HAZARDOUS LOCATION CLASSIFICATION

HAZARDOUS LOCATION CLASSIFICATION

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).

 

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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