NESC0779 IMPORTANCE
IMPORTANCE, Minimal Cut Sets and System Availability from Fault Tree Analysis
NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROBLEM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, UNUSUAL FEATURES OF THE PROGRAM, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES
[ top ]
[ top ]
To submit a request, click below on the link of the version you wish to order.
Only liaison officers are authorised to submit online requests. Rules for requesters are
available here.
| Program name | Package id | Status | Status date |
|---|---|---|---|
| IMPORTANCE | NESC0779/01 | Tested | 01-AUG-1979 |
Machines used:
| Package ID | Orig. computer | Test computer |
|---|---|---|
| NESC0779/01 | IBM 370 series | IBM 370 series |
[ top ]
3. DESCRIPTION OF PROBLEM OR FUNCTION
IMPORTANCE computes various
measures of probabilistic importance of basic events and minimal
cut sets to a fault tree or reliability network diagram. The
minimal cut sets, the failure rates and the fault duration times
(i.e., the repair times) of all basic events contained in the
minimal cut sets are supplied as input data. The failure and
repair distributions are assumed to be exponential. IMPORTANCE, a
quantitative evaluation code, then determines the probability of
the top event and computes the importance of minimal cut sets and
basic events by a numerical ranking. Two measures are computed.
The first describes system behavior at one point in time; the
second describes sequences of failures that cause the system to
fail in time. All measures are computed assuming statistical
independence of basic events. In addition, system unavailability
and expected number of system failures are computed by the code.
IMPORTANCE computes various
measures of probabilistic importance of basic events and minimal
cut sets to a fault tree or reliability network diagram. The
minimal cut sets, the failure rates and the fault duration times
(i.e., the repair times) of all basic events contained in the
minimal cut sets are supplied as input data. The failure and
repair distributions are assumed to be exponential. IMPORTANCE, a
quantitative evaluation code, then determines the probability of
the top event and computes the importance of minimal cut sets and
basic events by a numerical ranking. Two measures are computed.
The first describes system behavior at one point in time; the
second describes sequences of failures that cause the system to
fail in time. All measures are computed assuming statistical
independence of basic events. In addition, system unavailability
and expected number of system failures are computed by the code.
[ top ]
4. METHOD OF SOLUTION
Seven measures of basic event importance and
two measures of cut set importance can be computed. Birnbaum's
measure of importance (i.e., the partial derivative) and the
probability of the top event are computed using the min cut upper
bound. If there are no replicated events in the minimal cut sets,
then the min cut upper bound is exact. If basic events are
replicated in the minimal cut sets, then based on experience the
min cut upper bound is accurate if the probability of the top
event is less than 0.1.
Simpson's rule is used in computing the time-integrated
measures of importance. Newton's method for approximating the
roots of an equation is employed in the options where the
importance measures are computed as a function of the probability
of the top event, and a shell sort puts the output in descending
order of importance.
Seven measures of basic event importance and
two measures of cut set importance can be computed. Birnbaum's
measure of importance (i.e., the partial derivative) and the
probability of the top event are computed using the min cut upper
bound. If there are no replicated events in the minimal cut sets,
then the min cut upper bound is exact. If basic events are
replicated in the minimal cut sets, then based on experience the
min cut upper bound is accurate if the probability of the top
event is less than 0.1.
Simpson's rule is used in computing the time-integrated
measures of importance. Newton's method for approximating the
roots of an equation is employed in the options where the
importance measures are computed as a function of the probability
of the top event, and a shell sort puts the output in descending
order of importance.
[ top ]
[ top ]
[ top ]
7. UNUSUAL FEATURES OF THE PROGRAM
For systems where repair is not
allowed, the code accepts proportional hazards as input data. In
another option, where repair is permitted, failure rate data can
also be expressed in relative terms by representing the failure
rate and repair rate data for the basic events in terms of a
reference time unit.
For systems where repair is not
allowed, the code accepts proportional hazards as input data. In
another option, where repair is permitted, failure rate data can
also be expressed in relative terms by representing the failure
rate and repair rate data for the basic events in terms of a
reference time unit.
[ top ]
8. RELATED AND AUXILIARY PROGRAMS
Other qualitative evaluation
programs for system safety and reliability analysis are MOCUS
(NESC Abstract 653), PREP (NESC Abstract 528), COMCAN (NESC
Abstract 704), SETS (NESC Abstract 623), FTA (NESC Abstract 666),
and FTAP, Department of Operations Research, Berkeley. A
discussion of these and others is contained in reference 2.
The IMPORTANCE program was originally developed on the CDC7600
by Howard E. Lambert at Lawrence Livermore Laboratory, and was
later converted to the IBM370 by T. Chawla and G. Hauser of the
Reactor Analysis and Safety Division at Argonne National
Laboratory.
Other qualitative evaluation
programs for system safety and reliability analysis are MOCUS
(NESC Abstract 653), PREP (NESC Abstract 528), COMCAN (NESC
Abstract 704), SETS (NESC Abstract 623), FTA (NESC Abstract 666),
and FTAP, Department of Operations Research, Berkeley. A
discussion of these and others is contained in reference 2.
The IMPORTANCE program was originally developed on the CDC7600
by Howard E. Lambert at Lawrence Livermore Laboratory, and was
later converted to the IBM370 by T. Chawla and G. Hauser of the
Reactor Analysis and Safety Division at Argonne National
Laboratory.
[ top ]
10. REFERENCES
- Howard E. Lambert and Frank M. Gilman,
The IMPORTANCE Computer Code,
UCRL-79269 (Preprint), March 14, 1977.
- Howard E. Lambert and Frank M. Gilman,
The IMPORTANCE Computer Code,
UCRL-79269 (Preprint), March 14, 1977.
NESC0779/01, included references:
- H.E. Lambert:Fault Trees for Decision Making in Systems Analysis,
UCRL-51829 (October 9, 1975) (Ph.D. thesis)
- H.E. Lambert and B.J. Davis:
The Use of the Computer Code IMPORTANCE with SETS Input,
NUREG/CR-1965 (SAND81-7068) (March 1981)
[ top ]
[ top ]
[ top ]
[ top ]
[ top ]
NESC0779/01
| File name | File description | Records |
|---|---|---|
| NESC0779_01.001 | SOURCE PROGRAM (F4,EBCDIC) | 1586 |
| NESC0779_01.002 | SAMPLE INPUT DATA | 123 |
| NESC0779_01.003 | SAMPLE OUTPUT | 147 |
[ top ]
- G. Radiological Safety, Hazard and Accident Analysis
- P. General Mathematical and Computing System Routines
Keywords: fault tree analysis, probability, reliability, system failure analysis.