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Understanding Human Failure

Human Failure model

Human failure is often cited as a contributing cause to incidents and accidents. By understanding the types of human failure; why humans fail and the techniques to reduce the possibilities of human failure, we can significantly reduce incidents and accidents. To learn more about Human Failure, here is a link to an excellent resource: The Field Guide to Understanding Human Error.

Main Types of Human Failure

According to the UK’s Health & Safety Executive, human failure can be broken down into two main categories: Errors and Violations. When investigating the human failure component of an incident, it’s important for the investigation team to dig a little deeper and understand if the failure was related to a violation or if it was a human error.

Human Failure Analysis: Violations

Violations are deliberate deviations from a rule or procedure. For example, driving faster than the speed limit or removing a guard from a dangerous piece of machinery.

Health risks can also be increased if for example a worker knowingly breaks a rule about wearing ear defenders in a noisy environment. The risk of permanent occupational hearing loss is certainly increased.

Three Types of Violation – Routine, Situational and Exceptional

Routine Violations – Routine violations occur, as the name suggests, routinely during work. These are typical violations and are often cited in Safety Observation cards. Common routine violations include:

  • Not wearing PPE when its required to be worn. If there was an incident where someone sustains a cut on their hand that could have been prevented by wearing gloves then this is a human failure from routine violation of rules. However, you will also have to dig further as to “why” the person wasn’t wearing hand protection. We will get into that later in the article.
  • Cutting corners to save time and energy. This is an interesting violation and the astute investigator will want to understand why this is the case. Many times, its due to the procedure itself. The procedure may not be designed, in what Todd Conklin calls “work as imagined” versus “work as done”. You can find out more from his book called Safety Differently : Human Factors for a New Era
  •  The belief that “rules no longer apply”. This is a potentially dangerous type of violation because the worker believes that the rule is either irrelevant or somehow does not apply to him/her. Once again, seek to understand how work is actually done and gain an understanding of why the worker thinks the rule doesn’t apply. 
  • Lack of rule enforcement. This is also a common violation. If the site is lax on implementation & enforcement of safety rules then workers may just not think they are important and stop following the rules. Safety Officers who either aren’t available (sitting in offices) or are also lax on enforcement.
  • New workers may not know the correct way of working. They are violating the rules perhaps because the way they are doing is how they were trained somewhere else.

Situational Violations – Situational violations are where the rules are broken due to pressures from the job such as : 

  • Time pressure
  • Insufficient staff for the workload
  • The right equipment not being available
  • Extreme weather conditions.

During investigations, these situational violations are very difficult to prove. However, look into how the jobs were prepared and how risks were analysed and communicated. 

Exceptional Violations – Exceptional violations are when time pressures preclude following procedures strictly. An example would be a project or task that is running behind schedule so shortcuts are taken to get the job done. When this happens, the risk levels can increase dramatically, supervision becomes poor and bad decisions get made. 

Additionally, there may also be situations where there aren’t enough people available for the workload. Take a look at my article on the costs of incidents which points out that if a member (or members) of the team is injured, then others have to take up the slack. 

Exceptional violations may occur when the right equipment isn’t available but with proper risk analysis and job preparation (planning), this should be a case to be avoided.  Accordingly, when the right equipment isn’t available, workers may find a workaround that adds risk to the job. This is a common violation in many incidents. 

Exceptional violations rarely happen and only really occur when something goes wrong. In order to solve the problem, the employee believes that a rule must be broken. 

As a real-life example consider what happened during the Chornobyl nuclear accident in 1986. There, a series of tests were undertaken and when an operator failure led to low power levels, the test should have been abandoned. However, operators and engineers continued to improvise in an unfamiliar and increasingly unstable regime in order to protect the test plan (time pressure), with disastrous results. 

Human Failure Analysis: The Human Error Component

Human errors, as opposed to violations, occur because of either a”skill-based” error or just by making a mistake. Errors like this are often the most common types of errors and are frequently cited as contributing to incident root causes.

Skill-Based Errors –  These are errors that can be further broken into two types: A Slip of Action or a Lapse of Memory. 

Slips of the Mind

When a human error is identified to be a “Slip of the mind”, typically this entails:

  • Performing the action too soon or too late. 
  • Omitting a step in a work instruction or task.
  • Carrying out an action with too little or too much strength (i.e bolt flogging, opening a valve too far)
  • Performing the action in the wrong direction (i.e. turning a control knob in the wrong direction)
  • Doing the action on the wrong equipment (i.e. opening the wrong valve thinking its the right valve)
Lapses (of memory)

Lapses of memory are another form of human error. Forgetting to carry out an action or losing a place in a task is an example.

This is often a result of being distracted (i.e. interruptions) or perhaps running too many concurrent operations at the same time.

I recall a panel operator at a facility I worked at who was required to run two panels, one of which was extremely busy that day. He was so focused on that activity that he lost his place in another activity on a separate panel. A loss of containment was the result.  


The second type of Error is the “Mistake”. Essentially, There are two types of mistakes that can occur and those are: Rules Based Mistakes and Knowledge-Based Mistakes

A rules-based mistake is centred around a mistake based on the forgetting of the rule or procedure. Enforcing the use of checklists helps to remove these kinds of mistakes.  Having well thought out checklists should be encouraged (with the participation of the workers) and enforcement of the checklist should also happen. 

Knowledge-based mistakes occur when the worker simply lacks the knowledge to do the job. This is often a result of incomplete (or poor) training of the individual.

Furthermore, it could also indicate that the competency of the worker was not verified. When it comes to using contractors, ensure that your contractor safety management program is comprehensive and well managed by the safety and procurement teams.

In developing countries, be aware that many craft workers do not always have the skills and training to be able to do the work at a sufficient level. 

Causes of Human Failure

Three factors contribute to human failure.

  • The job
  • The Individual
  • Organisational factors

The Job

The job must be suited to the physical and mental capabilities of the person doing it. Tasks should be designed to take account of the limitations and strengths of human performance. This applies in general, such as combining a series of tasks, which are capable of being performed by any individual with the right general characteristics, into a job in a coherent way.

It also applies in particulate, by adapting jobs where possible to meet the capabilities of the job holder.

Matching the job to the person in this way allows for the most effective contribution to the business results.

The concept of matching jobs to the person involves two aspects:

  1. A physical match – this covers the design of the general and immediate workplace and working environment to facilitate both performances of the manual tasks involved and also ensure safety during such operations.
  2. Mental match – this covers the “brain power” parts of the job, or those involving information processing and decision-making on the part of the job holder.

Mismatches between job requirements and people’s capabilities provide for the potential for human error.

The Individual

People bring to their job their own personal mix of physical characteristics, knowledge and skills, attitudes, habits and personality, any or all of which may be strengths or weaknesses depending on the task demands.

These individual characteristics influence behaviour in complex and significant ways, and it is important, therefore, that individuals are appointed to jobs and roles to which they are individually suited.

Some of these characteristics are fixed and cannot be changed, or at least not easily or in the short term – for example, physical characteristics and personality. Others, though, may be altered, adapted and enhanced through learning.

This applies to an individual’s knowledge and skills, attitudes and habits – all attributes which contribute significantly to competence in the job or role. People can, therefore, be developed in their jobs to become more effective.

Organizational Factors

Jobs are allocated, and individuals perform their tasks, within the context of the organisation.

The organisation itself is, therefore, an important factor in conditioning the behaviour of individuals and groups at the workplace.

The two key elements in this are the management of the organisation and its culture:

  • The style of management dictates the way in which people work:
    • The priorities that are seen as important, such as speed, quality, working safely, etc.
    • The type of controls operated.
    • The degree of individual responsibility allowed.
    • The way in which people are motivated.
    • The support offered to individuals through instruction and training, etc.
  • The organisation’s culture sets the tone for individual and group behaviour:
    • The priorities that they see as important.
    • The involvement and attachment people have to the organisation.
    • Their ability to influence its operations, etc.

Both management and the culture should promote employee involvement and commitment at all levels, emphasising that deviation from established health and safety standards is not acceptable.

Examples of Why Humans Fail

Inadequate Training Can Cause Human Failure

Humans will fail if they are not properly skilled to perform a task.

Training is the process of equipping people with the right skills at the right level to perform a task correctly (and safely).

Poor training will lead to workers having to find out for themselves how a task is performed. This invariably will lead to the old “Trial and Error” method of learning which is not appropriate in workplace situations where the health and safety of workers are at stake.

Limits of Capabilities Can Cause Human Failure

Even a person of limited capabilities may find a routine, production-line type of employment very taxing, while a person of higher capabilities could find this boring in the extreme.

If the workload requires an attention level that is beyond the mental capabilities of the employee, then a state of stress will occur.

There needs to be enough mental stimulation but, equally, not too much. This can be applied to physical capabilities, as well as mental.

If work is beyond the physical capabilities of an individual worker, then their health and safety, and perhaps the health and safety of others, will be jeopardised.

Tiredness & Fatigue is a Cause of Human Failure

Fatigue can be defined as ‘weariness after exertion’ or can occur after repeated variations of stress.

Severe fatigue can lead to poorer performance on tasks requiring attention, decision-making or high levels of skill.

Shift work, working at night or extended hours can all result in fatigue and have an adverse effect on health.

For safety-critical work, such as train driving, for example, the effects of fatigue can give rise to increased risks.

Shift work, especially night work, can impact safety. During the night, job performance may be poor and tasks completed more slowly.

The hours between 02.00 and 05.00 are the highest risk for fatigue-related conditions. Sleep loss can lead to lowered levels of alertness.

Sleep debt, which is a build-up of sleep loss, leads to reduced levels of productivity and attention. These effects can also affect early morning shift workers and people that are on call.

Boredom Can be Cause Human Failure

If a person of high intelligence is set a mundane task, he will probably employ himself in finding new and less arduous, but not necessarily safer, ways of completing a task.

Intelligence is required to defeat interlocking safety devices. Correctly employed, such a person could be using his intelligence and ability to devise safer work methods.

Boredom can be a significant contributing factor in many workplace accidents. It can cause both lack and loss of attention and can lead to ‘habituation’ – where individuals will disengage from their surroundings and perform in a ‘pre-programmed’ way, simply following a routine without conscious thought.

When this happens, the individual may not respond in the correct way to situations outside the norm.

Degradation of Human Performance Resulting from Poor Ergonomic Design

It is important to note that an ergonomist (if you have one) can make a contribution at the design stage of equipment and workplaces in order to try to prevent problems from occurring later.

Poorly Designed Workstations The HSE leaflet, INDG 90, “Understanding Ergonomics at work”, suggests a number of questions that should be asked when considering whether a workstation and process are ergonomically suitable:

  • Does it suit your body size?
  • Does it suit all other users?
  • Can you readily see and hear all you need to?
  • Do you understand all the information that is presented?
  • Do errors occur frequently, and is it easy to recover from them?
  • Does the equipment or system cause discomfort if you use it for any length of time?
  • Is it convenient to use?
  • Is it easy to learn to use?
  • Is it compatible with other systems in use?
  • Could any of these aspects be improved?
  • Do other users have similar reactions?

Workstations are usually designed for the ‘average’ person.If a doorway was designed just to pass the average person, then some of the population would have problems getting through.Workstations need to be capable of adjustment. Unsuitable workbench height causes the operator to develop musculoskeletal problems:

  • If the workbench is too high, then the operator has to adopt an unnatural posture, with the elbows away from the body and the shoulders raised. This causes discomfort in the shoulders and neck.
  • If the work surface is too low then the operator will have to lean forwards. This causes neck and lower back problems.
  • Repetitive motions, particularly those requiring the operator to exert force or use some unnatural motion, can lead to repetitive strain injury.

Inappropriate Equipment: Examples

Production Process Control Panels

The operator of a production process control panel must be able to operate the panel from a safe place.

For some production processes, this may be from an adjacent area or for more dangerous operations the panel will be located at a safe distance or even within an enclosed area away from the production area.

Noise, dust and fumes must all be considered. The operator must be able to reach all the dials, switches, etc. easily.

Emergency controls must be clearly identifiable and easy to operate.

The operator must also be able to see the production area so that they can see what is happening and react, as necessary.

Crane Cab Controls

A crane driver has to be in absolute control of the load that is being moved because the slightest slip of the controls may result in damage to buildings, materials or people.

For this reason, it is vital that the controls in the cab are within easy reach and move in straight lines to permit ease and delicacy of control. In addition, the driver needs to have a satisfactory view of the operations below.

This means that the seat provided must be adjustable (to fit accurately 90% of all possible sizes) so as to provide the driver with a full view of the working area.

The driver must also be protected from the ingress of dust, fumes and heat from the external environment.

The provision of filtered and refrigerated air, where necessary, ensures cool and comfortable working conditions.

Aircraft Cockpit

Clearly, it is vital that a pilot flying an aircraft can interface easily with all the controls in the cockpit.

It is important that the controls/displays are fitted around the cockpit in a logical way so that the pilot can easily reach/see the more important controls/displays, e.g. speed and altitude dials, whilst he/she may need to move to reach the less important ones.

It is important that safety-critical switches cannot be inadvertently operated. These should be designed so that there has to be a positive action by the operator in order to instigate them.

Emergency controls must be clearly identifiable, easy to use and situated in a suitable location. The emergency controls must be accessed quickly to prevent unnecessary delay in stopping the activity that they control.

It is also important that the pilot can adjust his/her position to obtain the best field of vision and enable quick responses for the movement of the various controls.

For this reason, it is vital that the pilot can alter the height and position of his/her chair in order to ensure that the controls are within comfortable reach.

It is also important that the temperature, ventilation and lighting in the cockpit are adequate and that these can be adjusted to suit the individual.

Computer Numerical Controlled (CNC) Lathe

The CNC lathe is computer-operated using a keypad or keyboard. It is important, therefore, to ensure that the operator can access the keypad or keyboard easily and that they can use the keys comfortably. For this reason, it is important that the operator can adjust their operating position, i.e. chair height and position, as well as the actual position of the keyboard.

Poor Health

You will be aware, on occasions, of not seeing or hearing something that was very plain to someone else.

Sensory defects increase with age and failing health. Some people need spectacles and hearing aids, and you should have a general idea of why this could be so.

The safety practitioner probably needs to be more concerned about those who don’t know that they have sensory defects or those who try to forget about it.

An individual’s general state of health will have obvious effects on both their physical and mental capabilities.

The unfit worker may struggle to maintain concentration over the full length of the working day.

Similarly, an individual’s specific state of health at a particular time will influence their physical and mental capabilities.

The worker suffering the effects of a cold or flu will not remain as alert as they normally would when completely healthy. This may result in errors of judgment that could be crucial, for instance, when handling dangerous equipment.

For example, a forklift truck driver suffering from flu, whose judgment has been impaired, is more likely to cause an accident when driving around a warehouse than a driver who is completely healthy.

In the next article, we will discuss techniques for the Assessment of Risks from Human Failure in the Workplace.