No. 552 August 2013 

A New Visual Warning System to Reduce Struck-by and Pinning Accidents 

Objective

The objective of this technology is to provide an 

intervention that reduces the risk of underground mine workers 

being struck-by or pinned by mobile mining equipment such as 

the continuous mining machine (CMM). 

Background

Mobile mining equipment poses a significant safety risk to 

workers who can be accidentally struck-by or pinned by the 

equipment, resulting in worker injury or death. Because of their

severity and frequency, these machine-related accidents are at 

the forefront of the stakeholder concerns of the National 

Institute for Occupational Safety and Health (NIOSH). Mine 

Safety and Health Administration (MSHA) accident data from 

2002–2011 indicates that 44 fatalities and 4,754 nonfatal days 

lost (NFDL) occurred in the underground coal mining industry 

and were described as struck-against or struck-by and caught or 

pinned in-under-between. An MSHA report [MSHA 2011] 

indicates that 33 fatalities involving a CMM occurred from 1984 

through March 2011. The operators controlling the CMMs were 

identified as the workers with the highest accident frequency in 

these incidents; the most dangerous activity identified was 

moving the CMM to a new location. Performing maintenance 

was the second most dangerous activity. Most of the fatalities 

occurred at the right rear of the CMM. In all accidents described 

by the MSHA report, poor work practices were contributing 

factors given that the accidents occurred when miners were 

positioned within the turning radius of an active CMM. 

One mitigation strategy to address struck-by or pinning 

accidents is to provide guidance to help CMM operators to 

understand and avoid potentially dangerous areas near mobile 

mining equipment. During 2004, a “red zone” pictorial was 

developed from real-life experiences by MSHA and the Virginia 

Department of Mines, Minerals and Energy [MSHA 2004]. This 

red zone pictorial depicts hazardous zones to avoid during 

various CMM operations. Another mitigation strategy is to use a 

proximity detection system (PDS) that would alert miners if 

they are too close to the CMM, or potentially shut down the 

machine if they are within an unacceptable distance from the 

machine. Some PDS’s use both an audible and a visual alert. 

Each of the mitigation strategies has its own strengths and 

limitations. For instance, PDS’s hold much promise but require 

complex technology, and performance issues can result from 

magnetic interference. 

A simpler alternative to these strategies was developed by 

NIOSH researchers and named the Visual Warning System 

(VWS), which visually alerts miners of impending machine 

movements and conveys the type and direction of machine 

movement. Although visual alerts are used in PDS’s, they do 

not convey the type and direction of machine movement 

because the visual alerts are limited to small indicator lights. 

Approach

To verify the practicality (viability) of the new VWS, 

NIOSH researchers conducted human subject testing in a 

controlled, laboratory environment [Sammarco et al. 2012] with 

a CMM as the test machine. The VWS mounts to the CMM and 

electrically interfaces to the CMM’s control subsystem. The 

VWS has its own control subsystem and eight luminaires with 

each using a red, 1-W light-emitting diode (LED) to illuminate a 

0.6-m-long, 14-mm-diameter side-emitting optical fiber (Figure 

1). 

Figure 1. The new Visual Warning System (VWS) installed on a 

continuous mining machine (CMM). The LED warning light (see 

arrow) indicates that the conveyor is going to swing to the right. 

Due to safety concerns during testing, researchers used a 

 
high-definition, video-based CMM simulator developed by 

NIOSH. Additionally, the CMM simulator enabled consistent 

rates of movements to be presented for every test. Actual CMM 

movement rates often vary due to machine control variations 

and floor conditions, which can confound the data. Video scenes 

of a CMM with a VWS installed were recorded. These scenes 

included 30 combinations of machine movements and various 

VWS lighting conditions. Five visual warning conditions were 

studied: (1) None: no visual warning is given at any time; 

(2) Static: the luminaires for a given machine movement will 

turn on and stay on as long as the machine function is actuated; 

(3) Flashing: the luminaires for a given machine movement will 

flash at 4 Hz as long as the machine function for movement is 

actuated; (4) Directional: the luminaires for a given machine 

function will provide a directional warning (4-Hz direction 

sequence), as long as the machine function is actuated; (5) 

Progressive: each luminaire turns on sequentially and stays on 

until the last luminaire in the sequence is on. The simulator also 

included a data acquisition and control system that enabled the 

collection of the test subjects’ reaction times in detecting 

various machine movements. 

Of the 36 test subjects, there were 27 males and 9 females 

who took part in the testing. There were 12 participants each in 

three age groups. The mean ages for each group were 21.6 

years, 47.3 years, and 56.5 years. Subjects that had radial 

keratotomy, monocular vision, glaucoma, or macular 

degeneration were excluded. Only the volunteers that passed 

vision tests for distance visual acuity of 20/40 or better, log 

contrast sensitivity values of 1.72 to 1.92, the absence of color 

vision deficiency, and peripheral vision of at least 80° for each 

eye were accepted for the study. 

 

 

Reported Findings 

The differences between the no-lighting condition and any 

VWS lighting condition were dramatic. For instance, for the 

forward and reverse CMM movements, the average detection 

time for the no-lighting condition was 1.96 s, but the average 

time using the VWS flashing condition was 0.49 s. During this 

1.47-s difference, or 75% improvement, the CMM travels 0.485 

m given the fast speed of 19.8 m/min. This distance traveled is 

significant especially when considering the tightly confined 

spaces of a mine. The most dramatic time difference results 

were with the machine pivots, where the average detection time 

for the no-lighting condition was 2.23 s, but the average for 

the flashing and directional conditions was 0.47 s. During this 

1.76-s difference, the CMM would pivot 5.63° given the pivot 

rate of 3.2°/s, and the end of the CMM conveyor would move 

about 0.6 m. Our analysis of the 33 fatalities documented by 

MSHA [2011] indicated that 30 fatalities involved machine 

forward, reverse, or pivot movements. 

The visual warning system research, which began in late 

2010, had the interest of RSL Fiber Systems. During 2012, RSL 

Fiber Systems licensed the VWS, and a commercial product is 

now available. Most recently, a NIOSH research project for a 

proximity warning system is using the VWS for identification of 

proximity detection events [Jobes et al., forthcoming] given that 

the VWS can be used as a standalone system or with a 

proximity detection system. 

Summary 

The test results clearly demonstrate that the new VWS, as 

installed on a CMM, vastly improves an individual’s ability to 

detect hazardous machine movements. Results of this 

experiment suggest that dynamic lighting conditions 

(directional, flashing, and progressive conditions) enhance 

movement detection time to a greater extent than a simple static 

light. The use of the VWS appears to be an important tool in

alerting underground miners to impending or active machine 

movements and may help prevent the incidence of struck-by or 

pinning accidents. The VWS has application to other moving 

machinery used in mining or other industries where moving 

machinery poses struck-by or pinning hazards. 

References 

Jobes C, Carr J, Reyes M [forthcoming]. A visual warning 

system for the identification of proximity detection events 

around a continuous mining machine. HFES 2013 International 

Annual Meeting. San Diego, CA . Sept. 30–Oct. 4, 2013. 

MSHA [2004]. Red zones are no zones for mining with remote 

control continuous miners. Arlington, VA: U.S. Department of 

Labor, Mine Safety and Health Administration. 

MSHA [2011]. Remote control fatal accidents analysis report of 

victims physical location with respect to the mining machine. 

By: Dransite J and Huntley C. Arlington, VA: U.S. Department 

of Labor, Mine Safety and Health Administration. 

Sammarco JJ, Gallagher S, Mayton A, Srednicki J [2012]. A 

visual warning system to reduce struck-by or pinning accidents 

involving mobile mining equipment. Appl Ergon 43(6): 1058–

65. April 2012. 

For More Information 

For more information on the new Visual Warning System 

(VWS), contact John J. Sammarco (jsammarco@cdc.gov), RSL 

Fiber Systems (http://rslfibersystems.com), or the Health 

Communications Coordinator (OMSHR@cdc.gov), NIOSH 

Office of Mine Safety and Health Research, P.O. Box 18070, 

Pittsburgh, PA 15236-0070. Technical details concerning the 

VWS are described by Sammarco et al. [2012]. 

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occupational safety and health topics, contact: 1-800-CDCINFO (1-800-232-4636), 1-888-232-6348 (TTY), or request 

information at the CDC Web site at www.cdc.gov/info, or 

visit the NIOSH Web site at www.cdc.gov/niosh. 

Mention of any company or product does not constitute 

endorsement by the National Institute for Occupational Safety 

and Health (NIOSH). In addition, citations to Web sites 

external to NIOSH do not constitute NIOSH endorsement of 

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Furthermore, NIOSH is not responsible for the content of these 

Web sites. All Web addresses referenced in this document 

were accessible as of the publication date.

DHHS (NIOSH) Publication No. 2013–151