Fault Tree Analysis Sample Template

Fault Tree Analysis
FTA involves the following steps:
1. Defi ne the top event.
2. Know the system.
3. Construct the tree.
4. Validate the tree.
5. Evaluate the tree.
7. Consider alternatives and recommend action.
Defi ne the top event. To defi ne the top event the type of fail-
ure to be investigated must be identifi ed. This could be whatever
the end result of an incident may have been, such as a forklift
overturning.
Determine all the undesired events in operating a system.
Separate this list into groups having common characteristics.
Several FTAs may be necessary to study a system completely.
Finally, one event should be established representing all events
within each group. This event becomes the undesired event to
study.
Know the system. All available information about the system
and its environment should be studied. A job analysis may prove
helpful in determining the necessary information.
Construct the fault tree. This step is perhaps the simplest
because only the few symbols are involved and the actual con-
struction is pretty straightforward.
Principles of constructionPrinciples of construction. The tree must be constructed using
the event symbols listed above. It should be kept simple. Main-
tain a logical, uniform, and consistent format from tier to tier.
Use clear, concise titles when writing in the event symbols. The
logic gates used should be restricted to the and gate and or gate
with constraint symbols used only when necessary. An example
would be the use of the oval constraint symbol to illustrate a
necessary order of events that must happen to have an event
occur. The transfer triangle should be used sparingly if at all.
The more the transfer triangle is used, the more complicated the
tree becomes. The purpose of the tree is to keep the procedure as
simple as possible.
Validate the tree. This requires allowing a person knowl-
edgeable in the process to review the tree for completeness and
accuracy.
Evaluate the fault tree. The tree should then be scrutinized
for those areas where improvements in the analysis can be made
or where there may be an opportunity to utilize alternative proce-
dures or materials to decrease the hazard.
Study tradeoffs. In this step, any alternative methods that
are implemented should be further evaluated. This will allow
evaluators to see any problems that may be related with the new
procedure prior to implementation.
Consider alternatives and recommend action. This is the last
step in the process where corrective action or alternative mea-
sures are recommended.
Example
Benefi ts: The primary advantages of fault tree analyses are
the meaningful data they produce which allow evaluation and
improvement of the overall reliability of the system. It also evalu-
ates the effectiveness of and need for redundancy.
Limitation: A limitation of the fault tree analysis is that the
undesired event evaluated must be foreseen and all signifi cant
contributors to the failure must be anticipated. This effort may be
very time consuming and expensive. And fi nally, the overall suc-
cess of the process depends on the skill of the analyst involved.
Primary
Cause
Logic Gates
Accident/
Incident
Events
Example
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