Standards Development

Scope

This document sets out safety integrity related considerations for fixed gas detection systems and associated equipment in terms of the framework and philosophy of IEC 61508 (all parts). The document introduces the requirements described by Figure 2 and includes equipment for the detection of flammable and toxic gases and vapours, and oxygen.

Other local, national and international standards specify the performance requirements of gas detection equipment. These standards are commonly known as Metrological Performance Standards and are concerned with the accuracy of the measured value, the overall system performance, but not with the device or system integrity with respect to the safety function.

This document applies to the integrity of the safety instrumented function.

NOTE 1 In some jurisdictions, it can be a requirement to certify the performance of equipment for the measurement of flammable gases, vapours, toxic gases and/or oxygen used in life safety applications.

Please see draft for Figure 2 – Related Safety Instrumented System Standards

This document does not consider the Safety Integrity Level SIL 4. SIL 4 is considered to be practically unattainable for gas detection systems

NOTE 2 It is rare for any risk study to determine a Safety Integrity higher than SIL 2 for a fixed gas detection system.

This document is applicable to fixed gas detection systems which can include the following functional units: 

– Gas sensor/transmitter

– Gas detection control unit (logic solver)

– Gas sampling (single and multiplexed streams)

– Gas conditioning

– Automatic gas calibration and adjustment

– Output module (if not part of the control unit)