Hazardous areas can contain flammable gases, vapors, or dusts that could cause fires or explosions. These areas are classified based on the type of hazard and likelihood of a hazardous atmosphere being present. The Class/Division system used in North America categorizes areas based on whether hazardous materials are likely to be present continuously or occasionally. The international Zone system defines three zones based on the probability and duration of hazardous atmospheres. Equipment used in hazardous areas must use explosion-proof techniques to prevent ignition, such as flame-proofing or intrinsic safety.

2. Hazardous Areas
A “Hazardous area” can be
defined as an area or location where
the atmosphere contains, or may
contain the quantities of flammable
or explosive gases, dusts or
vapours. In such an atmosphere a
fire or explosion is possible.

3. Classification of Hazardous area
• Presently there are two systems
used for classification of these
hazardous areas;
– The Class/Division system,
– The Zone system
• The Class/Division system is used in
the United States and Canada,
whereas the rest of the world
generally uses the Zone system.
Referred Std - BS EN 60079/10; BS EN 61241/3

4. Classification
• Class I—Locations in which
flammable gases or vapors
may or may not be in
sufficient quantities to produce
explosive or ignitable
mixtures.
• 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.
• Class III—Locations in which
ignitable fibers may or may
not be in sufficient quantities
to produce explosive or
ignitable mixtures
• 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.
• 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.

5. Group-The Group defines the type of hazardous material in the
surrounding atmosphere.
– Group A—Atmospheres containing acetylene.
– 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. Typical gases include hydrogen, butadiene, ethylene oxide, propylene
oxide, and acrolein
– 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.
– 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.
– Group E—Atmospheres containing combustible metal dusts such as aluminum,
magnesium, and their commercial alloys.
– Group F—Atmospheres containing combustible carbonaceous dusts with 8% or more
trapped volatiles such as carbon black, coal, or coke dust.
– Group G—Atmospheres containing combustible dusts not included in Group E or Group
F. Typical dusts include flour, starch, grain, wood, plastic, and chemicals

6. Zone System
Zone—The Zone defines the probability of the hazardous material, gas or dust, being
present in sufficient quantities to produce explosive or ignitable mixtures.
Gas
Zone 0—Ignitable
concentrations of flammable
gases or vapors which are
present continuously or for long
periods of time.
Zone 1—Ignitable
concentrations of flammable
gases or vapors which are likely
to occur under normal operating
conditions.
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.
Dust
Zone 20—An area where
combustible dusts or ignitable
fibers and flyings are present
continuously or for long periods
of time.
Zone 21—An area where
combustible dusts or ignitable
fibers and flyings are likely to
occur under normal operating
conditions.
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.

7. Group I
Equipment used
in mines with
atmospheres
containing
methane or
gases and vapors
of equivalent
hazard
Group II
IIA - Atmospheres containing
propane, or gases and
vapors of equivalent hazard.
IIB -Atmospheres containing
ethylene, or gases and
vapors of equivalent hazard.
IIC - Atmospheres
containing acetylene or
hydrogen, or gases and
vapors of equivalent hazard.
Sub Division of Gas Group

8. 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.
Group II Temperature Class
T Code Maximum Surface Temperature Ignition temperature
T1 450 0C > 450 0C
T2 300 0C > 3000C ≤ 450 0C
T3 200 0C > 200 0C ≤ 300 0C
T4 130 0C > 130 0C ≤ 200 0C
T5 100 0C > 100 0C ≤ 135 0C
T6 85 0C > 85 0C ≤ 100 0C
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 2000C provided it is operated in a
ambient temperature defined by the manufacturer

9. Protection Techniques and Methods
• Class/Division system
– Explosion-proof
– Intrinsically Safe
– Dust Ignition-proof
• Zone system
– Flame-proof
– Intrinsically Safe

10. Gas Dust Hazardous Area Characteristics
Zone 0 Zone 20
A hazardous atmosphere is highly likely
to be present and may be present for
long periods of time (>1000 hours per
year) or even continuously
Zone 1 Zone 21
A hazardous atmosphere is possible but
unlikely to be present for long periods
of time (>10 <1000 hours per year
Zone 2 Zone 22
A hazardous atmosphere is not likely to
be present in normal operation or
infrequently and for short periods of
time (<10 hours per year)
Hazardous Area Characteristics