safety in instrumentation

8/6/2019 Safety in Instrumentation

1/46


2/46

INSTRUMENTATION

AND CONTROLS

FOR SAFETY


3/46

Process Instrumentation


4/46

Fundamentals of Instrumentation

Systems

The operation of many industrial processes

involve inherent risks due to the presence of

dangerous material like Explosive gases andchemicals.

Instrumentation Systems are designed to protect

personnel, equipment and the environment by

reducing the likelihood (frequency) or the impact

severity of an emergency event.


5/46


Systems

The safe state is a state of the processoperation where the hazardous event cannotoccur.

Instrumentation Systems provides safe

isolation of flammable or potentially toxicmaterial in the event of a fire or accidentalrelease of fluids


6/46


Systems

Instrumentation system requires a series of equipment tofunction properly. It must have sensors capable ofdetecting normal/abnormal operating conditions

Instrumentation system receive the sensor input signal(s),make appropriate decisions based on the signal(s), andchange its outputs according to user-defined logic.

The final element(s) taking action on the process to bring

it to a safe state. Support systems, such as power, instrument air, are

required for Instrumentation system operation.


7/46

Pressure Measurement Devices

Bourdon Tube Gauge


8/46

Plant Safety

A chemical plant has several plant safetysystems to ensure safe operation of their

processes. These can be a combination ofthe following:

Alarm and Annunciators

Safety Trips Interlocks

Process control systems.


9/46

Alarm andAnnunciators

Alarms are used to alert operators of abnormal,

serious, and/or potentially hazardous, deviations in

process conditions. .

Alarms are triggered when a process variable

moved away from its normal operating conditions

Examples : high pressure, high temperature, low

level etc.


10/46

Safety Trips

A trip system to take action

automatically to avert thehazard, such as:shutting

down pumps or compressors, cutting off steam supply to

reboileretc


11/46

Interlocks

An interlock system is a group of devices arranged

to sense an operating limit or an improper

sequence of events, and to shutdown the processdeviating from normal condition.

An interlock system includes various alarm

annunciations and trips.

The functioning of an interlock system can be

achieved using relays.


12/46

Process control system Process control system perform some or all of the

following functions:

Monitoring, recording and logging of plant statusand process parameters;

Provision of operator information regarding theplant status and process parameters;

Automatic process control for start-up, normaloperation, shutdown, and disturbance. i.e. controlwithin normal operating limits.


13/46

Basics of Safety and Layers of

Protection


14/46


Protection

Safety is provided by layers of protection. These

layers start with safe and effective process control,

extend to manual and automatic prevention layers,and continue with layers to mitigate the

consequences of an event.

The first layer is the Basic Process Control System

The control system itself provides significant

safety through proper design of process control.


15/46


Protection

The next layer of protection is also provided bythe control system and the system operators.

Automated shutdown sequences in the processcontrol system combined with operatorintervention to shut down the process are the nextlayer of safety.

The third layer is a safety system independent of

the process control system. It has separate sensors,valves and logic system. No process control isperformed in this system, its only role is safety. Ex:MVWS system


16/46


Protection

The fourth layer is an active protection layer. Thislayer may have valves or rupture disks designed to

provide a relief point that prevents a rupture, largespill or other uncontrolled release that can causean explosion or fire.

The fifth layer is a passive protection layer. It may

consist of a dike or other passive barrier thatserves to contain a fire or channel the energy of anexplosion in a direction that minimizes the spreadof damage.


17/46


Protection

The final layer is plant and emergency

response. If a large safety event occurs this

layer responds in a way that minimizes

ongoing damage, injury or loss of life. It

may include evacuation plans, fire fighting,

etc. Overall safety is determined by how these

layers work together


18/46

Examples of I&C systems important

to safety

Systems which provide unit/Plant shutdown (trip)initiation;

Ex : General Emergency Shutdown ,Unit 12/16Shutdown, Unit 14 Shutdown,Unit 17 Shutdown switcheslocated at CCR.

Systems used to monitor or maintain plant parameterswithin operational limits important to safety (such as unit

16 cracker pressure control systems) Systems that perform functions important to maintaining

safe shutdown conditions,

e.g. TEC PCV 101, 12 PCV 61


19/46

HAZARDOUSAREA

DEF

INITIO

NS

Hazardous area is an area in

which an explosive gasatmosphere is present, or

likely to be present.


20/46

Explosionprotection

Explosion protection is the

science of designing anddeveloping electrical

products for safe use inhighly explosive areas


21/46

Explosionprotection Introduction

Petroleum products and chemicals in the liquid or

vapour form, leads to the formation of highlyexplosive atmospheres due to the leakage of gasesand vapours.

When these combine with the oxygen in the

atmosphere, potentially explosive mixtures comesinto accidental contact with an electrical spark orhot surface, with the resulting explosion causingextensive damage to life and property.


22/46

Instrumentation Safety (Preventing

Fire andExplosion)

. Safety can be achieved by removing at least any

one of the elements in the environment around instrumentation


23/46

CombustionPrinciples

Three basic conditions must besatisfied for a fire or explosion to occur

A flammable, liquid, vapour or combustible dustmust be present in sufficient quantity.

The flammable liquid, vapour or dust must bemixed with air or oxygen in the proportionsrequired to produce an explosive mixture.

A source of energy must be applied to theexplosive mixture.


24/46

C

onditions for explosion

% ConcentrationEnergy:

ElectricalHeatMechanical

Upper

explosive limit

Lowerexplosive limit


25/46


26/46

Flammable gas/vapour risk

Flammable liquids generally have a low

Flash Point. This is the lowest temperature

at which vapour is given off at a sufficient

rate to form an explosive mixture with air.

Therefore liquids with flash points below

ambient temperature will automaticallyrelease vapour in sufficient quantities to

provide an explosive mixture.


27/46

Flammable gas/vapour risk

The power of any explosion depends upon

the inherent properties of the gas and its

concentration in the atmosphere. Not all

concentrations of the flammable gas in air

will burn or explode.

Vapour Density form concentrationsbetween the LEL and UEL ready to explode

as soon as a source of ignition is introduced.


28/46

Sources of Ignition Ignition source has two essential characteristics.

Temperature :This must be equal to or higher than the

ignition Temperature.

Energy :The source must supply sufficient energy at a

high enough rate, to raise enough gas mixture

to the ignition point to start a self sustaining

explosion.

The different sources of energy : Flames

Sparks - electric or percussive

Hot surfaces.


29/46

M

inimum IgnitionEnergyGAS GROUP O. MI IMUM

I GNI ION

ENERGY

Methane

Propane

thyleneydrogen

I

II A

II BII

280 jo les

260 jo les

85 joles19 jo les


30/46

Classification ofHazardous

materials

Class 1:Locations are made hazardous bythe presence of flammable gases, liquids or

vapors. Class 2:Locations are described as

hazardous because of the presence ofcombustible dusts.

Class 3:Locations contain easily ignitablefibers or flyings.


31/46

Zone Classification

Zone O Areas where an explosive gas atmosphere is

continuously present. eg.: inside of containers or reactors. Zone 1 Areas where an explosive gas atmosphere is likely

to occur under normal operation. eg.: areas surroundingZone 0 & areas surrounding drains, discharge equipment.

Zone 2 Areas where an explosive atmosphere is not

likely to occur in normal operation and if it does it is onlyfor short periods. eg.: areas surrounding flanged gaskets,areas surrounding Zone 0 orZone 1.


32/46

Gas Grouping

Group classifications made based on the energy requirement forcausing the explosion.

APPARAUS

TYPEOFGAS

EIT ERGASESANDLIQUIDS

I.S.EQPTAPPROVAL

REQUIRED

IIII B

II A

I

Hydrogenthylene

Propane

Methane

arbon di- sulphitearbon monoxide

AcetoneHexane

aphtha,Ammonia

II onlyII B or II

IIAor II B

II


33/46

Temperature Class

T Code Max Surface Temp Ignition Temp

T1 450C >450C

T2 300C > 300C 450C

T3 200C > 200C 300C

T4 130C > 130C 200C

T5 100C > 100C 135C

T6 85C > 85C 100C


34/46

Types ofProtection

Worldwide, seven different types of protection arecurrently recognised

Ex i : Intrinsic Safety

Ex d : Flameproof

Ex e : Increased Safety

Ex p : Pressurised

Ex o : Oil Immersion Ex q : Powder filling

Ex n : Non sparking (basically in UK and India)


35/46


36/46

IEC 60079-1 Flame-Proof Enclosure

Marking EEx d

This enclosure will contain the pressure of an

explosion, and preventing ignition of f

lammab

legas outside the enclosure. Gaps in the enclosure

are so small and their lengths are restricted so thatany hot gas released through them will have lostits power to cause ignition.


37/46

IEC 60079-7 Increased Safety

Marking EExe

A type of protection inwhich measures areapplied with the higherdegree of safety.

No possibility of hightemperature and of the

occurance of arc or sparksin the interior & on theexternal parts of apparatusin the normal service


38/46

IEC60079-2 PressurizedEnclosure

Marking EExp

The formation of a potentially explosive atmosphere

inside a casing is prevented by maintaining a positive internal

pressure of protective gas in relation to the surrounding

atmosphere and by supplying the inside of the casing with a

constant flow of protective gas acting to dilute any

combustible mixtures.


39/46

IEC 60079-6 Oil-FilledEnclosure

Marking EExo

Electrical apparatus or parts of electrical apparatus

are immersed in a protective fluid (such as oil),

such that a potentially explosive atmosphere existing

over the surface or outside of the apparatus cannot

be ignited.


40/46

IEC 60079-5 Powder-FilledEnclosure

Marking EExq

Filling the casing of an electrical apparatus with a fine

granular packing material has the effect of making it

impossible for an electric arc created in the casing

under certain operating conditions to ignite a

potentially explosive atmosphere surrounding the

casing.


41/46

IEC 60079-15 Type of protection

EExn

Electrical apparatus cannot

ignite a explosive atmospheresurrounding them (in normal

operation and under defined

abnormal operating conditions).


42/46

IPCode

As defined in international standard IEC

60529, IP Code classifies and rates the

degrees of protection provided against the

intrusion of solid objects (including body

parts like hands and fingers), dust,

accidental contact, and water in mechanicalcasings and with electrical enclosures


43/46

Solids (First Digit)

Level Object size Effective against

0 No protection against contact and

ingress of objects

1 >50 mm Any large surface of the body, such

as the back of a hand

2 >12.5 mm Fingers or similar objects

3 >2.5 mm Tools, thick wires, etc.

4 >1 mm Most wires, screws 5 Dust protected Ingress of dust is not entirely prevented

Complete protection against contact

6 Dust tight No ingress of dust


44/46

Liquid (Second Digit)

Level Protected against Testing for

0 Not protected

1 Dripping water vertically falling drops

2 Dripping water up to 15Vertically dripping water 3 Spraying water spray at any angle up to 60

4 Splashing water from any direction

5 Water jets a nozzle (6.3mm) against enclosure

from any direction

6 Powerful water jets powerful jets (12.5mm nozzle)

against the enclosure from any direction

7 Immersion up to 1 m immersed in water under up to 1 m

8 Immersion beyond 1 m suitable for continuous immersion


45/46

The Setting of a high pre-trip alarm

Abnormal

Operating Region

Alarm Setting

Limit of largest normal operational fluctuation

A

B

Limit at which protection operates

Time for operator

to respond to alarm

and correct fault


46/46

THANK YOU

safety in instrumentation

Documents