IEC: ZONE LOCATIONS
Zone:
a method of specifying the probability that a location is made hazardous by the presence, or
potential presence, of flammable concentrations of gases and vapors, or combustible mixtures of
dusts.
Zone 0 (IEC):
an area in which an explosive gas atmosphere is present continuously or for long periods.
Zone 0, Class I (NEC):
a Class I, Zone 0 location is a location (1) in which ignitable concentrations of flammable gases or
vapors are present continuously; or (2) in which ignitable concentrations of flammable gases or
vapors are present for long periods of time. (NEC Section 505-9(a))
Zone 1 (IEC):
an area in which an explosive gas atmosphere is likely to occur in normal operation.
Zone 1, Class I (NEC): Same as Class I, Division 1
a Class I, Zone 1 location is a location (1) in which ignitable concentrations of flammable gases or
vapors are likely to exist under normal operating conditions; or (2) in which ignitable
concentrations of flammable gases or vapors may exist frequently because of repair or
maintenance operations or because of leakage; or (3) in which equipment is operated or
processes are carried on, of such a nature that equipment breakdown or faulty operations could
result in the release of ignitable concentrations of flammable gases or vapors and also cause
simultaneous failure of electrical equipment in a mode to cause the electrical equipment to
become a source of ignition; or (4) that is adjacent to a Class I, Zone 0 location from which
ignitable concentrations of vapors could be communicated, unless communication is prevented
by adequate positive-pressure ventilation from a source of clean air and effective safeguards
against ventilation failure are provided. (NEC Article 505-9(b))
Zone 2 (IEC):
an area in which an explosive gas atmosphere is not likely to occur in normal operation
and, if it does occur, is likely to do so only infrequently and will exist for a short period
only. (IEV 426-03-05, modified)
Zone 2, Class I (NEC): Same as Class I, Division 2
a Class I, Zone 2 location is a location (1) in which ignitable concentrations of flammable gases or
vapors are not likely to occur in normal operation, and if they do occur, will exist only for a short
period; or (2) in which volatile flammable liquids, flammable gases, or flammable vapors are
handled, processed, or used, but in which the liquids, gases, or vapors normally are confined
within closed containers or closed systems from which they can escape only as a result of
accidental rupture or breakdown of the containers or system, or as the result of the abnormal
operation of the equipment with which the liquids or gases are handled, processed, or used; or
(3) in which ignitable concentrations of flammable gases or vapors normally are prevented by
positive mechanical ventilation, but which may become hazardous as the result of failure or
abnormal operation of the ventilation equipment; or (4) that is adjacent to a Class I, Zone 1
location from which ignitable concentrations of flammable gases or vapors could be
communicated, unless such communication is prevented by adequate positive-pressure
ventilation from a source of clean air, and effective safeguards against ventilation failure are
provided. (NEC Section 505-9(c))
Area (location) classification
Area classification schemes should specify the kind of flammable material that may be present
and the probability that it will be present in ignitable concentrations. Area classification schemes
and systems of material classification have been developed to provide a succinct description of
the hazard so that appropriate safeguards may be selected. The type of protection technique
selected and the level of protection it must provide depend upon the potential hazard caused by
using electrical apparatus in a location in which a combustible, flammable, or ignitable substance
may be present.
Area classification definitions used in the United States and Canada include the following:
a) CLASS the generic form of the flammable materials in the atmosphere, which may include
gas or vapor, dusts, or easily ignitable fibers or flyings (see Clause 3 for detailed definitions);
b) DIVISION (or ZONE) an indication of the probability of the presence of the flammable
material in
ignitable concentration (see Clause 3 for detailed definitions); and
c) GROUP the exact nature of the flammable material (see 4.1.1 & 4.1.2).
Groups (NEC Article 500 / CEC Annex J18)
The United States and Canadian Electrical Codes recognize seven groups: Groups A, B, C, D, E,
F, and G. Groups A, B, C, and D apply to Class I locations; Groups E, F, and G apply to Class II
Locations.
In NEC these groups are defined as:
Group A - Acetylene
Group B - Flammable gas, flammable liquid-produced vapor, or combustible liquid-produced
vapor mixed with air that may burn or explode, having either a MAXIMUM EXPERIMENTAL SAFE GAP
(MESG) less than or equal to 0.45 mm or a MINIMUM IGNITING CURRENT RATIO (MIC RATIO) less
than 0.4.
.
Group C - Flammable gas, flammable liquid-produced vapor, or combustible liquid-produced
vapor mixed with air that may burn or explode, having either MAXIMUM EXPERIMENTAL SAFE GAP
(MESG) values greater than 0.45 mm and less than or equal to 0.75 mm or a MINIMUM IGNITING
CURRENT RATIO (MIC RATIO) greater than or equal to 0.4 and less than or equal to 0.80.
Group D - Flammable gas, flammable liquid-produced vapor, or combustible liquid-produced
vapor mixed with air that may burn or explode, having a MAXIMUM EXPERIMENTAL SAFE GAP (MESG)
greater than 0.75 mm or a MINIMUM IGNITING CURRENT RATIO (MIC RATIO) greater than 0.80, or
gases or vapors of equivalent hazard.
.
Additional information on group classification can be found in NFPA 497, Classification of
Flammable Liquids, Gases or Vapors and of Hazardous (Classified) Locations for Electrical
Installations in Chemical Process Areas.
Group E – Atmospheres containing combustible metal dusts, including aluminum, magnesium,
and their commercial alloys, or other combustible dusts whose particle size, abrasiveness, and
conductivity present similar hazards in the use of electrical equipment.
Group F – Atmospheres containing combustible carbonaceous dusts that have more than 8
percent total entrapped volatiles (see ASTM D3175-89 for coal and coke dusts) or that have been
sensitized by other materials so that they present an explosion hazard. Coal, carbon black,
charcoal, and coke dusts are examples of carbonaceous dusts.
Group G – Atmospheres containing other combustible dusts, including flour, grain, wood flour,
plastic, and chemicals. Additional information on Group Classification can be found in NFPA 499
Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical
Installations in Chemical Process Areas.
(NEC Article 505/CSA C22.1 Section 18/IEC 60079-12/prEN 60079-12)
These groups are defined as:
Group IIC - Flammable gas, flammable liquid-produced vapor, or combustible liquid-produced
vapor mixed with air that may burn or explode, having either MAXIMUM EXPERIMENTAL SAFE GAP
(MESG) less than or equal to 0.5 mm or MINIMUM IGNITING CURRENT RATIO (MIC RATIO) less than
0.45, or gases or vapors of equivalent hazard.
Group IIB - Flammable gas, flammable liquid-produced vapor, or combustible liquid-produced
vapor mixed with air that may burn or explode, having either MAXIMUM EXPERIMENTAL SAFE GAP
vapor mixed
with air that may burn or explode, having MAXIMUM EXPERIMENTAL SAFE GAP(MESG) greater than
0.9 mm or MINIMUM IGNITING CURRENT RATIO (MIC RATIO) greater than 0.80, or gases or vapors of
equivalent hazard.
