An approximate-reasoning-based method for screening flammable gas tanks Page: 86 of 126
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1 VU QU U QL VL
0
0 1
Aggregate Likelihood, LB
Fig. 5-7. Membership functions for Le.
The screening criteria to which these expressions are compared are the same as for LF. For values of X(LB)
that correspond to the natural language expression "unresolved," an additional classification step was
used. It was found that this classification could be subdivided based on either the shape of the CDF or
the magnitude of the standard deviation. Figure 5-8 shows the two distinctive CDF curves that can occur
for tanks that are classified as "unresolved." For the curve labeled UP, corresponding to the expression
"unresolved with poor evidence," it can be seen that for small values of cumulative probability P, the
value of X(LB) is 0.5. This is also the value at the median. Logically, this represents the case where the
evidence is judged to be of insufficient quality to allow a judgment regardless of the numerical values of
the primary inputs. For the curve labeled UG, "unresolved good evidence," the value of X(LB) depends
on the distributions of the primary inputs. In this case, the evaluation is that the evidence is acceptable
but allows no definitive inference of the likelihood of a significant quantity of retained gas to be drawn.
The shape of the cumulative distribution in the UP case implies a small value for the standard deviation,
a. Therefore, by examining the results, it is possible to classify tanks as being in UP with the simple
threshold criterion that a tank is a member of UP if a 5 0.025.
1 lUP UG
a
CO
0
0
0 .5 1
X(LF)
Fig. 5-8. Shapes of cumulative probability distributions for 9k for tanks classified "unresolved, poor
evidence" (UP) and "unresolved, good evidence" (UG).5-9
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Eisenhawer, S.W.; Bott, T.F. & Smith, R.E. An approximate-reasoning-based method for screening flammable gas tanks, report, March 1, 1998; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc674754/m1/86/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.