Miguel A. Reyes

Evaluation of Visual Performance When Using Incandescent, Fluorescent, and LED Machine Lights in Mesopic Conditions

This experiment investigated the effects of different machine-mounted area lighting technologies on visual performance in a simulated underground mine environment. The primary objective was to conduct a comparative evaluation of the lighting technologies based on the visual performance of 36 human subjects in a simulated underground mine environment. Incandescent (Incand), fluorescent (Fluor), and light-emitting diode (LED) technologies were used to create four lighting combinations. Visual performance was quantified for the detection of movement in the peripheral field of view and the identification of ground hazards. Measurements were made of the speed (response time measured in milliseconds), the accuracy (the number of targets and objects missed), and the subjective discomfort rating of the glare experienced for each lighting combination. A secondary objective explored the effects of aging on visual performance. The results indicate that lighting combinations which consisted of LED area lights significantly improved visual performance for the detection of hazards found in the peripheral field of view, as well as those found on the ground. They furthermore indicate that age plays a significant role in visual performance.

Comparative evaluation of Light Emitting Diode cap lamps with an emphasis on visual performance in mesopic lighting conditions

Conducted at the National Institute for Occupational Safety and Healths (NIOSH) Office of Mine Safety and Health Research, the experiment described in this paper is part of ongoing mine illumination research designed to explore the benefits of solid-state lighting technologies when applied to the underground mining industry. This experiment involves the comparative evaluation of cap lamps with similar spectral power distributions, focusing on the electrical and battery discharge characteristics, with a secondary objective being the benefits gained through alternative light beam distributions. NIOSH researchers conducted the investigation by comparing three commercially available light-emitting diode cap lamps and an NIOSH prototype cap lamp at varying power settings. Visual performance for the detection of hazards was quantified by recording times of detection for finding rotating targets in the peripheral field of view and objects representing trip and fall hazards on the ground. The NIOSH prototype cap lamp resulted in improvements ranging from 15% to 43% for peripheral motion detection time and 5%-23% for slip, trip, and fall object detection time, respectively, as compared with the referent incandescent cap lamp.

Visual performance for trip hazard detection when using incandescent and led miner cap lamps

INTRODUCTION Accident data for 2003-2007 indicate that slip, trip, and falls (STFs) are the second leading accident class (17.8%, n=2,441) of lost-time injuries in underground mining. Proper lighting plays a critical role in enabling miners to detect STF hazards in this environment. Often, the only lighting available to the miner is from a cap lamp worn on the miners helmet. The focus of this research was to determine if the spectral content of light from light-emitting diode (LED) cap lamps enabled visual performance improvements for the detection of tripping hazards as compared to incandescent cap lamps that are traditionally used in underground mining. A secondary objective was to determine the effects of aging on visual performance. METHOD The visual performance of 30 subjects was quantified by measuring each subjects speed and accuracy in detecting objects positioned on the floor both in the near field, at 1.83 meters, and far field, at 3.66 meters. Near field objects were positioned at 0 degrees and +/-20 degrees off axis, while far field objects were positioned at 0 degrees and +/-10 degrees off axis. Three age groups were designated: group A consisted of subjects 18 to 25 years old, group B consisted of subjects 40 to 50 years old, and group C consisted of subjects 51 years and older. RESULTS Results of the visual performance comparison for a commercially available LED, a prototype LED, and an incandescent cap lamp indicate that the location of objects on the floor, the type of cap lamp used, and subject age all had significant influences on the time required to identify potential trip hazards. The LED-based cap lamps enabled detection times that were an average of 0.96 seconds faster compared to the incandescent cap lamp. Use of the LED cap lamps resulted in average detection times that were about 13.6% faster than those recorded for the incandescent cap lamp. The visual performance differences between the commercially available LED and prototype LED cap lamp were not statistically significant. IMPACT ON INDUSTRY It can be inferred from this data that the spectral content from LED-based cap lamps could enable significant visual performance improvements for miners in the detection of trip hazards.

Comparative Evaluation of Light-Emitting Diode Cap Lamps With an Emphasis on Visual Performance in Mesopic Lighting Conditions

Conducted at the National Institute for Occupational Safety and Healths (NIOSH) Office of Mine Safety and Health Research, the experiment described in this paper is part of ongoing mine illumination research designed to explore the benefits of solid-state lighting technologies when applied to the underground mining industry. This experiment involves the comparative evaluation of cap lamps with similar spectral power distributions, focusing on the electrical and battery discharge characteristics, with a secondary objective being the benefits gained through alternative light beam distributions. NIOSH researchers conducted the investigation by comparing three commercially available light-emitting diode cap lamps and an NIOSH prototype cap lamp at varying power settings. Visual performance for the detection of hazards was quantified by recording times of detection for finding rotating targets in the peripheral field of view and objects representing trip and fall hazards on the ground. The NIOSH prototype cap lamp resulted in improvements ranging from 15% to 43% for peripheral motion detection time and 5%-23% for slip, trip, and fall object detection time, respectively, as compared with the referent incandescent cap lamp.

Intelligent Machine Guard Monitoringing: A Wireless System to Improve Miner Safety

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are developing an intelligent machine guard monitoring and proximity detection system designed to mitigate machine entanglement and maintenance-related injuries and fatalities prevalent in the mining industry. This experiment was designed to develop a monitoring system consisting of mechanical/magnetic switches and sensor beacons capable of wirelessly transmitting information about a belt conveyors machine guards to a remote computer. The data transfer was carried out via an off-the-shelf wireless communication system and displayed on a Web-based user interface. Successful operational tests demonstrated the functionality and effectiveness of the system in monitoring guard placement status and remotely identifying the location of any removed guards using each sensors unique identification number. The integration of wireless safety technologies such as this system is expected to improve the safety of miners by providing additional protections against machine guardingrelated injuries.

Wireless machine guard monitoring system

National Institute for Occupational Safety and Health (NIOSH) researchers are developing an intelligent machine guard monitoring and proximity detection system designed to mitigate machine entanglement and maintenance-related injuries and fatalities prevalent in the mining industry. This experiment was designed to develop a monitoring system consisting of mechanical/magnetic switches and sensor beacons capable of wirelessly transmitting information about a belt conveyors machine guards to a remote computer. The data transfer was carried out via an off-the-shelf wireless communication system and displayed on a web-based user interface. Successful operational tests demonstrated the functionality and effectiveness of the system in monitoring guard placement status and remotely identifying the location of any removed guards using each sensors unique identification number. The integration of wireless safety technologies such as this system is expected to improve the safety of miners by providing additional protections against machine guarding-related injuries.

Mathematical modeling and measurement of electric fields of electrode-based through-the-earth (TTE) communication

There are two types of through-the-earth (TTE) wireless communication in the mining industry: magnetic loop TTE and electrode-based (or linear) TTE. While the magnetic loop systems send signal through magnetic fields, the transmitter of an electrode-based TTE system sends signal directly through the mine overburden by driving an extremely low frequency (ELF) or ultralow frequency (ULF) AC current into the earth. The receiver at the other end (underground or surface) detects the resultant current and receives it as a voltage. A wireless communication link between surface and underground is then established. For electrode-based TTE communications, the signal is transmitted through the established electric field and is received as a voltage detected at the receiver. It is important to understand the electric field distribution within the mine overburden for the purpose of designing and improving the performance of the electrode-based TTE systems. In this paper, a complete explicit solution for all three electric field components for the electrode-based TTE communication was developed. An experiment was conducted using a prototype electrode-based TTE system developed by National Institute for Occupational Safety and Health. The mathematical model was then compared and validated with test data. A reasonable agreement was found between them.

Time Domain and Frequency Domain Deterministic Channel Modeling for Tunnel/Mining Environments

Understanding wireless channels in complex mining environments is critical for designing optimized wireless systems operated in these environments. In this paper, we propose two physics-based, deterministic ultra-wideband (UWB) channel models for characterizing wireless channels in mining/tunnel environments - one in the time domain and the other in the frequency domain. For the time domain model, a general Channel Impulse Response (CIR) is derived and the result is expressed in the classic UWB tapped delay line model. The derived time domain channel model takes into account major propagation controlling factors including tunnel or entry dimensions, frequency, polarization, electrical properties of the four tunnel walls, and transmitter and receiver locations. For the frequency domain model, a complex channel transfer function is derived analytically. Based on the proposed physics-based deterministic channel models, channel parameters such as delay spread, multipath component number, and angular spread are analyzed. It is found that, despite the presence of heavy multipath, both channel delay spread and angular spread for tunnel environments are relatively smaller compared to that of typical indoor environments. The results and findings in this paper have application in the design and deployment of wireless systems in underground mining environments.

Measurement and modeling of radio propagation from a primary tunnel to cross junctions

In this paper, we propose a new model for predicting around-corner coupling loss associated with radio signals propagating from a primary tunnel to cross junctions. The proposed model is based on the classic modal method that has been widely used for predicting power distribution in straight tunnels. The uniform theory of diffraction (UTD) is applied to calculate mode coupling coefficients. Simulation results based on the proposed model are compared to measurement results taken in a concrete tunnel and show good agreement.

Propagation parameters for medium frequency signals in a transmission line at different positions within a mine entry

A medium frequency (MF) communication system used in underground coal mines generally couples its electromagnetic signals to existing conductors in a mine entry (tunnel), and exchanges signals with transceivers near the conductors. The conductors act as a transmission line (TL). The propagation characteristics of the TL, which play a major role in determining the performance of an MF communication system, can be affected by a mine environment. This paper compares the measured propagation parameters of a TL in three different positions within a mine entry. This comparison shows that the differences between the electrical properties of local coal and rock close to the TL can influence the propagation characteristics of the TL when in a different position.