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Special-purpose motors 7/179

IEC 60079-14 provides general guidelines for the selection safety motor, type Ex. ‘e’ or a pressurized motor, type
of electrical equipment for hazardous areas. Ex. ‘p’ may also be considered to be safe.

7.11.1 Classification of hazardous locations Zone 2
It is important to identify areas in accordance with the This is a location safer than Zone 1 with a likelihood of
expected degree of fire hazard to facilitate an appropriate concentration of explosive gases, chemical vapour or
and economical selection of electric motors. These areas, volatile liquids during processing, storage or handling.
according to IEC 60079-10, are classified into three This would become a fire hazard only under abnormal
categories as follows. conditions, such as a leakage or a burst of joints or pipelines
etc. Such a condition may exist only for a short period.
Zone 0 A standard motor with additional features, as discussed
below, may also be safe for such locations. A non-sparking
This is a location which is continuously contaminated type, Ex. ‘n’, or an increased safety motor, type Ex. ‘e’,
with explosive gases, chemical vapours or volatile liquids may also be chosen for such locations.
and thus is highly susceptible to fire hazards. Installation
of electrical machines in such areas should be avoided Nore Some applications creating hazardous conditions are
as far as possible, to reduce cost, facilitate maintenance petrochemical or fertilizer plants, refineries, coal mines etc., where
and take other precautions. inflammable gases and volatile liquids are handled, processed and
IEC 60079-14 recommends the use of only intrinsically stored.
safe apparatus in such locations. Intrinsically safe
apparatus and their electrical circuits are basically low- Mines, collieries and quarries
energy devices and release only small amounts of energy,
insufficient to ignite the surrounding atmosphere. The In view of the magnitude and intensity of explosion and
devices may be to record, sense or monitor the operating fire damp hazards at such locations, a motor with superior
parameters of equipment operating in such locations or electrical and construction design is recommended. IEC
the condition of the surroundings. They may be mounted 60079-0 categorizes such areas as Group I and recom-
on the surface rather than the interior of an enclosure. mends only flame-proof motors, type Ex. ‘d’, depending
Circuits connecting such devices and instruments are upon the nature and the ignition temperature of the gases,
also made intrinsically safe for use in such areas. We chemical vapour or volatile liquids at such locations.
show in Section 7.12 that an electric motor is not suitable The maximum permissible temperature at the external
for such locations (see also Section 7.16). surface of the machine must also be limited so that it
does not ignite the inflammable substances at the
Zone 1 installation.

This is a location which is not permanently contaminated 7.11.2 Classification of gases, chemical vapour
but is likely to be prone to fire hazards during processing, and volatile liquids
storage or handling of explosive gases, chemical vapour
or volatile liquids, although under careful and controlled Based on the ignition temperature of these inflammable
conditions. For such locations in addition to a flame- or substances, Table 7.4 shows the groups of substances
explosion-proof enclosure, type Ex. ‘d’, an increased requiring specially constructed motors.
Table 7.4 Grouping of gases, chemical vapour and volatile liquids, their ignition temperature and limits of permissible temperature
at the external surface of the motor based on IEC 60079-20

Ignition group TI T2 T3 T4 T5 T6
1 Ignition temp. (“C) Above 450 300/450 200/300 135/200 100/135 85/100
2 Grouping Acetone Acetylene Acetaldehyde Ethyl-ether Carbon
Ethane Ethyl amine Ethyl glycol disulphide
Ethyl-acetate Ethylene Crude oil Ethyl Nitrite
Ammonia Iso-amyl acetate n-Hexane
Benzene Butane Turpentine
Acetic acid n-Butyl alcohol Mineral oils
Carbon monoxide n-Propyl alcohol Cyclo hexene
Methane (fire damp) Butanol
Methanol
Naphthalene
Propane
Coal gas (town gas)
Petroleum
Toluene
Water gas
Hydrogen