SIST EN IEC 60079-28:2026

Explosive atmospheres - Part 28: Protection of equipment and transmission systems using optical radiation (IEC 60079-28:2025)

IEC 60079-28:2025 specifies additional requirements for Ex Equipment, Ex associated equipment or Ex Components containing optical systems emitting optical radiation, which is exposed to explosive atmospheres. These additional requirements are applicable for all equipment groups and all Equipment Protection Levels (EPL).
This document contains requirements for optical radiation in the wavelength range from 380 nm to 10 µm. It covers the following ignition mechanisms:
• Optical radiation is absorbed by surfaces or particles, causing them to heat up, and under certain circumstances this might allow them to attain a temperature which will ignite a surrounding explosive atmosphere.
• In rare special cases, direct laser induced breakdown of the gas at the focus of a strong beam, producing plasma and a shock wave both eventually acting as ignition source. These processes can be supported by a solid material close to the breakdown point.
• Annex A provides guidance when considering ignition mechanisms that influence the hazard of optics in explosive atmospheres.
This document applies to
a) laser equipment; and
b) optical fibre equipment; and
c) any optical system that converts light into convergent beams with focal points within the hazardous area only.
This document does not apply to:
d) laser equipment for EPL Mb, Gb, Gc, Db or Dc applications which complies with Class 1 limits in accordance with IEC 60825-1; or
e) Single or multiple optical fibre cables not part of optical fibre equipment if the cables:
1) comply with the relevant industrial standards for optical fibre cables, along with additional protective means, for example robust cabling, conduit or raceway (for EPL Gb, Db, Mb, Gc or Dc); or
2) comply with the relevant industrial standards for optical fibre cables (for EPL Gc or Dc); or
f) Optical radiation sources as defined in i) to iii) above where the optical radiation is fully contained in an enclosure complying with one of the following Types of Protection suitable for the EPL, or the minimum ingress protection rating specified:
1) flameproof "d" enclosures (IEC 60079-1); or
2) pressurized "p" enclosures (IEC 60079-2); or
3) restricted breathing "nR" enclosure (IEC 60079-15); or
4) dust protection "t" enclosures" (IEC 60079-31); or
5) an enclosure that provides a minimum ingress protection of IP 6X and where no internal absorbers are to be expected and complying with "Tests of enclosures" in IEC 60079-0.
This document does not cover ignition by ultraviolet radiation and by absorption of the radiation in the explosive mixture itself. Explosive absorbers or absorbers that contain their own oxidizer as well as catalytic absorbers are also outside the scope of this document.
This document supplements and modifies the general requirements of IEC 60079-0. Where a requirement of this document conflicts with a requirement of IEC 60079-0, the requirement of this document takes precedence.
This third edition cancels and replaces the second edition published in 2015. This edition constitutes a technical revision

Explosionsgefährdete Bereiche - Teil 28: Schutz von Geräten und Übertragungssystemen, die mit optischer Strahlung arbeiten (IEC 60079-28:2025)

Atmosphères explosives - Partie 28: Protection du matériel et des systèmes de transmission utilisant le rayonnement optique (IEC 60079-28:2025)

IEC 60079-28:2025
spécifie les exigences supplémentaires applicables aux appareils Ex, aux appareils associés Ex ou aux composants Ex contenant des systèmes optiques émettant un rayonnement optique, qui sont exposés à des atmosphères explosives. Ces exigences supplémentaires s'appliquent à tous les groupes d'appareils et à tous les niveaux de protection du matériel (EPL, Equipment Protection Levels).
Le présent document contient les exigences relatives aux rayonnements optiques dans la plage de longueurs d'onde comprise entre 380 nm et 10 µm. Il couvre les mécanismes d'allumage suivants:
– le rayonnement optique est absorbé par les surfaces ou particules, provoquant leur échauffement et, dans certaines circonstances, celles-ci peuvent atteindre une température qui amorce l'inflammation de l'atmosphère explosive environnante;
– dans certains cas rares particuliers, le craquage direct d'un gaz par laser, au point de focalisation d'un faisceau puissant, produisant un plasma et une onde de choc, les deux agissant en définitive comme source d'inflammation. Ces processus peuvent prendre naissance dans un matériau solide proche de son point de craquage;
– Annexe A fournit des recommandations lors de l'examen des mécanismes d'inflammation qui influencent le danger optique dans les atmosphères explosives.
Le présent document s'applique:
a) aux équipements laser; et
b) aux équipements à fibres optiques; et
c) à tout système optique qui convertit la lumière en faisceaux convergents avec des points focaux situés dans la zone dangereuse uniquement.
Le présent document ne s'applique pas:
d) aux équipements laser pour les applications EPL Mb, Gb, Gc, Db ou Dc qui satisfont aux limites de Classe 1 conformément à l'IEC 60825-1;
e) aux câbles à fibres optiques simples ou multiples ne faisant pas partie des équipements à fibres optiques si les câbles:
1) satisfont aux normes industrielles pertinentes pour les câbles à fibres optiques, ainsi que les moyens de protection supplémentaires, comme les câblages robustes, les conduits ou les chemins (pour EPL Gb, Db, Mb, Gc ou Dc); ou
2) satisfont aux normes industrielles pertinentes pour les câble à fibres optiques (pour EPL Gc ou Dc); ou
f) aux sources de rayonnement optique telles que définies aux points a) à c) ci-dessus, lorsque le rayonnement optique est totalement contenu dans une enveloppe satisfaisant à l'un des modes de protection suivants adaptés à l'EPL, ou à la caractéristique assignée minimale de protection contre les pénétrations spécifiée:
1) les enveloppes "d" antidéflagrantes (IEC 60079-1); ou
2) des enveloppes "p" sous pression (IEC 60079-2); ou
3) une enveloppe "nR" à respiration limitée (IEC 60079-15); ou
4) les enveloppes "t" de protection contre la poussière (IEC 60079-31); ou
5) une enveloppe qui fournit une protection minimale contre la pénétration IP 6X et lorsqu'aucun absorbeur interne n'est attendu, et qui satisfait aux "Essais des enveloppes" de l'IEC 60079-0.
Le présent document ne couvre pas l'inflammation par rayonnement ultraviolet et par absorption du rayonnement dans le mélange explosif lui-même. Les absorbeurs explosifs ou absorbeurs qui contiennent leur propre oxydant/comburant de même que les absorbeurs catalytiques sont également hors du domaine d'application du présent document.
Le présent document complète et modifie les

Eksplozivne atmosfere - 28. del: Zaščita opreme, ki uporablja optično sevanje, in sistemov za prenos optičnega sevanja (IEC 60079-28:2025)

IEC 60079-28:2025 določa dodatne zahteve za Ex opremo, Ex povezano opremo ali Ex komponente, ki vsebujejo optične sisteme, ki oddajajo optično sevanje in so izpostavljeni eksplozivnim atmosferam. Te dodatne zahteve veljajo za vse skupine opreme in vse ravni zaščite opreme (EPL).
Ta dokument vsebuje zahteve za optično sevanje v valovni dolžini od 380 nm do 10 µm. Pokriva naslednje mehanizme vžiga:
- Optično sevanje se absorbira na površinah ali delcih, kar povzroči njihovo segrevanje, in pod določenimi pogoji lahko dosežejo temperaturo, ki bo vžgala okoliško eksplozivno atmosfero.
- V redkih posebnih primerih neposreden laserski induciran razpad plina v fokusu močnega žarka, ki proizvaja plazmo in udarni val, ki oba delujeta kot vir vžiga. Ti procesi so lahko podprti s trdnim materialom blizu točke razpada.
- Priloga A nudi smernice pri obravnavi mehanizmov vžiga, ki vplivajo na nevarnost optike v eksplozivnih atmosferah.
Ta dokument se uporablja za
a) lasersko opremo; in
b) opremo z optičnimi vlakni; in
c) kateri koli optični sistem, ki pretvarja svetlobo v konvergentne žarke s fokalnimi točkami znotraj nevarnega območja.
Ta dokument se ne uporablja za:
d) lasersko opremo za aplikacije EPL Mb, Gb, Gc, Db ali Dc, ki ustreza mejam razreda 1 v skladu z IEC 60825-1; ali
e) enojne ali večkratne optične vlakenske kable, ki niso del opreme z optičnimi vlakni, če kabli:
1) ustrezajo ustreznim industrijskim standardom za optične vlakenske kable, skupaj z dodatnimi zaščitnimi sredstvi, na primer robustno kabliranje, cevovod ali kanal (za EPL Gb, Db, Mb, Gc ali Dc); ali
2) ustrezajo ustreznim industrijskim standardom za optične vlakenske kable (za EPL Gc ali Dc); ali
f) vire optičnega sevanja, kot so opredeljeni v i) do iii) zgoraj, kjer je optično sevanje popolnoma zaprto v ohišju, ki ustreza enemu od naslednjih tipov zaščite, primernih za EPL, ali minimalni stopnji zaščite pred vdorom, določeni:
1) ognjevarno ohišje "d" (IEC 60079-1); ali
2) tlačno ohišje "p" (IEC 60079-2); ali
3) ohišje z omejenim dihanjem "nR" (IEC 60079-15); ali
4) ohišje za zaščito pred prahom "t" (IEC 60079-31); ali
5) ohišje, ki zagotavlja minimalno zaščito pred vdorom IP 6X in kjer ni pričakovati notranjih absorberjev ter ustreza "Testom ohišij" v IEC 60079-0.
Ta dokument ne pokriva vžiga z ultravijoličnim sevanjem in absorpcijo sevanja v sami eksplozivni zmesi. Eksplozivni absorberji ali absorberji, ki vsebujejo svoj oksidant, kot tudi katalitski absorberji, so prav tako zunaj področja uporabe tega dokumenta.
Ta dokument dopolnjuje in spreminja splošne zahteve IEC 60079-0. Kjer zahteva tega dokumenta nasprotuje zahtevi IEC 60079-0, ima prednost zahteva tega dokumenta.
Ta tretja izdaja preklicuje in nadomešča drugo izdajo, objavljeno leta 2015. Ta izdaja predstavlja tehnično revizijo.

General Information

• Status: Published
• Public Enquiry End Date: 24-Nov-2024
• Publication Date: 13-Apr-2026
• ICS: 29.260.20 - Electrical apparatus for explosive atmospheres
• Technical Committee: EXP - Product for explosive atmospheres
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 24-Feb-2026
• Due Date: 01-May-2026
• Completion Date: 14-Apr-2026
• Directive: Harmonized Standard2014/34/EU - Directive 2014/34/EU Of The European Parliament And Of The Council of 26 February 2014 on the harmonisation of the laws of the Member States relating to equipment and protective systems intended for use in potentially explosive atmospheres (recast)
• Mandate: M/596 - [C(2023)4798] Commission Implementing Decision of 20.7.2023 on a standardisation request as regards equipment and protective systems intended for use in potentially explosive atmospheres in support of Directive 2014/34/EU (ATEX) of the European Parliament and of the Council
• Ref Project: EN IEC 60079-28:2026 - Explosive atmospheres - Part 28: Protection of equipment and transmission systems using optical radiation

Relations

• Refers: SIST EN ISO 7380:2004 - Hexagon socket button head screws (ISO 7380:2004)
• Effective Date: 09-Feb-2026
• Refers: SIST EN IEC 60079-0:2018 - Explosive atmospheres - Part 0: Equipment - General requirements
• Effective Date: 03-Feb-2026
• Refers: SIST EN 60079-7:2016 - Explosive atmospheres -- Part 7: Equipment protection by increased safety "e" (IEC 60079-7:2015)
• Effective Date: 03-Feb-2026
• Refers: SIST EN 60079-1:2015 - Explosive atmospheres - Part 1: Equipment protection by flameproof enclosures "d"
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 60079-11:2025 - Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i" (IEC 60079-11:2023 + COR1:2023)
• Effective Date: 03-Feb-2026
• Refers: SIST EN IEC 60079-15:2019 - Explosive atmospheres - Part 15: Equipment protection by type of protection "n"
• Effective Date: 03-Feb-2026
• Referred By: kSIST FprEN IEC 61757:2026 - Fibre optic sensors - Generic specification
• Effective Date: 31-Mar-2026
• Referred By: SIST EN IEC 62246-4:2023 - Reed switches - Part 4: Application in conjunction with Magnetic Actuator used for Magnetic Sensing Devices
• Effective Date: 20-Feb-2026
• Referred By: SIST EN 16314:2013 - Gas meters - Additional functionalities
• Effective Date: 20-Feb-2026
• Referred By: SIST EN 12405-2:2013 - Gas meters - Conversion devices - Part 2: Energy conversion
• Effective Date: 20-Feb-2026
• Referred By: SIST-TP CLC/TR 60079-33:2015 - Explosive atmospheres - Part 33: Equipment protection by special protection 's '(IEC 60079-33:2012)
• Effective Date: 20-Feb-2026
• Referred By: SIST EN 17673:2022 - Protective clothing - Protection against heat and flame - Requirements and test methods for garments with integrated smart textiles and non textile elements
• Effective Date: 20-Feb-2026
• Referred By: SIST EN IEC 60079-14:2025 - Explosive atmospheres - Part 14: Electrical installation design, selection and installation of equipment, including initial inspection (IEC 60079-14:2024)
• Effective Date: 20-Feb-2026
• Referred By: SIST EN 50849:2018 - Sound systems for emergency purposes
• Effective Date: 20-Feb-2026
• Referred By: SIST EN IEC 61757-1:2018 - Fibre optic sensors - Part 1: Generic specification (IEC 61757:2018)
• Effective Date: 20-Feb-2026

Overview

kSIST FprEN IEC 60079-28:2025, titled "Explosive atmospheres - Part 28: Protection of equipment and transmission systems using optical radiation," is an essential standard published by the CLC (European Committee for Electrotechnical Standardization). This standard specifies additional safety requirements tailored for equipment, associated devices, and components that emit optical radiation within explosive atmospheres. Covering optical radiation in the wavelength range from 380 nm to 10 µm, it addresses risks inherent to systems such as lasers and optical fiber equipment prone to ignite explosive gases or dust.

The standard updates and replaces the second edition from 2015, introducing technical revisions to enhance safety for all equipment groups and Equipment Protection Levels (EPL). This latest edition is part of the broader IEC 60079 series focused on electrical apparatus for explosive atmospheres.

Key Topics

• Scope and Applicability: The standard applies to explosive atmospheres where optical radiation-based equipment is used - including laser equipment, optical fiber systems, and convergent-beam optical setups with focal points in hazardous zones. It excludes systems with radiation fully enclosed in flameproof or pressurized housings, and certain fiber optic cables meeting specified mechanical protection criteria.

• Ignition Mechanisms: EN IEC 60079-28 identifies key optical ignition risks:

  • Thermal ignition through absorption: Optical radiation heating surfaces or particles to temperatures that may ignite the surrounding explosive atmosphere.
  • Direct laser-induced breakdown: High-energy laser pulses causing plasma and shock waves that can act as ignition sources.
  • The standard covers these prominent mechanisms while excluding ultraviolet radiation-induced ignition and gaseous absorption ignition due to their limited scope here.

• Types of Protection: Defines protective methodologies such as inherently safe optical radiation ("op is"), protected optical radiation ("op pr"), and optical systems with interlock ("op sh"). Each type includes tailored limits on continuous and pulsed radiation power, safe optical power thresholds, and fault protection.

• Verification and Testing: Details test procedures for optical detectors, measurement of optical power and irradiance, ensuring compliance with safety criteria before equipment deployment.

• Marking Requirements: Provides guidelines for labeling equipment with pertinent protection information to ensure traceability and operational safety.

Applications

kSIST FprEN IEC 60079-28:2025 is specifically designed for industries that utilize optical technologies within explosive atmospheres, such as:

• Oil and Gas: Protection of systems involving fiber optic sensors, laser measurement and communication equipment in petrochemical plants, offshore platforms, and refineries.

• Mining and Processing: Safe deployment of optical equipment in dust-prone environments, preventing ignition while leveraging optical sensing and communication.

• Manufacturing: Use of laser material processing tools and optical transmission systems in hazardous production areas.

• Industrial Automation: Incorporation of optical radiation-based detection and control equipment within explosive atmospheres to enhance operational safety and reliability.

By adhering to this standard, manufacturers and operators ensure both technical compliance and reduced risk of accidents caused by ignition from optical radiation sources.

Related Standards

kSIST FprEN IEC 60079-28:2025 builds upon and supplements several notable standards, including:

• IEC 60079-0: General requirements for electrical equipment in explosive atmospheres. EN IEC 60079-28 takes precedence over IEC 60079-0 when conflicting requirements exist.

• IEC 60079-1: Requirements for flameproof enclosures ("d" type), referenced for equipment fully enclosing optical radiation sources.

• IEC 60079-2: Covers pressurized enclosures ("p" type), relevant for optical equipment inside pressurized housings.

• IEC 60825-1: Governs laser safety, with specific exclusions in EN IEC 60079-28 for laser equipment compliant with Class 1 limits under this standard.

• IEC 60079-15 and IEC 60079-31: Address restricted breathing enclosures ("nR") and dust protection enclosures ("t") which may house optical radiation sources.

Together, these standards create a comprehensive framework ensuring safe operation of optical equipment in explosive atmospheres.

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Keywords: EN IEC 60079-28, explosive atmospheres, optical radiation protection, laser safety, optical fiber equipment, ignition prevention, hazardous area equipment, Equipment Protection Level (EPL), IEC 60079 series, flameproof enclosures, explosive gases and dust.

Standards Content (Sample)

SLOVENSKI STANDARD
01-maj-2026
Eksplozivne atmosfere - 28. del: Zaščita opreme, ki uporablja optično sevanje, in
sistemov za prenos optičnega sevanja (IEC 60079-28:2025)
Explosive atmospheres - Part 28: Protection of equipment and transmission systems
using optical radiation (IEC 60079-28:2025)
Explosionsgefährdete Bereiche - Teil 28: Schutz von Geräten und
Übertragungssystemen, die mit optischer Strahlung arbeiten (IEC 60079-28:2025)
Atmosphères explosives - Partie 28: Protection du matériel et des systèmes de
transmission utilisant le rayonnement optique (IEC 60079-28:2025)
Ta slovenski standard je istoveten z: EN IEC 60079-28:2026
ICS:
29.260.20 Električni aparati za Electrical apparatus for
eksplozivna ozračja explosive atmospheres
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60079-28

NORME EUROPÉENNE
EUROPÄISCHE NORM February 2026
ICS 29.260.20 Supersedes EN 60079-28:2015; EN 60079-
28:2015/A11:2024
English Version
Explosive atmospheres - Part 28: Protection of equipment and
transmission systems using optical radiation
(IEC 60079-28:2025)
Atmosphères explosives - Partie 28 : Protection du matériel Explosionsgefährdete Bereiche - Teil 28: Schutz von
et des systèmes de transmission utilisant le rayonnement Geräten und Übertragungssystemen, die mit optischer
optique Strahlung arbeiten
(IEC 60079-28:2025) (IEC 60079-28:2025)
This European Standard was approved by CENELEC on 2025-12-26. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2026 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60079-28:2026 E

European foreword
The text of document 31/1887/FDIS, future edition 3 of IEC 60079-28, prepared by TC 31 "Equipment
for explosive atmospheres" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 60079-28:2026.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2027-02-28
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2029-02-28
document have to be withdrawn
This document supersedes EN 60079-28:2015 and all of its amendments and corrigenda (if any).
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.
This document is read in conjunction with EN IEC 60079-0.
This document has been prepared under a standardization request addressed to CENELEC by the
European Commission. The Standing Committee of the EFTA States subsequently approves these
requests for its Member States.
For the relationship with EU Legislation, see informative Annex ZZ, which is an integral part of this
document.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60079-28:2025 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standard indicated:
IEC 60079-2 NOTE Approved as EN 60079-2
IEC 60079-10-1 NOTE Approved as EN IEC 60079-10-1
IEC 60079-10-2 NOTE Approved as EN 60079-10-2
IEC 60079-31 NOTE Approved as EN 60079-31
IEC 61508 (series) NOTE Approved as EN 61508 (series)
IEC 60825-1 NOTE Approved as EN 60825-1
IEC 61511 (series) NOTE Approved as EN 61511 (series)
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod),
the relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is
available here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60079-0 - Explosive atmospheres – Part 0: Equipment EN IEC 60079-0 2018
– General requirements
+ AC 2020-
+ A11 2024
IEC 60079-1 - Explosive atmospheres – Part 1: Equipment EN 60079-1 2014
protection by flameproof enclosures "d"
+ AC 2018-
+ A11 2024
IEC 60079-7 - Explosive atmospheres - Part 7: Equipment EN 60079-7 2015
protection by increased safety "e"
+ A1 2018
+ A11 2024
IEC 60079-11 - Explosive atmospheres – Part 11: EN 60079-11 2012
Equipment protection by intrinsic safety "i"
IEC 60079-15 - Explosive atmospheres – Part 15: EN IEC 60079-15 2019
Equipment protection by type of protection
"n"
IEC 60825-2 - Safety of laser products – Part 2: Safety of EN 60825-2 2004
optical fibre communication systems (OFCS)
+ A1 2007
+ A2 2010
Annex ZZ
(informative)
Relationship between this European Standard and the Essential
Requirements of 2014/34/EU [2014 OJ L96] aimed to be covered
This European Standard has been prepared under a Commission’s standardization request as
regards equipment and protective systems intended for use in potentially explosive atmospheres in
support of Directive 2014/34/EU “M/596 C(2023)4798 final” to provide one voluntary means of
conforming to the essential health and safety requirements of Directive 2014/34/EU of 26 February
2014 on the harmonisation of the laws of the Member States relating to equipment and protective
systems intended for use in potentially explosive atmospheres (recast).
Once this standard is cited in the Official Journal of the European Union under that Directive,
compliance with the normative clauses of this standard given in Table ZZ.1 confers, within the limits of
the scope of this standard, a presumption of conformity with the corresponding essential requirements
of that Directive, and associated EFTA regulations.
Table ZZ.1 — Correspondence between this European standard and Annex II of Directive
2014/34/EU [2014 OJ L96]
Essential Requirements of Clause(s) / sub-clause(s) of this
Remarks / Notes
2014/34/EU EN
1.0.1 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
1.0.2. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
1.0.3.  Not covered
1.0.4. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
1.0.5. 6
1.0.6. 4.3.2, 5.2
1.1.1.  Not covered
1.1.2.  Not covered
1.1.3.  Not covered
1.2.1. 4.1, 4.2, 4.3, 4.4,
1.2.2. 4.1, 4.2, 4.3, 4.4,
1.2.3.  Not covered
1.2.4.  Not covered
1.2.5.  Not covered
1.2.6.  Not covered
1.2.7.  Not covered
1.2.8.  Not covered
1.2.9.  Not covered
1.3.1. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
1.3.2.  Not covered
1.3.3.  Not covered
Essential Requirements of Clause(s) / sub-clause(s) of this
Remarks / Notes
2014/34/EU EN
1.3.4.  Not covered
1.3.5.  Not covered
1.4.1.  Not covered
1.4.2.  Not covered
1.5.1  Not covered
1.5.2.  Not covered
1.5.3.  Not covered
1.5.4.  Not covered
1.5.5.  Not covered
1.5.6.  Not covered
1.5.7.  Not covered
1.5.8.  Not covered
1.6.1.  Not covered
1.6.2.  Not covered
1.6.3.  Not covered
1.6.4.  Not covered
1.6.5.  Not covered
2.0.1 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.0.2 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.1.1. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.1.2. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.2.1 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.2.2 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.3.1. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
2.3.2. 4.1, 4.2, 4.3, 4.4, 5.1, 5.2, 5.3
3.  Not covered
WARNING 1 — Presumption of conformity stays valid only as long as a reference to this European
standard is maintained in the list published in the Official Journal of the European Union. Users of this
standard should consult frequently the latest list published in the Official Journal of the European
Union.
WARNING 2 — Other Union legislation may be applicable to the product(s) falling within the scope of
this standard.
IEC 60079-28 ®
Edition 3.0 2025-11
INTERNATIONAL
STANDARD
Explosive atmospheres -
Part 28: Protection of equipment and transmission systems using optical
radiation
ICS 29.260.20  ISBN 978-2-8327-0789-0

IEC 60079-28:2025-11(en)
IEC 60079-28:2025 © IEC 2025
CONTENTS
FOREWORD . 3
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 8
3 Terms and definitions . 8
4 Types of Protection . 11
4.1 General . 11
4.2 Requirements for inherently safe optical radiation "op is" . 12
4.2.1 Continuous wave radiation . 12
4.2.2 Pulsed radiation . 14
4.2.3 Over-power/energy fault protection . 15
4.3 Requirements for protected optical radiation "op pr" . 16
4.3.1 General . 16
4.3.2 Radiation inside optical fibre or cable . 16
4.3.3 Radiation entering or leaving enclosures . 16
4.4 Optical system with interlock "op sh" . 17
5 Type verifications and tests. 18
5.1 Optical detector . 18
5.2 Optical power . 18
5.3 Optical irradiance . 19
6 Marking . 20
,
Annex A (informative) Ignition mechanisms . 21
Annex B (informative) Typical optical fibre cable design . 27
Annex C (informative) Overview for the assessment of pulsed radiation . 28
Bibliography . 29

Figure 1 – Optical ignition delay times and safe boundary curve with safety factor of 2 . 17
Figure A.1 – Minimum radiant igniting power with inert absorber target
(α = 83 %, α = 93 %) and continuous wave-radiation of 1 064 nm . 25
1 064 nm 805 nm
Figure A.2 – Minimum radiant igniting power with inert absorber target
(α = 83 %, (α = 93 %) and continuous wave-radiation (PTB: 1 064 nm,
1 064 nm 805 nm
HSL: 805 nm, [19]: 803 nm) for some n-alkanes . 26
Figure B.1 – Example Multi-Fibre Optical Cable Design For Heavy Duty Applications . 27
Figure B.2 – Typical Single Optical Fibre Cable Design . 27
Figure C.1 – Flow diagram for the assessment of pulses according to 4.2.2 . 28

Table 1 – EPLs achieved by application of Types of Protection for optical systems . 12
Table 2 – Safe optical power and irradiance for Group I and II equipment, categorized by
Equipment Group and temperature class . 13
Table 3 – Safe optical power for Group II equipment for temperature classes T1 to T4. 13
Table 4 – Safe optical power and irradiance for Group III equipment . 13
Table A.1 – AIT (auto ignition temperature), MESG (maximum experimental safe gap) and
measured ignition powers of the chosen combustibles for inert absorbers as the target
material (α = 83 %, α = 93) . 23
1 064 nm 805 nm
IEC 60079-28:2025 © IEC 2025
i,min
Table A.2 – Comparison of measured minimum igniting optical pulse energy (Q ) at
e,p
90 μm beam diameter with auto ignition temperatures (AIT) and minimum ignition
energies (MIE) from literature [20] at concentrations in percent by volume (φ) . 26

IEC 60079-28:2025 © IEC 2025
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Explosive atmospheres -
Part 28: Protection of equipment and transmission
systems using optical radiation

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all
national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-
operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition
to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly
Available Specifications (PAS) and Guides (hereafter referred to as "IEC Publication(s)"). Their preparation is
entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate
in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also
participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO)
in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all interested
IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence between
any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services
carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or other
damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising
out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s).
IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof.
As of the date of publication of this document, IEC had not received notice of (a) patent(s), which may be required
to implement this document. However, implementers are cautioned that this may not represent the latest information,
which may be obtained from the patent database available at https://patents.iec.ch. IEC shall not be held responsible
for identifying any or all such patent rights.
IEC 60079-28 has been prepared by IEC technical committee 31 Equipment for explosive
atmospheres. It is an International Standard.
This International Standard is to be used in conjunction with IEC 60079-0.
Users of this document are advised that interpretation sheets clarifying the interpretation of this
document can be published. Interpretation sheets are available from the IEC webstore and can be
found in the "history" tab of the page for each document.
This third edition cancels and replaces the second edition published in 2015. This edition
constitutes a technical revision.
IEC 60079-28:2025 © IEC 2025
The significance of the changes between the current edition of IEC 60079-28 (Edition 3) and
IEC 60079-28 (Edition 2) is as listed below:
Significance of changes with respect to IEC 60079-28:2015
Type
Significant Changes Clause Minor and Extension Major
editorial technical
changes changes
Ignition test is removed Clause 6;
Annex A C1
(of Ed.2)
Clarification of the applicability of IEC 60079-28 for laser
equipment, optical fibre equipment and any optical system
1 X
that converts light into convergent beams with focal points
within the hazardous area only.
Change title from "Radiation inside enclosures" to
"Radiation entering or leaving enclosures" and text
4.3.3 X
reworded
The structure of this document was modified; new clause
5 X
"Type verifications and tests" added
New subclause "Optical detector" 5.1 X
The possibility to do calculations for the assessment of
5.2 X
optical power is clarified
Additional examples for the marking are added. 6 X
Annex C removed Annex C X
(of Ed.2)
NOTE 1 The technical changes referred to include the significance of technical changes in the revised IEC Standard,
but they do not form an exhaustive list of all modifications from the previous version. More guidance can be found by
referring to the Redline Version of the standard.
Explanation of the types of significant changes:
a) Definitions
1) Minor and editorial clarification
changes:
decrease of technical requirements
minor technical change
editorial corrections
These are changes which modify requirements in an editorial or a minor technical way. They
include changes of the wording to clarify technical requirements without any technical
change, or a reduction in level of existing requirement.
2) Extension: addition of technical options
These are changes which add new or modify existing technical requirements, in a way that
new options are given, but without increasing requirements for equipment that was fully
compliant with the previous standard. Therefore, these will not have to be considered for
products in conformity with the preceding edition.
3) Major technical addition of technical requirements
changes:
increase of technical requirements
IEC 60079-28:2025 © IEC 2025
These are changes to technical requirements (addition, increase of the level or removal)
made in a way that a product in conformity with the preceding edition will not always be able
to fulfil the requirements given in the later edition. These changes have to be considered for
products in conformity with the preceding edition. For these changes additional information
is provided in clause B) below.
NOTE 2 These changes represent current technological knowledge. However, these changes should not
normally have an influence on equipment already placed on the market.
b) Information about the background of changes
C1 The alternative option of an ignition test is removed because questions have been
raised regarding the repeatability of the verification test across test labs. Additionally,
it was identified that an application of a safety factor is not sufficiently defined and
not possible to apply for real test samples.

The text of this International Standard is based on the following documents:
Draft Report on voting
31/1887/FDIS 31/1933/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available at
www.iec.ch/members_experts/refdocs. The main document types developed by IEC are described
in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 60079 series, published under the general title Explosive atmospheres,
can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the specific
document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
IEC 60079-28:2025 © IEC 2025
INTRODUCTION
Optical systems in the form of light sources utilizing optical components such as filters or lenses,
optical fibres etc. include but are not limited to communications, surveying, sensing and
measurement. In material processing, optical radiation of high irradiance is used. Where the
installation is inside or close to explosive atmospheres, the radiation from such systems can pass
through these atmospheres. Depending on the characteristics of the radiation it might then be able
to ignite a surrounding explosive atmosphere. The presence or absence of an additional absorber,
such as particles, significantly influences the ignition.
There are four possible ignition mechanisms:
a) Optical radiation is absorbed by surfaces or particles, causing them to heat up, and under
certain circumstances this might allow them to attain a temperature which will ignite a
surrounding explosive atmosphere.
b) Thermal ignition of a gas volume, where the optical wavelength matches an absorption band
of the gas or vapour.
c) Photochemical ignition due to photo dissociation of oxygen molecules by radiation in the
ultraviolet wavelength range.
d) Direct laser induced breakdown of the gas or vapour at the focus of a strong beam, producing
plasma and a shock wave both eventually acting as ignition source. These processes can be
supported by a solid material close to the breakdown point.
The most likely case of ignition occurring in practice with lowest radiation power of ignition
capability is case a). Under some conditions for pulsed radiation, case d) also will become relevant.
These two cases are addressed in this document. Although it is important that users be aware of
ignition mechanisms b) and c) explained above, they are not addressed in this document due to
the very special situation with ultraviolet radiation and with the absorption properties of most gases
(see Annex A).
This document describes precautions and requirements to be taken when using optical radiation
in explosive gas or dust atmospheres.
There are optical systems outside the scope of this document because the optical radiation
associated with these systems is considered not to be a risk of ignition for the following reasons:
– due to low radiated power or divergent light; and
– as hot surfaces created due to a too small distance from the radiation source to an absorber
which is already considered by general requirements for lighting equipment.
When optical systems are associated with electrical Ex Equipment and where the electrical Ex
Equipment is located in a hazardous area then other parts of the IEC 60079 series will also apply.
This document provides guidance for:
– Ignition hazards associated with optical systems in explosive atmospheres as defined in
IEC 60079-10-1 and IEC 60079-10-2; and
– Control of ignition hazards from Ex Equipment using optical radiation in explosive atmospheres.

IEC 60079-28:2025 © IEC 2025
1 Scope
This part of IEC 60079 specifies additional requirements for Ex Equipment, Ex associated
equipment or Ex Components containing optical systems emitting optical radiation, which is
exposed to explosive atmospheres. These additional requirements are applicable for all equipment
groups and all Equipment Protection Levels (EPL).
This document contains requirements for optical radiation in the wavelength range from 380 nm to
10 µm. It covers the following ignition mechanisms:
– Optical radiation is absorbed by surfaces or particles, causing them to heat up, and under
certain circumstances this might allow them to attain a temperature which will ignite a
surrounding explosive atmosphere.
– In rare special cases, direct laser induced breakdown of the gas at the focus of a strong beam,
producing plasma and a shock wave both eventually acting as ignition source. These processes
can be supported by a solid material close to the breakdown point.
– Annex A provides guidance when considering ignition mechanisms that influence the hazard
of optics in explosive atmospheres.
NOTE 1 See a) and d) of the Introduction.
This document applies to
a) laser equipment; and
b) optical fibre equipment; and
c) any optical system that converts light into convergent beams with focal points within the
hazardous area only.
This document does not apply to:
d) laser equipment for EPL Mb, Gb, Gc, Db or Dc applications which complies with Class 1 limits
in accordance with IEC 60825-1; or
NOTE 2 The Class 1 limits are below 15 mW measured at a distance from the optical radiation source in accordance
with IEC 60825-1, with this measured distance reflected in the Ex application. The Class 1 limit values are not
considered capable of igniting an explosive atmosphere.
NOTE 3 Compliance with Class 1 limits is typically documented in the form of a datasheet or user manual provided
by the manufacturer of the laser equipment.
e) Single or multiple optical fibre cables not part of optical fibre equipment if the cables:
1) comply with the relevant industrial standards for optical fibre cables, along with additional
protective means, for example robust cabling, conduit or raceway (for EPL Gb, Db, Mb, Gc
or Dc); or
2) comply with the relevant industrial standards for optical fibre cables (for EPL Gc or Dc); or
f) Optical radiation sources as defined in a) to c) above where the optical radiation is fully
contained in an enclosure complying with one of the following Types of Protection suitable for
the EPL, or the minimum ingress protection rating specified:
NOTE 4 Fully contained means that no optical radiation can escape.
1) flameproof "d" enclosures (IEC 60079-1); or
NOTE 5 A flameproof "d" enclosure is suitable because an ignition due to optical radiation in combination with
absorbers inside the enclosure is contained.
2) pressurized "p" enclosures (IEC 60079-2); or
NOTE 6 A pressurized "p" enclosure is suitable because there is protection against ingress of an explosive
atmosphere.
IEC 60079-28:2025 © IEC 2025
3) restricted breathing "nR" enclosure (IEC 60079-15); or
NOTE 7 A restricted breathing "nR" enclosure is suitable because there is protection against ingress of an
explosive atmosphere.
4) dust protection "t" enclosures" (IEC 60079-31); or
NOTE 8 A dust protection "t" enclosure is suitable because there is protection against ingress of an explosive
dust atmosphere.
5) an enclosure that provides a minimum ingress protection of IP 6X and where no internal
absorbers are to be expected and complying with "Tests of enclosures" in IEC 60079-0.
NOTE 9 An enclosure of a minimum ingress protection of IP 6X and complying with "Tests of enclosures" in
IEC 60079-0 is suitable because there is protection against the ingress of absorbers. It is anticipated that when
the enclosures are opened, entrance of any absorbers is avoided.
This document does not cover ignition by ultraviolet radiation and by absorption of the radiation in
the explosive mixture itself. Explosive absorbers or absorbers that contain their own oxidizer as
well as catalytic absorbers are also outside the scope of this document.
This document supplements and modifies the general requirements of IEC 60079-0. Where a
requirement of this document conflicts with a requirement of IEC 60079-0, the requirement of this
document takes precedence.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any amendments)
applies.
IEC 60079-0, Explosive atmospheres - Part 0: Equipment - General requirements
IEC 60079-1, Explosive atmospheres - Part 1: Equipment protection by flameproof enclosures "d"
IEC 60079-7, Explosive atmospheres - Part 7: Equipment protection by increased safety "e"
IEC 60079-11, Explosive atmospheres - Part 11: Equipment protection by intrinsic safety "i"
IEC 60079-15, Explosive atmospheres - Part 15: Equipment protection by type of protection "n"
IEC 60825-2, Safety of laser products - Part 2: Safety of optical fibre communication systems
(OFCS)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
NOTE Additional definitions applicable to explosive atmospheres can be found in IEC 60050-426.
IEC 60079-28:2025 © IEC 2025
3.1
absorption
conversion of electromagnetic wave energy into another form of
energy, for instance heat
3.2
beam diameter
beam width
distance between two diametrically opposed points where the irradiance is a specified fraction of
the beam's peak irradiance
Note 1 to entry: The concept is most commonly applied to beams that are circular or nearly circular in cross-section.
[SOURCE: IEC 60050-731:1991/AMD6:2021-04, 731-01-35, modified - Note 2 to entry deleted.]
3.3
beam strength
optical beam's power, irradiance, energy, or radiant exposure
3.4
fibre bundle
assembly of unbuffered optical fibres
[SOURCE: IEC 60050-731:1991, 731-04-09]
3.5
fibre optic terminal device
assembly including one or more opto-electronic devices which converts an electrical signal into an
optical signal, and/or vice versa, which is designed to be connected to at least one optical fibre
Note 1 to entry: A fibre optic terminal device always has one or more integral fibre optic connector(s) or optical fibre
pigtail(s).
[SOURCE: IEC 60050-731:1991, 731-06-44]
3.6
optical radiation types of protection
3.6.1
inherently safe optical radiation
"op is"
visible or infrared radiation that is incapable of producing sufficient energy under normal or
specified fault conditions to ignite a specific explosive atmosphere
Note 1 to entry: This definition is analogous to the term "intrinsically safe" applied to electrical circuits.
Note 2 to entry: Inherently safe optical radiation means that the visible or infrared radiation is incapable of supplying
sufficient energy under normal or specified fault conditions to ignite a specific explosive atmosphere. The concept is a
beam strength limitation approach to safety. Ignition by an optically irradiated target absorber requires the least amount
of energy, power, or irradiance of the identified ignition mechanisms in the visible and infrared spectrum. The inherently
safe concept applies to unconfined radiation and does not require maintaining an absorber-free environment.
3.6.2
protected optical radiation
"op pr"
visible or infrared radiation that is confined inside optical fibre or other transmission medium under
normal constructions or constructions with additional mechanical protection based on the
assumption that there is no escape of radiation from the confinement
IEC 60079-28:2025 © IEC 2025
3.6.3
optical system with interlock
"op sh"
system to confine visible or infrared radiation inside optical fibre or other transmission medium
with interlock cut-off provided to reliably reduce the unconfined beam strength to safe levels within
a specified time in case the confinement fails and the radiation becomes unconfined
3.7
irradiance
DEPRECATED: intensity
radiant power incident on an element of a surface divided by the area of that element
[SOURCE: IEC 60050-731:1991, 731-01-25]
3.8
light
visible radiation
optical radiation capable of causing a visual sensation directly on a human being
Note 1 to entry: Nominally covering the wavelength in vacuum range of 380 nm to 800 nm.
Note 2 to entry: In the laser and optical communication fields, custom and practice in the English language have
extended usage of the term light to include the much broader portion of the electromagnetic spectrum that can be handled
by the basic optical techniques used for the visible spectrum.
[SOURCE: IEC 60050-731:1991, 731-01-04]
3.9
optical fibre
waveguide shaped as a filament, made of dielectric materials for guiding optical waves
[SOURCE: IEC 60050-151:2019, 151-12-35]
3.10
optical fibre cable
assembly comprising one or more optical fibres or fibre bundles inside a common covering
designed to protect them against mechanical stresses and other environmental influences while
retaining the transmission quality of the fibres
[SOURCE: IEC 60050-731:1991, 731-04-01]
3.11
optical power
radiant power
time rate of flow of radiant energy with time
[SOURCE: IEC 60050-731:1991, 731-01-22]
3.12
optical radiation
electromagnetic radiation at wavelengths in vacuum between the region of transition to X-rays and
the region of transition to radio waves, that is approximately between 1 nm and 1 mm
Note 1 to entry: In the context of this document, the term "optical" refers to wavelengths ranging from 380 nm to 10 μm.
[SOURCE: IEC 60050-731:1991, 731-01-03, modified - addition of Note 1 to entry.]
IEC 60079-28:2025 © IEC 2025
3.13
protected optical fibre cable
optical fibre cable protected from releasing optical radiation into the atmosphere during normal
operating conditions and foreseeable malfunctions by additional armouring, conduit, cable tray or
raceway
3.14
radiant exposure
radiant energy incident on an element of a surface divided by the area of that element
3.15
optical system
arrangement of optical or other components which form elements of a light emitting source
Note 1 to entry: The optical system is deemed to include the source, optical components including filters or lenses
where these are appropriate.
[SOURCE: IEC 60050-845:2020, 845-31-118, modified - "sign" replaced by "source" in definition,
Note 1 to entry modified.]
4 Types of Protection
4.1 General
The following three Types of Protection can be applied to prevent ignitions by optical radiation in
explosive atmospheres:
a) inherently safe optical radiation, Type of Protection "op is";
b) protected optical radiation, Type of Protection "op pr"; and
c) optical system with interlock, Type of Protection "op sh".
The EPLs that can be achieved by the application of Types of Protection for optical systems are
shown in Table 1.
IEC 60079-28:2025 © IEC 2025
Table 1 – EPLs achieved by application of Types of Protection for optical systems
Type(s) of Protection EPLs
Ga, Da, Ma Gb, Db, Mb Gc, Dc
Inherently safe optical radiation "op is" (see 4.2)
– safe with two faults or using optical source based on the Yes Yes Yes
thermal failure characteristic (see 4.2.3)
– safe with one fault or using optical source based on the thermal No Yes Yes
failure characteristic (see 4.2.3)
– safe in normal operation No No Yes
Protected fibre optic media with ignition capable beam "op pr"
(see 4.3)
– with additional mechanical protection No Yes Yes
– according to fibre manufacturers specification for normal No No Yes
industrial use, but without additional mechanical protection
1)
Gb, Db, Mb Gc, Dc
Ga , Ma
Fibre optic media with ignition capable beam interlocked in case of
fibre breakage "op sh" (see 4.4)
2) 1) 1)
– Protected fibre optic cable "op pr" for Gb/ Mb + shutdown
Yes Yes Yes
functional safety system based on ignition delay time of the
explosive gas atmosphere
2)
– Protected fibre optic cable "op pr" for Gc/Dc + shutdown No Yes
Yes
functional safety system based on eye protection delay times
(IEC 60825-2)
– Unprotected fibre optic cable (not "op pr") + shutdown No No Yes
functional safety system based on eye protection delay times
(IEC 60825-2)
None (unconfined, ignition capable beam) No No No
1)
Only applicable for Group I and Group IIA temperature class T1 and T2
2)
Shutdown system safe with one fault

4.2 Requirements for inherently safe optical radiation "op is"
4.2.1 Continuous wave radiation
For Group I, the optical power or optical irradiance shall not exceed the values listed in Table 2.
For Group II,
– the optical power or optical irradiance shall not exceed the values listed in Table 2, or
– for temperature classes T1, T2, T3 and T4, the optical power shall not exceed the values listed
in Table 3.
For Group III, the optical power or optical irradiance shall not exceed the values listed in Table 4.
IEC 60079-28:2025 © IEC 2025
Table 2 – Safe optical power and irradiance for Group I and II equipment,
categorized by Equipment Group and temperature class
Optical radiation sources with Can be used for the Remarks
following explosive
Radiated power Irradiance
atmospheres
(temperature classes in
(no irradiance limit (no radiated power limit
combination with
applies) applies)
equipment groups)
mW
mW/mm
No limit to the involved
≤ 150 IIA with T1, T2 or T3, and I
irradiated area
IIA, IIB independent of T-
No limit to the involved
≤ 35 Class, IIC with T1, T2, T3
irradiated area
or T4, and I
No limit to the involved
≤ 15 All atmospheres
irradiated area
Irradiated areas limited to
≤ 20 IIA with T1, T2 or T3, and I
≤ 30 mm
No limit to the involved
≤ 5 All atmospheres
irradiated area
NOTE For "op is", the use of the term 'temperature class' when applying this table does not relate to the maximum
temperature measured on the equipment. Instead, it relates to the ignition properties of the gases associated with
the various equipment groups.
Table 3 – Safe optical power for Group II equipment for temperature classes T1 to T4
limited irradiated area Maximum radiated power value
mW
mm
–3
< 4 * 10
–3
≥ 4 * 10
–2
≥ 1,8 * 10
–2
≥ 4 * 10
≥ 0,2 80
≥ 0,8 100
≥ 2,9 115
≥ 8 200
≥ 70 < 130 400
2 2
For irradiated areas equal to or above 130 mm the irradiance limit of 5 mW/mm applies (see Table 2).

Table 4 – Safe optical power and irradiance for Group III equipment
Equipment Group IIIA, IIIB and IIIC
EPL Da Db Dc
Radiated power (no irradiance limit applies) mW ≤ 35 ≤ 35 ≤ 35
≤ 5 ≤ 5 ≤ 10
Irradiance (no radiated power limit applies) mW/mm

IEC 60079-28:2025 © IEC 2025
Compliance with Table 2, Table 4 or Table 3 shall be based on the following:
a) measurement of the maximum optical power in accordance with 5.2; or
b) measurement of the maximum optical irradiance in accordance with 5.3; or
c) calculation based on comparison of optical parameters with electrical parameters in
accordance with 5.2.
4.2.2 Pulsed radiation
4.2.2.1 General
Optical pulse duration for Gc or Dc equipment may be determined based on modulation frequency
and duty cycle ratings specified by the manufacturer. For example, pulse duration (or 'on-time') is
equal to the product of the period (or 'time between pulses') and the duty cycle, with the period
being equal to the inverse of the frequency.
Optical pulse duration for Ga, Gb, Da, Db, Ma or Mb equipment shall be measured under required
fault conditions in accordance with the over-power/energy fault protection criteria required for
'Optical devices incorporating the inherently safe concept'. An electrical oscilloscope may be used
to measure the pulse durati
...