it turned out that the passive sampler was more consistent with the impactors. The mass distribution (the ratio of small to large particles) of the passive sampler also showed the same shape as the comparative instrument used. In the personal sampling (with the passive sampler) the particles on the sampler were from the working environment and not particles generated from the person. Using the new model, it once again led to an expected shape of the mass distribution, while the old model did not. The old model was more advantageous for the largest particles, which therefore led to a skewed distribution. However, the passive sampler measured much higher concentrations compared to the cyclone.

Taking into account that the model needs to be changed when there is no wind, the passive sampler can be used for onsite measurements in the mining environment. For personal sampling, the passive sampler measured the dust from the working environment and not for example skin or textiles. However, it showed much higher concentrations of dust than the comparison sampler. Thus, the passive sampler can be used for onsite measurements in the mining environment, but it is not yet ready for personal sampling.

Reference: Measuring occupational dust exposure with a passive sampler (2018).

Read more