Safety Integrity Level

The assurance level is a term from the field of functional safety and is referred to in international standards IEC 61508/IEC61511 as Safety Integrity Level (SIL). It is used for evaluation of electrical / electronic / programmable electronic (E / E / PE ) systems in terms of the reliability of safety functions. From the required level, the safety-related design principles that must be adhered to so that the risk of malfunction can be minimized result.

Definition

In the safety standard EN 61508, derived from the international standard IEC 61508 Safety Integrity Level is defined as follows:

Security functions are used in the industry to protect the health of persons working in, the environment and of goods. These security functions are realized by a safety circuit, which may consist of different equipment such as sensors, control elements and actuators. The assurance level is a measure of the reliability of the system depending on the threat dar. processes with a lower risk are constructed by a safety circuit with a lower level than processes with a higher risk, in which, for example, people can be killed. Typical safety functions are emergency stop, switch off overheated equipment or monitoring hazardous movements.

The operators of systems with safety features put in the context of a risk assessment of the safety integrity level determined for each safety function. According to this specification the suitable devices are selected and combined to form a system.

Device manufacturers rate their equipment according to the standards. Up to level 2 this can make the manufacturer on his own responsibility; at level 3, this is carried out by an independent third party who issues a certificate after successful certification.

For determining the level of safety integrity for a necessary one considering the failure behavior of the considered module. Furthermore, it is precisely assess whether redundant structures are present, such as the relationship between safe and unsafe errors errors and whether the safety function must be considered continuously or on request in the assessment. From this information, then the failure rates are determined. These characteristics serve an assessment of the safety integrity level according to the specifications of the standard.

An examination of the figures, however, is not sufficient for the classification of the device. It is still a consideration of the service life of the process equipment required. Here, for example, the safety-related construction and similar areas. The standard work is here on special measures for the different levels of functional safety. Of special significance is this part in the consideration of resources with complex assemblies, these are, for example, microprocessors have an internal program. Here, special measures are set forth in order to respond to programming errors in the standards. A particular problem here, for example, errors that are not caused by their own development activities, but already in software tools such as compilers and the like are included. Only the consideration of all points allows for an assessment of whether the equipment can be used in a safety circuit of the appropriate safety integrity level.

A classification of the individual modules according to the safety integrity level is not useful because the standard requirements relating to the safety circuits. This means that the determination of the step can only be made for the interconnection of the various well-known equipment such as sensors, actuators, controls, etc..

Standardization

  • EN 61508-1, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 1: General requirements (IEC 61508-1:1998 Corrigendum 1999)
  • EN 61508-2, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 2: Requirements for safety-related electrical / electronic / programmable electronic systems (IEC 61508-2:2000 )
  • EN 61508-3, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 3: Software requirements (IEC 61508-3:1998 Corrigendum 1999)
  • EN 61508-4, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 4: Definitions and abbreviations (IEC 61508-4:1998 Corrigendum 1999)
  • EN 61508-5, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 5: Example for the determination of safety integrity levels (IEC 61508 - 5:1998 corrigendum 1999)
  • EN 61508-6, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 6: Guidelines for IEC 61508-2 and IEC 61508-3 (IEC 61508-6:2000 )
  • EN 61508-7, Functional safety of electrical / electronic / programmable electronic safety- related systems - Part 7: Overview of techniques and measures ( IEC 61508-7:2000 )
  • EN 61511-1, Functional safety - Safety instrumented systems for the process industry sector - Part 1: Framework, definitions, requirements for systems, software and hardware (IEC 61511-1:2003 Corrigendum 2004)
  • EN 61511-2 Functional safety - Safety instrumented systems for the process industry sector - Part 2: Guidelines for the application of Part 1 (IEC 61511-2:2003 )
  • EN 61511-3 Functional safety - Safety instrumented systems for the process industry sector - Part 3: Guidance for the determination of the required safety integrity levels (IEC 61511-3:2003 Corrigendum 2004)

(Note: These standards were published in Germany, Austria and Switzerland as a national standard, prefixed by marking DIN, OVE / ÖNORM or SN)

  • EN 50 129 Safety in the Rail Industry
  • U.S. RTCA DO- 178B North American Avionics Software
  • U.S. RTCA DO-254 North American Avionics Hardware
  • EUROCAE ED -12B European Airborne Flight Safety Systems
  • IEC 62304 - Medical Device Software
  • ISO 26262 - Road vehicles - Functional safety
Root cause analysis
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