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CEE 597
–
Risk Analysis and Management
Evening Midterm Exam
March 5, 2009
Test is open book and open notes.
You have 90 minutes to complete this 90 point exam.
Please show work.
1. (4 pts) How have the major causes of death changed in the United States over the last
hundred years, and why?
2. (8 pts) Accidents are often
imagined
as simple linear chains of events: chemical
reaction at Bhopol gets out of control, toxic gas escapes from plant, people die. Based
upon our study of
historic
accidents, how should the causes and consequences of
accidents best be
understood
?
<Remember Prof. Stedinger’s remarks about essays. Provide at least
one good example to support your conclusion. Use words & concepts from 5970. Answer this question!>
3. (14 pts) The identification of new security breaches in critical software (Adobe
Reader, mail programs, MS_Word …) is a continuing and critical concern. The
occurrence of such events can be described by a Poisson process, wherein on average
1 such breach is identified every four months.
a) What then is the probability of having at least two breaches in the 6 months between
1 Jan 2010 and 1 July 2010? What is the probability of exactly 4 breaches in a year?
b) On average, how many months will pass until 10 of these events occur? What is the
standard deviation of that waiting time?
c) How can the Disaster Management Cycle be used to understand activities associated
with software security breaches.
4. (12 pts) Consider the reliability of the system described by the network below:
D
G
C
J
B
F
H
A
E
K
a)
What are ALL the MINIMAL cut sets with 4 or fewer components?
b)
If all elements are 95% reliable, what
approximately
is reliability of entire system?
c)
What component is most critical to the reliability of the system? Why?
What 2 components individually are least critical? Why?
5. (8 pts) a) Consider the network in problem 4. If components C and J failed, describe
the remaining network as a fault tree so that its failure probability could be evaluated.
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Risk Analysis and Management – Midterm 2009
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b) Consider the fault tree below, if each component is 95% reliable, what is the
reliability of this system?
A
C
B
D
6. (9 pts) Consider a system with
two
independent components in
parallel
. Assume
component failures are independent Poisson processes with arrival rates of
0.002
/week
and 0.010/week, respectively. (a) What is the reliability function for the system?
(b) What is the mean time before failure? (c) For how long can one be 99.5 percent
certain the system will still be operating?
7. (15 pts) A research laboratory handles a lot of very unpleasant chemicals and
performs some tricky experiments. Still, accidents happen. Assume that the probability
of an accident is 1 per thousandemployeeworkingdays (i.e. 0.001 per employeeday),
and that 82 employees work at the laboratory 5 days a week.
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 Spring '07
 Stedinger

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