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Guidance on fixed gas detection systems for use in Safety Instrumented Systems

Author : Dr. Hassan EL-Sayed, BSc (Hons) MSc PhD CEng FInstMC, CSA Group

30 October 2019

Manufacturers of fixed gas detectors must conform to the protection concepts from the EN/IEC 60079 series of standards to demonstrate full compliance against the ATEX Directive 2014/34/EU in order for their products to be suitable for use in hazardous areas.

Complying with electrical protection standards demonstrates that the products have met the electrical safety requirement, but not the performance requirement standards, because gas detectors are designed to measure different types of gases, such as combustible (Methane, Propane), Oxygen, or even toxic gases. Hence these gas detectors shall comply also with specific harmonised performance standards such as IEC/EN 60079-29-1 and 4. In addition, the software developed for processing the gas measurement shall be assessed to EN 50271 and/or EN 50402 or even IEC/EN 61508 for safety related system. The question becomes apparent when looking at the measures and guidance that the system integrator or manufacturer must follow to ensure that these fixed gas detectors are installed correctly in the correct spots to perform correctly and provide maximum safety coverage for safety related systems. 

It is well known in functional safety that system integrators must comply with IEC /EN 61511 and IEC/EN 61508 for Safety Instrumented Systems (SIS), but those standards do no provide guidance or clarification on fixed gas detectors for use in SIS in terms of the sensing points, appropriate locations, management of regular maintenance, system response time, calibration and gas sampling, competency requirement, all these factors have greater effect on the integrity of the overall SIS than the required safety Integrity Level (SIL) capability. 

The IEC/EN 60079-29-3 provides such a guidance on fixed gas detectors for SIS since it is based on the safety lifecycle as detailed in IEC 61508, where specific requirements under “Functional Safety Management” must be adhered to so that all persons or companies involved in the supply chain are compliant. This IEC 60079-29-3 defines safety related consideration in connection to any associated peripheral fixed gas detection equipment in terms of the framework and use of IEC 61508 and IEC 61511.

Dr. Hassan El-Sayed

Dr. Hassan El-Sayed started at CSA Group in early 2010 and has held the position of Functional Safety (FS) team lead for six years. He became Functional Safety Business Manager during the last four years and has executed many projects in functional safety assessment for oil and gas sectors, where IEC 61508 & IEC 61511 are heavily used, in addition to the safety of machinery. With over 30 years of industrial experience in FS applications & product design for HazLoc use, Hassan has published several functional safety papers at various conferences, such as ISA, HazardEx, Robots Automation and Fieldbus Foundation.

Dr. Hassan El-Sayed, BSc MSc PhD, CEng FIET FInstMC
Dr. Hassan El-Sayed, BSc MSc PhD, CEng FIET FInstMC

Hassan invented the first redundant fieldbus system (Trunksafe) for use in Foundation Fieldbus which is widely used by Chevron, BP, Shell, and others. He has been awarded at least 10 USA and European patents in instrumentation and fieldbus and received an award of excellence for a paper presented at ISR (49th Symposium on Robotics, held in July 2017 in Shanghai, China). Hassan is an active member in TC31 / WG42 / WG09, SC65/MT 61508-1/2, and GEL 65/01.

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