<p>Federal mining regulations in the United States mandate that underground coal mines install refuge alternatives (RA) for miners to seek refuge after an inescapable disaster. RAs are required to isolate and protect occupants from hazardous conditions and to provide a life-sustaining, breathable air environment for a minimum of 96 hours. According to federal Mine Safety and Health Administration (MSHA) RA regulations, the RA oxygen levels must be maintained between 18.5%–23% with carbon dioxide levels less than 1%. Once an RA is occupied, due to human breathing, the oxygen levels can decrease, and carbon dioxide levels can increase quickly. One method of providing an RA with a breathable air environment is to use a borehole air supply (BAS) to provide fresh air from the surface, purge existing harmful gases, and prevent harmful gas build-up. RA regulations require air supplies to provide air at 12.5 cubic feet per minute (cfm) per person. To investigate the minimum fresh air flow rate needed to maintain interior oxygen and carbon dioxide levels within the mandated levels, researchers conducted testing in a modified shipping container that represented the volume of an RA. During these tests, propane combustion and additional carbon dioxide supplied from cylinders were used to match human oxygen consumption and carbon dioxide generation. The fresh air flow rate supplied to the shipping container was varied to determine the minimum air flow required for the carbon dioxide level inside the shipping container to stabilize below 1%. The test results showed that the minimum fresh air flow rate was between 1.76–2.12 cfm per person. Therefore, the mandated per-person flow rate provides a 6x–7x safety factor.</p><p>In this paper, researchers at the National Institute for Occupational Safety and Health (NIOSH) provide a repeatable test method that can be used to evaluate the fresh air flow rate versus interior oxygen and carbon dioxide concentrations for various occupancy levels to ensure a breathable air environment within a refuge alternative. The paper provides insight to the hazards associated with harmful levels of each gas and discusses MSHA regulations and previous NIOSH research. Additionally, the paper provides an experimental concept and set-up description, including the propane combustion and carbon dioxide delivery with gas flow rates used to simulate human breathing, data collection sensors, laboratory modifications, and safety measures. Lastly, the paper discusses test results including the amount of time taken to reach hazardous interior gas levels, as well as oxygen and carbon dioxide levels resulting from several fresh air flow rates which have been used to validate a predictive model.</p>

Fresh Air Flow Required to Maintain Safe Carbon Dioxide Levels and Provide a Breathable Air Environment in a Refuge Alternative

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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