Accident investigation 101

18 April 2008

“ Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth”

Arthur Conan Doyle, creator of Sherlock Holmes

In 1845, when William Armstrong invented the hydraulic crane, it could be argued that he had no idea the impact his invention would have on the world in which we live. I type this from the 29th floor of a glass and steel monstrosity in the heart of Chicago's Loop and marvel at that the plethora of tower cranes that grace its kingly skyline - compliments, in part, to Mr. Armstrong.

Cranes have not only changed the shape of the world's cities, literally, but they have put food on the table for millions of families for much longer than I have been alive. But as the construction industry continues to boom and crane rental shops from the West Coast all the way to the East continue to work their machines from dawn through dusk, the potential for accidents dramatically increases.

But what do we do when an accident happens? What do we do when Mr. Murphy decides to use one of our job sites to prove his seemingly infallible theory-that whatever can go wrong, will go wrong?

We investigate

Thousands of accidents occur throughout the United States every day. The failure of people, equipment, supplies, or surroundings to behave or react as expected causes most of the accidents. The accident investigation determines how and why these failures occur. By using the information gained throughout an investigation, a similar, or perhaps worse, accident may be prevented. Accident investigations should focus on prevention - not seek to place blame.

Most accidents are more complex than they are simple and, more often than not, have 10 or more events that can be labeled as causes. A comprehensive breakdown of an accident will, by and large, divulge three standard cause levels: basic, indirect, and direct. At the lowest level, an accident results only when a person or object receives an amount of energy that cannot be absorbed safely. This energy is the ‘direct cause' of the accident. The direct cause is usually the result of one or more unsafe acts or unsafe conditions, or both. These unsafe acts and conditions are the ‘indirect causes' or symptoms. In turn, indirect causes are usually traceable to poor management policies and decisions, or to personal or environmental factors. These are the ‘basic causes'.

In spite of their complexity, most accidents are preventable by eliminating one or more of the causes. Accident investigations determine not only what happened, but also how and why. The information gleaned from these investigations can prevent recurrence of similar events and, hopefully, prevent even more tragic events. Investigators should not only be interested in each individual event, but also in the sequence of events leading up to an accident. Furthermore, the accident type itself is also important, for it is the recurrence of accidents of a particular nature, or those with common causes, that highlight areas in dire need of prevention measures.

Accidents come in many different shapes and sizes so the Occupational Safety and Health Administration (OSHA) put together this outline to help structure your investigation.

1 Define the scope of the investigation.

2 Select the investigators. Assign specific tasks to each (preferably in writing).

3 Present a preliminary briefing to the investigating team, including:

a. Description of the accident, with damage estimates.

b. Normal operating procedures.

c. Maps (local and general).

d. Location of the accident site.

e. List of witnesses.

f. Events that preceded the accident.

4 Visit the accident site to get updated information.

5 Inspect the accident site. a. Secure the area. Do not disturb the scene unless a hazard exists.

b. Prepare the necessary sketches and photographs. Label each carefully and keep accurate records.

6 Interview each victim and witness. Also interview those who were present before the accident and those who arrived at the site shortly after the accident. Keep accurate records of each interview. Use a tape recorder if desired and if approved.

7 Determine

a. What was not normal before the accident?

b. Where the abnormality occurred.

c. When it was first noted.

d. How it occurred.

8 Analyze the data obtained in step 7. Repeat any of the prior steps, if necessary.

9 Determine

a. Why the accident occurred.

b. A likely sequence of events and probable causes (direct, indirect, basic).

c. Alternative sequences.

10 Check each sequence against the data from step 7.

11 Determine the most likely sequence of events and the most probable causes.

12 Conduct a post-investigation briefing.

13 Prepare a summary report, including the recommended actions to prevent a recurrence. Distribute the report according to applicable instructions.

Remember, an investigation is not complete until all data has been analyzed and a final report has been prepared. In practice, the investigative work, data analysis, and report preparation proceed simultaneously with the investigation.

When we deal in construction, we know we will eventually deal with accidents. Safety and prevention only carry us so far and we find ourselves relying on our preparedness when the accident occurs. Having a specific game plan, an appointed team leader, and good old reliance on scientific method, are key all ingredients in the recipe for a successful investigation.      

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