7 Steps to Help Achieve Functional Safety
Automated safety systems are increasingly being integrated around the world and across diverse industries – including process, household and commercial products, medical, nuclear, automotive, railway, and avionics
This has significantly elevated the importance of functional safety evaluation and certification internationally. A valuable tool in identifying, controlling, and mitigating hazards and risks, functional safety evaluation can help ensure a system’s safety operation responds promptly and correctly to potential errors or failures, helping to avoid or reduce the risk of damage, injury, or even death.
As more customers seek safety system products that comply with global functional safety standards, it is vital that companies understand and follow the requirements of the IEC 61508 series of standards for safety-related systems associated with electrical, electronic, and software-based technologies. Following these seven steps can help you achieve functional safety and gain consumer confidence in your product.
1. Conduct a Safety Integrity Level (SIL) Determination Study.
Identify the hazards and risks associated with your existing process and any associate control and instrumentation system, then undertake a SIL determination study to establish the amount of risk reduction required for the implementation of a safetyinstrumented system. It is at this point the SIL of the safety-instrumented function is defined. Keep in mind that each SIL has its own range, with an “order of magnitude” between end points. If the demand from the process on the safety function is predicted to be less frequent than once a year, it is classified as a low demand system. If the demand is more frequent, it is a high demand system.
2. Prepare Safety Requirements Specification
Functional safety standards emphasize the importance of capturing functional requirements, deriving more detailed design requirements (right down to low level hardware and software) and tracing these through the design and development stages, integration and testing process, and all the way through to final validation. At the end of every stage of the product lifecycle, a verification process must be followed to capture any details not fully addressed that can affect compliance. This can help avoid systematic failures.
3. Conduct a Quantitative Assessment to Address Risk of Random Hardware Failures
A theoretical model of the equipment’s reliability must be constructed, decomposing the design into functional blocks to form a reliability block diagram. An analysis of each block should follow, using methods such as failure modes and effects analysis. This helps to categorize both detected and undetected failures into “safe” and “dangerous,” helping to calculate the probability of failure on demand. You will also need to calculate the safe failure fraction and the hardware fault tolerance using information from circuit diagrams, mechanical assembly drawings, parts lists, and other sources following design
4. Establish Processes to Help Control and Avoid Systematic Failures
The verification of systematic failures (hardware or software) requires a qualitative assessment of the evidence of using the prescribed lifecycle, although the actual processes and work activities used will depend on the technologies in the design and type of safety equipment in question. For equipment developers, evidence of using these methods must be gathered during the design stage and made available for assessment. The verification task is applicable across the whole product lifecycle, from product safety specification to validation.
5. Establish Processes for Software
Special attention from developers is needed for software involved in performing safety functions. This includes, but is not limited to:
• Capturing and tracing requirements through the development lifecycle
• Fostering a software review culture
• Configuration management
• Investing in, and maximizing the use of automated test tools
• Using recommended development tools to facilitate the structure of the safety software compliance
6. Conduct a Functional Safety Assessment
All safety systems must undergo an independent functional safety assessment that covers hardware and software, as well as all related processes used in the realization of the instrument/system. The requirements for the assessment, including the methods and techniques prescribed, increase in rigor with higher SIL.
7. Manage Functional Safety
All organizations that deal with safety-instrumented systems must develop and maintain a functional safety management (FSM) process. This can be a companywide process, typically part of the company’s Quality Management System, or be implemented as an over-arching plan that covers a specific project and details how functional safety will be managed. An important part of the FSM is the development structure, deployment, and assessment of the competence of all staff who have any roles or responsibilities associated with safety systems. For companies starting a functional safety project for the first time, FSM is a good place to begin as it establishes the procedural infrastructure in advance.
In a highly complex, safety-related system where functional safety is a requirement, equipment suppliers should identify an accredited thirdparty agency, such as CSA Group, that can evaluate and certify compliance with the IEC 61508 or applicable industry-specific standard.
Download our functional safety white paper and contact CSA Group to learn more.
Tel: 01244 670 900
Published in Valve User Magazine Issue 45
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