Human Factors in Electrical Safety

INTRODUCTION

The energy sector has significantly contributed to our understanding of the influence of human factors in complex and technically challenging work. Notably, as data collection and analyses have accumulated over the past decade, the sizable role played by human factors in safety failures and accidents has become increasingly clear.

For example, a 1995-1999 Institute of Nuclear Power Operations (INPO) analysis of significant events in the commercial power industry indicated that three out of every four events were attributed to human error (DOE, Section 1, p. 10). Another report, an Idaho National Energy and Environment Laboratory (INEEL) 2001 study commissioned to examine the contribution of human error to risk in operating events, found the following for 37 qualitatively analyzed events:

• Each event had four or more human errors in combination with hardware failures.

• Engineering contributed to 81 percent of latent error.

• Maintenance contributed to 76 percent of latent error.

• Management and supervision contributed to 30 percent of latent error.

Latent errors (i.e., errors committed prior to an accident but not discovered until after the accident) were present four times more often than active errors (i.e., errors occurring during the event response). Human performance observations of root causes of errors considered the characteristics of work ( Table 1) and focused attention on whether employee assignments were

• task based

• rule based

• knowledge based.

===========

Table 1 Common work Characteristics*

Characteristics Examples Error mode

[ Skill based

Rule based

Knowledge based

]

[ Highly practiced, physical actions

Habitual movements with little conscious monitoring

Behavior driven by training or instructions relies on self-check

Modified work due to environmental change detection covered by procedures or past practices work being done when significant knowledge or familiarity is missing response to unfamiliar situation

]

[ Using a hammer

Operating manual controls

Hanging a tag responding to control alarm

Fitting a pipe

Performing an engineering calculation resolving conflicting control board indicators

]

[

Inattention to execution requirements

Misinterpretation Inaccurate information Inaccurate mental models

]

===========

The generation, transmission, distribution, design, installation, operation, and maintenance of electrical power occur in diverse situations. Additional examples of human factors considerations in the electrical industry are presented in Table 2. Given the diversity in workplaces, the applicable human factors depend in part on where in the power system the employee may be working. Employees assigned to a control room at a nuclear power station can reasonably be expected to confront demands in their work that differ from those of employees wiring a house under construction or doing maintenance in a cogeneration facility. So it follows, then, that the human factors in a control room can be expected to differ from those at the construction site.

Industry data confirm the expected variation. With 1.5 million person-years of work analyzed from 17 utilities during the period from 1995 to 2008, review of 52,000 recordable and lost-time injuries showed the following:

• Percent total injuries were highest for line workers (18.2 percent), mechanics (14 percent), meter readers (13.4 percent), maintenance workers (8.7 percent), and plant and equipment operators (7.9 percent).

• Percent total injuries were lowest for custodians/cooks (0.5 percent), managers (0.9 percent), coordinators (0.9 percent), security (1.1 percent), drivers/delivery and drivers/inspectors (1.3 percent), engineers (1.4 percent), machinists (1.4 percent), foremen (1.4 percent), and welders (1.8 percent).

• Percent total injuries fell in the midrange for technical/professional support (5.9 percent), supervisors (3.7 percent), electricians (3.7 percent), administrative support (3.3 percent), and material handlers (2.4 percent).

Overall reported injury rates per 100 employee-years were highest in transmission and distribution (9.94) and shop (9.11) locations and lowest in office (2.15), customer service (2.08), and training (1.08) locations. Midrange rates were reported for field (4.77), substation (4.23), and generation station (4.18) locations.

Across all years of available data among 16 utilities, 1409 full-time equivalents were lost due to injury or illness, and 988 of these losses were due to ergonomic injuries.

==========

Table 2 Power Systems Environments and Human Factors Considerations workplace Human factors considerations

[

Generation

Transmission

Distribution

Construction

]

[ Dust, fumes, noise in fossil fuel environments Features common to control rooms, including

Compact workstations using visual displays

Large overview displays

Increased cognitive workloads as staffing changes

Information multiplicity virtual workspaces

with

Serial access to information and controls

More time spent on secondary tasks

Live-line work , with

Helicopter approaches at high elevations

Moving parts (helicopter rotors)

required calculations: minimum approach distance

Placing person with tools in air gap 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 respirators repetitive motion and lifting heavy loads

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

]

===========

Total medical claims cost amounts were dominated by sprains and strains cases (45.8 percent), fracture/dislocation (14.6 percent), and cumulative trauma/repetitive strain injuries (12.8 percent), leading to further research and interventions to reduce injury risk, considering in particular human factors in ergonomic tool and task design.

OVERVIEW

The next sections include a brief look at the safety strategy called Defense in Depth as well as a summary of the evolution of human factors and a discussion addressing visualization and cognitive ergonomics.

Defense in Depth

As demand for energy has escalated, security and reliability considerations along with safety priorities have given rise to the Defense in Depth strategy. Originally used to defeat enemies during war, Defense in Depth is a layering tactic to achieve comprehensive protective coverage.

First applied to power generation, transmission, and distribution as an out come of analyses of possible terrorist threats against utilities in the Global war on Terror (GwOT), the strategy has as its foundation the creation of multiple independent and redundant defensive layers to compensate for potential unintentional or intentional human as well as mechanical failures.

FIG. 1 Defense in Depth strategy. Increasing safety, security, and reliability in the energy sector depends on complex, layered interactions among people, technology, and organizational operations.

===========

Table 3 Examples of Error Precursors

Precursor type Examples

[

Task

work environment

]

[ Time pressures High workload Multistep or multiaction requirements Boring or monotonous action requirements Ambiguous goals, roles, or assignments Absence of standard work Multiple distractions Multiple interruptions Unexpected conditions Unresolved conflicts

]

===========

The Defense in Depth strategy allows electrical safety to be viewed as an interdependence among individuals, engineered systems, and operational environment, including the organizational culture. The premise is that continuous interactions among people, technology, and organizational operations drive safety, security, and reliability performance ( FIG. 1). With this illustration providing a framework, the contributing factors or "error precursors" to safety failures can be identified (Table 3). Advances in how people work with technology and improvement in an organization's operations are basic approaches used in the Defense in Depth strategy.

Evolution of Human Factors

The study of human factors evolves from the obvious statement that, "People are not machines." In the early 19th century, during the early periods of industrialization, a persistent question arose as to how to optimize the placement of people in "machine systems."

Predating electrical power, when jobs involved assembly-line operations with repetitive tasks requiring uniformity and efficiency of physical movements among operations, materials, and employees, management used studies of "time-and-motion" and human "anthropomorphics" or "average body part sizes" to FIG. out problems such as "how far can an average worker reach to push or pull this piece" on the assembly line.

In the early 20th century, as electrification enabled industrialization to move beyond manufacturing across all economic sectors, the complexity of machine systems increased.

More than one "process" could be pulled into a work environment, leading to multiple operations situated in geographic proximity, running concurrently, and producing output at high speeds.

With electrification, increasing industrial complexity, and faster production rates, the demands on people working with the machine systems grew. As suggested by Rasmussen, at this stage the study of human factors more commonly included measures of human physical abilities along with measures of physical reliability. In this context, "knob-and dial" ergonomics was a research focus-for example, identifying the correct size of knob for an employee to easily grasp doing a turning task and measuring how often the knob would be incorrectly versus correctly turned.

Then, in the 1930s, as automation was introduced into the chemical process industries, the link between machines and people often became indirect.

Automatic control engineering made it possible for individual employees to have wide reach over large scale and significantly hazardous production.

As production failures occurred, interest in the role that human factors played in these failures extended from human "physical" reliability to include the reliability people might show in understanding process information and executing successful decisions.

This specialty later became known as "cognitive ergonomics."

Research on human error developed as an aspect of studies into human factors, with the goal being to "break down" or "untangle" causes of human physical and/or cognitive mal function from machine or process malfunction in post accident studies. Engineers planning installation design and development also considered, human error probability-or human reliability assessment (HRA) as an aspect of human factors during operational engineering analysis.

In the mid-20th century, military experience in world war II aviation and the post world war II growth in civilian aviation further emphasized how interactions between humans and engineered systems could lead to potentially tragic results, as demonstrated by news reports of plane crashes. By the early 1970s, a generally accepted professional approach within the industrial engineering community led to practices regarding how to evaluate the fit between work and workers.

Concurrently, within the electrical power industry, the post-world war II development of the civilian nuclear power industry resulted in an active application of ideas regarding human factors to the management of civilian nuclear power operations. This transfer of ideas developed further following two major tragedies: the Unit 2 scram at the Three Mile Island Power Station (TMI-2) in Pennsylvania on March 28, 1979, and the explosion of Unit 4 of the Chernobyl Nuclear Power Station in the Ukrainian former Soviet Union on April 26, 1986. With TMI-2 and Chernobyl, nations learned that human error in complex operational environments producing electrical power could potentially result in global disaster.

Investigations identified human factors in the causal chain of events leading to these tragedies. This knowledge drew additional focus on basic concepts of human performance.

Continuing to the present, the subject of human factors has moved beyond "human machine interactions" to "human-systems interfaces," or HIS.

The term human factors may have two meanings. Human factors may refer to various traits or "elements of the human" as individuals, which should be considered as priority considerations when engineering systems. Or the term may mean "the applied science technology" relating fundamental human sciences (like anatomy, physiology, neuro-psychology) to industrial systems.

The following discussion about vision later in this section highlights the two meanings.

Researchers turned their focus to environmental influences on human factors as failures continued to occur. Relating Hawkins's "SHEL" illustration of this concept, Kawano described the acronym as follows:

• S: for software, including, for example, computer software, paper documents or instructions, 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 situation8 Kawano added an "M" to Hawkins's SHEL acronym, to include "managing systems" as a dynamic part of the model. As suggested by Hawkins and amended by Kawano, the M-SHEL model provided a step toward an "integrated systems" approach to human factors.

The model offered another strategy for thinking about electrical safety so that the programmatic focus could go beyond the individual to include the technologies, engineering, inter personal, and environmental contributions to individuals' experiences in the system of production where they work.

Today, human factors, errors, risk, and performance are addressed with Defense in Depth strategies and included in integrated safety management, probabilistic risk analyses, and reliability engineering, and inherently safe design programs, policies, and practices.

For example, U.S. Department of Energy (DOE) publications focus on design for the ease of maintenance and performance improvement.

Developing from research on the utility industry, ergonomics handbooks are available for electrical workers, plant operators, and mechanics in fossil-fueled power plants and generating stations.

3,13-16 Additional research is under way regarding construction, operation, and maintenance of wind turbines.

3 Another resource is a guide for developing an ergonomics program titled Elements of Ergonomics Programs: A Primer Based on Workplace Evaluations of Musculoskeletal Disorders, released by the National Institute for Occupational Safety and Health (NIOSH).

The document includes a seven-step approach to reducing musculoskeletal injuries, including guidance for "proactive" human factors design ( Table 4).

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Table 4 Proactive Design Suggestions to Optimize Human Factors

Design focus --- Examples

[ workstation

repetitive

hand/wrist

]

[ Adjust heights to fit for work, seating, and reading surfaces

Position equipment to reduce twisting/reaching/pulling

Position work above elbow height for fine visual tasks

Position workload below elbow height for heavy physical effort

Eliminate excessive noise, heat, humidity, cold, or poor lighting

Minimize work placement causing arm movements that are straight-lined or jerking extended repeatedly through more than 15 inches pivoted around the shoulder

Optimize neutral "handshake" position at wrist/hand

Substitute partial or full automation to reduce repetitions

Limit force required for hand gripping, carrying, or pinch grasp

Limit trigger finger in favor of full finger or automation controls

Control or limit vibration to hands/wrists through power tool selection protective gloves and vibration-absorbing materials

]

===========

===========

Table 5 Examples of Tips to reduce Ergonomic Injuries during Construction

Ergonomic hazard -- Common work activity --- Solution

[

Repetitive stooping with task completed at floor or ground

Screeding concrete bent over with heavy gripping to pull board over concrete repetitive bending and reaching with hand tools

Frequent kneeling, squatting, or stooping

Bending and twisting while lifting repetitive strain at shoulder

Forceful pushing at shoulder/upper back

Heavy repetitive lifting

]

[ Bending over to attach screw to floor-level fixture

Concrete finishing

Tying rebar by hand

Kneeling to lay floor tile

Loading masonry onto a scaffold

Overhead screwing

Finishing drywall

Laying standard concrete block

]

[ Auto-feed screw gun with an attachment

Motorized screed rebar-tying tool with extension

Using kneeling creepers with chest support

Split-level adjustable scaffolding

Bit extension shaft on screw gun

Spring-assisted mud box

Pneumatic drywall finishing system

Lightweight block materials

]

===========

With examples noted in Table 5, NIOSH has also published a series of tip sheets to inform construction enterprises and their employees of cost-effective solutions to ergonomic hazards during

• floor and ground-level work.

• overhead work.

• lifting, holding, and handling materials.

• hand-intensive work.

Visualization

Anything that inhibits an employee's vision creates risk for an electrical event. Consider the two definitions of human factors applied to vision. As a human factor relating to the individual, vision may be understood as limited to the measurement of visual acuity (or accuracy of how well an employee sees a wall chart). A test of visual acuity ensures that an employee has adequate vision ability to read a computer screen or see a stoplight.

On the other hand, vision can be understood as a target of the engineering advancement 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 excessive ohmic heating of installed conductors vision is a critically important human factor. About 80 percent of information about machines and systems comes to employees via their vision.

Note that visual acuity decreases as the complexity of the visual target increases. In other words, when there is more to look at, it is harder to see. Multiple physical factors influence visual acuity, including the following:

• Illumination

• Contrast

• Time of exposure to the visual target

• Color of the visual target and the target's background

The smallest detectable threshold for vision is 10-6 milliliter. Vision ability is decreased with vibration; hypoxia, or low oxygen; and motion of the visual target.

Rasmussen suggested that automation relieved employees of repetitive manual tasks; consequently, work with more decision-making or troubleshooting content became common in the industrial setting. Today, information technology, including the use of computer based approaches that require employees to do intense visual work with multiple screens, has placed volumes of data at the center of employee tasks.

Researchers describe the methods available with computer visualization and graphics that can support perception and cognition, or the human abilities to sense (via eyes, ears, nose, taste, touch) and think. Table 6 gives electrical safety examples in which these methods can serve as cognitive aids.

=============

Table 6 Cognitive Aids with Computer visualization Technologies

[

Cognitive challenge:

Multiple permits per job step

Monitoring for breaker trips, power surges, or faults

Switching procedures in power outage or routine maintenance

]

[

visualization method:

reducing search via data grouping or structure with multiple steps in a job

Perceptual monitoring using pre-attentive visual characteristics Enhancing data recognition, abstraction, and aggregation

]

==============

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Table 7 Employee Attitudes Detrimental to Safety

[

Pride

Heroic Fatalistic

Invulnerability

Pollyanna

Complacency

]

[

Attitude ---

High opinion of self without recognizing the importance of team

Fearlessness and boldness emphasized

Defeated or worse feeling

Immunity to the threats, forces, limits, or risks

Finding the good in everything

Comfortable and accepting of deviations

]

[ Attitude expression---

"I'm doing it my way!"

"I'm always the fireman here!"

"Nothing to do about it . . . it is what it is."

"That's never going to happen to me."

"This is routine and never goes wrong."

"Always happens . . . so what?"

]

===============

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

A key insight from this research is that context is hugely influential over thought. Using the metaphor of the brain as a computer, one way to appreciate the role of context is to suggest that people do not come to their 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 surroundings; what they believe; and how they physically feel. This information loads the "drive and screen," occupying space alongside where "the programs run" or thought happens.

Cognitive ergonomics specifically addresses how to modify what occupies an employee's "hard drive and screen" when work is being done, to improve the way thought unfolds and thereby improve decisions.

Context is not simply the employee's physical background. Context can also take the form of detrimental attitudes and background beliefs. Attitudes highlighted in the Human Performance Improvement Handbook published by DOE12 (Section 2, pp. 5-6) and illustrated in Table 7 shape employee actions as do background beliefs or "work myths." The dictionary defines a myth as "an old traditional story or legend, especially one concerning fabulous or supernatural beings, giving expression to early beliefs, aspirations, and perceptions of a people and serving to explain natural phenomena or the origins of a people."

Following are examples of myths that can affect electrical safety. Exploring these myths offers promise to improve electrical safety by helping employees better understand how their detrimental attitudes and inaccurate background beliefs can influence their safety.

"I'm experienced, so I won't get injured." This belief assumes that experiences protect against injury and death. However, as the statistics in Section 9 suggest, the employee who is most at risk of an electrical event is between the ages of 25 and 45 years and with accident-free years on the job. To the extent that employees' experience dulls their awareness of the distinctive features of the job they are performing, their experience may create a false context for thinking about situational facts such as the following:

• 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 isn't paying attention." This mythic belief 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 been inattentive.

Comments like the following presume inattention as an explanation for electrical events:

• "He wandered off in his thinking."

• "She was daydreaming on the job."

• "He was worried about something else."

However, through many debriefings of electrical accidents, engineers have come to appreciate that modern electrical work unfolds in highly complicated situations. If an electrical safety failure occurs, as the earlier data presented about latent and active errors suggest, typically more than one thing goes wrong. Multiple system faults or personnel errors contribute to the event. This understanding suggests that attention alone is not sufficient to prevent an electrical accident. Given the embedded complexity in the power system, multiple actions are required to preserve safety. How to sharpen or focus the actions of human attention is a research target of cognitive ergonomics.

Related to attention is the ability to hear. If employees can't hear instructions they are being given verbally, they can be expected to have difficulty in their focus on the instructions or attention to the verbal guidance given.

Hearing as a limited human factor depends on sound. Sound pressures needed for hearing are a function of the material or media (e.g., air) through which the sound or acoustic waves are propagating.

The threshold for hearing in the frequency range of the spoken word, from about 1000 to 5000 Hz, is about 20 µ pascals (2.9 × 10-9 psi).

According to Chapanis, a listener's ability to detect sound depends on multiple factors, including the following:

• The listener's age

• The listener's history of past or ongoing noise exposure whether the listener is using one ear or two to hear, with the use of one ear (monoaural listening) requiring 3 decibels more sound pressure

• The sound's acoustic frequency, expressed in hertz

• The presence of competing sounds, or masking

• The complexity of the bandwidth tones

• The sound's duration, with durations less than 200 milliseconds requiring increased intensity (i.e., as acoustic signal duration is halved, the intensity of the signal must double to be audible) returning to the M-SHEL model of human factors, the interaction of "liveware," or people, depends on successful communication. To the extent that employees cannot adequately communicate because they cannot hear each other talk, safety is jeopardized.

So the physical ability or individual human factor of hearing can affect the ability to communicate, which can affect attention, which is influenced in part by background belief, or context.

"As long as I don't touch an electrical source, I won't get shocked." This belief correctly identifies the need to avoid exposure to shock hazard. However, mechanical contact is not necessary for an employee to be shocked. Returning to the M-SHEL model, the mythic belief here underplays the role of environment in its influence over the individual human factors of body size and positioning in relationship to electrical conductivity, resistivity, and impedance.

Electricity is conducted along copper or aluminum wires in power generation, transmission, and distribution. Depending on the current, when an employee's body comes sufficiently near to an electrical source, the charge that is carried by electrons in copper or aluminum wires may be converted through 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 a role in whether electricity can cross an air gap by arcing and flow through or around the employee. The resulting shock can be destructive, even fatal, if adequate personal protection is not being used.

Human factors studies suggest that employees have little opportunity to react during an electrical hazard exposure. Reaction times for responses to stimuli (like buzzing or light shocks), "word" information, or other prompts have been studied as a human 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 the same 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 efficiency and lengthen reactions. Responses are relatively slower when language is involved. For example:

• A printed word is registered in the reader's brain in about an eighth of a second (0.125 s).

• A spoken word is accessed by a listener's 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 and another quarter of a second (0.250 s) to program the mouth and tongue to pronounce the name (total: 0.500 s).

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

• An average physical movement (motor) response time of >0.600 s in healthy people tested

• An average nonmotor response time of >1.050 s in adults asked to say verbs for printouts of words shown as visually presented nouns In Section 1, the thresholds for neuromuscular responses in response to electrical cur rent were reviewed. Compared to electrical responses, motor and nonmotor responses to language 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 electrical 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 for which maximum risk is present from the fault. This time mismatch is even more pronounced when there is a need to sequence perception, 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 younger than 15 years. Certain situational conditions generally slow reaction time and increase its variability for a person, including the following:

• Sleep deprivation

• Fatigue

• Time of day

• Environmental extremes

• Alcohol or other drug use

• Medical problems

• Nutritional status

Notably, sleep research studies have found that on-the-job reaction times may be many times longer than what is found in a "lab" setup, especially for specific kinds of tasks requiring physical exertion and mental concentration, such as those found in electrical work.

Summary

Innovations resulting from the study of human factors have led to increased safety, security, and reliability of electrical energy generation, transmission, and distribution. To maximize success, layered strategies must extend beyond the individual across technology platforms and organizations. Employees have physical and mental limits when they perform complex and potentially hazardous tasks; reducing precursors and latent errors requires management, engineering, and maintenance approaches.