Lecture 1

Question 1

What are my options to reduce total risk?

Answer 1

a. Prevention (Reduce probability of fault)
b. Mitigation (Reduce the effects)

Question 2

What is the definition of Reliability?

Answer 2

Reliability is the PROBABILITY that an item functions under given conditions DURING a stated TIME-INTERVAL

Or

Ability of an item to remain functional

–> For a reliability number to make sence it must also define a time interval! Eg. 0.9 reliable (0, 1 min)

Question 3

Definition of Availability?

Answer 3

Availability is the probability that the item will perform its required function under the given condition AT a given TIME Point

Availability/Dependability are ofthen interchangeable

Average Availability is the expected mean value of the time during whitch the item performs as expected

Question 4

What is Farmer’s curve and how can it be used?

Answer 4

Farmer’s curve is a risk analysis tool that plots the logarithm of scenario probabilities (logP) against the logarithm of consequences (logN), helping to visualize and compare the frequency and severity of various risk events.

It is used to assess and prioritize risks, aiding in decision-making and regulatory compliance by providing a clear, comparative view of different risk scenarios.

Question 5

Is failure accepted in reliability analysis?

Answer 5

NO - failure is not allowed -

Redundunt components may fail - and be repaired - but the function performed by the item cannot be interrupted

Question 6

Is failure accepted in Availability analysis?

Answer 6

Yes failure is allowed on an item level

Question 7

What is a Cut Set?

Answer 7

logical combinations of primary events (combination of component failures) which render
TRUE the top event (system failure event)

Question 8

What is a Minimal Cut Set?

Answer 8

cut set that does not have another cut set as a subset, i.e. repairing one element of
the set repairs the system. Therefore, removing one element from a minimal cut set makes the set
thereby obtained no longer a cut set

Question 9

Define Hazard Rate:

Answer 9

probability that a component fails in dt, given that it survived till t. It is measured
through experimental campaigns and usually follows the bathtub curve

bathtube Curve:

a. Infant Mortality - time dependent - gets safes as time goes by
b. Useful life - time Independent - random failure possible
c. Aging - time dependent - as you age more probable death