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.

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 and IEC 62061) as the benchmark for achieving functional safety and manageing risks in a proportionate way.

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 SIL4 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 (join us).

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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