STAMP/STPA and SCDL Diagrams
Astah System Safety supports a range of diagrams for System-Theoretic Process Analysis (STPA) and System-Theoretic Accident Model and Processes (STAMP) and SCDL(Safety Concept Description Language). These diagrams are essential tools for conducting thorough and effective safety analyses using the STPA methodology. The specific types of diagrams supported can vary, each designed to visualize different aspects of system control and safety.
Safety Concept Diagram
[ASAM SCDL]
The Safety Concept Diagram, aligned with ASAM SCDL (Safety Concept Description Language), is a structural diagram designed to represent the architecture of functional safety, as developed by the Safety Concept Notation Study Group. It effectively visualizes interactions between various requirements and the allocations between elements and requirements. Additionally, it allows for the inclusion of “weight” properties in decompositions. This diagram bears similarities to the Function Block Diagram (FBD) and is versatile enough to be utilized beyond the confines of ISO 26262, making it broadly applicable in various safety analysis contexts.
User Guide
Precondition Table
[STAMP/STPA]
The Precondition Table is a key tool used in the first step of STPA analysis. Its primary function is to help define the purpose of the analysis. By using this table, you can determine and document the preconditions and assumptions that are essential for the analysis. This step is crucial as it sets the foundation and scope for the entire STPA process, ensuring that the analysis is guided by clearly defined parameters and objectives.
Loss Hazard Safety Constraint Table
[STAMP/STPA]
The Loss Hazard Safety Constraint Table is another crucial component used in the first step of STPA analysis. This table is instrumental in defining the losses that the system should prevent. It helps in identifying hazards, which are states or sets of conditions that could lead to a loss, and outlines the necessary safety constraints to mitigate these risks.
Control Structure Diagram
[STAMP/STPA]
The Control Structure Diagram, used in STEP 2 of the STPA analysis, is crucial for constructing and visualizing the control structure of a system. It illustrates the relationships between various components within the system. This diagram helps in understanding how control actions are distributed and interact across the system, laying the groundwork for identifying potential unsafe control actions and system vulnerabilities in the subsequent stages of STPA analysis.
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.
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.
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.
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.