HAZARDOUS LOCATION CLASSIFICATION
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Hazardous Locations consist of areas where there is the potential for a fire or explosion due to electrical equipment that is in operation in this area with a reaction to flammable or ignitable gases, liquids, vapors, combustible dusts, fibers or flyings. The need for Explosion-Proof equipment then arises due to this potential for fire or explosion.
The National Electrical Code (NEC) along with the National Fire Protection Association (NFPA) and Underwriters Laboratories (UL) have published a guide along with codes that classify hazardous areas into classes, divisions and zones.
The “Combustion” or “Fire” Triangle is used to classify Hazardous Locations in the Explosion-Proof industry. A source of fuel (explosive gases,liquids, or vapors), source of ignition (fire, spark, or explosion) and oxygen must be present in the appropriate consistencies for an explosion to occur. Our Explosion-Proof Enclosures & Systems operate to prevent these three criteria from mixing in such a way that would generate an explosion and be hazardous to the surrounding environment.
CLASS I
Class I locations consist of areas where gases, vapors or liquids may exist that have the potential to become flammable or ignitable. There are two different divisions that exist in Class I, Division 1 and Division 2, along with three Zones; Zone 0, 1 & 2. Locations that would be considered to be Class I include Petroleum Refineries, Gasoline Storage Areas, Dry Cleaning Plants, Spray Finishing Areas, Fuel Servicing Areas, etc.
Division 1 is a subset of Class I and is classified as an area where the explosive or flammable gases, vapors or liquids mentioned above can exist under normal, everyday operating conditions.
Division 2 is also a subset of Class I and is classified as an area where the explosive or flammable gases, vapors or liquids mentioned above are not likely to exist during regular operation.
Zone 0 is described as the presence of explosive or flammable gases, vapors or liquids for long periods of time during operating conditions or during a large portion of the operating conditions.
Zone 1 is described as the presence of explosive or flammable gases, vapors or liquids for some of the time during normal operating conditions.
Zone 2 is described as there not being a likelihood of explosive or flammable gases, vapors or liquids present during normal operating conditions.
CLASS II
Class II locations consist of locations where combustible dusts may exist that have the potential to become flammable or ignitable. Locations that would be considered to be Class II include Grain elevators, Flour and feed mills, Metal powder manufacturers, and Coal plants, etc.
Division 1 is a subset of Class II and is classified as an area where the explosive or flammable combustible dusts mentioned above can exist under normal, everyday operating conditions.
Division 2 is also a subset of Class II and is classified as an area where the explosive or flammable combustible dusts mentioned above are not likely to exist during regular operation.
CLASS III
Class III locations consist of locations where fibers and flyings may exist that have the potential to become flammable or ignitable. Locations that would be considered to be Class III include Cotton Gins, Cotton Seed Mills, Sawdust or flyings plants, or Textile mills.
Division 1 is a subset of Class III and is classified as an area where ignitable fibers or flyings may be manufactured, stored or handled.
Division 2 is also a subset of Class III and is classified as an area where ignitable fibers or flyings may be stored or handled.
NEMA & NEC ENCLOSURE TYPES
TYPE 3 - Type 3 enclosures are intended for outdoor use primarily to provide a degree of protection against windblown dust, rain, sleet and external ice formation.
TYPE 3R - Type 3R enclosures are intended for outdoor use primarily to provide a degree of protection against falling rain and external ice formations
TYPE 4 - Type 4 enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against windblown rain, dust, splashing water, hose directed water, and external ice formation
TYPE 4X - Type 4X enclosures are intended for indoor and outdoor use primarily to provide a degree of protection against corrosion, windblown dust and rain, splashing water, hose directed water and external ice formation.
TYPE 7 - Type 7 enclosures are for use indoors in locations classified Class I, Div. 1 & 2, Groups A, B, C & D, as defined in the National Electric Code.
TYPE 4/7 - Type 4/7 enclosures are for use outdoors in locations classified to be hazardous as defined in the National Electric Code.
TYPE 9 - Type 9 enclosures are for use in indoor locations classified Class II, groups E, F or G as defined in the National Electric Code.
CLASSIFICATION OF HAZARDOUS ATMOSPHERES
NEC ENCLOSURE CLASSIFICATIONS
Explosion-Proof Enclosure: An enclosure which can withstand the pressures resulting from an internal explosion of specified gases, and contain such an explosion sufficiently to prevent the ignition of the explosive atmosphere surrounding the enclosure (for Class I, II and III).
Oil Immersion: The electrical apparatus are arranged such that the arcing contacts, connections, etc., are immersed in oil. Arcing is confined under the oil such that it will not ignite an explosive mixture of specified gases above the oil or in the atmosphere surrounding the enclosure (for Class I, II and III).
Purged & Pressurized Enclosures: The accumulation of ignitable gases or vapors in the enclosure is prevented by maintaining, inside the enclosure, sufficient flow of clean air or inert gas (for Class I, II and III).
Intrinsically Safe Equipment: Wiring that is incapable of releasing sufficient electrical or thermal energy, under normal and abnormal conditions, to cause ignition of a specific hazardous atmospheric mixture in its most easily ignitable concentration (for Class I, II and III).
Dust Ignition-Proof: The enclosure prevents the entrance of dust, and external surfaces shall not reach temperatures capable of igniting or discoloring dust on the enclosure or igniting dust-air mixtures in the surrounding atmospheres (for Class II).
ATEX ENCLOSURE CLASSIFICATIONS
Type “d” (Exd): Explosionproof/Flameproof Enclosure. An enclosure that can withstand the pressure developed during an internal explosion of specified gases and which prevents the transmission of the explosion to the explosive atmosphere surrounding the enclosure (for Zones 1 and 2).
Type “o” (Exo): Oil immersion. The electrical apparatus is immersed in oil in such a way that an explosive atmosphere, which may be above the oil or outside the enclosure cannot be ignited (for Zone 1).
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Type “p” (Exp): Pressurized enclosure. The entry of a surrounding atmosphere into the enclosure is prevented by maintaining inside the enclosure a protective gas at a higher pressure than that of the surrounding atmosphere (for Zones 1 and 2).
Type “i” (Exi): Intrinsically Safe Systems are incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause and ignition of a given explosive atmosphere (for all Zones, 0, 1 and 2).
Type “e” (Exe): Increased Safety. Measures are taken to prevent, with a minor degree of security, the possibility of excessive temperatures and the occurrence of arcs or sparks in the interior and on the external parts of the electrical apparatus which do not occur in normal service (for Zones 1 and 2).
Type “q” (Exq): Powder filled. The enclosure is filled with finely granulated material such that, in the intended service conditions, any arc occurring within the enclosure of an electrical apparatus will not ignite the surrounding atmosphere. No ignition shall be caused by flame or excessive temperature of the surfaces of the enclosure (for Zone 1).
Type “N” (Exn): Not CENELEC recognized. Measures are applied to the electrical apparatus such that, in normal operation, it is not capable of igniting a surrounding explosive atmosphere and a fault capable of causing ignition is not likely to occur (for Zone 2).
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In explosive environment applications, Electrical Equipment or machine needs to be employed where fire or explosion hazards may exist. Sources of such hazards include gases, vapours, dust, fibers, and flying’s, which are combustible or flammable.
Electrical equipment installed in such locations could provide an ignition source, due to electrical arcing, or high temperature. Hence there is standards and regulations provided to identify such locations, classify the hazards, and design equipment for safe use in such locations.
According to the National Electrical Code (NEC), Ex Proof standard applies to an apparatus enclosed in a case that can withstand a gas or vapor explosion. It means that, should there be an explosion, it will be contained within an enclosure.
The interaction of three elements is needed for creation of a fire. If one element is removed, the fire will extinguish.
Heat – allow fire to spread by evaporating moisture in the fuels, allowing it to ignite and travel more easily.
Oxygen – 16% is required. Oxygen supports the oxidation process, creating heat & gases.
Fuel – gives a fire a burnable material, allowing the fire to advance.
Following are the industries where electrical equipment’s work in explosive environment as follows:
1.Oil & Gas Refineries
2.Chemical industry
3.Solar Energy equipment factories
4.Wood working industry
5.Wastewater treatment
6.Paint-spray companies
7.Gas Power Plants
8.Printing
9.Alcohol Distilleries
Based on the design and certain material selections, Equipment manufacturer design product that does not cause sparks or heat. As such, it does not act as an ignition source in explosive atmospheres.
Typical ATEX and IECEx marking on Ex proof equipment.
All components are labelled on their nameplate with the distinct classification in which they have been tested and approved for installation.
The Ex certification ensures that equipment will work safely in explosive environment without causing any accident and will not act itself as an explosive source if used as per the manufacturer's recommendations.
There are different Ex certifications require for product based on different region installation to prove the quality of products are as follows:
IECEx for the world
ATEX for Europe
CSA US for United States
INMETRO for Brazil
TR CU for Russia
Products manufactured for safe installation in explosive atmospheres and hazardous area zones and categorized according to ATEX as follows:
Zone 0 - An area where ignitable concentrations of flammable gases, vapours or liquids are present continuously or for long periods of time under normal operating conditions. The ANSI/NEC classification method consider this environment a Class I, Division 1 area.
Zone 1 - An area where ignitable concentrations of flammable gases, vapours or liquids are likely to exist under normal operating conditions.
Zone 2 - An area where ignitable concentrations of flammable gases, vapours or liquids are not likely to exist under normal operating conditions. In this area the gas, vapor or liquids would only be present under abnormal conditions.
Zone 20 - ignitable concentrations of dust/fibers/flying’s are present for long periods of time.
Zone 21 - ignitable concentrations of dust/fibers/flying’s are likely to exist under normal conditions.
Zone 22 - ignitable concentrations of dust/fibers/flying’s unlikely to exist under normal conditions.
Class I, Division 1 classified locations - An area where ignitable concentrations of flammable gases, vapours or liquids can exist all the time or some of the time under normal operating conditions. A Class I, Division 1 area encompasses the combination of Zone 0 and Zone 1 areas.
Class I, Division 2, or Zone 2 classified locations - An area where ignitable concentrations of flammable gases, vapours or liquids are not likely to exist under normal operating conditions.
Class II, Division 1 - Ignitable concentrations of combustible dust can exist, under normal conditions.
Class II, Division 2 - Ignitable concentrations of combustible dust are unlikely to exist normally.
Class III, Division 1 - Ignitable fibers, or materials producing combustible flying’s, are handled, manufactured, or used.
Class III, Division 2 - Easily ignitable fibers are stored or handled.
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