Mining Project: Human-centric Lighting for Mitigating Mineworker Circadian Disruption and Improving Well-being

Research Summary

The mining industry often uses shift work to ensure a productive working mine around-the-clock. However, one potential side effect of operating on a 24/7 basis can be worker fatigue and the disruption of circadian rhythms. This can result in an increase in accidents due to sleep loss, fatigue, and reduced alertness. There are also consequences to health that include obesity, diabetes, and cancer.

The lack of natural light is an important factor for fatigue. Underground miners have much less natural light exposure than other workers, even when they are on a steady daylight schedule. For instance, for a typical workday from 7:00 AM to 3:30 PM, a miner in the Pittsburgh, PA, area would at best receive 47% of daylight on June 21 (the summer solstice), and only about 15% of daylight on December 21 (the winter solstice). Secondly, underground miners work in conditions with artificial lighting where the ambient light levels are much lower compared to other workers in workplaces using artificial lighting. Thus, there is a very high likelihood of fatigue and circadian disruption (CD) even if miners work the daylight shift. Circadian disruption can lead to sleepy and fatigued workers, who are more likely to be involved in accidents. Related health risks include type 2 diabetes, obesity, heart disease, stroke, and cancer.

No one is known to be conducting research involving underground mineworkers that studies lighting for reducing fatigue and specifically targeting the related safety and health issues. To address this need, this project used HCL that incorporated the visual and non-visual effects of light that can benefit health, safety, and well-being. Under this project, NIOSH researchers began to address the above issues by way of two research aims and related tasks, as summarized below.

1. Reduce circadian disruption by using human-centric lighting interventions during pre-shift, lunch, and post-shift times of day for miners working fixed shifts. In undertaking this aim, researchers developed a repeated-measures design because of the need to control factors that result in variability between subjects and because fewer subjects are needed to detect an effect size. The approach to reduce CD was planned to be to subject miners to blue-enriched, polychromatic lighting during the nonworking periods of pre-shift, lunch, and post-shift. The intent was to provide a minimum circadian stimulus (CS) of greater than 0.30, because that level can potentially reduce sleepiness and increase alertness. The CS metric indicates the circadian effectiveness of the control and HCL light sources. Inadequate circadian-effective light exposure during the day can result in CD.
2. Improve mineworker well-being (i.e., increase alertness, reduce workload perception, and reduce fatigue) through HCL intervention exposure during working hours. For this aim, researchers again used a repeated-measures design. The approach to improve fatigue and alertness was to subject miners to high-intensity and high-correlated color temperature (CCT) polychromatic lighting during work hours. This HCL intervention was planned to be installed inside the cab of ore haulage machines and on a roof bolter machine.

The overall approach of these two research aims was to use field case studies to conduct “proof of concept” experimental research that used two lighting conditions: the existing lighting that serves as the control and the HCL interventions that were experimental. The experimental lighting conditions were planned to change between the different studies (i.e., the lighting intervention for CD reduction might be different from the lighting intervention to improve well-being). This approach enables a realistic, focused research scope given that there are numerous mining subsectors of surface and underground mines for coal, metal, stone, and non-metal commodities, where each type of mining has many types of mining equipment and lighting. The case studies were planned to target underground metal and coal miners because national survey results indicate a predominance of shift work in the coal and metal sectors, where 68.3% of coal and 64.7% of metal mines have multiple shifts. The research targeted shift workers because they typically have poor sleep that causes decreased alertness and increased fatigue; thus, shift workers in general are more likely to be involved in accidents than well-rested, alert workers. Mining equipment operators were the target population at these mines because machine-related incidents accounted for 41% of all serious incidents in the mining industry according to a study of 562 accidents that occurred during 2000–2007.

NIOSH planned to develop several prototype lighting interventions from this research. The planned near-term impact was the use of these lighting interventions by mine lighting equipment manufacturers and mine operators. The planned long-term impact was a reduction in traumatic injuries, accidents, and illnesses for underground miners. The successful conclusion of this research was planned to result in several new HCL interventions for underground metal and coal mines to improve the safety and health of miners by reducing fatigue and CD. This project aimed to answer several research questions that would help establish the efficacy of the new HCL interventions so that mine lighting companies could commercialize them for use by underground coal and metal mining companies.