BACKGROUND: Though mining remains a vital shiftwork industry for U.S. commerce, problems of continued prevalence of mineworker fatigue and its mitigation persist. Publications and reports on fatigue in mining appear to be rich and diverse, yet variable and remote, much like the industry itself. METHODS: The authors engaged in a brief nonexhaustive overview of the literature on sleep and fatigue among mineworking populations. RESULTS: This overview covers: potential sources of fatigue unique to mine work (e.g., monotonous and disengaging Work Tasks, underground environments and light exposure, remote work operations); evaluation of mitigation strategies for mineworker fatigue or working hours (e.g., shift-scheduling and training); and areas for future research and practice (e.g., fatigue risk management systems in mining, mineworker sleep and fatigue surveillance, lighting interventions, and automation). CONCLUSIONS: Fatigue continues to be a critical challenge for the mining industry. While research on the problems and solutions of mineworker fatigue has been limited to date, the future of fatigue research in mining can expand these findings by exploring the origins, nature, and outcomes of fatigue using advancements in lighting, automation, and fatigue risk management.

The Mine Safety and Health Administration (MSHA) enforces underground coal mining lighting regulations in the United States and for issues approvals for electrical devices and machines. Companies submit standard test and evaluation (ST&E) documentation to MSHA when seeking approval on a machine with mounted lighting. Subsequent machine modifications, such as changing the type of light lamp from incandescent to light-emitting diode (LED), will require an update via the Revised Approval Modification Program (RAMP). Older incandescent and fluorescent lamps are being replaced by light-emitting diode (LED) technology having many advantages. Today, thousands of obsolete compact fluorescent lamps (CFLs) are used in underground coal mines. Replacing these with LED lamps requires RAMP documentation for each ST&E and requires MSHA to review virtually thousands of RAMPS that would require an exorbitant amount of resources and would create backlogs that would take MSHA potentially years to process. This problem is addressed by the Luminaire Comparison Method (LCM) that determines if the luminous intensity from a luminaire with a replacement lamp meets or exceeds the luminous intensity of the luminaire with a legacy lamp. If it does, then the replacement lamp is determined as equivalent and can be used as a replacement. One RAMP can then replace multiple RAMPs that would be required without the method. One company estimates over <formula><tex>$700,000 USD in savings; another company has saved about $</tex></formula>200,000 USD using the LCM. It is projected that the LCM will save millions of dollars. This paper provides several examples to illustrate the LCM. USGov

It is critical for the safety of miners to be able to escape, unaided, during a mine emergency. Self-escape is challenging in the presence of smoke that can occur during a mine emergency. To assist self-escape, coloured markers in underground mines designate the primary/secondary escapeways, but no universal colour code exists. Ten participants were tested to recognize the colour and designation (primary/secondary) of fluorescent yellow–green (FYG), yellow (Y), white (W) and green (G) escapeway markers in both a clear and smoked-filled environment. The overall misidentification rate for all colours was 1.9% and 18.1%, respectively, in clear and smoke conditions. FYG had the highest misidentification percentage for both conditions. For the marker designation tests, participants were most accurate in clear conditions (100.0%) for the FYG + W, Y + G, G + W and W + FYG combinations, and least accurate (89.6%) for the Y + FYG combination, while for smoke conditions participants were most accurate for the G + Y combination (95.8%). The overall effect of colour combination was significant, indicating that the colour combination for primary/secondary recognition is a significant factor where the G + Y combination was best. It can be inferred from these data that the colour combination is an important factor in participants’ ability to recognize primary/secondary escapeway markers in smoke conditions.

Researchers from the National Institute for Occupational Safety and Health (NIOSH) developed a light-emitting diode (LED) area luminaire called the Saturn and conducted a laboratory study using a Fletcher High Dual-boom Mast Feed (HDDR) roof bolting machine. The Saturn luminaire was designed to (1) enhance floor illumination to enable better detection of trip hazards in the interior spaces of a roof bolter and (2) reduce glare that has typically been an issue of concern on roof bolters. This paper reports on the results of achieving the second objective. The existing roof bolter lighting was the baseline and was compared with three versions of the Saturn luminaire relative to light intensity (100%, 75%, and 50%). Discomfort and disability glare data were obtained from 30 participants that comprised three age groups. Discomfort glare perceptions were obtained using the De Boer rating scale, and disability glare was quantified by using Mars Letter Contrast Sensitivity tests. Discomfort glare was reduced at least 3 levels with all Saturn versions. Also, a predictive model was used to estimate discomfort glare, and the results were similar. Disability glare was the least for the Saturn’s 50% intensity, and all Saturn versions had significantly less disability glare than with the baseline lighting. Veiling luminance was calculated and used as another indicator of disability glare. Veiling luminance was 28 to 42 times greater with the baseline lighting as compared with that of the Saturn lighting. Lastly, visibility levels were calculated. The Saturn versions were 4 to 6.5 times better in terms of visibility level.

Lighting regulations for luminance in U. S. coal mines are verified in the field by using a luminance photometer calibrated to the Standard Illuminant A light source. Significant measurement errors can exist when measuring light sources that are dissimilar to light sources used to calibrate the photometer. This paper quantifies the measurement errors when measuring these dissimilar light sources commonly used in U.S. underground coal mines-an LED, a CFL with a clear cover, a CFL with an amber cover, and a tungsten halogen. The impact of photometer quality was also evaluated. Three different luminance measuring instruments of high, medium, and low quality were compared-a PR-650, LS-100, and PMEX, respectively. The PMEX was under evaluation for measuring luminance compliance in U.S. underground coal mines. The PR-650 was used as the referent to which the other photometers were compared. The PMEX error ranged from -17.0% to -26.5% with the highest error for the amber CFL. The LS-100 closely matched the luminance measurement for the LED and halogen; however, it had a percent error of -10.4% for the amber CFL. After the initial experiment, MSHA made improvements to the PMEX resulting in the PMEX-MSHA. The experiment was replicated using the new photometer and the newer PR-670. After repeating the experiment, the measurement errors ranged from -16% to -19% for the PMEX-MSHA, thus indicating an improvement over the PMEX. These results show that the spectral content of a light source and the photometer quality can greatly impact the accuracy of luminance measurement.

Lifelines are used to aid self-escape of underground miners, but they are difficult to find in low-visibility conditions of smoke, therefore a self-illuminating lifeline could facilitate miners in locating the lifeline. The detection distance, colour recognition, and miss rate for 10 subjects were determined for red-, green- and blue-lighted diffuse fibre-optic cables, used to create a lighted lifeline, and a traditional rope lifeline in a smoked-filled environment. The testing was conducted with and without a cap lamp. The use of a cap lamp resulted in all cases being undetected in 98.3% of trials. With the cap lamp off, there was no significant difference in the detection distance for blue- and green-lighted fibres; however, the miss rate for the green-lighted fibre was slightly higher. The red-lighted fibre was not detected in 93.3% of trials. The green- and blue-lighted fibres enabled the best visual performance, but subjects had difficulty correctly identifying the colour of the fibre. The lighted fibre-optic cable appears to have merit for improving self-escape from underground mines, and may have other mining and non-mining applications that include improving self-escape visibility.

At the dawn of the 20th century, a potentially game-changing underground materials conveyance system was being trialed in north Britain. At a Derwent Colliery mine, near Newcastle, a prototype steel and cast-iron centipede snaked along a longwall face. The conveyor, comprised of a series of linked 6-ft-long, 6-in.-deep sheet-iron troughs, and was nothing short of revolutionary in its application. Prior to it, “the idea of carrying the coal along the face of longwall workings by means of a conveyor never seems to have been considered seriously.”1

Proper lighting plays a critical role in enabling miners to detect hazards when operating a roof bolter, one of the most dangerous mining machines to operate; however, there has not been any lighting research to address the walk-thru type of roof bolter commonly used today. To address this, the Saturn light was designed to directly address walk-thru roof bolter safety by improving trip hazard illumination. The visual performances of 30 participants that comprised three age groups were quantified by measuring each participant's visual performance in detecting trip objects positioned on the two floor locations within the machine's interior working space. The lighting conditions were the existing compact fluorescent lights (CFLs) and the Saturn LED area light developed by NIOSH researchers. Three intensities of the Saturn lights were used, 100%, 75%, and 50%, all of which resulted in better visual performance, and up to a 48% reduction in average trip detection time compared to the CFL. For the Saturn trip object miss rates were <0.5% for all age groups in contrast to the CFL, which ranged between 32.5% for the youngest group and 50.4% for the oldest group.

Roof bolting typically follows the extraction of a commodity to help keep the roof from collapsing. During 2004 to 2013, roof bolter operators had the highest number of machinery-related injuries, accounting for 64.7 percent, at underground coal mines. This paper analyzes U.S. roof bolter fatal and nonfatal lost-time injury data at underground work locations for all commodities from 2004 through 2013 and determines risk indices for six roof bolting tasks. For fatal and nonfatal incidences combined, the roof bolting tasks in order of the highest to lowest risk index were bolting, handling of materials, setting the temporary roof support (TRS), drilling, tramming, and traversing. For fatalities, the roof bolting tasks in order of the highest to lowest risk index were handling of materials, setting the TRS, bolting, drilling, traversing, and tramming. Age was found to be a significant factor. Severity of injury, indicated by days lost, was found to increase with increasing age as well as with increasing experience, largely due to the confounding of age and experience. The operation of the roof bolting machine used in underground mining should be a research priority given the high frequency and severity of incidents. The results also suggest that temporal factors may exist, so additional research is warranted to better understand these factors and potentially develop interventions. This research provides a data-driven foundation from which future research can be conducted for safety interventions to reduce the frequency and severity of incidences involving the roof bolter activities of bolting, handling of materials, and setting the TRS.

A comparative human performance evaluation of a miner's walking speed and head pitch was conducted on miners wearing two types of LED cap lamps. Walking speed and head pitch are indirect indicators of improved lighting. The better that miners can see the floor, the faster they can walk and the less they pitch their heads downward to illuminate the floor with their cap lamps. NIOSH researchers developed a non-contact way to quantify human performance by using two small wireless, wearable inertial measurement units. Data were collected in the field from nine coal miners in an underground coal mine. The field results showed no statistical difference between the two cap lamps for walking speed. However, there was a trend of 2\circ lower head pitch for one of the cap lamps. The field testing procedures were then replicated in a controlled laboratory environment and the results indicated a 5-degree lower head tilt when using the same cap lamp and a corresponding difference in walking speed. A novel application of magnetometers for distance flagging is also presented. Finally, study limitations and a follow-up study are discussed.

Conducted at the National Institute for Occupational Safety and Health's (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. 1972-2012 IEEE.

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.

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are conducting mine illumination research with the objective of improving miner safety. Slips, trips, and falls (STFs) are the second leading accident class (18.1%, n = 2,374) of nonfatal lost-time injuries at underground mines (MSHA, 2005-2009). Factors contributing to STFs include recognition of hazards as well as postural balance and age. Improved lighting may enable better hazard recognition and reduce the impact of postural balance and age. Previous research has shown that cap lamp technology that used light-emitting diodes (LEDs) has improved hazard detection. This study was an initial investigation to determine if cap lamp lighting significantly influences measures of static postural stability (displacement and velocity of center of pressure). Results of this investigation showed no significant differences in the balance measures of interest between cap lamps tested. However, balance was shown to significantly decline (p< 0.05) when tested in an underground coal mine compared to the laboratory testing condition. Relevance to industry Underground coal mine workers wear cap lamps on their hard hats as their primary light source to illuminate nearby areas where their vision is directed. Proper illumination may improve miner safety by improving their STF hazard recognition and balance.

This paper describes an experiment to examine whether a visual warning system can improve detection of moving machine hazards that could result in struck-by or pinning accidents. Thirty-six participants, twelve each in one of three age groups, participated in the study. A visual warning system capable of providing four different modes of warning was installed on a continuous mining machine that is used to mine coal. The speed of detecting various machine movements was recorded with and without the visual warning system. The average speed of detection for forward and reverse machine movements was reduced by 75% when using the flashing mode of the visual warning system. This translated to 0.485 m of machine travel for the fast speed condition of 19.8 m/min, which is significant in the context of the confined spaces of a mine. There were no statistically significant differences among age groups in the ability to detect machine movements for the visual warning modes in this study. The visual warning system shows promise as a safety intervention for reducing struck-by or pinning accidents involving continuous mining machines. The methods and results of this study could be applied to other moving machinery used in mining or other industries where moving machinery poses struck-by or pinning hazards.

Miners depend most heavily on visual cues to recognize underground mining hazards; consequently, illumination plays a critical role in miners' safety. Some hazards are located in the miners' peripheral field of view (10 degrees to about 60 degrees off axis) or on axis (0 degrees). The objective of this research was to determine if there were visual performance improvements when using solid-state cap lamps with light-emitting diodes (LEDs) as compared to incandescent light bulbs commonly used in miner cap lamps. Recent research has indicated that an increased short-wavelength content of the spectral power distribution of LEDs relative to incandescent lamps improves peripheral visual performance for low-light (mesopic) conditions. The visual performances of nine subjects were quantified by measuring the subjects' speed and accuracy in detecting floor objects located on axis and at + / - 20 degrees off axis. The objects were located near field (1.83 m) and far field (3.66 m). Upon presentation of the objects, the subjects would count and point to each object using a red-laser pointer. The object detection response time and number of missed objects were recorded. The results of the visual performance comparison for an LED, a prototype LED, and an incandescent cap lamp are presented. There were no missed objects when the subjects used the LED-based cap lamps, but there were three missed-object occurrences when the subjects used the incandescent cap lamp. The mean detection time when using the incandescent cap lamp was 55.3 percent greater than that of the prototype LED cap lamp and 43.5 percent greater than that of the LED cap lamp. It can be inferred from these data that the spectral distribution of LED-based cap lamps could enable significant visual performance improvements as compared to incandescent cap lamps.

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are investigating different lighting technologies with the objective of improving mine safety. This paper presents the results from an ongoing study that compares discomfort glare for different light-emitting diode (LED) cap lamps using the de Boer glare rating scale. The cap lamps tested included two commercially-available LED cap lamps and one NIOSH prototype LED cap lamp tested at three different illumination levels. Prior research indicated that the NIOSH prototype enabled much better visual performance as compared to other LED cap lamps. It uses three LEDs that produce multiple illumination areas in comparison to commercially-available cap lamps that use one LED and projects a narrow spot pattern. Across subjects and cap lamp test conditions, measured illuminances (averaged at both eyes) varied from 0.62 to 3.73 lx, whereas the de Boer glare ratings varied from 4.86 to 7.71. An analysis of variance based on 15 subjects indicated a significant difference in the discomfort glare due to cap lamps (F4, 52 = 18.01, p 0.001). Post hoc tests indicate that one of the commercially available cap lamps exhibited lower discomfort scores, with no statistically significant differences detected between the others. Thus, the NIOSH prototype cap lamp does not cause excessive discomfort glare yet enables better visual performance. 2011 IEEE.

Research by the US National Institute for Occupational Safety and Health (NIOSH) indicates that light emitting diodes (LEDs) can be used to enhance safety by improving a miner's ability to see mining hazards and reducing glare. This paper investigates if LEDs provide another benefit by reducing miner exposure to hazards during maintenance and operation of LED lighting. LEDs could provide useful lives up to 50 times longer than incandescent lighting commonly used in mining and could enable design changes to reduce certain hazards. The mining accident records compiled by the Mine Safety and Health Administration (MSHA) were examined to determine the extent and nature of accidents involving the maintenance and operation of mine luminaries. A total of 140 relevant accident records were found for the years 2002-2006. These incidents resulted in 3668 days lost from work with an additional 925 days of restricted activity. The injury narratives were studied to determine if the implementation of LED-based luminaries could reduce injury severity and frequency. The greatest near-term potential impacts appear to be related to reducing maintenance and cap lamp redesign. Longer term (5 years), low-power and lightweight auxiliary LED lighting for surface mines could also have potential impact for improving safety.

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 miner's 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 subject's 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.

Illumination plays a critical role in an underground miner’s safety because miners depend most heavily on visual cues to recognize hazards. Mobile mining machinery, located in the miners peripheral field-of-view (±10° to about ±60° off-axis), may pose potential pinning and striking hazards. The main objective of this research was to determine if there were peripheral visual performance improvements for the detection of moving objects when using cool-white light-emitting diode (LED) cap lamps as compared to incandescent (INC) light bulbs commonly used in miner cap lamps. The cap lamp variable of interest is the spectral power distribution (SPD); the illuminances were normalized by a diffusion filter. The second objective was to determine if age is a factor for peripheral visual performance. This is important because the workforce is aging - the average miner age is about 43 years old. Thirty subjects participated in the study; ten subjects each in the age groups of younger (18 to 25 years), middle (40 to 50 years), and older (50+ years). Visual performance was quantified by the subjects’ speed and accuracy of response to detect the rotation of high-contrast (white) circular targets located 3.83 meters (m) away at -20°, 40°, and 50° off-axis. The speed of detection and the number of missed target rotations (accuracy) were measured. The prototype LED cap lamp results were best with a 11% to 15% improvement compared to the INC and LED cap lamps respectively. Age does appear to be a significant factor. For the middle and older age groups’, target movement detection time increased 75% and 60% and the number of missed targets increased 500% and 450% respectively in comparison to the youngest age group. The results also suggest that target location is a significant factor. The subjects’ target movement detection time for the 40° and 50° target movements increased 16% and 69% respectively as compared to the -20° target.

Light-emitting diodes (LEDs) are emerging as viable replacements for incandescent (INC)-based cap lamps used in mining. The photometric and energy characteristics of these light sources differ in important ways. This paper describes the performance of LED and INC sources in cap lamps in terms of correlated color temperature, color rendering, light output, electric power, ambient temperature and air flow, and light source aging. Importantly, these characteristics can influence a miner's ability to spot mining hazards thus impacting safety. Second, some of these characteristics interact with the operating life of the cap lamp's battery power, such that differences between LED and INC sources can be magnified toward the end of a 10-h battery discharge cycle. Empirically, we have determined that after 8 h at an ambient temperature of 25 degrees C, the average light output of an INC cap lamp can decrease to about 69% of its initial value when powered by a lead-acid battery, and it can decrease to about 65% of its initial value when powered by a nickel-hydride battery. An LED-based cap lamp using a constant current drive circuit can maintain about 96% of its initial value when powered by a nickel-hydride battery. Real-world tests addressing the effects of ambient temperature and air flow on the light output of an LED and INC cap lamp were conducted in the National Institute for Occupational Safety and Health Safety Research Coal Mine. The LED cap lamp yielded a vertical average illuminance improvement of approximately 9.5%, and the INC cap lamp yielded a vertical average illuminance degradation of approximately 4%. The differences between LED and INC cap lamps were further quantified by the calculation of "mesopic luminance" data that indicated for the same photopic luminance (i.e., as measured using a conventional light meter) the LED cap lamp could be up to 38% more efficient than the INC cap lamp with a lead-acid battery at the end of the 10-h driving cycle. Lastly, accelerated life tests were used to empirically determine light output depreciation as the INC light source age approached its useful life. There was about a 35% decrease in light output. This is quite considerable, particularly given that the light output will decrease an additional 30% to 45% over the period of a 10-h shift. The implications of the differences between LED and INC sources are discussed. This information is crucial in determining how visual performance could be affected for real-world conditions where batteries discharge during the work shift and as the light source ages. To date, only idealized conditions have been used for LED and INC cap lamp visual performance research.