First step to start analyzing using STAMP/STPA is to define the purpose of the analysis, and determine the preconditions and assumptions. Preconditions do not necessarily have to be determined first, but the minimum preconditions should be developed. Without having some preconditions, UCA (Unsafe Control Actions) could increase widely which would be ineffective for your analysis. The preconditions could be also used as:
– Complements to the original requirement specifications
– Additional requirement specifications as input to the subsequent development process or
– Definition of the analysis scope

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How to define Preconditions

In Astah, preconditions can be created in a table format.
To create one, go to [Diagram] – [STAMP/STPA] – [Precondition Table].
Create a Precondition Table
1. Go to [File] – [New]
2. Select [STPA Procedure] tab and double-click [Determine Precondition]
Create Precondition Table

3. A blank Precondition table opens.
Blank Precondition Table

4. Right-click on the table and select [Add a Precondition] from the context menu.
Add a precondition

5. A line will be added. Directly enter the precondition.

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