UL 60079-2-2017 pdf download

UL 60079-2-2017 pdf download.Explosive Atmospheres – Part 2: Equipment Protection by Pressurized Enclosure “p”.
3.20
Level of Protection pxb
pressurized enclosure providing Equipment Protection Level Mb. Gb or Db
Note 1 to entry This permits unprotected equipment to be installed wi*i the pressuriz•d .ncloswe except tor sately devices, see
323.
3.21
Level of Protection pyb
pressurized enclosure providing Equipment Protection Level Gb or Db with Equipment Protection Level Gc or Dc internal to the pressurized enclosure
Note I to entry: This permits Equipment Proteclion Level Gc or Dc equipment to be eletalled wlttwi the pi-exsunzed endoewe, except Sot satety devices, see 323
3.22
Level of Protection pzc
pressurized enclosure providing Equipment Protection Level Ge or Dc
Note 1 to entry- This permits unprotected equipment to be installed wrIm the preswirrzed enclosure except tar salely devices, see
323.
3.23
safety device
device used to implement or maintain the integrity of the type of protection
3.24
lower flammable limit
LFL
volume fraction of flammable gas or vapour in air below which an explosive gas atmosphere will not tomi, expressed as a percentage (see IEC 60079-20-1)
Note 1 to entry- Ths also known as Lower Explosive unit (LEL).
3.25
upper flammable limit Un.
volume traciton of flammable gas or vapour In air above which an explosive gas atmosphere will not form, expiessed as a percentage (see IEC 60079-20-1)
Note 1 to entry This is also known as Uer Explosive Lenht (UEL).
4 Protection levels
Protection by pressunzation is subdivided Into three Levels of Protection (pxb’, pyb and pzc”) which are selected based upon the Equipment Protection Level required (Mb. Gb. Db, Ge or DC), whether there is the potential for an internal release, and whether the equipment within the pressurized enclosure is ignition-capable: see Table 1. The Level of Protection then delines design criteria for the pressunzed enclosure and the pressurization system: see Table 2,
5.3.4 Group II and Group Ill pressurized enclosures with static pressurization
Doors and covers shall not be capable of being opened readily without the use 01 a key or tool
5.3.5 Group II and Group Ill Level of Protection pxb
A pressurized enclosure that contains hot parts requiring a cool-down period shall not be capable of being opened reaofy without the use of a key or tool.
5.3.6 Group II and Group Ill Door and Cover warning
To prevent the ignition of an explosive gas atmosphere or an explosive dust atmosphere which may be present when an enclosure is opened, doors and covers shall be marked:
WARNING — DO NOT OPEN WHEN AN EXPLOSIVE ATMOSPHERE IS PRESENT. 5.4 Mechanical strength
The pressurized enclosure, ducts if any, and their connecting parts shall withstand a pressure equal to 1.5 times the maximum overpressure specified by the manufacturer for normal service with all outlets closed with a minimum of 200 Pa.
5.4DV.1 DE Modification of Clause 5.4, second paragraph to replace with the following
5.4DV.1 .1 If a pressure can occur in service that can cause a deformation of the enclosure, ducts if any, or connecting parts, a safety device shall be fitted to limit the maximum internal overpressure to a level below that which could adversely affect the type of protection. If the manufacturer does not provide the safety device, the-eert#ieate,umber shell Include the ‘X’ suffix In accordance wIth the marking requirements of IEC 60079-0 and the Specific Conditions of Use listed on the certiticete in accordance with UL 60079-0 shall detail the necessary information required by the user to ensure conformity with the requirements of this standard.
5.5 Group I and Group II Apertures, partitions, compartments and internal components
5.5.1 Apertures and partitions shall be located In such a way that effective purging Is ensured.
Unpurged areas can be eliminated by the proper location of the protective gas supply inlet and outlet and by consideration of the effect of partitions.
For gases or vapours that are heavier than air the inlet for the protective gas should be near the top of the pressurized enclosure, with the outlet near the bottom of the enclosure.
For gases or vapours that are lighter than air, the iniet for the protective gas should be near the bottom of the enclosure, with the outlet near the top of the enclosure.
Locating inlets and outlets at opposite sides of the enclosure promotes cross ventilation.
Internal partitions (for example. circuit boards) should be located In such a way that the flow of protective gas is not obstructed. The use of a manifold or baffles can also improve the flow around obstructions.
The number of apertures should be chosen with regard to the design of the equipment, particuLar consideration being given to the purging of sub-compartments into which the equipment might be divided.