Effect of Operator Position on the Incidence of Continuous Mining Machinelworker Collisions 

John R. Bartels, Research Engineer-NIOSH, Dean H. Ambrose, Lead Research Engineer-NIOSH and Sean Gallagher, Senior Research 

Scientist-NIOSH 

Remote operation of continuous miners has enhanced the health and safety of underground miners in many 

respects; however, numerous fatal and non-fatal continuous miner struck-by accidents have occurred when 

using remote controls. In an effort to prevent these injuries, NIOSH researchers at Pittsburgh Research 

Laboratory examined the workplace relationships between continuous miner operators and various 

tramming modes of the equipment using motion captured data, predicted operator response times, and 

field- of- view data to determine causes of operator-machine struck-by events in a virtual mine 

environment. Factors studied included machine speed, direction of escape, operator facing orientation 

relative to the machine, work posture, distance from machine, and operator anthropometry. Close 

proximity to the machine, high machine tramming speeds, a right-facing orientation and operator 

positioning near the tail all resulted in high risk of being struck. It is hoped that this data will provide an 

improved rationale for operator positioning for remotely operated continuous miners. 

INTRODUCTION 	

The Mine Safety and Health Administration (MSHA) 

reports that both fatal and non-fatal remote-control 

continuous miner (figure 1) accidents are averaging 284 per 

year for 1999-2004 during routine mining activities, with the 

majority of accident victims working within the turning radius 

of moving continuous miners. The mining industry uses an 

educational aid called "Red Zones are No Zones" to help 

operators of 


remotely 


controlied vehicles, 

such as continuous 

miners, understand 

which areas around 

the machine to 

avoid (see figure 

2). Fatalities and 

injuries regrettably 

continue as a result 

of making contact 

withmoving 

machines.

MSHA 

is interested 

in reducing injuries and fatalities attributed to the operation of 

continuous mining machines (Clark et al. 1998, Colley et al. 

2006). As recently as February 2006, MSHA posted on its 

website information regarding protection of CM operators by 

using proximity warning devices to help recognize the redzone strategy. 

In an effort to better understand the influence of these 

issues on the risk of injury on operators not adhering to the 

red-zone strategy, it was decided that a digital human model 

(DHM) approach would be a useful methodology. The 

purpose of this investigation was to analyze factors 

influencing struck-by accidents during tramming of a 

continuous mining - machine using - DHM simulations driven by 

actual human motion analysis with a variety of subjects, 

postures, facing orientations, environmental constraints, and 

machine characteristics. The DHM used MSHA fatality 

information to validate the model parameters relating to 

operator position. Survival analysis of the results allowed an 

evaluation of a complex interaction of multiple parameters as 

they change over time. The fact that some of the scenarios 

simulated in this DHM study involved positions in the red 

zones does not imply that it is ok to operate a continuous 

miner there. 

Figure 1 -Continuous miner 

# *, ~ " V * 	 METHOD 

Motion Analysis Data 

Ten male subjects aged 32-59 years were recruited from 

the local mines to perform realistic movements in a laboratory 

setting (figure3) that mimic getting out of the way of a 

Figure 3 - Laboratory test setup 
moving machine. The subject's motions were measured by 

recording them using Motion Analysis Corporation's (MAC) 

motion tracking and capturing system. 

Human motion data were obtained from various operator 

work postures and escape paths (directions) typically used 

around tramming operations of underground remotecontrolled mining equipment such as continuous miners. The 

5 - 90" 

Figure 4 -Test area layout showing path 

number and orientation in demees 

tests were conducted using kneeling on two knees, squatting 

and standing postures that represented seam heights 36-, 48- 

and 60-inch, respectfully. At a given signal, a test subject 

moved in a given test posture from a starting location (see 

figure 4, solid circle) as quickly as possible along a given path 

(numbered 1 thru 8) labeled on a carpet (Figure 3). The 

sequencing of path direction was randomized for each subject. 

Prior to each path movement, the subject's orientation was 

either facing the signal source (S) or with the signal source to 

the subject's left or right side. When a light source at 'S' was 

turned on it cued the test subject to move. The subject 

stopped moving once he crossed the outer portions of the 

dash-circle (figure 4) on the carpet. 

Development of Human-Machine Model and Simulation 

Data Collection 

A human-machine model (figure 5) was developed to 

provide the means to measure parameters that would be used 

to predict struck-by events when the operator tries to move 

out of the way of the moving machine. The output parameters 

included: (1) the time when the machine first begins to move, 

Figure 5 -Human-machine model contains a continuous miner model 

and a digital human model of an operator. 

time when the operator is struck-by an object, (4) name of the 

object that struck the operator, and (5) the operator's distance 

from the start position when struck-by an object. MSHA's 

fatality report (Dransite and Huntley 2005) provided basic 

information to help validate the model regarding name of 

objects that struck the operator, operator's distance and 

location from the machine at the time of being struck. Struckby means collision occurs between the operator and machine 

or the mine wall. The data collection discussed in this paper 

uses captured motions, simulated scripts and collision 

detection from Jack digital human modeling and simulation 

software. 

The human-machine model was setup to generate and 

collect data during simulations from two different work 

locations: cutting drum or conveyor tail (see figure 1). From 

these work locations simulation scripts were programmed to 

rotate the machine (4.77'9.55 and 19.1 degls) until it came in 

contact with the virtual mine wall. In addition, during the 

machine's rotation, the captured motions of an operator would 

move away using one of the escape paths from the machine 

starting from a specific distance at one of the work locations. 

The operator movements were constrained to a digital human 

model by using capture motion data of test subjects discussed 

in the previous section. The operator was placed at 0.3,0.6, 

and 0.9 meter intervals from the conveyor tail or cutting 

drum. Captured motions of the experienced equipment 

operators were replayed in Jack software in the various 

combinations of kneeling, squatting and standing work 

postures, facing orientations and escape path directions. Only 

escape paths 4,5,6 and 7 .(Fig 4.) were used because they 

offered at least one direction that cleared the turning radius of 

the machine at each work location. To present a realistic 

operator response to the moving machine, researchers 

programmed the operator's movement using a delayed start in 

accordance with reaction times reported by Drowatzky (198 1) 

for different age groups that ranged from 0.19 to 0.24 

seconds 

The simulation database contained 19,440 cases that were 

collected from ten virtual subjects of which a number of cases 

involved instantaneous contact information such as collisions 

occurring at time zero. This happened in the simulation if the 

operator was already in contact with the machine before it 

moved or at the instant it began to move. Discounting these, 

the resulting database for analysis was comprised of 14,308 

cases depicting 1,296 possible test scenarios involving 

machine speeds and direction of rotations, work postures and 

facing orientations, work locations and distances from the 

machine, and escape paths. 

Variables 

Several independent variables were investigated. These 

variables included the machine speed, operator's distance 

away from the machine, operator's work posture and facing 

orientation, operator's work location and escape path 

direction. Dependent variables included time of a collision 
- - 

Table 1 - Frequency and cross-tabulation struck-by summary 

Work 

location Tail Drum 

% struck-by - 26.8- - - $7- - Work 

ti^^- D-l T-2 D-2 T-1 T-3 D-3 

~istance' 

% struck- 87.1 87.1 86.1 82.8 71.7 66.1 by ........................... 
 Speed 

deg/s 

% struck-by 89.9 73 71.7 - --- - - - - - - -- -. Speed- 19 19 9 9 4 4 

rotation2 CCW CW CCW CW CCW CW 

~ime~ (s) 0.1 0.5 1 2 3 4 4.4

24.6 69.9 85.4 96.4 97.5 99.7 100 

% .............................. 
 ~odypart Arms Head Legs Feet 

'~istance from work locations (Tail and Drum) 1-0.3m, 2-0.6m, 3-0.9m 

CW =clockwise; CCW =counterclockwise 

3~imeintervals during machine rotation 

4~umulativepercent of total struck-by events 

'percent of total struck-by events 

event, part of the body contacted and part of the machine 

contacted. 

Survival Analysis Model 

Survival analysis is a tool that allows an evaluation 

of a complex interaction of multiple parameters as they 

change over time. In this instance the parameters include 

machine speed, operator start location, facing direction and 

posture. The analysis identified the critical parameter 

interaction that impact operators at a given point in time. A 

Cox regression model was used to examine the influence of 

the independent variables on the time to contact. Cases where 

no contact was made were treated as censored observation. 

Main effects and all two way interactions were analyzed using 

a likelihood ratio stepwise technique. Proportional hazard 

checks were performed at all stages of the analysis. The type 

I error was set at 0.05. 

RESULTS 

Frequency and Cross-tabulation 

Frequency and cross-tabulation analyses considered 

14,308 simulations. Of the simulations examined, 10,254 

exhibited struck-by events between the operator and the 

continuous miner equipment. Struck-by events for some 

factors were compiled in Table 1, which shows that the 

operator was struck 76.8% of the time when working at the 

tail location. The table also includes cross-tabulations, for 

instance, the operator was struck 91.1% of the time when the 

machine moved counterclockwise at a speed of 19.1 deg/s. 

The cumulative percent of total struck-by events per time 

while the machine moved and percent of the total struck-by 

events, when a body part on the operator was most frequently 

contacted, are other information in the table. 

Figure 6 - Percent Struck vs. Distance from Machine 

0.3m 0.3m 0.6m 0.6m 0.9m 0.9m 

from from from from from from 

drum tail tail drum tail drum 

The two major factors that cross tabulations showed to have 

an effect on the operator's ability to avoid being struck by the 

machine were the operators distance from the machine and 

the speed of the machine. The effect of the operators distance 

can be seen in figure 6. The differences in incident rates 

between a distance of 0.3-m and 0.6-m is small and can be 

accounted for by the randomness of the simulation but at 0.9- 

m the incident rate is significantly reduced. Figure 7 shows 

the effect of machine speed on incident rates. There is an 

almost linear reduction in rates as machine speed is reduced. 

These results are not surprising but do indicate that 

recommendations on speed and operator distance from the 

machine could reduce operator injuries. The interaction of 

these factors and the influence of other parameters were 

further explored in the survival analysis. 

Figure 7 - Percent Struck vs. Machine Speed 

-....-.-.. 100% 

80%--

._ 60%-- - 40%--- -

20%-- -

O%- 19.1 ' 19.1 9.55 9.55 4.77 4.77 

deg/s deg/s deg/s deg/s deg/s deg/s 

CCW CW CCW CW CCW CW 

Relative Risk 

Based on the results of the Cox regression analysis, 

a model was developed that incorporated main effects and 

interactions of the independent variables on the time to 

contact. All main effects were found to be significant and 12 

of 15 two-way interactions were significant, resulting in a 

complex risk model. In addition, the proportional hazards 

assumption was rejected in almost all cases, save for the 

machine speed variable, indicating that the hazards associated 

with most of these variables were changing with time. 
Due to model complexity, analyses of relative risk were 

calculated while the machine was in motion at 0.1 s, 1 s and 3 

s. The times were chosen based on the first time recorded, the 

time when 98% of the cumulative incidents have occurred and 

a time in the middle. Using only the five lowest and the five 

highest relative risks calculated at these times, tables 2 - 4 

were compiled and included for each time period, distance, 

speed, work posture, facing orientation, work location, escape 

direction and relative risk. The coefficients in this model 

helped to evaluate the relative risk of experiencing a struck~by 

event at different points during the machine movement and 

showed the degree of influence for each variable in the model 

while controlling the effects of .all other covariates. 

DISCUSSION 

Machine speed was the most influential variable in terms 

of explaining the struck-by event occurring. Increases in 

machine speed resulted in increased chance of being struck 

and the increased risk associated with higher speeds was 

constant throughout the times investigated in the study. In 

general, compared to the 4.77 deg/s condition (referent 

condition), the 9.75 deg/s speed increased risk threefold and 

the 19.1 degls condition increased risk by 8 times the referent 

value. The distance from the machine at the start of the test, 

also had a significant influence. The relative risk of being 

struck-by the machine, while working within 0.3-m, was the 

greatest at the beginning of the simulation. 

Throughout the simulation the operator in a squat work 

posture was obviously at increased risk of being struck. In 

general, this posture was associated with an increase in 

relative risk that was 2.5 times the standing (referent) 

Table 2 -Lowest and highest relative risk at time 0.1 sec. 

Speed Dir Relative 

m degls Posture Facing Location deg risk 

0.9 4.77 standing front Drum 45 0.0017 

0.9 4.77 standing front Drum 90 0.0023 

G 

3 0.9 4.77 standing front Drum 135 0.0023 S 

0.9 4.77 standing front Drum 180 0.0025 

--0L9- -2.72 - - 5tanding - -fro?t- -- DE -- 32 - -!.go2 -, 

0.3 19.1 standing right Tail 180 45.79 

0.3 19.1 standing right Tail 135 42.62 

0.3 19.1 standing right Tail ' 90 41.55 .d 

3: 0.3 19.1 standing left Tail 180 32.89 

0.3 9.75 squatting right Tail 180 30.64 

condition. It seems clear that this posture increased the time 

it took to escape. On the other hand, the kneeling posture was 

found to be the lowest in terms of relative risk of all the 

postures. This posture may have positioned the body in a 

manner to avoid being struck by the machine, and still 

allowed for a relatively quick escape via crawling. At the 

beginning of the simulation, a front-facing orientation 

revealed a higher relative risk, which appeared to be due to 

the propensity of subjects to turn around before moving away 

from the machine. The extra time associated with this 

maneuver may result in subjects being unable to successfully 

avoid contact with the continuous miner. 

At later phases of the simulation (table 4), right-facing 

orientation becomes a lower relative risk. Except for machine 

speed, the relative risks associated with all variables were 

found to time dependent. This means that risks were found to 

be either increasing or decreasing with time for most 

variables, which explains why different activities were found 

to be higher risks at different points in the simulations. 

The operator at the tail location is at a much higher 

relative risk compared to the drum location throughout the , 

simulations.It should be noted that an operator location at the 

tail, drum or center portion of the machine are at risk of injury 

and all locations violate the red zone strategy, because 

tramming while positioned within the turning radius of the 

continuous miner can be fatal according to MSHA data 

(Dransite J and Huntley C., 2005). Unfortunately, the rotation 

of the machine around it's center point makes many think it 

would not lead to a risk of struck by accidents when the 

operator is so positioned. Like the other two locations, the 

center of the machine is not a safe location for the operator to 

be positioned, due to pinch points (MSHA 2006) should the 

machine slip toward the operator while tramming. 

The tail and drum locations were the only locations used, 

because of the potential escape routes from within the turning 

radius of the machine. The data presented here suggest that 

greater risk is present when the operator is positioned near the 

tailpiece as opposed to the drum (in terms of struck by 

accidents). A possible explanation is that the linear velocity is 

greater at the tailpiece than the drum. However, positioning 

near the drum may have other consequences associated with it 

that may need to be considered. Relative risk of being struckby the machine using the escape path direction 180" (path 

number 7) was the greatest throughout the simulation. It is 

clear that successful escape is less likely when moving 

parallel to the machine than when the escape vector has a 

component of motion that is away from the machine. 

In summary, the data obtained in this study revealed a 

complex interaction of factors that affect the risk of struck by 

accidents when tramming continuous miners in an 

underground mining environment. However, the increased 

understanding of these relationships should ultimately result 

in recommendations such as reduced turning speeds and 

better training emphasis on the red-zone strategy so to 

decrease the risk of these potentially fatal accidents for 

continuous miner operators. Further study and analysis are 

required before specific recommendations can be made. 
Table 3 -Lowest and highest relative risk: at time 1 seconds 


Table 4 - Lowest and highest relative risk: at time 3 seconds 


Speed Dir Relative 

Speed, Dir Relative m degls Posture Facing Location deg risk 

m degls Posture Facing Location deg risk 0.6 4.77 squatting front Drum 90 0.039 

0.6 4.77 squatting right Drum 90 0.0179 0.6 4.77 squatting left Drum 90 0.0407 

0.6 4.77 squatting left Drum 90 0.0195 b)

5 0.6 4.77 squatting right Drum 90 0.0423 e,

3 0.3 4.77 kneeling right Tail 45 0.021 3 

0.3 4.77 squatting front Drum 90 0.0447 3 

0.3 4.77 kneeling right Tail 135 0.021 --0,3- - 2.17- --s~:tti.g - - left_---D,E~- --R- _O,O+L- . _0,3- -57: - - sq_uatti_ng_- _ri& - - P?m- - 22 -- O.EL2- 0.9 9.75 squatting right Tail 180 42.6 

0.9 19.1 squatting front Tail 180 292.87 0.9 9.75 squatting left Tail 180 40.97 b) 

0.9 9.75 squatting front Tail 180 291.18 %k 0.9 9.75 squatting front Tail 180 39.21 .M 

5: 

0.9 19.1 squatting left Tail 180 267.07 0.3 9.75 squatting right Tail 180 30.5 

5 

0.9 9.75 squatting left Tail 180 265.53 0.3 9.75 squatting left Tail 180 29.34 

0.9 	 19.1 squatting right Tail 180 245.81 Mine Safety and Health Administration, Technical 

Support Approval & Certification Center, Dec 15,2005, 

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Clark G, Warnock B, Wease D, Dransite J [1998]. Remotely Practices, Second Edition, Burgess Publishing Company, 

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Remote Control Continuous Mining Machine Crushing address: http://mshaweba~ps.msl~a.novlwebcastsl 

Accident Data Study, MSHA Approval and Certification coa12005/ mshawebcast20060109 files/frame.htm# 

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Dransite J and Huntley C [2005] Remote Control Fatal 

Accident Analysis Report of Victims Physical Location 

with Respect to the Mining Machine, Dept. of Labor,