Root Cause Analysis

A root cause analysis is not a search for the obvious but an in-depth look at the basic or underlying causes of occupational accidents or incidents. This is a more technical analysis and is where engineering, mathematics, and statistics begin to infiltrate occupational safety and health (OSH). This is why the following should be considered when performing analyses:

  • • Chart events in chronological order, developing an events and causal factors chart as initial facts become available.
  • • Stress aspects of the accident that may be causal factors.
  • • Establish accurate, complete, and substantive information that can be used to support the analysis and determine the causal factors of the accident.
  • • Stress aspects of the accident that may be the foundation for judgments of needs and future preventive measures.
  • • Resolve matters of speculation and disputed facts through investigative team discussions.
  • • Document methodologies used in analysis: use several techniques to explore various components of an accident.
  • • Qualify facts and subsequent analysis that cannot be determined with relative certainty.
  • • Conduct preliminary analyses: use results to guide additional collection of evidence.
  • • Analyze relationships of event causes.
  • • Clearly identify all causal factors.
  • • Examine management systems as potential causal factors.
  • • Consider the use of analytic software to assist in evidence analysis.

A root cause analysis is only the beginning and a fraction of the analysis process and should not be considered the sole approach to an analysis of an accident.

The basic reason for investigating and reporting the causes of occurrences is to enable the identification of corrective actions adequate to prevent recurrence and thereby protect the safety and health of the public, the workers, the equipment/machinery/facility, and the environment. Every root cause investigation and reporting process should include five phases. While there may be some overlap between phases, every effort should be made to keep them separate and distinct. The phases of a root cause analysis are as follows:

  • • Phase I—data collection
  • • Phase II—assessment
  • • Phase III—corrective actions
  • • Phase IV—informing
  • • Phase V—follow-up

The investigation process is used to gain an understanding of the occurrence, its causes, and what corrective actions are necessary to prevent recurrence. The line of reasoning in the investigation process is as follows: (1) Outline what happened step by step. (2) Begin with the occurrence and identify the problem (condition, situation, or action that was not wanted and not planned). (3) Determine what program element was supposed to have prevented this occurrence. (Was it lacking or did it fail?) (4) Investigate the reasons why this situation was permitted to exist.

Programs can then be improved and managed more efficiently and safely.

This line of reasoning will explain why the occurrence was not prevented and what corrective actions will be most effective. This reasoning should be kept in mind during the entire root cause process. Effective corrective action programs include the following:

  • • Management emphasis on the identification and correction of problems that can affect human and equipment performance, including assigning qualified personnel to effectively evaluate equipment and human performance problems, implementing corrective actions, and following up to verify that corrective actions are effective.
  • • Development of administrative procedures that describe the process, identify resources, and assign responsibility.
  • • Development of a working environment that requires accountability for correction of impediments to error-free task performance and reliable equipment performance.
  • • Development of a working environment that encourages voluntary reporting of deficiencies, errors, and omissions.
  • • Training programs for individuals found at fault in root cause analysis.
  • • Training of personnel and managers to recognize and report occurrences, including early identification of significant and generic problems.
  • • Development of programs to ensure prompt investigation following an occurrence or identification of declining trends in performance to determine root causes and corrective actions.
  • • Adoption of a classification and trending mechanism that identifies those factors that continue to cause problems with generic implications.


Determining facts related to any accident is the key to an accurate and effective analysis. This is why a root cause analysis should do the following:

  • • Begin defining facts early in the collection of evidence
  • • Develop an accident chronology (e.g., events and causal factors chart) while collecting evidence
  • • Set aside preconceived notions and speculation
  • • Allow discovery of facts to guide the investigative process
  • • Consider all information for relevance and possible causation
  • • Continually review facts to verify accuracy and relevance
  • • Retain all information gathered, even that which is removed from the accident chronology
  • • Establish a clear description of the accident

Select the one (most) direct cause and the root (basic) cause (the one for which corrective action will prevent recurrence and have the greatest, most widespread effect). In cause selection, focus on programmatic and system deficiencies, and avoid simple excuses such as blaming the employee. Note that the root (basic) cause must be an explanation (the why) of the direct cause, not a repeat of the direct cause. In addition, a cause description is not just a repeat of the category code description; it is a description specific to the occurrence. Also, up to three (contributing or indirect) causes may be selected. Describe the corrective actions selected to prevent recurrence, including the reason why they were selected, and how they will prevent recurrence. Collect additional information as necessary.

Further Readings

Chiu, C. A Comprehensive Course in Root Cause Analysis and Corrective Action for Nuclear Power Plants, Workshop Manual. San Juan Capistrano, CA: Failure Prevention Inc., 1988.

Gano, D.L. "Root Cause and How to Find It," Nuclear News, August 1987.

Nertney, R.J., J.D. Cornelison, and W.A. Trost. Root Cause Analysis of Performance Indicators, (WP-21). System Safety Development Center, Idaho Falls: EG&G Idaho, Inc., 1989.

Reese, C.D. Accident/Incident Prevention Techniques (Second Edition). Boca Raton, FL: CRC Press, 2012.

Reese, C.D. Occupational Health and Safety Management (Third Edition). Boca Raton, FL: CRC Press, 2016.

Reese, C.D. and J.V. Eidson. Handbook of OSHA Construction Safety & Health (Second Edition). Boca Raton, FL: CRC/Lewis Publishers, 2006.

United States Department of Energy. Accident/Incident Investigation Manual, (SSDC 27, DOE/SSDC 76-45/27) (2nd Edition), Washington, DC: US Department of Energy, November 1985.

United States Department of Energy. Occurrence Reporting and Processing of Operations Information, (DOE Order 5000.3A). Washington, DC: US Department of Energy, May 30, 1990.

United States Department of Energy. User's Manual, Occurrence Reporting and Processing System (ORPS), (Draft, DOE/ID-10319). Idaho Falls: EG&G Idaho, Inc., 1991.

United States Department of Energy, Office of Nuclear Energy. Root Cause Analysis Guidance Document. Washington, DC: US Department of Energy, February 1992.

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