Control Loop Diagram is a diagram to show a control loop with actions and feedback. By creating a control loop diagram of “Unsafe Control Actions”, it will help you identify the hazard causal factor.

STAMP Control Loop Diagram Sample
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How to create a Control Loop Diagram

To create a Control Loop Diagram, open a Control Structure Diagram, right-click on a link or Control Action and click [Generate Control Loop Diagram] from the context menu.
How to create a control loop diagram

A new Control Loop Diagram is generated with the two Components that the selected Link/Control Action connects. Other related Components are shown as small boxes.
Control Loop Diagram Sample

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Open Hint Words

There is a [Hint Word Set] menu on the toolbar of the diagram. Clicking [Hint Word Set] will open up a window with hint words (guide phrases) and the structure. Use these hint words to analyze the loop to find out what makes this control action unsafe and identify the hazard causal factor.
STPA HintWords

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Switch Hint Word Set

You can switch to the Hint Word set that best fits your analysis.

To do so, click [Hint Word Set] on the toolbar to open the Hint Words.
STPA HintWords

Then switch to the set you want to use.
Change Hint Words

There are two pre-installed Hint Word sets in Astah System Safety.

Hint Word set: An STPA Primer
An STPA Primer
Hint Word set: STPA Handbook
STPA Handbook

You can also customize the Hint Words, create your own set, and select a default set. See Hint Word for details.