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BHOPAL

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OUTCOME

Differentiate safety and health

Type of hazard

Major hazard in chemical industry

Past industrial accident

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To know is to survive and to ignore

fundamentals is to court disaster 

H.H. Fawcett and W.S. Wood, Safety and Accident Prevention in chemical operation,

New York, Wiley, 1984.

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Safety vs health

Safety Health

 A state of environment A state of the individual

Typically injured related (not

only)

Typically disease related (but

not only)Does not include “positive

health”

Includes “positive health”

External Internal

Occupational safety – 

the protection ofpeople from physical injury 

Occupational health  –  the protection of the

bodies and minds of people from illness

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Term Definition

 Accident undesired event giving rise to death, ill health, injury, damage

or other loss

Incident event that gave rise to an accident or had potential to lead to

an accident (not all incidents propagate into accidents)

(An incident where no ill health, injury, damage, or other loss

occurs is referred to as „near -miss‟)

Near miss an unplanned event that did not result in injury, illness, or

damage – but had the potential to do so.

Hazard source or situation (chemical or physical) with a potential to

cause harm, injury or damage to either human, property or the

environment or some combination of these.

Risk combination of the likelihood (probability) of a specified

hazardous event occurring and its consequence(s)

I  m p

 or  t   an t   t   er mi  n o

l   o gi   e s 

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Hazard definition

Unsafe condition and unsafe acts that

could potentially cause accidents/ harm

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Unsafe act  A violation of an acceptable safe

procedure which could permit theoccurrence of an accident

 A hazardous physical condition or circumstances

which could directly permit the occurrence of an

accident.

This could be the result of an unsafe act by

someone

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Example of unsafe act:

Operating without authority Failure to warn or secure

Operating at improper speed

Making safety devices inoperable

Using defective equipment

Using equipment improperly

Failure to use PPE

Improper loading, placement

Servicing equipment in motion

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Example of unsafe condition:

Inadequate guards or protection Defective tools, equipment

Congestion, bad housekeeping

Inadequate warning system Fire and explosion hazards

Hazardous atmospheric condition

Excessive noise Inadequate illumination or ventilation

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IDENTIFY UNSAFE ACTS AND CONDITIONS; AND POSSIBLE

TYPES OF ACCIDENT

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Categories of hazards

Chemical

Thermodynamics

Electrical & electromagnet

Health

External

Mechanical

Biological

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examples

Chemical hazards○  Acidity

○  Alkalinity

○ Corrosivity

○ Explosiveness○ Flammability

○ Toxicity

○  Asphyxiation

○ Compressed orliquified gas

○ Dust

○ Oxidizers

Thermodynamicshazards High pressure

Vacuum

Heat transfer 

High temperature Low temperature

Fluid jets

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examples

Electrical &

electromagnet

hazards

○ High voltage

○ Radiation

○ Static electricity

○ Electrical current

○ Poor insulation

Health hazards

Noise Pollution

Vibration

Radioactivity

Temperature extremes

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examples

External threats

○  Accidental damage by

missile and vehicles

○  Act of God and natural

causes○  Abnormal

environmental

extremes

○ External interference

○ Instability of structures○ External releases of

energy or toxin, etc.

Mechanical hazards Mechanical energy

Stresses

Impact and forces

Contact laceration

Biological hazardsParasites

Viruses

Bacteria

fungi

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Major Hazards in Process

Industries

Toxic Release Fire

Explosion

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Hazard from Toxic Substances

There are no harmless substance,only harmless ways of using substances

Toxicants A chemical agents

 A physical (dusts, fibers, noise, and radiation)agents, e.g. asbestos

Toxicity is a property of toxicant that describeits effect on biological organism.

Toxic hazards is the likelihood of damage tobiological organism based on exposureresulting from the use/transport/storage of thetoxicants (hazardous material).

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Hazard from Toxic Substances

Effects that are Irreversible Carcinogen-cause cancer 

Mutagen-cause chromosome (gene) damage

Teratogen- cause birth defects

Effects that may or may not be irreversible Dermatotoxic – affects skin

Hemotoxic – affects blood

Hepatotoxic- affects liver 

Nephrotoxic – affects kidneys

Neutotoxic – affects nervous system

Pulmonotoxic- affects lungs

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Fire

• Jet Fire

• Flash Fire

• Pool Fire

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Jet fires

 A jet fire is the combustion of materialemerging with significant momentum froman orifice, from a source under pressure,e/g. a flammable liquid or gas is ignited

after its release from a pressurized,punctured vessel or pipe.

The pressure release generates a longflame which is stable under most

conditions. The duration of a jet fire is determined by

the release rate and the capacity of thesource.

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Flame length increase directly with flow

rate. Crosswinds affect flame length.

 An increase in crosswind velocity causes

the flame to bend over quickly and be

convected by the wind.

The flame length increases with crosswind

velocity.

 A jet flame is similar to a Bunsen burnerflame

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Jet Fire

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Flash Fire

Flash fire is the non explosive combustion of avapour cloud resulting from a release of flammable

material into the open air, which, after mixing with air,

ignites.

Combustion in a vapour cloud develops an explosive

intensity and attendant blast effects only in areas

where intensity turbulent combustion develops and

only if certain conditions are met.

Where these condition are not present, no blast

should occur.

The cloud than burns as a flash fire, and its major

hazard is from the effect of heat from thermal

radiation.

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Flash Fire

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POOL FIRE

 A pool fire is the combustion offlammable vapor evaporating from alayer of liquid at the base of the fire.

It occurs on ignition of an accumulationof liquid as a pool on the ground or onwater or other liquid.

 A steadily burning fire is rapidlyachieved as the vapor to sustain thefire is provided by the evaporation ofthe liquid by heat from the flames.

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Pool Fire

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Types of Explosion

Mechanical Explosion

Chemical Explosion Vapour Cloud Explosion

Confined

Unconfined

BLEVE

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Chemical Explosion

Deflagration Low level explosion

The reaction move front moves at

speeds less than the speed of sound in

the unreacted medium

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Detonation

High level explosion

Highly turbulent combustion

Very high flame speeds

Extremely high pressures >>10 bars

The reaction move front moves at speeds greater than

the speed of sound in the unreacted medium

V Cl d E l i

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Vapor Cloud Explosion

The most dangerous and destructive explosions in

the chemical process industries

Steps of explosion

Sudden release of a large quantity of flammable vapor 

Dispersion of the vapor throughout the plant whilemixing in the air 

Ignition of the resulting vapor cloud

 Any process containing quantities of liquefiedgases, volatile superheated liquid or high pressuregases is considered good candidate for VCE

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BLEVE

B L E VO

I

LI

N

G

I

Q 

UI

D

X

P

AN

D

I

N

G

X

P

LO

S

I

O

N

S

EA

P

OR

BLEVE is a consequence of holding a pressurizedflammable liquids above its boiling point.

C f BLEVE

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Causes of BLEVE

The immediate cause of the BLEVE isrupture of the container. If the pressureinside the vessel exceeds the outsidestrength of the walls the vessel will fail.

If the vessel is overfilled and expansion(due to boiling of liquid) results in a heavyhydrostatic pressure.

If the vessel is weakened by mechanical

damage or by high temperature resultingfrom immersion in a fire then failure canoccur.

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Mechanism of BLEVE

• When BLEVE is initiated, theliquid boils off rapidly

producing a reaction which

turns parts of the rupturedvessel into rockets which

can travel 2500 ft or more.

• The liquid can take fire if itis flammable and burningmaterial can spread over a

large area. If the gas orliquid mixes with air a

vapour cloud explosion can

occur.

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Major disaster

Past major industrial disasters :

-Flixborough, England 1974

-Bhopal, India 1984

-Seveso, Italy 1976

-Piper Alpha, 1988

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Flixborough, England 1974

 The Flixborough disaster was an

explosion at a chemical plant close

to the village of Flixborough Englandon 1 st June 1974.

It killed 28 people and seriouslyinjured 26

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 Two months prior to the explosion, acrack was discovered in the number 5reactor.

It was decided to install a temporary 50

cm (20 inch) diameter pipe to bypass theleaking reactor to allow continuedoperation of the plant while repairs weremade.

 The sketch of the repairs was made onlyon the floor using chalk withoutsupervision from an experiencedengineering personnel.

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Bhopal, India 1984

Contaminated methyl isocynate (MIC)caused runaway reaction.

Vapor released through pressure relief system but scrubber and flare system notworking. 25 tons of MIC vapor released.

 Toxic cloud spread nearby town killing2500 civilian, injured more than 20,000.No plant workers were injured or killed.No plant equipment was damaged.

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Seveso, Italy 1976

Reactor out of control, produced more side

product, TCDD (dioxin - more than originally

designed for).

Vapor TCDD released to atmosphere

through relief system and heavy rain washed

into soil.

 TCDD is toxic to man and other species can

contaminate drinking water.

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Piper Alpha, 1988

Worst offshore disaster ever that left

167 died

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Causes of accident

Accidents have direct, indirect and root

causes

• Direct cause  –  attribute to equipment

failure or unsafe operating conditions

• Indirect cause  –  not as readily apparent

and can generally be tied to some human

failure

• Root cause  –  result of poor management

safety policies, procedures or decisions

M t S f t P li & D i i

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Direct Causes

Indirect Causes(Symptoms)

Root CausesManagement Safety Policy & Decisions

Personal Factors

Environmental Factors

Unsafe Act Unsafe Condition

Unplanned Release of Energyand/or 

Hazardous material

ACCIDENT

Personal Injury

Property Damage

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EXAMPLE

 A drowning accident occurred during an openswim period. Approximately 100 children (5-16years old) were in and around a pool (3ft-9ftdeep). An older child unknowingly pushed 5

years old into deep water. The pool wasrelatively crowded and the 5 years old kidslipped under the water without being noticedby other including the lifeguard.

List out thefacts of the accident

occur, theimmediate causes and root causes. List outwhat you can propose for corrective action?

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Engineers professional ethics

Fundamental principles

Engineers shall uphold and advance the

integrity, honor and dignity of engineering

profession by :

- using knowledge & skill for

enhancement of human welfare.

- honest and impartial and serving with

fidelity to public, employers, clients.- striving to increase competence and

prestige of engineering profession.

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  conomics of safety

Lives, injuries, damages to plantand equipment

Loss production

Increased costs Insurance, medical, rehabilitation,

training and retraining

Lowering of workplace morale

Substantial loss of market share

Profitability