Cheberiachko Y. Development of the theory of designing and improving fit testing and dust mask use

The thesis, which is a complete academic research work, solves an important task for occupational safety and health of developing design and engineering of individual respiratory organs protective devices based on their fitting to a user's face and adjustment to operational conditions, which suggests considering a combination of factors of individual and production nature. It has been determined that the main respirator efficiency factors include reliable isolation of respiratory organs, high-quality air cleaning as well as timely and proper wearing of half-masks. As a result of studying protective and ergonomic properties of reusable half-masks in the working environment of a coal mine, it has been established that with the increasing dust content of the air in the working zone, the protection factor of respirators decreases on average from 20 to 10 with the dust particle concentration of 50 and 225 mg/m3; this is conditioned by rather rapid decrease in pores between fibres of filtering material because of coarse dust fraction settlement with corresponding increase in breathing resistance and penetration of dust through an obturation line. Moreover, under a respirator mask there prevails fine dust, which is the primary cause of occupational dust diseases. A 3-D algorithm of designing half-masks includes new stages: scanning workers' faces, developing a digital head model, constructing a digital half-mask model, testing the quality of new models at the design stage, selecting relevant filtering materials. The mathematical model of changing pressure drop at respirator filters with aerosol particles settling on them has been improved. Unlike the known models, it considers not only the phase of surface filtration, but also auto-filtration which is expedient to be described using the model of a thick fibre, in which dust aggregates are approximated by smooth cylinders with a radius equal to the particle radius. Influence of wind speed, aerosol particle concentration, and filter layer parameters during the auto-filtration phase are estimated. Techniques for automatic check of filtering respiration efficiency are suggested; setting a sensor in the space under the mask surface it is possible to estimate mask fitting while using it as well as during the filter operation till it reaches the critical value of pressure drop. Engineering solutions on improving the design of multilayer filters with low breathing resistance and high dust capacity are suggested, which have been introduced at TOV NVP "Standart" (a Research and Development enterprise). Recommendations have been developed on equipping masks with extra sealing along the obturation line, setting additional elements for fitting mask headsets with the purpose of providing even force distribution along the obturation line taking into account anthropometric face diversity, increasing the area of respirator filters, which enhances their protective properties.