Functional safety is a very versatile
and complex discipline. Functional safety is related to medical
engineering, aeronautic, automation, automotive and rail industry.
The international standard IEC 61508
is the basic standard with respect to functional safety. Out of IEC
61508 many product or area specific standards were derived. Some
specific standards are ISO 13849, ISO 26262, IEC 62061, IEC 61511, EN
50128, EN 50129, EN 50159. These standards are related to automation,
vehicles, machinery, process control and rail.
The decision about suitable solutions
will be done on basis of the system behaviour in case of faults. There
are three main reliability groups:
In case of a fault the system falls
into a safe state by itself or by external measures and remains in the
In case of a fault the system falls into a degraded mode with
limited functionality for a specified time before entering the safe
state. The system can be operated for a limited time in case of failure.
In case of a fault the system can be operated without degradation for a
specified time period before the system must be repaired. It's possible
to repair the system while operating. The system has to be repaired in
the specified time period.
Depending on the
above described reliability groups the fault tolerance shall be
specified for safety reasons. Any decision about a wrong architecture
can have impact to life of people or to the environment. A safety
concept has to be developed depending on the related safety standards.
In all phases of
the life cycle there is the need for using analytical methods to get
evidence about safety. Measures shall be used to reduce the risk to an
services of the Consulting Engineer's Office EDOH related to functional safety: