1. OVERVIEW OF
ACCIDENT
MODELING
APPROACHES
PART 1
ROSS APTED

2. SOCIO-TECHNICAL
SYSTEMS
Socio-technical system – The interactions between
people and their behavior with
technology while occupying
society's complex
infrastructures.
Examples:
Power plants, national healthcare system, space
missions, stock market , aviation systems.
What happens when they go wrong

3. THE NEED TO MODEL
ACCIDENTS
Accidents in these types of organizations are: have a high
cost, decrease efficacy and can lead to serous harm or death
of humans.
If the source of the accident is identified the potential
accidents can be eliminated.
To obtain this information must effectively represent the
system in which the accident occurred and the accident
itself.
Accident Models.

4. ACADEMIC
LITERATURE I
Understanding Accidents - From Root Causes to
Performance Variability
(Hollnagel, 2002)
Key points:
Discusses the general
modeling approaches and
identifies each what
approach shows or
highlights.
Main types of Accident
model. (Hollnagel, 2002)

5. ACADEMIC
LITERATURE I
The suitability of these approaches focusing on the human
aspects of Sociotechnical systems.
Humans actions are not black
and white and can only be judge
in hindsight.
People do what they think
is right at the time.
Different degrees of ‘being right’
not just correct or fail.
(Amalberti, 1996)

6. ACADEMIC
LITERATURE I
In the sequential model an element is either correct or has
failed, but human actions are not like this
Human actions are better suited to the epidemiological model
as it allows for latent conditions , it takes into account that action
may contribute to accident over time.
The systemic model is built on the concept of variability and
does not focus on failures. This is perfect for representing
variability of human action.

7. ACADEMIC
LITERATURE II
Comparison of some selected methods for
accident investigation
(Sklet, 2004)
Key points:
Compares a selection of
accident investigation
methods, theses methods
are commonly used and
widely acknowledge in
academic and accident
investigating community.
Methods compared in article

8. ACADEMIC
LITERATURE II
Details Framework of comparison highlighting the strengths
and weakness of each technique.
7 categories
Whether the methods give a graphical description of the event sequence
or not?
Can give overview of events
Allows for clear communication
Easy to see broken link
To what degree the methods focus on safety barriers?
Analysis of protective elements in the the system

9. ACADEMIC
LITERATURE II
The level of scope of the analysis.
Which levels of Rasmussen’s classification of
sociotechnical systems (Rasmussen, 1997) does the
method model.
(Rasmussen, 1997)

10. ACADEMIC
LITERATURE II
What kind of accident models that has influenced the methods?
sequential model, epidemiological model, systemic model
Whether the different methods are
inductive, deductive, morphological or non-system-oriented?
The way in which the method looks at the accident e.g.
does reason from the general to the specific.

11. ACADEMIC
LITERATURE II
Whether the different methods are primary or secondary
methods?
Primary Method – Self contained, stand alone method.
Secondary Method – used in conjunction with other
method to provide special input.
The need for education and training in order to use the methods.
Novice – no experience or training is needed.
Specialist – In between Novice and expert.
Expert – Formal education and training is needed.

12. ACADEMIC
LITERATURE II
Each method is briefly detailed, the comparison is analyzed
and discussed.
Characteristics of different methods.
(Sklet, 2004)
Conclusion: no one accident investigation technique is perfect and
that to be most effective they must be used in conjunction.

13. ACADEMIC
LITERATURE III
Models of accident causation and their application: Review
and reappraisal
(Lehto, 1991)
Key points
Categorizes and compares 54 different accident causing
models.
A fairly comprehensive at the time of publication list
categorized and cited.
Conclusion: modeling methods are to narrow and a better
model is need to take into account human and
technological interaction.

15. SEQUENTIAL ACCIDENT MODELS

16. SEQUENTIAL
ACCIDENT MODELS
Simplest form of accident modeling.
Describes the accident as a series of events that occur in a
particular order.
Events occur along a linear timeline.
Analysis: Identifies specific cause and broken links in
accident chain. Goal is to eliminate broken links.

17. DOMINO MODEL OF
ACCIDENT CAUSATION
(Ferry, 1988)
5 factors in the accident sequence
1. Social environment
Factors effect an individuals perception of risk
2. Fault of the person
Human error
3. Unsafe acts or environment
faulty equipment, hazards in the environment
4. Accident
5. Injury

18. DOMINO MODEL OF
ACCIDENT CAUSATION
Domino Diagram
Time

19. FAULT TREE
ANALYSIS
(Høyland & Rausand, 1994)
Graphical representation of normal events, system
failures, human errors and environmental factors.
Logic gate are used to construct chains of events.
Used to identify sequences off failure.
Advantages:
Root cause can be easily be identified.
Human readable easy to communicate events that lead to
accident.

20. FAULT TREE
ANALYSIS
Simple fault tree for a fire breakout

21. EVENTS AND CAUSAL
FACTORS CHARTING
(Department of Energy, 1999)
Diagram used to show the events of the accident in
chronological order.
Primary events – the main sequence of events that lead to
the accident are drawn in a horizontal line.
Secondary events – Placed above or below each primary
event that it directly relates to.
Conditions influencing the events – Passive and describe
states, place above
relevant events.

22. EVENTS AND CAUSAL
FACTORS CHARTING
(Department of Energy, 1999)

23. SEQUENTIAL ACCIDENT
MODELS SUMMARY
Advantages:
Human readable, easy to communicate chain of events.
Can identify root cause or break in chain of events that lead
to accident.
Good starting of point.
Disadvantages:
Does not take into account latent factors.
Inadequate to model the variability of Sociotechnical
systems.

24. SEQUENTIAL ACCIDENT
MODELS SUMMARY
More modeling techniques:
• Event tree analysis.
• Management and Oversight Risk Tree (MORT).
• Sequential Timed Events Plotting (STEP).
• Man, Technology and Organization (MTO)-analysis.
• TRIPOD
Links last accessed 29/06/12

25. REFERENCES
Amalberti, R. (1996). La conduite des systkmes ri risques. Paris: PUF.
Department of Energy. (1999). DOE Workbook, Conducting Accident Investigations .
Washington,: Department of Energy.
Ferry, T. (1988). Modern Accident Investigation and Analysis. Second Edition. New York:
Wiley.
Høyland, A., & Rausand, M. (1994). System reliability Theory: Models and Statistical
Methods. New York: Wiley.
Hollnagel, E. (2002). Understanding accidents-from root causes to performance
variability. Human Factors and Power Plants, 2002. Proceedings of the 2002 IEEE 7th
Conference on , (pp. 1 - 1-6 ).
Lehto, M. (1991). Models of accident causation and their application: Review and
reappraisal. journal of engineering and technology management , 173.
Rasmussen, J. (1997). Risk management in a dynamic society: a modelling problem.
Safety Sci. , 183–213.
Sklet, S. (2004). Comparison of some selected methods for accident investigation.
Journal of hazardous materials , 29-37.