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Re: Vulnerability
This exchange occured in the mailing list RISKANAL, but it
may be also of interest to some readers of RADSAFE because
it concerns the definition of risk.
Kaspar Peter wrote:
> Hi
>
> Beeing a civil engineer, I've studied now from several points of view
> "risk" and "vulnerability". I got the UNESCO definition of risk, that is:
>
> risk = hazard x vulnerability x potential loss
>
> I understand that vulnerability in this equation reflects the performance
> of an object under an impact with respect to damage. Reading publications,
> I became aware that not all authors do respect this definitions, but tend
> to call vulnerability what is for example the damage cost. (This equals in
> my opinion the part in the above equation "Vulnerability x potential loss").
>
> Are there other recognised definitions for vulnerabiliy than the UNESCO-
> definition?
>
> Thanks, Kaspar
>
A comment on the definitions of risks
by Fritz A. Seiler and Joseph L. Alvarez
Dear Kaspar,
As you point out, the concept of 'vulnerability' is actually a
generally unneeded addendum to a rather limited definition of the
quantity 'risk'. Indeed, it can be included in the dollar loss which
is incurred in the event. Nevertheless, without a definition of
vulnerability with appropriate units and the units of the entire
equation, we cannot draw conclusions about the term or the
equation.
(C'est bien de voir que mes compatriotes suisses a l'EFPL
s'occupent aussi des risques! Il est extremement important qu'
on y commence avec des definitions precises, et ce n'est pas le
cas. Pas du tout. C'est pourquoi nous ajoutons une discussion
de la definition du 'risque' qui est developee d'un chapitre d' une
publication que nous esperons de publier subitement! F.A.S.)
The concept 'risk' has been defined in the literature in a number
of different ways. The problem with most of these definitions is
that they are "word definitions" of the type found in dictionaries
and in lexica (Cohrssen and Covello, 1989; American Association
of Engineering Societies, 1996; U.S. Dept. of Health and Human
Services, 1986; Rowe, 1977; Bernstein, 1996). The UNESCO
definition that you mention is also a definition of the "word" type.
(By the way, once you find the reference for this UNESCO
definition, please let us know. We would like to have it so we can
add it to our list of word definitions).
In science, these "word definitions" are not really useful, even if
they cover the entire width and depth of the concept addressed.
Scientific definitions are quite different, as they are essentially based
not on one but on three requirements. This is a necessary condition
because, except for pure mathematics, the rest of science (even
applied mathematics) is based on measurements. Thus a definition
needs not only a concise, complete statement as to the nature of
the quantity, but it also needs to indicate a method to measure the
quantity (often by implication), and thus also needs a statement
about its dimension and its units.
A scientific definition which is sufficiently detailed to define
each risk uniquely, and is also sufficiently general to encompass
all the other definitions presented above, has been given by
Kaplan and Garrick (1981), based on ideas developed in the
Reactor Safety Study (Rasmussen, 1975). Recently, this
definition has been restated in a generalized form by Kaplan
(1997). It defines risk as an information triplet which, for a
particular case or component i, consists of, a) a complete
sequence of events, called scenario Si , which ranges from
the initiating event to the causation of the adverse consequence;
b) the definition of the adverse consequence Ci , and c) the
likelihood L i that both scenario Si and consequence Ci
occur.
We may ask at this point if this is not the definition that
UNESCO is attempting. It is the same definition if Hazard
equals Scenario, where the scenario Si contains source term,
exposure assessment and effects assessment, response
assessment, risk characterization, and the chain of events
which initiated the scenario. And further if Potential Loss equals
Consequence, where the consequence Ci defines the particular
component i of the risk. And finally if Vulnerability equals Likeli-
hood, where likelihood Li gives the appropriate numerical value
and the total uncertainty of the risk component i, and is measured
in units such as dollars, in fatalities, in injuries, or in years of lost
life expectancy.
The likelihood Li can be evaluated in several ways using
different approaches such as probability theory and fuzzy set
theory. Here, we will just use probabilities to make our point,
and define the probability Pi as the probability that first the
scenario Si , and then the consequence Ci come to pass. The
definition of a probability again presents the problem of how
to define a scientific quantity. Here, it results in the axiomatic
definition of a probability, but it also gives a prescription for its
measurement (usually a count of specific events in a series of
more general events), and finally it determines its dimension
and units (none and none). In this formulation, the spirited but
endless and tiresome discussions between protagonists of the
axiomatic definition and defenders of the counting of events are
completely pointless because both aspects are necessary
components of the same scientific definition!
Therefore, the word definition of risk by UNESCO "risk =
hazard x vulnerability x potential loss" may be equal to the
Kaplan definition if the scientific definition is included.
Bonne chance!
REFERENCES
American Association of Engineering Societies, Engineers' Public
Policy Council. 1996. Risk Analysis: The Process and its
Application. Institute for Regulatory Science, Columbia, MD.
Bernstein P.L. 1996. Against the Gods: The Remarkable Story
of Risk. Wiley & Sons, New York.
Cohrssen, J.J and Covello, V.T. 1989. Risk Analysis: A Guide
to Principles and Methods for Analyzing Health and
Environmental Risks. National Technical Information Service,
Springfield, VA. Kaplan, S. and Garrick, B.J. 1981. On the
quantitative definition of risk. Risk Anal. 1, 11-27.
Kaplan, S. 1997. The words of risk analysis. Risk Anal.
17, 407-417.
Pfeiffer, P.E. 1978. Concepts of Probability Theory. Dover
Publications, New York.
Rasmussen, N.C. 1975. Reactor Study - An Assessment of
Accident Risks in US Commercial Nuclear Power Plants. U.S.
Nuclear Regulatory Commission, Washington, D.C.,
WASH-1400 (NUREG-75/014).
Rowe, W.D. 1977. An Anatomy of Risk. Wiley & Sons,
New York.
U.S. Dept. Of Health and Human Services, Task Force on
Health Risk Assessment. 1986. Determining Risks to Health:
Federal Policy and Practice. Auburn House Publishing Co.,
Dover, MA.
*************************
Fritz A. Seiler, Ph.D.
Principal
Sigma Five Associates
P.O. Box 14006
Albuquerque, NM 87191-4006
Tel. 505-323-7848
Fax. 505-293-3911
e-mail: faseiler@nmia.com
**************************
Joe Alvarez, Ph.D., CHP
Auxier & Associates, Inc.
10317 Technology Dr., Suite 1
Knoxville, TN 37932
Phone (423)675-3669
FAX: (423)675-3677
Email: jalvarez@auxier.com
***************************
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