Evaluation of Thermal Displacement Ventilation in Contamination Purging Inside a 60-Person Built-in-Place Refuge Alternative (BIP RA) in an Underground Coal Mine

Working in an underground coal mine presents several unique safety challenges, including the possibility that coal dust or naturally occurring methane gas can be inadvertently ignited causing a fire or explosion, trapping miners underground. Following several mine disasters in 2006, Congress passed the Mine Improvement and New Emergency Response (MINER) Act to improve mine disaster response. In 2008, federal regulations required the presence of refuge alternatives (RAs) in underground coal mines to ensure miners have a safe place to take refuge after a fire or an explosion if escape is impossible. Both fires and explosions can generate dangerous or even lethal levels of carbon monoxide (CO) in a mine. As part of their function, RAs must be able to isolate miners from a CO-contaminated mine environment and to purge harmful gases that might enter the RA as miners enter. To ensure that RAs can function as intended, National Institute for Occupational Safety and Health (NIOSH) researchers tested two types of ventilation system configurations to purge contamination from inside a 60-person built-in-place (BIP) RA: mixing ventilation system configurations (MVSCs) and thermal displacement ventilation system configurations (TDVSCs). MVSCs deliver fresh air at a high velocity into a volume of low-velocity contaminated air causing the fresh air to mix with the contaminated air. Eventually, the mixed air is exhausted through one or two air outlets located at roof level. TDVSCs deliver fresh air to a volume of contaminated air at a low velocity across a large surface area. This has a piston-like effect on the air inside the volume. Thermal gradients inside the volume lift the contaminants and enhance contaminant removal. For the MVSCs, NIOSH researchers piped air into the BIP RA through one or two air inlets at a high velocity to mix with the stagnant, contaminated air and exhausted the mixed air through one or two air outlets in the BIP RA near roof level. For the TDVSC, NIOSH researchers used three air diffusers at ground level to deliver low velocity air, 60 heated simulated miners to warm the incoming air to create an upward convective air flow, and two air outlets near the roof to exhaust the contaminated air. In previous published research, the team tested 12 MVSCs to determine average purge times and to identify locations inside the BIP RA where the contamination is slow to purge. As a continuation of the purging research, this paper discusses TDVSC testing with the same objectives as the previous tests. All configurations were tested with air flow rates of 750 SCFM—the minimum required flow rate for a 60-person BIP RA—and 1000 SCFM— the maximum flow rate achievable with the air supply used. For both flow rates, the results showed that the average purge time for the more expensive TDVSC was one to two minutes slower than the average purge times of the more economical and simpler MVSCs. Mines can use this information to determine the most practical and effective method to purge contaminants inside BIP RAs.