“…there is a belief amongst many engineers and managers that human error is both inevitable and unpredictable. 

However, human error is inevitable only if people are placed in situations that emphasize human weaknesses and that do not support human strengths”

Martin Anderson, IChemE Safety and Loss Prevention Subject Group Newsletter, Spring 1999

In Part I, we discussed the different types of Human Error, which are summarized in the Table below. The conditions that produce the different error types have different forms of remediation.

Error Type


Description / Cause



Novice, Expert

Failure of attention where an action is carried out that is not intended or planned.

Change work situation to reduce opportunities for error



Memory failure resulting in the omission of an intended or planned action

Checklist or Explicit Reminder

Mistake (Rule-Based)


Using the wrong rule for the situation
Incorrect application of the correct rule
Failure to apply the correct rule

Better Training, Instructions, and Displays. Improve ability to plan course of action.

Mistake (Knowledge-Based)


Failure resulting from insufficient or incorrect knowledge
Misapplication of existing knowledge to new situations

Better Training, Instructions, and Displays. Improve ability to Assess Situation

Slips and Lapses, also known as skill-based errors, are linked to monitoring failures (lack of attention). An example of a slip is inadvertently hitting the email “send” key instead of the “save” key. The cause of slips may be bad or confusing links between display and control. Slips are often exhibited by expert operators who are performing a task without paying close attention (they may be multi-tasking). An example of a lapse would be when a maintenance technician fails to tighten a screw after completing a maintenance procedure. The use of checklists or explicit reminders helps prevent lapses; this is why even experienced pilots use a checklist for walking down an airplane before takeoff. Additional training will not typically help address slips and lapses.

Mistakes, which typically involve a problem-solving activity (like an operator response to an alarm), can be sub-divided into rule-based errors and knowledge-based errors. Rule-based errors can arise when a good rule is misapplied or when bad rules are applied. An example would be when a US tourist drives on the wrong side of the road in the UK. Knowledge-based errors, which include failures of understanding and perceptual errors, typically arise due to a lack of expertise and because a person does not have all the knowledge required to perform the task at hand. Since most mistakes reflect a lack of knowledge in the head or knowledge in the world, training and better displays can help address. Mistakes are common to the novice operator.

The figure below shows where the different types of errors originate in respect to the three steps of a typical operator response process. It illustrates why categorizing an error correctly is important to addressing it. Knowledge-based mistakes take place during the Situation Assessment step when the operator is interpreting the visual and audible queues provided by the control system and attempting to diagnose the situation. If better diagnosis skills are needed, the training methodology might involve showing the operator a mock-up graphic display with various process readings shown so that they can practice diagnosing the situation and describing the action they would take. 

Figure. Error Types and How they Relate to Human Information Processing (Wickens and Holland, 2000)

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


Medical Error Prevention, https://www.ncbi.nlm.nih.gov/books/NBK499956/

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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