The EN 50402 for Fixed Gas Detection Systems in Relation to the Generic Standard IEC 61508

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This article will discuss and demonstrate practical issues related to the application of EN 50402 for Fixed Gas Detection Systems in the context of the EN/IEC 61508 standard.

Description

The European Standard EN 50402 for fixed gas detection systems is a product family standard for all gas detection equipment; its subtitle is “Requirements on the functional safety of fixed gas detection systems”. The EN 50402 was transferred as new work item to IEC and will be published as IEC 60079‐29‐3; an IEC version will be available at the earliest in 2011. The EN 50402 will also be used outside Europe as “state of the art” technical specification. The standard is based on the generic standard IEC 61508 and covers the phase 9 “realisation”.

Gas detection systems differ strongly in structure, complexity and performance. The EN 50402 divides a gas detection system into functional modules to ensure that systems with different structures are handled in a comparable manner. Requirements are specified for each type of simple or complex modules and for different ranges of safe failure fraction (SFF). For each module the SIL‐capability is determined. Safety functions are specified by different combinations of modules that may result in different SIL‐capabilities.

The EN 50402 includes no requirements for the installation and maintenance of gas detection systems and does not specify the physical positioning of sensors. These items are covered by metrological standards, e.g., the EN/IEC 61779 series (the future EN/IEC 60079‐29‐1) and the related guide EN 50073 (the future EN/IEC 60079‐29‐2). The calculation of probability of failure on demand (PFD) and the conformity of the software development process are carried out according EN/IEC 61508 without further specification in EN 50402. For the implementation of a gas detection system into an overall safety system the type testing according to EN 50402 will deliver SIL‐capability, hardware failure probabilities and diagnostic test intervals for each safety function.

This article will discuss and demonstrate practical issues related to the application of EN 50402 in the context of the IEC 61508 standard. © 2014 Risknowlogy. All Rights Reserved.

  • Author: Dr. Dieter Wenker
  • Published: November 2014
  • Words: 4752

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