Innovate UK Real Time Detection of Respirable Crystalline Silica (RCS)

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The concept behind this project is based on the use of spatial light scattering (SLS) analysis and related optical technologies to enable differentiation of Respirable Crystalline Silica from other ambient dust particles. It will consist of a miniature optical particle sampling chamber that will enable RCS particles to be individually identified, counted and sized separately from the background dust. When coupled with suitable data processing electronics and software to include particle loss mechanisms, density and other factors, the completed detector unit will provide a real-time output of RCS mass concentration in the environment. Being crystalline in nature, fracking sand splinters into particles that have facetted surfaces, i.e. flat mirror-like fractures, and it is this particular characteristic of RCS dust that forms the basis of the project. When passed through an illuminating light beam (such as that from a laser), faceted particles result in scattering patterns which are highly asymmetric about the beam axis, unlike virtually all other particle morphologies. This means that the Centroid of Intensity (COI), or the 'centre of gravity' of the light pattern of an RCS particle lies a significant distance from the axis, in contrast to those of other particles which are close to it. So, by setting a discrimination radius around the axis only facetted particles will be registered. RCS particles may represent a small percentage of the total particle population so a viable sensor would need a high throughput (typically ~ 10,000/second) so calculating the COI using conventional image processing techniques is impractical. Position Sensitive Devices (PSD), offer an ideal solution being low cost and producing accurate X-Y analogue outputs defining the COI of the light falling on the chip. Thus, a simple empirically-determined 'threshold' distance of the COI from the pattern centre allows differentiation of facetted particles patterns. An additional 'orthogonal' optical measurement, such as birefringence or fluorescence, will also be incorporated to provide a high discrimination level and minimize false-positive RCS detection. The project will involve close collaboration between Trolex and the Particle Instruments Research Group at the University of Hertfordshire. The University will be responsible for the sensor technology development, the design of the detection chamber and optics, and laboratory evaluation using prepared dusts. Trolex will be responsible for producing a fieldable technology demonstrator instrument that will enable the detector output to be presented as a real-time RCS density in a real-world environment.