Mining Program Area: Illumination
Working in an underground mine presents many unique challenges. One significant challenge is providing adequate lighting for mine workers to safely do their jobs. According to the Illuminating Engineering Society of North America (IESNA), an underground mine is the most difficult environment to illuminate. Underground mines include dust, confined spaces, low reflective surfaces, and low visual contrasts. Lighting is critical to mine workers because they depend heavily on visual cues to see falls of ground, pinning and striking hazards, and slipping and tripping hazards. Consequently, illumination greatly affects a mine worker’s ability to perform a job safely.
Many of the higher frequency accidents in mining are related to inadequate lighting. This includes slip, trip, and fall (STF) hazards, which can be more difficult to detect in low light. STFs are the second highest accident category for underground mines. In 2006–2010, there were 148,007 nonfatal days lost due to STFs. Inadequate light can also prevent a mine worker from seeing an approaching machinery hazard; 33 mine workers were fatally pinned or crushed by continuous mining machines between 1984 and 2011.
Age is a significant factor in visual ability. It is especially important in mining, because the average age of the mining workforce is 43 years. As the workforce ages, the need for effective underground lighting becomes more pressing. Physiological changes that include reduced pupil size and cloudier lenses result in less light reaching the retina. For instance, 40% less light reaches the retina of a 45-year-old person compared to a 24-year-old person. Also, as people age they have fewer rod photoreceptors, which play a dominant role in vision as light levels decrease. Thus it can become more difficult for an older mine worker to see various hazards. They can also be more sensitive to glare, which can cause eye discomfort or reduce their ability to see various hazards.
OMSHR is conducting mine illumination research to addresses the visual needs of the aging workforce and to improve mine worker safety by improving their ability to see mine hazards associated with STFs and moving machinery accidents. This research leads to improvements in mine lighting so workers can better see hazards; therefore, this research will lead to a reduction in accidents.
OMSHR researchers are investigating the human factors issues and technological aspects of light-emitting diodes (LEDs) to improve the safety of mine workers. LED technology is poised to revolutionize mine illumination. High brightness LEDs are achieving up to 149 lm/W, compared to about 15 lm/W for an incandescent bulb. LEDs are robust because they do not have a glass envelope or filament that can break, and they can provide useful light in excess of 50,000 hours of operation, compared to about 1,000 to 3,000 hours for an incandescent bulb. The longer life and robustness of LED lighting systems can potentially reduce the frequency of mining injuries associated with maintenance, repair, and catastrophic lamp failures that occur during operation. OMSHR's research scope includes both underground and surface coal and metal/nonmetal mining. OMSHR has focused on cap lamps because they are a mine worker’s primary light source, but is also working on machine-mounted lighting.
Traditional approaches to improving lighting have centered on increasing illumination to improve visual performance; however, this strategy can have the undesirable consequences of increasing disability glare and increasing the electrical power drain on battery-powered lighting. OMSHR's cap lamp research took unique approaches to improve lighting, especially for older workers, by conducting research in two phases. The first phase focused on enhancing the color of light to improve visual performance in older workers. The second phase focused in the lighting distribution such that floor and moving machinery hazards received more illumination to make them more visible. The result of this research is an LED cap lamp approved by the Mine Safety and Health Administration that won the 2011 HHSinnovates Award. This cap lamp is now available for licensing. The visual performance improvements are impressive: 94% faster trip hazard detection, 79% faster peripheral motion detection, no increase in glare, and up to 50% less power required compared to commercially available LED cap lamps.
OMSHR's machine-mounted lighting includes the Visual Warning System (VWS) to reduce struck-by or pinning accidents involving moving machinery, such as a continuous mining machine. The VWS visually alerts mine workers that the machine is about to move, and it indicates the type of machine movement, such as forward or reverse, turn right or left, pivot right or left, and conveyor swing right or left. It can be used as a stand-alone system or to provide visual warnings for a proximity warning system. Human subject testing of the VWS, as mounted on a continuous mining machine, improved the ability to detect machine movement hazards by 71%. This improvement translates to up to 1.5 feet of machine movement.
OMSHR's illumination research has primarily been in-house, but in 2012 several contracts have been awarded to help develop a cap lamp specifically for metal/nonmetal mining and for machine-mounted lighting. These contracts give OMSHR access to the contractors’ modeling software and photometric instrumentation and enable OMSHR to develop lighting more quickly.