EN 50402:2017

• Abstract:

  This European Standard is applicable to apparatus and systems for the detection and measurement of flammable or toxic gases or vapours or oxygen. This European Standard is a product standard which is based on EN 61508 (all parts) and for gas detection systems covers both low and high demand mode at SIL capabilities of 1, 2 or 3 only. Gas detection apparatus and gas detection systems are developed as generic products. This standard covers part of the phase 10 “realisation” of the overall safety lifecycle defined in Figure 2 of EN 61508-1:2010. Configuration and integration into specific applications is not covered by this standard. In the event of conflict between the requirements of this standard and those of EN 61508, EN 50402 will take precedence. NOTE 1 Applications requiring a SIL capability of 4 for a gas detection system are not practicable. NOTE 2 This European Standard is dedicated mainly to fixed apparatus. For portable gas detectors claiming a SIL higher than 1, this European Standard may be applied. This European Standard supplements the requirements of the European Standards for electrical apparatus for the detection and measurement of flammable gases, vapours (e.g. EN 60079-29-1 or EN 60079-29-4), toxic gases (e.g. EN 45544) or oxygen (e.g. EN 50104). NOTE 3 These European Standards are called in the text "metrological standards". The examples above show the state of the standardisation for industrial applications at the time of publishing this European Standard. There may be other metrological standards covering other application fields, for which this European Standard is also applicable. EN 50271 specifies minimum requirements for apparatus using software and/or digital components. It also defines additional optional requirements for compliance with SIL 1 in low demand mode operation. EN 50402 includes all requirements of EN 50271. EN 50402 is also dedicated to apparatus and gas detection systems and/or components and should be used instead of EN 50271 in the following cases: - At SIL 1 when the system contains components not covered by EN 50271; - At SIL 2 and SIL 3; - At all SILs when non-digital based apparatus is used. Applying the above-mentioned metrological standards will ensure the measuring performance is adequate in normal operation of a gas detection system. Additionally the requirements of this European Standard address the functional safety of gas detection systems and encompass criteria for reliability, fault tolerance and avoidance of systematic failures. The avoidance and control of systematic failures will be covered by the requirements for the development processes and techniques and diagnostic measures chosen in the design. This European Standard will lead to the characterisation of the gas detection system by a SIL-capability and related hardware failure rate representing a hierarchical order of safety levels. This will allow the user to incorporate the gas detection system into an overall safety system according to the safety integrity levels of EN 61508 (all parts). This European Standard is applicable for gas detection systems, which may consist of the following functional units: - gas-sampling; - sensor; - signal transmission; - input to control unit; - signal processing in control unit; - output from control unit. This European Standard does not specify requirements for the installation and maintenance of gas detection systems. It also does not specify the physical positioning of measuring points / locations. This European Standard does not specify which SIL-capability is sufficient for which application. NOTE 4 The SIL-capability required for an application will be specified by the user (see Clause 9 and Annex A ).

• Status: Published
• Publication Date: 16-Mar-2017
• Withdrawal Date: 03-Feb-2020
• ICS: 13.320 - Alarm and warning systems
• Technical Committee: CLC/TC 31 - Electrical apparatus for explosive atmospheres - General requirements
• Drafting Committee: CLC/SC 31-9 - Electrical apparatus for the detection and measurement of combustible gases to be used in industrial
• Current Stage: 9093 - Decision to confirm - Review Enquiry
• Start Date: 11-Jan-2023
• Completion Date: 25-Aug-2026
• Ref Project: SIST EN 50402:2017 - Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen - Requirements on the functional safety of gas detection systems

• Replaces: EN 50402:2005 - Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen - Requirements on the functional safety of fixed gas detection systems
• Effective Date: 27-Jan-2023
• Replaces: EN 50402:2005/A1:2008 - Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen - Requirements on the functional safety of fixed gas detection systems
• Effective Date: 26-Jan-2023
• Referred By: EN 13423:2021 - Natural gas vehicles - Requirements for NGV workshops and the management of compressed natural gas (CNG) vehicles
• Effective Date: 09-Feb-2026
• Referred By: EN 17932:2024 - Natural gas vehicles - Requirements for liquefied natural gas vehicle (LNGV) workshops and the management of liquefied natural gas (LNG) vehicles
• Effective Date: 09-Feb-2026
• Referred By: EN 50270:2015 - Electromagnetic compatibility - Electrical apparatus for the detection and measurement of combustible gases, toxic gases or oxygen
• Effective Date: 03-Feb-2026

Overview

EN 50402:2017 - "Electrical apparatus for the detection and measurement of combustible or toxic gases or vapours or of oxygen - Requirements on the functional safety of gas detection systems" - is a European product standard focused on the functional safety of gas detection apparatus and systems. Based on EN 61508 (all parts), it defines requirements for low‑ and high‑demand modes with SIL-capabilities 1, 2 and 3 (SIL 4 is considered impracticable). The standard is primarily aimed at fixed gas detection equipment but can apply to portable detectors claiming SIL >1. It covers part of the safety lifecycle (phase 10 “realisation”) and addresses reliability, diagnostic measures, fault tolerance and avoidance of systematic failures.

Key topics and technical requirements

• SIL-capability and mapping: Procedures to determine SIL-capability for gas detection safety functions and transformation to EN 61508 safety integrity levels (Annex A, C).
• Modular characterization: Requirements and characterization for functional units such as:
  • Gas sampling (aspiration, conditioning, multiplexer)
  • Sensors (measuring principles and failure modes)
  • Signal transmission and interfaces
  • Input to control unit, signal processing, and output
• Hardware failure rates: Methods to determine hardware failure rates per safety function (Clause 8).
• Software requirements: Integrates and extends EN 61508‑3 software lifecycle expectations, with EN 50402‑specific levels of rigour and recommended techniques (Clause 6).
• Diagnostics & reduced modes: Requirements for diagnostics, automatic calibration/adjustment, reduced modes of operation, and special states.
• Documentation, validation and assessment: Functional safety management, validation, assessment and required documentation (Clauses 11–14).
• Scope limits: Does not cover installation, maintenance, or physical placement of detectors; configuration for specific applications is outside scope. In case of conflict with EN 61508, EN 50402 takes precedence.

Practical applications and who uses this standard

• Manufacturers of gas detectors and gas detection systems developing products with defined SIL-capabilities.
• Safety and reliability engineers specifying or verifying functional safety performance for industrial gas monitoring.
• System integrators and OEMs combining modules (sensors, samplers, control units) into safety functions.
• Asset owners, plant managers and procurement teams evaluating SIL-capable gas detection solutions for refineries, chemical plants, utilities and confined‑space monitoring.
• Certification bodies and testing labs performing compliance assessment against EN 50402 and related metrological standards.

Related standards

• EN 61508 (all parts) - Functional safety of electrical/electronic/programmable systems
• EN 50271 - Apparatus using software and/or digital components (EN 50402 includes EN 50271 requirements)
• Metrological standards (measurement performance): EN 60079‑29‑1, EN 60079‑29‑4 (flammable gases), EN 45544 (toxic gases), EN 50104 (oxygen)
• Note: EN 50402 supplements these metrological standards to address functional safety (reliability, diagnostics, systematic failure control).

EN 50402:2017 is essential for anyone designing, certifying or procuring gas detection systems where demonstrable SIL-capability, fault tolerance and documented functional safety are required.

SLOVENSKI STANDARD
01-julij-2017
1DGRPHãþD
SIST EN 50402:2005
SIST EN 50402:2005/A1:2008
(OHNWULþQHQDSUDYH]D]D]QDYDQMHLQPHUMHQMHJRUOMLYLKDOLVWUXSHQLKSOLQRYKODSRY
DOLNLVLND=DKWHYH]DIXQNFLRQDOQRYDUQRVWVLVWHPRY]DRGNULYDQMHSOLQD
Electrical apparatus for the detection and measurement of combustible or toxic gases or
vapours or of oxygen - Requirements on the functional safety of gas detection systems
Elektrische Geräte für die Detektion und Messung von brennbaren oder toxischen Gasen
und Dämpfen oder Sauerstoff - Anforderungen an die funktionale Sicherheit von
Gaswarnsystemen
Matériel électrique pour la détection et la mesure des gaz ou vapeurs combustibles ou
toxiques, ou de l'oxygène - Exigences relatives à la fonction de sécurité des systèmes de
détection de gaz
Ta slovenski standard je istoveten z: EN 50402:2017
ICS:
13.230 Varstvo pred eksplozijo Explosion protection
13.320 Alarmni in opozorilni sistemi Alarm and warning systems
29.260.20 (OHNWULþQLDSDUDWL]D Electrical apparatus for
HNVSOR]LYQDR]UDþMD explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 50402
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2017
ICS 13.320 Supersedes EN 50402:2005
English Version
Electrical apparatus for the detection and measurement of
combustible or toxic gases or vapours or of oxygen -
Requirements on the functional safety of gas detection systems
Matériel électrique pour la détection et la mesure des gaz Elektrische Geräte für die Detektion und Messung von
ou vapeurs combustibles ou toxiques, ou de l'oxygène - brennbaren oder toxischen Gasen und Dämpfen oder
Exigences relatives à la fonction de sécurité des systèmes Sauerstoff - Anforderungen an die funktionale Sicherheit
de détection de gaz von Gaswarnsystemen
This European Standard was approved by CENELEC on 2017-02-04. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50402:2017 E
Contents Page
European foreword . 7
Introduction . 8
1 Scope . 10
2 Normative references . 11
3 Terms and definitions . 12
4 General requirements . 17
4.1 Specification of safety functions . 17
4.2 Determination of safety function . 23
4.3 Functional safety characteristics of modules . 24
5 Functional modules and elements — Characterization and requirements . 25
5.1 General . 25
5.1.1 Structure of functional modules . 25
5.1.2 General requirements . 29
5.2 Gas sampling . 30
5.2.1 Gas aspiration . 30
5.2.2 Conditioning of measured gas . 30
5.2.3 Gas multiplexer . 31
5.2.4 Gas sampling by diffusion mode . 31
5.2.5 Automatic calibration and adjustment . 31
5.3 Sensor . 32
5.4 Signal-transmission . 33
5.4.1 General requirements . 33
5.4.2 Signal-transmission between spatially separated modules . 33
5.4.3 Signal-transmission between modules not spatially separated . 35
5.5 Input to signal processing . 36
5.5.1 General . 36
5.5.2 Interface for measured signal . 36
5.5.3 Input system communication . 36
5.5.4 User interface . 36
5.5.5 Input from periphery . 37
5.5.6 Power supply . 37
5.6 Signal processing . 37
5.6.1 General . 37
5.6.2 Calculation of measured values . 39
5.6.3 Special state . 39
5.6.4 Signal assessment . 40
5.6.5 Diagnostic means within a control unit . 41
5.6.6 Reduced mode of operation . 43
5.6.7 Aspiration control . 44
5.6.8 Gas multiplexer control . 44
5.6.9 Control of automatic calibration . 44
5.6.10 Control of automatic adjustment . 45
5.7 Output of the control . 45
5.7.1 Visual indication . 45
5.7.2 Switching output . 46
5.7.3 Output system communication . 47
5.7.4 Output to periphery . 48
5.7.5 Data archives . 48
6 Software . 49
6.1 General requirements . 49
6.2 Context of the Software Standard . 49
6.3 Requirements from EN 61508-3 . 49
6.4 List of replaced or not relevant clauses in EN 61508-3:2010 . 50
6.5 List of changes to clauses in EN 61508-3 . 51
6.6 EN 50402 Levels of rigour . 54
6.7 Tables of techniques and measures from EN 61508-3:2010, Annex A . 55
6.7.1 Explanation of terms . 55
6.7.2 Writing conventions in the tables of techniques and measures . 55
6.7.3 Software requirements specification . 55
6.7.4 Software architecture design . 58
6.7.5 Software design and development – Support tools and programming language . 62
6.7.6 Software detailed design . 62
6.7.7 Software module testing and integration. 65
6.7.8 PE integration (hardware + software) . 67
6.7.9 Software validation . 68
6.7.10 Modification . 69
6.7.11 Software Verification . 70
7 Combining Functional Modules to Safety Functions . 72
7.1 SIL-capability . 72
7.2 Determination of SIL-capabilities for a safety function . 73
7.2.1 General . 73
7.2.2 Summarizing of single chains . 74
7.2.3 Summarizing of parallel chains . 74
8 Determination of hardware failure rates for each safety function . 75
9 Gas detection as part of an overall safety function . 76
10 Information requirements . 77
11 Validation . 78
12 Functional safety management . 79
13 Functional safety assessment . 79
14 Documentation . 79
Annex A (normative) Transformation of the SIL-capabilities of gas detection systems . 80
A.1 Introduction . 80
A.2 Transformation of the SIL-capabilities of gas detection systems to the safety integrity
levels of EN 61508 (all parts) . 80
Annex B (normative) Transformation from generic standard requirements to modules . 81
B.1 General . 81
B.2 SIL-capability 1 . 81
B.3 SIL-capability 2 . 81
B.4 SIL-capability 3 . 82
Annex C (informative) Determination of SIL-capability of a safety function of the gas detection
system . 83
C.1 General . 83
C.2 Procedure of determination of SIL-capability . 83
C.3 Example: Determination of SIL-capability for a gas detection system . 89
C.3.1 General . 89
C.3.2 Example: Characterization of relay outputs of control units A and B . 89
C.3.3 Example: Characterization of relay output of common alarm . 91
Annex D (informative) Failure modes for specific measuring principles . 93
D.1 Introduction . 93
D.2 Failure modes relevant to most or all types of measuring principles and types of sensing
elements . 93
D.2.1 Generic failure modes . 93
D.2.2 Failure modes identified in the metrological standards. 93
D.3 Catalytic sensing elements . 94
D.4 Thermal conductivity sensing elements . 94
D.5 Infrared sensing elements . 94
D.5.1 Point detectors . 94
D.5.2 Open path detectors . 95
D.5.3 TDLAS (e.g. for oxygen). 95
D.6 Semiconductor sensing elements . 95
D.7 Electrochemical sensing elements . 95
D.7.1 Galvanic — Lead based oxygen . 95
D.7.2 Amperometric with organic or aqueous electrolyte . 96
D.8 FID sensing elements. 96
D.9 FTA sensing elements . 96
D.10 Paramagnetic sensing elements . 97
D.10.1 General . 97
D.10.2 Principle using a dumbbell . 97
D.10.3 Microflow Measuring Principle . 97
D.10.4 Measurement of magnetic susceptibility . 98
D.10.5 Paramagnetic thermal effect . 98
D.11 PID sensing elements . 98

Figures
Figure 1 — Definitions of measuring point, measuring group and measuring location. 14
Figure 2a — Gas detection system plus actuator for safety function . 18
Figure 2b — Gas detection system plus actuator for safety function . 19
Figure 2c — Gas detector with relay output plus actuator for safety function . 20
Figure 2d — Gas detection system plus actuator for safety function . 20
Figure 2e — Gas detection system plus actuator for safety function . 21
Figure 2f — Gas detection system plus actuator for safety function . 22
Figure 2 — Examples for the overall safety function of gas detection systems . 22
Figure 3 — Overview of safety-related system . 26
Figure 4 — Modules of a gas detection system . 28
Figure 5 — Architectures for data communication . 35
Figure 6 — Single and parallel chains . 73
Figure 7 — Handling of complex modules in a redundant structure . 75
Figure C.1 — Step 1 – Linkage of modules. 83
Figure C.2 — Step 2 – Identification of modules necessary for the safety function . 84
Figure C.3 — Step 3 – Elimination of modules and linkages without influence on the safety
function . 84
Figure C.4 — Step 4 (1st loop) – Summarizing of single chains . 84
Figure C.5 — Step 5 (1st loop) – Summarizing of parallel chains . 85
Figure C.6 — Step 6 (1st loop) – Adaptation of block diagram structure . 87
Figure C.7 — Step 4 (2nd loop) – Summarizing of single chains . 87
Figure C.8 — Step 5 (2nd loop) – Summarizing of parallel chains . 87
Figure C.9 — Step 6 (2nd loop) – Adaptation of block diagram structure – No action required . 88
Figure C.10 — Step 4 (3rd loop) – Summarizing of single chains . 88
Figure C.11 — Step 5 (3rd loop) – Summarizing of parallel chains . 88
Figure C.12 — Step 6 (3rd loop) – Adaptation of block diagram structure – No action required . 88
Figure C.13 — Step 4 (4th loop) – Summarizing of single chains – End of procedure . 89
Figure C.14 — Step 1 – Linkages between modules for the example . 89
Figure C.15 — Step 2 – Identification of modules with influence on the safety function . 90
Figure C.16 — Step 3 – Elimination of modules and linkages without influence on the safety
function . 90
Figure C.17 — Step 4 – Summarizing of single chains . 90
Figure C.18 — Step 5 – Summarizing of parallel chains – End of procedure . 90
Figure C.19 — Step 2 – Identification of modules with influence on the safety function . 91
Figure C.20 — Step 3 – Elimination of modules and linkages without influence on the safety
function . 91
Figure C.21 — Step 4 (1st loop) – Summarizing of single chains . 92
Figure C.22 — Step 5 (1st loop) – Summarizing of parallel chains . 92
Figure C.23 — Step 6 (1st loop) – Adaptation of block diagram structure – No action required . 92
Figure C.24 — Step 4 (2nd loop) – Summarizing of single chains – End of procedure . 92
Tables
Table 1 — Fault tolerance for simple modules according to EN 61508–2:2010, (Table 2) . 24
Table 2 — Fault tolerance for complex modules according to EN 61508–2:2010, (Table 3) . 25
Table 3 — Diagnostic measures for program sequence monitoring and clock from EN 61508–2 . 41
Table 4 — Diagnostic measures for memory from EN 61508–2 . 42
Table 5 — List of replaced or not relevant clauses in EN 61508–3:2010 . 50
Table 6 — List of changes to clauses in EN 61508–3:2010 . 51
Table 7 — EN 50402 levels of rigour . 54
Table 8 — EN 50402 software requirements specification (from EN 61508–3:2010, Table A.1) . 55
Table 9 — Semi formal and formal methods (from EN 61508–3:2010, Table B.7) as applied to
Table A.1 . 57
Table 10 — EN 50402 software architecture design (from EN 61508–3:2010, Table A.2) . 58
Table 11 — EN 50402 software design (from EN 61508–3:2010, Table A.3) . 62
Table 12 — EN 50402 software detailed design (from EN 61508–3:2010, Table A.4) . 62
Table 13 — Semi-formal methods (EN 61508–3:2010, Table B.7) as applied to Table A.4 . 64
Table 14 — EN 50402 software module testing and integration (from EN 61508–3:2010, Table A.5) . 65
Table 15 — EN 50402 PE integration (hardware + software) (from EN 61508–3:2010, Table A.6) . 67
Table 16 — EN 50402 software validation (from EN 61508–3:2010, Table A.7) . 68
Table 17 — EN 50402 modification (from EN 61508–3:2010, Table A.8) . 69
Table 18 — EN 50402 software verification (from EN 61508–3:2010, Table A.9) . 70
Table 19 — For low demand mode of operation (see EN 61508–1:2010, 7.6.2.9, Table 2) . 76
Table 20 — For high demand mode of operation or continuous mode of operation
(see EN 61508–1:2010, 7.6.2.9, Table 3) . 76
Table A.1 — Transformation of the SIL-capabilities of EN 50402 to SIL of EN 61508 (all parts) . 80
Table C.1 — Determination of SIL-capability for a parallel chain block (applicable for hardware
only) . 86

European foreword
This document (EN 50402:2017) has been prepared by CLC/SC 31-9 “Electrical apparatus for the detection
and measurement of combustible gases to be used in industrial and commercial potentially explosive
atmospheres” of CLC/TC 31 “Electrical apparatus for potentially explosive atmospheres” and by CLC/TC 216
“Gas detectors”.
The following dates are fixed:
• latest date by which this document has to be (dop) 2018-02-04
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) 2020-02-04
conflicting with this document have to
be withdrawn
This document supersedes EN 50402:2005.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
— In general, the standard is updated to consider the modifications in the second edition of EN 61508 for
hardware and software. Route 2 of the second edition of EN 61508 will not be permitted for gas detection
equipment.
— The standard is updated for the SIL 1 requirements to be in line with the second edition of EN 50271
specifying the minimum requirements for functional safety for performance approved gas detectors, gas
detection apparatus and complete gas detection systems.
— The latest revisions of the metrological standards have been considered.
— SIL 4 has been deleted as being not appropriate to gas detection.
— Clauses 4 and 5 have been updated for more detailed specification.
— Clause 6 for software is new.
— Clauses 7 to 11 are restructured for clarification of requirements and relation to EN 61508.
— Clause 10 is specifying more details for the customer information.
— The former normative Annex D is now Clause 12.
— The former informative Annex A has been deleted. Relevant text was moved to Clauses 7 to 9.
— The new informative Annex D is providing information on failure modes of sensing elements.

Introduction
This European Standard specifies requirements for the functional safety of gas detection systems. It
encompasses criteria for reliability, avoidance of faults and fault tolerance. Functional safety is that part of the
overall safety which relates specifically to the measures required within the gas detection system to avoid or to
handle failures so that the safety function is ensured. This includes not only design and the development
process requirements of the gas detection system but also the information requirements for planning, putting
into operation, maintenance and repair.
This European Standard is dedicated to the manufacturer. Information important for the safe use of the device
(gas detection system) will be specified in the instruction manual.
Gas detection systems will fail to function if dangerous failures occur in the equipment used. Failure to
function will also occur if such systems are not installed or maintained in an appropriate manner. In some
applications, failures of this type will dominate the functional safety achieved. This European Standard is only
targeted at reducing equipment failures to levels appropriate to the application. Users of gas detection
systems will therefore need to ensure installation and maintenance of such systems is carried out according to
the instruction manual. This European Standard does not specify the physical positioning of measuring points
/ locations.
Gas detection systems may differ widely in structure, complexity and performance. They may not be handled
in a uniform manner like low complexity devices, for this reason a general specification of requirements is not
possible.
Gas detection systems therefore need to be divided into functional modules for validation to ensure that
systems which have different structures are handled according to appropriate procedures. A gas detection
system will not normally include all the modules covered by this European Standard. Requirements are
specified for each of these modules in terms of hierarchical levels which represent one of the constituents of
functional safety performance. The hierarchical levels are termed as SIL-capabilities, with SIL-capability 1
representing the minimum and SIL-capability 3 the maximum levels of functional safety to comply with this
European Standard. The SIL-capability of a module is related to the maximum safety integrity level that may
be claimed for a safety function which uses modules of that specified SIL-capability. Modules will be
characterized in terms of their SIL-capability. Information is also required on failure rate characteristics of
modules or related physical components to enable the manufacturer to determine the overall level of
functional safety of a gas detection system. In this way, the manufacturer will take account of both random
failures of hardware components and systematic failures in hardware and software. This European Standard
also specifies the requirements that will enable determination of whether the gas detection system has a low
enough failure rate when used in conjunction with other equipment necessary for functional safety.
This European Standard will enable the functional safety characteristics of the gas detection system to be
determined from the characteristics of its modules and components (see Annex C). This will enable a gas
detection system to be used as a part of an overall safety system. The characterization including the
determination of a SIL-capability and failure rate data will only need to be carried out once for a particular
module or component.
Depending on characterization of each module and component, the properties of each chosen safety function
of the whole gas detection system will be specified. The procedure for determining the SIL-capability of a
safety function of a gas detection system will only need to be repeated for each new combination of modules
and components. Different combinations of equivalent modules may lead to gas detection systems which
reach different SIL-capabilities.
In this way a flexible adoption of the gas detection system into different applications will be possible without
repeating all steps of the validation procedure for every new configuration.
This European Standard does not include requirements for availability which will need to be considered
separately.
This European Standard is dedicated to manufacturers and is applicable to gas detection systems or parts of
them (e.g. gas detection transmitters or gas detection control units) as basis for functional safety testing. It
supplements the requirements of the relevant metrological standards. It should not be confused with
EN 60079–29–3 which is dedicated to system integrators to give guidance for combining gas detection
apparatus with other equipment (e.g. gas processing, filters, valves) not provided by the gas detection
manufacturer but part of a safety function under the responsibility of the system integrator.
1 Scope
This European Standard is applicable to detection and measurement apparatus and systems for flammable or
toxic gases or vapours or oxygen. It covers apparatus intended to measure reliably, gas concentration and to
provide an output signal (alarm and/or measurement signal), the purpose of which is to give a warning of a
potential hazard.
This European Standard is a product standard which is based on EN 61508 (all parts) and for gas detection
systems covers both low and high demand mode at SIL capabilities of 1, 2 or 3 only. Gas detection apparatus
and gas detection systems are developed as generic products. This European Standard covers part of the
phase 10 “realization” of the overall safety lifecycle defined in EN 61508-1:2010, Figure 2. Configuration and
integration into specific applications is not covered by this European Standard.
In the event of conflict between the requirements of this European Standard and those of EN 61508,
EN 50402 will take precedence.
NOTE 1 Applications requiring a SIL capability of 4 for a gas detection system are not practicable.
This European Standard is dedicated mainly to fixed apparatus and systems. However, it can also be applied
to transportable gas detectors which are intended to be used as temporary replacements for fixed apparatus.
This European Standard supplements the requirements of the European Standards for electrical apparatus for
the detection and measurement of flammable gases, vapours (e.g. EN 60079-29-1 or EN 60079-29-4), toxic
gases (e.g. EN 45544) or oxygen (e.g. EN 50104).
NOTE 2 These European Standards are called in the text “metrological standards”.
The examples above show the state of the standardization for industrial applications at the time of publishing
this European Standard. There may be other metrological standards covering other application fields, for
which this European Standard is also applicable.
EN 50271 specifies minimum requirements for apparatus using software and/or digital components. It also
defines additional optional requirements for compliance with SIL 1 in low demand mode operation. EN 50402
includes all requirements of EN 50271.
EN 50402 is also dedicated to apparatus and gas detection systems and/or components and should be used
instead of EN 50271 in the following cases:
— at SIL 1 when the system contains components not covered by EN 50271;
— at SIL 1 high demand mode operation;
— at SIL 2 and SIL 3;
— at all SILs when non-digital based apparatus is used.
Applying the above-mentioned metrological standards will ensure the performance is adequate in normal
operation of a gas detection system. Additionally, the requirements of this European Standard address the
functional safety of gas detection systems and encompass criteria for reliability, fault tolerance and avoidance
of systematic failures. The avoidance and control of systematic failures will be covered by the requirements for
the development processes and techniques and diagnostic measures chosen in the design. This European
Standard will lead to the characterization of the gas detection system by a SIL-capability and related hardware
failure rate representing a hierarchical order of safety levels. This will allow the user to incorporate the gas
detection system into an overall safety system according to the safety integrity levels of EN 61508 (all parts).
This European Standard is applicable for gas detection systems, which may consist of the following functional
units:
— gas-sampling;
— sensor;
— signal transmission;
— input to control unit;
— signal processing in control unit;
— output from control unit.
This European Standard does not specify requirements for the installation and maintenance of gas detection
systems. It also does not specify the physical positioning of measuring points / locations.
This European Standard does not specify which SIL-capability is sufficient for which application.
NOTE 3 The SIL-capability required for an application will be specified by the user (see Clause 9 and Annex A).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
EN 45544-1, Workplace atmospheres — Electrical apparatus used for the direct detection and direct
concentration measurement of toxic gases and vapours — Part 1: General requirements and test methods
EN 45544-2, Workplace atmospheres — Electrical apparatus used for the direct detection and direct
concentration measurement of toxic gases and vapours — Part 2: Performance requirements for apparatus
used for exposure measurement
EN 45544-3, Workplace atmospheres — Electrical apparatus used for the direct detection and direct
concentration measurement of toxic gases and vapours — Part 3: Performance requirements for apparatus
used for general gas detection
EN 45544-4, Workplace atmospheres — Electrical apparatus used for the direct detection and direct
concentration measurement of toxic gases and vapours — Part 4: Guide for selection, installation, use and
maintenance
EN 50104, Electrical apparatus for the detection and measurement of oxygen - Performance requirements
and test methods
EN 50159, Railway applications - Communication, signalling and processing systems - Safety-related
communication in transmission systems
EN 50270, Electromagnetic compatibility — Electrical apparatus for the detection and measurement of
combustible gases, toxic gases or oxygen
EN 50271:2010, Electrical apparatus for the detection and measurement of combustible gases, toxic gases or
oxygen - Requirements and tests for apparatus using software and/or digital technologies
EN 60079-29-1:2016, Explosive atmospheres - Part 29-1: Gas detectors - Performance requirements of
detectors for flammable gases (IEC 60079-29-1:2016)
EN 60079-29-2, Explosive atmospheres — Part 29-2: Gas detectors — Selection, installation, use and
maintenance of detectors for flammable gases and oxygen (IEC 60079-29-2)
EN 60079-29-3, Explosive atmospheres - Part 29-3: Gas detectors - Guidance on functional safety of fixed
gas detection systems (IEC 60079-29-3)
EN 60079-29-4, Explosive atmospheres - Part 29-4: Gas detectors - Performance requirements of open path
detectors for flammable gases (IEC 60079-29-4)
EN 61326-3-1, Electrical equipment for measurement, control and laboratory use - EMC requirements - Part
3-1: Immunity requirements for safety-related systems and for equipment intended to perform safety-related
functions (functional safety) - General industrial applications
EN 61326-3-2, Electrical equipment for measurement, control and laboratory use — EMC requirements —
Part 3-2: Immunity requirements for safety-related systems and for equipment intended to perform safety-
related functions (functional safety) — Industrial applications with specified electromagnetic environment (IEC
61326-3-2)
EN 61508-1:2010, Functional safet
...