THE HIDDEN PATTERNS OF HUMAN ERR:
AUG 29, 2025
UNDERSTANDING HOW MISTAKES HAPPEN.
In our previous blog post, we introduced the concept of accidents and explored some of their possible causes. In this post, we’ll take a closer look at the different types of human errors, which often play a central role in accidents—especially in complex systems and high-risk environments.
What Is a Human Error?
James Reason describes human error as “the failure of planned actions to achieve their desired outcomes, without the intervention of some unforeseeable event.” This definition builds on the work of Charles Perrow (1984), emphasizing that many errors are internal in origin—stemming not from unpredictable external events, but from how our minds work.
The Two Main Categories of Errors
Human errors are typically divided into two broad categories:
1. Skill-Based Slips and Lapses
- Slips are errors in execution. They occur when actions do not go as intended, often due to attentional or perceptual failures. These are observable mistakes—such as pressing the wrong button or skipping a step in a routine task.
- Lapses are internal and not directly observable. These involve memory failures, such as forgetting to carry out a step in a process, or losing track of where you are in a sequence.
2. Mistakes
Mistakes occur when the plan itself is flawed, rather than its execution.
- Rule-Based Mistakes happen when a normally reliable rule is applied incorrectly, or when an inappropriate rule is used. Sometimes, a good rule is intentionally ignored—this is referred to as a violation.
- Knowledge-Based Mistakes occur in novel situations where no pre-existing rules apply. Here, individuals must rely on problem-solving and reasoning—often under pressure. Errors in judgment or understanding lead to these types of mistakes.
Understanding Attentional Failures
Attentional failures often arise when a person is multitasking. When attention is divided between multiple tasks, the focus on any single task is likely to diminish, increasing the likelihood of an error.
Distractions—such as engaging in a conversation while working or driving—can also significantly impair attention and lead to critical oversights.
What Are Perceptual Failures?
Perception refers to how we interpret information from our senses—sight, hearing, touch, and smell. These senses are essential for interacting with our environment, especially in safety-critical settings.
Examples of Perceptual Failures:
- Poor Visual Design: If an instruction label is printed in very small text, an important step might be missed—potentially leading to an accident.
- Impaired Sensory Function: In industrial settings, a gas leak might be detectable by smell. If a worker’s sense of smell is impaired, they could miss this warning, increasing the risk of a serious incident.
- Masked Stimuli: Sometimes, important sensory signals are disguised or overridden by other factors—for instance, a flashing warning light may be overlooked in a brightly lit environment, or a critical sound alarm might be drowned out by ambient noise.
Final Thoughts
Understanding the different types of human errors—whether they stem from attention, perception, memory, or decision-making—is essential in designing safer systems, training programs, and work environments. By anticipating where and how these errors can occur, we can take proactive steps to reduce risk and improve overall safety.
Stay tuned for our next post, where we’ll explore how human error can be mitigated through system design and organizational culture.
Resources:
Reason J.(1997). Managing the Risks of Organizational Accidents.
