Hazardous Areas: Division and Zone Classification System

Hazards areas are associated with flammable
vapors or gases, ignitable fibers, and combustible dusts.

Hazardous areas refer to locations with a possible risk of explosion or fire due to dangerous atmosphere. The hazards can be associated with flammable vapors or gases, ignitable fibers, and combustible dusts.

Different hazardous area classifications exist in the North America and Europe. Generally, the National Electric Code (NEC) classifications govern hazardous areas in the US. While in Europe, hazardous area classification has been specified by the International Electrotechnical Commission (IEC).

Below is a description of the Division and Zone classification system.

CLASS	NATURE OF HAZARDOUS MATERIAL
CLASS I	Hazardous area due the presence of flammable vapors or gases in sufficient quantities to produce ignitable mixtures and cause an explosion. Examples include natural gas and liquified petroleum.
CLASS II	Hazardous area due the presence of conductive or combustible dusts in sufficient quantities to produce ignitable mixtures and cause an explosion. Examples include aluminum and magnesium powders.
CLASS III	Hazardous area due the presence of flammable *fibers* or other flying debris that collect around lighting fixtures, machinery, and other areas in sufficient quantities to produce ignitable mixtures and cause an explosion. Examples include sawdust and flyings

Division groups hazardous areas based on the chances of an explosion due to the presence of flammable materials in the area.

DIVISION	LIKELIHOOD OF HAZARDOUS MATERIAL
DIVISION 1	Areas where there is a high chance of an explosion due to hazardous material that is present periodically, intermittently, or continuously under normal operation.
DIVISION 2	Areas where there is a low chance of an explosion under normal operation.

Group categorizes areas based on the type of flammable or ignitable materials in the environment. As per NEC guidelines, Groups A to D classify gasses while Groups E to G classify dust and flying debris.

GROUP	TYPE OF HAZARDOUS MATERIAL IN THE AREA
GROUP A	Acetylene.
GROUP B	Area contains flammable gas, liquid, or liquid produced vapor with any of the following characteristics: Minimum Ignition Current (MIC) value equal to or less than 0.40 Maximum Experimental Safe Gap (MESG) value equal to or less than 0.45 mm Combustible gas with more than 30 percent volume Examples include hydrogen, ethylene oxide, acrolein, propylene oxide.
GROUP C	Area contains flammable gas, liquid, or liquid produced vapor with any of the following characteristics: Minimum Ignition Current (MIC) value between 0.40 and 0.80 Maximum Experimental Safe Gap (MESG) value greater than 0.75 mm Examples include carbon monoxide, hydrogen sulphide, ether, cyclopropane, morphline, acetaldehyde, isoprene, and ethylene.
GROUP D	Area contains flammable gas, liquid, or liquid produced vapor with any of the following characteristics: Minimum Ignition Current (MIC) value greater than 0.80 Maximum Experimental Safe Gap (MESG) value greater than 0.75 mm Examples include ammonia, gasoline, butane, benzene, hexane, ethanol, methane, methanol, natural gas, propane, naphtha, and vinyl chloride.
GROUP E	Area contains metal dusts such as magnesium, aluminum, chromium, bronze, titanium, zinc, and other combustible dusts whose abrasiveness, size, and conductivity present a hazard.
GROUP F	Area contains carbonaceous dusts such as charcoal, coal black, carbon black, coke dusts and others that present an explosion hazard.
GROUP G	Area contains combustible dusts not classified in Groups E and F. Examples include starch, grain, flour, wood, plastic, sugar, and chemicals.

NOTE: This post serves only as a guide to acquaint the reader with hazardous area classifications in the USA. It is imperative to discuss your instrumentation, valve, or process equipment requirement with a qualified applications expert prior to installing any electrical device inside of any hazardous area.