Feb. 8, 2000 ALBUQUERQUE, N.M. -- Taking a lesson from nuclear weapons surety, Chris Forsythe and Caren Wenner of the Department of Energy's Sandia National Laboratories have come up with a new approach to studying how and why engineered systems fail due to the actions or inaction of humans.
Engineered systems are systems designed by humans to operate in a certain way and encompassing all combinations of hardware, software, and people, including systems that consist entirely of people. And since engineered systems are found throughout the world in transportation, communications, financial institutions, utilities, and more, understanding what causes people to fail when working in them is crucial.
"Instead of systematically trying to determine all the possible things a person might do wrong -- the traditional method -- we are looking at identifying conditions and environmental factors that make any one of the universe of potential human failures more probable," says Forsythe, a member of Sandia's Statistics and Human Factors Department. "Mitigating these factors can lead to enhanced surety of engineered systems, such as nuclear weapons."
The idea for the new way of studying human involvement in an engineered system came to Forsythe and Wenner while involved in an internal Sandia surety project last year.
"Surety involves assuring nuclear weapons safety, security, and reliability without precisely characterizing all possible threats," Forsythe says. "It occurred to us that a similar approach might work for studying why people make mistakes when working in engineered systems."
The standard human factors technique for figuring out how to prevent error is to conduct a detailed analysis that attempts to establish a near-exhaustive list of everything that is likely to go wrong.
"After you've done this a long time, you get good at it," says Forsythe, who has a Ph.D. in cognitive psychology. "But it can be labor intensive. Also, you always miss some things. The problem that humans bring to systems is the infinite number of ways they can fail. You can never hope to anticipate all that can go wrong."
Instead of focusing on the output, the errors, Forsythe and Wenner are concentrating on input, what causes failure. Their goal is to identify and correct conditions that make errors more likely to occur.
They call their method the Organic Model -- organic because an engineered system grows, changes, and becomes more vulnerable with each human interaction. They recognize that introduction of humans in an engineered system actually causes the entire system to take on organic properties (properties that are associated with all living systems) and that to fully evaluate the performance, safety, security, etc., of a system, these properties must be considered.
"All engineered systems have a human footprint," Wenner says. "Humans design, build, and maintain the system. There's no getting the human factor out of an engineered system."
Taking into account that a primary effect of humans on an engineered system is the introduction of variability to the system, Forsythe and Wenner ask two fundamental questions -- what are factors that cause variability and when is a system intolerant of variability? Additionally, although the goal is obviously to reduce the potential for error, it is equally important to understand the potential impact of errors that do occur, and to mitigate this impact where possible, Wenner says.
For example, the pair might go to a production site to assess a system's vulnerability. While their analysis will pinpoint many likely human errors, much of their attention will focus on conditions that make human error more probable in general. Simple examples might include the number of people working rotating shifts in critical areas, overtime hours, and if the work is externally or self-paced -- all factors that could contribute to any one of a million possible mistakes by humans.
Forsythe and Wenner are building on work started more than 20 years ago by retired Sandian Alan Swain, who wrote the Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications, which has become a basic guide for many in the human factors field. This was one of the first publications in human factors to focus on conditions in the environment that make people fail, and not exclusively on how to improve human performance, making it faster and better. Human reliability has remained a core competency at Sandia.
Forsythe and Wenner have received invitations to discuss this work in professional arenas and have plans to conduct a workshop at the Annual Human Factors and Ergonomics Society Meeting in San Diego.
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