In 2008, the Mine Safety and Health Administration (MSHA) published a final rule on Refuge Alternatives (RAs) for Underground Coal Mines. The rule states that RAs shall be capable of sustaining trapped miners for 96 hours and that RAs can also be used to facilitate escape by sustaining trapped miners until they receive communications regarding escape options. As of 2014, there were three types of coal mine RAs manufactured by 10 different companies and at least 13 different communications systems approved for use underground. However, there is no specific guidance on how to determine if such a wide variety of systems will facilitate successful communication in an emergency. Examples in this study detail one representative example of each of the three types of RAs. Each example RA was tested underground in an experimental coal mine by researchers from the National Institute for Occupational Safety and Health (NIOSH). The purpose of the testing was to determine a representative signal attenuation caused by a specific RA’s wall material and entrance door. For each RA type, the signal loss was investigated using comparative measurements. Test results showed an average difference of 3 decibel milliwatts (dBm) for a tent type RA, 15 dBm for a metal RA and 14 dBm for a Built-in-Place RA for a frequency range of 150 to 3000 MHz. These results can be used in calculating the available link budget for a communication system to determine if a signal will reach the inside of the RA.

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