In critical system industries such as aerospace, railways, automotive, or nuclear, managing safety is crucial. A key element in ensuring this management is the development of a safety case. This safety case is a formal and structured document that compiles all relevant information about risks, analyses, and the measures implemented to ensure that the system meets safety requirements.
It also serves as the main reference for audits or certifications, ensuring compliance with the specific safety standards of the relevant industry (e.g., DO-178C in aerospace, ISO 26262 for automotive, or IEC 61508 in general industry).
What is a Safety Case?
A safety case is a critical document that presents the analyses, decisions, and technical justifications demonstrating that the system can operate safely. This document is required to show that safety-related risks have been identified, assessed, and that appropriate measures have been put in place to mitigate them.
It also acts as the reference point for audits and certifications, ensuring that the system complies with applicable safety regulations and standards.
Structure of a Safety Case
The safety case is typically composed of several key sections, each addressing a specific aspect of dependability. Below are its main components:
1. Project and System Context
- System Description: Overview of the system or product and its operational environment. This section includes the definition of the system’s primary functions and interfaces.
- Safety Requirements: A list of the regulatory and normative safety requirements applicable to the project. These requirements may include international standards and internal guidelines.
2. Risk Analysis (FMEA/FMECA)
- Risk Identification: Methods such as FMEA (Failure Mode and Effects Analysis) or HAZOP are used to identify potential failures.
- Risk Assessment: Analysis of the severity and likelihood of potential failures, as well as their effects on system safety.
- Risk Mitigation Measures: Identification of corrective or preventive actions (e.g., redundancy, securing critical components) to reduce risks.
3. Compliance Demonstration
- Technical Justifications: Description of tests, analyses, or simulations conducted to prove that the system meets safety requirements.
- Evaluation and Certification: Proof that the measures taken comply with normative standards and have been validated by competent authorities or independent auditors.
4. Verification and Validation (V&V) Plan
- Tests and Trials: Results of trials conducted to assess the system’s compliance with safety standards. This may include reliability, robustness, or integrity tests on critical systems.
- Failure Scenario Analysis: Case studies or simulations of worst-case scenarios and demonstrations of the system’s ability to respond safely to these situations.
5. Maintenance and Evolution Plan
- Maintainability Plan: Measures and recommendations to ensure that the system can be maintained and updated without compromising safety.
- Future Risk Management Plan: Strategy for assessing and integrating feedback to ensure safety is maintained throughout the system’s lifecycle.
6. Deviations Management
- Request for Deviation: Identification of any deviations from the initial safety requirements, along with solid justifications showing that these deviations do not compromise the overall safety of the system.
Importance of a Safety Case
A safety case is essential for several reasons:
- Ensuring System Safety: It guarantees that all risks have been identified and that appropriate measures are in place to reduce them to an acceptable level.
- Obtaining Certification: Regulatory authorities and certification bodies require evidence that the system complies with safety standards. The safety case is the primary reference for these evaluations.
- Facilitating Audits and Inspections: This document is used during internal or external audits to verify that safety procedures are followed throughout development and system operation.
- Maintaining Decision Traceability: It ensures that all safety-related decisions are documented, making it easier to review and implement future modifications.
- Preventing Accidents and Incidents: The case proves that all potential accident scenarios have been evaluated and that countermeasures are in place.
Project Phase of the Safety Case
The safety case is involved throughout all phases of the project lifecycle, including:
- Design Phase: From the start, risk identification and safety requirements should be integrated into the system’s definition.
- Development Phase: As the project progresses, safety analyses and validation tests are conducted and integrated into the case.
- Operational Phase: Once deployed, the safety case evolves by incorporating feedback, incidents, or system changes.
- Maintenance and Evolution Phase: It helps manage system updates and ensures that safety is maintained at an acceptable level.
The safety case is a fundamental part of dependability management. It ensures that all safety engineering steps are correctly followed, from risk analysis to system performance validation. It not only provides a rigorous working framework but also serves as an indispensable tool for proving compliance with standards, obtaining certifications, and ensuring the safety of systems throughout their lifecycle.