UL Standard for Safety Explosive Atmospheres – Part 28: Protection of Equipment and Transmission Systems Using Optical Radiation
|Publication Date:||15 September 2017|
1DV.1 DR Modification of Clause 1 to replace with the following:
1DV.1.1 DR This standard 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 UL 60079-0, 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.
1DV.1.2 This standard 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 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.
1DV.1.3 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.
1DV.1.4 This standard specifies requirements for equipment intended for use under atmospheric conditions.
1DV.1.5 DR Annex DVF outlines the application of this standard for equipment and transmission systems using optical radiation in areas classified using the Division method.
1DV.1.6 DR This standard supplements and modifies the general requirements of UL 60079-0. Where a requirement of this standard conflicts with a requirement of UL 60079-0, the requirement of this standard takes precedence.
1DV.1.7 DR Where references are made to IEC, IEC/IEEE, ISO, and ISO/IEC standards, the referenced requirements found in these standards shall apply as modified by any applicable US National Differences for that standard (see Clause 2).
1DV.1.8 DR This standard applies to:
1) laser equipment; and
2) optical fibre equipment; and
3) any other convergent light sources or beams where light is focused in one single point within the hazardous area.
NOTE 2 Some optical elements such as lenses and reflectors are able to convert divergent light into a convergent beam.
NOTE 3 In accordance with 1DV.1.9 DR, where the standard does not apply to equipment and transmission systems using optical radiation and therefore any associated certification does not reference UL 60079-28, the certificate or other supporting documentation may have the following statement, modified appropriately:
"In accordance with Clause 1DV.1.9 DR Item X) from the scope of UL 60079-28, this standard does not apply to the output of the optical radiation source with respect to explosion protection."
The reference to "Item X)" above is to be replaced by the actual Item number under Clause 1DV.1.9 DR from the scope of UL 60079-28, e.g. "Item 1)", "Item 2)", "Item 3a)", "Item 3b), "Item 4a)", "Item 4b)", "Item 4c)", "Item 4d)", "Item 4e)".
1DV.1.9 DR This standard does not apply to:
1) laser equipment for EPL Gb or Gc and Db or Dc applications which complies with Class 1 laser product limits in accordance with IEC 60825-1 or laser equipment for EPL Gc and Dc applications which complies with Class I laser product limits in accordance with the US Code of Federal Regulations, 21 CFR Part 1040; or
NOTE 4 The referenced Class 1 or Class I limits are those that involve emission limits below 15 mW measured at a distance from the optical radiation source in accordance with IEC 60825-1 or the US Code of Federal Regulations, 21 CFR Part 1040, respectively, with this measured distance reflected in the Ex application. Class 1 limits are based on normal operating and single fault conditions, as opposed to Class I limits which are only based on normal operating conditions.
2) divergent light sources or beams where light is not focused within the hazardous area; or
3) Single or multiple optical fibre cables not part of optical fibre equipment if the cables:
a) comply with the relevant industrial standards, along with additional protective means, e.g. robust cabling, conduit or raceway (for EPL Gb, Db, Gc or Dc); or
b) comply with the relevant industrial standards (for EPL Gc or Dc).; or
4) Optical radiation sources as defined in 1DV.1.8 DR above where the optical radiation is fully contained in an enclosure complying with one of the followings Types of Protection suitable for the EPL, or the minimum ingress protection rating specified:
a) flameproof "d" enclosures (UL 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.
b) pressurized "p" enclosures (UL 60079-2); or
NOTE 6 A pressurized "p" enclosure is suitable because there is protection against ingress of an explosive atmosphere.
c) restricted breathing "nR" enclosure (UL 60079-15); or
NOTE 7 A restricted breathing "nR" enclosure is suitable because there is protection against ingress of an explosive atmosphere.
d) dust protection "t" enclosures" (UL 60079-31); or
NOTE 8 A dust protection "t" enclosure is suitable because there is protection against ingress of an explosive dust atmosphere.
e) 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 UL 60079-0.
NOTE 9 An enclosure of a minimum ingress protection of IP 6X and complying with "Tests of enclosures" in UL 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.