Mining Feature: Announcing New Publication on Refuge Alternatives
Wednesday, April 1, 2015
The NIOSH Mining Program has published a new Report of Investigations (RI) on refuge alternatives used in underground coal mines. This is the third RI published by NIOSH on refuge alternatives in the past year, and this RI, entitled “Facilitating the Use of Built-in-place Refuge Alternatives in Mines,” is specifically devoted to examining the use of built-in-place (BIP) refuge alternatives (RAs). By comparison to portable refuge alternatives, BIP RAs are more substantial in size and are constructed in place by the mine operator. In an emergency when immediate escape is not possible due to toxic gases or a blocked escapeway, BIP RAs offer the potential to provide miners with an improved psychological and physiological environment, both because the available air makes the space more comfortable and due to the larger amount of space provided per occupant. Boreholes or protected compressed air line air supply systems also provide a much higher probability of there being communications to the RA.
Despite the advantages of BIP refuge alternatives, as currently designed they cannot be moved frequently from a practical standpoint. Movement of the RA location is required to keep up with dynamic mining production, and as such it would generally be impractical to keep BIP RAs within 1,000 feet of the nearest working face, as prescribed in 30 CFR 75.1506(c), because of the number of times the RA would have to be rebuilt. Currently, there are approximately 30 BIP RAs in U.S. underground coal mines; however, all of these are located outby the face area and none are designed to be advanced with the working face. The usage of BIP RAs that can be advanced with the working face will only be practical if three issues can be addressed:
- locating BIP RAs further from the face;
- providing a consistent process for the design and approval of RA stoppings;
- delivering a reliable supply of clean, breathable air to a BIP RA.
This new Report of Investigations from NIOSH explores these three issues in detail. To obtain relevant and current information, OMSHR researchers visited a number of underground coal mines to view BIP RAs and discuss with mine officials why they employ them. Researchers gathered extensive information on the construction, location, capacity, air supply, and provisioning. Mines in Colorado, Kentucky, Montana, and New Mexico were visited, with the specific mines selected to obtain a cross section of the industry including high and low coal seams and eastern and western coal mines.
To investigate the first issue—the possibility of locating BIP RAs further from the face—NIOSH used three different approaches to determine how far from the face area miners could practically travel, given the 120 minutes of breathing time afforded them by currently available self-contained self-rescuers (SCSRs). This available 120 minutes of breathing time is based on 30 CFR 75.1714-4(a)(1), which calls for the mine operator to provide “at least one additional SCSR, which provides protection for a period of one hour or longer, for each person at a fixed underground work location.” The three approaches used by NIOSH to address this issue were as follows: examining the current distance criteria for SCSR-mandated storage cache locations; performing a timeline study based on worst-case SCSR usage times; and examining established travel times and escape probabilities determined from past NIOSH and U.S. Bureau of Mines research.
To address the second issue—design and approval of RA stoppings—NIOSH analyzed the criteria that engineers must consider when submitting RA stopping designs for approval under the requirements of MSHA’s Refuge Alternatives for Underground Coal Mines rule and MSHA guidelines for coal mine seals. Using the MSHA application guidelines as a model, NIOSH developed extensive guidelines for RA stopping design applications as well as specifications for an RA stopping design to serve as an example. The example stopping design is presented in this RI to illustrate how the proposed design guidelines can be applied in preparing a design submittal to MSHA District Managers for approval.
To explore the third and critical issue—delivering a reliable supply of clean, breathable air to a BIP RA—NIOSH considered the available technologies approved by MSHA for providing breathable air to an RA via a protected compressed air line. NIOSH also analyzed the practical and technical considerations for the surface compressor station and the protected compressed air line.
Combining the results from this investigation, conservative maximum distances from the face to the RA for various entry heights were established, grounded in the assumption that miners have 90 minutes of available travel time in the escapeway to reach the RA. Based on these findings, NIOSH believes that mines could locate built-in-place refuge alternatives at distances from the working face based on the guidance provided by the table below. This table summarizes the study findings, rounding down the most conservative distances arrived at in this report as the maximum BIP RA distances from the face, with these distances varying based on entry height. As noted in the right-most column, the maximum distance that built-in-place refuge alternatives could be located from the face increases as entry height increases.
|Entry height||Approach 1: Based on SCSR-mandated storage cache locations||Approach 2: Based on worst-case SCSR usage times||Approach 3: Based on NIOSH and BOM established travel times and escape probabilities||Maximum BIP RA distance from the face (based on rounded-down most conservative distances)|
|<40 inches||2,200 feet||2,640 feet||NA||2,000 feet|
|>40–<50 inches||3,300 feet||3,960 feet||NA||3,000 feet|
|>50–<65 inches||4,400 feet||5,280 feet||6,000 feet||4,000 feet|
|>65 inches||5,700 feet||6,480 feet||6,500–7,000 feet||5,000 feet|
Allowing mines to locate BIP RAs at greater distances from the working face, as outlined in this table, introduces a number of advantages: (1) a higher likelihood of the BIP RA avoiding damage from both primary and secondary explosions that often occur at the face area, which also increases the likelihood that the communication system to the RA survives a disaster; (2) a reduction in the number of BIP RAs required to be constructed; and (3) the introduction of a wider variety of BIP RA designs, which could potentially improve the safety as well as the psychological and physiological comfort and mental well-being of confined miners.
Despite these advantages, consideration should be given to allowing mines to locate RAs further from the face only if they employ new RA technologies that meet several criteria—specific pressure requirements for the interior atmosphere, the provision of a constant supply of air, and additional RA space per occupant—as detailed in this report.
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