Safetip #133: Classify Causes of Incidents in Five Categories

July 18, 2018

This week’s Safetip is about classifying causes of incidents in five categories to help identify potential underlying organizational issues.

Five Categories of Incidents

The causes of incidents should be categorized to determine if there are certain types of organizational weaknesses or issues that are leading to more incidents. But how should you categorize the causes of incidents?

There are many models of causation proposed. In this post we share a simple one from the Canadian Centre for Occupational Health & Safety (CCOHS). The model from CCOHS groups the causes of any incident into five categories: Task, Material, Environment, Personnel, and Management. When an incident occurs, possible causes in each category should be investigated.

Categories of Incidents

Let’s look at each category with some sample questions (CCOHS emphasizes that the sample questions are examples only. They don’t make up complete checklists).


The actual work procedure being used at the time of the incident must be explored. 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/tagout used when necessary?

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


To seek out possible causes from the equipment and materials used, ask these questions:

  • Was there an equipment failure? What caused it to fail?
  • Was the machinery poorly designed?
  • Were hazardous chemical products involved?
  • Were they clearly identified?
  • Was a 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?

Each time the answer reveals an unsafe condition, ask why the situation was allowed.

Work Environment

The physical work environment, especially sudden changes to the 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. Try to find out the following:

  • 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?


Physical and mental conditions of individuals directly involved in the incident must be explored, as well as the psychosocial environment they were working in. The purpose is not to blame someone, but to make sure the investigation is complete by considering personal characteristics or psychosocial factors. Here are some sample questions to ask:

  • Did workers follow safe operating procedures?
  • Were workers experienced in the work being done?
  • Had they been adequately educated and trained?
  • Could 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?


The role of supervisors and management, and the role or presence of management systems must always be considered in an incident investigation. 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 safe work procedures being enforced?
  • Was there adequate supervision?
  • Were workers educated and trained to do the work?
  • Were hazards and risks previously identified and assessed?
  • Were procedures 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?

Uncover Underlying Issues

The model from CCOHS provides a guide for uncovering all possible causes, and helps to avoid looking at facts in isolation. There is some overlap between the five categories, and an incident can easily fit in more than one. This is normal.

The greatest benefit of using a model for classifying causes of incidents is the ability to determine if there are certain types of organizational weaknesses or issues that are leading to more incidents. Analyze all incidents and verify if one or two of the five categories are appearing much more frequently than others. This may indicate an underlying weakness or issue in your organization.

For example, if category “Personnel” is showing up at an unusually higher rate than others, it may be an indication that there’s a problem with the safety culture in your company, or that employees are not receiving proper training or support. Or, if category “Task” is showing up very frequently, it may indicate that either procedures are not being followed properly or they are not as inherently safe as previously thought.

Finally, the entire process of analyzing categories of causes of incidents to determine if there are underlying issues can be greatly facilitated and accelerated with incident management software.

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