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162 Accident Investigation: Basic
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162 Accident Investigation: Basic

Developing the Sequence

The challenge at this point in the investigation process is to accurately arrange the events to determine their correct sequence leading up to the accident to understand why the accident event, itself, happened. Once the sequence of events is developed, we can then study each event in the sequence to determine the surface and contributing root causes.

1 red and 4 white dominos that represent accident events that need to be put in correct sequence
The challenge is to properly sequence the events resulting in the accident event.
  • Hazardous conditions: Objects and physical states that directly caused or contributed to the accident.
  • Unsafe behaviors: Actions taken/not taken by an actor that directly caused or contributed to the accident.
  • System weaknesses: Underlying inadequate or missing policies, programs, plans, processes, procedures and practices that contributed to the accident.

Verify you are constructing only one event. If an event is difficult to understand, the description may be too vague or general. To solve this problem, increase the level of detail. Strategies to increase detail:

  1. Look around: Determine if anything else was said or done before or after the event you are currently assessing.
  2. Separate the actors: Remember, an actor may be a person or an object performing a specific action. If an event involves actions by more than one actor, break it down into two events. If the event contains the conjunction "and," it is likely a combination of two events. You can identify some combined events in the sample sequence of events in the example below.

Sample Sequence of Events

Below is an example of a sequence of events of an actual fatality investigation conducted by OSHA. It gives you a good idea what a sequence looks like.

In this accident, a worker was fatally electrocuted when he oriented a long irrigation pipe that contacted a high power electrical line. Most events are corrected developed. Notice that a couple of events could be further divided because more than one action occurred.

Worker laying in ditch injured by electrocution
Each event has one actor and one action.

Key: Actor, Action Conjunction

  1. At 12:30 PM Employee #1 returned to the worksite from lunch.
  2. At 12:35 PM Employee #1 started laying irrigation pipes into a 2-ft deep ditch.
  3. At approximately 12:40 PM employee #1 oriented an irrigation pipe vertically.
  4. The pole contacted a high voltage power line directly over the work area.
  5. Employee #2 heard a 'zap' and turned to see the mainline pipe and Employee #1 falling into an irrigation ditch.
  6. Employee #2 ran to Employee #1 and noticed that he appeared to be unconscious.
  7. Employee #2 pulled Employee #1 out of the irrigation ditch.
  8. Employee #2 ran about 600 ft to his truck.
  9. At 12: 45 PM Employee #2 placed a call for help on his mobile phone.
  10. Employee #2 ran back to Employee #1.
  11. At 12:55 PM paramedics arrived.
  12. At 12:57 PM paramedics started administering CPR on Employee #1 using a heart defibrillator.
  13. At approximately 1:10 PM the paramedics transported Employee #1 to the hospital.
  14. At 1:30 PM the attending physician pronounced Employee #1 deceased.

Knowledge Check Choose the best answer for the question.

1-9. What must be completed before the accident investigator can analyze events to determine surface and root causes?

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