Editing Fault tree analysis (section)

==Analysis==
Many different approaches can be used to model a FTA, but the most common and popular way can be summarized in a few steps. A single fault tree is used to analyze one and only one undesired event, which may be subsequently fed into another fault tree as a basic event. Though the nature of the undesired event may vary dramatically, a FTA follows the same procedure for any undesired event; be it a delay of 0.25&nbsp;ms for the generation of electrical power, an undetected cargo bay fire, or the random, unintended launch of an [[ICBM]].

FTA analysis involves five steps:
# Define the undesired event to study.
#* Definition of the undesired event can be very hard to uncover, although some of the events are very easy and obvious to observe. An engineer with a wide knowledge of the design of the system is the best person to help define and number the undesired events. Undesired events are used then to make FTAs. Each FTA is limited to one undesired event.
# Obtain an understanding of the system.
#* Once the undesired event is selected, all causes with probabilities of affecting the undesired event of 0 or more are studied and analyzed. Getting exact numbers for the probabilities leading to the event is usually impossible for the reason that it may be very costly and time-consuming to do so. Computer software is used to study probabilities; this may lead to less costly system analysis.<br /> System analysts can help with understanding the overall system. System designers have full knowledge of the system and this knowledge is very important for not missing any cause affecting the undesired event. For the selected event all causes are then numbered and sequenced in the order of occurrence and then are used for the next step which is drawing or constructing the fault tree. <!-- These two paragraphs could do with some copyediting to trim them down. -->
# Construct the fault tree.
#* After selecting the undesired event and having analyzed the system so that we know all the causing effects (and if possible their probabilities) we can now construct the fault tree. Fault tree is based on AND and OR gates which define the major characteristics of the fault tree.
# Evaluate the fault tree.
#* After the fault tree has been assembled for a specific undesired event, it is evaluated and analyzed for any possible improvement or in other words study the risk management and find ways for system improvement. A wide range of qualitative and quantitative analysis methods can be applied.<ref>{{Cite journal
  |last1= Ruijters
  |first1= Enno
  |last2= Stoelinga
  |first2= Mariëlle I. A.
  |date= February–May 2015
  |title= Fault tree analysis: A survey of the state-of-the-art in modeling, analysis and tools
  |journal= Computer Science Review
  |volume= 15–16
  |pages= 29–62
  |doi= 10.1016/j.cosrev.2015.03.001
|url= https://research.utwente.nl/en/publications/fault-tree-analysis-a-survey-of-the-stateoftheart-in-modeling-analysis-and-tools(88c7ba34-fe51-4f9d-b2f3-cb04aeffaa6e).html
 }}</ref> This step is as an introduction for the final step which will be to control the hazards identified. In short, in this step we identify all possible hazards affecting the system in a direct or indirect way.
# Control the hazards identified.
#* This step is very specific and differs largely from one system to another, but the main point will always be that after identifying the hazards all possible methods are pursued to decrease the probability of occurrence.