Functional safety

Functional safety is the part of the overall safety of a system or piece of equipment that depends on the system or equipment operating correctly in response to its inputs, including the safe management of likely operator errors, hardware failures and environmental changes.

The objective of functional safety is freedom from unacceptable risk of physical injury or of damage to the health of people either directly or indirectly (through damage to property or to the environment).

Functional safety is intrinsically end-to-end in scope in that it has to treat the function of a component or subsystem as part of the function of the whole system. This means that whilst functional safety standards focus on electrical, electronic, and programmable systems (E/E/PS), the end-to-end scope means that in practice functional safety methods have to extend to the non-E/E/PS parts of the system that the E/E/PS actuates, controls or monitors.

Functional safety is achieved when every specified safety function is carried out and the level of performance required of each safety function is met. This is normally achieved by a process that includes the following steps as a minimum:

Neither safety nor functional safety can be determined without considering the system as a whole and the environment with which it interacts. Functional safety is inherently end-to-end in scope.

Any claim of functional safety for a component, subsystem or system should be independently certified to one of the recognized functional safety standards. A certified product can then be claimed to be Functionally Safe to a particular Safety Integrity Level or a Performance Level in a specific range of applications: the certificate is provided to the customers with a test report describing the scope and limits of performance.

An important element of functional safety certification is on-going surveillance by the certification agency. This follow-up surveillance ensures that that product, sub-system, or system is still being manufactured in accordance with what was originally certified for functional safety. Follow-up surveillance may occur as various frequencies depending on the certification agency, but will typically look at the product's hardware, software, as well as the manufacturer's ongoing compliance of functional safety management systems.

The principles underpinning functional safety were developed in the military, nuclear and aerospace industries, and then taken up by rail transport, process and control industries developing sector specific standards. Functional safety standards are applied across all industry sectors dealing with safety critical requirements. Thousands of products and processes meet the standards based on IEC 61508: from bathroom showers, automotive safety products, medical devices, sensors, actuators, diving equipment, Process Controllers and their integration to ships, aircraft and major plant.

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