This document provides an overview of hazardous locations and the classification of areas where combustible materials may be present. It discusses the three classes of hazardous locations (I, II, III), which are based on the materials present, as well as the division ratings (1, 2) which indicate if a hazard is present under normal or abnormal conditions. The document also covers equipment requirements, protection methods, and standards for intrinsically safe, flameproof, and increased safety equipment used in different hazardous location classes and zones. Key factors like gas/vapor properties, temperature limits, and enclosure types are examined to determine the appropriate precautions for electrical equipment in hazardous areas.

1. Hazardous (Classified)
Locations
1910.307

2. INTRODUCTION
• A hazardous location is any location
where a potential hazard, either a fire or
an explosion can exist due to the presence
of flammable, combustible, or ignitable
materials.
• These materials can consist of gases,
vapors, liquids, dusts, fibers, etc.

3. HAZARDOUS LOCATION
TYPES
• Class I Locations:
An area where flammable gases or vapors are
or can be present in the air in quantities
sufficient to produce explosive or ignitable
mixtures. For Example
* Petroleum Refineries, Gasoline storage and
dispensing areas, Dry cleaning plants, Spray
Finishing areas, utility gas plants.

4. Continued
• Class II Locations:
An area where presence of combustible
dust present a fire or explosion hazard.
For example:
Grain elevators, flour and feed mills, Use
or store of magnesium or aluminum
powders, producers of plastics,
fireworks.

5. Continued
• Class III Locations:
An area made hazardous due to the
presence of easily ignitable fibers or
flyings. For example:
Textile mills, cotton gins, cotton seed
mills, plants that shape or cut wood and
create sawdust or flyings.

6. Hazardous Location Conditions
• In addition to the types of hazardous
locations, the kind of conditions under
which these hazards are present are very
important : Normal Conditions,
Abnormal Conditions.
• Division 1: Normal Conditions
• Division 2 : Abnormal Conditions

7. Continued
• Class I, Class II, and Class III hazardous
locations can be either Division 1 or
Division 2
• Good examples of Class I, Division 1
locations: areas near open dome loading
facilities or adjacent to relief valves in a
petroleum refinery, because the
hazardous material would be present
during normal plant operations.

8. Continued
• Closed storage drums containing
flammable liquids in an inside storage
room would not normally allow
hazardous vapors to escape into the
atmosphere but, what happens if one of
the containers is leaking? You have got a
Division 2 – Abnormal – condition … A
Class I, Division 2 hazardous location.

9. Class I, Division 1
• Where ignitable concentration of flammable gases,
vapors or liquids can exist all of the time or some of
the time under normal operating conditions.
• Where ignitable concentrations of such gases or
vapors may exist frequently because of repair or
maintenance operations or because of leakage.
• Faulty operations of equipment or processes might
release ignitable concentrations of flammable gases
or vapors and might cause simultaneous failure of
electrical equipment in such a way as to directly
cause the electrical equipment to become a source of
ignition.

10. Class I, Division 2
• Is a location in which volatile flammable
liquids or flammable gases are handled,
processed, or used, but in which the liquids,
vapors, or gases will normally be confined
within closed containers or closed systems
from which they can escape only in case of
accidental rupture or breakdown of such
containers or systems or in case of abnormal
operation of equipment.

11. Class I, Division 1 & Class I, Division 2

12. Class II, Division 1 & Class II, Division 2

13. Class III, Division 1 & Class III Division 2

14. Nature of Hazardous Substances
• The gases and vapors of class I locations
are broken into four groups : A, B, C,
and D. These materials are grouped
according to the ignition temperature of
the substance, its explosion pressure, and
other flammable characteristics.

15. Group A
• Group A is an atmosphere containing
acetylene.
• Equipment with rating up to 536º F
(280ºC) can be utilized.

16. Group B
• Group B is an atmosphere containing
hydrogen, or gases or vapors with a
hazard equal to hydrogen. Butadiene,
and ethylene and propylene oxide are
included in this group.

17. Group C
• Group C is an atmosphere containing
cyclo-propane, ethyl ether, or gases or
vapors with hazard equal to these gases.

18. Group D
• Group D is an atmosphere containing
acetone, alcohol, benzene, butane,
gasoline, propane, natural gases or gases
with vapors with a hazard equal to these
gases.

19. Nature of Hazardous
Substances
• In Class II - dust locations – we find the
hazardous materials in Groups: E, F, G.
These groups are classified according to
the ignition temperature and the
conductivity of the hazardous substance.
• Conductivity is an important
consideration in Class II locations,
especially with metal dusts.

20. Group E
• Group E is an atmosphere containing
metallic dusts or other dusts with a
similar hazard that is equivalent, such as
Aluminum and Magnesium dusts.

21. Group F
• Group F is an atmosphere containing
Carbon Black, Charcoal Coal, or Coke
dusts with 8% or less total volatile
material.

22. Group G
• Group G is an atmosphere containing
grain dusts, flour , starch, cocoa, and
similar types of materials.

23. Continue
• Class III locations are not
broken into groups.

24. North America Optional Area
Classification
Class I, Zone 0, 1, and 2

25. Class I, Zone 0 is a Locations in
which:
• Ignitable concentration of flammable
gases or vapors are present continuously;
or
• Ignitable concentrations of flammable
gases or vapors are present for long
periods of time.

26. Class I, Zone 1 is a location:
• In which ignitable concentrations of flammable gases
or vapors are likely to exist under normal operating
conditions; or
• May exist frequently because of repair or maintenance
operations or because of leakage;
• In which equipment is operated or processes are
carried on, of such a nature that equipment breaking
down 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.

27. Class I, Zone 2 is a location
• 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.
• Ignitable gases and liquids are confined within
closed containers from which they can escape,
only as a result of accidental rupture or breaking
of the containers or system, or as a result of
abnormal operation of the equipment.

29. Elements of Hazardous Area
Classification
• Sparks can occur by electrical or mechanical
activity.
• Electrically the sparks are usually made by:
• Switching contacts
• Loose contacts in circuit carrying current
• Poorly mating metallic faces that are carrying
current
• Static discharge.

31. Mixtures of Gases, Vapors and Air
•
Ignition can only lead to a fire or explosion if
three necessary components occur
simultaneously, these are:
1. Flammable gas or vapor is present in sufficient
quantities. (leakage)
2. Sufficient air (oxygen)
3. Source of ignition (this could be spark having
sufficient energy or hot surface that will cause
spontaneous or auto-ignition.

33. Gases and Vapors
• Imagine a flammable gas or vapor slowly leaking
into confined volume of air that is not replenished.
• The concentration of gas or vapor in the mixture
will be too low to support combustion
• As concentration increases until we reach LEL.
• More increase we reach UEL.
• LEL is very important in case of hazardous areas
to dilute it by air to low and safe levels

34. Temperature Class
• It is important to know how hot equipment gets, so
that hot surfaces cannot be ignition sources.
• Six temperature classes are used T1 – T6
• The lower the number the higher the maximum
allowable surface temperature
• Temperature classification is based on fault
conditions.
• T-class must be below Auto-ignition Temperature
of the gas.

36. Example of AIT
•
•
•
•
•
•
•
•
Material
Carbon Disulfate
Diethyl Ether
Kerosene
Ethylene
Propane
Methane
Hydrogen
AIT (°C)
102
170
210
450
466
538
560

37. Apparatus Group
•
All flammable gases are sub-grouped into
IIA, IIB or IIC on the bases of:
1. How easily the burning gas will burn
through a narrow gap (measured as the
maximum experimental safe gap (MESG)
2. The maximum spark ignition energy
(MIE)

38. Apparatus Group
• A group IIA gas or vapor is the hardest of
these sub-groups to ignite by a spark.
• Conversely a group IIC gas or vapor is the
easiest to ignite.

39. Explosion Groups
• The maximum experimental safe gap is determined
using a test apparatus.
• Each gas or vapor/air mixture in its most volatile form,
under normal temp. and pressure is filled into the
interior and exterior chambers of the test apparatus.
• The circumferential gap between the two chambers is
accurately adjusted to the desired value.
• The explosive mixture in the interior chamber is ignited
and the flame propagation, if any is observed through
the windows in the exterior chamber.
• To find the maximum value of gap which prevents
ignition of the explosive mixture in the exterior
chamber.

40. MESG (Maximum Experimental
Safe Gap)
• The maximum clearance between two
parallel metal surfaces that has been
found, under specified test conditions, to
prevent an explosion in a test chamber
from being propagated to a secondary
chamber containing the same gas or
vapor at the same concentration.

41. MIC (Minimum Igniting Current)
Ratio
• The ratio of the minimum current
required from an inductive spark
discharge to ignite the most easily
ignitable mixture of a gas or vapor,
divided by the minimum current
required from an inductive spark
discharged to ignite methane under the
same test conditions.

42. Explosion Classes
Apparatus group
Minimum Ignition
for flameproof Current for Intrinsically
enclosure “d”
Safe Circuits “i”
Limiting Gap
Ratio in relation to
Width
Methane
A
B
C
> 0.9 mm
> 0.8
> Or = 0.5 to > Or = 0.45 to 0.8
0.9 mm
< 0.5 mm
< 0.45

43. Example of MIE
•
•
•
•
•
Material
Hydrogen
Ethylene
Propane
Methane
Ignition Energy µJ
40
120
320
525

45. Explosion Groups & Temp. Classes
Exp.
Groups
T1
T2
I
IIA
Hydrogen
T5
T6
Town Gas Ethylene
Diethyl
ether
CO
IIC
T4
Methane
IIB
T3
Acetone
Ethane
Propane
Ammonia
Ethane
Ethyl
Alcohol
N-Butane
N-Hexane
Petrol
Diesel
Fuel
Heating
oil
Acetaldehyde
Ethyl-ether
Carbon
Disulfide

46. Equipment for Hazardous
Locations
• Equipment for Class I locations:
The equipment used in Class I locations
are housed in enclosures designed to
contain any explosion that might occur if
hazardous vapors were to enter the
enclosure and ignite.
Also it is designed to cool and vent the
products of this explosion.

51. Equipment for Class II
Locations
• Class II locations make use of equipment
designed to seal out dust. The enclosures
are not intended to contain an internal
explosion, but rather to eliminate the
source of ignition so no explosion can
occur within the enclosure.

52. Equipment for Class III
Locations
• Equipment used in class III locations
need to be designed to prevent fibers and
flyings from entering the housing. It also
needs to be constructed in such a way as
to prevent the escape of sparks or
burning materials.
• It must also operate below the point of
combustion.

53. Types of Protection
1.
2.
3.
4.
5.
6.
7.
8.
9.
Flameproof Enclosures “d”
Intrinsic Safety “i”
Increased Safety “e”
Powder/Sand Filled “q”
Pressurized Apparatus “p”
Oil Immersion “o”
Special Protection “s”
Encapsulation “m”
Type of protection N “N”

54. Flameproof Enclosures “d”
Type of protection, for which
the parts which can ignite an
explosive atmosphere are
inside an enclosure which will
Withstand the pressure of the
Explosion within the enclosure.
Prevent the transmission of the
Explosion to an explosive
Atmosphere surrounding the
Enclosure.

57. Intrinsic Safety “i”
• Type of protection, for which the
energy in the electrical circuit is held
so low that sparks, arcs or
temperatures capable of causing
ignition cannot occur.
• Includes sub-division into the
categories ia & ib
• Ia must not produce any ignition when
any combination of two faults is
present.
• Ib must not produce any ignition, in
normal operation, when one fault is
present.

58. Increased Safety “e”
• Type of protection, for
which measures are taken to
prevent the possibility of
non-permissible high
temperatures and the
formation of sparks or arcs
on inner or outer parts of
electrical apparatus, on
which these do not occur in
normal operation, with an
increased level of safety.

59. Powder/Sand Filled “q”
• The electrical apparatus
enclosure is filled with
powder or sand.
• An arc occurring in the
enclosure does not ignite
an explosive
atmospheres
surrounding the
enclosure.

60. Pressurized Apparatus “p”
• Preventing the entry of
surrounding atmosphere
into the enclosure by
holding an ignitionprotection gas (air, inert
gas) under over-pressure
in relation to the
surrounding atmosphere

61. Oil Immersion “o”
• Electrical apparatus or
parts thereof are made
safe by immersion in oil
such that potentially
explosive atmosphere
above the surface of the
oil or outside the
enclosure will not be
ignited.

66. European System

67. Hazardous Zones
•
•
•
•
•
Zone 0
Zone 1
Zone 2
Non-Hazardous area
Area that was deemed to be completely
free of potential hazards.

68. Area (Zone) Classification
• In order to evaluate and stipulate the necessary
protective measures, hazardous areas have been
classified into different zones in respect to the
probable occurrence of an explosive atmosphere.
• Hazardous area is defined as three-dimensional space
in which a flammable atmosphere may be expected to
be present at such frequencies as to require special
precautions for the construction and use of electrical
apparatus.
• The European classification: Hazardous areas are
divided into three zones:
• Zone 0 , Zone 1, and Zone 2

69. Zone 0
• Is a zone in which an explosive gas/air
mixture is continually present for long
periods of time.

70. Zone 1
• Is a zone in which an explosive gas/air
mixture is likely to occur under normal
operating conditions.

71. Zone 2
• Is a zone in which an explosive gas/air
mixture is unlikely to occur under
normal operating conditions, and if it
does it will exist only for a short period of
time.

72. Extend of zone
• The distance in any direction, vertical and
horizontal, from the source of release to the
point where the flammable atmosphere has
been diluted by air to a sufficiently low level
• For a given release the extend will vary with
the vaporizing potential of the fluid release,
the ventilation state and the bouyancy factor
of the vapor.

75. Area Classification
Oil Water Separator

76. Floating-Roof Tank

77. Fixed Roof Tank

79. Selection of apparatus
Zone
0
Type of Protection
Intrinsically safe Ex ia
Special protection Ex s
1
Any type of protection suitable for zone 0
Flameproof Ex d
Intrinsically safe Ex ib
Pressurized Ex p
Increased safety Ex e
Special protection Ex s
2
Any type of protection suitable for Zone 0 or Zone 1
Ex N or Ex n
Oil immersion Ex o
Quartz Filled Ex q

80. Types of Protection for Ingress of
Water and Solid Particles
European Practice

81. Enclosure (IP) Protection
•
The measures required to be applied to the
enclosure to provide a chosen degree of
protection to:
1. Persons against contact with internal live or
rotating parts inside the enclosure, and to the
apparatus against ingress of solid objects, dusts,
etc.
2. The apparatus against the ingress of water,
spray, jets, heavy seas and even total immersion.

83. Ingress Protection against Particles
3rd Digit
Degree of Protection
0
1
2
No mechanical protection
3
Protection against the ingress of foreign bodies greater
than 2.5 mm thick.
4
Protection against the ingress of foreign bodies greater
than 1 mm thick
5
Protection against the ingress of dust, whereby dust shall
not enter the enclosure in sufficient quantities to cause
equipment malfunction.
6
Complete protection from ingress of dust.
Protection against large-sized foreign bodies (hands)
Protection against 12.5 mm diameter foreign bodies
(finger)

84. Ingress Protection against Liquids
3rd Digit
Degree of Protection
0
1
2
No protection
3
Protection against rain falling at an angle of 60 degree or
less from vertical
4
5
6
Protection against water splashed from any direction
Protection against drops of condensed water
Protection against drops of liquid with the equipment
tilted at any angle up to 15 degree from the vertical
Protection against jets of water
Protection against water from heavy seas

85. Continue
7
Protection against immersion in water
under stated conditions of pressure and
time
8
Protection against immersion in water
under specified pressure, for an indefinite
period of time.

86. Ingress Protection
• The degree of protection depend upon whether the
equipment will be installed outdoors and exposed
to the extremes of the weather, or indoors and
exposed (or not) to dust or liquid ingress.
• If the location is outdoors, then the IP code will
typically vary between IP54 and IP66
• For indoor equipment in a hazardous area not
exposed to particles or water, the minimum IP
code would be typically IP44

87. Commonly Used IP Codes
0
0
1
2
3
4
5
6
1
2
3
4
5
6
7
8
IP11 IP12
IP21 IP22 IP23
IP31 IP32 IP33 IP34
IP41 IP42 IP43 IP44
IP54 IP55
IP65 IP66 IP67 IP68

88. Marking
• Applicable national or international standard
(BS5501 Part 5, IEC60079 Part 2
• Name or abbreviation of the testing lab
(BASEEFA)
• Approved symbol for the certifying authority EEX
hexagonal symbol
• Type of protection EEX “d” EEX “e”
• Gas Group IIA IIB IIC
• Temperature Class T6
• Serial or certificate number

89. Example
• EEx de
IIC
T6

90. EEx ib IIB T4
• E: European Standards
• Ex ib: Intrinsically safe to category ib
• II: Certification for use in apparatus group II
•
•
(in other industries) (I is for mines)
B: Explosion classes
T4: The ignition temperature of any gas or
vapor with which this device will be used is not
less than 135 degree C