3. HAZARDOUS AREA :-
“AREA WHICH CONTAINS
EXPLOSIVE AIR , GAS MIXTURE OR
EXPECTED TO BE PRESENT IN A
QUANTITY SUCH AS A REQUIRE
SPECIAL PRECAUTION
, CONSTRUCTION & USED OF
ELECTRICAL APARATUS”
4. In the 1700's, certain gases or the lack of oxygen were detected with various
hit and miss types of detection. The candles on miners caps, or if carried by
the miner, would either go out from the lack of oxygen or the flame would get
larger with a different coloring of the flame if certain gases were in the area.
Of course, in some instances these open flames caused fires or explosions. By
1815, the Davy's Safety Lamp came into use in the mines. This certainly
changed the way for miners to check for certain gases.
They took these canaries in small cages with them down the coal mines where
they worked. The canaries were the miners alarm signal to show them when
the coal-gas levels got too high. The canary stopped singing and was most
likely to be laid feet up on the bottom of the cage, poisoned by the mine gas.
5. FLAMMABLE MATERIAL :-
CONTAIN FLAMMABLE GAS ,
VAPOURS , DUST etc
Eg- GASOLINE, PROPANE, HEXANE,
AMMONIA etc
6. Hazardous atmosphere is an atmosphere that
may expose a worker to the risk of death or
incapacitation, or prevent a worker from
getting out of the confined space because of
an injury or critical illness. Such an
atmosphere can be
explosive, flammable, poisonous, corrosive,
oxidizing, irritating, oxygen
deficient, toxic, or otherwise harmful which
can result in death, illness ..
7. IGNITION ENERGY :-
A specific mixture of fuel and oxidant
that yields the most rapid combustion at
a specific measured quantity.
FLASH POINT :-
The flash point of a volatile material is
the lowest temperature at which it can
vaporize to form an ignitable mixture
in air.
8. Gas Representative Gas Ignition Energy
Group (mj)
I Methane 280
II A Propane 260
IIB Ethylene 95
IIC Hydrogen 18
10. Why Area Classification???
HAC is a method of analyzing and
classifying the environment where
explosive gas atmospheres may
occur to allow the proper selection
of electrical apparatus to be
installed in that environment.
11. 1.The flammable materials that may be present;
2. The physical properties and characteristics of each
of the flammable materials;
3. The source of potential releases and how they can
form explosive atmospheres;
4. Prevailing operating temperatures and pressures;
5. Presence, degree and availability of ventilation
(forced and natural);
6. Dispersion of released vapours to below flammable
limits;
7. The probability of each release scenario.
12. Zone 0: An area in which an explosive gas
atmosphere is present continuously or for long
periods;
Zone 1: An area in which an explosive gas
atmosphere is likely to occur in normal
operation;
Zone 2: An area in which an explosive gas
atmosphere is not likely to occur in normal
operation and, if it occurs, will only exist for a
short time.
13. ZONE EXPLOSION LIMIT
ZONE 0 > 1000 h/year
ZONE 1 more than 10 but less than 1000 h/yr
ZONE 2 less than 10
15. FLAMMABLE GASSES &
VAPOURS.
PRESENT DURING NORMAL
OPERATION.
POSSIBLY PRESENT DURING
BREAKDOWN CONDITION.
Eg.-
PROPANE,GASOLINE, HEXANE,
AMMONIA etc.
16. COMBUSTABLE DUST.
COULD BE PRESENT DURING
BREAKDOWN.
Eg.- CORN,WHEAT,SOYABEAN
DUST,FLOUR,DUST FROM
WOODS & PLASTICS etc.
17. EASILY IGNITABLE FIBERS &
MATERIAL that PRODUCES
FLAMMABLE FLYING.
COULD BE PRESENT WHERE
MATERIAL
HANDELED,MANUFACTURED OR
USED.
Eg.- WHERE RAW COTTON IS
STORED.
19. IGNITABLE CONCENTRATION
OF FLAMMABLE GASSES &
VAPORS.
POSSIBLY PRESENT DURING
BREAKDOWN & FAULTY
CONDITION.
Eg.- WHERE DELIVERY TRUCKS
ARE UNLOADED.
20. CONTAIN DUST OF ELECTRICALLY
CONDUCTIVE NATURE.
MECHANICAL FAILURE OR
ABNORMAL OPEARATION MIGHT
PRODUCE IGNITABLE OR EXPLOSIVE
MIXTURE.
Eg.- AREAS OF OPEN
CONVEYORS,OPEN TOP BINS, DUST OF
MAGNESSIUM OR ALLUMINIUM.
21. WHERE FLAMMABLE
GASSES HANDELED BUT
NORMALLY ENCLOSED.
ACCEDENTIAL RUPTURE OR
BREAKDOWN.
Eg- ROOMS NEAR TO CLASS
I DIVISION 1 AREAS.
24. CLASS I HAS 4 GROUPS ie
A,B,C,D
VARIABLE FALAMMABLE
GASSES ARE ARRANGED BY
SIMILAR CHARACTIREISTICS
- IGNITION TEMPERATURE
-SAFE CLEARANCE DISTANCE
25. CLASS II HAS 2 GROUPS ie E,F
VARIABLE COMBUSTABLE DUSTS
ARE ARRANGED BY SIMILAR
CHARACTIREISTICS
- IGNITION TEMPERATURE
-HOW TIGHT EQUIPMENT SEALS
NEED TO PREVENT DUST
ENTERING IN EQUIPMENT
26. COMBUSTABLE DUST SUCH AS
FLOUR ,GRAIN,WOOD,PLASTICS
PRIMARY CONCERN OF GRAIN
ELEVATORS
27. 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.
28. T Class Max. Surface Temperature
(Deg. C)
T1 450
T2 300
T3 200
T4 135
T5 100
T6 85
29. S No Name of the Minimum Flash point Iignition Flammable limit
chemical Ignition Deg. Cen. temperature LEL UEL
Current (Deg C)
(MIC) mA
1 Methane 85 - 595 5% 15%
2 Ammonia - - 630 105 mg/l 200 mg/l
3 Ethylene 45 - 425 2.7% 34%
4 Propane 70 - 470 2% 9.5%
5 Acetylene 24 - 305 1.5 % 100%
