UL-60079-2:2017 pdf free download – STANDARD FOR SAFETY Explosive Atmospheres一Part 2: Equipment Protection by Pressurized Enclosure “p”.
6.2 For Level of Protection “pxb” or Level of Protection “pyb”
6.2DV DR Modification of Clause 6.2 to replace with the following:
The temperature class shall be based on the higher of the following temperatures:
a) the hottest external surface of the enclosure; or
b) the hottest internal component surface.
Exception: An internal component may exceed the marked temperature class if
i) it complies with the relevant “small component” requirements of IEC J,
60079-0, or
ii) the pressurized enclosure is Level of Protection “pxb” and complies with the requirements for opening times in IEC 60079-0. Appropriate measures shall be taken to prevent, if pressurization ceases, any explosive gas atmosphere which may exist making contact with the hot component surface before it has cooled below the permitted maximum value.
This may be achieved either by the design and construction of the joints of the pressurized enclosure and ducts or by other- means, for example, by bringing auxiliary ventilation systems into operation or by arranging that the hot surface within the pressurized enclosure is in a gas-tight or encapsulated housing.
NOTE Examples of “appropriate measures” Include but are not limited to the design and construction of the loints of the pressurized enclosure and ducts or by bringing auxiliary ventilation systems into operation or by placing the hot surface within the pressurized enclosure in a gas-tight or encapsulated housing.
For Level of Protection “pyb”, hot ignition-capable parts in normal operation are not permitted within the enclosure.
6.3 For Level of Protection “pzc”
The temperature class shall be based on the hottest external surface of the enclosure.
In determining temperature class, account should be taken of any internal equipment with its own explosion protection, which may remain energized when the pressurization system is switched off. 7 Safety provisions and safety devices (except for static pressurization)
7.1 Suitability of safety devices for hazardous area
7.1 DV DE Modification of Clause 7.1 to replace with the following:
All safety devices used to reduce the likelihood of electrical equipment protected by pressurization from causing ignition shall themselves not be capable of causing ignition (see 7.15) or shall be mounted outside the hazardous area.
If a regulator is provided and if it is of a type that a single failure mode will put full inlet pressure on the regulator outlet, then a means (e.g. relief vent) shall be provided that will limit the internal pressure of an enclosure to a defined value. This value is to be stated in the instructions and established by either test or calculation. If multiple regulators or relief vents are provided as options, then the value for each set of available regulator/relief vent options shall be determined.
The pressurization system shall be tested to verify correct operation.
7.4.2 Pressurization systems for Level of Protection “pyb”.
The pressurization system shall include: a means for controlling the minimum overpressure, (e.g. a regulator), a means to verify the minimum overpressure, (e.g. a pressure sensor) and an automatic safety device all in accordance with 7.11.
If a regulator is provided and if it is of a type that a single failure mode will put full inlet pressure on the regulator outlet, then a means (e.g. relief vent) shall be provided that will limit the internal pressure of an enclosure to a defined value. This value is to be stated in the instructions and established by either test or calculation. If multiple regulators or relief vents are provided as options, then the value for each set of available regulator/relief vent options shall be determined.