Hazardous Area Classification

The National Electric Code (NEC) defines hazardous locations are those areas "where fire or explosion hazards may exit due to flammable gas or vapors,flammable liquids,combustible dust or ignitable fibers or flyings." The hazardous location are classified as Classes,Divisions,Groups.

Classes

The classes define the type of hazardous in terms of whether it is a gas or vapors,a combustible dust or ignitable fibers or fyings.The type of hazards divided into following three classes.

Class I

Any location in which flammable gases or vapors are may present in the air in sufficient quantities to produce an explosive or ignitable mixture.

Class II

Any area made hazardous by the presents of combustible dust.

Class III

Any area made hazardous by the presents  of easily ignitable fibers or flyings, but in which such   fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixture.

Divisions

Divisions defines the probability of the hazardous material being present during normal or abnormal conditions.

Division 1

Area in which contain hazardous mixtures under normal operating conditions.

Division 2

Area in which atmospheres is normally non- hazards.But may become hazards under abnormal circumstances such as an accidental rapture of a vessels or container or system breakdown.

Groups

Groups classify the exact nature of the hazardous substance.Flammable gas and vapors of class I location are separated into the four Groups A,B,C and D.Flammable dust and debris of class II location are separated into three Groups E,F,and G.

Group A

Atmospheres containing Acetylene.

Group B

Atmospheres containing Hydrogen or gases or vapors of equivalent hazards.

Group C

Atmospheres containing Cyclopropane,Ethylene, Ethyl ether or gases or vapors of equivalent hazards.

Group D

Atmospheres containing Gasoline, Acetone, Ammonia, Benzine, Butane, Ethanol, Hexane, Methane, Naphtha, Natural gas, Propane or Equivalent hazards.

Group E

Atmospheres containing combustible metal dust including Aluminum, Magnesium and other metal dust of similar nature.

Group F 

Atmospheres containing carbonaceous dusts, Carbon black, Coal black, Charcoal, coal or Cock dusts which have more than 8% total volatile material or atmospheres containing these dusts sensitized by other materials so they present an explosion hazards.

Group G

Atmospheres containing Flour, Starch or Grain dust or similar type of materials.