Functional Safety and the IEC

IEC 61508

Functional Safety


Functional Safety

Power plant control room

What is functional safety?

Let's start with a definition of safety:
Freedom from unacceptable risk of physical injury or of damage to the health of people, either directly, or indirectly as a result of damage to property or to the environment.


Functional safety is the part of the overall safety that depends on a system or equipment operating correctly in response to its inputs.


Functional safety is the detection of a potentially dangerous condition resulting in the activation of a protective or corrective device or mechanism to prevent hazardous events arising or providing mitigation to reduce the consequence of the hazardous event.



Functional safety relies on active systems. The following are two examples of functional safety:

  • The detection of smoke by sensors and the ensuing intelligent activation of a fire suppression system; or,
  • The activation of a level switch in a tank containing a flammable liquid, when a potentially dangerous level has been reached, which causes a valve to be closed to prevent further liquid entering the tank and thereby preventing the liquid in the tank from overflowing.

Safety achieved by measures that rely on passive systems is not functional safety.

  • A fire resistant door or insulation to withstand high temperatures are measures that are passive in nature and can protect against the same hazards as are controlled by functional safety concepts but are not instances of functional safety.

A brochure is also available:


Brochure cover:  Functional safety: Essential to overall safety


Functional safety
Essential to overall safety

An introduction to Functional safety and the IEC 61508 series.

English pdf file 765 kB