Since the introduction of standards IEC 61508 and IEC 61511 for Functional Safety (SIL), there has been ever-increasing demand for analysing equipment and process instruments that meet the requirements according to the SIL (Safety Integrity Level) classification. The European directives EN 12952 and 12953 demand that a hazard analysis shall be carried out for each limiting device function and appropriate Safety Integrity Levels implemented.
Note 1 states: "Typical Safety Integrity Level (SIL) requirements for boiler protection systems demand a level of at least 2".
Functional Safety is part of the overall safety of a system that depends on the correct functioning of safety-related (sub)systems and external equipment for risk reduction. This means that Functional Safety covers only one aspect of overall safety. Other issues such as electrical safety, fire and radiation protection, etc. do not fall within the scope of Functional Safety.
In modern systems, safety functions are increasingly performed by electronic and, in particular, programmable systems. Consequently, the fundamental challenge facing Functional Safety is to ensure the correct functioning of complex, programmable systems. It is therefore essential to establish suitable methods for preventing systematic faults (usually due to human error committed during the specification and implementation phase) and for controlling failures, abnormalities and loss of function (usually physical phenomena). In this context the expression "functional safety of the protective or safety function" is used.
The European standard IEC 61508, "Functional Safety of Electrical/Electronic/ Programmable Electronic Safety-related Systems" defines the various aspects of Functional Safety for electrical or electronic (programmable) systems.