Electrical Maintenance in Hazardous area

-Bhagawan Prasadamieclub@gmail.com

Objective of Area classification

It is a method of: -Analyzing & classifying the environment where Explosive atmosphere may occur during.

a) Normal Conditions b) Abnormal Conditions.

Advantage:-Classification Provides a basis for the selection of suitable electrical apparatus for safe operation

Why is this Important?

Prevent Electrical Hazards from Starting Fires and Explosions.

These can be Devastating Loss of Life Loss of Facilities Preventable by Following Guidelines Established Cost of Installing

Wrong Type of New & Replacement Electrical Equipment

Fire Explosion Triangle

These oxidation reactions normally involves the release of heat & pressure, which is the major criteria of an explosion.

Important Termology

Hazard: Risk of presence of flammable gas and air mixture.

-Hazardous atmosphere: An atmosphere/ environment containing any hazard in a concentration capable of ignition.

-Hazardous area: An area/ surrounding where, hazardous atmosphere is likely to occur during normal/ abnormal operation.

-Ignition temperature: The lowest temp at which ignition occurs in vapour air mixture.

Flammable substances

Flammable substances may be gaseous, liquid or solid

- Flammable gas: Are often hydrocarbons & require very little energy to react with atmospheric oxygen.Ex : Methane, Ethane, Hydrogen

- Flammable Liquids: Which evaporates at room temperature in sufficient quantities to form flammable atmosphere. Ex: Lighter fuel (MS, Naphtha ….)

- Flammable Solids: Flammable Dust & fibers which react with atmospheric air to cause explosions in the presence of source of ignition. Ex: (Wood,Coal Dust, metals…..)

Concentration: Explosive Limits

-LEL Lower explosive limit:Lower or Minimum level of concentration of flammable vapour/gas in atmosphere which can ignite by arc/spark

-HEL/UEL: Upper or maximum level of concentration of flammable vapour/gas in atmosphere which can ignite by arc/spark

-Explosive/Flammability Range: Range between LEL to HEL

Concentration: Explosive Limits

Area Classification

There are two major classifications prevalent world wide:

•NEC (National Electrical Code) of USA

•BIS/IEC (Bureau of Indian standard/International Electro technical Commission)

NEC CODE

Classifies combustible media as:•Class I (Flammable gases, vapour & liquid)•Class II (Combustible dusts)•Class III (Ignitable Fibers)

Groups under different class:Class 1 Class 2 Class 3Group-A (acetylene) Group-E (Combustible metal dust) No Group (Ignitable fibers)

Group-B (Hydrogen) Group-F (Combustible dust having volatile material like: charcoal, coke dust)

Group-C (Ethylene)

Group-D (Propane)

Extent of Hazard:•Division 1: Hazardous media can exist under normal operating condition

•Division 2: Hazardous media can exist under abnormal operating condition

IEC CODE

Classifies combustible media as:•Group I: Mining (Methane)•Group II: Other than mining (Gases & Vapors)

Gas Group:Group-A : PropaneGroup-B : EthyleneGroup-C : Acetylene, Hydrogen & carbon Di Sulphide.

Extent of Hazard is defined by Zone:

•Zone 0: Hazardous media is continuously present or likely to be present for longer period.•Zone 1: Hazardous media can exist under normal operating condition.•Zone 2: Hazardous media can exist under abnormal operating condition & for a short duration.

- Zone-0: - Area like vapour space above storage tank,

process tank, container having flammable material open or close.

- Zone-1:- Inadequately ventilated pump house handling

flammable material.- Area around imperfectly fitted rim seal of floating

roof tank.- Loading of rail Waggon & TT, dispensing stations- Normal start up & shut down of refinery.

- Zone-2: - All other area where handling of flammable

product is being done in ventilated area & system is designed that vapours are confined within the system,& cannot escape except during abnormal condition.

Examples

Zone presentation

Group Representative Gases I All Underground Coal Mining.

Firedamp (methane) IIA Industrial methane, propane, petrol

and the majority of industrial IIB Ethylene, coke oven gas and other industrial gases IIC Hydrogen, acetylene, carbon

disulphide

Gas group

Temperature class

IP (Ingress Protection)

1st(Protection against solid) 2nd(Protectionagainst liquid)

0 No protection 0 No protection

1 Solids size > 50 mm 1 Vertically following drops

2 Solids size > 12 mm 2 15 deg from vertical

3 Solids size > 2.5 mm 3 60 deg from vertical

4 Solids size > 1.0 mm 4 Water from all direction

5 Against dust 5 Water jet from all direction

6 Complete against dust 6 Water jet with force

7 Immersion

Type of Protections

Various method of protection is prevalent & is suitable for use in hazardous location depending on the extent of hazard. They are:

- Explosion proof or flame proof (Ex d)- Increased safety (Ex e)- Intrinsically safe (Ex i)- Purge protected (Ex p)- Non sparking (Ex n)

-Oil filled (Ex o)

Electrical gadgets

Likelihood of gas/vapour (Above LEL)

Hazardous Area Rating

Likelihood of Ignition Source

Common Protection Basis for Electrical Equipment

Certain Zone -0 Extremely rare Intrinsic Safety Exi

Likely Zone-1 Rare Flame Proof Ex d

Pressurization Ex p

Un likely Zone-2 Un likely Increase Safety- Ex e

Non Sparking – Ex n

Most Un likely Non Hazardous

Possible Normal Electrical Equipment

Electrical gadgets zone wise

FLAME PROOF EX D

Performance Requirements:It is a method of protection, where the equipment is enclosed in an enclosure, which-Will withstand the internal explosion of flammable gases that enter it, without damage.

- Do not allow the internal explosion to permeate to the surroundings through any joints.

Constructional Features:•Flame path (length & clearances) is ensured as per code.

Suitability:•For use in Zone-1 & Zone-2.

INCREASED SAFETY EX EPerformance Requirements:It is a method of protection, -Wherein additional precautions are taken to provide additional safety against excessive temperature, occurrence of arc & spark.

-These are not capable of withstanding explosion inside enclosure.

Constructional Features:•No arcing devices such as fuse & switchgears are used.•Ignition is prevented by use of non sparking components.•Clearances & creep age distances are maintained as per code.Suitability:•For use in Zone-2.

INTRINSICALLY SAFE EX IPerformance Requirements:It is a method of protection, -Explosion is prevented by ensuring that sufficient energy for ignition of flammable gases is not available.

-The Surface temperature does not exceeds auto ignition temperature of surrounding flammable gases.

Constructional Features:

•These equipments are primarily low energy electronic device. Operates at lower voltage & amp.(28V,93mA,0.65W)

Suitability:•For use in Zone-0 (ia) & Zone-1 (ib).

INTRINSICALLY SAFE EX PPerformance Requirements:It is a method of protection,

-Explosion is prevented by purging flammable media & ensuring non-ingress of flammable media by keeping positive pressure.

•The Surface temperature does not exceeds auto ignition temperature of surrounding flammable gases.

Constructional Features:•Components & devices are installed inside a purge panel. A positive pressure of uncontaminated air or other neutral gas is maintained inside the panel.Suitability:•For use in Zone-1.

NON SPARKING SAFE EX NCONCEPT SHARES SIMILARITIES WITH EX E PHILOSOPHY

Performance Requirements:It is a method of protection,

-Wherein in normal condition, it is not capable of igniting the surrounding explosive atmosphere.

-Fault capable of causing the ignition is not likely to occur.Constructional Features:•Components selected are non arcing, non sparking•Enclosed break-Incendive components.•Restricted breathing by sealing & gasketing.

Suitability:•For use in Zone-2.

MATERIAL OF CONSTRUCTION

Following material is generally specified:

For enclosure:

•Casting: Al Alloy, CI & CS

•Sheet fabrication: Al Alloy, SS & MS

Leveling

Once certified, the equipment is marked by the ‘CE’ (meaning it complies with ATEX and all other relevant directives) and ‘Ex’ symbol to identify it as approved under the ATEX directive.

The letters "CE" stand for "Conformité Européenne" ("European Conformity"). The Product confirmas to all requièrent of Heath, Safety & Environnent.

Labeling

Once certified, the equipment is marked by the ‘CE’ (meaning it complies with ATEX and all other relevant directives) and ‘Ex’ symbol to identify it as approved under the ATEX directive.

The letters "CE" stand for "Conformité Européenne" ("European Conformity"). The Product confirmas to all requièrent of Heath, Safety & Environnent.

Labeling

DO’S IN HAZARDOUS AREA

Use brass made tools Ensure gasket/seal is not missing Use recommended 3 pin top/socket only Care for glass/fragile items Stop working if too much smell is there Ensure earth connection in switch board/DB box Ensure no glass or sharp item is in working area Use dustbin for cotton waste/CRC/ used bottle Ensure all wiring is neatly tied or dressed Area is not dry grassy Carry recommended torch at night Carry panel key, tool box with you

Don’ts IN HAZARDOUS AREA Don’t overload wire /MCB Don’t use so many jig jag connection or tops Don’t leave the cover open Don’t stand/rest under tank Don’t discharge the capacitor in side

LPG/tank area Don’t use rusted or strained nut bolt Don’t use un-sleeved pliers /screw driver Don’t hit metal part with hammer Don’t disconnect the earth bonding

Thank you