EN IEC 60079-28:2026

SLOVENSKI STANDARD
oSIST prEN IEC 60079-28:2024
01-november-2024
Eksplozivne atmosfere - 28. del: Zaščita opreme, ki uporablja optično sevanje, in
sistemov za prenos optičnega sevanja
Explosive atmospheres - Part 28: Protection of equipment and transmission systems
using optical radiation
Explosionsgefährdete Bereiche - Teil 28: Schutz von Geräten und
Übertragungssystemen, die mit optischer Strahlung arbeiten
Atmosphères explosives - Partie 28: Protection du matériel et des systèmes de
transmission utilisant le rayonnement optique
Ta slovenski standard je istoveten z: prEN IEC 60079-28:2024
ICS:
29.260.20 Električni aparati za Electrical apparatus for
eksplozivna ozračja explosive atmospheres
oSIST prEN IEC 60079-28:2024 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

oSIST prEN IEC 60079-28:2024
oSIST prEN IEC 60079-28:2024
31/1793/CDV
COMMITTEE DRAFT FOR VOTE (CDV)
PROJECT NUMBER:
IEC 60079-28 ED3
DATE OF CIRCULATION: CLOSING DATE FOR VOTING:
2024-09-06 2024-11-29
SUPERSEDES DOCUMENTS:
31/1726/CD, 31/1761A/CC
IEC TC 31 : EQUIPMENT FOR EXPLOSIVE ATMOSPHERES
SECRETARIAT: SECRETARY:
United Kingdom Mr Tom Stack
OF INTEREST TO THE FOLLOWING COMMITTEES: HORIZONTAL FUNCTION(S):

ASPECTS CONCERNED:
SUBMITTED FOR CENELEC PARALLEL VOTING NOT SUBMITTED FOR CENELEC PARALLEL VOTING
Attention IEC-CENELEC parallel voting
The attention of IEC National Committees, members of
CENELEC, is drawn to the fact that this Committee Draft
for Vote (CDV) is submitted for parallel voting.
The CENELEC members are invited to vote through the
CENELEC online voting system.
This document is still under study and subject to change. It should not be used for reference purposes.
Recipients of this document are invited to submit, with their comments, notification of any relevant patent rights of which they
are aware and to provide supporting documentation.
Recipients of this document are invited to submit, with their comments, notification of any relevant “In Some Countries” clau ses
to be included should this proposal proceed. Recipients are reminded that the CDV stage is the final stage for submitting ISC
clauses. (SEE AC/22/2007 OR NEW GUIDANCE DOC).

TITLE:
Explosive atmospheres - Part 28: Protection of equipment and transmission systems using optical
radiation
PROPOSED STABILITY DATE: 2029
NOTE FROM TC/SC OFFICERS:
electronic file, to make a copy and to print out the content for the sole purpose of preparing National Committee positions.
You may not copy or "mirror" the file or printed version of the document, or any part of it, for any other purpose without
permission in writing from IEC.

oSIST prEN IEC 60079-28:2024
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1 CONTENTS
3 FOREWORD . 4
4 INTRODUCTION . 7
5 1 Scope . 8
6 2 Normative references . 9
7 3 Terms and definitions . 9
8 4 Types of Protection . 12
9 4.1 General . 12
10 4.2 Requirements for inherently safe optical radiation “op is” . 13
11 4.2.1 Continuous wave radiation . 13
12 4.2.2 Pulsed radiation . 14
13 4.2.3 Over-power/energy fault protection . 16
14 4.3 Requirements for protected optical radiation “op pr” . 16
15 4.3.1 General . 16
16 4.3.2 Radiation inside optical fibre or cable . 17
17 4.3.3 Radiation inside enclosures . 17
18 4.4 Optical system with interlock “op sh” . 17
19 5 Type verifications and tests . 18
20 5.1 Optical detector . 18
21 5.2 Optical power . 19
22 5.3 Optical irradiance . 20
23 6 Marking . 20
24 Annex A (informative) Ignition mechanisms . 22
25 Annex B (informative) Typical optical fibre cable design . 27
26 Annex C (informative) Overview for the assessment of pulsed radiation . 28
27 Bibliography . 29
29 Figure 1 – Optical ignition delay times and safe boundary curve with safety factor of 2 . 18
30 Figure A.1 – Minimum radiant igniting power with inert absorber target (
31 =83 %,  =93 %) and continuous wave-radiation of 1064 nm . 25
nm 805 nm
32 Figure A.2 – Minimum radiant igniting power with inert absorber target
33 ( nm=83 %,  nm=93 %) and continuous wave-radiation (PTB: 1064 nm,
1 064 805
34 HSL: 805 nm, [8]: 803 nm) for some n-alkanes . 26
35 Figure B.1 – Example Multi-Fibre Optical Cable Design For Heavy Duty Applications . 27
36 Figure B.2 – Typical Single Optical Fibre Cable Design . 27
37 Figure C.1 – Flow diagram for the assessment of pulses according to 4.2.2 . 28
39 Table 1 – EPLs achieved by application of Types of Protection for optical systems . 12
40 Table 2 – Safe optical power and irradiance for Group I and II equipment, categorized
41 by Equipment Group and temperature class . 13
42 Table 3 –Safe optical power for Group II equipment for temperature classes T1 to T4 . 14
43 Table 4 – Safe optical power and irradiance for Group III equipment. 14

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44 Table A.1 – AIT (auto ignition temperature), MESG (maximum experimental safe gap)
45 and measured ignition powers of the chosen combustibles for inert absorbers as the
46 target material ( =83 %,  =93) . 24
1 064 nm 805 nm
47 Table A.2 – Comparison of measured minimum igniting optical pulse energy
i,min
48 (Q ) at 90 m beam diameter with auto ignition temperatures (AIT) and
e,p
49 minimum ignition energies (MIE) from literature [9] at concentrations in percent by
50 volume () . 26
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54 INTERNATIONAL ELECTROTECHNICAL COMMISSION
55 ____________
57 EXPLOSIVE ATMOSPHERES –
59 Part 28: Protection of equipment and transmission
60 systems using optical radiation
64 FOREWORD
65 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
66 all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
67 co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
68 in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
69 Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
70 preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
71 may participate in this preparatory work. International, governmental and non-governmental organizations liaising
72 with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for
73 Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
74 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
75 consensus of opinion on the relevant subjects since each technical committee has representation from all
76 interested IEC National Committees.
77 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
78 Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
79 Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
80 misinterpretation by any end user.
81 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
82 transparently to the maximum extent possible in their national and regional publications. Any divergence between
83 any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter.
84 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
85 assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
86 services carried out by independent certification bodies.
87 6) All users should ensure that they have the latest edition of this publication.
88 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
89 members of its technical committees and IEC National Committees for any personal injury, property damage or
90 other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
91 expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
92 Publications.
93 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
94 indispensable for the correct application of this publication.
95 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
96 rights. IEC shall not be held responsible for identifying any or all such patent rights.
97 International Standard IEC 60079-28 has been prepared by MT 60079-28, of IEC technical
98 committee 31 Equipment for explosive atmospheres.
99 This third edition cancels and replaces the second edition published in 2015. This edition
100 constitutes a technical revision.
101 Users of this document are advised that interpretation sheets clarifying the interpretation of this
102 document can be published. Interpretation sheets are available from the IEC webstore and can
103 be found in the “history” tab of the page for each document.
104 The significance of the changes between IEC 60079-28, Edition 3 and IEC 60079-28, Edition 2
105 is as listed below:
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106 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 5.4 to 5.7;
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.
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
107 NOTE 1 The technical changes referred to include the significance of technical changes in the revised IEC
108 Standard, but they do not form an exhaustive list of all modifications from the previous version. More guidance may
109 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 changes: addition of technical requirements
increase of technical requirements
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.
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111 The text of this International Standard is based on the following documents:
FDIS Report on voting
XX/XX/FDIS XX/XX/RVD
113 Full information on the voting for the approval of this International Standard can be found in the
114 report on voting indicated in the above table.
115 The language used for the development of this International Standard is English.
116 This document has been drafted in accordance with the ISO/IEC Directives, Part 2, and
117 developed in accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC
118 Supplement, available at www.iec.ch/members_experts/refdocs. The main document types
119 developed by IEC are described in greater detail at www.iec.ch/publications.
120 The committee has decided that the contents of this document will remain unchanged until the
121 stability date indicated on the IEC website under webstore.iec.ch in the data related to the
122 specific document. At this date, the document will be
123 • reconfirmed,
124 • withdrawn,
125 • replaced by a revised edition, or
126 • amended.
128 The National Committees are requested to note that for this document the stability date
129 is 20XX.
130 THIS TEXT IS INCLUDED FOR THE INFORMATION OF THE NATIONAL COMMITTEES AND WILL BE DELETED
131 AT THE PUBLICATION STAGE.
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133 INTRODUCTION
134 Optical systems in the form of light sources utilizing optical components such as filters or
135 lenses, optical fibers etc. include but are not limited to communications, surveying, sensing and
136 measurement. In material processing, optical radiation of high irradiance is used. Where the
137 installation is inside or close to explosive atmospheres, the radiation from such systems can
138 pass through these atmospheres. Depending on the characteristics of the radiation it might then
139 be able to ignite a surrounding explosive atmosphere. The presence or absence of an additional
140 absorber, such as particles, significantly influences the ignition.
141 There are four possible ignition mechanisms:
142 a) Optical radiation is absorbed by surfaces or particles, causing them to heat up, and under
143 certain circumstances this may allow them to attain a temperature which will ignite a
144 surrounding explosive atmosphere.
145 b) Thermal ignition of a gas volume, where the optical wavelength matches an absorption band
146 of the gas or vapour.
147 c) Photochemical ignition due to photo dissociation of oxygen molecules by radiation in the
148 ultraviolet wavelength range.
149 d) Direct laser induced breakdown of the gas or vapour at the focus of a strong beam,
150 producing plasma and a shock wave both eventually acting as ignition source. These
151 processes can be supported by a solid material close to the breakdown point.
152 The most likely case of ignition occurring in practice with lowest radiation power of ignition
153 capability is case a). Under some conditions for pulsed radiation case d) also will become
154 relevant. These two cases are addressed in this document. Although one should be aware of
155 ignition mechanism b) and c) explained above, they are not addressed in this document due to
156 the very special situation with ultraviolet radiation and with the absorption properties of most
157 gases (see Annex A).
158 This document describes precautions and requirements to be taken when using optical radiation
159 in explosive gas or dust atmospheres.
160 There are optical systems outside the scope of this document because the optical radiation
161 associated with this systems is considered not to be a risk of ignition for the following reasons:
162 – due to low radiated power or divergent light; and
163 – as hot surfaces created due to a too small distance from the radiation source to an absorber
164 which is already considered by general requirements for lighting equipment.
165 When optical systems are associated with electrical Ex Equipment and where the electrical Ex
166 Equipment is located in a hazardous area then other parts of the IEC 60079 series will also
167 apply. This document provides guidance for:
168 – Ignition hazards associated with optical systems in explosive atmospheres as defined in
169 IEC 60079-10-1 and IEC 60079-10-2; and
170 – Control of ignition hazards from Ex Equipment using optical radiation in explosive
171 atmospheres.
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173 EXPLOSIVE ATMOSPHERES –
175 Part 28: Protection of equipment and transmission
176 systems using optical radiation
180 1 Scope
181 This part of IEC 60079 specifies additional requirements for Ex Equipment, Ex associated
182 equipment or Ex Components containing optical systems emitting optical radiation, which is
183 exposed to explosive atmospheres. These additional requirements are applicable for all
184 equipment groups and all Equipment Protection Levels (EPL).
185 This document contains requirements for optical radiation in the wavelength range from 380 nm
186 to 10 µm. It covers the following ignition mechanisms:
187 • Optical radiation is absorbed by surfaces or particles, causing them to heat up, and under
188 certain circumstances this may allow them to attain a temperature which will ignite a
189 surrounding explosive atmosphere.
190 • In rare special cases, direct laser induced breakdown of the gas at the focus of a strong
191 beam, producing plasma and a shock wave both eventually acting as ignition source. These
192 processes can be supported by a solid material close to the breakdown point.
193 NOTE 1 See a) and d) of the introduction.
194 This document applies to
195 i) laser equipment; and
196 ii) optical fibre equipment; and
197 iii) any optical system that converts light into convergent beams with focal points within
198 the hazardous area.
199 This document does not apply to:
200 1) laser equipment for EPL Mb, Gb or Gc and Db or Dc applications which complies with
201 Class 1 limits in accordance with IEC 60825-1; or
202 NOTE 2 The referenced Class 1 limits are those that involve emission limits below 15 mW measured at a
203 distance from the optical radiation source in accordance with IEC 60825-1, with this measured distance reflected
204 in the Ex application. The Class 1 limit values are not considered suitable for igniting an explosive atmosphere.
205 NOTE 3 Compliance with Class 1 limits is typically documented in the form of a datasheet or user manual
206 provided by the manufacturer of the light source.
207 2) Single or multiple optical fibre cables not part of optical fibre equipment if the cables:
208 a) comply with the relevant industrial standards, along with additional protective means, for
209 example robust cabling, conduit or raceway (for EPL Gb, Db, Mb, Gc or Dc); or
210 b) comply with the relevant industrial standards (for EPL Gc or Dc).; or
211 3) Optical radiation sources as defined in i) to iii) above where the optical radiation is fully
212 contained in an enclosure complying with one of the following Types of Protection suitable
213 for the EPL, or the minimum ingress protection rating specified:
214 a) flameproof "d" enclosures (IEC 60079-1); or
215 NOTE 4 A flameproof “d” enclosure is suitable because an ignition due to optical radiation in combination
216 with absorbers inside the enclosure is contained.
217 b) pressurized "p" enclosures (IEC 60079-2); or

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218 NOTE 5 A pressurized “p” enclosure is suitable because there is protection against ingress of an explosive
219 atmosphere.
220 c) restricted breathing “nR” enclosure (IEC 60079-15); or
221 NOTE 6 A restricted breathing “nR” enclosure is suitable because there is protection against ingress of an
222 explosive atmosphere.
223 d) dust protection "t" enclosures" (IEC 60079-31); or
224 NOTE 7 A dust protection “t” enclosure is suitable because there is protection against ingress of an
225 explosive dust atmosphere.
226 e) an enclosure that provides a minimum ingress protection of IP 6X and where no internal
227 absorbers are to be expected and complying with “Tests of enclosures” in IEC 60079 -0.
228 NOTE 8 An enclosure of a minimum ingress protection of IP 6X and complying with “Tests of enclosures”
229 in IEC 60079-0 is suitable because there is protection against the ingress of absorbers. It is anticipated that
230 when the enclosures are opened, entrance of any absorbers is avoided.
231 This document does not cover ignition by ultraviolet radiation and by absorption of the radiation
232 in the explosive mixture itself. Explosive absorbers or absorbers that contain their own oxidizer
233 as well as catalytic absorbers are also outside the scope of this document.
234 This document supplements and modifies the general requirements of IEC 60079-0. Where a
235 requirement of this document conflicts with a requirement of IEC 60079-0, the requirement of
236 this document takes precedence.
237 2 Normative references
238 The following documents are referred to in the text in such a way that some or all of their content
239 constitutes requirements of this document. For dated references, only the edition cited applies.
240 For undated references, the latest edition of the referenced document (including any
241 amendments) applies.
242 IEC 60050, International Electrotechnical Vocabulary
243 IEC 60079-0, Explosive atmospheres – Part 0: Equipment – General requirements
244 IEC 60079-1, Explosive atmospheres – Part 1: Equipment protection by flameproof enclosures
245 "d"
246 IEC 60079-7, Explosive atmospheres – Part 7: Equipment protection by increased safety "e"
247 IEC 60079-11, Explosive atmospheres – Part 11: Equipment protection by intrinsic safety "i"
248 IEC 60079-15, Explosive atmospheres – Part 15: Equipment protection by type of protection
249 "n"
250 IEC 60825-2, Safety of laser products – Part 2: Safety of optical fibre communication systems
251 (OFCS)
252 3 Terms and definitions
253 For the purposes of this document, the following terms and definitions apply.
254 ISO and IEC maintain terminological databases for use in standardization at the following
255 addresses:
256 • IEC Electropedia: available at http://www.electropedia.org/

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257 • ISO Online browsing platform: available at http://www.iso.org/obp
258 NOTE Additional definitions applicable to explosive atmospheres can be found in IEC 60050-426.
259 3.1
260 absorption
261 in a propagation medium, the conversion of electromagnetic wave energy into another form of
262 energy, for instance heat
263 [SOURCE: IEC 60050-731:1991, 731-03-14]
264 3.2
265 beam diameter (or beam width)
266 distance between two diametrically opposed points where the irradiance is a specified fraction
267 of the beam's peak irradiance
268 Note 1 to entry: Most commonly applied to beams that are circular or nearly circular in cross section.
269 [SOURCE: IEC 60050-731:1991, 731-01-35]
270 3.3
271 beam strength
272 optical beam’s power, irradiance, energy, or radiant exposure
273 c
274 3.4
275 fibre bundle
276 assembly of unbuffered optical fibres
277 [SOURCE: IEC 60050-731:1991, 731-04-09]
278 3.5
279 fibre optic terminal device
280 assembly including one or more opto-electronic devices which converts an electrical signal into
281 an optical signal, and/or vice versa, which is designed to be connected to at least one optical
282 fibre
283 Note 1 to entry: A fibre optic terminal device always has one or more integral fibre optic connector(s) or optical
284 fibre pigtail(s).
285 [SOURCE: IEC 60050-731:1991, 731-06-44]
286 3.6
287 optical radiation types of protection
288 3.6.1
289 inherently safe optical radiation
290 “op is”
291 visible or infrared radiation that is incapable of producing sufficient energy under normal or
292 specified fault conditions to ignite a specific explosive atmosphere
293 Note 1 to entry: This definition is analogous to the term “intrinsically safe” applied to electrical circuits.
294 Note 2 to entry: Inherently safe optical radiation means that the visible or infrared radiation is incapable of
295 supplying sufficient energy under normal or specified fault conditions to ignite a specific explosive atmosphere. The
296 concept is a beam strength limitation approach to safety. Ignition by an optically irradiated target absorber requires
297 the least amount of energy, power, or irradiance of the identified ignition mechanisms in the visible and infrared

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298 spectrum. The inherently safe concept applies to unconfined radiation and does not require maintaining an absorber -
299 free environment.
300 3.6.2
301 protected optical radiation
302 “op pr”
303 visible or infrared radiation that is confined inside optical fibre or other transmission medium
304 under normal constructions or constructions with additional mechanical protection based on the
305 assumption that there is no escape of radiation from the confinement
306 3.6.3
307 optical system with interlock
308 “op sh”
309 system to confine visible or infrared radiation inside optical fibre or other transmission medium
310 with interlock cut-off provided to reliably reduce the unconfined beam strength to safe levels
311 within a specified time in case the confinement fails and the radiation becomes unconfined
312 3.7
313 irradiance
314 DEPRECATED: intensity
315 radiant power incident on an element of a surface divided by the area of that element
316 [SOURCE: IEC 60050-731:1991, 731-1-25]
317 3.8
318 light (or visible radiation)
319 optical radiation capable of causing a visual sensation directly on a human being
320 Note 1 to entry: Nominally covering the wavelength in vacuum range of 380 nm to 800 nm.
321 Note 2 to entry: In the laser and optical communication fields, custom and practice in the English language have
322 extended usage of the term light to include the much broader portion of the electromagnetic spectrum that can be
323 handled by the basic optical techniques used for the visible spectrum.
324 [SOURCE: IEC 60050-731:1991, 731-01-04]
325 3.9
326 optical fibre
327 filament shaped optical waveguide made of dielectric materials
328 [SOURCE: IEC 60050-731:1991, 731-02-01])
329 3.10
330 optical fibre cable
331 assembly comprising one or more optical fibres or fibre bundles inside a common covering
332 designed to protect them against mechanical stresses and other environmental influences while
333 retaining the transmission qualities of the fibres
334 [SOURCE: IEC 60050-731:1991, 731-04-01]
335 3.11
336 optical (or radiant) power
337 rate of flow of radiant energy with time
338 [SOURCE: IEC 60050-731:1991, 731-01-22]

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339 3.12
340 optical radiation
341 electromagnetic radiation at wavelengths in vacuum between the region of transition to X -rays
342 and the region of transition to radio waves, that is approximately between 1 nm and 1000 m
343 Note 1 to entry: In the context of this standard, the term “optical” refers to wavelengths ranging from 380 nm to
344 10 m.
345 [SOURCE: IEC 60050-731:1991, 731-01-03, modified (addition of Note 1 to entry)]
346 3.13
347 protected optical fibre cable
348 optical fibre cable protected from releasing optical radiation into the atmosphere during normal
349 operating conditions and foreseeable malfunctions by additional armouring, conduit, cable tray
350 or raceway
351 3.14
352 radiant exposure
353 radiant energy incident on an element of a surface divided by the area of that element
354 3.15
355 optical system
356 arrangement of optical or other components which form elements of a light emitting source
357 Note 1 to entry: The optical system is deemed to include the source, optical components including filters or lenses
358 where these are appropriate.
359 [SOURCE: IEC 60050-845:2020, 845-31-118, modified]
360 4 Types of Protection
361 4.1 General
362 The following three Types of Protection can be applied to prevent ignitions by optical radiation
363 in explosive atmospheres:
364 a) inherently safe optical radiation, Type of Protection “op is”;
365 e) protected optical radiation, Type of Protection “op pr”; and
366 f) optical system with interlock, Type of Protection “op sh”.
367 The EPLs that can be achieved by the application of Types of Protection for optical systems
368 are shown in Table 1.
369 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

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Type(s) of Protection EPLs
Ga, Da, Ma Gb, Db, Mb Gc, Dc
– 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)
No No Yes
– Unprotected fibre optic cable (not “op pr”) + shutdown 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
371 4.2 Requirements for inherently safe optical radiation “op is”
372 4.2.1 Continuous wave radiation
373 For Group I, the optical power or optical irradiance shall not exceed the values listed in Table
374 2.
375 For Group II, the optical power or optical irradiance shall
376 • not exceed the values listed in Table 2, or
377 • not exceed the values for temperature classes T1, T2, T3 and T4 in Table 3.
378 For Group III, the optical power or optical irradiance shall not exceed the values listed in Table
379 4.
380 Table 2 – Safe optical power and irradiance for Group I and II equipment,
381 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
IIA with T1, T2 or T3, and I
 20
 30 mm
No limit to the involved
 5 All atmospheres
irradiated area
oSIST prEN IEC 60079-28:2024
31/1793/CDV -14- IEC 60079-28 ED3 © IEC 2024
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.
383 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
 0,8
 2,9 115
 8
 70  130
2 2
For irradiated areas equal to or above 130 mm the irradiance limit of 5 mW/mm applies (see Table 2).
385 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
Irradiance (no radiated power limit applies) mW/mm  5  5  10
387 Compliance with Table 2, Table 4 or Table 3 shall be based on the following:
388 a) measurement of the maximum optical power in accordance with 5.2; or
389 b) measurement of the maximum optical irradiance in accordance with 5.3. maximum optical
390 irradiance in accordance with 5.3; or
391 c) calculation based on comparison of optical parameters with electrical parameters in
392 accordance with 5.2.
393 4.2.2 Pulsed radiation
394 4.2.2.1 General
395 Optical pulse duration for Gc or Dc equipment may be determined based on modulation
396 frequency and duty cycle ratings specified by the manufacturer. For example, pulse duration
397 (or ‘on-time’) is equal to the product of the period (or ‘time between pulses’) and the duty cycle,
398 with the period being equal to the inverse of the frequency.
399 Optical pulse duration for Ga, Gb, Da, Db, Ma or Mb equipment shall be measured under
400 required fault conditions in accordance with the over-power/energy fault protection criteria
401 required for ‘Optical devices incorporating the inherently safe concept’. An electrical
402 oscilloscope may be used to measure the pulse duration of the voltage at the input to the optical
403 device under each fault condition.
404 The flow diagram in Annex C shows the assessment procedure for Group II.

oSIST prEN IEC 60079-28:2024
IEC 60079-28 ED3 © IEC 2024 -15- 31/1793/CDV

405 4.2.2.2 Optical pulse duration of less than or equal to 1 s for Group II
406 For optical pulse duration of less than 1 ms, as determined in accordance with the applicable
407 EPL, the optical pulse energy shall not exceed the minimum spark ignition energy (MIE) of the
408 respective explosive gas atmosphere.
409 For optical pulse duration from 1 ms to 1 s inclusive, as determined in accordance with the
410 applicable equipment protection level, an optical pulse energy equal to 10 times the MIE of the
411 explosive gas atmosphere shall not be exceeded.
412 For a single pulse, optical pulse energy is equal to the product of the average power and the
413 optical pulse duration of that single pulse.
414 NOTE In accordance with the ‘Comparison of measured minimum igniting optical pulse energy (Qe,pi,min) at 90 m
415 beam diameter with auto ignition temperatures (AIT) and minimum ignition energies (MIE) from literature Table A.2,
416 the applicable minimum spark ignition energy (MIE) is based on the equipment group subdivision.
417 The MIE values for the application of this document are:
418 • Group IIA: 240 J
419 • Group IIB: 82 J
420 • Group IIC: 17 J
421 4.2.2.3 Optical pulse duration greater than 1 s for Group II
422 For optical pulse durations greater than 1 s, the peak power shall be measured in accordance
423 with the ‘Continuous wave radiation’ requirements and shall not exceed the safety levels for
424 continuous wave radiation (see 4.2.1, Table 2 or Table 3). Regardless of the involved EPL,
425 such pulses are considered as continuous wave radiation.
426 4.2.2.4 Additional requirements for optical pulse trains for Group II
427 For optical pulse trains involving pulse duration less than or equal to 1 s, the following shall
428 apply:
429 1) For all repetition rates, compliance with the single pulse criterion according 4.2.2.2 applies
430 for each pulse.
431 2) For repetition rates above 100 Hz, the average power shall not exceed the safety levels for
432 continuous wave radiation in Table 2 or Table 3.
433 For repetition rates at or below 100 Hz, the average power shall not exceed the safety levels
434 for continuous wave radiation in Table 2 or Table 3.
435 4.2.2.5 Additional requirements for optical pulses for Group I and Group III
436 equipment
437 The output parameters of optical sources of equipment for EPL Ma or Mb and Da or Db shall
438 not exceed 0.1 mJ/mm for pulse lasers or pulse light sources with pulse intervals of at least
439 5 s.
440 The output parameters of optical sources of equipment of EPL Dc shall not exceed 0,5 mJ/mm
441 for pulse lasers or pulse light sources.
442 Radiation sources with pulse intervals of less than 5 s are regarded as continuous wave
443 sources.
oSIST prEN IEC 60079-28:2024
31/1793/CDV -16- IEC 60079-28 ED3 © IEC 2024
444 4.2.3 Over-power/energy fault protection
445 4.2.3.1 General
446 Optical devices incorporating the inherently safe concept shall provide over -power/energy fault
447 protection to prevent excessive beam strengths in explosive atmospheres. The risk/hazard
448 analysis shall determine if additional limitation is required. The failure modes of the optical
449 source, the driver circuitry, and the intended EPL shall be considered during normal operation
450 and during fault conditions to determine the requirement for additional limitation.
451 4.2.3.2 Self-limiting optical sources
452 Optical sources such as laser diodes, light-emitting diodes (LED) or lamps will fail if over-heated
453 under over-power fault conditions. The thermal failure characteristic of certain optical sources
454 provides the necessary over-power fault protection if a test of 10 samples shows that a defined
455 fail-safe shutdown or foldback will occur (see 5.2 and 5.3). The highest obtained optical output
456 power value of the 10 samples is to be taken as the maximum power or irradiance value. The
457 thermal failure characteristic of such low power optical sources is acceptable to provide
458 adequate over-power protection for any EPL.
459 4.2.3.3 Optical sources requiring power limiting circuitry
460 Where the beam strength of the optical device is limited by the driver circuitry, the faults to be
461 considered apply to that circuitry and not to the optical device itself.
462 An LED current limited by the driver circuitry to values within the data sheet specifications is
463 not considered to exceed the maximum forward voltage given in the data sheet for that current.
464 Faults to be considered include the opening or shorting of any component that could impact the
465 beam strength of the optical device. Printed wiring board traces need not be considered for
466 shorting because they comply with the creepage distance, clearance or through solid insulation
467 requirements of the relevant general industrial standard.
468 Electrical circuits such as current and/or voltage limiters placed between the optical source and
469 the electrical power source may provide over-power fault protection. Electrical over-power fault
470 protection shall be provided to the degree necessary for the intended EPL (see for example
471 IEC 60079-11 for an example methodology for conducting the fault analysis, but other
472 methodologies may also be applied). For Ga, Da or Ma equipment, current and/or voltage
473 limiters shall provide over-power fault protection in normal operation and after one or two
474 countable faults are applied to the current and/or voltage limiter. For Gb, Db or Mb equipment,
475 over-power fault protection shall be provided in normal operation and after one countable fault
476 is applied to the current and/or voltage limiter. For Gc or Dc equipment the rated electrical
477 values shall be taken without assuming any fault.
478 4.3 Requirements for protected optical radiation “op pr”
479 4.3.1 General
480 This concept requires radiation to be confined inside optical fibre or other transmission medium
481 based on the assumption that there is no escape of radiation from the confinement. In this cas
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