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June 27, 2001

What is an accident and why should it be investigated?

By Maureen Alvarez, CIH, CSP

The term "accident" can be defined as an unplanned event that interrupts the completion of an activity, and that may (or may not) include injury or property damage.  There are many reasons to conduct a workplace accident investigation, such as:

  • to fulfill the legal requirement
  • to determine the cost of an accident
  • to determine compliance with applicable safety regulations
  • to process workers' compensation claims

Most importantly accident investigations are conducted to find out the cause(s) of accidents and to prevent similar accidents in the future. When accidents are investigated, the emphasis should be concentrated on finding the root cause(s) of the accident rather than the investigation procedure itself.

Who should do the accident investigating?

Ideally, an investigation should be conducted by an expert in accident causation who is experienced in investigative techniques, fully knowledgeable of the work processes, procedures, persons, and industrial relations environment of a particular situation. Unfortunately, such persons are hard to find. Especially in smaller organizations, both workers and supervisors with little, if any,previous investigative experience maybe called upon to participate in an accident investigation.

Who and how many people should investigate an accident?

The best team to conduct an accident investigation includes the injured worker, their supervisor and a safety representative. It is critical that the injured worker’s supervisor is on the accident investigation team because this person will be the most knowledgeable about the work conditions and the people involved.  Furthermore, the supervisor can usually take immediate remedial action if an immediate corrective action is identified.  Other members that are valuable to the accident investigation team include maintenance, engineering, process support and other technical staff members that have a good understanding of the incident and the corrective action. 

How to make sure that investigators are impartial?

An investigator who believes that accidents are caused by unsafe conditions will likely try to uncover conditions as causes.  On the other hand, one who believes they are caused by unsafe acts will attempt to find the human errors that are causes.  Therefore, it is necessary to examine briefly some underlying factors in a chain of events that ends in an accident. 

The important point is that even in the most seemingly straightforward accidents, seldom, if ever, is there only a single cause. For example, an "investigation" which concludes that an accident was due to worker carelessness, and goes no further, fails to seek answers to several important questions such as:

  • Was the worker distracted? If yes, why was the worker distracted?
  • Was a safe work procedure being followed? If not, why not?
  • Were safety devices in order? If not, why not?
  • Was the worker trained? If not, why not?

An inquiry that answers these and related questions will probably reveal conditions that are more open to correction than attempts to prevent "carelessness."

What are the steps involved in investigating an accident?

The accident investigation process involves the following steps:

  • Report the accident occurrence to a designated person within the organization
  • Provide first aid and medical care to injured person(s)
  • Investigate the accident
  • Identify the causes
  • Report the findings
  • Develop a plan for corrective action
  • Implement the plan
  • Evaluate the effectiveness of the corrective action

Make changes for continuous improvement

As little time as possible should be lost between the moment of an accident or near miss and the beginning of the investigation. This approach allows the investigator to observe the conditions as they were at the time, prevent disturbance of evidence, and identify witnesses.  It is recommended that you have a pre-assembled “toolbox” prepared when you need to conduct an accident investigation.  The tools that members of the investigating team may need are pencil, paper, camera, film, tape measure, statement forms, etc.  These items should be immediately available so that time is not wasted.

What should be looked at as the cause of an accident?

Accident Causation Models

Many models of accident causation have been proposed, ranging from Heinrich's domino theory to the sophisticated Management Oversight and Risk Tree (MORT).  A simple model attempts to illustrate that the causes of any accident 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 accident is explored. Members of the accident 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 substances involved?
  • Were they clearly identified?
  • Was a less hazardous alternative substance possible and available?
  • Was the raw material substandard in some way?
  • Should personal protective equipment (PPE) have been used?
  • Was the PPE used?

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


The physical environment, and especially sudden changes to that environment, are factors that need to be identified. The situation at the time of the accident is what is important, not what the "usual" conditions were. For example, accident 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. The purpose for investigating the accident is not to establish blame against someone, but the inquiry will not be complete unless personal characteristics are considered. Some factors will remain essentially constant while others may vary from day to day:

  • Were workers experienced in the work being done?
  • Had they been adequately trained?
  • Can they physically do the work?
  • What was the status of their health?
  • Were they tired? (how many hours had they been working?)
  • Were they under stress (work or personal)?


Management holds the legal responsibility for the safety of the workplace and therefore the role of supervisors and higher management must always be considered in an accident investigation. Answers to any of the preceding types of questions logically lead to further questions such as:

Were safety rules communicated to and understood by all employees?

  • Were written procedures available?
  • Were they being enforced?
  • Was there adequate supervision?
  • Were workers trained to do the work?
  • Had hazards been previously identified?
  • Had procedures been developed to overcome them?
  • Were unsafe conditions corrected?
  • Was regular maintenance of equipment carried out?
  • Were regular safety inspections carried out?

This model of accident investigations 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 pertinent question is asked. Obviously there is considerable overlap between categories; this 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.

How are the facts collected?

You may want to take photographs before anything is moved, both of the general area and specific items. Careful study of these may reveal conditions or observations missed previously. Sketches of the accident scene based on measurements taken may also help in subsequent analysis and will clarify any written reports. Broken equipment, debris, and samples of materials involved may be removed for further analysis by appropriate experts. Even if photographs are taken, written notes about the location of these items at the accident scene should be prepared.

Background Information

A very useful background source, but often overlooked, is the information that can be found in documents such as technical data sheets, maintenance reports, past accident reports, formalized safe-work procedures, and training reports.  Any pertinent information should be studied to see what might have happened, and what changes might be recommended to prevent recurrence of similar accidents.

Why should recommendations be made?

The most important final step is to come up with a set of well-considered recommendations designed to prevent recurrences of similar accidents.  Once you are knowledgeable about the work processes involved and the overall situation in your organization, it should not be too difficult to come up with realistic recommendations.  Resist the temptation to make only general recommendations to save time and effort.

In the unlikely event that you have not been able to determine the causes of an accident with any certainty, you probably still have uncovered safety weaknesses in the operation.  It is appropriate that recommendations be made to correct these deficiencies.

Remember, the purpose of an accident investigation is to determine the cause(s) of the incident and to implement corrective actions in order to prevent this accident from happening again.  A thorough accident investigation is always worth the time and effort!

For additional information regarding accident investigations and accident prevention, please refer to the many links located on our safety page located on the Osh.Net home page at http://www.osh.net/directory/safety/index.htm

Copyright © 2001 by WorkCare™ All Rights Reserved

See you next month, editor@osh.net

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Original articles © WorkCare™; Orange, California.