What is Functional Safety?
At its simplest functional safety is the part of the overall safety relating to the equipment under control and its associated control system that depends on the correct functioning of the safety-related system.
What is Functional Safety?
Functional safety is achieved when all the specified safety functions, of the safety-related system, can satisfy their required safety performance. Functional safety is undertaken by active systems. We recognise IEC 61508 and related standards (e.g., IEC 61511, IEC 62061, IEC 61800-5-2, IEC 60730-1) as the benchmark for achieving functional safety and managing risks in a proportionate way.
Functional safety is the engineering discipline / section of the overall safety concept that depends on a system or equipment operating correctly in response to inputs. Ensuring functional safety requires greater and more traceable management and justification when compared to systems that cannot influence safety. Functional safety does not equal or mean SIL; SIL is a grading of the probability of a safety function satisfactorily performing under stated conditions and within a stated period.
The international standard IEC 61508-4:2010 (basic safety publication) defines functional safety as “part of the overall safety relating to the EUC and the EUC control system that depends on the correct functioning of the E/E/PE safety-related systems and other risk reduction measures” (where EUC is equipment under control).
The international standard ISO 26262-1:2018 (automotive sector) defines functional safety as “absence of unreasonable risk due to hazards caused by malfunctioning behaviour of E/E systems” (where E/E is electrical and electronic).
The international standard IEC 60730-1:2022 (home and commercial sector) defines functional safety as “correct operation of the declared safety related output function(s), failure or malfunction of which, can cause a hazard”.
IEC 61508 sets out the requirements for ensuring that systems are designed, implemented, operated and maintained to provide the required safety integrity level (SIL). Four SILs are defined according to the risks involved in the system application, with SIL 4 being used to protect against the highest risks. The standard specifies a process that can be followed by all links in the supply chain so that information about the system can be communicated using common terminology and system parameters.
Some organisations or people can find functional safety and IEC 61508 compliance as a daunting prospect. One of the key principles of the Association is to promote and support the best routes for compliance to IEC 61508 and related standards. Please review the CASS webpages and consider joining the Association if you are new to functional safety.
What is a Safety-Related System?
Typically a system will comprise a sensor which provides information on the value of a variable, a processor which compares the value with a predetermined limit and initiates action and an actuator which either corrects the variable or performs an emergency function.
Apart from the reference to danger, this description could be applied equally to the process controls for the equipment performing its function. In the past it was regarded as essential that the safety function operated independently from the process function. The advent of microprocessors enabled vast amounts of data to be collected and analysed in real time thus providing the possibility of sophisticated safety systems including such features as self-diagnosis. With many different parties involved in the specification, design, manufacture, installation, operation and maintenance of safety systems, the need for a standardised approach was recognised and IEC 61508 is the result.
What is Functional Safety Engineering?
Functional safety engineering is where studies are performed with the objective of providing assurance that safety-related products, devices and systems deliver the appropriate level of risk reduction, protection or mitigation.
The objective is to support functional safety assurance by reviewing the engineering design with an aim to:
- Manage and plan the safety-related requirements and the associated systems / controls;
- Manage and plan the safety-related requirements and the associated software;
- Reduce the likelihood of systematic failures;
- Reduce the likelihood of random hardware failures;
- Enhance the overall safety management (incl. operation and maintenance); and
- Support demonstration of continuous improvement in safety culture.
Functional safety engineering can generally be considered as a combination of studies, analysis, audits, assessments, and reviews to enable an engineering judgement to assure functional safety.
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