🎯 STPA Analysis

Process: CT (Discovered)

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STPA (System-Theoretic Process Analysis) - 5 Steps:

STPA is a systems-based hazard analysis technique that focuses on identifying unsafe control actions.

  1. Define the purpose of the analysis (losses, hazards, safety constraints)
  2. Model the control structure (controllers, control actions, feedback)
  3. Identify unsafe control actions (UCAs)
  4. Identify loss scenarios (how UCAs can occur)
  5. Generate safety requirements and recommendations

Step 1: Define Purpose of Analysis

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STPA Step 1 Guidance: Define what losses you want to prevent, identify hazards that could lead to those losses, and establish safety constraints.

📋 Guided Questions
  • What are the unacceptable losses we're trying to prevent?
  • What hazards (system states) could lead to these losses?
  • What safety constraints must be maintained to prevent hazards?
  • What is the scope and boundaries of this analysis?

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Step 2: Model the Control Structure

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STPA Step 2 Guidance: Create a hierarchical control structure model showing controllers, controlled processes, control actions, and feedback loops.

📋 Guided Questions
  • Who are the controllers in the system?
  • What processes are being controlled?
  • What control actions do controllers issue?
  • What feedback do controllers receive?
  • How is information communicated through the system?

🏗️ Control Structure Diagram

Create control structure showing Controllers, Control Actions, Controlled Processes, and Feedback as per STPA methodology

Interactive Control Structure: Each component shows control actions and feedback loops with hierarchical layout and clear relationships.
📦 Component Management
🔗 Relationship Management
🎯 Diagram Actions

Step 3: Identify Unsafe Control Actions (UCAs)

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STPA Step 3 Guidance: For each control action, identify how it could be unsafe in four categories: Not Providing, Providing Causes Hazard, Wrong Timing, Wrong Duration.

📋 UCA Categories
  • Not Providing: When the control action is not provided but should be
  • Providing Causes Hazard: When providing the control action causes a hazard
  • Wrong Timing: When the control action is provided too early or too late
  • Wrong Duration: When the control action is applied for wrong duration

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Step 4: Identify Loss Scenarios

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STPA Step 4 Guidance: Identify scenarios that could lead to the unsafe control actions identified in Step 3.

📋 Scenario Types
  • Why might a controller provide an unsafe control action?
  • Why might a safe control action not be executed properly?
  • What could cause delays or timing issues?
  • What feedback or information could be missing or incorrect?

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Step 5: Generate Safety Requirements and Recommendations

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