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1、Definitions of Classes and ZonesHazardous Areas are locations where the potential for fire or explosion exists because of gases, dust, or easily ignitable fibers or flyings in the atmosphere. In North America, hazardous areas are separated by classes, divisions, and groups to define the level of saf
2、ety required for equipment installed in these locations. Classes define the general form of the flammable materials in the atmosphere. Divisions define the probability of the presence of flammable materials. Groups classify the exact flammable nature of the material.In Europe and countries outside o
3、f North America, classification of hazardous areas is accomplished differently. Zones are used to define the probability of the presence of flammable materials. Protection Types denote the level of safety for the device. Groups classify the exact flammable nature of the material. These groups are se
4、parated differently than North American Groups. Temperature Identifications convey the maximum surface temperature of the apparatus based on 104 F (40 C) ambient. These temperature codes are selected carefully not to exceed the ignition temperature of the specific gas or vapor to be encountered in t
5、he application.Some classifications are not shown here. For further detailed information, see specific standards published by approval organizations.Common Terms:Class I, Division 1A Class I, Division 1 location is a location where ignitable concentrations of flammable gases, vapors or liquids: can
6、exist under normal operating conditions; may exist frequently because of repair or maintenance operations or because of leakage; or may exist because of equipment breakdown that simultaneously causes the equipment to become a source of ignition Equipment intended for use in a Class I , Division 1 ar
7、ea is usually of the explosionproof, intrinsically safe, or purged/pressurized type. Explosionproof apparatus: Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor sur
8、rounding the enclosure by sparks, flashes, or explosion of the gas or vapor within and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby. (See NFPA 70)Intrinsically safe apparatus: Apparatus in which all the circuits are intrinsically s
9、afe. (See UL 913)Intrinsically safe circuit: A circuit in which any spark or thermal effect is incapable of causing ignition of a mixture of flammable or combustible material in air under prescribed test conditions. (See UL 913) Purging: The process of supplying an enclosure with a protective gas at
10、 a sufficient flow and positive pressure to reduce the concentration of any flammable gas or vapor initially present to an acceptable level. (See NFPA 496)Pressurization:The process of supplying an enclosure with a protective gas with or without continuous flow at sufficient pressure to prevent the
11、entrance of a flammable gas or vapor, a combustible dust, or an ignitable fiber. (See NFPA 496)Class I, Division 2A Class I, Division 2 location is a location: where volatile flammable liquids or flammable gases or vapors exist, but are normally confined within closed containers; where ignitable con
12、centrations of gases, vapors or liquids are normally prevented by positive mechanical ventilation; or adjacent to a Class I, Division 1 location, where ignitable concentrations might be occasionally communicated. Equipment intended for use in a Class I, Division 2 area is usually of the nonincendive
13、, non-sparking, purged/pressurized, hermetically sealed, or sealed device type.Nonincendive circuit: A circuit in which any arc or thermal effect produced under intended operating conditions of the equipment is not capable, under the test conditions specified, of igniting the specified flammable gas
14、- or vapor- air mixture.(See UL 1604)Nonincendive component: A component having contacts for making or breaking an incendive circuit and the contacting mechanism shall be constructed so that the component is incapable of igniting the specified flammable gas- or vapor-air mixture. The housing of a no
15、nincendive component is not intended to: exclude the flammable atmosphere, or contain an explosion. (See UL 1604) Nonincendive field circuit: A circuit that enters or leaves the equipment enclosure and that under intended operating conditions is not capable, under the test conditions specified, of i
16、gniting the specified flammable gas- or vapor-air mixture or combustible dust. (See UL 1604)Non-sparking apparatus: Apparatus that has no normally arcing parts or thermal effects capable of ignition. Examples of normally arcing parts are relays, circuit breakers, servo-potentiometers adjustable resistors, switches, non-latching type connectors and motor brushes. (See UL 1604)Purging: See definition under Class I, Division 1Pressurization: See definition
