Functional safety: a useful definition

First of all, what is “Functional Safety” ?

We must start with a suitable 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.

After that we can provide the meaning of Functional Safety:

“Functional Safety” is a part of the overall safety that depends on a system or equipment operating correctly in response to its inputs; in other words Functional Safety is the detection of a potentially dangerous condition. It results in the activation of a protective or corrective device, either to prevent the arising of hazardous events, or to provide mitigation to reduce their harmful consequences.

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 (for example: a fire resistant door) is not functional safety.

(Previous definitions and examples are derived from IEC web site).