adequately with technical uncertainties
& Quality Management
Safety vs. Reliability
IEC 61508 vs. ISO 13849
there is neither clear nor precise definition of the term "functional
safety". However, the term is used for those safety means that differ
from simple passive safety means like hand rails, warning signs, etc.
Functional safety deals with such systems that
systems consisting only of switches and cabling fulfill all three
minimum dimension of complexity. They are not apparently self
explaining and therefore need special attention during development,
an active role in a dedicated safety context; they carry out a safety
a realistic (but hopefully little) chance to fail. This is expressed in
probability of failure per hour.
With functional safety being a universal philosophy, you would think
that it is not restricted to certain industrial branches.
However, the origin of what we today call "functional safety" proves
the opposite, which will be outlined in the following paragraph.
In 1988, a chain of mishaps led to 170
fatalities and the
complete loss of piper alpha oil platform.
At that time, military, aviation, energy supply, railway and probably
other major industries, already had their own particular processes and
standards, which, from today's perspective, could have been called
"functional safety". While these standards differed (and today still
differ) significantly between industries, it was (and still is) the
overall integrated safety process approach which they had in common.
The root cause for the piper alpha disaster was especially the lack of
such approach, resulting in each department just
their own job.
While this has been state of the art
in many civil industries, a new systemic approach began to establish
and finally ended up with the release of IEC 61508 in 1998.
Consequently, "functional safety"
applies for all those industries which hadn't such systemic safety
approach until the 1990s, and which today use either the IEC 61508 or
one of its derivatives.
Railway industry however is an exception. Although there had been
systemic safety approaches in place, they have been replaced with IEC