hazardous area classification

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Hazardous Area Classification

• 1. Hazard Its Causes/ Types
• 2. Hazardous Area Definitions
• 3. Material Classification
• 4. Area Classification
• 5. Prevention

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1. Hazard Its Causes/ Types

• Introduction Any area in plant where
  manufacturing processes emit/ may emit gases,
  vapours or mists if mixed with air in correct
  proportions will produce explosive medium.
• For an ignition to occur there must be
• A Hazard
• A Source of Energy (Ignition or Hot Surface)
• Air (To Support Combustion)

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1. Hazard Its Causes/ Types

• Fire Triangle

Air
Temperature
Fuel
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1. Hazard Its Causes/ Types

• Terminology
• Flammable Mixture Rich flammable fuel/ air
  combination in atmospheric conditions
• Hazard The Presence/ Risk of presence of
  flammable mixture
• Hazardous Area An area where during normal
  operations, a flammable mixture is likely to be
  present. The material involved is Crude oil its
  derivatives, natural synthetic process gases,
  Hydrocarbons, Metal dusts, fibers etc.

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1. Hazard Its Causes/ Types

• Non-Hazardous (Safe Area) An area, which is
  neither Hazardous nor remotely hazardous.
• Electrical Apparatus For Hazardous Area The
  apparatus which will not ignite the surrounding
  Hazardous Atmosphere, where it is used.
• Types of Protection Specific measures applied to
  electrical apparatus to prevent ignition in
  Hazardous Area.

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1. Hazard Its Causes/ Types

• Combustion
• Polymers
• Explosive
• Corrosive
• Ignition

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1. Hazard Its Causes/ Types

• Spontaneous Combustion Many hazardous material
  have property known as auto ignition Temperature
  at which ignition occurs without source of
  ignition.
• Polymers

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2. Definitions

• Prime Considerations
• Ease of Ignition The type of Material is
  classified as per property of various materials
  for ease of ignition.
• Area classification basis Area over Hazard may
  extend.
• Auto-Ignition Temperature Temperature Class of
  Apparatus Used.

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3. Material Classification

• Standards Followed
• Europe CENELEC IEC
• North America NEC
• IEC Gases and Vapours in two groups
• GR I Mining (Sub-Surface) Industry
• GR II Surface Industry Sub-Groups A,B,C.

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3. Material Classification

• As per NEC
• Class 1 Gases Vapours further divided into 4
  groups A,B,C,D.
• Class 2 Combustible Dusts further divided into
  3 groups based on their resistivity G,E,F.
• Class 3 Combustible fibers or flyings.

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3. Material Classification Gas GroupingGases
belonging to IIC are most dangerous with severity
decreasing to IIA.
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3. Material Classification

• Flammable Liquids
• Classified on basis of Flash Point.
• Class A Flash Pt lt 23oC. They produce
  large volumes of vapour
• Class B 23oCltFlash Ptlt65oC
• Class C 65oCltFlash Ptlt93oC

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4. Area Classification

• Basis
• Probability of presence of explosive mixture.
• IEC 3 zones (Zone 0,1,2)
• Zone 0 Explosive Mixtures continuously present /
  Present for long (gt1000 Hrs/Yr). e.g. Inside
  Tanks, Vessels etc.
• Zone 1 Explosive Mixtures likely to occur in
  normal operation / (Between 10 to 1000 Hrs/ Yr).
  eg Production Area, area surrounding zone 0.

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4. Area Classification

• Zone 2 Explosive Mixtures not likely to occur
  /occur short duration in normal operation (lt10
  Hrs/ Yr).
• NEC 2 Divisions (Div 1 2)
• Division I Comprising of Area Same as Zone 0
  1.
• Division II Comprising of Area Same as Zone 2.

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4. Area ClassificationThe max surface temp. of
exposed surface of equipment must always be lower
than Auto-Ignition Temp of the Prevailing Gas.

• Class
• T1
• T2
• T3
• T4
• T5
• T6

• Temperature(oC)
• 450
• 300
• 200
• 135
• 100
• 85

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5.Prevention Methods

• 5.1 Selection Process
• 5.2 Protection Methods
• 5.3 Intrinsic Safety
• 5.4 Enclosure Protection

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5.Prevention Methods

• 5.1 Selection Process
• Selection of electrical apparatus is based on
  likelihood of the simultaneous presence of
  hazardous area and source of ignition
• Steps
• 1. Identify the gas/ vapour.
• 2. Define the Zone ie 0 or 1 or 2.
• 3. Select type of protection appropriate for the
  zone.
• 4. Select equipment based on gas group and
  temperature class.

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5.Prevention Methods

• Required Information
• 1. Zone of the Area
• 2. Ignition Temp of gas/ vapour involved or
  lowest value of
  ignition temperature if more than one explosive
  material is involved.
• 3. Characteristic of gas/ vapour related to
• Ignition current (in case of IS apparatus)
• Safe gap data (in case of FP apparatus)

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5.Prevention Methods

• 5.2 Protection Method
• Methods are Zone dependent ie
• 5.2.1 Zone 0
• 5.2.2 Zone 1
• 5.2.3 Zone 2

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5.Prevention Methods

• 5.2.1 Zone 0
• No electrical apparatus allowed OR When not
  practical only intrinsically safe apparatus is
  allowed.
• Protection Method
• Intrinsic Safety (IS)
• A circuit or part of it is IS when any spark
  or thermal effect is incapable, under prescribed
  conditions, of causing ignition of prescribed
  gas/ vapour.
• Cat Ex-ia Sustainable to Two Faults
• Cat Ex-ib Sustainable to One Fault

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5.Prevention Methods

• 5.2.2 Zone 1
• Type of protection as applied to Zone 0.
• Flameproof, Pressurized, Sand filled, Oil
  Immersed.
• Protection Methods
• 1. Flameproof Enclosure (Ex-d)
• Apparatus will withstand and not pass to
  outside an internal explosion of flammable
  mixture, which may originate inside enclosure.
• 2. Pressurized Enclosure (Ex-p)
• Apparatus in which, the entry of flammable
  mixture is prevented by maintaining air pressure
  within the enclosure above atmospheric pressure.

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5.Prevention Methods

• Protection Methods
• 3. Sand filled (Ex-q)
• An apparatus that has alive parts embedded in
  powdery material.
• 4. Oil Immersed (Ex-o)
• An apparatus that has alive parts embedded in
  oil to a sufficient depth to prevent ignition.

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5.Prevention Methods

• 5.2.3 Zone 2
• Type of protection as applied to Zone 0 or Zone
  1.
• Other methods are
• Protection Methods
• 1. Non-Sparking Apparatus (Ex-n)
• Apparatus that is not capable of igniting
  surrounding.
• 2. Increased Safety Apparatus (Ex-e)
• Increased security against excessive
  temperatures and occurrence of arcs/ sparks.
• 3.Hermetically Sealed (Ex-s)
• Enclosure is so designed that gases cant enter
  in it.

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5.Prevention Methods

• 5.3 Intrinsic Safety
• Based on min ignition levels established for
  various flammable mixtures.
• Limits availability of energy even in fault
  conditions to lt min ignition energy.
• Ex-ia suitable for all zones.
• Ex-ib suitable for zones 1 2.
• Achieved by using Zener Barriers or Galvanic
  Isolators.

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5.Prevention Methods

• Zener Barrier
• In event of fault Zener diodes limit the voltage
  that can reach hazardous area and resistor limits
  current.
• Requires safe grounding otherwise will not
  function.
• Galvanic Barriers
• Isolated by transformers.
• Voltage regulator provided.
• Does not require grounding.
• Designed for special applications.
• Preferred now-a-days.

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5.Prevention Methods

• Entity Concept
• Modular approach to assemble IS systems.
• User to identify acceptable combinations of
  intrinsically safe apparatus and associated
  apparatus.
• Intrinsically safe apparatus is assigned Vmax,
  Imax, Ci, and Li.
• Associated apparatus is assigned Voc, Isc, Ca,
  and La.
• The length of cable connecting intrinsically safe
  equipment with associated equipment maybe limited
  because of the energy-storing characteristics of
  the cable.

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5.Prevention Methods

• Simple And Non-Simple Apparatus
• Simple Apparatus
• Purely resistive devices.
• Does not exceed 1.2v, 0.1A, 20 microjules, 25
  mwatts.
• Hence, does not require certification.
• Eg Thermocouples, RTD, Photocells, LEDs.
• Cable Parameters for IS
• Energy storage due to L, C L/R.
• Voltage Limitation 1/2 CV2
• Current Limitation 1/2LI3

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5.Prevention Methods

• Earthing Requirements
• High integrity Earth
• Dual Earth Cable
• Max impedance lt 1 ohm
• All screens of IS cables to be properly earthed
• No Earth Loops (Single Earthing)

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6. Conclusion

• Precautions/ Guidelines
• Permit System
• Work Permits
• Hot Permits
• Usage of Proper Tools and Tackles
• Avoid spark, use non-sparking tools.
• Use IS Multimeters

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5.Prevention Methods

• 5.4 Enclosure Protection
• Environmental Hazardous Suitability- NEMA codes
• ie protection against
• Falling Dirt, Oil spraying, splashing, Rain etc
• Also Specifies for Hazardous Locations
• ie Class-IC requires type 7C/ 8C.
• Ingress Protection - IP Table
• Specifies degree of protection against solids and
  liquids.
• Ie IP-65 for complete protection for solid
  ingress and against water jets for liquid.