Accident Investigation
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CHAPTER 7
Events and Causal Factors Analysis
One of the most important steps in performing a comprehensive accident investigation is documenting the accident sequence, and one of the best ways to do this is to use events and causal factors ana/ysis. This technique has two parts---creating an events and causal factors chart and using the chart to ana!Jze the accident. The events and causal factors analysis will help you to determine the accident sequence, analyze the sequence, and find the causal factors of
the accident.
About Events and Causal Factors Analysis The concept of events and causal factors analysis has been around for more than thirty years under a variety of names. The National Transportation Safety Board used a similar technique called Multilinear Event Sequences to document the events of an accident (Benner 1975) (Ferry 1981). The ?epartment of Energy incorporated events and causal factors charting into tts 1:0RT system. In System Sefery 2000, Joe Stephenson introduced the idea of VIS aliz' · . u 1ng and analyzing the chart to find causes and develop corrective acnons. He called this process causal factors ana/ysis (Stephenson 1991 ). The refinements made through the years are incorporated into the description of events and causal factors analysis discussed in this chapter.
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The Events and Causal Factor Analysis Approach s
As an accident investigation progresses, more and more info . . d rtnatton is I
about the accident. Events an causal factors analysis pro •d earned . v1 es a tool
events and causal factors chart-for chronologically arranging this in£ :--the create a timeline of the accident. As facts are uncovered th orrnatJ.on to , e correspo din events and conditions are incorporated into the chart. The inve . n g Stlgator an ,,, the chart to find the causal factors of the accident only after al/ of a;,ze, have been discovered. Figure 7-1 illustrates the events and ca
th 1 fe facts . . . usa actors
analysis t1meline approach.
Events and Causal Factors Charting
Some of the functions of the events and causal factors analysis chart are listed and discussed below (OSHA Institute 1995) (Department of Energy 1999):
• Graphic portrayal of the accident sequence
• Recording of events and conditions
• Validation and verification of facts
Exhibit 7.1 EVENTS AND CAUSAL FACTORS ANALYSIS TIMELINE APPROACH
FACT FACT FACT
C:'.:'.Tl:':'.:M'.:E======================"- V ------
> Chapter 7: Events and Ca11sal Factors Ana!Jsis
. ery of holes in the accident sequence , D1scov , Identification of multiple causes , Elimination of memorization as a means of documentation
, Aid in report writing , Determination of causal factors (in the analysis part of the technique)
Graphic Portrayal of the Accident Sequence Start constructing the chart as soon as you obtain facts about the accident. Many investigators find it convenient to write information on removable adhesive notes and place them in chronological order on a wall or table . Notecards also work, but they must be taped in place. Computer programs can print an events and causal factors chart, but it is best to use them after the wall or table chart is completed.
Recording of Events and Conditions Three types of information are recorded on an events and causal factors chart: events (occurrences with time and date), conditions (what was going on during the events), and the accident itself. At the top of the adhesive note for each event, write the event as a sentence with a subject and an action verb to describe the event (example: "Bill dropped the hammer."). At the bottom of the note write the time and date the event happened and the source of the information. On separate notes write conditions that existed at the time of the event. See "Documentation Procedures" later in this chapter for more information on recording events and conditions.
Validation and Verification of Facts You may encounter conflicting information as you examine evidence and lnterview people. If you write on each event or condition, note where you obtained the information-witness statement, interview of foreman, lockout/ tag_out log, plant procedures, etc.-you will have a way to decide which piece ofmfio · · rmatton ts valid.
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. of }-{oles in the Accident Sequence Discovery
. • the eve nts and causal factors chart is an excellent w Exarn101 ng . . . . . . ay to find
h I . our invest1""t10n. Swee the chart 1s 1n chronological time d o es in Y ,,,- . . . . . . or er, it
. t cell whether information 1s nusswg. It 1s unportant to find all f 1s easy o . o the
ail hie information and facts about the accident before you start anal .
wa the accident sequence.
Identification of Multiple Causes As you document the facts of the accident on the events and causal factors chart, che chart actually becomes the accident sequence, and it can be used co identify multiple causes as well as a single cause.
Elimination of Memorization as a Means of Documentation
As you start investig:iting an accident, you may rely on memory rather than a chart to keep track of the information you discover. However, it is extremely difficult to memorize the events and conditions for complex accidents-there is just coo much information to keep track of mentally. The events and causal factors chart is a concrete way to document the facts so that you do not
depend on memorization.
Aid in Report Writing \'v'hen you write an accident investig:ition report, an events and causal factors chart will provide an excellent outline of the accident.
Charting Procedures MoSt investigators construct charts in a secure controlled location using removable adhesive notes or notecards taped t~ a wall or cable. After_ tbe chart is complete, some investig:itors transfer the information to a specialized computer program. (See "Computerized Charts" later in this chapter.)
..... ,ng Various Types of Events Cha•=·
Chapter 7: Events and Causal Factors Ana!Jsis
events Record each event, along with the date and time it occurred and the information source, on a separate note and place the note in chronological order in the chart- Events should be written with a subject (noun) and a verb.
Assumed Events 'Ibese are events that you know must have happened but have not yet been verified. Write them on notes of a different color from those used for verified events. This will remind you that more investigation is needed.
Non-events-Events That Did Not Occur If a worker did not place a lock and tag on an electrical panel, this is a non- event. Non-events can be important in determining causal factors. Some accident investigators do not include non-events on their charts, while others include them until all of the other information is received. Information about non-events should be captured somehow, and the chart is a good place to document it. Although they are not events, they may be cited as conditions or causal factors when the chart is analyzed.
Events That Occur Simultaneously It is possible for two events to occur at the same time. In this case, place the second set of events and conditions directly below the first to signify that they occurred at the same time. Exhibit 7.2 displays a secondary event sequence.
Charting Conditions Conditions are situations related to an event, such as what caused the event to happen, what was happening during the event, or even non-events. For example, suppose that the event is that a worker turned off an electrical panel Ill Room A. Conditions associated with this event might be that the worker was about t .
ll . 0 service a machine (what caused the event); Room A was not
we -lit bee Ii and h didause a ghtwas burned out (what was happening during the event); th he not place a lock and tag on the electrical panel (non-event). On
e c art, use different color notes for events and conditions.
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Exhibit 7.2 EVENT SEQUENCE
ACCIDENT
Charting the Accident The last cype of information to chart is the accident itself. Place a note on the chart (in a different color from those used for events and conditions) describing the accident along with a time and date. It is possible for events to occur both before and after an accident; usually the ones after the accident will be emergency response actions. When you look at the chart, it will be obvious where the accident falls in relation to the events and conditions
leading up to and following it.
Computerized Charts If you transfer your chart to a computer, it is customary to place events in rectangles, conditions in ovals, and accidents in diamonds. For assumed events and conditions, dashed rectangles and ovals are used. There are computer programs specifically designed to create events and causal factors charts; however, many other programs-such as PowerPoint™, Visiou.i, and CAD
or graphic programs--<:an be used as well.
Exhibit 7.3 illustrates a typical event, condition, and the accident.
How Much Should You Include on the Chart? The chart's ft · . . · eluded . e ecuveness 1s linked to the amount of informauon Ul .11 on 11. You must · f thr . d place""
f h . si t ough all of the information you receive an ,j]]
o t e 1mporca t mple 11
ill n events and conditions on the chart. A short exa ustrate an eve d nts an causal factors chart.
Chapter 7: Events and Causal Factors Ana/ysis
An office worker noticed that a light bulb in the break room was burned out and decided to change the bulb himself. He found a new light bulb and a step ladder. He had one of his lunch partners hold the ladder as he climbed to the top rung. As he reached to screw in the light bulb, he fell off the ladder and broke his arm.
Exhibit 7.4 depicts an events and causal factors chart for this simple example. Note that each event note contains a sentence describing the
Exhibit 7.3 liliili~""'--..;;;E...;.VE_N_TS, CONDITIONS, AND THE ACCIDENT __ _
Subject + Action Verb
------1----------T------- : Source of:
Date : infor- : Time : mation :
& I
[Note: This information can be written on the back of the paper to ensure confidentiality. This is important if conflicts develop.]
Situation related to the event or circumstance
[Note: Including the source of the information can be useful
if conflicts develop.]
ACCIDENT
Date and time
EVENTS
Media for posting events:
• removable adhesive notes
• notecards •computer
CONDITIONS
ACCIDENT
Worker turned off electrical panel in
Room A [Note: The event should be as specific as possible. There should be only one noun and verb; record one event at a time.] --------r-------~--------
' Shift I 12/14/11 : log- : 10:41 AM
: book ' I
No approval received from building supervisor
OR Did not use LOTO
procedure
Worker received electric
shock 12/14/11 10:42 AM
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Parl Ill: Ana/ytical Techniques
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event and the date and time of the event. The sour . . . . ce of the.
in this case the miured worker, ls Offiltted in this lnfottti. . . . exaniple b atton
written on the back of the note. Conditions associat d . Ut could ' e With th be
written on notes placed above each event note st ki e events . , ac ng th ate
if there are several. As with event notes, source inc . em V-etticau . . iorniauo y
written on each condition note. n should be
Exhibit 7.4
Very dark in one comer of lunch room.
Worker noticed a
light out in lunchroom. 1/9/2011
11 :20
Did not notify
mainte- nance
depart- ment
Worker found new light bulb. 1/9/2011
11 :21
EXAMPLE CHART
Not normal job duty-no training
Violated safety rule
Used top rung of ladder
Worker climbed ladder to
replace bulb. 1/9/2011
11:24
Worker fell off ladder. 1/9/2011
11 :25
Co-worker called
ambulance 1/9/2011
11:26
Chapter 1: Events and Causal Factors Ana/ysis
Charting Tips
• Fill your chart with information. Do not be too concerned with charting style and correctness-just include as much information as you can.
• Make room for your chart. Charts for complex accidents grow from day to day as new information is received. Place adhesive event and condition notes on a wall or large table, depending on the size of the investigation. For larger investigations the notes may wrap around an entire room!
• Keep the notes sticky. Especially in humid offices, do not depend on adhesive notes to keep sticking as they are moved to make room for others-use additional tape.
• Leave some expansion room. Leave some breaks in the chart for expansion to avoid having to move all of the notes every time you insert a new one. Put space between events when you think additional information will be received.
• Mark time breaks. For complex accidents, tape day, hour, and possibly minute markers to the wall so you can find and place notes easily.
• Be thorough, but be aware that being thorough takes time. For complex accidents, creating events and causal factors charts is extremely time-consuming, but the more time you take, the more thoroughly you will have investigated the accident. If all pertinent information is not included in your chart, your analysis is not representative of the entire accident sequence, and you may not discover the true causal factors of the accident.
• Archive the chart. Once the chart is finished and the causal factors have been analyzed, it can be taken down and the information entered into a computer. When you take the chart down, disassemble it carefully, keeping the event notes in order and the condition notes behind their corresponding event notes. If you need to revisit the chart, you will be able to reconstruct it easily. Store chart notes and computer printouts in a protected area.
• Use the chart as the basis of a report.You may wish to include a summary of the chart in your accident investigation report. Pick ten to fifteen events th
at summarize the accident sequence. The events you choose should include all of the events that were identified as causal factors. A chart like this tells
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Part Ill: A nalytical Techniques
the story of the accident-it gives the reader the eve . . nts, conditi
causal factors m an easily understood chronological pictur S ons, and e. urnrnary are also very effective as management tools (Stephenson 1991
). charts
Events and Causal Factors Analysis
Analysis of the events and <;onditions-a qualitative approach to visua!izin the accident-begins when the chart is finished. Exhibit 7.5 portrays this p~ of the process . You must evaluate each event to determine its significance to the accident, asking, "What occurred? How did it occur? Why did it occur? What is its relevance? What are the circumstances surrounding it?" As you answer these questions, you will discover the accident's causal factors. It is usually best to start with the first event and proceed until you reach the
Exhibit 7.5
C EVENTS AND CAUSAL FACTORS '.~ NALYSIS f
Causal Factors
V
3. Analyze to see if a causal factor or relationship involved in the accident, if corrected, would have prevented the accident.
Conditions
iJ Events
1. Analyze each event to determine significance.
2. Analyze each condition related to the event and ask: What caused this event? . What wa~ happ~~,ng during this even . Why did this event occur?
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Chapter 7: Events and Causal Factors Ana!Jsis
. Do not skip events-sometimes the more obscure ones turn out cc1dent. . . a ry important. When you have firushed the analysis, you may wish to to be ve
. . h the events that were causal factors with a color code or symbol dist:IDgu1S h as a hexagon. sue
Example Scenario
In the forklift-hitting-the-ladder example given in the introduction to Part III, two accidents may be identified-the forklift hitting the ladder and the supervisor falling off the ladder. While investigating either should yield the same causal factors, the one in which injury or damage is involved-in this case the supervisor falling off the ladder-is usually identified as the primary accident.
Exhibit 7.6 illustrates the first stage of the events and causal factors chart. All of the facts and information related to this accident are not included in this chart; other analysis methods discussed later in the book will add information and the chart will continue to grow until it includes all of the information necessary for analysis.
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Exhibit 7.6 EVEN_T,...S .,.A,..ND~ CAUSAL ANAL YSI ----
Bill received promotion to
New wing of warehouse
finished. 1/6/2011
1----; warehouse t----- supervisor.
Bill arrived at work.
2/5/2011 7:35
1/23/2011
Bill retrieved a ladder. 2/5/2011
7:41
Fire inspection
found violations in warehouse. 2/4/2011
Bill walked with ladder to
end of row. 2/5/2011
7:43
Chapter l: Events and Causal Factors Ana/ysis
s·AND ,AUSAL ANALYSIS OF EXAMPLE SCENARIO continued EVENT ·· '
Bill climbed ladder to
install sign. 2/5/2011
7:44
No barricades
Forklift hit ladder.
2/5/2011 7:45
Difficult
thed driv
Forklift driver loaded last load of the
day. 2/5/2011
7:44
Forklift driver turned corner
~---1 of aisle. 2/5/2011
7:45
Bill fell off ladder.
2/5/2011 7:45
Forklift driver immediately
notified medical. 2/5/2011
7:46.
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Summary
Events and causal factors analysis is a comprehensive accid . . ent Investj . tool that develops the accident sequence as well as determinin gation
. . g causal fac The accident sequence is separated lilto events and condition Th tors. · li f h ·d Af s. e event illustrate a time ne o t e acci ent. ter a complete chart · d s
. is evelo d from the facts of the accident, the events and conditions are a al pe n yzed and causal factors are determined. Many hours of work are needed to p d
ro uce an effective events and causal factors analysis; however, the result is that .d . acc1 ent investigators understand the accident sequence and are confident that the
causal factors of the accident have been found. This technique ensures that an adequate investigation is performed and a documented accident sequence is developed. This technique answers the ultimate question for accident investigators: "Why did this accident occur?"
REVIEW QUESTIONS 1. What are the advantages of using an events and causal factors analysis to
investigate an accident?
2. What analysis errors might be caused by an incorrect timeline?
3. Why is it important to document the source of each item of information?
4. When should an events and causal factors chart be started?
. e7 5. How do you display two events that occurred at the same t,m ·
6. How do you perform the analysis portion of the event an d causal factors analysis?
. . . d causal 7- How do you make a summary chart from a completed events an factors chart?
. le scenario B. Continue the events c1nd causal factors chart for the examp
(Exhibit 7.6).
