IEC 60079-28-2015 pdf download

IEC 60079-28-2015 pdf download.Explosive atmospheres – Part 28: Protection of equipment and transmission systems using optical radiation.
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 IEC 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 Types of protection
5.1 General
Three types of protection can be applied to prevent ignitions by optical radiation in explosive atmospheres. These types of protection encompass the entire optical system.
These types of protection are:
a) inherently safe optical radiation, type of protection op isa,
b) protected optical radiation, type of protection op pr, and
c) optical system with interlock , type of protection op sh”
Where the ignition hazard assessment given in Annex C shows that ignition due to optical radiation may be possible, the principles of using the types of protection shown in Table 1 shall be applied.
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 u 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.
— For limited irradiated areas not greater than 130 mm2. maximum radiated power values other than those as permitted by Table 2 for temperature classes Ti, T2. T3 and T4 and Groups IlA. lIB or lIC are detailed in Table 4.
— Passing the ignition tests in accordance to with 5.2.4.IEC 60079-28 pdf download.