Computers in Delivery of Ergonomic Technology forSafety in the Workplace: ErgoRisk©, an Example

Shrawan KumarDepartment of Physical Therapy, University of Alberta,Edmonton, Alberta, AB T6G 2G4 Canada

ABSTRACT

The computer is one of the essential tools in the delivery of ergonomic technology for achievingoptimized safety at work. This article rationalizes the rightful place of computers in the hierarchyof ergonomics. Clearly, science and knowledge have the central place from which the technologyflows. Harnessing discrete bits of technology into effective techniques lends us the ability to prac-tice and apply ergonomic technology for safety. One of the most versatile and powerful media forapplication of these technologies is the computer. In an application sense, the computer acts as afunnel. Complex signals, involved functional relationship, and sophisticated processing usingcomplex physiological, biomechanical, and cognitive models are systematically and accuratelyexecuted through the medium of the computer. Examples are presented to illustrate these argu-ments. © 2002 Wiley Periodicals, Inc.

1. INTRODUCTION

Ergonomics arguably has the rarest density of scholars and practitioners given the vast-ness of its span. Ergonomics has not yet become a mainstream field of study and practiceat par with its sister disciplines. Perhaps due to the economic and relevance pressures,many ergonomists increasingly seem to visualize ergonomics as technology. A technol-ogy establishes an immediate economic rationalization attractive to an ever-increasinglyeconomically competitive world. This readily available direction of assertion is too at-tractive for most ergonomists to pass up. The foregoing may also be an inbuilt trap forthem. The challenge the ergonomists face is that they need to quantify and communicatethe degree of improvement that ergonomics can make. This becomes doubly difficult asergonomics is not a casual factor, rather a mere modifier. To have the continual challengeto prove the value of what could have happened if only ergonomics were employed is atask of tall order. However, if any success is to be realized, it necessitates developingvalid scientific knowledge and technology and putting them to work. Thus, though theinitial driver of ergonomics may be technology, its continued well-being will be doomedwithout strong, rigorous, and valid science. By the same token, if application is forsaken,the field of ergonomics will lose its purpose. In the given special circumstances ergo-nomics, science and technology are interwoven as knowledge and practice. In short, wehave to have knowledge to practice our trade. If the knowledge becomes stagnant, thetrade will become obsolete.

Apart from the interdependence of science and technology, the practice of the lattercan be achieved only through appropriate media, depending on the goal. The tools em-

Human Factors and Ergonomics in Manufacturing, Vol. 12 (3) 321–330 (2002)© 2002 Wiley Periodicals, Inc.Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/hfm.10015

321

ployed in the practice of technology are multifarious, for example, checklists, question-naires, ergonomic audit, models of varying complexity, and so forth. Appropriate matchingof the problem with ergonomic tool is likely to provide greatest success. These ergo-nomic tools require appropriate media through which they can be executed. These in-clude oral communication, written communication, demonstration, intervention, and soforth. Given the complexity of human beings and their interaction with complex workenvironments, the multitudes of factors and their relative magnitudes overwhelm the abil-ity of the human sensory and cognitive systems to discern any meaningful information.Many times, although the relevant information may be readily perceived, its impact onthe human may have to be derived through complex and tedious processing. It is underthese circumstances that computers offer their enormous strength in resolving our prob-lems. Thus, computers are slaves rather than masters. Their use has facilitated perfor-mance and application in most areas of ergonomics by taking the tedium out. Theseapplications have primarily been in the following three areas: (a) sensory ergonomics, (b)cognitive ergonomics, and (c) physical ergonomics.

2. APPLICATIONS

2.1. Example of Sensory Ergonomics Application

The field of consumer ergonomics is economically very competitive. In many areas, themanufacturers are looking for any competitive edge. The cosmetic industry in our societyis a multibillion-dollar industry. Cosmetic products appeal to our senses. Whereas largedifferences are readily discernable subjectively, small differences can be elusive, yet theycan lead to significant competitive advantage. In order to improve a product for humanappeal, one of the Japanese industries conducted the following experiment. Subjects wereseated in a comfortable, slightly reclining chair with a breathing mask and air-circulationsystem. The subjects were instrumented for electroencephalogram (EEG) recording with24 electrodes on the skull at standardized positions. These 24 outputs were fed to a com-puter through a data acquisition board for analysis and production of EEG traces. Ini-tially, a standard air mixture, devoid of any smell, was circulated through the system andbaseline EEG recording was made. Subsequently, traces of desired fragrant substanceswere remotely released in the air circulation system to record EEG changes signalingpleasurable sensory input. Through such testing, the most appealing fragrance of opti-mum concentration was determined for marketing. This objective could not be achievedwithout the aid of computers.

2.2. Cognitive Ergonomics

Even in continuous human speech there are periods or microperiods of pauses. Elim-ination of these pauses from prerecorded materials without impairing intelligibility ofcommunication can lead to significant time saving (approximately 50%) and thus is eco-nomically profitable. Sony (2000) has developed a system of pause elimination causingvoice compression through computer processing without compromising intelligibility ofcommunication.

2.3. Physical Ergonomics

Applications in physical ergonomics are extensively computer aided due to multiple vari-ables involved, and each of them may, and generally does, have unique properties and

322 KUMAR

relation. Simultaneous processing of all these variables to arrive at a desirable result goesbeyond the human capability. While these applications are numerous, some of the exam-ples are: biomechanical models of upper and lower extremities and biomechanical mod-els of the trunk (both two-dimensional and three-dimensional, either of which can bestatic or dynamic). Anthropometric proportions and constants, vibrational properties, phys-ical strength profiles with predictive capabilities, endurance, and recovery are some ofthe examples where computer assistance is essential in solving ergonomic problems (uni-variate models). Models of the next level of complexity are those that involve two vari-ables and are required to produce composite results (bivariate models). An assessment ofcumulative load is one such example.

2.3.1. Bivariable Model: Cumulative Load. Due to the viscoelastic nature of thebiological materials, human tissues are significantly and precipitously affected by thetemporal factor (Brinkmann, Johannelweling, Hileg, & Biggemann, 1987). Kumar (1990)reported that time-weighted mechanical loading was a significant risk factor in precipi-tation of low back pain among institutional aides. This approach required fusion of tra-ditional two- or three-dimensional biomechanical models (which calculated instantmechanical loading) and the time duration along with the time-varying mechanical load.This allowed him to develop a composite measure of load and time (e.g., mega Newtonsecond [MNs]), of which he reported a threshold range of loading beyond which most ofthe injuries precipitated and below which there were no injuries.

2.3.2. Trivariate Model: Overexertion, Safety, and Risk of Injury Model. Mostindustrial tasks require force exertion through a range of postures over a period of time,and the task cycles are repeated over and over again. The occupational safety or risk ofinjury can be quantitatively assessed only by combining all three factors; that is, force,duration, and posture and range of motion. Any task can then be represented on thesethree axes (Figure 1).

Figure 1 A three-dimensional representation of generic tasks.

ERGONOMIC TECHNOLOGY FOR SAFETY 323

Due to the reciprocal relationship between safety and risk of injury, the two variablessum to 1. Based on this concept and providing for relation proportionality constant andvariable weighting, Kumar (1994) presented the following expression for estimating mar-gin of safety (MOS).

MOS � 1 � [K$(1 � ▫1R1)x(1 � ▫2R2)y(1 � ▫3R3)z%] .

In order to calculate the MOS, the calculation of individual variables, their integrationover time in different postures through the range of motion, significant computing powerbeyond human capability is required. Such feats cannot be accomplished without the aidof computers. Delivery of ergonomic technology requires a partnership with computers.

3. MULTIVARIATE SYNTHESIS COMPOSITE MODEL—AN EXAMPLE

The ErgoRisk© (Kumar, 1997) software system is designed to analyze quantitatively therisk of musculoskeletal injuries due to work activities of a wide variety of tasks incorpo-rating various univariate, bivariate, and trivariate models synergistically. This conceptu-ally, as well as mathematically, complex task can be performed only by using a computersystem. This software is a multiple-knowledge-based, relationship-driven, problem-solving tool for the delivery of ergonomics technology in a form useful to industry andworkers.

The software system ErgoRisk© enables the user to interactively execute various mod-ules from a mouse-driven shell. The modules will interact with each other through datafiles that will be read and/or updated if necessary. The core of the data will come from anexternal file produced by a number of input devices depending on relevance. ErgoRisk©

will also allow the user to manually enter new data or coordinates if desirable. If an ex-treme condition occurs, that is, when the stress on the worker exceeds the maximum tol-erable limit, the user will be notified by a screen message. ErgoRisk© will then manipulatethe data to produce outputs describing the forces that are exerted on the joints of interest.These outputs will then be further correlated into risk factors for the worker.

An important benefit of ErgoRisk© is the elimination of redundant data input. This hasbeen done by sorting the subject’s information in a personal record file that will containthe height, weight, age, and so forth, of the subject along with coordinates describing theposture of the subject and all external loadings that are exerted on each joint. Anotherproperty of ErgoRisk© is the ability to view the output of several or all modules simul-taneously. These benefits in turn will allow the user to, in a very short time, determine thehazardousness of the task.

ErgoRisk© stands alone, yet when viewed as a shell to simply launch other programs,it can be compared to a bundle of other shell systems. However, this system is not just atool for launching other programs, but an environment that will be used to retrieve nec-essary information for making risk assessments. ErgoRisk© is totally self-contained; itdoes not exit itself to run a separate existing module or modules. The shell of the systemis given in Figure 2.

Figure 3 shows how each of the individual functions that ErgoRisk© provides are re-lated and where the input and output of each are connected to other functions in the sys-tem. These are briefly described below.

324 KUMAR

Loading Data. There are two major services this function provides. The first is ac-cepting new data, if not read from a file, and the other is the ability to edit existing oralready entered data. The only source of input to this function is from the input devices.The output from this function will be sent to databases, regression equations for the firstlevel of processing.

Figure 2 Flowchart of ErgoRisk©.

ERGONOMIC TECHNOLOGY FOR SAFETY 325

Regression Equations. This function will be used only to determine the maximumpossible force that a worker could generate in a given posture. Notice that the only inputto Regression Equations is from the loading data that contain the necessary informationto determine the maximum lifting load. The output from this function is directed to theunivariate models.

Motion/Constant Data. This function is a dialogue box that is used to enter in almostall of the data that are necessary to calculate the Risk. It will feed data to only two func-tions, the Recovery/Endurance Formulae and the Risk Formulae.

Recovery/Endurance Formulae. This function calculates the total required time andtotal endurance time for a given task. If the maximum voluntary contraction (the maxi-mum load that a person is capable of lifting) is not available from the Motion/ConstantData, it will have to be determined by a call to Regression Equations.

Univariate Models. This function is an essential output function. It will calculate anddisplay the total compression shear that exists on the joint of interest while in a singlegiven posture (Kumar & Hill, 1990). The data contains the personal information for eachsubject and a set of coordinates and angles that describes the postures that exist on file forthe patient. Also input to the two-dimensional model is the output from Regression Equa-tions. This input will be the maximum possible load a person is capable of lifting asopposed to the actual load he or she is lifting. The output for both cases, that is, with theactual load and the maximum load, will be compared and displayed together. We can alsosee that the output from the two-dimensional model is sent to the Cumulative Load func-tion. This is because for each posture, the total compression shear will be added togetherand averaged to determined a cumulative value to be used for the total stress that a personhas experienced while performing a certain task.

Three-Dimensional Model. This function (Cheng & Kumar, 1991) is similar to thetwo-dimensional model except that the inputs and outputs are of different forms. Theydiffer in that the input to the three-dimensional model is a set of joint coordinates, and theinput to the two-dimensional model is a set of angles. Also the output of the three-dimensional model will involve not only forces but moments as well. The cumulativeload of the three-dimensional model outputs will also be determined as it will be for thetwo-dimensional model.

Seats. This function (Cheng & Kumar, 1993) will also take input from the loading dataand, in turn, give output representing the effect on the subject’s joints after performing atask of sitting, rising, or both. The output of the function will also be the forces that theperson experienced on his joints, but it will not be fed to the Cumulative Load function.

Figure 3 Diagram to show input and output levels in ErgoRisk©.

326 KUMAR

3.1. Bivariate Model

Cumulative Load. The purpose of this function (Kumar 1990) is to determine an aver-age of the load that was exerted on the subject’s back while performing an operation thatcontained more than one task over either a period of time or during entire lifetime. Thelatter was derived as follows:

From the line drawings on the completed questionnaire, the postural angles of the wrist,elbow, shoulder, hip, knee, and ankles were measured and recorded for static postures.For dynamic activities, initial and final postures were used to measure the above posturalangles. The change from initial to final posture was assumed to be smooth and continu-ous. The intermediate postures were taken to be proportional to the time lapsed.

The angles were calculated at 200-ms intervals. These angles, along with the magni-tude of the load (if any), height, and weight of the institutional aide, were kept on file.The data from the entire questionnaire were logged on an electronic spreadsheet. Special-purpose programs were written to accomplish all manipulation of the data.

Anthropometric, postural, and load data served as input to a biomechanic model, whichwas modified to yield compressive and shear forces at the thoracolumbar and lumbosa-cral discs. This being a static model, it did not account for the dynamic components of thebiomechanic stresses. By the using of this modified model, compressive and shear forceswere calculated for each static posture and for the initial, final, and all projected inter-mediate postures at 200-ms intervals for all dynamic activities. Because of the impossi-bility of accurate recordings of the minor variations in the activities performed, the loadshandled, and the postures assumed over the duration of the total work experience of anygiven job, retrospectively, the calculated stresses were considered to be close approxima-tions. These were termed overall stress. The overall stress for static postures was ob-tained simply by multiplying the compressive and shear forces with the duration of activity.The overall load (compression or shear load) for dynamic activities was obtained as follows:

OL � S .02L1 � .02L2 � . . . .02Ln (1)

where

OL � overall load (compression or shear)L1 � average compression or shear force of the first segment of the taskL2 � average compression or shear force of the second segment of the taskLn � average compression or shear force of the nth segment of the task0.02 � time interval—fraction of a secondNs (Newton second) � unit of overall cumulative load “force time” product

The biomechanical loads of different categories were treated separately within their cat-egory. The cumulative biomechanical loads for each category and each institutional aidewere determined in the following steps:

1. identification of stressful tasks i to n;2. determination of magnitude ~M ! of each load, overall compression ~CO!, and over-

all shear ~SO! for tasks i to n;

ERGONOMIC TECHNOLOGY FOR SAFETY 327

3. determination of the frequency ~F! per day of the tasks i to n;4. calculation of the cumulative biomechanical compression and shear per day for

overall loads according to the following equations:

CDCo � S~MC0i xFi !� ~MCojxFj !� . . . � ~MCon xFn ! (2)

CDSo � S~MSoi xFj !� ~MSoj xFj !� . . . � ~MSon xFn! (3)

where

CDCo � cumulative daily overall compression for jobs i to nCDSo � cumulative daily overall sheer for jobs i to n

5. Deduction of the cumulative loads for other time periods as follows:

CWS � [CDL � 5] (4)

CMS � [(CDL � 5) � 4] (5)

CYS � [(CDL � 5) � 4] � 12 (6)

where

CDL � cumulative daily loadCWL � cumulative weekly loadCML � cumulative monthly loadCYL � cumulative yearly load

3.2. Trivariate Risk Model

This function (Kumar, 1994) is the basis of ErgoRisk© and is the final stage in determin-ing the probability of an injury. Risk is a function that takes the outputs of almost all otherfunctions as its inputs and calculates the MOS, or the probability of back injury. Input toRisk will come from the Motion/Constant Data file and the Recovery/Endurance For-mulae, which will be assessed from within Risk, and each will simply return a numberthat is used in the calculation, which is, of course, the output of Risk. These inputs will beonly numbers that have already been calculated or entered into the Motion/Constant Datafile. Since the core of the data comes from the camera file, some data that are manuallyentered are checked for validity in the Motion/Constant Data file before being saved. Theinputs to Risk can only be assumed to be correct. Therefore, there will be no situation inwhich the input to Risk is invalid, and, hence, it will not give invalid output. The opera-tion of risk is a plug-in-the-numbers formula that uses the mathematical expression givenbelow Kumar (1994):

328 KUMAR

MOS � K�1 � a1�1 �CWL � PWL

MVC � PWL�X�X

�1 � a2��1 �CWD � PDL

ET � PDL��1 �

CF � PF

MF � PF��1 �

RR � AR

RR�� Y�X

�1 � a3��1 �MRQp � MDRp

PE � MDRp��1 �

MRQd � MDRd

DE � MDRd�� Z�

where,

MOS is the margin of safety (takes a value such that 0 � MOS � 1)

From the Motion/Constant Data file:

These inputs will be manually entered in a dialogue box and saved in the Motion/Constant Data file. The values that are entered in the first time are saved as default valuesuntil they are changed. The units of the variables are given in [ ], where F � force, L �length, and T � time. If there is no [ ] next to the variable description, it means that it isunit less.

Where,

a1 is the constant for the stress index (defaulted as 1 unless otherwise known)a2 is the constant for the duration index (defaulted as 1 unless otherwise known)a3 is the constant for the motion index (defaulted as 1 unless otherwise known)X is the exponent of the stress index (defaulted as 1 unless otherwise known)Y is the exponent of the duration index (defaulted as 1 unless otherwise known)Z is the exponent of the motion index (defaulted as 1 unless otherwise known)K is the constant of proportionality (defaulted as 1 unless otherwise known)

CWL is the constant work level @F#PWL is the preferred work level @F#CWD is the constant work duration @T #PDL is the preferred duration level @T #CF is the constant job frequencyPF is the preferred job frequencyMF is the maximum frequency possible for job activityAR is the allowed recovery period @T #MRQp is the motion required in proximal direction @L#MDRp is the midrange in proximal direction @L#MRQd is the motion required in distal direction @L#MDRd is the midrange in distal motion @L#DE is the distal extreme motion [L]PE is the proximal extreme motion [L]MVC is the maximum voluntary contraction [N]

ERGONOMIC TECHNOLOGY FOR SAFETY 329

From the Recovery/Endurance Formulae

RR is the required recovery period @T #ET is the endurance time @T #

Before ErgoRisk© begins its calculations it will prompt the user with the current valueof MVC. At this time, the user will have the option to either continue with the currentvalue, change it to another value, or, if the task is a lifting operation, call RegressionEquations to determine it. The final value of the MOS will be output to the screen orprinter along with other information pertaining to the subject being analyzed. Since, asdescribed earlier, all errors in data are checked before entering Risk, by the time the out-put of Risk is to be processed, there will be no sources of error that will cause an incorrectresult.

4. USER CHARACTERISTICS

The eventual user of ErgoRisk© will have a minimal knowledge of modeling, databases,constants, and computers and, therefore, the system use as far as technical know-how isconcerned. The system is designed to be easy to use, very reliable, and easily maintained,because the user will most likely be unable to correct a system-related problem.

5. CONCLUSIONS

The foregoing is a brief account of a selection of ergonomic applications that cannot bedelivered without the medium of computer. The complexity of our work environmentgrows by leaps and bounds, changing the stress profile and the possible response that mayemerge. Therefore, the technology available today, which we may have exploited reason-ably well, is also in danger of becoming obsolete. Thus, an undue emphasis on techniquesand technology may have a diversionary effect on the basis of technology—the knowl-edge, the science. A focused and persistent effort to define and develop our science andknowledge base is the only strategy that will address the need for developing technologyto match changing needs and continue to deliver through the computer medium.

REFERENCES

Brinkman, P., Johannelweling, N., Hilweg, D., & Biggemann, M. (1987). Fatigue fractures ofhuman lumbar vertebrae. Clinical Biomechanics, 2, Supplement 1, S1–S23.

Cheng, R.C.K., & Kumar, S. (1991). A three dimensional biomechanical model of human back.International Journal of Industrial Ergonomics, 7, 53– 62.

Cheng, R.C.K., & Kumar, S. (1993). An analysis of sitting and rising activity. Unpublished software.Kumar, S. (1990). Cumulative load as a risk factor for low-back pain. Spine, 15, 1311–1316.Kumar, S. (1994). A conceptual model of overexertion, safety and risk of injury in occupational

settings. Human Factors, 36, 197–209.Kumar, S. (1997). ErgoRisk©—A physical work risk assessment software. Unpublished.Kumar, S., & Hill, D. (1990). A biomechanical task analysis program. Unpublished.

330 KUMAR