Emerson Fisher 4200, Fisher 546, Fisher 646, Fisher 846, Fisher 3582 Data Sheet
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Hazardous Area Classifications
D103222X012
Hazardous Area Classifications and
Protections
Product Bulletin
9.2:001
June 2012
The intent of this document is to provide a broad
overview of hazardous area classifications and the
types of protection techniques involved. The
information provided in this bulletin is for educational
purposes and should not be used in place of any other
source or governing documents.
Not all approvals are covered in this bulletin. Contact
your Emerson Process Management sales office for
information on approvals not covered in this bulletin.
Contact your Emerson Process Management sales
office for product specific hazardous area approval
information or visit our website at www.Fisher.com.
Hazardous Area
Classifications
When electrical equipment is used in, around, or near
an atmosphere that has flammable gases or vapors,
flammable liquids, combustible dusts, ignitable fibers
or flyings, there is always a possibility or risk that a fire
or explosion might occur. Those areas where the
possibility or risk of fire or explosion might occur due
to an explosive atmosphere and/or mixture is often
called a hazardous (or classified) location/area.
Currently there are two systems used to classify these
hazardous areas; the Class/Division system and the
Zone system. The Class/Division system is used
predominately in the United States and Canada,
whereas the rest of the world generally uses the Zone
system.
1. Class—The Class defines the general nature (or
properties) of the hazardous material in the
surrounding atmosphere which may or may not be in
sufficient quantities.
a. Class I—Locations in which flammable gases or
vapors may or may not be in sufficient quantities to
produce explosive or ignitable mixtures.
b. Class II—Locations in which combustible dusts
(either in suspension, intermittently, or
periodically) may or may not be in sufficient
quantities to produce explosive or ignitable
mixtures.
c. Class III—Locations in which ignitable fibers may
or may not be in sufficient quantities to produce
explosive or ignitable mixtures.
2. Division—The Division defines the probability of the
hazardous material being able to produce an explosive
or ignitable mixture based upon its presence.
a. Division 1 indicates that the hazardous material
has a high probability of producing an explosive or
ignitable mixture due to it being present
continuously, intermittently, or periodically or from
the equipment itself under normal operating
conditions.
b. Division 2 indicates that the hazardous material
has a low probability of producing an explosive or
ignitable mixture and is present only during
abnormal conditions for a short period of time.
3. Group—The Group defines the type of hazardous
material in the surrounding atmosphere. Groups A, B,
C, and D are for gases (Class I only) while groups E, F,
and G are for dusts and flyings (Class II or III).
Class/Division System
Hazardous locations per the Class/Division system are
classified according to the Class, Division, and Group.
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a. Group A—Atmospheres containing acetylene.
b. Group B—Atmospheres containing a flammable
gas, flammable liquid-produced vapor, or
combustible liquid-produced vapor whose MESG is
less than 0.45 mm or MIC ratio is less than 0.40.
Product Bulletin
9.2:001
June 2012
Hazardous Area Classifications
D103222X012
Typical gases include hydrogen, butadiene,
ethylene oxide, propylene oxide, and acrolein.
c. Group C—Atmospheres containing a flammable
gas, flammable liquid-produced vapor, or
combustible liquid-produced vapor whose MESG is
greater than 0.45 mm but less than 0.75 mm or
MIC ratio is greater than 0.40 but less than 0.80.
Typical gases include ethyl either, ethylene,
acetaldehyde, and cyclopropane.
d. Group D—Atmospheres containing a flammable
gas, flammable liquid-produced vapor, or
combustible liquid-produced vapor whose MESE is
greater than 0.75 mm or MIC ration is greater than
0.80. Typical gases include acetone, ammonia,
benzene, butane, ethanol, gasoline, methane,
natural gas, naphtha, and propane.
e. Group E—Atmospheres containing combustible
metal dusts such as aluminum, magnesium, and
their commercial alloys.
f. Group F—Atmospheres containing combustible
carbonaceous dusts with 8% or more trapped
volatiles such as carbon black, coal, or coke dust.
c. Zone 2—Ignitable concentrations of flammable
gases or vapors which are not likely to occur under
normal operating conditions and do so only for a
short period of time.
Group—Electrical equipment used in gas atmospheres
is divided into two groups.
n Group I—Equipment used in mines with
atmospheres containing methane or gases and
vapors of equivalent hazard.
n Group II—All other equipment; which is further
subdivided into three subgroups.
- Group IIA—Atmospheres containing
propane, or gases and vapors of equivalent
hazard.
- Group IIB—Atmospheres containing
ethylene, or gases and vapors of equivalent
hazard.
- Group IIC—Atmospheres containing
acetylene or hydrogen, or gases and vapors of
equivalent hazard.
g. Group G—Atmospheres containing combustible
dusts not included in Group E or Group F. Typical
dusts include flour, starch, grain, wood, plastic, and
chemicals.
Zone System
Hazardous locations per the Zone system are classified
according to its Zone which can be gas or dust. For gas
atmospheres electrical equipment is further divided
into Groups and Subgroups.
Zone—The Zone defines the probability of the
hazardous material, gas or dust, being present in
sufficient quantities to produce explosive or ignitable
mixtures.
1. Gas
a. Zone 0—Ignitable concentrations of flammable
gases or vapors which are present continuously or
for long periods of time.
b. Zone 1—Ignitable concentrations of flammable
gases or vapors which are likely to occur under
normal operating conditions.
2. Dust
a. Zone 20—An area where combustible dusts or
ignitable fibers and flyings are present continuously
or for long periods of time.
b. Zone 21—An area where combustible dusts or
ignitable fibers and flyings are likely to occur under
normal operating conditions.
c. Zone 22—An area where combustible dusts or
ignitable fibers and flyings are not likely to occur
under normal operating conditions and do so only
for a short period of time.
Protection Techniques and
Methods
Various protection techniques and methods have been
developed and employed, thus reducing or minimizing
the potential risks of explosion or fire from electrical
equipment located in hazardous locations. Not all
methods are listed.
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Hazardous Area Classifications
D103222X012
Product Bulletin
9.2:001
June 2012
Class/Division system
n Explosion-proof—A type of protection that utilizes
an enclosure that is capable of withstanding an
explosive gas or vapor within it and or preventing
the ignition of an explosive gas or vapor that may
surround it and that operates at such an external
temperature that a surrounding explosive gas or
vapor will not be ignited thereby.
n Intrinsically Safe—A type of protection in which the
electrical equipment under normal or abnormal
conditions is incapable of releasing sufficient
electrical or thermal energy to cause ignition of a
specific hazardous atmospheric mixture in its most
easily ignitable concentration.
n Dust Ignition-proof—A type of protection that
excludes ignitable amounts of dust or amounts that
might affect performance or rating and that, when
installed and protected in accordance with the
original design intent, will not allow arcs, sparks or
heat otherwise generated or liberated inside the
enclosure to cause ignition of exterior
accumulations or atmospheric suspensions of a
specified dust.
n Intrinsically Safe—A type of protection in which the
electrical equipment under normal or abnormal
conditions is incapable of releasing sufficient
electrical or thermal energy to cause ignition of a
specific hazardous atmospheric mixture in its most
easily ignitable concentrations. This type of
protection is referred to as “Ex i”.
n Increase Safety—A type of protection in which
various measures are applied to reduce the
probability of excessive temperatures and the
occurrence of arcs or sparks in the interior and on
the external parts of electrical apparatus that do not
produce them in normal service. Increased safety
may be used with flame-proof type of protection.
This type of protection is referred to as “Ex e”.
n Type n—A type of protection applied to electrical
equipment such that in normal operation it is not
capable of igniting a surrounding explosive
atmosphere. This type of protection is referred to as
“Ex n”.
n Non-incendive—A type of protection in which the
equipment is incapable, under normal conditions,
of causing ignition of a specified flammable gas or
vapor-in-air mixture due to arcing or thermal effect.
Zone system
n Flame-proof—A type of protection in which an
enclosure can withstand the pressure developed
during an internal explosion of an explosive mixture
and that prevents the transmission of the explosion
to the explosive atmosphere surrounding the
enclosure and that operates at such an external
temperature that a surrounding explosive gas or
vapor will not be ignited there. This type of
protection is referred to as “Ex d”.
Temperature Code
(T Code)
A mixture of hazardous gases and air may be ignited by
coming into contact with a hot surface. The conditions
under which a hot surface will ignite a gas depends on
surface area, temperature, and the concentration of
the gas. The same can be said about combustible
dusts. The T code of a product denotes the maximum
surface temperature that a given product will not
exceed under a specified ambient temperature. For
example, a product with a T code of T3 means that its
maximum surface temperature will not exceed 200_C
provided it is operated in a ambient temperature
defined by the manufacturer.
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