Carl Sunderman

A Handheld Electrostatic Precipitator for Sampling Airborne Particles and Nanoparticles

Researchers at NIOSH are developing methods for characterizing ultrafine aerosols in workplaces. One method includes the detailed analysis of collected particles using electron microscopy (EM). In order to collect samples for EM at remote workplaces including mining and manufacturing facilities, researchers have developed a handheld electrostatic precipitator (ESP) particle sampler capable of collecting airborne particles including nanoscale materials, for subsequent EM analysis. The handheld ESP has been tested in the laboratory and is currently undergoing beta testing in the field. Gross collection efficiencies were measured with a CPC and net efficiencies by EM analysis of collected samples. Using laboratory-generated NaCl aerosols in the 30–400 nm size range at a flow rate of 55 cc/min and ESP operating voltages between 5.6–6.8 kV, both gross and net efficiencies were measured and showed a similar correlation with voltage, with maximum efficiency of approximately 86% at 6.4 kV. EM images from samples were also used to estimate particle size distributions of the original aerosols and the size-dependent deposition was evaluated for upstream versus downstream locations on the sample media. Results suggest that the number concentration and particle size distribution of sampled aerosols may potentially be estimated from a single ESP sample, but that the accuracy and repeatability of such quantification need to be investigated and refined. NIOSH is planning to license the ESP sampler for commercial manufacturing.

Measurements and Modeling of Through-the-Earth Communications for Coal Mines

This paper presents modeling results from the National Institute for Occupational Safety and Health research into through-the-earth (TTE) communications technology for underground coal mines. Research focuses on the factors controlling the propagation and coupling of radio signals between transmit and receive antennas separated by earth or coal. Most TTE systems use single or multiturn loops of conductor for the transmit antenna. We compare the magnetic field distribution predicted from analytical formulas to the predictions of a method of moments computational electromagnetic (CEM) code. The predictions are compared in free space, in a homogeneous earth, and with the effect of the presence of the surface of the earth. The evaluations are done with the transmit loop buried in the earth and with the loop above the surface. The analytic results are shown to agree reasonably well with the more detailed CEM predictions for the situations considered, reducing the need for expensive and complicated CEM codes in analyzing simple TTE configurations. The predictive methods are applied to TTE measurements made in 94 different coal mines by the Bureau of Mines in the 1970s, and the implications for the apparent conductivity of the earth are discussed.

Measurements and modeling of through-the-earth communications for coal mines

This paper presents modeling results from the National Institute for Occupational Safety and Health research into through-the-earth (TTE) communications technology for underground coal mines. Research focuses on the factors controlling the propagation and coupling of radio signals between transmit and receive antennas separated by earth or coal. Most TTE systems use single or multiturn loops of conductor for the transmit antenna. We compare the magnetic field distribution predicted from analytical formulas to the predictions of a method of moments computational electromagnetic (CEM) code. The predictions are compared in free space, in a homogeneous earth, and with the effect of the presence of the surface of the earth. The evaluations are done with the transmit loop buried in the earth and with the loop above the surface. The analytic results are shown to agree reasonably well with the more detailed CEM predictions for the situations considered, reducing the need for expensive and complicated CEM codes in analyzing simple TTE configurations. The predictive methods are applied to TTE measurements made in 94 different coal mines by the Bureau of Mines in the 1970s, and the implications for the apparent conductivity of the earth are discussed.

An overview of underground coal miner electronic tracking system technologies

Since the passage of the Mine Improvement and New Emergency Response Act (MINER Act) of 2006, several electronic tracking systems that inform personnel on the surface of a coal mine about the location of miners underground have become commercially available. These systems can be broadly categorized into technology groups that are described in this paper. In addition, several other technologies have been identified by the National Institute for Occupational Safety and Health (NIOSH) Office of Mine Safety and Health Research (OMSHR) that show promise to increase location accuracy, reduce installed infrastructure, or otherwise improve the performance of existing systems. This paper will describe tracking system technologies currently installed in US coal mines and discuss some emerging technologies.

Statistical analysis and modeling of VLF/ELF noise in coal mines for through-the-earth wireless communications

The through-the-earth (TTE) wireless communication system, in which the RF signal can directly penetrate the earth separating a transmitter and receiver, is likely to survive a mine disaster because it requires no cabling between the surface and underground. One of the biggest challenges for TTE communication is that the ambient electromagnetic (EM) noise can be significant and impose a limitation on the reception sensitivity. Both underground and surface RF noise characteristics were obtained and analyzed from experimental data collected at several coal mines. The results show the surface has a higher noise level than underground. Moreover, the parameters obtained in an empirical noise model can be used to predict a TTE systems performance at a specific mine site.

A novel application of photogrammetry to ground convergence monitoring in underground excavations

Researchers from the National Institute for Occupational Safety and Health (NIOSH) Spokane Mining Research Division (SMRD) are evaluating the comparative performances of ground convergence monitoring methods currently utilized in underground mining. A portion of this research is exploring applications of photogrammetry for periodic visual assessment of slow-converging ground. This paper describes the photogrammetric systems evaluated, including their components and methodology. These systems include light-weight equipment easily carried by a single individual traversing rough terrain in underground mine environments. This study demonstrates how photogrammetric methods may complement or replace existing underground convergence monitoring techniques on the basis of time and personnel requirements, equipment cost and robustness, and overall data quality. This research supplements previous studies into photogrammetric and laser scanning methods, and enhances understanding of how digital technology may be utilized to maximize safety in underground excavations. NIOSH SMRD is committed to improving workforce health and safety through innovative research and applications of technology.

Instrumentation and data acquisition for dynamic testing of ground support

The Spokane Mining Research Division (SMRD) of the National Institute for Occupational Safety and Health has recently developed a dynamic testing machine that imparts a controlled shock to a ground support test panel in order to investigate the effects of seismic loading on the material. Dynamic testing is critical for understanding the mechanical response of ground support used in seismically active locations of a mine. In the past, dynamic testing of ground support has generally been somewhat qualitative, but currently more quantitative testing is being employed. This paper describes the sensors and data acquisition system used to record the dynamic measurements of the shock tests performed by SMRD. It includes a discussion of sensor selection and installation to serve as an initial guide for future research. Testing of ground support and its response to dynamic loading can lead to developments that improve mine worker safety in seismically active underground mines.

Antenna arrangement investigation for through-the-earth (TTE) communications in coal mines

The MINER Act of 2006 requires the installation of post-accident, two-way, communications and electronic tracking systems for all coal mines. A through-the-earth (TTE) wireless communication system sends its signal directly through the overburden of a mine but can have limitation relative to performance, reliability, and transmission range. The National Institute for Occupational Safety and Health (NIOSH) conducted experiments at a coal mine for different TX/RX antenna arrangements using a NOISH TTE prototype system. This system uses multi-turn, relative small TX loop antenna instead of single turn, relative large TX loop antenna. The objectives of the test are to evaluate the performance of the system, to evaluate the path loss and optimize working frequency for the mine, to characterize surface and underground electromagnetic noise, and to investigate the feasibility of horizontal TTE communication and its advantage over vertical TTE communications. In this paper, the performance of a magnetic loop TTE communication system was evaluated for various antenna arrangements. A fairly large communication range was achieved for horizontal TTE transmission. While vertical TTE communication between underground and the surface may be restricted by factors like deployment challenges of the surface TX antenna and short transmission ranges, horizontal TTE communication within the tunnel can reach relative large distances and can thus establish a more reliable communication. Moreover, the combination of vertical and horizontal TTE communication may provide a way to considerably increase communication range.

Loop coupling and field distribution in earth for horizontal positioning in VLF/ELF through-the-earth wireless mine communications

A through-the-earth (TTE) wireless communication system is the system most likely to survive after a mine disaster because its signal penetrates the earth directly and does not use wires connecting the surface and underground components. Typically, the transmit (Tx) and receive (Rx) antennas are vertically separated by the earth overburden in a coaxial arrangement. In this paper, we show that there are advantages to separating the Tx and Rx antennas horizontally (co-planar arrangement), hence, communicating within the mine itself, and offering the advantage of mobility for one of the antennas. In this paper, we present a two-layer model, with both Tx loop and Rx loop antennas buried at the same depth underground. The magnetic field distribution results at the Rx loop are obtained for various conditions, such as earth conductivity, conductivity contrast between two layers, and co-planar and co-axis for the same Tx and Rx separation distance, providing us with an understanding of the parameters that control the performance and a concise method to predict the performance of a co-planar TTE loop communication system.

A system for measuring through-the-earth radio propagation

A measurement system used in through-the-earth magnetic field signal attenuation measurements is described. In addition, an associated calibration system for determining the magnetic antenna factor of a receive antenna is also described. Attenuation data at frequencies ranging from 300 to 3000 Hz was collected at an active coal mine with 201 m of overburden using the system. Results suggest that the data collected fits existing analytical models. Use of this system assists researchers by validating Through-the-earth (TTE) models and increases our understanding of the performance limitations of TTE systems.