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BS EN 60079-28:2015

BS EN 60079-28:2015

$189.07

Explosive atmospheres – Protection of equipment and transmission systems using optical radiation

Published By Publication Date Number of Pages
BSI 2015 46
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This part of IEC 60079 specifies the requirements, testing and marking of equipment emitting optical radiation intended for use in explosive atmospheres. It also covers equipment located outside the explosive atmosphere or protected by a Type of Protection listed in IEC 60079ā€‘0 , but which generates optical radiation that is intended to enter an explosive atmosphere. It covers Groups I, II and III, and EPLs Ga, Gb, Gc, Da, Db, Dc, Ma and Mb.

This standard contains requirements for optical radiation in the wavelength range from 380 nm to 10 Āµm. It covers the following ignition mechanisms:

  • Optical radiation is absorbed by surfaces or particles, causing them to heat up, and under certain circumstances this may 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.

NOTE 1

See a) and d) of the introduction.

This standard 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 standard.

This standard specifies requirements for equipment intended for use under atmospheric conditions.

This standard supplements and modifies the general requirements of IEC 60079ā€‘0 . Where a requirement of this standard conflicts with a requirement of IEC 60079ā€‘0 , the requirement of this standard takes precedence.

This standard applies to optical fibre equipment and optical equipment, including LED and laser equipment, with the exception of the equipment detailed below:

  1. Non-array divergent LEDs used for example to show equipment status or backlight function.

  2. All luminaires (fixed, portable or transportable), hand lights and caplights; intended to be supplied by mains (with or without galvanic isolation) or powered by batteries:

    • with continuous divergent light sources (for all EPLs),

    • with LED light sources (for EPL Gc or Dc only).

    NOTE 2

    Continuous divergent LED light sources for other than EPL Gc or Dc are not excluded from the standard due to the uncertainty of potential ignition concerns regarding high irradiance.

  3. Optical radiation sources for EPL Mb, Gb or Gc and Db or Dc applications which comply with Class 1 limits in accordance with IEC 60825ā€‘1 .

    NOTE 3

    The referenced Class 1 limits are those that involve emission limits below 15 mW measured at a distance from the optical radiation source in accordance with IEC 60825ā€‘1 , with this measured distance reflected in the Ex application.

  4. Single or multiple optical fibre cables not part of optical fibre equipment if the cables:

    • comply with the relevant industrial standards, along with additional protective means, e.g. robust cabling, conduit or raceway (for EPL Gb, Db, Mb, Gc or Dc),

    • comply with the relevant industrial standards (for EPL Gc or Dc).

  5. Enclosed equipment involving an enclosure that fully contains the optical radiation and that complies with a suitable type of protection as required by the involved EPL, with the enclosure complying with one of the following conditions:

    • An enclosure for which an ignition due to optical radiation in combination with absorbers inside the enclosure would be acceptable such as flameproof “d” enclosures ( IEC 60079ā€‘1 ), or

    • An enclosure for which protection regarding ingress of an explosive gas atmosphere is provided, such as pressurized “p” enclosures ( IEC 60079ā€‘2 ), restricted breathing ā€œnRā€ enclosure ( IEC 60079ā€‘15 ), or

    • An enclosure for which protection regarding ingress of an explosive dust atmosphere is provided, such as dust protection “t” enclosures” ( IEC 60079ā€‘31 ), or

    • An enclosure for which protection regarding ingress of absorbers is provided (such as IP 6X enclosures) and where no internal absorbers are to be expected.

NOTE 4

For these scope exclusions based on enclosure constructions, it is anticipated that the enclosures are not opened in the explosive atmosphere, so that ingress is protected.

PDF Catalog

PDF Pages PDF Title
7 English
CONTENTS
9 FOREWORD
13 INTRODUCTION
14 1 Scope
15 2 Normative references
3 Terms and definitions
18 4 General requirements
5 Types of protection
5.1 General
Tables
Table 1 ā€“ EPLs achieved by application of types of protection for optical systems
19 5.2 Requirements for inherently safe optical radiation ā€œop isā€
5.2.1 General
5.2.2 Continuous wave radiation
20 Table 2 ā€“ Safe optical power and irradiance for Group I and II equipment, categorized by Equipment Group and temperature class
Table 3 ā€“ Safe optical power and irradiance for Group III equipment
21 Table 4 ā€“ Safe limit values for intermediate area, Group I or II, constant power, T1 ā€“ T4 atmospheres, equipment Groups IIA, IIB or IIC (Data derived from Figure B.1 including a safety factor)
23 5.2.3 Pulsed radiation
24 5.2.4 Ignition tests
5.2.5 Over-power/energy fault protection
25 5.3 Requirements for protected optical radiation ā€œop prā€
5.3.1 General
5.3.2 Radiation inside optical fibre or cable
26 5.3.3 Radiation inside enclosures
5.4 Optical system with interlock ā€œop shā€
27 6 Type verifications and tests
6.1 Test set-up for ignition tests
6.1.1 General
6.1.2 Test vessel
Figures
Figure 1 ā€“ Optical ignition delay times and safe boundary curve with safety factor of 2
28 6.1.3 Criteria to determine ignition
6.2 Verification of suitability of test set-up for type tests
6.2.1 Reference gas
6.2.2 Reference absorber
6.2.3 Reference test for continuous wave radiation and pulses above 1 s duration
6.2.4 Reference test for pulsed radiation below 1Ā ms pulse duration
29 6.3 Type tests
6.3.1 Ignition tests with continuous wave radiation and pulses above 1 s duration
6.3.2 Ignition tests with single pulses less than 1 ms duration
6.3.3 Tests for pulse trains and pulses from 1Ā ms to 1Ā s duration
6.3.4 Absorber targets for type tests
30 6.3.5 Test acceptance criteria and safety factors
7 Marking
32 Annex A (informative) Reference test data
Table A.1 ā€“ Reference values for ignition tests with a mixture of propane in air at 40 Ā°C mixture temperature
33 Annex B (informative) Ignition mechanisms
35 Table B.1 ā€“ AIT (auto ignition temperature), MESG
(maximum experimental safe gap) and measured ignition powers
of the chosen combustibles for inert absorbers as the target
material (Ī±1 064 nm=83 %, Ī±805 nm=93)3
36 Figure B.1 ā€“ Figure B.1 ā€“ Minimum radiant igniting power with inert absorber target
(Ī±1064 nm=83 %, Ī±805 nm=93 %) and continuous wave-radiation of 1064 nm
37 Figure B.2 ā€“ Minimum radiant igniting power with inert absorber target
(Ī±1 064 nm=83 %, Ī±805 nm=93 %) and continuous wave-radiation
(PTB: 1064 nm, HSL: 805 nm, [8]: 803 nm) for some n-alkanes
Table B.2 ā€“ Comparison of measured minimum igniting optical pulse energy
(Qe,p
i,min) at 90 Ī¼m beam diameter with auto ignition temperatures (AIT) and minimum
ignition energies (MIE) from literature [9] at concentrations in percent by volume (Ļ•)
38 Annex C (normative) Ignition hazard assessment
Figure C.1 ā€“ Ignition hazard assessment
40 Annex D (informative) Typical optical fibre cable design
Figure D.1 ā€“ Example Multi-Fibre Optical Cable Design For Heavy Duty Applications
Figure D.2 ā€“ Typical Single Optical Fibre Cable Design
41 Annex E (normative) Flow diagram for the assessment of pulses
Figure E.1 ā€“ Flow diagram for the assessment of pulses according to 5.2.3
42 Bibliography

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BS EN 60079-28:2015
$189.07