Modern Techniques
of
Accident Investigation
C.Jayasuriya, S.V.Karthikeyan and S.E.Kannan
IGCAR
Kalpakkam
Modern Techniques of Accident Investigation
and Analysis:
* Core Analytical Techniques
* Complex Analytical Techniques
* Specific Analytical Techniques
Core Analytical Techniques:
These are more effective when applied to a basic
accident with few system failures.
- Change Analysis
- Barrier Analysis
- Event and Causal Factor Analysis and
- Root Cause Analysis
Change Analysis:
• Generally used for single occurrence and focuses on elements
that have changed
• Looks at a problem by analyzing the deviation(s) between what
is expected and what actually happened
• The investigation should focus on the systematic deficiencies
that allowed the accident to happen and not just accept the
changes identified as the sole cause of it
eg. -Through a platform panel that was modified, while
working, a tool fell down on a worker who was
standing below the platform on his head
- Investigation revealed that when the modified platform
was put back in position, there was a gap between the
panels which was not closed, through which the tool fell
down
Deficiency: gap between the panels not kept closed ,
improper supervision
Barrier Analysis:
¤ It is a systematic process that can be used to identify physical,
administrative and procedural barriers/controls that should
have prevented the accidents
¤ Barrier is something that separates an affected component
from undesirable condition / situation
eg. for the previous example, Barrier Analysis indicated:
- absence of a physical barrier that did not close the gap
between the panels and
- lack of administrative and procedural barrier/control in
not checking whether the gap was closed or not
¤ The basic principle is that there is unwanted flow of energy
associated with all accidents and to prevent accidents the
energy has to be isolated, shielded and controlled from
people/ valuable objects
¤ It clearly portrays the energy flow and failed or unused
barriers that led to accidents
¤ The principal advantage of this method is that it identifies
safety system elements that failed and the results can be
succinctly presented
Event and Causal Factor Analysis:
‫ ٭‬It identifies the time sequence of a series of tasks and/or
actions and the surrounding conditions that lead to an event
‫ ٭‬It is used when there are multiple problems and the event
factor chain is long and /or complex. Used in conjunction with
other techniques
Root Cause Analysis:
• Used to identify deficiencies, actual root cause, contributing
causes and management systems that need to be corrected to
prevent recurrence
• It has an in-depth look at the basic causes that led to the accident
• A no.of methods are available for performing this analysis; many
of them are specialized and apply to specific situations
/objectives
Complex Analytical Techniques:
# These are applied to multiple system failures resulting in
complex accident scenario.
# Covers Fault Tree Analysis, Management Oversight and
Risk Tree and Project Evaluation Tree
Fault Tree Analysis:
• It is commonly used in safety engineering
• It is a deductive approach that is very powerful as a
qualitative analysis tool.If the probability data of events are
known results could be quantified
• Fault branches down from top event, listing the faults in the
system that occurred from general to specific event. Branches
of the tree are contd until independent events are reached
• Faults can be events associated with component hardware
failures, software problems, human errors, environmental
conditions or any other element
• It is a very powerful technique requiring complex
mathematical calculations
Specific Analytical Techniques:
These are used in specific investigations depending on the
nature and complexity of the event.
° Human Factors Analysis
° Energy Trace Barrier Analysis
° Sneak Circuit Analysis
° Cause Consequence Analysis
° Dispersion Modeling
° Kepner-Tregoe Problem Solving and Decision
Making
° Sequential Timing and Events Plotting
Human Factors Analysis:
• Here the focus is on the operability, work environment and
management factors. It identifies the factors that influence
task performance
• Can be used to analyze most of the occurrences since many
conditions and situations leading to an occurrence have
ultimately originated from some performance problems
• Training in ergonomics and human factors is needed to
perform adequately in man-machine interface situations
Energy Trace Barrier Analysis:
• Its purpose is to identify hazards ( energy sources that can
adversely affect an unprotected or vulnerable target ) by tracing
energy flow into, through and out of the system
• By following the energy path one can determine if adequate
controls were in place to prevent undesired energy release
• It is relatively inexpensive and rapid
Sneak Circuit Analysis:
*Here analysis is conducted on every possible combination of paths
that a process could take (though used for electrical circuits,
could be applied to other process flows ) and identify the sneak
paths that are not designed in and but created due to failures
(Sneak or latent paths are found in systems that are not operated
frequently and hence are not easily identified)
*The procedure is to review the system engineering drawings and
translate them into a series of topological patterns that describe
the entire circuit and trace the sneak paths.
*Usually performed with complex computer codes and is expensive.
It can be made cost-effective if performed on sub-systems that are
safety critical.
Cause-consequence Analysis:
*It uses symbolic logic trees.
*The investigator starts with an accident scenario that adversely
impacts the system and then develops a bottom-up analysis.
Failure probabilities are calculated and incorporated into each
step to quantify the tree.
*A fault tree can be used to arrive at the event that challenges the
system. From the top event the consequences are identified and
severity of each consequence is determined.
Dispersion Modeling:
• It is performed in plants where chemical emission can occur , to
assess seriousness of the consequences.
• Maps and calculations are part of the system so that a total
dispersion map for hazard analysis could be generated.
eg. For the Monju fast reactor in Japan, when there was a
sodium leak incident, this method was used to assess the
sodium aerosol concentration at the site boundary to
ensure that it was well within the permissible limits
Kepner-Tregoe problem Solving and Decision
Making:
¤ This method is used when a comprehensive analysis is needed
for all phases of investigation process
¤ Its strength lies in providing an efficient and systematic
framework for gathering, organizing and evaluating informn
¤ It is a four step process that can be used for more than causal
factor analysis
¤ This has a systems approach that prevents overlooking any
aspect
Sequential Timing and Events Plotting:
• It is a comprehensive approach to reconstruct an accident and
is based on events /causal factors charting
• It is based on development of mental motion picture of the
accident sequence as reconstructive tool
• The worksheet illustrates the beginning and end of the
accident sequence along column that represents time ; the
rows lists the actors, either people or things, which acted to
produce the harmful outcome. Each actor performs one action
termed as event , that when displayed along timeline shows
interactions between among actors and events
eg.The accident involving a reversing heavy
vehicle running over a worker at site
 Time
Actors
vehicle
Worker
DAE Hospital
CGL Hospital
• Adequate tests are performed to make sure that
events sequence is accurate and for completeness