Hazardous areas outside North
America are classified by gas groups and zones.
- Zones are used to define the
probability of the presence of flammable materials.
- Groups classify the exact flammable
nature of the material.
Protection
Types are used to denote the level of
safety for the device. Equipment approved receives a temperature code
indicating the maximum surface temperature of the equipment.
Zones
The zone defines the probability of
hazardous material being present in an ignitable concentration in the
surrounding atmosphere.
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Zone 0
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Area in which an explosive gas-air
mixture is continuously present or present for long periods.
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Zone 1
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Combustible or conductive dusts
are present. Area in which an explosive gas-air mixture is likely to occur
for short periods in normal operation.
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Zone 2
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Area in which an explosive gas-air
mixture is not likely to occur, and if it occurs it will only exist for a
very short time due to an abnormal condition.
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Protection
Types
Different protection techniques are
used to address the hazardous zones.
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Zone
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Ex d
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Flameproof (Explosion proof)
Enclosure
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1, 2
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Ex e
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Increased Safety
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1, 2
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Ex ia
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Intrinsically Safe
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0, 1, 2
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Ex ib
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Intrinsically Safe
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1, 2
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Ex o
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Oil Immersion
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2
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Ex p
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Pressurized Apparatus (Purged
Apparatus)
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1, 2
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Ex q
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Powder Filling (Sand Filling)
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2
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Ex m
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Encapsulation
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1, 2
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Ex n or Ex N
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Non incentive or/and normally no
sparking circuits
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2
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Flameproof
(Explosion proof) Enclosure
All electrical circuits are enclosed
in a house strong enough to contain any explosion or fire that may take place
on the inside.
Increased
Safety
Electrical circuits incorporates
special measures to reduce the probability of excessive temperatures and the
occurrence of arcs and sparks in normal service.
Intrinsically
Safety
The electrical energy available in
circuits and equipment, is limited to a level to low to ignite the most easily
ignitable mixtures in a hazardous area.
Intrinsically safe barriers, as
Zener, are installed in the circuit to limit current and voltage in the
hazardous areas to avoid sparks or hot spots under fault conditions.
Temperature
Codes
A mixture of air and hazardous gases
may ignite by coming in contact with a hot surface. An ignition depends on
surface area, temperature and the concentration of the gas.
Certified equipment are tested for
maximum temperature ratings by approval agencies. Equipment for Group II
receives a temperature code indicating the maximum surface temperature.
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Temperature
Code
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oF
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oC
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T1
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842
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450
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T2
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572
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300
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T3
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392
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200
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T4
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275
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135
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T5
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212
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100
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T6
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185
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85
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The coding is based on a 104 oF
(40 oC) ambient temperature.
Groups
Electrical equipment are divided
into two groups where Group I covers equipment used in mines and Group II
covers all other applications. Group II is subdivided into three subgroups
where the specific hazardous materials within each group can be found in CENELEC EN 50014.
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Group I
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For application in below ground
installations (mines) where methane (firedamp) and coal dust may be present.
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Group IIA
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For application in above ground
installation where hazards due to propane may exist.
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Group IIB
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For application in above ground
installations where hazards due to ethylene may exist.
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Group IIC
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For application in above ground
installations where hazards due to hydrogen or acetylene may exist.
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