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Course 702 - Effective Accident Investigation

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

Step 5: Conduct 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:

Do Accidents Just Happen?
  • 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 podcast by Dan Clark ( Folklore that 'accidents happen' has been proven wrong. But are people naturally accident prone? In this podcast, Dan Clark delves into these topics.

1. _____ determines the surface causes of the accident.

a. Injury analysis
b. Event analysis
c. Cause analysis
d. System analysis

Three Phases of Cause Analysis

Worker holding a magnifying glass
Analyze the injury, the events, and the systems.

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 unique 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't serve as a proactive safety process unless system improvements effectively prevent future accidents.

2. During _____, you are analyzing the root causes contributing to the accident.

a. system analysis
b. injury analysis
c. event analysis
d. cause analysis

Injury Analysis

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

What is the Direct Cause of Injury?

In a comprehensive accident report, you'll be asked to determine the direct cause of the worker's injury. It's important to understand the nature of cause that resulted in the injury so that you can write a clearly describe what directly caused the injury in terms of a "cause and effect" relationship. Here's the cause-effect relationship: the harmful transfer of energy is always the cause of an injury which is the effect. Let's take a look at some examples that illustrate this important principle.

  • If Bob falls off a ladder and hits the ground so hard that it fractures his lower leg, the direct cause of injury is the transfer of excessive kinetic energy (the cause) that breaks the leg bone (the effect).
  • A harsh acid splashes on Brenda's face causing a serious burn. The direct cause of Brenda's injury is the harmful chemical reaction (the cause) as energy is transferred from the acid to her skin causing the burn (the effect).

As you can see, in each example above, we identify some form of harmful energy transfer that results in an injury. And, simply put, that's how you describe the direct cause of an injury. If you don't describe the type of energy transfer involved and resulting injury, you're not writing an adequate statement.

3. The direct cause of an injury will always identify _____.

a. the unsafe behavior
b. the hazardous condition
c. the type of energy transfer involved
d. the resulting accident scenario

Injury Analysis (Continued)

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

As mentioned in the previous section, injuries are always caused by the harmful transfer of energy to the employee'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.

4. Which form of harmful energy involves stored energy?

a. Kinetic energy
b. Potential energy
c. Acoustic energy
d. Thermal energy

Surface Cause Analysis

Guarded grinder
Proper guards prevent hazardous conditions.

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

Hazardous Conditions

Let's look at some characteristics and examples of hazardous conditions:

  • Unique things or objects that are somehow defective or unsafe
  • Employee physical or psychological conditions such as fatigue or stress
  • 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

5. _____ are unique hazardous conditions within the sequence of events that have directly caused or contributed to the accident.

a. Potential causes
b. Indirect causes
c. Surface causes
d. Actual causes
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. Let's look at some characteristics of unsafe or inappropriate behaviors:

  • 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

6. Which of the following is true regarding unsafe behaviors in the workplace?

a. They are the result of a lack of common sense
b. They always happen because employees do not care
c. They are not the result of root causes
d. They may exist at any level of the organization
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 to get at the root causes!
    (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 6Ps): you're getting to the real root causes!

7. When analyzing an accident, how many "why" questions should you ask about the condition of the actors?

a. 2
b. 3
c. None
d. At least five

Root Cause Analysis

After we have identified the unique conditions and behaviors during event analysis, we need to analyze them to determine their related root causes.

Workers in chemical protective suits working to fix a hazardous substance leak from a train
Safety managers should work with safety engineers to eliminate or reduce exposure to hazards through effectively improving safety system components.

The root causes for accidents are the underlying safety management system (SMS) weaknesses that somehow contribute to the conditions and behaviors we have identified. SMS weaknesses may 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-Ps) 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.

8. The _____ for accidents are the underlying safety management system weaknesses.

a. root causes
b. actual causes
c. surface causes
d. indirect causes

Hierarchy of Causes

This video describes hazards, but what are possible unsafe behaviors and system weaknesses that may contribute to a potential accident?

Most accidents in the workplace result from a hierarchy of causes:

  • System weaknesses which are the root causes that contribute to unsafe behaviors and hazardous conditions for most workplace accidents;
  • Unsafe behaviors which are the surfaces causes for the majority of workplace accidents;
  • Hazardous conditions which are the surfaces causes for only a small percentage of workplace accidents; and
  • Uncontrollable (unknowable) causes, which account for the least number of workplace accidents.

This hierarchy implies that, ultimately, management system weaknesses contribute in some way to the vast majority of all workplace accidents. When you conduct accident investigations, assume contributing system weaknesses exist because it's true for most accidents. This fact also implies that it is usually inappropriate to discipline employees when they have accidents.

To effectively fulfill your responsibilities as an accident investigator, you must not close the investigation until you identify the root causes or prove they don't exist.

9. Ultimately, the majority of of workplace accidents are due to _____.

a. a lack of training
b. a lack of management involvement
c. safety management system weaknesses
d. employees who just don't care

Check your Work

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