| Summary: | Fogging is a common safety hazard observed especially in the declines of underground mines located in sub-arctic regions. Fog forms when saturated air loses internal energy by mixing with a colder air stream, by simply ascending through the ventilation system of the mine, or when contact with cold wall-rock decreases air temperature. Studies concerning fogging in underground mines are rare. Technological advances and more complete theoretical knowledge gained by research in many other fields offer possibilities for thorough fogging research in mines. This research aims to better understand underground fog formation, related parameters, characteristics, and fog behaviour. Interviews, literature review, psychrometric and particle concentration measurements, on-site field tests of the existing fog removal methods, and developing and testing a new fog removal approach are used as research methods. The interviews show that there are methods not mentioned in the literature that are used for fog removal in mines. Case studies provide fascinating insight into fogging problems and how to solve them. From literature review the complicated behaviour of fog is uncovered, and the role of visibility, optical attenuation, and droplet size distribution studies are evaluated. Ideas concerning further research are presented according to the findings. Basic study results demonstrate the situation in declines of three underground mines; Pyhäsalmi Mine, Orivesi Mine, and Louhi Mine in Finland. Studies concerning increasing air velocity show that the value suggested by literature to be high enough for fog dispersal, 0.25 m/s, is not nearly enough in the declines of these mines. Installing an additional fan, showed that the change in relative humidity and thus fog thickness was based on the quantity of heat the fan added to the air. Heating decreased fog thickness noticeably. Only local fog removal was observed for both methods. Trials concerning new method development gave mainly positive results. The method is based on the water ...
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