Human Factors Experts, Article 1; Buffalo Law Journal, January 23, 2003

Robert C. Sugarman, PhD, PE; RCS Performance Systems, Inc., Buffalo NY

Back in graduate school, the Psychology Department chair at MIT liked to tell his classes about the three Laws of Nature: the Law of Falling Bricks, the Law of Falling Cats, and the Law of Falling People. Physicists have formulated the precise laws that describe how a brick falls from a table to the floor. Biologists have discovered how cats fall differently from bricks, twisting reflexively to always land on their feet. But what laws completely describe a person falling from a roof? This is the challenge of behavioral scientists.

To the professor, the Law of Falling Bricks implied all of the physical science laws that explain why and how physical and chemical events happen, such as what happens to the light of headlights as it reflects off a wet highway and what factors affect the image that appears on photographic film. And he included all of the biological sciences in the Law of Falling Cats. This knowledge tells us much about how the brain works and how our bodies react to force and the environment.

But the professor’s point was that unlike bricks, the behavior of people is influenced by many factors, some of which are not easily observed. He would ask, Why did the person fall off the roof? Was he pushed? Did he slip? Was he trying to commit suicide? Did he simply lean over the edge too far because there was no railing? Was he not paying attention? Did he disobey a safety rule or remove a guardrail? Did he not perceive that he was at the edge? Human factors specialists consider these possibilities to explain and predict human behavior

Human factors specialists come mostly from backgrounds in experimental or cognitive psychology and industrial engineering, as well as other fields that deal with human behavior in the context of equipment, the environment, and other people in a work or play situation. Some of us are educated in more than one discipline which is often important in understanding all of the factors that contribute to behavior.

The traditional role of the human factors specialist is to aid in making a person efficient, safe, and comfortable in any activity. We not only design work environments and procedures to meet those goals, but ensure that information and training is provided when and where needed. In cases where those measures did not prevent an accident, we are asked to use this expertise to figure out why and how it occurred, and how it could have been prevented.

Typical forensic applications of human factors expertise are answering questions about human abilities and limitations for attention, memory, motivation, perception, movement, and strength. These questions often come up in the context of auto accidents, slip and fall, warnings and labels inadequacy, and industrial accidents. An area that is rapidly gaining attention is medical accidents, especially caused by device design errors.

A question posed to me during an industrial accident trial early in my career made me think about what we can know about another person. I was asked, “Don’t people have an obligation to protect themselves from danger?” I answered that the question is more a matter of philosophy and not within the domain of human factors. If people always protected themselves as a matter of obligation, no one would take on a job that was not inherently safe. That would include almost every occupation we depend on for our well being.

On the other hand, we all have the obligation not to put others in danger by designing or using unsafe work situations, including tools, equipment, and environmental factors. We should also be expected to obey rules and instructions that are provided to keep us safe. Sometimes people rely on common sense to guide other people into doing the right thing, but common sense is not common.

As human factors experts we know that when we cannot rely on the Laws of Falling Bricks and Falling Cats to make a person safe, we must use behavioral research, human factors design guidelines and handbooks, and thorough job analyses to minimize danger in an environment. Lawyers should expect us to account for every relevant factor, whether under the domain of Bricks, Cats, or People.

When I became Chair of the Forensics Professional Group of the Human Factors and Ergonomics Society I posed these questions to our members: Just what do we mean when an accident is attributed to “human error”? Under what circumstances could two human factors experts arrive at opposite conclusions? In future installments, I will address some interesting issues based on these questions, as well as some misapplications of scientific studies that often find their way into testimony.

Human Factors Experts, Article 2; Buffalo Law Journal, April 24 2003

Robert C. Sugarman, PhD, PE; RCS Performance Systems, Inc., Buffalo NY

It was a dark and lonely night – as your client, a middle aged man, drove along an unfamiliar country road, watching out for deer that often jump out in front of cars at that time of year. Soon after the road curved to the right he realized that a disabled car with no lights on was angled across the road in front of him. He was driving well within the speed limit, but, as you may have guessed, he couldn’t stop soon enough to avoid a collision.

During his deposition, your client responds to a question by stating that he saw the car just as he was passing a driveway to a farm. He recollected that he saw a driveway just at that time and knows the driveway was there because he saw it again upon revisiting the scene.

The plaintiff claims your client had plenty of time to see the disabled vehicle and should have come to a stop without a collision. His expert uses the knowledge that perceptual reaction time for a driver is 2.5 seconds and given the sight distance from the driveway to the disabled vehicle, your client’s acknowledged speed, and the braking distance for his car, your client would have had 3.5 seconds to react.

Reaction time is at the heart of many human factors analyses. The answer to the question, “What is the minimum human reaction time”, is that it can be as short as about 1/5 of a second or as long as “never”.

Shorter reactions times can occur when the signal and response are simpler – remember the game where you hold your hands under someone else’s and then you try to slap their hands before they can pull them away? In contrast, an unfamiliar or unexpected stimulus can require a longer reaction time.

Reliable research shows that reaction time for a driver to see a signal and move from the gas pedal to the brake is around 1/2 second. That’s when very little else is competing for attention and the driver knows that the signal will occur and what it looks or sounds like. Controlled on-road and driving simulator studies can satisfy those conditions.

So where does perceptual reaction time (PRT) come from? Why is it accepted to be 2.5 seconds?

Decades ago, highway designers needed to know how far ahead a driver should be able to see in order to react quickly enough to hazards. Studies of driver reaction time showed that within 2.5 seconds just about all drivers will see and react to an object placed in the road. Most drivers reacted more quickly than that. So the American Association of State Highway and Transportation Officials (AASHTO) adopted 2.5 seconds as the standard to determine how much of a curve, rise, or fall that may be built into a road. The experiments were not designed to account for night driving or the fact that headlights do not bend around a curve before the car does. Nor that a prudent driver must time-share attention to what is in front of him with looking at the mirrors and the sides of the road to watch out for those deer.

What else accounts for longer reaction times in driving? Ambiguous or unexpected hazards lengthen mental processing time, and shared attention with other critical driving tasks lengthens detection time (it takes at least a third of a second to glance in the rearview mirror). Focusing intently on some potential hazard is a situation that may produce an effect named “Inattentional Blindness”. Researchers have concluded from a number of scientific studies that there is no conscious perception without attention. Inattentional Blindness explains why we fail to perceive major things that go on right in front of our eyes. In essence, Inattentional Blindness is people’s inability to detect--or perhaps to remember--unexpected, unrelated, or irrelevant objects to which they are not paying attention.

Driving down the dark street, once your client focused attention and detected something in the roadway, he had to discriminate it from normal shadows and reflections seen at night, and then identify it as an obstacle.

But the mental processing isn’t over yet. He must decide if there is enough time for a panic stop. If he thinks not, should he choose to swerve off the road? But it’s dark and there may be additional and potentially lethal hazards there, so he slams on the brakes. All of this can easily require more than 2.5 seconds.

Perceptual reaction time may be useful for designing highways driven in the daytime, but it does not represent what may be expected of the typical driver under all driving conditions.

How much time was actually available for your client to react? The opposing expert used the statement that your client made that he saw the disabled vehicle just as he passed the driveway. Research shows that a person’s memory for the order of events during stress is poor. Your client picked a landmark more likely because he remembers passing it than because he was somehow paying attention simultaneously to irrelevant features on the side of the road while analyzing his predicament straight ahead. When did he see the car? His more realistic answer should have been, “I don’t know.”

Human Factors Experts, Article 3; Buffalo Law Journal, July 31, 2003

Robert C. Sugarman, PhD, PE; RCS Performance Systems, Inc., Buffalo NY

To err is human; to design is divine.

Forensic Human Factors specialists help lawyers analyze the root cause of an accident by determining who erred and why.

Human factors applies research from a number of fields to design and evaluate things that people use in work and everyday activities. The goal of human factors, now also known as ergonomics, is to provide efficient, safe, and comfortable equipment and work environments. Human factors is a specialty that began to mature during World War II when the need became urgent to make military equipment safer for our personnel to use. Military psychologists determined the capabilities and limitations of operators and maintainers so that equipment and jobs could be better designed and people could be selected and trained properly for their jobs.

When people become involved in an accident, observers often apply the phrase “human error” (or the related “pilot error” when aircraft go down) and seek out an obvious individual to blame. A human factors analysis that takes the entire situation into account might find that the “an accident waiting to happen” is a more applicable description.

To understand an accident, human factors looks at what caused the chain of unfortunate events and differentiates between errors made by the people directly involved and errors made by the “designers” of the accident environment, while also considering the role of chance (“acts of God”).

Part of the accident environment is made up of the pre-existing natural environment and ongoing natural processes such as the weather on the highway and aging processes in the body. The rest of the environment includes the features designed by people and their corresponding policies, procedures, regulations and laws.

The people who are the designers may make errors and those errors may be caused by knowledge limitations or by the designer’s intentions.

Knowledge limitations include unforeseen or unknown phenomena that cause accidents. For example, before it was recognized and studied, wind shear caused aircraft to crash during landing. It was not predictable when airplanes were first invented. Because of its importance, engineers and scientists developed instruments and procedures that have taken it out of the realm of acts of God and now have reduced the incidents.

But when designers make no attempt to understand the implications of their designs for the human users or the relevant science that should be considered, the result can be design-induced errors. The infamous Three Mile Island nuclear power plant accident is a classic example of the “accident waiting to happen”. Displays were located far from the controls that they were related to. Displays showed inappropriate information and some important information was left out. Information overload as the accident progressed made matters worse. These errors were foreseeable if the designers had only looked beyond their own specialties.

And then there were Florida’s butterfly ballots!

All too often, engineers and designers do not seek out the wealth of knowledge we have about human abilities and limitations and the decades-old scientific methods we have for including human characteristics in the design of their systems.

This happens when the designers would rather count on the adaptability and trainability of people to overcome any leftover or future problems.

The remaining errors in design are caused when knowledge is available, but is incorrect or misapplied. When laws regarding safety are influenced by politics or economics, designers may follow the regulations but end up with, for example, no sprinklers in a nightclub where knowledge of human behavior would dictate otherwise. Then, of course, there are designers and inspectors who know the rules and regulations and choose to ignore them. When an airline installed a cabinet in the bulkhead of an aircraft’s galley, the FAA inspection ignored its own prohibition for objects to project into workspaces. Sure enough, a flight attendant was hurt on the cabinet during turbulence.

Design errors in the medical field are finally receiving the attention they demand. These include instructions that are not standardized, names of medications that are easily confused, equipment with inadequate instructions or operation that is contrary to other equipment, connections for different gasses that are interchangeable so that nitrogen can be connected to where oxygen is needed, inadequate instructions for patients, and on and on. We have long known how to identify and eliminate these design problems.

Design error leads to accidents when designers do not take into account people’s abilities, characteristics, experience and the task’s complexity.

Finally we come to the errors made by people directly involved in the accident. If people make errors because of human limitations then a negative connotation to their behavior is a bad rap.

People are limited in their information gathering and processing capabilities and those may be different from one person to the next. When a situation places sudden or high extra demands on a person they may not be able to detect the cues that would otherwise warn them to alter their action. Any event that causes a person to narrow their focus of attention may result in their not perceiving other events happening. It is understandable that a driver might stop looking at the road when suddenly coming upon a mass of warning, directional, and advertising signs. Inadequate training or defective equipment may also cause or allow a person to take a dangerous action. These errors fall into the category of design-induced errors.

That leaves the final category of error which is where the negative connotations of “human error” correctly applies. This is when a person willfully disregards procedures, rules and laws or commits inappropriate acts that put other people in danger. This includes actions like removing a guard from a machine, driving too fast for conditions, showing up for work drunk, not wearing a hard hat in a construction area, and not attending to one’s responsibilities. But even then, the person must have been given sufficient training, warnings, instructions and equipment to be expected to perform adequately or safely.

When the same person is both the designer and the accident initiator, analysis becomes more complex. Consider a surgeon who operates on the wrong knee. This would be “human error” because it is likely that an established procedure was not followed. But what if in the middle of a delicate operation, the surgeon must make a choice between two procedures that seem equally likely to be acceptable, and the choice made ultimately leads to disaster? Was a “human error” committed? This depends on many factors, both natural and fabricated, including the knowledge available to the surgeon before and during the operation, but also on a multitude of “behavioral” factors that could affect perception and bias judgment.

Errors made by humans are rarely simple. For any accident, many errors may have been made by many people.

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