UL-60079-28:2017 pdf free download – STANDARD FOR SAFETY Explosive Atmospheres一Part 28: Protection of Equipment and Transmission Systems Using Optical Radiation.
3.12
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 qualities of the fibres
[SOURCE: IEC 60050-731:1991, 731 -04-01]
3.13
optical (or radiant) power
rate of flow of radiant energy with time
[SOURCE: IEC 60050-731:1991, 731 -01-22]
3.14
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 1000 pm
Note 1 to entry: In the context of this standard, the term “optical” refers to wavelengths ranging from 380 nm to 10 pm.
[SOURCE: IEC 60050-731 :1991, 731-01-03, modified (addition of Note 1 to entry)]
3.15
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
3.16
radiant exposure
radiant energy incident on an element of a surface divided by the area of that element
4 General requirements
Electrical equipment and electrical Ex Components (e.g. fibre optic terminal devices) shall comply with one or more of the specific electrical equipment protection technique standards listed in lEG 60079-0 suitable for the application if intended to be installed inside the hazardous area.
Optical equipment shall be subjected to a formally documented ignition hazard assessment using the principles stated in Annex C. This assessment shall be made to determine which possible optical ignition source can arise in the equipment under consideration, and which measures may need to be taken to mitigate the risk of ignition.
If a source of optical radiation is inside an enclosure providing a protection of minimum IP 6X, after the tests specified in IEC 60079-0 for enclosures, the ingress of absorbing targets from the outside of the enclosure need not be taken into consideration, but the existence of internal targets shall be taken into consideration. However where the optical radiation may leave such an enclosure, the requirements of this standard also apply to the emitted optical radiation.
5.2 Requirements for inherently safe optical radiation “op is”
5.2.1 General
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.
5.2.2 Continuous wave radiation
5.2.2.1 General
Either optical power or optical irradiance shall not exceed the values listed in Table 2, Table 3 and Table 4, categorized by equipment group and temperature class.
As an alternative to compliance with Table 2 the following options are available:
— For irradiated surface areas above 400 mm2, the maximum temperature measured on the irradiated surface shall be used to establish the temperature class, with no limit on irradiance. The temperature measurement shall consider the possibility of nonhomogeneous beam strength.