STAMP/STPA and SCDL Diagrams

Astah System Safety supports the following diagrams for SCDL and STAMP/STPA.

Astah System Safety
Safety Concept Description Language Sample

Safety Concept Diagram

[SCDL]
Safety Concept Diagram is a structure diagram to represent architecture of the functional safety that is formed by Safety Concept Notation Study Group. It visualizes interactions between requirements, allocations between elements and requirements, and you can add the “weight” properties to decompositions.

This is a similar diagram to Function Block Diagram (FBD), so that it can be widely used not limited to ISO 26262.

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Preconditions

Precondition Table

[STAMP/STPA]
Precondition Table is what you use at STEP1 of STPA analysis to define the purpose of the analysis, and determine the preconditions and assumptions.

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Accident Hazard Safety Constraint Table Sample

Accident Hazard Safety Constraint Table

[STAMP/STPA]
Accident Hazard Safety Constraint Table is also what you use at STEP1 of STPA analysis to define the accidents and losses that you want the system to prevent throughout this analysis, and identify hazards – system state or set of conditions that will lead to a loss and the safety constraints.

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Sample STPA Control Structure Diagram

Control Structure Diagram

[STAMP/STPA]
Control Structure Diagram is what you use at STEP2 of STPA analysis to construct and visualize the control structure and relationships between the Components.

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STPA UCA (Unsafe Control Action) Table

UCA (Unsafe Control Action) Table

[STAMP/STPA]
The UCA (Unsafe Control Action) table is what you use at STEP3 of STPA analysis to identify unsafe control actions. When you create a UCA table, Astah automatically lists up all the control actions you defined in the Control Structure Diagram and puts them in a table.

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Hint words on STPA Control Loop Diagram

Control Loop Diagram

[STAMP/STPA]
Control Loop Diagram is what you use at STEP4 of STPA analysis. This diagram shows 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 factors.

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Loss Scenario Sample

Loss Scenario Table

[STAMP/STPA]
Loss Scenario Table is what you use at STEP4 of STPA analysis to identify hazard causal factors and loss scenarios for unsafe control actions.

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Countermeasure Table Sample

Countermeasure Table

[STAMP/STPA]
The Countermeasure Table is where you identify the countermeasures for all the scenarios you created throughout the STPA analysis. This table will help you make sure that countermeasures you have created for specific scenarios are aligned and do not contradict to the system as a whole.

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