Absence of conflict of interest.
Sammarco, J., Gallagher, S., Mayton, A., & Srednicki, J. (2012). A visual warning system to reduce struck-by or pinning accidents involving mobile mining equipment. Applied Ergonomics, 43(6), 1058-1065. https://doi.org/10.1016/j.apergo.2012.03.006
- The study’s objective was to examine the impact of a visual warning system on motion detection time.
- The study was an experiment conducted in a laboratory setting. The authors assessed whether installing a visual warning system on a continuous mining machine improved participant motion detection time.
- The study found that the visual warning system significantly improved speed of detection for a variety of machine movements. Also, dynamic and flashing lighting patterns significantly enhanced motion detection time compared to static or non-flashing lights.
- The quality of causal evidence presented in this report is high because it was based on a well-implemented randomized controlled trial. This means we are confident that the estimated effects are attributable to the visual warning system, and not to other factors.
Features of the Study
The study was conducted at the National Institute for Occupational Safety and Health’s (NIOSH) Mine Illumination Laboratory in Pittsburgh, Pennsylvania. The authors used a laboratory experiment to assess whether a visual warning system (VWS) improved participant motion detection time. The VWS is a safety intervention designed to decrease the frequency of mine worker injury due to machine accidents. It features red lights mounted to machinery, in this case a continuous mining machine (CMM) that flashes when the VWS recognizes machine movement in an area of the machine that could pose a striking or pinning hazard to workers. The VWS activates the red warning lights in the dangerous machine areas to help workers see the machine’s operations and indicate the type of movement the machine is undergoing or will undergo.
The authors recruited 36 NIOSH personnel for the experiment. All study participants had to pass a number of visual tests and were screened for ocular diseases or conditions. The participants were seated in front of a video monitor in a darkened environment that played diverse video scenes of CMM movement and warning light combinations. First, participants completed six warm-up scenes to acclimate to the testing machine. Next, each participant viewed the 30 video scenes but viewed them in a random order. The participants identified when they detected a visual warning light or movement from the CMM by releasing the computer mouse button. In each of the video scenes, the CMM movement occurred at random times so that the participants could not anticipate the movement.
Outcomes included participants’ reaction time (time from the CMM activation to the release of the computer mouse) across five visual warning modes:
- None: no visual warning is given at any time;
- Static: the lights for a given machine movement will turn on and stay on as long as the machine function is activated;
- Flash: the lights for a given machine movement will flash as long as the machine function for movement is activated;
- Directional: the lights for a given machine function will provide a directional warning as long as the machine function is activated; and
- Progressive: each light turns on sequentially and stays on until the last light in the sequence is on.
The authors tested participants’ ability to detect the motion of the machine with visual warning modes on seven machine movements: 1) reverse fast, 2) reverse slow, 3) pivot left, 4) conveyor swing, 5) forward fast, 6) forward slow, and 7) pivot right. However, all warning light modes were not used for all movements. Using reaction time data, the authors conducted statistical tests to examine the impact of the visual warning system on detection time for the machine movement and warning light mode combinations.
Health and safety
- The study found that any lighting (static, progressive, directional, and flashing) was significantly associated with quicker average motion detection time when compared to no lighting. These significant differences were found for forward/reverse motions (0.59 seconds versus 1.96 seconds), pivoting machine motions (0.49 s versus 2.23 s), and conveyor swing motions (0.42 s versus 0.65 s).
- The study also found that dynamic lighting (progressive, directional, and flashing) was significantly associated with faster average motion detection time when compared to static lighting. These significant differences were found for forward/reverse motions (0.56 s versus 0.71 s) and pivoting machine motions (0.47 s versus 0.54 s).
- Within the dynamic lighting modes, flashing lights were detected the fastest, followed by directional lighting, and progressive lighting for forward/reverse motions (0.49 s, 0.57 s, and 0.71 s, respectively).
- For pivoting machine motions, there were statistically significant differences on average between directional and progressive lighting (0.53 s versus 0.65 s). However, static lighting was detected more quickly from the front (by 0.8 s) than dynamic lighting (this difference was statistically significant).
Considerations for Interpreting the Findings
The authors did not explicitly provide information to calculate attrition. However, the authors conducted the experimental conditions in a laboratory setting, implying no attrition. Additionally, the study was conducted in a simulated environment, so detection times might differ when individuals are in a harsher mining environment and engaged in multiple tasks. Further, the research was limited to visual warning detection of machine movement and did not address other movements that might contribute to machine operator accidents.
Causal Evidence Rating
The quality of causal evidence presented in this report is high because it was based on a well-implemented randomized controlled trial. This means we are confident that the estimated effects are attributable to the visual warning system, and not to other factors.