intrinsic safety
TRANSCRIPT
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Intrinsic
Safety
& Hazardous Areas
by
Steve Mackay
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EIT Micro-Course Series• Every two weeks we present a 35 to 45
minute interactive course
• Practical, useful with Q & A throughout
• PID loop Tuning / Arc Flash Protection, Functional Safety, Troubleshooting conveyors presented so far
• Upcoming: – Electrical Troubleshooting and much,
much more…..
• Go to:http://www.idc-online.com/slideshare
• You get the recording and slides
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Overall Presentation
The focus of this session is the building blocksof electrical engineering, the fundamentals ofelectrical design and integrating electricalengineering know-how into the other disciplineswithin an organisation.
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ObjectivesThe identification of: Terminology Fundamentals of Ex i Protection
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Ex Protection DefinitionExplosion Protection:
The measures applied in the construction of electrical apparatus to prevent ignition of surrounding explosive atmosphere by such apparatus.
Need to understand: ‘ignition’
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InspectorateInspectorate
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The Fire TriangleThe Fire Triangle
Airwith
21% OxygenFuel
Sufficient Vapour
27.2
!Bang
Source of IgnitionSource of Ignition
O2
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Electricity as a Source of Ignition
Sources of IgnitionSources of Ignition
HeatHeatSparksSparks
Electrical SourcesElectrical Sources
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Spark Ignition Characteristic
(LEL)Lower Explosive Limit
(UEL)Upper Explosive Limit
Minimum Ignition Energy (MIE)
IgnitionEnergy
(milliJoules)
Volumeconcentration (%)
1.0
0.1
0.01 0 10 20 30 40 50 60 70 80 90 100
Flammable Range
Propane-air (1 atmos.)
Most-easily ignitable mixture
Hydrogen-air(1 atmos.)
Ethylene-air(1 atmos.)
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Explosive limits for materials Gas/air mixtures are ignitable over a range of concentrations called the
“Flammable Range”
Material Lower Explosive Limit Upper Explosive Limit Minimum
LEL UELignition
energy*
Propane 2 % 9.5 %180µJ
Ethylene 2.7 % 34 % 60µJ
Hydrogen 4 % 76 % 20µJ
* of most easily ignitable mixture (Note: MESG assessed for Ex d)
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Ignition Temperature Definition
The lowest temperature of a flammable gas or vapour at which ignition occurs.
Ignition Temperature
Sometimes referred to as:
Auto-ignition temperature
Or
Spontaneous ignition temperature
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Flashpoint Definition
The temperature at which the free surface of a liquid emits sufficient vapour to be ignited by a small flame
Flashpoint
Kerosene:Flashpoint = 38°C; Ignition Temp. = 210°C) Only liquids have flashpoints
Operation below Flashpoint constitutes no actual hazard
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Personnel HazardsFor Hydrogen Sulphide, H2S:
a very common danger when dealing with oil products
Property VolumeConcentration
Smell detection level 0.1 ppm
Safe working level 10
Serious health danger level 50
Lower Flammable Limit 40,000 (4%)
Upper Flammable Limit 460,000 (46%)
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Area Classification
Nature of the Hazard
Locations of hazard
Probability of presence
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Requirement for plant classification Plant and Installations
are classified according to:-
The nature of the Hazardous Atmosphere
The probability that the Hazardous Atmosphere will be present
- Gas Classification- Ignition Temperature
- Area Classification
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Requirement for equipment classification
- Apparatus Group
- Temperature Classification
Equipment is classified according to:-
The maximum spark energy it can produce
Its maximum surface temperature
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Gas classification: the two main systems
Representative(Test) gas
Gas classification
IgnitabilityIEC countries(including Europe) USA & Canada
AcetyleneHydrogenEthylenePropane
Methane
Metal dustCarbon dustFlour, starch,Grain
Fibres & Flyings
Group IICGroup IICGroup IIBGroup IIA
Group I(Mining)
(IEC 1241)
(No classification)
Class I, Group AClass I, Group BClass I, Group CClass I, Group D
(No classification)
Class II, Group EClass II, Group FClass II, Group G
Class III
Moreeasilyignited
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Temperature classification (IEC/European)
450°C T1
300°C T2
200°C T3
135°C T4
100°C T5
85°C T6
Temperatureclassification
Maximumsurface
temperature
Tamb = 40oCunless otherwise
stated
Operation abovestated Tamb mayde-rate T Class
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Temperature classification in North America
T1 450
T2 300
T2A 280
T2B 260
T2C 230
T2D 215
T3 200
T3A 180
T3B 165
T3C 160
T4 135
T4A 120
T5 100
T6 85
T class
Apparatus is marked with either T rating or maximum surface temperature
User has responsibility to ensure that the T-rating is below the Spontaneous
Ignition Temperature ( SIT )
°C
Tamb = 40oC
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Gas/Apparatus compatibility Ammonia 630
Gas Ignition Temperature
600
500
400
300
200
100
ApparatusTemperatureClassification
Carbon Disulphide 105
T1T1
T2T2
T4T4
T6T6T5T5
T3T3
Hydrogen 560 Methane 595
Propane 470Ethylene 425
Butane 365
Cyclohexane 259
Diethyl Ether 170
T4 for apparatus is usually OKException:Carbon Disulphide, requiring T5Don't confuse T Class with maximum operating temperature!
TAMB=40oCoC
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Properties of Gases
Extract from IEC79-18
Compound Vapour LFL UFL Ignition T Apparatus Density Temp °C Class Group
AcetoneAmmoniaButaneCarbon DisulphideCyclohexaneDiethyl EtherEthyleneHydrogenKeroseneMethanePropane
2.000.592.052.642.902.550.970.07
0.551.56
2.015 1.5 1.0 1.2 1.7 2.7 4.0 0.7 5.0 2.0
1328 8.560 7.8363475.6 515 9.5
535630365100259170425560210595470
T1T1T2T5T3T4T2T1T3T1T1
IIAIIAIIAIICIIAIIBIIBIICIIAI / IIAIIA
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Area classification in IEC/European countriesAreas classification:
The probability of a potentially explosive atmosphere being present
and
The length of time for which it is likely to exist
Zone 0:
Zone 1:
Zone 2:
in which an explosive gas-air mixture is continuously present or present for long periods
in which an explosive gas-air mixture is likely to occur in normal operation
in which an explosive gas-air mixture is not likely occur in normal operation, and if it occurs it will exist only for a short time
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Area classification in North America
Division 1Hazardous atmosphere is likely to be present in normal operation
Division 2Hazardous atmosphere is unlikely to be present in normal operation
Zone 0:
Zone 1:
Zone 2:
Div.1 Zone 0 sometimes specified
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Area Classification Example
Bund wall
Tank vents
Liquid surface
Area Classificationfor a fixed-roof tank
withheavier than air
vapour
Zone 1
Zone 0
Zone 2
Key
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Typical Area Classification Plan Drawing
T1
T2 T3
T4
IIB T3 Hazard
T1-4Tanks
Zone 2 Radius4.5 metres
Zone 1 Radiusto bund wall2.5 metres
4 Flow ValvesZone 1: in pipetrench 1.75metres wideacross CL
Zone 2: 3 metresacross CL
Boudary
Fence
Name and Location of Company
N
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Thermocouple in a hazardous are
Inside of pipe orprocess vessel
Zone 0Zone 1
Outside of pipe
Zone 2
Division 2
Division 1
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Why Area Classify?Probability of
Gas/Air Mixturebeing present
Probability ofSource ofIgnitionX = Acceptable
Risk
Matched to
Type ofProtection
d, i, q, o, p, m, e, n, s
Zone 0,1,2 Nothing is100% Safe
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Methods of Explosion ProtectionE Technique: IEC Description: Zone: Application:x 79-p Separation (Gas) 2 Pressurisation 1,2 Control rooms, analyserso (Liquid) 6 Oil-filling 2 Transformers switchgearq (Semi-solid) 5 Quartz/Sand 2 Instrumentationm (Solid) 18 Encapsulation 1,2 Instrumentation, control gearn Construction 15 Non-incendive 2 Transformers, switchgeare Construction 7 Increased Safety 1,2 Motors, lighting, boxes (Draft)d Containment 1 Flameproof 1,2 Switchgear, motors, pumpsi Electrical design 11 Intrinsic Safety 0,1,2 Instrumentation, control gears Special Special 0,1,2 Gas detection
0 GeneralRequirements
Ex s Not adoptedZones are ‘permitted Zone of use’
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Intrinsic Safety
Ex i
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Definition of ‘intrinsic’
Intrinsic:“in-built”
or “of its nature”
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Definition
“A circuit in which no spark or thermal effect in any part of
the circuit intended for use in a hazardous area is capable
of causing ignition.”
Intrinsically Safe Circuit
IEC79-11
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V & I Limiting Network
Current limiting resistor
RCLR
Vinput VZ
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Energy limiting arrangement
Current limiting resistor
VZ
RCLR
HazardousArea
Safe AreaCircuit
FUSE
Vinput
Infallible Components
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Intrinsic safety categories
Intrinsic safety is the only protection concept which considers failure of the field wiring
Ex ia Ex ibIntrinsically safe
withtwo countable faults
Intrinsically safe with
one countable fault
Zones 0, 1 and 2 Zones 1 and 2
Countable Faults: Faults in infallible components
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System
+
-
RELAY
Hazardous
N LE
Fault 1
Fault 2
Note! Earth Connection
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Current Limiting from C V Supply
SupplySupply
+
-
RelayHazardous
N L E
Barrier
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Component Failure
Current limiting resistor
VZ
RCLR
Hazardous area Safe area
FUSE
Vinput
Infallible Components
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Thank You For Your Interest
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