OVERVIEW OF ACCIDENT MODELING APPROACHES PART 1 ROSS APTED

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

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.

ACADEMIC LITERATURE I

Key points:

Discusses the general modeling approaches and identifies each what approach shows or highlights.

Main types of Accident model. (Hollnagel, 2002)

Understanding Accidents - From Root Causes to Performance Variability (Hollnagel, 2002)

ACADEMIC LITERATURE I

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.

The suitability of these approaches focusing on the human aspects of Sociotechnical systems.

(Amalberti, 1996)

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.

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

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

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)

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.

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.

ACADEMIC LITERATURE II

Each method is briefly detailed, the comparison is analyzed and discussed.

Characteristics of different methods.

Conclusion: no one accident investigation technique is perfect and that to be most effective they must be used in conjunction.

(Sklet, 2004)

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.

SEQUENTIAL ACCIDENT MODELS

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.

DOMINO MODEL OF ACCIDENT CAUSATION

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

(Ferry, 1988)

DOMINO MODEL OF ACCIDENT CAUSATION

Domino Diagram

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FAULT TREE ANALYSIS

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.

(Høyland & Rausand, 1994)

FAULT TREE ANALYSIS

Simple fault tree for a fire breakout

EVENTS AND CAUSAL FACTORS CHARTING

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.

(Department of Energy, 1999)

EVENTS AND CAUSAL FACTORS CHARTING

(Department of Energy, 1999)

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.

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

REFERENCESAmalberti, 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.