Miners working in underground coal mines are at risk of encountering explosions, as well as various other types of emergency situations. As a result, the Mine Safety and Health Administration (MSHA) requires underground coal mines to have refuge alternatives (RAs). Although these RAs could serve as safe havens in the event of an emergency, heat build-up and changes in humidity could cause severe discomfort to the occupants of RAs.
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MSHA Requirements
To address these challenges, MSHA requires that RAs provide a sustainable environment and breathable air for trapped miners for at least 96 hours. MSHA specifies that the maximum allowable apparent temperature (AT) of RAs must be below 35°C. To comply with these standards, frequent heat and humidity tests inside RAs must be performed by the management team of the mines. In addition to these maintenance requirements, various other methods are often employed in underground mines to monitor and control the thermal environment.
Regulatory Bodies Ensuring Miners’ Safety
The National Institute for Occupational Safety and Health (NIOSH) periodically conducts inspections to assess the functionality of the RAs in mines to ensure the safety of personnel. NIOSH has used various simulation models and conducted several tests to validate both portable and built-in-place (BIP) types of RA. Various kinds of test methods, sensors and devices that heat input devices are used to perform these tests.
A recent 2014 NIOSH test involved the inspection of a 23-person tent-type RA in an experimental mine. During the course of this test, they also assessed the efficacy of a 6-person metal RA and a 60-person BIP RA, both of which were constructed in the experimental mine. These prototypes have been designed to simulate the thermal behavior of an occupied RA and provide useful information on how to improve the development of future RAs.
Quality Assessment and Quality Control of RAs
The regulations set by both MSHA and NIOSH, while crucial for ensuring personnel safety, have caused RA manufacturers some distress as a result of the extensive tests that are required to be performed by their laboratories. For example, consider the fact that a heat input of 117W per person is used to mimic the metabolic heat of a single miner during the course of these inspection tests.
It is therefore challenging for manufacturers to incorporate the miners’ physiological conditions when exposed to certain worst-case scenarios, such as an interruption in mine ventilation during an accident, into a true laboratory test. While there has been steady progress in this area, more work needs to be done to design valid tests that accurately mimic the conditions in the underground mines.
Managing the Thermal Environment in Underground Mines
Surface temperature can vary across the area of the mine, depending on the presence of various major heat sources in the local area. Heat-stress indices installed in underground mines assist during the assessment and regulation of the thermal environment. However, the performance of these underground heat-stress indices varies depending on the environment they are in, as well as the level of activity. Therefore, selecting the appropriate heat-stress index is critical to properly assess the thermal environment of the mines.
Continuous climatic monitoring systems can also be a useful tool in monitoring the thermal environment of mines in real time by providing users with important information on the local thermal environment over a prolonged period. These devices can therefore provide important information that can be used during the designing and engineering of advanced systems used to dissipate the heat generated by the major heat sources inside the mines.
Other climatic models have also been designed to simulate local climatic conditions inside the mine based on airflow conditions and heat load along the ducting system. New generation auxiliary ventilation systems generate less heat as a result of the integration of multiple auxiliary fans. Most importantly, adjusting or upgrading the auxiliary ventilation systems in specified areas of concern could greatly improve the thermal environment of the mines.
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