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.
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.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.

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