Human Factors and Ergonomics

"HUMAN FACTORS," "HUMAN FACTORS ENGINEERING," AND "HUMAN ERROR"

Terms associated with "human factors" include "human characteristics," "human factors engineering," "ergonomics," "human engineering," and "the human element."

"Human Factors" Viewed as "Human Characteristics"

The phrase "human factors" is often used to mean "human characteristics." Various human factors in this sense generally fall into one of three groups of human characteristics: (1) physical characteristics, (2) physiological characteristics, and (3) psychological or behavioral characteristics. These groups of human factors are not necessarily mutually exclusive. Here human factors defines the nature of our "humanness," that is, the characteristics of "being human."

Physical human factors include physical attributes of the human body such as height, weight, arm reach, center of gravity, etc. Physiological human factors include such things as muscle strength and endurance in different body positions, visual acuity, tolerance to extremes of temperature, frequency range of human hearing, etc. Psychological or behavioral human factors include things such as mental reaction time to various stimuli, various acquired meanings associated with certain colors (red often means "danger"), the capabilities and limitations of short term memory, "expectancy" as an element of perception, etc. In addition, there are cultural norms that must also be taken into account. For example, in the U.S. cultural environments, electrical switches go "up" to turn on and "down" to turn off; hot water valves are on the left of the faucet outlet and cold water valves are on the right; electrical dials turn clockwise to increase flow, but a fluid valve turned clockwise will decrease flow, etc.

As a scientist, the human factors specialist or engineer does not attempt to judge human factors as right or wrong, correct or incorrect. Rather, the human factors scientist merely attempts to understand and define these factors, or human characteristics, so that their strengths and weaknesses, and their capabilities and limitations might be taken into account when designing systems where persons are to be an essential component, in the same way that a mechanical engineer must understand, define, and take into account the characteristics of physical materials included in a structural design.

Human Factors Engineering

Human factors engineering is the discipline dedicated to optimizing the relationship between technology (system hardware and software) and the human operator of various systems. Any man-machine system can and should be the target of human factors engineering. Anywhere you find technology and people interacting, there is a need for human factors engineering. (Kantowitz, 1983, paraphrased)

During the design stage of system, product, and facility development, for the purposes of optimizing efficiency and safety, the human factors engineer is trained to take into account certain relevant human characteristics of the people who will operate or use such things, and then design such systems to be compatible with those characteristics. That is, a human factors engineer designs things to provide the "best match" between system user capabilities and limitations and the relevant system hardware components that impose physical, physiological, and/or psychological demands on such users.

A competent mechanical or civil engineer will design a structure to take advantage of the particular strength characteristics of the material being used for construction. A competent mechanical or civil engineer would not design a structure outside the strengths and limitations of the materials being used, as this would pose a foreseeable and unacceptable risk of structural collapse. In like fashion, a human factors engineer, or any engineer using human factors engineering design principles, when designing a system that will contain a human component (such as a human operator), will design the system to "fit" or take advantage of the strongest and most effective human characteristics related to system requirements, and will not design a system that makes demands on human performance that are near or outside the areas of human strengths or the most effective human capabilities.

Ergonomics

The terms ergonomics and human factors are often used synonymously. Both describe the interaction between the operator and task demands, and both are concerned with trying to reduce unnecessary stress and resulting injury to persons engaged in a certain activity or operating certain equipment. The term ergonomics originated as a European term while human factors is more often used in the United States.

Ergonomics has traditionally focused on how work affects people, while the emphasis in human factors (engineering) is on the design of systems that reduce the potential for system operation errors and prevent injury. Ergonomics may involve studies of physiological response to physically demanding work; environmental stressors such as heat, noise, and illumination; the performance of complex psychomotor tasks; and activity involving elements of visual-monitoring. The emphasis in ergonomics has been on ways to reduce fatigue by designing tasks within people's work capabilities. The goal of an ergonomics work program is to achieve the optimal match between persons doing work and the overall work environment.

Human Engineering

Human engineering has been defined (similar to the term "human factors engineering") as a discipline concerned with designing man-made systems so that people can use them effectively and safely, and the creation of environments suitable for human living and work (Huchingson, 1981).

Human engineering is often used interchangeably with "human factors," or "human factors engineering." Unfortunately, it is a term that begs to be misinterpreted and should be avoided in light of better available terms such as "human factors" and "human factors engineering." The words and order of words used in this term can imply to the uninformed that it is the human that is to be "engineered," or "changed," rather than the system.

"Human Factors" Viewed as "The Human Element"

The term "the human element," or "the human factor" is often heard in conversations of persons having little or no true knowledge of "human factors" or "human factors engineering." It is often used by persons to express their personal bias or prejudice concerning the behavior of certain people related to a specific event being examined. When something goes wrong, the term "the human element" is typically used as follows: "Well, what do you expect when you're dealing with 'the human element'?" In this sense, it is an attempt to blindly judge or blame people as being "idiots," or "stupid," or worse. It is also a term that typically is arrogantly intended to apply to everyone except the speaker. As such, it is a term that should not be used by human factors professionals.

"Human Error" vs. "Human Nature"

Just as one should take human factor strengths and limitations into account during the design process, one should also take human factor strengths and limitations into account when assessing the contribution of the "human element" in accident analysis. One must distinguish between the concepts of "human error" and "human nature." Human nature is the "given" and relatively unchangeable part of humanness. Human error can only be a valid concept under certain specific conditions.

This concept is at the core of human factors engineering. It recognizes that humans are complex creatures having not only a wide range of capabilities but a corresponding wide range of limitations. Humans are bound by specific innate characteristics, that are not subject to significant change, which dictate specific behavior under particular circumstances. Such behavior must be considered as part of human nature and not mislabeled as human error.

"Human error" may result from a combination of "human nature," "random error," "design induced human error," and "true human error."

"Human Error" vs. "Random Error"

True human error must be distinguished from "random error." Random errors committed by system operators are nonpredictable by both system designers and operators. An example of a random error would be the reflex action that causes a wrong control to be activated as the result of an unexpected mosquito bite. Random errors can also involve improbable but "normal" extremes of human variation. For example, even persons who are well trained and have repeatedly used a well designed system will occasionally make inadvertent errors related to rare and unintended (and uncontrollable) variations in required hand-eye coordination.

"Human Error" vs. "Design Induced Human Error"

An axiom of human factors engineering states that, "How a system is designed will dictate how it can and will be used." True human error must be distinguished from "design induced human error" where some (engineering or administrative) aspect of the system design (such as a lack of safety features, the presence of reasonably anticipated operator distraction or overload, or the presence of excessive or contradictory system demands) predisposes such error; that is, where the system operator is "set up" to make the error by some design aspect of the system. Such "errors," if they can rightfully be called errors at all, are predictable and therefore preventable through re-design. Design induced human errors can be viewed as procedural deviations that reasonable foresight should have anticipated as likely to occur under the design conditions created by system designers or managers. Reasonably discoverable foreknowledge that such errors might potentially occur implies a primary responsibility for such errors by those who failed to reasonably foresee them to the extent that such error could have been eliminated or minimized at the design (or administrative planning) stage of system development.

True Human Error

Although human error can be simply defined as "any person's actions that are inconsistent with established behavioral patterns considered to be normal or that differ from prescribed procedures" (Hammer, 1989), if culpability is to be assigned to such error, the "established behavioral patterns" (considered "normal" by whom?) and "prescribed procedures" must be reasonable under the circumstances.

True human error is most properly defined as an action that would not have been committed (or an action that would not have been omitted) by ordinary, reasonably prudent persons under the same or similar circumstances, while taking common human factor limitations into account, and after eliminating other forms of "human error" from consideration.

True human error may be error that is deemed to be inconsistent with well established behavioral patterns or that differs from well established prescribed procedures after (a) it has been determined that system designers or managers did not fail to reasonably anticipate or foresee such (or similar) error, (b) the system in which the error takes place has been designed to minimize such errors, and (c) persons involved are well informed (properly and adequately trained). Such training must include not only an understanding of the full nature (consequences) of potential errors and the proper procedure to avoid them, but it must also assure the system demands imposed on such persons that might detract from correct performance have also been taken into account and eliminated, or at least minimized and deemed acceptable by applying all readily available safety or human factors engineering or administrative means. Otherwise, such distractions or system features that fall short of reasonable system design or administrative standards must be recognized as mitigating factors to the designation of true human error.

True human error can only be said to occur when the system in which it takes place has been well engineered (according to the basic principles and reasonable application of safety engineering and human factors engineering) and the demands imposed on adequately trained system operators are realistic in relation to human factor (human nature) capabilities and limitations of such persons. Only under such circumstances is the system operator truly free to choose his or her actions.

One method that can be useful to distinguish between true human error and other forms of alleged human error is to ask this question: If a thousand reasonably prudent persons were placed in the same or similar circumstances, would a significant number make the same or similar error? If so, one's search for causation must go beyond the apparent identification of simple human error.

"Dynamic" vs. "Static" Human Error

"Static" human error can be thought of as error that occurs under relatively quiescent conditions; that is, it is error made while one has almost unlimited time to focus on an issue with relatively little distraction. It is, in effect, error made while having time to "put your feet up on your desk" and contemplate.

"Dynamic" human error, on the other hand, is error made "in an instant" when related conditions or activities involve significant complexity and distraction. That is, dynamic human error is error made in "the heat of battle" or while engaged in some form of dynamic activity.

"Primary" Human Error vs. "Incidental" Human Error

"Primary" human error can be thought of as error made by those who have a primary assigned or special responsibility and the special expertise to focus on the subject matter of the error. An "incidental" human error, in contrast, is error made by those who have a secondary or oversight responsibility or lack the special expertise to focus on the same issue.

Thus, a "primary" error made by a professional, if made by a layman, would be an "incidental" error; a "primary" error made by a "teacher," if made by a student, would be an "incidental" error; a "primary" error made by top management regarding the establishment of adequate work procedures, if made by a worker in the absence of such established procedures and adequate training, would be an "incidental" error; and failure to incorporate a safety feature into a particular system design would be a "primary" error on the part of the system designer, while not being able to compensate for or cope with the lack of such a safety feature on the part of a system operator, would at best be called an "incidental" error.

Select References

Huchingson, R. Dale, New Horizons for Human Factors in Design, McGraw-Hill, 1981.

Kantowitz, Barry H., Human Factors: Understanding People-System Relationships, John Wiley & Sons, 1983.

Meister, David, Human Factors: Theory and Practice, John Wiley & Sons, 1971.

Rodgers, Suzanne H., and Elizabeth M. Eggleton, Editors, Eastman Kodak Company, Ergonomics Design for People at Work, Volume 1, Van Nostrand Reinhold, 1983.