Hazardous area

HAZARDOUS AREA

By UMAJI BHABAL

OMKAR NAIK

CONTENT

BASIC CONCEPT FIRE TRIANGLE CLASSIFICATION OF

HAZARDOUS AREA MIC PROTECTION METHODS

BASIC CONCEPT

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”

HISTORY OF CRUDE WAYS OF DETECTING METHANE GAS!!

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.

FLAMMABLE MATERIAL :- CONTAIN FLAMMABLE GAS , VAPOURS , DUST etc Eg- GASOLINE, PROPANE,

HEXANE, AMMONIA etc

HAZARDOUS ATMOSPHERE

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 ..

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.

IGNITION ENERGY

Gas Representative Gas Ignition Energy

Group (mj)

I Methane 280

II A Propane260

IIB Ethylene95

IIC Hydrogen18

FIRE TRIANGLE

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CLASSIFICATION OF HAZARDOUS AREA

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.

CONSIDERATION WHILE CLASSIFICATION

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.

CLASSIFICATION BASED ON ZONES

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.

ZONE LIMITS

ZONE EXPLOSION LIMIT

ZONE 0 > 1000 h/year

ZONE 1 more than 10 but less than 1000 h/yr

ZONE 2 less than 10

“CLASS” DESIGNATION

PRIMARY DESIGNATION

THREE CLASSES

LISTED WITH ROMAN NUMERAL NOMEMCLATURE

“CLASS I” HAZARDOUS AREA

FLAMMABLE GASSES & VAPOURS. PRESENT DURING NORMAL OPERATION. POSSIBLY PRESENT DURING BREAKDOWN CONDITION. Eg.- PROPANE,GASOLINE, HEXANE, AMMONIA etc.

“CLASS II” HAZARDOUS AREA

COMBUSTABLE DUST. COULD BE PRESENT DURING BREAKDOWN. Eg.- CORN,WHEAT,SOYABEAN DUST,FLOUR,DUST FROM WOODS & PLASTICS etc.

“CLASS III” HAZARDOUS AREA

EASILY IGNITABLE FIBERS & MATERIAL that PRODUCES FLAMMABLE FLYING. COULD BE PRESENT WHERE MATERIAL HANDELED,MANUFACTURED OR USED. Eg.- WHERE RAW COTTON IS STORED.

“DIVISION” DESIGNATION

SECONDARY DESIGNATION

TWO DIVISIONS

LISTED WITH NUMERIC NOMEMCLATURE

“CLASS I DIVISION1” HAZARDOUS AREA

IGNITABLE CONCENTRATION OF FLAMMABLE GASSES & VAPORS. POSSIBLY PRESENT DURING BREAKDOWN & FAULTY CONDITION. Eg.- WHERE DELIVERY TRUCKS ARE UNLOADED.

“CLASS II DIVISION1” HAZARDOUS AREA

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.

“CLASS I DIVISION2” HAZARDOUS AREA

WHERE FLAMMABLE GASSES HANDELED BUT NORMALLY ENCLOSED. ACCEDENTIAL RUPTURE OR BREAKDOWN. Eg- ROOMS NEAR TO CLASS I DIVISION 1 AREAS.

“CLASS II DIVISION2” HAZARDOUS AREA

AREAS NEAR ELECTRICAL EQUIPMENT. Eg- AREAS ARROUND CLOSED CONVEYOR;

AREAS AROUND ENCLOSED

PROCESS EQUIPMENT.

“GROUP” DESIGNATION

SECONDARY DESIGNATION SEVERAL GROUPS LISTED WITH ALPHABETIC NOMENCLATUREMATERIALS ARE GROPED BY ONES WITH SIMILAR CHARECTIRISTICS

“CLASS I GROUP….”

CLASS I HAS 4 GROUPS ie A,B,C,D VARIABLE FALAMMABLE GASSES ARE ARRANGED BY SIMILAR CHARACTIREISTICS

- IGNITION TEMPERATURE -SAFE CLEARANCE

DISTANCE

“CLASS II GROUP….”

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

“CLASS II GROUP G”

COMBUSTABLE DUST SUCH AS FLOUR ,GRAIN,WOOD,PLASTICS

PRIMARY CONCERN OF GRAIN ELEVATORS

MIC (Minimum Ignition Current)

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.

TEMPERATURE CLASSIFICATION

T1

T Class Max. Surface Temperature

(Deg. C) 450 T2

T3

T4

T5

T6

300

200

135

100

85

S No Name of the

chemical

Minimum

Ignition

Current

(MIC) mA

Flash point

Deg. Cen.

Iignition

temperature

(Deg C)

Flammable limit

LEL UEL

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%

PROTECTION METHODS

Thank you !!!