Transcript Hazardous Area Classification

Hazardous Area Classification
1.
2.
3.
4.
5.
Hazard & Its Causes/ Types
Hazardous Area Definitions
Material Classification
Area Classification
Prevention
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)
1. Hazard & Its Causes/ Types
• Fire Triangle:
Air
Temperature
Fuel
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.
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.
1. Hazard & Its Causes/ Types
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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:
– 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.
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.
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.
3. Material Classification
Gas Grouping
Gases belonging to IIC are most dangerous with severity
decreasing to IIA.
Representative Gas
Methane
As per IEC
(EU)
I
As per NEC
(US)
D
Propane
IIA
D
Ethylene
IIB
C
Hydrogen
IIC
B
Carbon Disulphide
IIC
-
Acetylene
IIC
A
3. Material Classification
• Flammable Liquids
– Classified on basis of Flash Point.
– Class A: Flash Pt < 23oC. They produce
large volumes of vapour
– Class B: 23oC<Flash Pt<65oC
– Class C: 65oC<Flash Pt<93oC
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 (>1000
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.
4. Area Classification
• Zone 2: Explosive Mixtures not likely to
occur /occur short duration in normal
operation (<10 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.
4. Area Classification
The max surface temp. of exposed surface of
equipment must always be lower than AutoIgnition Temp of the Prevailing Gas.
Class
T1
T2
T3
T4
T5
T6
Temperature(oC)
450
300
200
135
100
85
5.Prevention Methods
5.1
5.2
5.3
5.4
Selection Process
Protection Methods
Intrinsic Safety
Enclosure Protection
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.
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)
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
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
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.
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.
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 can’t enter in it.
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 < 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:
– 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:
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Isolated by transformers.
Voltage regulator provided.
Does not require grounding.
Designed for special applications.
Preferred now-a-days.
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.
5.Prevention Methods
• Simple And Non-Simple Apparatus:
– Simple Apparatus:
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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
5.Prevention Methods
• Earthing Requirements:
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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:
– Permit System
• Work Permits
• Hot Permits
– Usage of Proper Tools and Tackles
• Avoid spark, use non-sparking tools.
• Use IS Multimeters
5.Prevention Methods
5.4 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.