SAFETY IN CHEMICAL ENGINEERING presented by Dr. Arvind Kumar.ppt

SAFETY �IN �CHEMICAL ENGINEERING PROCESS

1. NIT- Rourkela 1
SAFETY SAFETY
IN IN
CHEMICAL ENGINEERING PROCESSCHEMICAL ENGINEERING PROCESS
Dr. Arvind Kumar
Department of Chemical Engineering
NIT Rourkela- 769 008
10/12/24

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OUTLINEOUTLINE

IDENTIFICATION OF PROCESS SAFETYIDENTIFICATION OF PROCESS SAFETY

IDENTIFICATION OF HAZARDIDENTIFICATION OF HAZARD

RISK ASSESSMENT TECHNIQUERISK ASSESSMENT TECHNIQUE

FIRES AND EXPLOSFIRES AND EXPLOSIONSIONS
–REQUIREMENTSREQUIREMENTS
–DESIGN TO PREVENT THEMDESIGN TO PREVENT THEM
»InertingInerting
»Controlling Static ElectricityControlling Static Electricity
»VentilationVentilation
»Sprinkler SystemSprinkler System
»Relief SystemsRelief Systems

CASE EXAMPLESCASE EXAMPLES

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What is process safety?What is process safety?
It is It is prevention of accidents by use of appropriate technologiesprevention of accidents by use of appropriate technologies

It starts withIt starts with hazardshazards identification identification of a chemical plant of a chemical plant

It ends withIt ends with eliminationelimination them before them before accident occursaccident occurs

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Components Of A Succesful Safety ProgramComponents Of A Succesful Safety Program
Safety Knowledge and Experience
Technical Competence
Safety Management
Support
Commitment
A succesful
safety
program

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HAZARDSHAZARDS
Mechanical hazards worker injuries from Mechanical hazards worker injuries from
tripping, falling or moving tripping, falling or moving
equipment equipment
fire and explosion hazardsfire and explosion hazards
Chemical Hazards reactivity hazardsChemical Hazards reactivity hazards
toxic hazardstoxic hazards

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ChemChemiical Hazardscal Hazards
A chemical reaction that goes out of control and A chemical reaction that goes out of control and
runs away can create a serious incident with the risk of runs away can create a serious incident with the risk of
injury to people and damage to property and the injury to people and damage to property and the
environment.environment.

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Categories of Categories of
Hazardous ChemicalsHazardous Chemicals

CorrosiveCorrosive

FlammableFlammable

ToxicToxic

ReactiveReactive

Biological (infectious)Biological (infectious)

Carcinogen (cancer-causing)Carcinogen (cancer-causing)

RadioactiveRadioactive

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Physical States of Physical States of
Hazardous MaterialsHazardous Materials

LiquidLiquid

SolidSolid

GasGas

VaporVapor

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Difficulties in chemical Difficulties in chemical safetysafety

Each chemical has a different hazardEach chemical has a different hazard

Users usually cannot analyse hazardsUsers usually cannot analyse hazards

Safe handling cannot be ensured without safety Safe handling cannot be ensured without safety
informationinformation

Information flow should be from suppliers (manufacturers, Information flow should be from suppliers (manufacturers,
importers, distributors) to employers and then to the importers, distributors) to employers and then to the
workforceworkforce

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Means for providing informationMeans for providing information

Labelling (concise information providing the intrinsic Labelling (concise information providing the intrinsic
properties of the chemical on the container)properties of the chemical on the container)

Chemical safety data sheets (comprehensive safety Chemical safety data sheets (comprehensive safety
information for use on the shopfloor)information for use on the shopfloor)

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Agencies That Regulate Agencies That Regulate
Hazardous Chemical Storage and their Hazardous Chemical Storage and their
MissionsMissions
–OSHA – Protection of employees from workplace injury and illness.OSHA – Protection of employees from workplace injury and illness.
–NFPA - National Fire Protection Association NFPA - National Fire Protection Association
–EPA – Protection of people, animals and the environment from EPA – Protection of people, animals and the environment from
chemical injury.chemical injury.
–DOT – Safety of shipments during transportation: road, rail, air, sea or DOT – Safety of shipments during transportation: road, rail, air, sea or
pipeline.pipeline.

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Chemical Plant AccidentsChemical Plant Accidents
Type of accidentType of accidentProbability of Probability of
occuranceoccurance
Potential for Potential for
fatalitiesfatalities
Potential for Potential for
economical losseconomical loss
FIREFIRE HighHigh LowLow IntermediateIntermediate
EEXPLOSIONXPLOSION IntermediateIntermediate IntermediateIntermediate HighHigh
TOXIC TOXIC
RELEASERELEASE
LowLow HighHigh LowLow

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RISK ASSESSMENTRISK ASSESSMENT
We need to carry out a riskWe need to carry out a risk assessment of our process to assessment of our process to
have a safe chemical plant.have a safe chemical plant.

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A typical cA typical chemical process risk hemical process risk
assessmentassessment

Defining The Process, Operating Conditions And Plant;Defining The Process, Operating Conditions And Plant;

Identifying The Hazards; Identifying The Hazards;

Evaluating The Risks Arising From The HazardsEvaluating The Risks Arising From The Hazards

Deciding Whether Existing Precautions Are Adequate Deciding Whether Existing Precautions Are Adequate

Selecting And Specifying Appropriate Safety Measures;Selecting And Specifying Appropriate Safety Measures;

Implementing and maintaining the selected safety measures. Implementing and maintaining the selected safety measures.

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Evaluating reaction hazardsEvaluating reaction hazards
DeterminDetermination ofation of the hazards of a reaction the hazards of a reaction includesincludes search on search on::

The possibility of thermal decomposition of raw materials, The possibility of thermal decomposition of raw materials,
intermediates, products and by-products; intermediates, products and by-products;

Whether exothermic runaway can occur Whether exothermic runaway can occur

The rate and quantity of heat and gas produced by the reaction. The rate and quantity of heat and gas produced by the reaction.

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FIRES AND EXPLOSIONSFIRES AND EXPLOSIONS
REQUIREMENTSREQUIREMENTS
–Explosive SubstanceExplosive Substance
–OxygenOxygen
–Start of fireStart of fire
»Ignition SourceIgnition Source
»Auto Ignition Auto Ignition
TemperatureTemperature
–Suitable ConditionsSuitable Conditions
»UFLUFL
»LFLLFL

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UFL AND LFLUFL AND LFL

UFL (upper flammability limit)UFL (upper flammability limit)
Maximum concentrationMaximum concentration of fuel that will support of fuel that will support
combustioncombustion

LFL (lower flammability limit)LFL (lower flammability limit)
Minimum concentrationMinimum concentration of fuel that will support of fuel that will support
combustioncombustion

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IGNITION SOURCESIGNITION SOURCES
• Mainly heat and sparks,flames,static electricityMainly heat and sparks,flames,static electricity
• Ignition sources are normally the easiest toIgnition sources are normally the easiest to eliminate.eliminate.

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DESIGN TO PREVENT FIRES AND DESIGN TO PREVENT FIRES AND
EXPLOSIONSEXPLOSIONS

InertingInerting

Controlling Static ElectricityControlling Static Electricity

VentilationVentilation

Sprinkler SystemSprinkler System

Relief SystemsRelief Systems

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INERTINERTIINGNG
–Inerting is the process of adding an inert gas Inerting is the process of adding an inert gas
to a combustible mixture to reduce the to a combustible mixture to reduce the
concentration of oxygen below the minimum concentration of oxygen below the minimum
oxygen concentration.oxygen concentration.
–Nitrogen,carbon dioxide and sometimes Nitrogen,carbon dioxide and sometimes
steam can be used as inert gas.steam can be used as inert gas.
–For many gases the minimum oxygen For many gases the minimum oxygen
concentration is 10% and for many dusts 8%.concentration is 10% and for many dusts 8%.

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Inerting ProcedureInerting Procedure

begins with an initial purge of the vessel with inert gas to begins with an initial purge of the vessel with inert gas to
bring the oxygen concentration.bring the oxygen concentration.

Then,the flammable material is charged.Then,the flammable material is charged.

An automatic inert gas addition system maintains the An automatic inert gas addition system maintains the
oxygen concentration below the MOC.oxygen concentration below the MOC.

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Static Static ElectricityElectricity
Formation Formation
Grounded thermowell
grounds all metal
Propagating
Brush
Discharge
Metal to Metal
Spark
Solids
Metal Shell
Conical Pile
Discharge
Lightening Like
Discharge
Solids
Brush
Discharge
Solids
Tramp Metal

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PreventionPrevention

Natural grounding and static electricity prevention Natural grounding and static electricity prevention
mechanisms mechanisms

Avoiding use of highly insulator materialAvoiding use of highly insulator material

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VENTVENTIILATLATIIONON
Ventilation is a common protection against exposure to inhalation. Ventilation Ventilation is a common protection against exposure to inhalation. Ventilation
is based on two principles.is based on two principles.

Dilute the contaminant below the target concentration.Dilute the contaminant below the target concentration.

Remove the contaminant before workers are exposed.Remove the contaminant before workers are exposed.

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Why ventilation?Why ventilation?

Can quickly remove dangerous concentrations of flammable and Can quickly remove dangerous concentrations of flammable and
toxic materials.toxic materials.

Can be highly localized, reducing the quantity of air moved and Can be highly localized, reducing the quantity of air moved and
the equipment size.the equipment size.

Can be easily installed.Can be easily installed.

Can be added to an existing facility.Can be added to an existing facility.

Ventilation systems are composed of fans and ductsVentilation systems are composed of fans and ducts, , as a as a
disadvantage, they have hdisadvantage, they have high operating costsigh operating costs

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Types of ventilationTypes of ventilation
There are two types of ventilation techniques:There are two types of ventilation techniques:

¤¤ Local Local ventilationventilation
¤¤ Dilution ventilation.Dilution ventilation.

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Local ventilationLocal ventilation

The most common example is the hood.The most common example is the hood.

A hood is a device that either completely encloses the source of A hood is a device that either completely encloses the source of
contaminant or moves the air in such a fashion to carry the contaminant or moves the air in such a fashion to carry the
contaminant to an exhaust device. contaminant to an exhaust device.

Fume hoods provide a flow of air away from the person.Fume hoods provide a flow of air away from the person.

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Dilution ventilationDilution ventilation

if the contaminant cannot be placed in a hood and must be used in an open if the contaminant cannot be placed in a hood and must be used in an open
area or room, dilution ventilation is necessaryarea or room, dilution ventilation is necessary

requires more airflow than the local ventilationrequires more airflow than the local ventilation

When ventilation system is designed occupational health standards such as When ventilation system is designed occupational health standards such as
TLV must be considered. TLV must be considered. TLV (TTLV (Threshold hreshold LLimit imit VValuesalues)): Below this : Below this
dose the body is able to detoxify.dose the body is able to detoxify.

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SPRINKLER SYSTEMSSPRINKLER SYSTEMS

These systems are used to contain fires.These systems are used to contain fires.

They are consist of an array of splinkler heads connected They are consist of an array of splinkler heads connected
to a water supply.to a water supply.

The heads are put in a high location and they disperse a The heads are put in a high location and they disperse a
fine spray of water over an area.fine spray of water over an area.

Altough splinkler systems may cause water damage Altough splinkler systems may cause water damage
depending over the building or process structure,this water depending over the building or process structure,this water
damage is never as great as the damage from damage is never as great as the damage from
fires,statistically.fires,statistically.

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Methods activate the sprinkler headsMethods activate the sprinkler heads

Closed Head Area System:Activates the heads individually Closed Head Area System:Activates the heads individually
by melting of fusible link holding a plug in the haed.This by melting of fusible link holding a plug in the haed.This
system is used for storage areas,laboraties,control rooms.system is used for storage areas,laboraties,control rooms.

Open Head Area System:Activates the entire sprinkler Open Head Area System:Activates the entire sprinkler
array from a common control point.the control point is array from a common control point.the control point is
connected to an array of heat or smoke detectors.This connected to an array of heat or smoke detectors.This
system is used for plant process areas and larger pilot system is used for plant process areas and larger pilot
plants.plants.

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Why relief systems are required?Why relief systems are required?

tto protect personnel from the dangers of o protect personnel from the dangers of
overpressurizing equipmentoverpressurizing equipment

tto minimize chemical losses during pressure upseto minimize chemical losses during pressure upset

tto prevent damage to equipmento prevent damage to equipment

tto prevent damage to adjoining propertyo prevent damage to adjoining property

tto reduce insurance premiumso reduce insurance premiums

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RReliefelief TypesTypes
1- Spring operated1- Spring operated
–ConventionalConventional
»The relief set pr is usually specified 10%above the normal pressureThe relief set pr is usually specified 10%above the normal pressure
»To minimise the back pressureTo minimise the back pressure
–Balanced belloBalanced belloww
»If the substantial pr. is presentIf the substantial pr. is present
2-R2-Rupture discsupture discs

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What is relief system?What is relief system?
–A relief system protects the process from the damaging effects of A relief system protects the process from the damaging effects of
high or low pressurehigh or low pressure
–A relief system removes energy from a process by discharging A relief system removes energy from a process by discharging
mass with an energy contentmass with an energy content

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How can high pressures develop?How can high pressures develop?

Overheating or freezingOverheating or freezing
Failure of regulatorFailure of regulator

External fireExternal fire
Runaway reactionRunaway reaction

Combustion of gases and dustsCombustion of gases and dusts

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In order to relieve the high pressureIn order to relieve the high pressure

Spring loaded reliefs Spring loaded reliefs
Set Presure
Adjust screw
Spring
Bonnet
Disc Holder
Seat Disc
Nozzle
Body
Blowdown
Adjustment
Ring

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
Set pressure: Pressure at which the device begins to openSet pressure: Pressure at which the device begins to open

Back pressure: The pressure downstream of the device Back pressure: The pressure downstream of the device
during the reliefduring the relief

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In spring loaded reliefsIn spring loaded reliefs

Set pressure and flow are affected by back pressureSet pressure and flow are affected by back pressure
- Set pressure increases- Set pressure increases
- Flow decreases- Flow decreases

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
AdvantagesAdvantages
- Most reliable type if properly sized and operated- Most reliable type if properly sized and operated
- Versatile -- can be used in many service- Versatile -- can be used in many service

DisadvantagesDisadvantages
- Relieving pressure affected by back pressure- Relieving pressure affected by back pressure

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Rupture DiscsRupture Discs

a thin diaphragma thin diaphragm

a weak elementa weak element to protect vessels and piping against to protect vessels and piping against
excessive pressureexcessive pressure

Primary pressure relief devicePrimary pressure relief device
- in runaway reactions,- in runaway reactions,
- when PR valve can not respond quickly- when PR valve can not respond quickly

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
AdvantagesAdvantages
- Protect against rapid pressure rise - Protect against rapid pressure rise
- Less expensive - Less expensive
- Provide secondary protective device for large relief areas- Provide secondary protective device for large relief areas

DisadvantagesDisadvantages
- Don- Don’’t reclose after relieft reclose after relief
- Burst pressure cannot be tested - Burst pressure cannot be tested
- Greater sensitivity to temperature- Greater sensitivity to temperature

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Closes and minimise
losses
Against toxicity and corrosion

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Piston Type Pilot Operated Safety Relief Piston Type Pilot Operated Safety Relief
ValveValve

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
AdvantagesAdvantages
- Relief pressure is not affected by backpressure- Relief pressure is not affected by backpressure
- Can operate at up to 98% of set pressure- Can operate at up to 98% of set pressure

DisadvantagesDisadvantages
- Limited temperature range- Limited temperature range
- Potential for back flow- Potential for back flow

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RUPTURE PINSRUPTURE PINS

non re-closing similar to rupture disc non re-closing similar to rupture disc

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
AdvantagesAdvantages
- can operate closer to its set point- can operate closer to its set point
- suitable for liquid service- suitable for liquid service
- replacement of pins are 1/3 to 1/4 the cost of replacement of - replacement of pins are 1/3 to 1/4 the cost of replacement of
discsdiscs

DisadvantagesDisadvantages
- maximum operating temperature is about 230 - maximum operating temperature is about 230 ººC, elastomer C, elastomer
o-ring sealso-ring seals
- cost of installation is greater than for a rupture disc- cost of installation is greater than for a rupture disc

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CASE STUDCASE STUDYY
Bhopal AccidentBhopal Accident in Indiain India
“ “Leakage of an intermediate,Methyl Leakage of an intermediate,Methyl
Isocyanate(MIC)”Isocyanate(MIC)”

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Possible suggestionPossible suggestion
 
   
The scrubber and flare system should have been The scrubber and flare system should have been
fully operational to prevent the release.fully operational to prevent the release.

The tank The tank shoulshouldd have been have been tested to be sure it is tested to be sure it is
safe.safe.  ItIt cannot cannot be be knowknownn that it is safe until after that it is safe until after
the testing.the testing.
An alternative reaction scheme that involves a less An alternative reaction scheme that involves a less
dangerous intermediate than methly isocyanate dangerous intermediate than methly isocyanate
such as chloroformate could have been used.such as chloroformate could have been used.
One such plant that produces or consumes One such plant that produces or consumes
dangerous materials could have been constructed dangerous materials could have been constructed
in residential areas.in residential areas.

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Bhopal (MP)Bhopal (MP)

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2000 people died in Bhopal disaster2000 people died in Bhopal disaster

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More than 20000 civilians were injured.More than 20000 civilians were injured.

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FINAL REMARKFINAL REMARK
After reviewing these incidents, as seen it is very essential to After reviewing these incidents, as seen it is very essential to
see how knowing what caused past accidents can prevent see how knowing what caused past accidents can prevent
future accidents from happeningfuture accidents from happening

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THANK THANK
YOU YOU
FORFOR
ATTENTIONATTENTION
