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The origins of Functional Safety


The topic "Functional Safety" and the often in this context used abbreviation "SIL" lead us back to an accident which has happened in the year 1976 in Seveso, Italy. As a result of this incident was released the extremely acid substance dioxin due to an uncontrolled overheating reaction. The plant was not equipped with automatic cooling system nor with a warning system. An emergency plan was not available either. The released dioxin caused diseases and tremendous, long-term environmental harms. Numerous animals died in the following days. The facts: 200.000 people have been evaluated, about 200 people suffered serious skin diseases, 70.000 animals have been slaughtered. The cleaning up of the contaminated soil and other measures have cost a lot of money.

As a consequence of this accident it was decided to tighten up legislation and ordinances aimed at protecting humans, living organisms and the environment. 

Safety standards IEC 61508 and 61511

IEC 61508 "Functional Safety of Safety - Related Electrically/Electronically Programmable Electronic Systems" which has been valid Europe-wide as EN 61508 since August 2002, was published in the year 1998. This new Safety Standard, for the first time, defined the safety requirements in automation engineering comprehensively, independently of the application, and also allowes for modern, microprocessor-based systems.

While IEC 61508 is aimed primarily at manufacturers of components for protection equipment and devices, IEC 61511 >Functional Safety - Technical Safety Systems for the Process Industry<  is aimed at users and planners of safety devices and equipment. IEC 61511 provides recommendations and targets for assessment of the damage risk of installations and provides assistance in selection of appropriate, safety-related components. 


SIL itself is an abbreviation for "Safety Integrity Level" and has now become a synonym for Functional Safety. SIL defines a measure of the safety-related performance or reliability of an electronic or electrical control device. SIL focuses on assessment of the safety chain, also referred to as SIF "Safety Instrumented Function". Typically, this safety chain consists of a fail-safe control, an actuator and a sensor. The SIS "Safety Instrumented System" consists of one or more safety chains. 

Functional safety and explosion protection

Were we to place the Standards and regulations of these two specialist areas side by side and compare their content, we could easily conclude that these two topics have nothing to do with one another and coexist with no interrelationship whatsoever. Many operators and planners will confirm, on the basis of their own experience, that this is not the case and that both topics are even frequently inseparably linked.

R. STAHL as manufacturers of explosion protected apparatus recognised this interrelationship at an early stage, and the required knowledge was acquired in parallel with product developments and certifications. Consequently, now also supply the components and systems specified for functional safety circuits together with the required specialist knowledge.