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The Human Factors Analysis and Classification System (HFACS) was developed by American doctors Scott Shappell and Doug Wiegmann. On the basis of many cases of human error in the US Air Force, they revealed the various causes of human error.


The HFACS provides a reading model to help analyze problems being caused by human errors. Rather than assigning a reprimand, the challenge is to understand the underlying causal factors that lead to an accident. The HFACS provides a reading model to help analyze problems being caused by human errors. Rather than assigning a reprimand, the challenge is to understand the underlying causal factors that lead to an accident. The tool consists of:

  • Of a principle of causality
  • Of four levels of failure

The principle of causality

HFACS is based on the Swiss cheese model (the “holes” of cheese Being Human errors) by James reason (reason 1990). Reason describes four levels of human error, each influencing the following:

  1. Influence by the organization, we do not get involved from the first incident. We continue to work as usual. Many dangerous acts are carried out but for the moment the accident is only latent.
  2. Not guarding enough, the supervisory teams do not see the situation and all these dangerous acts are at this stage transparent since there is no accident yet.
  3. The situation is still deteriorating with the non-updating and the non-observance of the standards.
  4. Last stage, the regular regression of conditions, of the organization… generates more and more dangerous facts. One leads then to the accident 1, which is only after investigation due to a succession of negligence of the system.

Failure levels

HFACS Level 1: Dangerous acts

The level of dangerous actions is divided into two categories, errors and violations, and these two categories are then subdivided into sub-categories. Errors are unintentional behaviour, while violations are a deliberate disregard for rules and regulations.

The errors

  • Skill-based errors: Errors that occur in the operator’s execution of a routine task relating to procedure, training or competence and result in a dangerous situation (for example, lack of prioritization of attention, error in the list of control, negative habit).
  • Decision Errors: Errors that occur when the behaviors or actions of the operators unfold as planned, but the chosen plan proves inadequate to reach the desired end state and creates a dangerous situation (rule-based error, procedure Inappropriate, for example).
  • Perception errors: Errors that occur when an operator’s sensory input is degraded and a decision is made on the basis of erroneous information.


  • Current Violations: Violations which constitute a habitual action on the part of the operator and which are tolerated by the competent authority.
  • Exceptional Violations: Violations constituting an isolated departure from the authority, neither typical of the individual nor tolerated by management.

HFACS Level 2: prerequisites for risky acts

The level of prerequisites for dangerous acts is divided into three categories.

Environmental factors

  • Physical environment: Refers to factors that include both the operational context (e.g., weather, altitude, Gemba) and the ambient environment (e.g., heat, vibration, lighting, toxins).
  • Technological Environment: Refers to factors that include a variety of design and automation problems, including equipment and control design, display/interface characteristics, checklist structure, tasks and automation.

Condition of the operators

  • Unfavorable mental state: Refers to factors that include mental conditions that affect performance (for example, stress, mental fatigue, motivation).
  • Adverse Physiological Status: Refers to factors that include medical or physiological conditions that affect performance (e.g. disease, physical fatigue, hypoxia).
  • Physical/Mental Limitations: Refers to the situation in which an operator lacks physical or mental capabilities to cope with a situation and this affects performance (e.g. visual limitations, insufficient reaction time).

Personnel factors

  • Crew Resource management: refers to factors such as communication, coordination, planning and teamwork.
  • Personal readiness: Refers to activities outside the working hours required to perform the work in an optimum manner, such as compliance with rest requirements, alcohol restrictions and other mandates outside Hours of work.

HFACS Level 3: Dangerous supervision

The level of unsecured supervision is divided into four categories.

  • Inadequate Supervision: The role of any supervisor is to give its staff the opportunity to succeed and to provide advice, training, leadership, supervision or incentives for the task to be done in a safe and effective manner.
  • Schedule an inappropriate operation: Refers to operations that may be acceptable and different in the case of an emergency but unacceptable in normal operation.
  • Failure to correct the known problem: Refers to cases in which the supervisor is aware of defects while being allowed to continue without modification.
  • Violation of Supervision: Refers to cases where supervisors voluntarily ignore existing rules and regulations.

HFACS Level 4: Organizational Influences

The level of organizational Influences is divided into three categories.

  • Resource management: Refers to the organization-level decision-making process for the allocation and maintenance of the Organization’s assets.
  • Organizational climate: Refers to the working atmosphere within the organization.
  • Business process: refers to the organizational decisions and rules that govern the daily activities of an organization.
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