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

1. Hazard & Its Causes/ Types Introduction: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:For an ignition to occur there must be: –A Hazard –A Source of Energy (Ignition or Hot Surface) –Air (To Support Combustion)

1. Hazard & Its Causes/ Types Fire Triangle:Fire Triangle: Temperature Fuel Air

1. Hazard & Its Causes/ Types TerminologyTerminology : –Flammable Mixture: –Flammable Mixture: Rich flammable fuel/ air combination in atmospheric conditions –Hazard: –Hazard: The Presence/ Risk of presence of flammable mixture –Hazardous Area: –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.

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

1. Hazard & Its Causes/ Types Combustion Polymers Explosive Corrosive Ignition

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:

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

3. Material Classification Standards Followed :Standards Followed : –Europe: –Europe: CENELEC & IEC –North America: –North America: NEC IEC : Gases and Vapours in two groupsIEC : Gases and Vapours in two groups: –GR I : –GR I : Mining (Sub-Surface) Industry –GR II : –GR II : Surface Industry; Sub-Groups A,B,C.

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

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

3. Material Classification Flammable LiquidsFlammable Liquids –Classified on basis of Flash Point. –Class A: –Class A: Flash Pt < 23 o C. They produce large volumes of vapour –Class B: –Class B: 23 o C<Flash Pt<65 o C –Class C: –Class C: 65 o C<Flash Pt<93 o C

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

4. Area Classification Zone 2:Zone 2: Explosive Mixtures not likely to occur /occur short duration in normal operation (<10 Hrs/ Yr). NEC:NEC: 2 Divisions (Div: 1 & 2) –Division I: –Division I: Comprising of Area Same as Zone 0 & 1. –Division II: –Division II: Comprising of Area Same as Zone 2.

4. Area Classification The 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( o C)

5.Prevention Methods 5.1Selection Process 5.2Protection Methods 5.3Intrinsic Safety 5.4Enclosure Protection

5.Prevention Methods 5.1Selection 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 Select type of protection appropriate for the zone. 4. Select equipment based on gas group and temperature class.

5.Prevention Methods –Required Information –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)

5.Prevention Methods 5.2Protection Method: Methods are “Zone” dependent ie: Zone Zone Zone 2

5.Prevention Methods Zone 0: No electrical apparatus allowed OR When not practical only intrinsically safe apparatus is allowed. Protection Method 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

5.Prevention Methods Zone 1: –Type of protection as applied to Zone 0. –Flameproof, Pressurized, Sand filled, Oil Immersed. Protection MethodsProtection 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.

5.Prevention Methods Protection MethodsProtection 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.

5.Prevention Methods Zone 2: –Type of protection as applied to Zone 0 or Zone 1. –Other methods are: Protection MethodsProtection 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 can’t enter in it.

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

5.Prevention Methods Zener Barrier: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:Galvanic Barriers: –Isolated by transformers. –Voltage regulator provided. –Does not require grounding. –Designed for special applications. –Preferred now-a-days.

5.Prevention Methods Entity Concept: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.

5.Prevention Methods Simple And Non-Simple Apparatus: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 ISCable Parameters for IS: –Energy storage due to L, C & L/R. –Voltage Limitation: 1/2 CV 2 –Current Limitation: 1/2 LI 3

5.Prevention Methods Earthing Requirements:Earthing Requirements: –High integrity Earth –Dual Earth Cable –Max impedance < 1 ohm –All screens of IS cables to be properly earthed –No Earth Loops (Single Earthing)

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

5.Prevention Methods 5.4Enclosure 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.