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Human Performance Science & Technology

Human Factors is the scientific discipline concerned with the understanding of interaction between humans and products, equipment, facilities, procedures, and the environments in which they are used in work and everyday living. The field is a blend of engineering, psychology, anatomy, physiology, and several other complementary disciplines.  It takes information regarding human capabilities, limitations, behaviors, and cognitive/sensory phenomena and applies it to the analysis, design, and use of products, equipment, built structures, and environments to maximize both safety and productivity.

Unlike traditional engineering disciplines in which the focus is almost exclusively on the machine component, Human Factors focuses primarily on the human element of the human-machine-environment system, and how the operator’s interaction with machinery of all types must influence its design and implementation, as well as how this human-machine interaction influences the performance and safety of users in real-world situations.

Traditional engineering builds products for users, but the knowledge base of the most engineers is almost exclusively focused on the machine itself, and not on either the individuals who will be employing it or the environment in which it will be used. Human factors employs scientific data regarding the capabilities, limitations and behaviors of the user in real-world environments to the design and analysis of machinery in order to magnify the overall effectiveness, efficiency, and safety of the end product.

Virtually all accidents involve human factors issues of some type. ITC has some of the most skilled and highly-educated human factors experts in the industry. We provide consulting and expert services for litigation, risk assessment, insurance investigations, consumer product design, and industrial safety. Our staff employs a multi-disciplinary approach, blending theories and techniques from the biological, behavioral, and engineering sciences. In the investigation of accidents, our staff uses their in-depth knowledge of user sensory, physical, and cognitive capabilities to analyze and interpret how and why an accident occurred, as well as how (or even if) they might have potentially been prevented.

Human Behavior, Capabilities, and Limitations

Cognition is a very broad term, though one which is not necessarily easily defined.  In general, it refers to human intellectual processes such as perception, attention, learning, memory, thought, concept formation, reading, problem solving, planning and reasoning. All of these factors directly influence the use, misuse, or possible abuse of products, potentially leading to or contributing to accidents. Human factors involves the nature of the how and why human beings think, reason and process information.  It is often a truism that users do not interact with products so much as they interact with their own mental models (representations) of the products.  These representations involve their understanding of how they believe the product functions, their past experience with the particular product or others they believe to be mechanically or functionally similar to it, and other information that they believe is appropriate or relevant to it. The greater the level of similarity between their mental model of a product or process and the actuality, the more their behavior using a product will approach that which the manufacturer intended.It is also necessary to understand what a user can do as well as what an operator should do in understanding the nature of accidents. Suggesting that an operator should have been attending to all of the activity around them during the course of their activities is often alleged in the courtroom, but is frequently impossible in the real world.  Users only have a limited amount of attention to bring to a task, and it must be apportioned parsimoniously and appropriately.  Suggesting, for example, that a driver should have focused as much attention on their rearview mirror as they do on their forward path of travel may be “safer”, but is unlikely to occur in actuality.  Human factors focuses on how individuals actually perform real world tasks based on empirical science, not abstract ideals or employing hindsight.Much of the science of human factors is focused on the experimentally-derived determination of the capabilities and limitations of the human operator, both in terms of maximum possible performance and most likely performance under particular sets of circumstances.  The fact that an individual alerted prior to an “emergency” (i.e., who is aware of both what is to occur and what they need to do about it) can react within a certain amount of time says very little about the performance of the same individual in a real world situation. Understanding how situations and environments affect real-world performance is often a key component to understanding how and why and accident could or could not have occurred.

Perception, Vision and Visibility

In many cases, the question of what could have been seen by one of the parties involved in an accident is a critical one.   Vision and visibility are affected by a wide variety of factors, both internal and external to the individual.  Internal factors include such variables as age and visual infirmities, abnormalities, or corrective measures.  External factors include variables such as illumination level, color, contrast, and target size.Oftentimes these variables interact with one another and an understanding of the human visual system and how its native capabilities and limitations are affected by both types of factors is of critical importance.  A “one size fits all” or “cookie cutter” answer is rarely either appropriate or correct.Perception is often thought of as being synonymous with the term sensation, but this is an almost total misunderstanding of the concept. William James (a pioneering American psychologist and natural philosopher) may have put it best when he said, “Whilst part of what we perceive comes through our senses from the object before us, another part (and it may be the larger part) always comes out of our own mind.” “Sensation” refers to the immediate response of our sensory receptors (eyes, ears, nose, mouth, fingers, etc.) to such basic stimuli as light, color, and sound. “Perception”, on the other hand refers to the process by which sensations are selected, organized, and interpreted by the individual.People only process a small amount of information available to them, and an even smaller amount is actually attended to and thus given meaning.  The process of perception involves long-term memory and experience and is therefore subject to assumptions and biases and involves considerable hypothesizing and guessing with regard to what is and is not important.“Attention” refers to the extent to which processing activity is paid to a particular stimulus.  Witnesses often suffer from sensory overload (i.e., exposure to far more information than they are willing or able to process.) Inattentional blindness may result when the focusing of attention on certain tasks or scene elements prevents noticing other stimuli (this is a common cause of car/motorcycle collisions.)

Human-machine Interaction and Performance

It has long been recognized that not all human-machine interfaces result in equal performance or safety, but this does not indicate that non-optimal designs are inherently unsafe or unreasonably dangerous.  The concepts of styling and product differentiation implies that there is often a range of acceptable designs and alternatives.Understanding how the interaction between humans and products/equipment is affected or influenced by the design of the product is a key component to minimizing or mitigating unwanted or unsafe operator behaviors.  Human factors research has contributed such an understanding of such issues since prior to World War II.

Operator-vehicle Interaction and Performance

Operator behavioral issues range from the nature of expertise behind the wheel (i.e., the difference between novice and experienced drivers) to the effects of secondary tasks on the performance of the driver (i.e., what is commonly referred to as “driver distraction” in the popular press) to such issues as driver fatigue or emergency reactions/responses.  There is an extensive body of human factors research in this arena dealing with normal or typical driver performance parameters, as well as research dealing with subpopulations such as older drivers and cell phone users.  Much of this research does not conform to the “conventional wisdom” which witnesses from other disciplines (e.g., accident reconstructionists) may believe to be true.

Warnings and Instructions

While necessary in many cases, warnings are either unnecessary or actually inappropriate in others. Although counsel may lobby for additional warnings as a defense against potential litigation, “over warning” itself may actually be harmful for at least four reasons. Excess warnings increase the likelihood that the reader will simply skip over all the warnings. This can create a quandary for the product manufacturer. The decision whether a warning should be included with or on a product is a complicated one and no “one size fits all” answer is possible.One of the better guidelines for when a warning is necessary was published by American Society of Safety Engineers. According to their guidance, the purpose of warnings is to call attention to ahazard and to change or reinforce the way it will be perceived by the viewer in order to avoid accidents or injuries. Generally, a warning is desirable when a hazard is foreseeable, in addition to meeting the following criteria:(1) The hazard is, by definition, dangerous;
(2) The danger posed by the hazard is or should be known to the producer, manufacturer, supplier, or facility manager;
(3)The danger is not one which is obvious, known, or readily discoverable by the user (viewer);
(4) The danger is not one which arises because the product or substance is put to some completely irrational use by a viewer.Instructions follow similarly.  Instructions are necessary when the proper use of a product needs to be conveyed to the end-user of a product. The nature and extent of instructions are predicated on the lowest likely level of experience and/or training of the end user. For example, it is unlikely that a completely naïve user will be placed at the controls of a multi-million jet aircraft. The instructions to the user of such a product should be geared to the potential user, not necessarily be reflective of the lowest common denominator of the public at large. Approaching training from the standpoint that everything must be trained, no matter how trivial or unlikely normally results in the loss of attention of the trainees and the lack of conveyance of significant information (think of the results of staring an introductory calculus class with such fascinating facts as 1+1=2).


Training is one means by which residual risk in products or activities can be reduced. Training should be focused both on that which is appropriate for the likely users of a product, as well as that which is unknown by them. One potential example of unnecessary training is the seatbelt portion of the lecture which is provided to passengers after boarding an aircraft. The last American automobile which did not require seatbelts was built in 1971. While it is potentially possible that some passenger may have never traveled in a vehicle less than 40 years old, the likelihood is vanishingly small. The need for instruction on the operation of the seatbelt is unnecessary, and (based on personal observation) counterproductive in that the overwhelming majority of passengers quickly “tune-out” when such well known information is presented and never tune back in. Alternatively, training which focuses on information which the user obviously needs and benefits from knowing usually is better attended to and retained by the audience.

General, Industrial, and Operational Safety

Black’s Law Dictionary defines the word “safe” to mean “Not exposed to danger; not causing danger” and cites as an example “driving at a safe limit of speed”.  Black’s definition and example are internally inconsistent with each other. The mere fact that one is traveling at a particular speed does not render one free from danger. Consider the potential for being injured or killed if one elects to bring one’s vehicle to a complete stop in the middle of a roadway. Arguably, based on the amount of kinetic and potential energy involved in the vehicle, zero would under this definition would arguably be the “safest” speed under Black’s definition. Such a position is logically unsupportable.  The National Safety Council’s Accident Prevention Handbook provides a much more rational definition of the word safeas “The control of recognized hazards to attain an acceptable level of risk.” The same source defines “safety” as “A condition of relative freedom from danger.”

ANSI B11.0 defines the term “acceptable risk” as “A risk level achieved after risk reduction measures have been applied. It is a risk level that is accepted for a given task (hazardous situation) or hazard.” The same document in its Informative Notes on this topic states that “The expression “acceptable risk” usually but not always refers to the level at which further technologically-functionally and financially feasible risk reduction measures or additional expenditure of resources will not result in significant reduction in risk. The decision to accept (tolerate) a risk is influenced by many factors including the culture, technological and economic feasibility of installing additional risk reduction measures the degree of protection achieved through the use of additional risk reduction measures, and the regulatory requirements or best industry practice.”

ITC recognizes that all product design represents a series of tradeoffs between various alternatives with different strengths and weaknesses relative to each other.  There is rarely a viable absolute “best” alternative across all of the variables that must be considered in the design of a product, nor is continuous risk reduction the only criterion of importance. Even when risk reduction is determined to be necessary, ANSI B11.0 specifically notes the following:

Not all potential risk reduction measures are practicable. Many factors determine the risk reduction measure is practicable. It is necessary to evaluate the application of the risk reduction measure against the following factors:

  • regulatory obligations
  • effectiveness
  • usability
  • durability and maintainability
  • ergonomic impact
  • cost
  • introduction of new hazards
  • productivity
  • machine performance
  • technological feasibility

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David Curry, Ph.D.                               
(630) 701-7703
Mary Pappas
(630) 757-5369