Last data update: Apr 29, 2024. (Total: 46658 publications since 2009)
Records 1-19 (of 19 Records) |
Query Trace: Yantek D [original query] |
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Cryogenic air supply feasibility for a confined space: Underground refuge alternative case study
Yan L , Yantek DS , DeGennaro CR , Srednicki JR , Lambie B , Carr J . ASME J Heat Mass Transf 2024 146 (3) A breathable air source is required for a confined space such as an underground refuge alternative (RA) when it is occupied. To minimize the risk of suffocation, federal regulations require that mechanisms be provided and procedures be included so that, within the refuge alternative, the oxygen concentration is maintained at levels between 18.5% and 23% for 96 h. The regulation also requires that, during use of the RA, the concentration of carbon dioxide should not exceed 1%, and the concentration of carbon monoxide should not exceed 25 ppm. The National Institute for Occupational Safety and Health (NIOSH) evaluated the cryogenic air supply's ability to provide breathable air for a refuge alternative. A propane smoker was used to simulate human breathing by burning propane gas which will consume O(2) and generate CO(2) and H(2)O. The rate of propane burned at the smoker was controlled to represent the O(2) consumption rate for the breathing of a certain number of people. Two 96-h tests were conducted in a sealed shipping container, which was used as a surrogate for a refuge alternative. While burning propane gas to simulate human oxygen consumption, cryogenic air was provided to the shipping container to determine if the cryogenic air supply would keep the O(2) level above 18.5% and CO(2) level below 1% inside the shipping container as required by the federal regulations pertaining to refuge alternatives. Both of the 96-h tests simulated the breathing of 21 persons. The first test used the oxygen consumption rate (1.32 cu ft of pure oxygen per hour per person) specified in federal regulations, while the second test used the oxygen consumption rate specified by (Bernard et al. 2018, "Estimation of Metabolic Heat Input for Refuge Alternative Thermal Testing and Simulation," Min. Eng., 70(8), pp. 50-54) (0.67 cu ft of pure oxygen per hour per person). The test data shows that during both 96-h tests, the oxygen level was maintained within a 21-23% range, and the CO(2) level was maintained below 1% (0.2-0.45%). The information in this paper could be useful when applying a cryogenic air supply as a breathable air source for an underground refuge alternative or other confined space. [DOI: 10.1115/1.4064062]. |
Evaluation of a prototype local ventilation system to mitigate retail store worker exposures to airborne particles
Lee T , Barone T , Yantek DS , Portnoff L , Zheng Y . J Occup Environ Hyg 2023 20 (7) 1-22 The objective of this study is to evaluate a prototype local ventilation system (LVS) intended to reduce retail store workers' exposures to aerosols. The evaluation was carried out in a large aerosol test chamber where relatively uniform concentrations of polydisperse sodium chloride and glass-sphere particles were generated to test the system with nano- and micro-size particles. In addition, a cough simulator was constructed to mimic aerosols released by mouth breathing and coughing. Particle reduction efficiencies of the LVS were determined in four different experimental conditions using direct reading instruments and inhalable samplers. The particle reduction efficiency (%) depended on the position beneath the LVS, but the percentage was consistently high at the LVS center as follows: 1) > 98% particle reduction relative to background aerosols, 2) > 97% in the manikin's breathing zone relative to background aerosols, 3) > 97% during mouth breathing and coughing simulation, and 4) > 97% with a plexiglass barrier installation. Lower particle reduction (<70%) was observed when the LVS airflow was disturbed by background ventilation airflow. The lowest particle reduction (<20%) was observed when the manikin was closest to the simulator during coughing. |
Mathematical modeling for carbon dioxide level within confined spaces
Yan L , Yantek DS , DeGennaro CR , Fernando RD . ASCE ASME J Risk Uncertain Eng Syst Part B Mech Eng 2023 9 (2) Federal regulations require refuge alternatives (RAs) in underground coal mines to provide a life-sustaining environment for miners trapped underground when escape is impossible. A breathable air supply is among those requirements. For built-in-place (BIP) RAs, a borehole air supply (BAS) is commonly used to supply fresh air from the surface. Federal regulations require that such a BAS must supply fresh air at 12.5 cfm or more per person to maintain the oxygen concentration between 18.5% and 23% and carbon dioxide level below the 1% limit specified. However, it is unclear whether 12.5 cfm is indeed needed to maintain this carbon dioxide level. The minimal fresh air flow (FAF) rate needed to maintain the 1% CO2level will depend on multiple factors, including the number of people and the volume of the BIP RA. In the past, to predict the interior CO2concentration in an occupied RA, 96-h tests were performed using a physical human breathing simulator. However, given the infinite possibility of the combinations (number of people, size of the BIP RA), it would be impractical to fully investigate the range of parameters that can affect the CO2concentration using physical tests. In this paper, researchers at the National Institute for Occupational Safety and Health (NIOSH) developed a model that can predict how the %CO2in an occupied confined space changes with time given the number of occupants and the FAF rate. The model was then compared to and validated with test data. The benchmarked model can be used to predict the %CO2for any number of people and FAF rate without conducting a 96-h test. The methodology used in this model can also be used to estimate other gas levels within a confined space. © 2023 American Society of Mechanical Engineers (ASME). All rights reserved. |
Cryogenic air supply for cooling built-in-place refuge alternatives in hot mine
Yan L , Yantek D , Reyes M , Whisner B , Bickson J , Srednicki J , Damiano N , Bauer E . Min Metall Explor 2020 37 (3) 861-871 Built-in-place (BIP) refuge alternatives (RAs) are designed to provide a secure space for miners who cannot escape during a mine emergency. Heat and humidity buildup within RAs may expose miners to physiological hazards such as heat stress. To minimize the risk of heat stress, Title 30 Code of Federal Regulations (CFR), or 30 CFR, mandates a maximum allowable apparent temperature (AT) for an occupied RA of 35 °C (95 °F) (MSHA 2008 [1]). The National Institute for Occupational Safety and Health (NIOSH) has conducted extensive research on the thermal environment of occupied RAs intended for use in underground coal mines. NIOSH research has demonstrated that a fully occupied BIP RA can exceed the AT limit by > 5.6 °C (10 °F) in mines with elevated mine strata and air temperatures (Bissert et al. 2017 [2]). In this circumstance, an RA cooling system could provide a solution. This paper provides an overview of test methodology and findings as well as guidance on improving the performance of a cryogenic air system prototype by optimizing the flow rate, increasing the tank storage capacity, and improving the efficiency of the heat exchanger of the cryogenic system. This may enable BIP RAs to meet the 35 °C (95 °F) AT limit in mines with elevated temperatures. The information in this paper is useful for RA manufacturers and mines that may choose to implement a cryogenic air system as a heat mitigation strategy. |
Underground mine air and strata temperature change due to the use of refuge alternatives
Yan L , Yantek DS , Reyes MA . Min Metall Explor 2019 37 (2) [Epub ahead of print] Heat and humidity buildup withn refuge alternatives (RAs) may expose occupants to physiological hazards such as heat stress. The Mine Safety and Health Administration (MSHA) regulations require RAs in underground coal mines to provide a life-sustaining environment for miners trapped underground when escape is impossible. RAs are required to sustain life for 96 h while maintaining an apparent temperature (AT) below 95 degrees F (35 degrees C). The National Institute for Occupational Safety and Health (NIOSH) tested a 10-person tent-type RA, a 23-person tent-type RA, and a 6-person metal-type RA in its underground coal mine facilities to investigate the thermal environment over a 96-h period. The test results showed that mine air and mine strata temperatures surrounding an RA occupied by simulated miners (SMs) increased over the 96-h test period. The test results suggest that RA manufacturers should consider this increase in temperatures when calculating and evaluating RA components during surface and laboratory tests. The findings can equip stakeholders with additional considerations for calculating the interior heat and humidity temperature profiles for occupied RAs not tested in situ. |
Underground mine refuge alternatives heat mitigation
Yan L , Yantek D , Lutz T , Yonkey J , Srednicki J . J Therm Sci Eng Appl 2020 12 (2) 021019 In case of an emergency in an underground coal mine, miners who fail to escape from the mine can enter a refuge alternative (RA) for protection from adverse conditions, such as high carbon monoxide levels. One of the main concerns with the use of both portable and built-in-place (BIP) RAs, especially for hot or deep mines, is the interior temperature rise due to the occupants' metabolic heat and the heat released by devices such as the carbon dioxide (CO2) scrubbing system. The humidity within the RA will also increase through occupants' respiration and perspiration and from the chemical reaction within the CO2 scrubbing system. Heat and humidity buildup can subject the occupants to hazardous thermal conditions. To protect RA occupants, Mine Safety and Health Administration regulations mandate a maximum apparent temperature of 95F within an occupied RA. The National Institute for Occupational Safety and Health (NIOSH) tested both an air-conditioned borehole air supply (BAS) and a cryogenic air supply for RAs in the NIOSH Experimental Mine in Bruceton, Pennsylvania. The BAS was tested on a 60-person BIP RA, while the cryogenic air supply was tested on a 30-person BIP RA and a portable 23-person tent-type RA. Multiple tests were conducted with both air supplies to assess their ability to cool RAs. The test results show that the BAS and the cryogenic air supply were able to maintain the apparent temperature within the tested RAs under the 95F limit. The BAS and the cryogenic air supply are potential RA heat mitigation strategies that mines could use to prevent heat/humidity buildup within RAs. |
A test method for evaluating the thermal environment of underground coal mine refuge alternatives
Yantek DS , Yan L , Damiano NW , Reyes MA , Srednicki JR . Int J Min Sci Technol 2019 29 (3) 343-355 Since 2009, the Mine Safety and Health Administration (MSHA) has required mines to install refuge alternatives (RAs) in underground coal mines. One of the biggest concerns with occupied RAs is the possible severity of the resulting thermal environment. In 30 CFR 7.504, the maximum allowable apparent temperature (AT) for an occupied RA is specified as 35 °C (95 °F). Manufacturers must conduct heat/humidity tests to demonstrate that their RAs meet the 35 °C (95 °F) AT limit. For these tests, heat input devices are used to input the metabolic heat of actual miners. A wide variety of test methods, sensors, and heat input devices could be used when conducting such tests. Since 2012, the National Institute for Occupational Safety and Health (NIOSH) has conducted over thirty 96-hour heat/humidity tests on four different RAs. This paper discusses the test equipment and procedures used during these investigations. This information is useful for RA manufacturers conducting RA heat/humidity tests, for other researchers investigating RA heat/humidity buildup, and for those who need to assess the thermal environment of any confined space where people may be trapped or are seeking refuge. |
Portable refuge alternatives temperature and humidity tests
Yan L , Yantek D . Min Eng 2018 70 (10) 43-49 Federal regulations require refuge alternatives in underground coal mines to sustain life for 96 h while maintaining an apparent temperature below 35 C (95 F). Research by the U.S. National Institute for Occupational Safety and Health (NIOSH) has shown that heat and humidity buildup is a major concern with refuge alternatives because they have limited ability to dissipate heat, and high internal air temperature and relative humidity (RH) may expose occupants to heat stress. The heat transfer process within and surrounding a refuge alternative is complex and not easily defined, analytically or experimentally. To investigate heat and humidity buildup in refuge alternatives, NIOSH conducted multiple in-mine, 96-h tests on a 10-person tent-type refuge alternative, a 23-person tent-type refuge alternative and a six-person metal-type refuge alternative. The results show that when moisture was introduced to represent perspiration and respiration from miners (wet tests), the average temperature at midheight increased by 10.5 C (18.9 F) and the RH approached 88 percent for the 10-person tent-type refuge alternative; the average temperature at midheight increased by 9.4 C (16.9 F) and the RH approached 94 percent for the 23-person tent-type refuge alternative; and the average temperature at midheight increased by 7.7 C (13.9 F) and the RH approached 95 percent for the six-person metal-type refuge alternative. For the dry tests, where no moisture was introduced, the average internal temperature increased by 12.6 C (22.7 F) for the 10-person tent-type refuge alternative, by 10.3 C (18.5 F) for the 23-person tent-type refuge alternative and by 8.4 C (15.1 F) for the six-person metal-type refuge alternative. These results may provide refuge alternative manufacturers and mine operators with guidelines and considerations for evaluating temperature profiles for portable refuge alternatives. The information may then be used to make decisions on occupancy ratings and heat mitigation strategies based on the thermal environment in which the refuge alternatives will be installed. |
Estimation of metabolic heat input for refuge alternative thermal testing and simulation
Bernard TE , Yantek DS , Thimons ED . Min Eng 2018 70 (8) 50-54 Refuge alternatives provide shelter to miners trapped underground during a disaster. Manufacturers must demonstrate that their refuge alternatives meet the U.S. Mine Safety and Health Administration (MSHA) requirements for oxygen supply, carbon dioxide removal, and management of heat from the occupants and mechanical/chemical systems. In this study, miner size and activity level were used to determine the metabolic heat rate, oxygen requirements and carbon dioxide generation that are representative of miners in a refuge situation. A convenience sample of 198 male miners was used for the distribution of current U.S. coal miners, and the composite 95th percentile height and weight were determined to be 193 cm (76 in.) and 133 kg (293 lb). The resting metabolic rate (RMR) was determined to be representative of activity level in a refuge alternative. The highest likely metabolic heat generation ranged from 113 to 134 W, depending on occupancy. The highest required oxygen supply and carbon dioxide removal were estimated to be 23 L (0.81 cu ft) of oxygen per hour per person and 20 L (0.71 cu ft) of carbon dioxide per hour per person, which means the margin of safety is 50 percent or more compared with the MSHA requirements. The information on metabolic heat generation can be used to assess refuge alternative thermal environments by testing or simulation. The required oxygen supply and carbon dioxide removal can be used to assess refuge alternative requirements. |
Prediction of human core temperature rise and moisture loss in refuge alternatives for underground coal mines
Klein M , Yantek DS , Hepokoski M , Yan L . Trans Soc Min Metall Explor Inc 2017 342 29-35 Research by the U.S. National Institute for Occupational Safety and Health (NIOSH) has shown that heat/humidity buildup is a major concern within coal mine refuge alternatives. High temperature and humidity levels inside a refuge alternative may expose occupants to heat stress. Due to the safety risks associated with testing using human subjects, NIOSH partnered with ThermoAnalytics Inc. to create detailed thermal simulation models of refuge alternatives with human occupants. The objective of this effort was to predict a miner's core temperature response and moisture loss in environments that may be encountered in a coal mine refuge alternative. These parameters were studied across a range of temperatures and relative humidity values to determine if the current 35 °C (95 °F) apparent temperature limit for refuge alternatives is reasonable. The results indicate that the apparent temperature limit is protective, provided that miners are supplied with sufficient water. The results also indicate that the body core temperature does not reach dangerous levels even at an apparent temperature of 54 °C (130 °F). However, the results show that moisture loss increases with apparent temperature. Therefore, if the apparent temperature limit were raised, the water provided in a refuge alternative would have to be increased to offset moisture loss. |
Effects of mine strata thermal behavior and mine initial temperatures on mobile refuge alternative temperature
Yantek DS , Yan L , Bissert PT , Klein MD . Min Eng 2017 69 (4) 41-48 Federal regulations require the installation of refuge alternatives (RAs) in underground coal mines. Mobile RAs have a limited ability to dissipate heat, and heat buildup can lead to a life-threatening condition as the RA internal air temperature and relative humidity increase. The U.S. National Institute for Occupational Safety and Health (NIOSH) performed heat testing on a 10-person tent-type training RA and contracted ThermoAnalytics Inc. to develop a validated thermal simulation model of the tested RA. The model was used to examine the effects of the constant mine strata temperature assumption, initial mine air temperature, initial mine strata surface temperature (MSST), initial mine strata temperature at depth (MSTD) and mine strata thermal behavior on RA internal air temperature using 117 W (400 Btu/h) of sensible heat input per simulated miner. For the studied RA, when the mine strata temperature was treated as a constant, the final predicted RA internal air temperature was 7.1 C (12.8 F) lower than it was when the mine strata thermal behavior was included in the model. A 5.6 C (10 F) increase in the initial MSST resulted in a 3.9 C (7.1 F) increase in the final RA internal air temperature, whereas a 5.6 C (10 F) increase in the initial MSTD yielded a 1.4 C (2.5 F) increase in the final RA internal air temperature. The results indicate that mine strata temperature increases and mine strata initial temperatures must be accounted for in the physical testing or thermal simulations of RAs. |
Temperature rise within a mobile refuge alternative - experimental investigation and model validation
Yan L , Yantek D , Klein M , Bissert P , Matetic R . J Therm Sci Eng Appl 2017 9 (2) 021003 Mine Safety and Health Administration (MSHA) regulations require underground coal mines to install refuge alternatives (RAs). In the event of a disaster, RAs must be able to provide a breathable air environment for 96 h. The interior environment of an occupied RA, however, may become hot and humid during the 96 h due to miners' metabolic heat and carbon dioxide scrubbing system heat. The internal heat and humidity may result in miners suffering heat stress or even death. To investigate heat and humidity buildup with an occupied RA, the National Institute for Occupational Safety and Health (NIOSH) conductedtesting on a training ten-person, tent-type RA in its Safety Research Coal Mine (SRCM) in a test area that was isolated from the mine ventilation system. The test results showed that the average measured air temperature within the RA increased by 11.4 ±C (20.5 °F) and the relative humidity approached 90% RH. The test results were used to benchmark a thermal simulation model of the tested RA. The validated thermal simulation model predicted the average air temperature inside the RA at the end of 96 h to within 0.6 °C (1.1 °F) of the measured average air temperature. |
Analysis of heat loss mechanisms for mobile tent-type refuge alternatives
Bissert PT , Yantek DS , Klein MD , Yan L . Trans Soc Min Metall Explor Inc 2016 340 (1) 70-74 Federal regulations require that refuge alternatives (RAs) be located within 305 m (1,000 ft) of the working face and spaced at one-hour travel distances in the outby area in underground coal mines, in the event that miners cannot escape during a disaster. The Mine Safety and Health Administration mandates that RAs provide safe shelter and livable conditions for a minimum of 96 hours while maintaining the apparent temperature below 35 °C (95 °F). The U.S. National Institute for Occupational Safety and Health used a validated thermal simulation model to examine the mechanisms of heat loss from an RA to the ambient mine and the effect of mine strata composition on the final internal dry bulb temperature (DBT) for a mobile tent-type RA. The results of these studies show that 51 percent of the heat loss from the RA to the ambient mine is due to radiation and 31 percent to conduction. Three mine width and height configurations and four mine strata compositions were examined. The final DBT inside the RA after 96 hours varied by less than 1 °C (1.8 °F) for the three mine width/height configurations and by less than 2 °C (3.6 °F) for the four mine strata compositions. |
Examination of a newly developed mobile dry scrubber (DS) for coal mine dust control applications
Organiscak J , Noll J , Yantek D , Kendall B . Trans Soc Min Metall Explor Inc 2016 340 38-47 The Office of Mine Safety and Health Research of the U.S. National Institute for Occupational Safety and Health (NIOSH OMSHR) conducted laboratory testing of a self-tramming, remotely controlled mobile Dry Scrubber (DS) that J.H. Fletcher and Co. developed under a contract with NIOSH OMSHR to reduce the exposure of miners to airborne dust. The scrubber was found to average greater than 95 percent dust removal efficiency with disposable filters, and 88 and 90 percent, respectively, with optional washable filters in their prewash and post-wash test conditions. Although the washable filters can be reused, washing them generated personal and downstream respirable dust concentrations of 1.2 and 8.3 mg/m(3), respectively, for a 10-min washing period. The scrubber's velocity-pressure-regulated variable-frequency-drive fan maintained relatively consistent airflow near the targeted 1.42 and 4.25 m(3)/s (3,000 and 9,000 ft(3)/min) airflow rates during most of the laboratory dust testing until reaching its maximum 60-Hz fan motor frequency or horsepower rating at 2,610 Pa (10.5 in. w.g.) of filter differential pressure and 3.97 m(3)/s (8,420 ft(3)/min) of scrubber airflow quantity. Laboratory sound level measurements of the scrubber showed that the outlet side of the scrubber was noisier, and the loaded filters increased sound levels compared with clean filters at the same airflow quantities. With loaded filters, the scrubber reached a 90 dB(A) sound level at 2.83 m(3)/s (6,000 ft(3)/min) of scrubber airflow, indicating that miners should not be overexposed in relation to MSHA's permissible exposure level - under Title 30 Code of Federal Regulations Part 62.101- of 90 dB(A) at or below this airflow quantity. The scrubber's washable filters were not used during field-testing because of their lower respirable dust removal efficiency and the airborne dust generated by filter washing. Field-testing the scrubber with disposable filters at two underground coal mine sections showed that it could clean a portion of the section return air and provide dust reduction of about 50 percent at the face area downstream of the continuous-miner operation. |
Validation of temperature and humidity thermal model of 23-person tent-type refuge alternative
Yan L , Yantek D , Klein M , Bissert P , Matetic R . Min Eng 2016 68 (9) 97-103 U.S. Mine Safety and Health Administration (MSHA) regulations require underground coal mines to use refuge alternatives (RAs) to provide a breathable air environment for 96 hours. One of the main concerns with the use of mobile RAs is heat and humidity buildup inside the RA. The accumulation of heat and humidity can result in miners suffering heat stress or even death. MSHA regulations require that the apparent temperature in an occupied RA not exceed 95 °F. To investigate this, the U.S. National Institute for Occupational Safety and Health (NIOSH) conducted testing on a 23-person tent-type RA in its Experimental Mine in a test area that was isolated from the mine ventilation system. The test results showed that the average measured air temperature within the RA increased by 9.4 °C (17 °F) and the relative humidity approached 94 percent at the end of a 96-hour test. The test results were used to benchmark a thermal simulation model of the tested RA. The validated thermal simulation model predicted the volume-weighted average air temperature inside the RA tent at the end of 96 hours to within 0.06 °C (0.1 °F) of the average measured air temperature. |
Evaluations of a noise control for roof bolting machines
Azman AS , Yantek DS , Alcorn lA . Min Eng 2012 64 (12) 64-70 In collaboration with Kennametal Inc. and Corry Rubber Corporation, the U.S. National Institute for Occupational Safety and Health (NIOSH) developed a drill bit isolator to address noise overexposures associated with roof bolting machines in underground coal mines. NIOSH laboratory studies confirmed that the drill bit isolator reduces noise during drilling. Field studies were needed to confirm that a noise reduction could be obtained under working conditions and that the device was sufficiently durable. This paper reports results of field tests of the device conducted at five underground coal mines. Noise reduction was assessed by comparing the operator’s noise exposure during drilling with and without the drill bit isolator. Durability was assessed by recording the number of holes and total feet drilled with each bit isolator until either the test period ended or the device failed. The results from these tests showed that the device is an effective noise control in a mine environment. The field-tested drill bit isolators provided a noise reduction of 3-5 dB(A). Of nine devices tested for durability, five exceeded 610 m (2,000 ft) drilled and two exceeded 762 m (2,500 ft) drilled before failure. Durability issues found in the field tests led to final production optimizations that have resulted in a commercially available product for drilling with 35-mm- (1.3-in.-) diameter roof bits and hexagonal drill steels. |
Acoustic testing facilities at the Office of Mine Safety and Health Research
Peterson JS , Yantek D , Smith AK . Noise Control Eng J 2012 60 (1) 85-96 The National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) maintains a noise control program as part of its Hearing Loss Prevention Branch (HLPB). This program utilizes two large acoustic laboratories-a reverberation chamber and a hemi-anechoic chamber-to assist OMSHR engineers with the development and evaluation of noise controls. This paper discusses the design, instrumentation, and use of the NIOSH acoustics laboratories and the important role they play in noise control development and evaluation. The NIOSH reverberation chamber meets the absorption, reverberation time, and test room broadband qualification requirements specified in the ISO 3741/ANSI S12.51 acoustics standard for precision method sound power testing. As part of a qualification testing program, NIOSH conducted an uncertainty estimate for sound power level testing in the chamber. For an overall sound power measurement, this uncertainty estimate was 0.4 dB. The NIOSH hemi-anechoic chamber, which uses Eckel Industries SuperSoft Panels on the walls and ceiling, is used primarily for noise source identification to determine significant noise sources on equipment. Testing was completed to ensure that the chamber functions as a free-field. The SuperSoft panels met NIOSH requirements and the chamber was verified as a free-field per the test room qualification criteria set forth in ISO 3745. ((C) 2012 Institute of Noise Control Engineering.) |
Development of elastomeric isolators to reduce roof bolting machine drilling noise
Michael R , Yantek D , Johnson D , Ferro E , Swope C . Noise Control Eng J 2011 59 (6) 591-612 Among underground coal miners, hearing loss remains one of the most common occupational illnesses. In response to this problem, the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) conducts research to reduce the noise emission of underground coal-mining equipment, an example of which is a roof bolting machine. Field studies show that, on average, drilling noise is the most significant contributor to a roof bolting machine operator's noise exposure. NIOSH OMSHR has determined that the drill steel and chuck are the dominant sources of drilling noise. NIOSH OMSHR, Corry Rubber Corporation, and Kennametal, Inc. have developed a bit isolator that breaks the steel-to-steel link between the drill bit and drill steel and a chuck isolator that breaks the mechanical connection between the drill steel and the chuck, thus reducing the noise radiated by the drill steel and chuck, and the noise exposure of the roof bolter operator. This paper documents the evolution of the bit isolator and chuck isolator including various alternative designs which may enhance performance. Laboratory testing confirms that production bit and chuck isolators reduce the A-weighted sound level generated during drilling by 3.7 to 6.6 dB. Finally, this paper summarizes results of a finite element analysis used to explore the key parameters of the drill bit isolator and chuck isolator to understand the impact these parameters have on noise. (2011 Institute of Noise Control Engineering.) |
Analysis of a mechanism suspension to reduce noise from horizontal vibrating screens
Yantek DS , Lowe MJ . Noise Control Eng J 2011 59 (6) 568-580 A-weighted sound levels around vibrating screens in coal preparation plants often exceed 90 dB. The National Institute for Occupational Safety and Health (NIOSH) is developing noise controls to reduce noise generated by horizontal vibrating screens. Horizontal vibrating screen noise is dominated by sound radiated from the screen body. NIOSH researchers analyzed a mechanism suspension system that could reduce screen body-radiated noise. A finite element (FE) model of the entire screen was used to analyze the screen with the added mechanism suspension. The spring rates for the mechanism suspension were tuned to transmit vibration at the mechanism operating speed while attenuating vibration transmitted from the mechanisms to the screen body at frequencies above 100 Hz. The FE results were used to estimate the A-weighted sound power level radiated by the screen sides and feedbox for various mechanism suspension spring rates. The results indicate that a tuned mechanism suspension could reduce the A-weighted sound power level radiated by the screen body due to gear and bearing forces inside the mechanisms by 7 to 18 dB. |
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