Seguridad Electrica 11

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HUMAN FACTORS IN

ELECTRICAL SAFETY

INTRODUCTION

In this chapter, the topic of human factors is reviewed in the context of electrical safety.Background information is followed by examples for power systems. Brief discussion isalso presented on the topics of visualization and cognitive ergonomics.

Background

The topic of human factors evolves from the obvious statement that, People are notmachines. In the early 19th century, during the early periods of industrialization, a persis-tent question was how to optimize the placement of people in machine systems. Pre-datingelectrical power, when jobs involved assembly line operations with repetitive tasks requir-ing uniformity and efficiency of physical movements between operations, materials, andemployees, studies of time-and-motion and human anthropomorphics, or averagebody part sizes were used by management to figure out problems, like how far can anaverage worker reach to push or pull this piece on the assembly line.

In the early 20th century, as electrification enabled industrialization to move beyond man-ufacturing across all economic sectors, the complexity of machine systems increased. Morethan one process could be pulled into a work environment, leading to multiple operations sit-uated in geographic proximity, running concurrently, and producing output at high speeds.

With electrification, increasing industrial complexity, and faster production rates, thedemands on people working with the machine systems grew. As suggested by Rasmussen1

at this stage, human factors more commonly studied measures of human physical abilitiesalong with measures of physical reliability. In this context, knob-and-dial ergonomicswas a research focus, for example, identifying the correct size of knob for an employee toeasily grasp doing a turning task, and measuring how often the knob would be incorrectly

versus correctly turned.Then, in the 1930s, Rasmussen notes that as automation was introduced into the chem-

ical process industries, the link between machines and people often became indirect. Theinterface of automatic control engineering made the wide reach of individual employeespossible over large scale and significantly hazardous production.

As production failures occurred, interest in human factors extended from humanphysical reliability to include the reliability people might show in understandingprocess information and executing successful decisions. This specialty later became knownas cognitive ergonomics.

CHAPTER 11

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Then human error research developed as an aspect of human factors studies, with thegoal being to break down or untangle causes of human physical and/or cognitive malfunctionfrom machine or process malfunction in post-accident studies. In anticipation of installationdesign and development, human error probability, or human reliability assessment (HRA)also came into human factors consideration as part of operational engineering analysis.

In the mid-20th century, military experience in World War II aviation and the post-WorldWar II growth in civilian aviation added more information about how humans and engineeredsystems could interact with potentially tragic results of plane crashes. By the early 1970s, gen-erally accepted ideas about how to evaluate the fit between work and workers were maturinginto an accepted professional approach within the industrial engineering community.

Concurrently, within the electrical power industry, the post-World War II develop-ment of the civilian nuclear power industry resulted in an active transfer of human fac-tors ideas into the management of civilian nuclear power operations. This developmentbecame more substantial following two major tragedies: the Unit 2 scram at the ThreeMile Island Power Station (TMI-2) in Pennsylvania on March 28, 1979; and the explo-sion of Unit 4 of the Chernobyl Nuclear Power Station in the Ukrainian former SovietUnion on April 26, 1986.2

With TMI-2 and Chernobyl, nations learned that human error in complex operationalenvironments producing electrical power could potentially result in global disaster.Investigations identified human factors in the causal chain of events leading to these disas-ters. This learning created additional focus on basic concepts of human performance.

Continuing to the present, the topics of human factors have moved beyond humanmachine interactions3 to human-systems interfaces or HIS4. The term human factors mayhave two meanings. Human factors may refer to various traits or elements of the human2 asindividuals which should be considered for safe and effective results from engineered systems.Or, the term may mean the applied science technology relating fundamental human sciences(like anatomy, physiology, neuro-psychology) to industrial systems.2

To illustrate these definitions, consider that electrical work demands intense integrationof visual and spatial information to successfully complete tasks. Anything that inhibits anemployees vision creates risk for an electrical event. Considering the two definitions ofhuman factors applied to vision, as a human factor relating to the individual, vision may beunderstood as limited to the measurement of visual acuity (or accuracy of how well anemployee sees a wall chart) to ensure that they have adequate vision ability to read a com-

puter screen or see a stoplight; or the factor may be as complicated as the engineeringadvancement of vision assistance devices, such as these examples:

Infrared cameras installed in vehicle dashboards for night driving

Infrared intrusion detection systems

Infrared monitors used in heat tracing as a safety monitoring strategy to identify exces-sive ohmic heating of installed conductors

For an individual, vision is a critically important human factor. About 80 percent of infor-mation about machines and systems comes to employees via their vision.5 Note visual acuities

go down as the complexity of the visual target increases. In other words, when there is moreto look at, it is harder to see. Multiple physical factors influence visual acuity, including:

Illumination

Contrast

Time of exposure to the visual target

Color of the visual target and the targets background

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The smallest detectable threshold for vision is 106 milliliter (mL). Vision ability isdecreased with vibration, hypoxia or low oxygen, and motion of the visual target.

POWER SYSTEMS AND HUMAN FACTORS

As the previous comments suggest, the power industry has significantly contributed tounderstanding about human factors. Here further examples of human factors in the electri-cal industry are presented. In Table 11.1, selected workplace environments are identified.

The generation, transmission, distribution, design, installation, operation, and mainte-nance of electrical power happens in diverse situations. Given the diversity in workplaces,the human factors of relevance to electrical safety depend in part on where in the power sys-

tem the employee may be working. An employee assigned to a control room at a nuclearpower station can reasonably be expected to confront demands in his/her work that differcompared to an employee wiring a house under construction or doing maintenance in acogeneration facility. So, it follows then that the human factors in a control room can beexpected to differ from those at the construction site.

HUMAN FACTORS IN ELECTRICAL SAFETY 11.3

TABLE 11.1 Power Systems Environments and Human Factors Examples

Workplace Human factors considerations

Generation Dust, fumes, noise in fossil fuel environments

Common features to control rooms,11 including

Compact workstations using visual displays

Large overview displays

Increased cognitive workloads as staffing changes

Information multiplicity

Virtual workspaces4 with

Serial access to information & controls

More time spent on secondary tasks

Transmission Live line work,12 withHelicopter approaches at high elevations

Moving parts (Helicopter rotars)

Required calculations: minimum approach distance

Placing Person with Tools in Air Gap13

Distribution Voltage protection personal equipment, including

Rubber goods

Extended tool handles

Recognition of minimal power line approach distances

At or above shoulder work requiring stressful postures

Work in vaults or confined space requiring respiratorsRepetive motion and lifting heavy loads14

Construction Crouching, kneeling, or reaching in various spaces

Vibration in powered equipment

Environmental temperature extremes

Heavy equipment operation, with noise, moving parts

Potential contact with power lines above and below


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The influence of the environment on human factors is not isolated. Relating Hawkins6

SHEL illustration of this concept, Kawano2 describes the acronym as:

S for software, including for example, computer software, paper documents or instruc-

tions, permits, or procedures

H for hardware, or the engineered or constructed aspects of the environment

E for the environment or ambient conditions, such as geography, meteorology, humidity,or altitude

L for liveware, or the people involved directly or indirectly in the work situation

Kawano adds an m to Hawkins SHEL acronym, to include managing systems as adynamic and represented part of the model. As suggested by Hawkins and amended byKawano, the m-SHEL model provides a step towards an integrated systems approach to

human factors. The model offers another strategy for thinking about electrical safety so thatthe programmatic focus goes beyond the individual to include the technologies, engineer-ing, interpersonal, and environmental contributions to the individuals experience in thesystem of production where they work.

Visualization

Rasmussen1 has suggested that automation relieved employees of repetitive manual tasks;consequently, work with more decision-making or trouble-shooting content became commonin the industrial setting. Today, information technology, including the use of computer-basedapproaches, has placed volumes of data at the center of employee tasks.

Tory and Moller7 describe the methods available with computer visualization andgraphics which can support perception and cognition, or the human abilities to sense (viaeyes, ears, nose, taste, touch) and think. Table 11.2 gives electrical safety examples wherethese methods can serve as cognitive aids.

Cognitive Ergonomics

The early 21st century is notable for the promise of new horizons in research advancing

cognitive ergonomics to fully benefit the industrial workplace. As brain science maps the

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TABLE 11.2 Electrical Safety Examples of Cognitive Aids with Computer

Visualization Technologies

Cognitive Challenge Visualization method

Multiple permits per job step Reducing search via data grouping or structure

with multiple steps in a job

Monitoring for breaker trips, Perceptual monitoring using pre-attentivepower surges, or faults visual characteristics

Switching procedures in Enhancing data recognition, abstraction, and

power outage or routine aggregation

maintenance

Note: Visualization methods are based on Table 1 of Tory and Mollers report,7 which isadapted in part from work by Card, et al. in Information Visualization: Using Vision to Think. SanFrancisco: Morgan Kaufmann Publishers, 1999.


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terrain of thought and mind-body interactions using scanning technologies like magneticresonance imaging (MRI), positron emission tomography (PET), and photon emissioncomputerized tomography (SPECT), data is accumulating to explain how people think indifferent scenarios.

A key insight from this research is that context is hugely influential over thought. Using themetaphor of the brain as a computer, one way to appreciate the role of context is to suggest thatno person comes to his/her work with a blank hard drive or screen. Rather people do their

jobs with the advantage and disadvantage of what they see, hear, smell, and touch in their sur-rounding; what they believe; and how they physically feel. This information loads the driveand screen occupying space alongside of where the programs run or thought happens.

Cognitive ergonomics specifically addresses how to modify what occupies an employeeshard drive and screen when work is being done, to improve the way thought unfolds, andthereby, improve decisions.

Context can be appreciated not simply as a physical background to the employee.Context can also be in the form of background beliefs or work myths. The dictionarydefines a myth as an old traditional story or legend, especially one concerning fabulous orsupernatural beings, giving expression to early beliefs, aspirations, and perceptions of apeople and serving to explain natural phenomena or the origins of a people.8

Following are examples of myths which can affect electrical safety. Exploring thesemyths offers promise to improve electrical safety by reducing the chance that an employeewill act based on an inaccurate background belief.

Im experienced, so I wont get injured. This belief assumes that experiences protect

against injury and death. However, as the statistics shown in Chap. 8 suggest, the employeewho is most at risk of an electrical event is between the ages of 25 to 45 years and with acci-dent-free years on the job. To the extent that an employees experience dulls his/her aware-ness of the distinctive features present in the job he/she is immediately doing, his/herexperience may create a false context for thinking about situational facts like:

Task electrical configuration

Personal protection and barrier needs

Required resources (like people, equipment, and time) to complete the job

Electrical accidents happen when an employee isnt paying attention. This mythicbelief is based on a logic that goes as follows: As long as an employee does pay attention,no accidents will occur; therefore, if an accident happens, an employee must have beeninattentive.

As an explanation for electrical events, inattention is assumed by the comments like:

He wandered off in his thinking.

He was daydreaming on the job.

He was worried about something else.

However, through many debriefing of electrical accidents, engineers have come toappreciate modern electrical work unfolds in highly complicated situations. If an electricalsafety failure occurs, typically more than one thing goes wrong. Multiple system faults orpersonnel errors contribute to the event. This understanding suggests that attention alone isnot sufficient to prevent an electrical accident. Given the embedded complexity in thepower system, multiple actions are required to preserve safety. How to sharpen or focus theactions of human attention is a research target of cognitive ergonomics.



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Related to attention is the ability to hear. If an employee cannot hear instructions he isbeing given verbally, that employee can be expected to have difficulty in his/her focus onthe instructions or attention to the verbal guidance given. Hearing as a limited human factordepends on sound. Sound pressures needed for hearing are a function of the material ormedia (for example, air) through which the sound or acoustic waves are propagating.5 Thethreshold for hearing in the frequency range of the spoken word, from about 1,000 to 5,000 Hz,is about 20 Pascals (2.9 109 psi).

According to Chapanis, there are multiple aspects to a listeners ability to detect sound,including:

The listeners age

The listeners history of past or ongoing noise exposure

Whether the listener is using one ear or two to hear, with the use on one ear (mono-aural

listening) requiring 3 decibels (dB) more sound pressure The sounds acoustic frequency, expressed in hertz (Hz)

The presence of competing sounds or masking

The complexity of the bandwidth tones

The sounds duration, with durations less than 200 mili-seconds (ms) requiring increasedintensity (that is, as acoustic signal duration is halved, the intensity of the signal mustdouble to be audible).

Returning to the M-SHEL model of human factors, the interaction of liveware or peo-

ple depends on successful communication. To the extent that employees can not ade-quately communicate because they can not hear each other talk, safety is jeopardized.So the physical ability or individual human factor of hearing can affect the ability tocommunicate, which can affect attention, which is influenced in part by backgroundbelief or context.

As long as I dont touch an electrical source, I wont get shocked. This belief cor-rectly identifies the need to avoid exposure to shock hazard. However, mechanical contactis notnecessary for an employee to be shocked. Returning to the M-SHEL model, the

mythic belief here under-rates the role of environment in its influence over the individualhuman factors of body size and positioning in relationship to electrical conductivity, resis-tivity, and impedance.

Electricity is conducted along copper wires in power generation, transmission, and dis-tribution. Depending on the current, when an employees body comes sufficiently near toan electrical source, the charge that is carried by electrons in copper wire may be convertedthrough an electrochemical reaction to charge conducted by the ions in the human body.Employee size and positioning, as well as meteorological conditions and geography play arole in whether electricity can cross an air gap by arcing, and flow through or around theemployee. The resulting shock can be destructive, even fatal, if adequate personal protec-

tion is not being used.During an electrical hazard exposure, human factors studies suggest how little opportu-

nity the employee may be left with to react. Reaction times for responses to stimuli (likebuzzing or light shocks), word information, or other prompts have been studied as ahuman factor. These times are studied in laboratory and real world scenarios. Generally,reaction times vary from person to person, and sometimes between successive trials by thesame person.

Environmental stress, such as heat exhaustion, altitude sickness, or hyperbaric conditions(such as work in mining, undersea, or in certain medical facilities) can change mental

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efficiency and lengthen reactions. Responses are relatively slower when language isinvolved. For example,

A printed word is registered in the readers brain in about an eighth of a second (0.125 s)

A spoken word is accessed by a listeners brain in about a fifth of a second (0.200 s),before the speaker has finished pronouncing the word

The brain takes about a quarter second (0.250 s) to find a word to name an object, andanother quarter of a second (0.250 s) to program the mouth and tongue to pronounce thename (total: 0.500 s).9

Psychologists have studied attention and voluntary action in responses, finding:

An average physical movement (motor) response time of >0.600 s in healthy peopletested; and

An average non-motor response time of >1.050 s in adults asked to say verbs for print-outs of words shown as visually presentednouns.

In Chap. 1, the thresholds for neuromuscular responses in response to electrical currentwere reviewed. In comparison to electrical responses, motor and non-motor responses tolanguage stimuli generally take much longer.

The implication of this human performance limitation can be shown with this example:If a coworker needs 250 ms to process a spoken word like STOP or HELP, while an elec-trical incident like an arcing fault is unfolding, say in less than 6 cycles, there is going to be

a mismatch between The amount of time the coworker needs to detect, process, and respond to the fault; and

The amount of time where in maximum risk is present from the fault.

This time mismatch is even more pronounced when there is a need to sequence percep-tion, thought, and response in a rapid amount of time, as in to:

Sense physical stimuli

Perceive and process information; and

Act.

Age influences reaction time, with times slower for those older than 60 and youngerthan 15 years. Certain situational conditions generally slow reaction time and increase itsvariability for a person, including

Sleep deprivation

Fatigue

Time of day

Environmental extremes

Alcohol or other drug use

Medical problems

Nutritional status

Through a number of research studies it has been found that on the job reaction timemay be many time longer than what is found in a lab set up, especially for specific kinds oftasks requiring physical exertion and mental concentration,10 such as is found in electricalwork.



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SUMMARY

Future protective human factors innovations in electrical safety will depend in part on maxi-

mizing opportunities to integrate the demands of power systems, environments, and advancesin human factors studies, visualization research and cognitive ergonomics insights. Until then,employees must be prepared with knowledge of the limits of their physical and mental perfor-mance in the complex and potentially hazardous tasks required to deliver electrical power.

REFERENCES

1. J. Rasmussen, Human Factors in High Risk Systems, IEEE Fourth Conference on HumanFactors and Power Plants, Conference Record, Monterey, CA, pp. 4348, 1988.

2. R. Kawano, Steps Toward the Realization of Human-Centered Systems-An Overview of theHuman Factors Activities at TEPCO, In Global Perspectives of Human Factors in PowerGeneration, IEEE Sixth Conference on Human Factors and Power Plants, ConferenceProceedings, Orlando, pp. 13/2713/32, 1997.

3. W.H. Hawkins, Where Does Human Factors Fit in R&D Organizations?IEEE Aerospace andElectronic Systems Magazine, vol. 5, no. 9, pp. 3133, September, 1990.

4. J. OHara, W.F. Stubler, J. Kramer, Human Factors Considerations in Control RoomModernization: Trends and Personnel Performance Issues, In Global Perspectives of HumanFactors in Power Generation, IEEE Sixth Conference on Human Factors and Power Plants,Conference Proceedings, Orlando, pp. 4/74/10, 1997.

5. A. Chapanis,Human factors in systems engineering, John Wiley & Sons, Inc., New york, pp. 186;218220; and 228, 1996.

6. F.H. Hawkins, Human Factors in Flight, Ashgate Publishing Limited Gower House, Hants,England, 1987.

7. M. Tory, and T. Moller, Human Factors in Visualization Research, IEEE Transactions onVisualization and Computer Graphics, vol. 10, no. 1, pp. 7284, January/February, 2004.

8. New Lexicon Websters Dictionary of the English Language, Lexicon Publications, Inc., NewYork, 1989, p. 660.

9. S. Pinker, Words and Rules, HarperCollins, New York, p. 335, 1999.

10. A.N. Beare, R.E. Dorris, and E.J. Kozinsky, Response Times of Nuclear Plant Operations:

Comparison of Field and Simulator Data. In Proceedings of the Human Factors Society 26thAnnual Meeting, Human Factors Society, Santa Monica, CA, pp. 669673, 1982.

11. J.W. Lee, I.S. Oh, H.C. Lee, Y.H. Lee, and B.S. Sim, Human Factors Researches in KAERI forNuclear Power Plants, In Global Perspectives of Human Factors in Power Generation, IEEE SixthConference on Human factors and Power Plants, Conference Proceedings, Orlando, pp. 13/1113/16, 1997.

12. IEEE Task Force 15.07.05.05, Recommendedd Practices for Helicopter Bonding Procedures forLive Line Work,IEEE Transactions on Power Delivery, vol. 15, no. 1, 333349, January, 2000.

13. ESMOL Subcommittee 15.07, Safety Considerations When Placing a Person With Tools in anAir Gap to Change Porcelain and Glass Insulators on Transmission Systems of 345 kV and

Above, Using Ladder and Aerial Lift Methods,IEEE Transactions on Power Delivery, vol. 17,no. 3, pp. 805808, July, 2002.

14. OSHA, Ergonomics Solutions for Electrical Contractors, URL: www.osha.gov/SLTC/etools/electricalcontractors/index.html

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