ATEX & Hazardous location definition


Regarding ATEX 99/92/EC directive, the requirement is that Employers must classify areas where hazardous explosive atmospheres may occur into zones. The classification given to a particular zone, and its size and location, depends on the likelihood of an explosive atmosphere occurring and its persistence if it does. Areas classified into zones (0, 1, 2 for gas-vapor-mist and 20, 21, 22 for dust) must be protected from effective sources of ignition. Equipment and protective systems intended to be used in zoned areas must meet the requirements of the directive. Zone 0 and 20 require Category 1 marked equipment, zone 1 and 21 require Category 2 marked equipment and zone 2 and 22 require Category 3 marked equipment. Zone 0 and 20 are the zones with the highest risk of an explosive atmosphere being present.

Zone classification


European and IEC Classification Definition of zone or division North American Classification
Zone 0 (gases / Vapors) An area in which an explosive mixture is continuously present or present for long periods Class I Division 1 (gases)
Zone 1 (gases / Vapors) An area in which an explosive mixture is likely to occur in normal operation Class I Division 1 (gases)
Zone 2 (gases / Vapors) An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time. Class I Division 2 (gases)
Zone 20 (dusts) An area in which an explosive mixture is continuously present or present for long periods Class II Division 1 (gases)
Zone 21 (dusts) An area in which an explosive mixture is likely to occur in normal operation Class II Division 1 (dusts)
Zone 22 (dusts) An area in which an explosive mixture is not likely to occur in normal operation and if it occurs it will exist only for a short time. Class II Division 2 (gases)

Hazardous Location Definition


The National Electrical Code (NEC) and the Canadian Electrical Code (CEC) defines hazardous areas as the following: An area where a potential hazard (e.g., a fire, an explosion, etc.) may exist under normal or abnormal conditions because of the presence of flammable gases or vapors, combustible dusts or ignitable fibers or flyings.

Class Definition


The NFPA Publication 70, NEC, and CEC define three categories of hazardous materials that have been designated as Class I, Class II, or Class III. The Classes define the type of explosive or ignitable substances which are present in the atmosphere such as:
• Class I locations are those in which flammable vapors and gases may be present.
• Class II locations are those in which combustible dust may be found.
• Class III locations are those which are hazardous because of the presence of easily ignitable fibers or flyings.

Division Definition


Each of the three Classes, discussed earlier, is further subdivided into two Divisions, Division 1 or Division 2. The Division defines the likelihood of the hazardous material being present in a flammable concetration.

Division Definitions
Division 1 In which ignitable concentrations of hazards exists under normal operation conditions and / or where hazard is caused by frequent maintenance or repair work or frequent equipment failure.
Division 2 In which ignitable concentrations of hazards are handled, processed or used, but which are normally in closed containers or closed system from which they can only escape thriugh accidental repture or breakdown of such containers or systems.



Group Definition


The explosive characteristics of the air mixtures of the gases, vapors, or dusts vary with the specific material involved. Materials have been placed in groups based on their ignition temperatures and explision pressures. Class I and Class II Divisions are further subdivided into Groups of hazardous materials. The group define substances by rating their flammatable nature in relation to other known substances.

Class Division Group Flammable Material Maximum Experimental
Safe Gap(MESG)
Minimum Igniting Current
Ratio(MIC)
Class I Division I & II A Acetylene    
Class I Division I & II B • Hydrogen
• Butadience
• Ethylene Oxide
• Proplene Oxide
≦0.4mm ≦0.4
Class I Division I & II C • Ethylene
• Cyclopropane
• Ethyl Ether
﹥0.45mm
≦0.75mm
﹥0.4
≦0.8
Class I Division I & II D • Propane
• Acetone
• Ammonia
• Bezene
• Butane
• Ethanol
• Gasoline
• Methanol
• Natural Gas
≧0.75mm ﹥0.8


Temperature Class Definition


The temperature classes are used to designate the maximum operating temperatures on the surface of the equipment which should not exceed the ignition temperature of the surrounding atmosphere.