What should be looked at as the cause of an incident in a Workplace?

Causation Models

Many models of causation have been proposed, ranging from Heinrich’s domino theory to the sophisticated Management Oversight and Risk Tree (MORT).

Any incident can be grouped into five categories – task, material, environment, personnel, and management. When this model is used, possible causes in each category should be investigated. Each category is examined more closely below. Remember that these are sample questions only: no attempt has been made to develop a comprehensive checklist.


Here the actual work procedure being used at the time of the incident is explored. Members of the investigation team will look for answers to questions such as:

– Was a safe work procedure used?
– Had conditions changed to make the normal procedure unsafe?
– Were the appropriate tools and materials available?
– Were they used?
– Were safety devices working properly?
– Was lockout used when necessary?

For most of these questions, an important follow-up question is “If not, why not?”


To seek out possible causes resulting from the equipment and materials used, investigators might ask:

– Was there an equipment failure?
– What caused it to fail?
– Was the machinery poorly designed?
– Were hazardous products involved?
– Were they clearly identified?
– Was a less hazardous alternative product possible and available?
– Was the raw material substandard in some way?
– Should personal protective equipment (PPE) have been used?
– Was the PPE used?
– Were users of PPE properly educated and trained?

Again, each time the answer reveals an unsafe condition, the investigator must ask why this situation was allowed to exist.

Work Environment

The physical work environment, and especially sudden changes to that environment, are factors that need to be identified. The situation at the time of the incident is what is important, not what the “usual” conditions were. For example, investigators may want to know:

– What were the weather conditions?
– Was poor housekeeping a problem?
– Was it too hot or too cold?
– Was noise a problem?
– Was there adequate light?
– Were toxic or hazardous gases, dusts, or fumes present?


The physical and mental condition of those individuals directly involved in the event must be explored, as well as the psychosocial environment they were working within. The purpose for investigating the incident is not to establish blame against someone but the inquiry will not be complete unless personal characteristics or psychosocial factors are considered. Some factors will remain essentially constant while others may vary from day to day:

– Did the worker follow the safe operating procedures?
– Were workers experienced in the work being done?
– Had they been adequately educated and trained?
– Can they physically do the work?
– What was the status of their health?
– Were they tired?
– Was fatigue or shiftwork an issue?
– Were they under stress (work or personal)?
– Was there pressure to complete tasks under a deadline, or to by-pass safety procedures?


Management holds the legal responsibility for the safety of the workplace and therefore the role of supervisors and higher management and the role or presence of management systems must always be considered in an incident investigation. These factors may also be called organizational factors. Failures of management systems are often found to be direct or indirect causes. Ask questions such as:

– Were safety rules or safe work procedures communicated to and understood by all employees?
– Were written procedures and orientation available?
– Were the safe work procedures being enforced?
– Was there adequate supervision?
– Were workers educated and trained to do the work?
– Had hazards and risks been previously identified and assessed?
– Had procedures been developed to eliminate the hazards or control the risks?
– Were unsafe conditions corrected?
– Was regular maintenance of equipment carried out?
– Were regular safety inspections carried out?
– Had the condition or concern been reported beforehand?
– Was action taken?

This model of incident investigation provides a guide for uncovering all possible causes and reduces the likelihood of looking at facts in isolation. Some investigators may prefer to place some of the sample questions in different categories; however, the categories are not important, as long as each question is asked. Obviously there is considerable overlap between categories; this overlap reflects the situation in real life. Again it should be emphasized that the above sample questions do not make up a complete checklist, but are examples only.

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