Human error: Symptom or cause?

Dom Cooper analyses the definition of human error and whether it can in fact be a root cause instead of a ‘symptom of systems’.

There is much talk in OSH these days about human error being a symptom (of a bad system or something else being wrong), rather than a cause of an incident or adverse event; many adopt this posture because it completely avoids ‘blaming a person’ for an adverse event, with the cause(s) lying somewhere within a multitude of systems and/or contributing influences, from near or far. Of course, the truth lies somewhere between these two positions: Human error(s) can arise from the influence of systems and situations, but may also arise solely from a person’s conscious choices ^[[i],[ii]].

This perspective appears to arise from a lack of knowledge about human error types and traps, leading to incident investigations using the generic term without specifying what error types were involved and how the situation or system influenced these.

Introducing human error

Everyone has experienced their own human errors, all of which have helped us to learn and develop various competencies ^[[iii]]. By and large, we do what makes sense to us in the moment, given our level of focus and attention, the knowledge we possess, and what we are trying to achieve. We usually self-reflect when things go wrong, and self-regulate thereafter, but sometimes we can be entirely unaware we have made an error ^[[iv]].

If others are present, they may let us know, as human error is usually detected by looking at how people behave, or could behave, in certain situations. The outcome of a human error may be beneficial (e.g., smoke detectors, inkjet printers), inconsequential, or harmful (e.g., an injury or catastrophe).

Connected to the design and use of tools, tasks, processes and the working environment, human errors are rarely random; that is, they can often be predicted, and in some situations, they are inevitable. Experiencing many similar adverse events at a particular workplace, or from a particular task, most likely indicates the working environment/situation could be driving unwanted behaviours.

A classification of human error types

Making use of James Reason’s approach ^[[v]], human error is commonly defined as ‘the failure of planned actions to achieve their desired ends’. To be termed ‘human error’, a failure must comprise three elements: [1] a plan or intention; [2] a sequence of actions initiated by the plan; and [3] a failure of the actions involved to achieve the plan’s goal ^[[vi]].

Unintended failures of planning

People may fail to achieve their goal because the plan itself is faulty, rather than the actions being incorrectly performed (e.g., a person may work on a vehicle’s carburettor thinking they have a fuel problem, when the condenser in the distributor is malfunctioning).

These human error types are termed ‘unintended failures of planning’ and usually refer to people making ‘knowledge-based mistakes’ (e.g., filling a diesel car with petrol) or ‘rule-based mistakes’ when someone is trying to do the right thing, but actually does the wrong thing (e.g., using a water or foam fire extinguisher instead of a dry powder extinguisher on an electrical fire). Primarily, these are unintentional errors of judgment or decision-making where people do the wrong thing, believing it to be right.

These errors tend to occur in situations where the person lacks knowledge because they have not been properly trained, and/or because it is an unfamiliar task. In such circumstances, people often rely on their previous experience in similar situations, which may or may not provide the correct response for that situation.

Unintended failures of execution

Conversely, even though the plan itself is adequate, people may fail to achieve their goals because their actions are not executed correctly. These ‘skill-based’ human error types are termed ‘unintended failures of execution’ and are usually related to ‘attentional failures’ (e.g., being distracted in some way) or ‘memory failures’ (e.g., forgetting to do something).

Execution errors often occur during tasks highly familiar to the person and include slips (e.g., not fully closing all the valves after fuel bunkering) and lapses (e.g., forgetting to log out of your internet banking on a public computer) which may only be evident to the person who experiences them.

These error types commonly occur in cases where people are highly trained in their job procedures but don’t concentrate on what they are doing when carrying them out, as they involve automatic and habitual behaviour(s) (e.g., driving). Being preoccupied with a personal issue, or being frustrated could lead to both slips and lapses.

‘Failures of planning’ and ‘failures of execution’ primarily refer to people’s unintentional actions or inactions that result in [1] a system or person performing outside of acceptable limits; [2] deviations from a set of rules or expectations; and [3] undesirable or unwanted conditions.

Intentional behavioural choices

Another human error type is related to people’s ‘intentional behavioural choices^[[vii]]’. These conscious actions are committed for a multitude of well-meaning reasons to get the job done as efficiently as possible, and can be [a] routine (e.g., we do the job this way all the time and nobody notices or cares), or [b] overcoming organisational failings (e.g., improvising to get a job done without the necessary equipment/materials being available).

Behavioural choices related to routine short-cutting (e.g., cutting corners to save time and energy) and organisational failings (e.g., deliberately doing something different to overcome problems related to equipment, procedures or the working environment) are often linked: If people do not experience an adverse consequence when overcoming any organisational failings, they learn that the short-cuts taken are usually harmless, which increases the likelihood they will be repeated.

A third type of behavioural choice is when people deliberately choose to engage in optimising (e.g., improvise to get the job done more efficiently), exceptional behaviour (e.g., attempt to solve a problem in highly unusual circumstances) or using a method other than the one specified, while still achieving the original goal.

Figure 1: Reason’s (1990) Human Error Model

Prevalence and prevention of the human error types

The most common human error types in the workplace appear to be skill-based failures in execution (slips and lapses), followed by failures in planning (e.g., rule-based errors & knowledge-based errors), with behavioural choices being less of a problem ^{[[viii],[ix],[x]]}.

However, the author has analysed observation data related to 642 potential serious injuries & fatalities(SIFs) showing behavioural choices dominate, followed by failures in execution, and failures in planning[xi]. Such discrepancies indicate the likelihood of unique Human Error profiles in different entities.

Using checklists as an aide memoire has been shown to reduce failures in execution ^[[xii]]. People taking brief pauses to allow quick reviews of a task is also recommended ^[[xiii]]. Similarly, addressing the known human error traps in the working environment can eliminate or reduce failures in planning and execution, while behavioural choices can also be addressed via formal behavioural safety processes that help reset group norms.

Human Error Traps

Situational features are often referred to as human error traps, ^[[xiv]] many of which are known to have been involved in catastrophic incidents and injuries. People’s behaviour is often dictated by organisational, job and individual factors, individually or collectively.

In principle, the organisational and job factors that shape and influence performance are controlled by leadership and line management. This means the onus is on leadership to optimise situations, and thereby help optimise people’s behaviour (although it is recognised that people’s behaviour can change a situation).

Organised using the 5 M’s (Management, Manpower, Methods, Materials & Machinery) from quality management, table 1 attempts to link known error traps with their associated error types. Readers may have their own views on these; regardless, they are offered to help workplace assessments identify any human error potential involved in tasks and processes so that appropriate risk controls can be developed.

Table 1: Typical Human Error Traps ^[[xv]]

Summary

Human error is a well-worn but often misunderstood concept within the OSH profession. Many of the newer approaches to safety assert that it is a symptom of systems, not a root cause of incidents. Revisiting the original research of Norman, Petersen, Rasmussen and Reason shows this thinking is erroneous: all specified the interactional or reciprocal relationships between factors in the wider working environment (e.g., systems) and people’s behaviour.

As such, human error can indeed be a root cause of an incident. Some human errors are unintentional (e.g., failures in planning and failures in execution), while others are intentional (i.e., behavioural choices). Incident investigations can and should do a much better job of recognising these distinctions and specifying what they mean by a human error, what type of error it is, and what factors contributed to it. Recent work indicates that an unintended consequence of the newer approaches treating human error as a symptom is to limit learning and, in extreme cases, take incident investigations back to classifying root causes as ‘acts of god’, thereby providing the ultimate excuse for an industrial incident or catastrophe ^[[xvi]].

References

[i] Rasmussen, J. (1982). Human errors. A taxonomy for describing human malfunction in industrial installations. Journal of Occupational Accidents, 4(2-4), 311-333.

[ii] Reason, J. (2000). Human error: models and management. BMJ, 320(7237), 768-770.

[iii] Frese, M. & Altmann, A. (1989). The treatment of errors in learning and training. Developing Skills with Information Technology, 65.

[iv] Rizzo, A., Bagnara, S., & Visciola, M. (1987). Human error detection processes. International Journal of Man-Machine Studies, 27(5-6), 555-570.

[v] Reason, J. (1990). Human Error. Cambridge University Press.

[vi] Norman, D. A. (1981). Categorization of action slips. Psychological Review, 88(1), 1.

[vii] Smetzer, J., Baker, C., Byrne, F. D., & Cohen, M. R. (2010). Shaping systems for better behavioral choices: lessons learned from a fatal medication error. The Joint Commission Journal on Quality and Patient Safety, 36(4), 152-AP2.

[viii] Shappell, S., Detwiler, C., Holcomb, K., Hackworth, C., Boquet, A., & Wiegmann, D. A. (2017). Human error and commercial aviation accidents: an analysis using the human factors analysis and classification system. In Human error in aviation (pp. 73-88). Routledge.

[ix] Fabri, P. J. & Zayas-Castro, J. L. (2008). Human error, not communication and systems, underlies surgical complications. Surgery, 144(4), 557-565.

[x] Salminen, S. & Tallberg, T. (1996). Human errors in fatal and serious occupational accidents in Finland. Ergonomics, 39(7), 980-988.

[xi] https://peer-leader.com/images/PEER_Reduces_SIFs.pdf

[xii] Teoh, L., McCullough, M. J., & Moses, G. (2022). Preventing medication errors in dental practice: An australian perspective. Journal of Dentistry, 119, 104086.

[xiii] Wachter, J. K. & Yorio, P. L. (2013). Human performance tools: engaging workers as the best defense against errors & error precursors. Professional Safety, 58(02), 54-64.

[xiv] Petersen, D. C. (1981). Human error reduction and safety management. NY: Van Nostrand Reinhold.

[xv] Cooper, M. D. & Finley, L. J. (2013), Strategic Safety Culture Roadmap. Franklin, IN: BSMS.

[xvi] Sherratt, F., Thallapureddy, S., Bhandari, S., Hansen, H., Harch, D., & Hallowell, M. R. (2023). The unintended consequences of no blame ideology for incident investigation in the US construction industry. Safety Science, 166, 106247.

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