The IEC 61508 series of standards
IEC 61508 is a globally recognized standard that provides a framework for achieving functional safety in the design and implementation of safety instrumented systems. The standard encompasses various aspects, including hardware, software, overall system development and the required underlying processes. Only in combination, these aspects can contribute to achieving the required systematic capability of a safety instrumented system.
Management of Functional Safety
The functional safety development process needs to be embedded within an overarching management system to deliver the intended guidance in an efficient manner.
This involves conducting hazard and risk assessments to identify the needed safety integrity levels, defining safety requirements and the necessary verification & validation activities on several levels and conducting a series of analyses. All those activities are enabled by a complete and unambiguous safety management system, supported by a series of processes like Change-, Configuration and Document management.
Requirement Specification
Clearly defined and unambiguous requirements are crucial for the entire safety lifecycle.
Requirements are defined to cover safety goals from the high level hazard analysis and need to be traceable throughout the development lifecycle, ensuring that each design and implementation decision can be linked back to a specific requirement.
Design and Implementation
The design and implementation phase, transforming requirements into concrete development artifacts, must adhere to established safety standards and guidelines.
Measures should be in place to detect and rectify errors in the design phase before they propagate into the final product – an approach of different types of analysis, combining qualitative analyses on system- and software level with quantitative analysis of the hardware, can be applied to create an overview of necessary safety functions.
Verification and Validation
Rigorous testing and validation processes must be executed to confirm that the implementation meets the specified safety requirements.
This involves dynamic- and static analysis, function- and fault injection testing, robustness- and stress testing and several other techniques to identify and eliminate defects as early as possible.
Quality Management
In all functional safety management processes, it must not be forgotten that a proper quality management process needs to be in place to enable all higher-level safety activities.
Regular audits, reviews, and assessments contribute to maintaining and improving the effectiveness of all involved processes. The management of quality during the production phase is itself worth a separate blogpost – it must be considered, that all safety measures defined in the development phase depend on correct implementation, so that the production phase deserves just the same attention than the preceding steps.
Conclusión:
Safety capability, as defined by IEC 61508, is combination of several processes, of which none can provide the desired output on its own. Adhering to the guidelines set forth in the standard helps to mitigate most of the pitfalls one can encounter when developing safety instrumented systems, however, as the state of the art is continuously advancing, organizations must continuously improve themselves in order to reach the overarching goal of safe products.
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