Increases in levels of automation and system complexity impact human error. Medical errors in hospitals and clinics result in approximately 100,000 people dying each year and cost the healthcare industry between $4B – $20B each year. In the petrochemical industries, operational error can cost upwards of $80M per incident. “Operator error” is a significant causal factor in 60 to 85% of industrial accidents.  

To address human error, we need to understand the different types of human error and the cause of each one. Firstly, the use of the term “human error” does not mean that there is a faulty human on the job.  More likely a technology-centered design has been employed that is not effective at delivering high levels of sustained human performance (“design-induced error” is probably a better working term). Technology should be organized around the way users process information and make decisions.

Various taxonomies have been defined for classifying human error; there is no universal taxonomy that serves all purposes and applications. A useful human error taxonomy for operators in process and manufacturing industries is described below. 

Human error can be broken up into the following types; slips, lapses, and mistakes. A “slip” (execution failure) occurs when the operator has the correct intention but performs an incorrect action. A “lapse” (memory storage failure) occurs between the formulation of an intention and the execution of an associated action. A “mistake” (intention failure) occurs when the person initiates the wrong plan of action for the task at hand (typically when they are engaged in a problem-solving activity). Thus, errors can be attributed to issues with planning, storage (memory), or with the execution of an action.

Figure. Types of Human Error (adapted from Wickens, Lee, Liu, and Becker)

Some errors are more common to novice operators, while others commonly impact expert operators. The remediation for each is very different. This is the subject of Part II. 

Coming Soon to a Venue Near You: “Improve Operator Effectiveness: How to Manage Abnormal Situations so They Don’t Manage You”


Medical Error Prevention,

Wickens, Lee, Li, Becker, “An Introduction to Human Factors Engineering, 2nd Ed.”, Pearson Education Inc., 2004.

Kletz, “An Engineer’s View of Human Error, 3rd Ed.”, Institute of Chemical Engineers (IChemE), 2008.

Endsley and Jones, “Designing for Situation Awareness: An Approach to User-Centered Design, 2nd Ed.”, CRC Press, 2012.

Ritter, Frank E., Baxter, Gordon D., and Church, Elizabeth F., Churchill, “Foundations for Designing User-Centered Systems: What System Designers Need to Know about People”, Springer Verlag, 2014.

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