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Incident Investigation Blog Series – Part 2: Methodologies and Models

Posted by EHS Insight Resources on May 24, 2019 at 3:32 PM

An investigation methodology is how you think about, understand and resolve root causes of an incident. While software can support the process, the right methodology must first be selected and implemented.

The incidents we investigate— accidents and near misses—almost never result from one cause. Most of them involve multiple, interrelated causal factors. This complexity should also be reflected in the investigation methodology used. Selecting the right one for your situation can be challenging.

Before we dive into some example methodologies, let’s look at some analytical models. This will help us think about some of the mentioned methodologies such as Systematic Cause Analysis Technique, Management Oversight and Risk Tree, and Sequential Timed Events Plotting.

  • Systemic models focus on the systems and processes of the organizational culture and leadership to understand accident causes as mismatches or failures between those components.

  • Logical tree models attempt to analyze the causes of accidents as a set of events and conditions, paying particular attention to the logical relationships between them.

  • Sequence-of-Events (Domino, or Causal-sequence) models evaluate accidents as a continuous set of failures that set off a chain reaction.

  • Epidemiological models, from the medical term for the spread of disease, investigate accidents as emanating from hidden failures across all organizational components, including management, procedure and design.

  • Energy model, rooted in epidemiology, focuses on the transfer of energy causing injury to a person, and therefore seeks to find ways to prevent such a transfer.

  • Process models focus on ways in which a production system can deteriorate over time, making a clear distinction between a sequence of events and any underlying causal or contributing factors.

  • Human information-processing models analyze the situation from the perspective of a human operator and his interaction with his environment.

  • EHS management models explore the possible contributing and causal factors related to the failings of the organization and its management.

We’ll introduce at least one methodology as an example of each of the analytical models we just listed. These models help us understand how a particular methodology could be used to identify the direct causes and contributing factors of incidents. They can be used to evaluate and ultimately reduce the number of direct causes to which further analysis will be applied.

The best methodologies help investigators by utilizing multiple models of analysis to ensure thorough research into root causes and contributory causes.

Some of the methodologies discussed could be described as diagramming techniques. These can provide a useful framework for developing evidence by summarizing the events in a diagram, which provides a framework for documenting evidence, identifying causal factors, and identifying gaps in knowledge.

Diagrams help prevent inaccurate conclusions by exposing gaps in the logical sequence of events. Where gaps are identified, further analysis can uncover necessary detail. The best methodology for you might be a combination of several tools or methodologies. Some of those covered below are really a combination of tools and techniques that are assembled together to form a new methodology. Nothing prevents you from doing the same thing to make an ideal methodology for your organization.

Systematic Cause Analysis Technique (SCAT)

The International Loss Control Institute (ILCI) developed SCAT about 20 years ago for the purpose of occupational health and safety incident investigations.

SCAT is a systemic Model focused on the systems and processes of the organizational culture and leadership, and is based on root cause analysis methods1. This methodology provides a chart with a series of cross referenced categories. The investigator must identify the relevant factors by working systematically through the chart and identifying the contributing factors within each category.

Issues which lead to an incident are described as points at which the organization loses control over deficiencies, which in turn led to the undesired outcome. In other words, SCAT asks investigators to go back before the cause of the problem to where the roots of that cause were formed. One cause might be inadequate leadership, for example.

Management Oversight and Risk Tree (MORT)

The Management Oversight and Risk Tree (MORT) is an analytical procedure for determining causes and contributing factors. It arose from a project undertaken in the 1970s to provide the U.S. Nuclear industry with a risk management program competent to achieve high standards of health and safety2.

MORT, a logical tree model, is based on Fault Tree Analysis (FTA), a top down, deductive failure analysis procedure used to analyze causes and related factors of an undesired state using Boolean logic to combine a series of lower-level events and precursors.

Fault tree analysis maps the relationship between faults, subsystems, components, and controls by creating a logic diagram of the overall system. Every sufficiently complex system is subject to failure as a result of one or more individual components failing.

MORT uses a comprehensive analytical procedure that provides a disciplined method for determining the causes and contributing factors of major accidents. The method can also be used to proactively evaluate the quality of an existing system. Accidents are defined as unplanned events that produce losses when a harmful agent comes into contact with a person or asset. This contact can occur because of a failure of prevention or as an unfortunate, but acceptable, outcome of a risk that has been properly assessed and assumed. Most of the effort is directed at identifying problems in the control of a work process and deficiencies in the barriers involved, as in:

  • A vulnerable target exposed to...
  • an agent of harm in the...
  • absence of adequate barriers

The MORT methodology is less-used today in whole, but the charting technique is fairly common.

Sequential Timed Events Plotting (STEP)

A technique that can be used to depict a basic timeline of an incident is the Sequential Timed Event Plot3 also known as a STEP diagram. Events, activities, and state changes can be organized into a single diagram in a sequence-of-events analytical model.

The timeline can focus primarily on ‘what’ happened (the events) and less on why things happened (the causes). This is because there may be multiple (interacting) causes for any event on the timeline and causes may not be close together in time or place.

While other methodologies may be more helpful to identify the root causes of accident consequences, STEP can be extremely beneficial for understanding the interaction between multiple factors and outcomes. The timeline-based approach clearly and concisely gives a picture of the ‘what’ and ‘when’ to allow investigation teams to work backwards to the ‘why’ and the ‘how’.

STEP is a multilinear systems approach that view accidents as multiple avenues of causal factors that are interrelated and interact with other factors throughout the system to ultimately lead to an accident.

The STEP procedure relies on a worksheet that provides structure, visibility, and organization to data gathering and analysis. It graphically represents the beginning and end of an accident sequence, detailing actors and actions over time. The procedure accommodates events that occurred at the same time. These events allow investigators to visually recreate the mental map of a sequence of events and determine gaps.

In Closing 

These are just some of the incident investigation models and methodologies that can help improve your EHS program. Decades of research have provided a numerous models and methodologies to choose from. Incident investigators have such a wide array of tools available, it can be challenging to find the right ones. We hope this helps encourage them to explore new approaches. Although we’ve only provided some examples of the different methodologies, there are many more to research and evaluate. When designing or selecting a methodology, it is wise to research and evaluate several.


  1. SCAT: Systematic Cause Analysis Technique. Loganville, GA: International Loss Control Institute, 1990
  2. Johnson, William G. MORT: Safety Assurance Systems, Marcel Dekker, Inc. New York. 1980.
  3. Hendrick, Kingsley, and Ludwig Benner. Investigating Accidents with STEP. New York: M. Dekker, 1987.

Related Resources:

Incident Investigation Blog Series – Part 1: The Need for a Methodology

8 Investigation Methodologies to Uncover Root Causes

 

Topics: Performance Improvement, Workplace Health and Safety, Risk Management, EHS Management, Incident Management

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