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Course 702 - Effective Accident Investigation

Safety guides and audits to make your job as a safety professional easier

Cause Analysis

In this episode of "Safe in 60 Seconds" InterAct Safety Solution's president - Bart Spence, shares some tips on incident investigation - Root Cause Analysis.


You've completed the initial of the accident analysis by gathering information and using it to break the accident down into an accurate sequence of events. You have a good mental picture of what happened. Now it's time to continue the analysis process by completing each of the following three phases of analysis to determine what caused those events. This module will introduce us to the three phases of analysis below:

  • Injury Analysis to determine the direct cause of injury
  • Event Analysis to determine the surface causes of the accident
  • System Analysis to determine the root causes of the accident

Check out this short audio clip by Dan Clark of the Folklore that “accidents happen” has been proven wrong. But are people naturally accident prone? In this podcast, Dan Clark delves into these topics.

Three Phases of Cause Analysis

Worker holding a magnifying glass
Analyze the injury, events, and system root causes.

As mentioned earlier in the course, accidents are processes that culminate in an injury or illness. An accident may be the result of many factors (simultaneous, interconnected, cross-linked events) that have interacted in some dynamic way. In an effective accident investigation, the investigator will conduct three levels of cause analysis:

Injury analysis: At this level of analysis, we do not attempt to determine what caused the accident, but rather we focus on trying to determine how harmful energy transfer caused the injury. Remember, the outcome of the accident process is an injury.

Surface Cause Analysis: Here you determine the hazardous conditions and unsafe behaviors described in the sequence of events that dynamically interact to produce the accident. The hazardous conditions and unsafe behaviors uncovered are the surface causes for the accident and give clues that point to possible system weaknesses.

Root cause analysis: At this level, you're analyzing the weaknesses in the safety management system that contributed to the accident. You can usually uncover weaknesses related to inadequate safety policies, programs, plans, processes, or procedures. Root causes always pre-exist surface causes and may function through poor component design to allow, promote, encourage, or even require systems that result in hazardous conditions and unsafe behaviors. This level of investigation is also called "common cause" analysis (in quality terms) because you're identifying a system component that may contribute to common conditions and behaviors that exist or occur throughout the company.

I think the greatest challenge to effective accident investigation is to transition from event analysis to systems analysis.

One last important point to make is that most accident processes are far more complex than you might originally think. Some experts believe at least 10 or more factors come together to cause a serious injury accident. Other experts state that an average of 27 factors directly and indirectly contribute to a serious accident.

Only by thoroughly conducting all three levels of analysis can you design system improvements that effectively eliminate hazardous conditions and unsafe behaviors at all levels of the organization. The accident investigation can not serve as a proactive safety process unless system improvements effectively prevent future accidents.

Injury Analysis

Worker sitting on the ground holding an injured knee
What is the direct cause of this injury?

It's important to understand that all injuries to workers are caused by one thing: the harmful transfer of energy. Let's take a look at some examples that illustrate this important principle.

  • If a harsh acid splashes on your face, you may suffer a chemical burn because your skin has been exposed to a chemical form of energy that destroys tissue. In this instance, the direct cause of the injury is a harmful chemical reaction. The related surface causes might be the acidic nature of the chemical (condition) and working without proper face protection (unsafe behavior).
  • If your workload is too strenuous, force requirements on your body may cause a muscle strain. Here, the direct cause of injury is a harmful level of kinetic energy (energy resulting from motion), causing injury to muscle tissue. A related surface cause of the accident might be fatigue (hazardous condition) or improper lifting techniques (unsafe behavior).

In the next section, we'll take a closer look at each of the types of energy that might cause injury.

Image of a helmet on the floor and another image of a workers lower legs climbing a step ladder
Direct and Surface Causes.
(Click to enlarge)

The important point to remember here is that the "direct cause" of the injury is not the same as the "surface cause" of the accident event.

  • The direct cause of injury is the harmful transfer of energy as a consequence of your exposure to that energy. The direct result of the harmful energy transfer is injury. The cause is the harmful transfer of energy. The effect is the injury.
  • The surface cause of the accident is the condition and behavior that interacts in a way that results in the harmful transfer of energy. The interaction of the condition and behavior is the cause. The effect is the harmful transfer of energy.

Injury Analysis

Worker hitting his finger with a hammer
Example of kinetic energy.

Injuries always somehow result in the transfer of a harmful level of energy to a person's body. The severity of the injury depends on the magnitude of the harmful energy. Below are the various forms of energy that can be harmful.

Harmful Forms of Energy

  1. ACOUSTIC ENERGY - Excessive noise and vibration.
  2. CHEMICAL ENERGY - Corrosive, toxic, flammable, or reactive substances. Involves a release of energy ranging from "not violent" to "explosive" and "capable of detonation."
  3. ELECTRICAL ENERGY - Low voltage (below 440 volts) and high voltage (above 440 volts).
  4. KINETIC (IMPACT) ENERGY - Energy from "things in motion" and "impact," and are associated with the collision of objects in relative motion to each other. Includes impact between moving objects, moving object against a stationary object, falling objects or persons, flying objects, and flying particles. Also involves movement resulting from hazards of high pressure pneumatic, hydraulic systems.
  5. MECHANICAL ENERGY - Cut, crush, bend, shear, pinch, wrap, pull, and puncture. Such hazards are associated with components that move in circular, transverse (single direction), or reciprocating motion.
  6. POTENTIAL (STORED) ENERGY - Involves "stored energy." Includes objects that are under pressure, tension, or compression; or objects that attract or repulse one another. Susceptible to sudden unexpected movement. Includes gravity - potential falling objects, potential falls of persons. Includes forces transferred biomechanically to the human body during lifting.
  7. RADIANT ENERGY - Relatively short wavelength energy forms within the electromagnetic spectrum. Includes infra-red, visible, microwave, ultra-violet, x-ray, and ionizing radiation.
  8. THERMAL ENERGY - Excessive heat, extreme cold, sources of flame ignition, flame propagation, and heat related explosions.

Event Analysis

A chart helping to explain the difference between actions and actors
Analyze to find hazardous conditions and unsafe actions.
(Click to enlarge)

In the last module, you learned that each event in our sequence will include an actor and an action that may have contributed to the accident. Once we have identified the actors and actions in the sequence of steps, our next job is to conduct an event analysis to determine the surface causes for the accident.

What are Surface Causes?

The surface causes of accidents are those hazardous conditions and unsafe or inappropriate behaviors within the sequence of events that have directly caused or contributed in some way to the accident.

Hazardous Conditions

A belt on a motor exposed to workers
Analyze to find hazardous conditions and unsafe actions.
  • Are unique things or objects that are somehow defective or unsafe
  • Are "states of being" such as employee fatigue
  • May also be unique defects in processes, procedures or practices
  • May exist at any level of the organization
  • Are the result of deeper root causes

Hazardous conditions may exist in any of the categories below.

  • Materials
  • Machinery
  • Equipment
  • Tools
  • Chemicals
  • Environment
  • Workstations
  • Facilities
  • People
  • Workload

Event Analysis (Continued)

Any unsafe behaviors here?

Unsafe or Inappropriate Behaviors

It's important to know that most hazardous conditions in the workplace are the result of the unsafe or inappropriate behaviors that produced them.

  • Actions we take or don't take that increase risk of injury or illness
  • May also be thought to be unique performance errors in a process, procedure or practice
  • May exist at any level of the organization
  • Are the result of deeper root causes

Below are some examples of unsafe or inappropriate employee/manager behaviors.

  • Failing to comply with rules
  • Using unsafe methods
  • Taking shortcuts
  • Horseplay
  • Failing to report injuries
  • Failing to report hazards
  • Allowing unsafe behaviors
  • Failing to train
  • Failing to supervise
  • Failing to correct
  • Scheduling too much work
  • Ignoring worker stress
Ask "why" at Least Five Times

Analysis Tools

We recommend using both the "5-Why Analysis" and "Fishbone Diagram" to help you conduct an event analysis to uncover surface causes. Follow the steps below to conduct a Fishbone Diagram:

  1. Get a sheet of paper.
  2. At the top of the sheet write "Accident Analysis". Doing this reminds you that you are breaking down the process into a number of events.
  3. At the left side of the sheet, centered, write "The Injury".
  4. Extend a horizontal line out from the right of the box.
  5. Describe the injury event on the horizontal line.
  6. Chart showing how an investigator needs to ask why
    Keep asking why!
    (Click to enlarge)
  7. Identify and circle the actors and actions described in the event statement.
  8. Start asking why questions (at least five) about the condition of actors and actions to uncover hazardous conditions or unsafe behaviors.
  9. Draw lines either angling up or down from the circled actors and actions and write the answers to your questions.
  10. Repeat these steps with each of the new level of answers.

The diagram you'll produce using this procedure should look something like the diagram to the right. In fact, it will probably look more complex. Each level of questioning will get you closer to the root cause(s) that contributed to the hazardous conditions or unsafe behaviors. Ultimately, you'll start identifying inadequate policies, programs, plans, processes, procedures and practices (the 6P's): you're getting to the real root causes!

System Analysis

Now let's switch gears. Instead of talking about unique conditions and behaviors, let's take a look at analyzing the surface causes to determine possible safety management system weaknesses. There are many "general" conditions and behaviors (variables) inherent in the safety management system. Oh yes... to me the safety management system is "organic". By that I mean it is dynamic, ever-changing and behaves as though it were alive. Think about it. If that's a little too metaphysical for you... read on.

Workers in chemical protective suits working to fix a hazardous substance leak from a train

The root causes for accidents are the underlying safety management system weaknesses, which consist of thousands of variables, any number of which can somehow contribute to the surface causes of accidents. These weaknesses can take two forms.

  • System Design Root Causes: Inadequate design of one or more components of the safety management system. The design of safety management system policies, plans, programs, processes, procedures and practices (remember this as the 6-P's) is very important to make sure appropriate conditions, activities, behaviors, and practices occur consistently throughout the workplace. Ultimately, most surface causes will lead to system design flaws.
  • System Implementation Root Causes: Inadequate implementation of one or more components of the safety management system. After each safety management system component is designed, it must be effectively implemented. You may design an effective safety plan, yet suffer failure because it wasn't implemented properly. If you effectively implement a poorly written safety plan, you'll get the same results. In either instance, you'll eventually need to improve one or more policies, plans, programs, processes, procedures or practices.

Safety managers should work with safety engineers to eliminate or reduce exposure to hazards through effectively improving safety system components. Because systems design work common throughout the workplace, eliminating any single root cause may simultaneously eliminate many hazardous conditions and unsafe behaviors.

Since root causes reside within safety management systems, upper management -- those who formulate systems, are most likely going to be involved in making the necessary improvements. When analyzing for system weaknesses, it may be beneficial to coordinate closely with those who will be responsible for implementing system improvements.

Take a look at the Accident Weed, an excellent analogy that helps us understand the relationship between surface and root causes for accidents.

Last Words

SAIF's Action Form

Finally, according to SAIF Corporation in Oregon, most accidents in the workplace result from unsafe work behaviors.

  • unsafe behaviors represent the primary surface cause for about 95% of all workplace accidents;
  • hazardous conditions represent the primary surface cause for only about 3% of workplace accidents; and
  • uncontrollable (unknowable) causes account for the remaining 2%.

These statistics imply that management system weaknesses contribute in some way for fully 98% (conditions + behaviors) of all workplace accidents. So, ultimately, most accidents are the result of safety management system weaknesses.

To effectively fulfill your responsibilities as an accident investigator, you must not close the investigation until these root causes and solutions have been identified.

Whew! That was a lot to take in. Time for the quiz!


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the BEST answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Which of the following is a possible root cause contributing to an accident?

2. Which of the following may be a surface cause for an accident?

3. Surface causes describe hazardous _____ and unsafe _____. Root causes describe inadequate _____.

4. The _____ of the injury depends on the _____ of the transfer of harmful energy.

5. Which of the following would be the form of hazardous energy transferred if an employee falls to a lower surface?

Have a great day!

Important! You will receive an "error" message unless all questions are answered.