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Functional Safety

→ Functional Safety, Introduction

Safety vs. Reliability

IEC 61508

ISO 13849

IEC 61508 vs. ISO 13849

Summary

Unfortunately 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 devices like hand rails, warning signs, etc.

The term functional safety means systems that

have at least some complexity, therefore at least some attention is needed during product development,
play an active role in a dedicated safety context; they carry out a safety function on demand,
have a realistic (but hopefully little) chance to fail. This is expressed in probability of failure per hour.

For example, a safety device consisting only of switches and cabling would fulfil all three criteria, while being still simple.

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.

Piper Alpha Disaster

In 1988, a sequence 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 doing 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 61508 philosophy.

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