TABLE OF CONTENTS Cause, probability, and frequency analysis techniques are used in QRA in order to determine many different parameters, such as:
Potential causes that may lead to accidents.
Frequency of initiating events.
Conditional probability of failure of safety systems, in the case of an accident.
Probability that operating and/or environmental conditions are specially adverse.
Probability that a particular severe accidental consequence occurs.
Probability that personnel are present in an area when the accident occurs.
For quantitative purposes there are many tools that may be used in order to calculate probability or frequency, including simulation methods, theoretical modelling, and formal methods such as Fault Tree Analysis and Event Tree Analysis. Frequencies are often based on statistical analysis of failure and accident data. Failure Mode and Effect Analysis may also be employed for qualitative analysis. A brief overview of the most important methods is given below.
There are several good textbooks available which provide instruction on Fault Tree Analysis (FTA). In-depth introduction may be found in these sources, a brief introduction is provided below:
H yland and Rausand (1994)
Henley and Kumamoto (1981)
Vesely et al (1981)
Aven (1992)
Fault tree analysis is a logical, structured process that can help identify potential causes of system failure, such as causes of initiating events or failure of barrier systems.
The technique was developed to identify causes of equipment failure and was used primarily as a tool in reliability and availability assessment. The fault tree is a graphical...
