A space in which, due to the presence of flammable substances such as gases, vapours, mists or dusts in the air, an explosive atmosphere can occur is called a potentially explosive atmosphere.
In potentially explosive atmospheres, there is a need for explosion-proof solutions and intrinsically safe equipment.
Workplaces where explosive atmospheres may occur. are classified with regard to explosion risk zones, as required by § 5.1 of the Regulation of the Minister of Economy of 8 July 2010. "on minimum requirements for safety and hygiene at work related to the possibility of occurrence of an explosive atmosphere in the workplace" (Journal of Laws 2010, No. 138, item 931).
We distinguish between zones for gases, vapours and liquids/dust, powders and fibres:
Zone 0/20 - explosive atmosphere is present continuously or frequently
Zone 1/21 - explosive atmospheres may occasionally occur
Zone 2/22 - explosive atmospheres do not occur under normal operating conditions or, if they do occur, they persist for a short period of time
group I - equipment intended for use in mines with methane hazards
group II - equipment intended for use in areas other than mines with methane hazards
Categories of equipment ex
Within group II:
Category 1 - equipment providing a very high level of protection, intended for most hazardous locations (zones 0)
Category 2 - equipment offering a high level of protection and intended for zones 1 and 2
Category 3 - equipment providing a normal level of protection, suitable for use in zone 2
The letter G is assigned to the category for gas zones and D for dust zones.
Equipment intended for use in potentially explosive atmospheres is constructed in a way that ensures safety. Among other things, they use:
enclosures that prevent the transmission of an explosion from the enclosure to the environment
intrinsically safe cables
The various types of explosion-proof construction are covered by standards that detail the requirements for their construction and electrical testing. On this basis, the devices are assigned symbols, e.g:
ex-d - flameproof enclosure
ex-e - reinforced construction
ex-ia, ex-ib, ex-ic - intrinsically safe execution with different levels of protection
ex-ma, ex-mb - encapsulation with different levels of protection
ex-o - contacts immersed in insulating liquid
Ex-i is the symbol for explosion protection, where the electrical energy inside the device has been limited to a level that cannot cause ignition or heat up the surface of the device. Examples of devices marked "ex i" are the JUMO isolation amplifier for the Ex-zone and the float switch for the Ex-zone from the JUMO NESOS series.
Ex-i protection is divided into three sub-types: "ia", "ib" and "ic", depending on the level of protection.
"Ia" is the highest type of protection designed for use in zone 0 and means that ignition protection is guaranteed even during the occurrence of a combination of two faults during operation; type "ib" explosion protection allows one fault to occur during operation. Type "ic" guarantees protection against ignition of the device during normal operation, without faults.
Ex-d is a commonly used type of protection referred to as 'flameproof' or 'explosion-proof'. This means that the enclosure of 'ex-d' equipment has been designed in such a way that, in the event of an explosion occurring, the flame will be contained inside the enclosure and will not spread to the outside.
The ex-d enclosure has:
flame discharge ducts that allow the combustion gases produced during an explosion to cool down
thick walls to prevent the temperature of the outer surface of the enclosure rising to an explosive level.
Such devices are, for example, the JUMO dTRANS p20 Ex d pressure transmitter and the JUMO dTRANS p20 DELTA Ex ddifferential pressure transmitter.
Once you have an understanding of the hazardous area, category and enclosure designations of equipment designed for them, we can move on to discuss the main difference between "ex-d" and "ex-i" equipment. What distinguishes them from each other is their adaptation to work in different hazardous areas. We will explain this briefly on the basis of EN 60079-11:
Electrical equipment with the atex protection type "ex-ia" is "Category 1G/1D" equipment and, due to its very high degree of protection, can be used in explosion danger zones 0,1 and 2.
Electrical equipment with protection type "ex-d" is "Category 2G" equipment with a high degree of explosion protection. It is suitable for use in zones 1 and 2, but cannot be used in zone 0.
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