intrinsic safety

Technology Training that worksTechnology Training that Workswww.idc-online.com/slideshare1

Intrinsic

Safety

& Hazardous Areas

by

Steve Mackay

Technology Training that worksTechnology Training that Workswww.idc-online.com/slideshare

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


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.


ObjectivesThe identification of: Terminology Fundamentals of Ex i Protection


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’


InspectorateInspectorate


The Fire TriangleThe Fire Triangle

Airwith

21% OxygenFuel

Sufficient Vapour

27.2

!Bang

Source of IgnitionSource of Ignition

O2


Electricity as a Source of Ignition

Sources of IgnitionSources of Ignition

HeatHeatSparksSparks

Electrical SourcesElectrical Sources


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.)


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)


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


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


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%)


Area Classification

Nature of the Hazard

Locations of hazard

Probability of presence


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


Requirement for equipment classification

- Apparatus Group

- Temperature Classification

Equipment is classified according to:-

The maximum spark energy it can produce

Its maximum surface temperature


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


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


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


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


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


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


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


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


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


Thermocouple in a hazardous are

Inside of pipe orprocess vessel

Zone 0Zone 1

Outside of pipe

Zone 2

Division 2

Division 1


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


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’


Intrinsic Safety

Ex i


Definition of ‘intrinsic’

Intrinsic:“in-built”

or “of its nature”


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


V & I Limiting Network

Current limiting resistor

RCLR

Vinput VZ


Energy limiting arrangement


VZ

RCLR

HazardousArea

Safe AreaCircuit

FUSE

Vinput

Infallible Components


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


System

+

-

RELAY

Hazardous

N LE

Fault 1

Fault 2

Note! Earth Connection


Current Limiting from C V Supply

SupplySupply

+

-

RelayHazardous

N L E

Barrier


Component Failure


VZ

RCLR

Hazardous area Safe area

FUSE

Vinput

Infallible Components


Thank You For Your Interest

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