Abstract
Expert systems are
intended to solve problems in difficult, unstructured domains, where knowledge
guides the expert reasoning.
The paper presents
an expert based approach to the problem of risk assessment at various work
places, underlying the advantages in using expert system methods and techniques
to deal with risk identification and evaluation.
Classic
risk assessment
At the work place
we should consider in the risk assessment process, the man-machine system with
its four components, the human operator, the task, the machine and the working
environment. An efficient risk assessment must study all these components and
also their interaction that results in the activity being done at the work
place.
However, the
majority of risk assessment systems are centered on the machine. There are some
reasons for that approach, considering the great subjectivity of human risk
assessment. The programs that are implementing these methods could be called
classical programs, having a pre-defined algorithm to perform the risk
assessment. This classic, machine-centered approach is not very suitable in
many cases, especially where the man generated accidents are prevailing.
Expert
systems and their applications to risk assessment
What is an expert system?
Expert systems are
programs that offer advice or solve problems by reasoning with volumes of
knowledge highly specific to a particular domain. The activity of designing and
implementing expert systems is known as knowledge engineering.
A general
structure of an expert system is presented in the following figure.
Figure 1 General
schema of an expert system
Why an expert approach?
Risk assessment is
a very important process, regarding the safety and health of many workers. A
well done risk assessment process could lead to significant improvements not
only just to the work conditions but also to the efficiency of the work.
Considering the
core of the risk assessment process at the work place, it is mainly an expert
job. The human expert identifies specific risks, is giving them severity and
probability weight and is proposing measures to reduce risks at ALARP levels or
simply eliminate them. Risk assessment is not a repetitive process; the work
place conditions are unique. So, indifferent of how performing are classic
assessment programs, indifferent of the complexity of the implemented
assessment method (Hazop, FMEA,FMECA, or other such like) they could not
perform expert tasks regarding risk assessment but just the repetitive and
monotonous part of the process.
What could an expert system do regarding risk assessment?
Having established
that risk assessment is mainly an expert approach we could see the expert
system as an integrator and also as an assistant to the human assessor .The
expert system could:
-analyze and
logically validate the results obtained by running machine centered assessment
methods;
-interpret the
obtained results considering the global picture of the work place being
assessed;
-perform an
objective assessment for the human component at the work place;
-generate risk
models and use these models to predict risk development for short and medium
prognosis;
-integrate all
these pieces in a single view and use this view to develop prevention plans so
to reduce risks at ALARP levels or just eliminate them ; the next figure
presents a general schemata of a risk assessment expert system.
Figure 2 General
schema of an expert risk assessment system
Expert
elements in risk assessment
Machine risk assessment
There are many
programs that perform more or less efficiently machine risk assessment, using a
variety of assessment methods centered on the machine component
The classic
assessment methods are centered mainly on the machine, giving little importance
to the external risk sources[1].
But, in many situations, the external risk sources (such as environment
conditions, task design, and task execution) are triggers to incidents and
accidents. So, for the correct image of risks at the work place, there must be analyzed
all the chained components of the man-machine system. Classical programs are
not doing this-an expert system may perform this analysis.
Also, the expert
system may quantify the obtained results into significant cases that would
simplify further similar assessments:
-by using the
obtained results as a case oriented knowledge source and simply cross-check
these results against the real situation, instead of performing again all the assessment
process which can be very time consuming;
-by working as an
example for similar assessments;
The expert system
could work assisted by the human specialist to develop such cases and put those
cases into a specific case base. For example, results for similar work places
must be somehow similar; giving a similarity check-list for a specific machine,
such a check-list could be quickly cross-checked against the real situation and
established if the case and the real situation are perfectly matching,
partially matching or if there are singularity points that must be analyzed
separately.
Also, having the
risk assessment results, the expert system could develop and run scenarios that
will predict risk trends over a period of time, considering various degree of
intervention towards preventing risk effects. These scenarios could be very
efficient in developing and prioritizing prevention measures.
Using its learning
mechanism the expert system could also improve the machine risk assessment
process, mainly in his primary parts, establishing the data that will be
collected and processed.
To sumarize, in
the machine risk assessment process, the expert system can action as an
assistant to the human specialist and also as an improver of the assessment
results and as a predictor of risk trends.
Human operator assessment
The problem of
human operator assessment from the risk point of view is a crucial one. Most of
the occupational accidents have as their principal cause human operator
failures and mistakes.[2].The
principal problem with the risk assessment methods regarding human operator is
their subjectivity degree combined also with the environment and task
influence. A checklist results will be influenced by the operator’s
self-perception, stress and so on. In establishing a decent and objective human
risk assessment a very important role can be played by corporate specific
memories regarding the human operator (mode of behaviour, incidents, accidents,
capacity to work alone/to work inside a team, etc.).For a specific operator,
these memories could be invaluable-generally, an operator that performs badly a
task and is not corrected will be performing in the same way, till an incident
is happening. Defining best work procedures and checking up the real activity
against these procedures could be another objective assessment factor.[3].
Based on expert
system techniques, it is possible to define, inside expert assessment system
behaviour models (based on best work procedures and also on normal work
condition and physiologic paramethers) and follow the real situation by
cross-checking the actual behaviour of human operators against these models.
The over-passing of model defined thresholds could be alarm signals and could
lead to the stop of machines and of the whole process, so that the human
operator will not be hurt.
The human operator
assessment may be modeled by belief networks that will define, regarding the
human operator, believed relations (uncertain, stochastic, and imprecise)
between sets of risk relevant variables to build patterns toward the birth and
development of human operator related risks.
Belief updating
may be done for each new assessment, by:
-new cases;
-mistake-the
learning from trial and errors;
-new beliefs;
The expert system
may infere new beliefs from the already existing knowledge and also may check
the beliefs against the real situation.
An expert
approach to risk assessment
An integrated
expert approach to the risk assessment problem will be developed around the
expert system methods for solving specific problems. It will use a
goal-oriented strategy, choosing a goal (to exactly and correctly identify the
risks at work place and to establish the optimum prevention plan for the risks
being identified) and attempting to achieve it.
It is difficult to
think of a universal expert system[4]
that will be able to assess every risk in every industrial domain, regardless
of the specific activities, machinery and so on.
A better approach
would be, in this aspect, to imagine a dual expert system, with an external
knowledge base, containing risk assessment methods and also significant cases
and an internal, corporate specific knowledge base, which will contain the
internal knowledge required to perform an efficient risk assessment.
This internal
knowledge base (IKB) will be based on corporate knowledge and will act partly
like a corporate safety memory[5]
. IKB will be a guide for the external risk auditing system, having captured
and updated inside the significant aspects that deserve study. It will also
preserve safety events inside the corporation and will be a source of lessons
for safety specialists[6]
in learning from the past mistakes and improving safety at the work place.
A possible design
for such a base is shown in the next figure.
Figure 3-Possible
design for Corporate Internal Knowledge Base
Generally, the
risk assessment problem could be interpreted as a search problem[7]
in which a solution must be found in a state space pool.
This search may be
optimized using heuristic evaluation functions H(x)[8].How
does a heuristic evaluation function work? By asigning to each significant risk
state x an estimate of the minimum cost to reach the goal state-in our case the
definition of the subsequent risk. With such a function available, all we have
to do in order to obtain efficient risk identification will be to sort the
found risk list according to H(x).H(x) is only an estimator. To make it a
predictor it must be done to search exhaustively the state space. The risk
identifying performance varies directly with the accuracy of the heuristic
evaluation function. So, if
H(x) =d [1]
where d is the true remaining distance to the nearest risk identification for
all the risk states x, then, the search is optimal[9].
If
H(x) =1/d [2]
the search will always find the goal node last, after
exploring the entire state space. The perfect heuristic function, which will
lead to perfect balance between the assessment costs (g (x) and assessment
results H (x), could be defined using the following equation
H(x) =H’(x) for
all risk state spaces x [3]
We could also define a cost-results function
f(x) =g(x)
+H(x) [4]
The optimal path
to the risk identification, called P, must be perfect regarding the balance
assessment costs/assessment results. So, we could write
H’ (P) =0 [5]
and also
f (P) = g (P) +0 [6]
and the estimate
of P costs turns out to be perfect-the real cost
Conclusion
As presented
before, expert approach could improve the risk assessment for the machine
and lead to an objective and efficient
assessment regarding the human operator, giving also a global risk view for the work place,.It takes into account also the task and the working
environment.
In risk
assessment, the expert approach could give:
-a reality
approach evaluation, considering the corporate internal memories of past events
and also the expert internal capability of the corporation being assessed;
-optimum
prevention solutions, arranged in order of their efficiency;
-a efficient and optimized
assessment;
-reduced
assessment costs, time and resources;
There are also
some problems. Expert based assessment using cases as an assessment base may
lead to misjudgements in case of singularities existence. Also, expert based
assessment needs expert knowledge which, in some situations may be very
expensive.
We have realized
some progress towards the development of efficient expert tools for risk
assessment, some of our results being presented at various international scientific
congresses. One primary research direction was the development of tools for
human operator assessment from the risk/safety point of view.[10]
[11].We
hope that in the future, with a consistent international co-operation, to be
able to launch an expert system for risk assessment as soon as 2015.
References
[1] Siu N.-Risk assessment
for dynamic systems-an owerview-in Reliability Engineering and System Safety
60, pg.153-164,1994
[2] Rasmussen J.-Major
accident prevention:what is the basic research issue ? in Safety and
Reliability (eds:Lydersen and others),Balkema,Rotterdam, pg.739-740,1998
[5] T.A.Kletz-Accident
investigation-missed opportunities-keynote paper at the Hazards XVI-Analysing
the past, planning the future symposium, Manchester ,
2001,pg.1-12
[6] Dr.J.Bond-A Janus
approach to safety--keynote paper at the Hazards XVI-Analysing the past,
planning the future symposium, Manchester, 2001,pg.13-23
[10] Ph.D.Stefan Kovacs and
others-Human operator assessment-basis for a safe work place in the process
industry, Hazards XVI Proceedings, Symposium series no.148,ISBN 85295-441-7,
pg.819-832.
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